Parabolic-trough solar water heating is 

a well-proven technology that directly substitutes renewable energy for conventional

energy in water heating. Parabolic-trough

collectors can also drive absorption cooling

systems or other equipment that runs off a

thermal load. There is considerable potential

for using these technologies at Federal facilities in the Southwestern United States or

other areas with high direct-beam solar radiation. Facilities such as jails, hospitals, and

barracks that consistently use large volumes

of hot water are particularly good candidates. Use of parabolic-trough systems helps

Federal facilities comply with Executive

Order 12902's directive to reduce energy use

by 30% by 2005 and advance other efforts

to get the Federal government to set a good

example in energy use reduction, such as the

1997 Million Solar Roofs Initiative.

This Federal Technology Alert (FTA)

from the Federal Energy Management

Program (FEMP) is one of a series on new

energy-efficiency and renewable energy

technologies. It describes the technology of

parabolic-trough solar water-heating and

absorption-cooling systems, the situations 

in which parabolic-trough systems are likely 

to be cost effective, and considerations in

selecting and designing a system. This FTA

also explains energy savings performance

contracting (ESPC), a method for financing

Federal facility energy conservation and

renewable energy projects. ESPC is available for parabolic-trough systems and offers

many important advantages.

Parabolic-trough collectors use mirrored

surfaces curved in a linearly extended 

parabolic shape to focus sunlight on a darksurfaced absorber tube running the length 

of the trough. A mixture of water and

antifreeze or other heat transfer fluid is

pumped through the absorber tube to pick

up the solar heat, and then through heat

exchangers to heat potable water or a thermal storage tank. Because the trough mirrors will reflect only direct-beam sunlight,

parabolic-trough systems use single-axis

tracking systems to keep them facing 

the sun.

Application

Use of parabolic-trough systems is more

limited by geography and system size than

are other types of solar water heating, but

where parabolic troughs are usable they

often have very attractive economics. As

concentrating systems, parabolic troughs use

only direct radiation, so are less effective

The U.S. Department of Energy

requests that no alterations be

made without permission in any

reproduction of this document.

Federal

Technology

Alert

A publication series

designed to speed the

adoption of energyefficient and renewable

technologies in the

Federal sector

Prepared by the

New Technology

Demonstration Program

Parabolic-Trough Solar 

Water Heating

Renewable technology for reducing water-heating costs

Warren Gretz, NREL/PIX01019
where skies are cloudy and much more

likely to be effective in areas such as the

Southwestern United States that have good

solar resources dominated by direct-beam

sunlight. It is also more cost effective to

build large systems that will be used on a

continuous basis. Parabolic-trough solar

water heating (and air-conditioning) is

therefore most effective for large, 7-days-aweek, domestic hot-water users, such as

Federal hospitals, prisons, or barracks. (For

most situations, about 500 gallons per day

of hot water use is a minimum for a viable

parabolic-trough system.) Troughs also

work well for district space or water heating

systems serving multiple buildings from a

central steam or hot-water plant. The cost 

of the collector system is a main economic

factor, but as with any capital-intensive

energy conservation or renewable energy

installation, the critical factor is likely to 

be current cost of energy. Facilities that 

pay high utility rates for conventional water

heating will always be the best prospects for

cost-effective parabolic-trough solar water

heating or air-conditioning.

Technology Selection

The FTA series targets energy efficiency

and renewable energy technologies that

appear to have significant untapped Federalsector potential and for which some Federal

installation experience exists. Many of the

alerts are about new technologies identified

through advertisements in the Commerce

Business Daily and trade journals, and

through direct correspondence soliciting

technology ideas. This FTA describes a

renewable energy technology with known

energy, cost, and environmental benefits that

has substantial untapped potential for the

Federal sector. The U.S. Department of

Energy has signed a "Super ESPC" indefinite delivery/indefinite quantity (IDIQ) 

contract with Industrial Solar Technology

Corporation (IST), the only current manufacturer of parabolic-trough collectors. This

contract encourages Federal facilities to use

parabolic-trough technology by greatly

facilitating financing and implementation

through ESPC.

First, a preliminary analysis should be

conducted on whether solar water heating 

generally or parabolic-trough systems 

particularly would be cost effective for any

situation on the basis of energy load, conventional energy costs, and the location’s

solar radiation. Software that performs this

task is available from FEMP's Federal

Renewables Program at the National

Renewable Energy Laboratory (NREL).

(See Federal Program Contacts on page 20.)

IST can more specifically assess

prospects for a trough system at a particular

facility. The FEMP Help Desk can provide

manuals and software for detailed economic

evaluation and more information on ESPC

financing. (See manufacturer’s information

and Federal Program Contacts.) ESPC,

which IST can provide under the Super

ESPC IDIQ contract, allows Federal facilities to repay contractors for solar waterheating systems through bills for energy

savings instead of paying for initial construction. The Super ESPC with IST offers

many significant advantages:

• No financial outlay by the facility to 

determine feasibility

• No need to seek competitive proposals

• Pre-identified savings

• No responsibility for operation and 

maintenance

• The current system stays in place as a

backup for high reliability

• Guaranteed savings

• The facility pays only for energy savings

it realizes

• The facility can benefit indirectly from

tax incentives available only to private

companies

• The facility can get credit for energy use

reduction in compliance with Executive

Order 12902 (mandatory 30% reduction

by 2005) without reducing hot-water use

• Switching to a more economical conventional water heater or other related efficiency measures can be included in and

financed by the ESPC project.

Case Studies

This FTA describes two examples of 

parabolic-trough solar water heating installations by IST on a payment-for-energysavings basis. 

The first case study is the parabolictrough system at the Adams County

Detention Facility in Brighton, Colorado,

which has been operating since 1987. The

7200-square-foot (669-square-meter) collector system displaces about 2 billion British

thermal units (Btus) per year of natural gas

water heating, about 40% of that needed for

the more than 800 inmates.

In the second case study, IST is just 

starting construction of 18,000 square feet

(1672 square meters) of parabolic-trough

collectors to provide domestic hot water 

for the Federal Correctional Institution in

Phoenix, Arizona. Although this project was

negotiated prior to granting of the IDIQ

contract, it is being built on an ESPC basis.

The facility, which houses about 1200

inmates, now depends on electric-resistance

water heating. The new solar system was

specifically designed to avoid peak demand

charges from the utility by using a 21,000-

gallon (79,494-liter) thermal storage tank

controlled to deliver solar heat during facility peak periods. This will allow the system

to meet a projected 82% of the facility’s 

hot-water use. The solar system will displace 15 billion Btus per year of fossil fuel

combustion, avoiding more than 80,000

kilograms of nitrogen oxides and nearly

100,000 kilograms of sulfur dioxide pollution over the project’s life.

Implementation Barriers

There are no technological barriers to

using parabolic-trough solar water heating.

However, trough collectors are by nature

limited geographically to areas with high

direct-beam solar resources. They are also

by nature more cost effective for facilities

that use large amounts of hot water 7 days 

a week. But, because they directly replace

conventional energy use, parabolic-trough

collectors will provide energy savings and

environmental benefits proportional to their

use. From a financial perspective, however,

relatively high conventional water-heating

costs will be the biggest enabling factor.

ESPC financing also provides advantages

such as tax breaks for private investors that

are important to project economics.

Improvements in reflective and absorbent

coatings and development of triple-effect

absorption cooling will incrementally

improve economics, but there are no known

technological developments that could dramatically lower the cost of parabolic-trough

solar water-heating or absorption-cooling

systems. Much higher sales volume would

likely lower costs, but that would depend 

on the new technology being able to consistently compete with low-cost conventional

energy. Parabolic-trough solar water heating

is likely to remain most cost effective where

natural gas is not available or is relatively

expensive, and where consistent highvolume use provides economies of scale.
Federal

Technology

Alert

Parabolic-Trough Solar Water Heating

Renewable technology for reducing water-heating costs

Warren Gretz, NREL/PIX00327

Parabolic-trough solar water-heating system for Adams County Detention Facility,

Brighton, Colorado.

Abstract 

Parabolic-trough solar water heating is a

well-proven renewable energy technology

with considerable potential for application 

at Federal facilities. For the United States,

parabolic-trough water-heating systems are

most cost effective in the Southwest where

direct solar radiation is high. Jails, hospitals,

barracks, and other facilities that consistently use large volumes of hot water are

particularly good candidates, as are facilities

with central plants for district heating. As

with any renewable energy or energy efficiency technology requiring significant 

initial capital investment, the primary condition that will make a parabolic-trough system economically viable is if it is replacing

expensive conventional water heating. In

combination with absorption cooling systems, parabolic-trough collectors can also 

be used for air-conditioning.

Industrial Solar Technology (IST) of

Golden, Colorado, is the sole current manufacturer of parabolic-trough solar water

heating systems. IST has an Indefinite

Delivery/Indefinite Quantity (IDIQ) contract

with the Federal Energy Management

Program (FEMP) of the U.S. Department 

of Energy (DOE) to finance and install 

parabolic-trough solar water heating on an

Energy Savings Performance Contract

(ESPC) basis for any Federal facility that

requests it and for which it proves viable.

For an ESPC project, the facility does not

pay for design, capital equipment, or 

installation. Instead, it pays only for guaranteed energy savings. Preparing and implementing delivery or task orders against the

IDIQ is much simpler than the standard 

procurement process. 

This Federal Technology Alert (FTA) 

of the New Technology Demonstration

Program is one of a series of guides to 

renewable energy and new energy-efficient

technologies. It is designed to give Federal

facility managers the information they 

need to decide whether they should pursue

parabolic-trough solar water heating or airconditioning for their facility and to know

how to go about doing so. Software available from FEMP's Federal Renewables

Program at the National Renewable Energy

Laboratory (NREL) enables preliminary

1
2

analysis of whether parabolic-trough collectors would be cost effective for any situation

based on minimum data. (See Federal

Program Contacts on page 20.)

This FTA describes the technology of

parabolic-trough collectors, solar waterheating systems, and absorption cooling. 

It points out the types of situations where

parabolic-trough solar water heating is most

likely to be cost effective and describes the

ESPC process available to Federal facilities

for parabolic-trough projects. In addition,

sidebars provide indicators that a system

will be effective, tips for ensuring successful

operation, and sources for determining system data. Case studies for a 10-year-old 

system at a county jail and for one just starting construction at a Federal prison include 

economic evaluation data.
Contents

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

About the Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

Application Domain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

Energy Savings Performance Contracting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

Energy-Saving Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10

Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

Variations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

Federal-Sector Potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

Technology-Screening Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

Estimated Market Potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13

Laboratory Perspective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13

Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

Application Screening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

Where to Apply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15

What to Avoid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15

Equipment Integration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15

Maintenance Impact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15

Equipment Warranties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15

Codes and Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16

Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16

Utility and Government Incentives and Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16

Additional Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

Technology Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

Field Experience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

Energy Savings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

Maintenance, Environmental, and Other Impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

Case Study 1 — Adams County Detention Facility, Brighton, Colorado . . . . . . . . . . . . . . . . . .17

Case Study 2 — Federal Correctional Institution, Phoenix, Arizona . . . . . . . . . . . . . . . . . . . . .18

The Technology in Perspective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19

Manufacturers of Parabolic-Trough Collectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20

Manufacturers of Indirect-Fired Absorption Cooling Systems . . . . . . . . . . . . . . . . . . . . . . . . . .20

Federal Program Contacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20

Who is Using the Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20

For Further Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21

Appendixes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

Appendix A: Available Solar Radiation for Selected National Solar Radiation 

Data Base Stations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

Appendix B: Data Necessary for Evaluating Parabolic-Trough Solar Water-Heating Systems .31

Appendix C: Absorption Cooling Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32

Appendix D: Federal Life-Cycle Costing Procedures and the BLCC Software . . . . . . . . .34

Appendix E: Adams County Detention Facility Case Study: NIST BLCC 

Comparative Economic Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35

Appendix F: Adams County Detention Facility Case Study: ESPC Economic Analysis . .37

Appendix G: Federal Correctional Institution—Phoenix Case Study: NIST BLCC 

Comparative Economic Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38

Appendix H: Federal Correctional Institution—Phoenix Case Study:

ESPC Economic Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40

3
4

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About the Technology

The basic principle of solar water heating

is intuitive and straightforward. A dark surface is positioned to absorb sunlight and

convert it to heat. Water or another heat

transfer fluid passes along that hot surface

to pick up the heat—either for direct use or

for transfer through a heat exchanger to the

end use. Simple solar water heating has

been around since ancient times. More than

a million solar water heaters have been

installed in the United States. Most of these

were installed during the 1980s, when tax

credits were available, and nearly all use

"flat-plate" collectors, which essentially

place the absorber surface inside an insulated box. (See Figures 1 and 2.)

Parabolic-trough solar water-heating systems carry solar water-heating technology a

step further by concentrating the sunlight

before it strikes the absorber. Mirrored surfaces curved in a parabolic shape linearly

extended into a trough shape focus sunlight

on an absorber tube running the length of

the trough (Figure 3). A heat transfer

fluid—usually a solution of water and

antifreeze—is pumped around a loop

through the absorber tube of the collector.

There it picks up heat and then goes to a

heat exchanger where it either directly heats

potable water or heats a thermal storage

tank. (See Figure 4.)

As concentrating systems, parabolic

troughs use only direct radiation. Unlike

flat-plate collectors, they cannot use diffused

sunlight. Using tracking systems makes up

for this inability to collect more of the direct

light, but cloudy skies become a more critical factor. Parabolic-trough collectors are

therefore much more likely to be effective in

areas such as the Southwestern United

States that have good solar resources dominated by direct-beam sunlight. (See Figures

5 and 6.)

To make efficient use of the tracking systems and of the much higher temperatures

that can be generated by a concentrating

system, it is more cost effective to build a

larger system that will be used continuously.

Parabolic troughs are generally impractical

for small systems, but can be much less

expensive than flat-plate collectors if the

system is large enough. Parabolic-trough

5

Single or

double glazing

Glazing frame

Temperature

tolerant

gasket

Inlet

manifold

Outlet

manifold

Box

Flow passages

Absorber

plate Backing

Temperature

tolerant

insulation 02279809m

Figure 1. Flat-plate collector.

Figure 2. Flat-plate collector array providing domestic hot water for U.S.

Environmental Protection Agency headquarters in leased space in the Waterside Mall

in Washington, D.C.

Russ Hewett, NREL/PIX05642

02279803m

Parabolic shape

aluminum trough

with reflective coating

Glass encased

absorbent-coated

receiver tube

Flex-hose to carry

transfer fluid to/from

receiver tube

Figure 3. Parabolic-Trough Collector
solar water heating is therefore an effective

technology for serving large, 7-days-a-week,

domestic hot-water users such as Federal

hospitals, prisons, or barracks.

Application Domain

The Federal government provides energy

to approximately 500,000 buildings and

facilities with a total floor area of about

3 billion square feet (280 million square

meters). In fiscal year (FY) 1995 the Federal

government spent $3.6 billion for 365 trillion British thermal units (Btu) of energy for

those buildings and facilities. Water heating

accounts for a substantial portion of energy

use at many Federal facilities. Nationwide,

approximately 18% of energy use in residential buildings and 4% in 

commercial buildings is for water heating.

Federal facilities with large laundries,

kitchens, showers, or swimming pools will

likely devote even more energy to water

heating. Parabolic-trough solar waterheating systems can efficiently provide half

or more of the hot-water needs of many 

Federal facilities—cutting back on utility

charges and on pollution.

As for any solar water-heating system,

parabolic troughs are most likely to be cost

effective for facilities that otherwise must

heat water with expensive conventional

energy. As Table 1 on page 8 shows,

parabolic-trough collector systems can provide hot water at a levelized cost of $6 to

$12 per million Btu for most Southwestern

areas. Parabolic-trough solar water-heating

is therefore well worth investigating for economic viability if the available conventional

water heating uses electricity or fossil fuel

6

Figure 4. Parabolic-trough array for domestic hot-water service for the Jefferson

County Detention Facility, Golden, Colorado.

Warren Gretz, NREL/PIX01019

North-South Axis

Kilowatt-hours

per square meter

6 to 7

5 to 6

4 to 5

3 to 4

2 to 3

Map prepared by the NREL Resource Assessment Program 02279804m

Figure 5. Average daily direct-beam solar radiation for horizontal, north-south, single-axis tracking parabolic trough collector 

systems. A north-south axis is better in summer and on a yearly average basis than an east-west axis.
energy costing more than about $6 per 

million Btu. That is equivalent to about

2¢ per (kWh) of electricity, 55¢ per gallon

of propane, 83¢ per gallon of fuel oil, or

60¢ per therm of natural gas. Depending on

which conventional energy sources are

available to them, many Federal facilities

are likely to be paying more than $6 per

million Btu for their water heating. As can

be seen from Table 2 on page 6, national

average effective energy costs to Federal

facilities are greater than $6 per million Btu

(MBtu) for electricity and propane and

within possible regional variance for fuel oil

and natural gas. (The Federal government's

average cost for energy for buildings in

1995 was $9.95/MBtu.)

Parabolic-trough systems benefit greatly

from economies of scale and are not as well

suited to small projects as nonconcentrating

collectors. Typically, 3600 square feet of

collector (able to produce about 7500 gallons of hot water per day) would be the

minimum size for a viable project. Solar

water-heating economics are better when

there is a relatively constant demand for hot

water throughout the week and throughout

the year, or higher demand in the summer.

Facilities such as prisons, hospitals, and 

barracks that operate 7 days per week and

have relatively constant populations

throughout the year are therefore often

excellent candidates.

Clear skies are important for any solar

technology but are particularly so for parabolic troughs because they use only direct

radiation. Facilities located within the three

7

East-West Axis

Kilowatt-hours

per square meter

5 to 6

4 to 5

3 to 4

2 to 3

Map prepared by the NREL Resource Assessment Program 02279805m

Figure 6. Average daily direct-beam solar radiation for horizontal, east-west single-axis tracking parabolic-trough collector systems. 

An east-west axis is better in winter and more even throughout the year than a north-south axis.

The Power of the Parabola

The parabola is an intriguing geometric shape with important practical uses—including concentrating sunlight. The curve of a parabola is such that light travelling parallel

to the axis of a parabolic mirror will reflect to a single focal point from any place along

the curve. Because the sun is so far away, all light coming directly (excludes diffuse)

from it is essentially parallel, so if the parabola is facing the sun, the sunlight is concentrated at the focal point. A parabolic trough extends the parabolic shape to three

dimensions along a single direction, creating a focal line along which the absorber

tube is run.

02279802m

Axis

Focal point
highest level bands on Figure 5 or the two

highest level bands on Figure 6 (4 kWh per

square meter or more) are far more likely 

to be good candidates for parabolic-trough

systems. (See Appendix A for specific data

for nearly 70 locations with direct solar

radiation.)

Handling wind loading is the predominant design challenge for parabolic-trough

collector systems. High winds can exert torsional loads that are absorbed well by the

ground, whereas roof-mounted troughs may

require costly reinforcement to accommodate the stress. Also, trough systems require

large installation areas that may not be

available on a roof. Parabolic-trough systems therefore require large, unshaded

installation areas near the place of use.

Energy Savings Performance

Contracting

Industrial Solar Technology (IST) of

Golden, Colorado, has installed parabolictrough solar water-heating systems for several state or local facilities including prisons

and an indoor-pool recreation center. IST 

is also building a major domestic waterheating system for a Federal prison. (See

case studies on pages 15 and 17.)

The sole current manufacturer of parabolic-trough solar water-heating systems,

IST has installed all of its systems so far 

on a payment-for-energy-savings basis. IST

or a third-party investor typically builds,

operates, maintains, and owns the system.

The owner then bills the customer facility

for the amount of energy delivered by the

solar water-heating system at a rate slightly

less than currently being charged by the

facility's utility for supplying conventional

energy.

The Federal Emergency Management

Program (FEMP) of the U.S. Department 

of Energy (DOE) has now set up a program

of Energy Savings Performance Contracts

(ESPCs) that allows Federal facilities to

install energy efficiency measures or renewable energy equipment under payment-forenergy-savings arrangements similar to

those which IST has used. Many facilities

have used ESPCs and found them highly

advantageous.

ESPCs are Federal/private-sector partnerships in which an energy service company

(ESCO) installs and operates a system,

bearing all up-front design, installation, and

hardware costs (including financing) and 

the government repays the ESCO out of

budgeted utility dollars for a share of energy

savings resulting directly from the project

during the contract term. The agency never

pays more than what its utility bill would

have been without the ESPC project. Once

the contract is completed, the government

takes title to the equipment and retains all

subsequent savings. The disadvantage 

of ESPCs is that the government does not

immediately retain all savings generated, as

it would if the project were funded by direct

appropriations. The advantages of ESPCs,

however, make them an attractive alternative

for implementing energy savings,

8

Installed cost

per square

foot of Albuquer- Dallas, Denver, Phoenix, Sacramento, San Diego,

collector que, NM TX CO AZ CA CA

$20 $6.16 $ 7.26 $6.26 $6.72 $ 7.39 $ 8.14

$24 $6.78 $ 8.15 $6.94 $7.30 $ 8.09 $ 8.92

$28 $7.39 $ 9.04 $7.61 $7.87 $ 8.78 $ 9.71

$32 $8.00 $ 9.93 $8.29 $8.45 $ 9.48 $10.50

$36 $8.61 $10.82 $8.96 $9.03 $10.18 $11.28

$40 $9.21 $11.71 $9.64 $9.61 $10.88 $12.07

Array size 6000 7800 7200 4800 6600 7200

(sq. ft.)

% of load met 57% 53% 54% 54% 53% 55%

Calculations are based on F-chart analysis of energy savings for a 7,200-square-foot (669-square-meter)

collector system designed to meet domestic hot-water need of 17,000 gallons (64 kiloliters) of hot water

(140 ̊F/60 ̊C) per day (4652 MBtus) in the Denver, Colorado, area, adjusted in size to meet approximately

the same percentage of the hot-water load. Locations were selected that have both reasonably good solar

resources and a large number of Federal facilities nearby. Other assumptions include: Federal ownership

and operation; backup by natural gas with costs inflated at 3.0% per year; 2% operation and maintenance

costs inflated at 3.0% per year; continuous operation for a 25-year life with no salvage value; and present

value of savings calculated on the basis of an annual nominal discount rate of 6.6% (equal to real discount

rate of 3.4%). See "Costs" on page 16 for costs per square foot for some actual facilities. Note that costs

include the cost of backup heating. Thus, the levelized costs for Phoenix (which has higher conventional

energy costs) are higher than for Denver, even though the solar resource is better. 

Boiler Effective

Energy Cost Efficiency* Energy Cost*

Electricity 6.1¢/kWh $17.87/MBtu 98/91%* $18.23/19.64 per MBtu*

Propane 64¢/gal $ 6.99/MBtu 75/59% $ 9.33/11.85 per MBtu

Fuel oil 60¢/gal $ 4.33/MBtu 80/59% $ 5.41/7.34 per MBtu

Natural gas 35¢/therm $ 3.54/MBtu 75/59% $ 4.71/6.00 per MBtu

* (state-of-the art/typical) The first, state-of-the-art boiler efficiency figures (and corresponding effective

energy costs) are based on what is available for large modern boilers and are higher than those available for

individual home water heaters. The second, "typical" boiler efficiency figures are from the Gas Appliance

Manufacturers Association October 1997 Consumers' Directory of Certified Efficiency Ratings for

Residential Heating and Water-heating Equipment, pages 120, 142, and 144. Data are mid-range for a 

50-gallon, first-hour rating, except for fuel oil boilers, which are for a 100-gallon rating. Efficiencies are for

fuel conversion and do not include losses from the boiler or water heater, which also apply to heat 

supplied by solar collectors.

Sources: Energy costs are from Table 6-A, p. 47, Federal Energy Management Program Annual Report to

Congress on Federal Government Energy Management and Conservation Programs Fiscal Year 1995.

Table 2. Effective Energy Cost for Water Heating Based on 1995

National Average Federal Facility Utility Prices

Table 1. Effective Levelized Cost of Energy ($/MBtu)

for Solar Water Heating with Parabolic-Trough Collectors

at Selected Locations
particularly when appropriated funds are 

not available. (See the sidebar at bottom.)

FEMP has now made it particularly easy

for Federal facilities to have IST install a

parabolic-trough solar water-heating system.

FEMP has issued IST a Super ESPC—a

technology-specific Indefinite Delivery/

Indefinite Quantity (IDIQ) contract to install

parabolic-trough solar collector systems for

any Federal facility on an ESPC basis. If

after reading this FTA, a parabolic-trough

system seems feasible, contact IST. (See

Manufacturers of Parabolic-Trough Collectors on page 20.) With a minimum of

information, such as location, cost of conventional energy, and amount of hot-water

use, IST staff can determine if economics

are promising enough to warrant a visit and

detailed assessment. (See the sidebar on

page 14 and Appendix B.) The burden is

then on IST staff to decide if they can

design a viable project and obtain financing

for it. If so, then write a delivery-order

request for proposal (DORFP) to order a

system. This is considerably easier than the

standard procurement process, and DOE has

a simplified-format DORFP that may be 

used for this. It is available from the DOE

Golden Field Office. (See Federal Program

Contacts.)

Rather than being tied to future utility

prices or actual savings, delivery orders

under the IDIQ assume both a fixed utility

rate and projected, guaranteed savings to 

the facility. Monthly payments are made on

that basis. IST's systems include meters to

accurately measure the amount of energy

provided, but are used just to verify that

projected energy savings are being 

delivered.

ESPC contracts are highly suitable for

renewable energy installations at Federal

facilities and are a relatively easy procurement method. The facility doesn’t need to

make any initial capital outlay or budget

request, bears no burden for proving favorable economics, faces minimal risk, and has

no operation and maintenance responsibilities. (See sidebar at left.) At the end of the

contract (maximum 25 years under the

IDIQ), the government can own the system

and no longer pays for the energy provided.

The IDIQ also allows IST to include other

features in the project that relate to the 

parabolic-trough collector installation—

such as installing energy conservation measures or replacing the existing conventional

water heater.

9

First Things First

As a rule, conservation is the most cost-effective way to reduce water-heating bills.

For example, a low-flow showerhead costing $9 saves nearly $17 for 275 kWh of 

electrical energy per year, for payback in less than 7 months. Other examples of hotwater-saving measures include faucet aerators; timed or optical-sensor faucets; watersaving clothes washers, dishwashers or other appliances; water heater insulation;

lower-setting or timed water heaters; and swimming pool covers. If inexpensive conventional water heating is available, conservation measures alone may suffice and be

the most cost-effective action. If, however, conventional water heating is expensive,

solar water heating is also worth considering in addition to or in conjunction with 

conservation. Energy efficiency measures such as those mentioned above are all

compatible with solar water heating, and often reduce the size of the systems needed.

Reducing hot-water use saves on water and sewage as well as energy. For more

information, ask the FEMP Help Desk about the Water Conservation Program. (See

Federal Program Contacts.)

Next, check the conventional water-heating system. Is it the right size for the facility’s

needs? Is the system using the most cost-effective fuel in the area? Is it efficient? 

For larger systems, electric water heaters are now available with efficiency as high as

98%.* Large natural gas, propane, or fuel oil water heaters are available with 75% to

80% efficiency.* Switching boilers or water heaters alone may be the most effective

action, but it can also be done as related work as part of a contract for parabolictrough system installation. 

Then do a quick assessment of whether solar water heating is likely to be effective 

for the facility and whether parabolic-troughs or nonconcentrating flat-plate or evacuated-tube collectors are more likely to be appropriate. (See Application Screening 

section and sidebar on page 14 for information on FRESA, computer software that 

can quickly give a preliminary assessment of whether solar water heating will be 

feasible.) 

*These numbers are for fuel conversion and do not include heat losses from the tank

or delivery system. These losses can be significant—particularly for smaller water

heaters—so a better insulated tank or additional insulation may also be very effective.

Energy Savings Performance Contracting

Simplifies the Process

Energy Savings Performance Contracting under Industrial Solar Technology's IDIQ

contract makes it much simpler for Federal facilities to get a parabolic-trough solar

water-heating system. The IDIQ allows Federal facilities to investigate with IST

whether a parabolic-trough system would be effective for the facility, and if so, pursue

a delivery order. ESPC agreements provide many attractive features: 

• No financial outlay by the facility to determine feasibility

• No need to seek competitive proposals

• Pre-identified savings

• No responsibility for operation and maintenance

• The current system stays in place as a backup for high reliability

• Guaranteed savings

• The facility pays only for the energy savings it realizes

• The facility can benefit indirectly from tax incentives available only to private 

companies

• The facility can get credit for energy use reduction in compliance with Executive

Order 12902 (mandatory 30% reduction by 2005) without reducing hot-water use

• Switching to a more economical conventional water heater or other related 

efficiency measures can be included in and financed by the ESPC project.
Alternatively, a facility may pay for 

initial system installation itself using traditional appropriations and financial analysis

and project budgeting. (See Federal LifeCycle Costing Procedures in Appendix D.)

This brings the full energy cost savings

achieved back to the facility rather than

splitting it with an ESCO during the contract term, thus generating greater savings

over the project life. For most Federal facilities, however, ESPC is also very attractive

financially—especially for capital-intensive 

projects such as parabolic-trough systems.

Private companies can often take advantage

of tax credits for renewable energy or accelerated depreciation of the capital investment

that the facility itself cannot. Thus, many

projects for Federal facilities that do not

meet the 10-year simple payback criterion

that mandates construction, or the positive

life-cycle cost analysis that allows construction, could be attractive investments for 

private companies. IST has, in fact, used

third-party financing for all of its projects

thus far. The investor pays IST to build and

maintain the systems and then collects the

energy-savings payments from the facility.

Energy-Saving Mechanism

Parabolic-trough collectors are typically

used in active, indirect water-heating systems. Such systems use pumps to circulate

an antifreeze solution between the collectors

and the storage tank, where a heat exchanger

transfers heat from the circulating fluid to

water in the thermal storage tank. Potable

water flows through a second heat exchanger

in the storage tank, absorbing heat for the

water that will actually be used. (See

Figure 7). Parabolic-trough collectors generally require more supervision and maintenance than nonconcentrating solar

collectors—the reflectors must be cleaned

and checked for leaks two to four times per

year. These systems particularly benefit

from economies of scale, so are generally

used for larger systems.

Parabolic-trough solar collectors use

curved mirrors to focus sunlight on a

receiver tube running through the focal line

of the mirrors. The pressurized tube through

which the antifreeze solution circulates is

coated with a special heat-absorbent surface

and encased in a glass tube. IST parabolictrough collectors can heat their transfer fluid

to as much as 520 ̊F (271 ̊C) or more, but 

for domestic water supply systems, they

10

02279808m

Parabolic troughs

Sunlight

sensor

Controller

Temperature

sensor

Hot water to

existing system

Bypass

valve

Solar pump Cold water

supply

Hot water

storage tank

(non-pressurized)

Auxiliary

conventional

water heater

(pressurized)

Service

hot water

Figure 7. Typical parabolic-trough solar water heating system.

Industrial Solar Technology/PIX05641

Figure 8. Parabolic-trough collector systems also work well for central plants serving

district heating systems. This system at the California Correctional Institution at

Tehachapi augments a central boiler that provides several buildings with hot water 

for space heating as well as for domestic use. District systems such as this one will 

generally not include storage—contributing only when they are actually operating.

They will therefore meet a smaller portion of the load than the 50% to 60% typical 

for systems including storage.
typically operate at about 200 ̊F (93 ̊C) to

deliver water at about 120 ̊F to 140 ̊F (49 ̊C

to 60 ̊C ). Efficiency is highest with a temperature difference of about 60 ̊F (33 ̊C)

between input to the solar collector field and

output from the field to the thermal storage

tank.

In addition to the collectors, IST's parabolic-trough systems include an electric

tracking system (to keep troughs facing the

sun or turned downward when it’s dark or

too windy), a nonpressurized hot-water 

storage tank, a circulating pump to drive the

hot transfer fluid from the troughs through 

a closed-coil heat exchanger in the storage

tank to heat that tank (pressurized loop), a

loop that draws cold intake potable water

through a second heat exchanger in the 

storage tank on its way to the conventional

water heater, and various sensors to trigger

the proper operation. (See Figure 7.)

The system acts as a preheating system

for the facility's conventional water-heating

system. If the solar-heated water is too hot,

a tempering valve mixes in cold water. If the

water is not hot enough, the conventional

system heats it to the proper temperature. 

As hot water is used from the conventional

water heater, incoming cold water flows

through a heat exchanger, drawing heat

from the hot-water storage tank, and then 

to the conventional water-heating system.

In locations with no freeze danger, water

can be used instead of antifreeze because

it’s cheaper and is a better heat transfer fluid.

In the Southwestern United States, there is

sufficient sunlight for parabolic-trough collector systems to operate about 30% to 35%

of the time. The systems will generally be

most cost effective if sized so that on the

best summer days they are just able to meet

the demand—that is, there is no excess

capacity. Such a system will provide about

50% to 60% of annual water-heating needs.

If conventional energy costs are particularly

high, it may be economical to increase system size somewhat beyond this point.

Benefits

Solar water heating reduces the amount

of water that must be heated by a facility's

conventional water-heating system; it

thereby directly substitutes renewable

energy for electricity or fossil-fuel energy

and cuts utility bills. Each unit of energy

delivered to heat water with a solar heating

system yields an even greater reduction 

in use of fossil fuels. For example,

industrial-size water heating that uses natural gas, propane, or fuel oil is typically

only about 60% efficient and 75% to 80%

efficient at best. Electric water heating is

typically about 90% efficient and can be

98% efficient. However, producing that

electricity from fossil fuels is generally only

30% to 40% efficient. Furthermore, reducing fossil-fuel use for water heating not only

saves fossil fuel stock, but eliminates the 

air pollution and climate-changing gas emissions associated with burning those fuels.

Variations

As described in this FTA, domestic water

heating is the principal application for parabolic-trough collectors. They can, however,

be used for other water-heating needs. At

the Paul Beck Recreation Center in Aurora,

Colorado, these collectors provide water 

for an indoor swimming pool, showers, and

related facilities. (Smaller swimming pools—

particularly outdoor ones—can generally 

be more effectively heated by inexpensive,

low-temperature collectors that are nonconcentrating and uninsulated.)

Parabolic-trough solar collectors can also

power air-conditioning. Air-conditioning

systems are typically based on a compression cycle driven by an electric motor. But

an alternative, mechanically simpler system

is based on an absorption cycle driven by a

heat source. One type of system that can 

be operated efficiently using solar energy is

the water/lithium bromide absorption chiller.

Water at very low pressure is used as the

refrigerant and lithium bromide is used as

the absorbent. Absorption chillers can be

either direct-fired (usually by natural gas) 

or indirect-fired (by hot water or steam).

They are produced commercially by heating, ventilation, and air-conditioning

(HVAC) equipment manufacturers in the

United States and abroad. Several major 

air-conditioning equipment manufacturers

make indirect-fired absorption chillers that

can run on solar-heated water or steam. 

(See manufacturer’s information on

page 20.)

Two varieties of indirect-fired absorption

chillers are available—single-effect and

double-effect. (See Appendix C.) Singleeffect absorption cooling systems can use

solar-heated fluid (usually water) at temperatures of 77 ̊C–99 ̊C (170 ̊F–210 ̊F) to drive

absorption refrigeration cycles. Doubleeffect systems are more efficient but require

temperatures of about 177 ̊C (350 ̊F), usually in the form of steam. Parabolic-trough

collectors efficiently heat water to these

required temperatures.

Double-effect absorption coolers usually

have coefficients of performance (COPs) of

about 0.9 to 1.2, compared to about 0.6 to

11

Warren Gretz, NREL/PIX05640

Figure 9. Parabolic-trough collectors at Paul Beck Recreation Center in Aurora,

Colorado, heat water for a swimming pool and related facilities.
0.8 for single-effect systems. COP is the

ratio of the heat energy removed divided by

the work required to remove it. That work is

defined differently for absorption cooling

than for compression cooling (based on heat

input rather than electrical input). Therefore,

these COPs cannot be directly compared to

those for electrical compression cooling 

systems (generally 2.0 to 4.0).

Solar heat is well suited to heat water or

generate steam for indirect-fired absorption

cooling because of the close time match

between solar heat generation and the need

for cooling. Because air-conditioning frequently drives peak electrical demand, the

time match of parabolic-trough energy 

collection to air-conditioning needs is significant. Electric utilities frequently charge

commercial facilities two to three times 

as much for power during peak demand

periods and may even subsidize customer

projects that reduce peak demand.

Absorption cooling offers a critical 

additional benefit for hospitals and other

facilities that cannot tolerate being without

air-conditioning—only minimal electricity is

necessary to keep a parabolic-trough system

operating during a power outage. Facilities

with parabolic-trough collector/absorption

cooling systems need far smaller backup

generators than those with electric compression cooling.

Nearly all solar absorption cooling systems include subsystems for space and

water heating. This allows the expensive

solar equipment to be used throughout the

year, rather than just during the cooling 

season. Figure 10 shows how paraboliccollector and absorption cooling systems

work together.

As with parabolic-trough water heating,

the economic viability of parabolic-trough

air-conditioning will largely be a function 

of the system cost and conventional utility

costs. Absorption chillers will cost from 

1.5 to 2.5 times as much as electriccompression air conditioners or chillers. But

if the electricity cost is high enough relative

to solar heat or fuel such as natural gas or

propane, the extra equipment cost for

absorption cooling may be a good investment. Similarly, if the conventional fuel 

cost is high enough, the cost of a parabolictrough collector system to drive the absorption cooler may be a good investment. With

a 9-month or longer cooling season and

electricity costing about 10¢/kWh or more,

a parabolic-trough/absorption chiller system

is worth investigating. Because the parabolic-trough collector portion will usually

account for more than half the cost of such a

system, it is important for economic reasons

that the system also be used for water heating and space heating.

Parabolic-trough systems can also be

used to heat industrial or industrial-like

process water or other fluids to high temperatures. (IST's systems can generate temperatures as high as 520 ̊F [271 ̊C]). Federal

facility activities that might need such hightemperature water include cleaning engines

or other equipment, industrial laundries, and

certain hospital uses. For higher-temperature

uses, oil is often used instead of antifreeze,

both in the collector loop and in the thermal

storage tank.

In addition, parabolic-trough collectors

can be used to generate electricity. During

the 1980s Luz International (no longer in

business) built nine plants for solar thermal

electrical generation. All are still operating.

These systems, which encase the collector

tube in a vacuum, use oil as a transfer fluid 

and reach temperatures of 730 ̊F (388 ̊C).

Electrical generation facilities can also use

parabolic dish systems that concentrate light

in two directions instead of one, but nearly

all existing solar thermal electrical generation is from parabolic-trough systems.

Installation

Because they use only direct-beam 

sunlight, parabolic-trough systems require

tracking systems to keep them focused

toward the sun and are best suited to areas

with high direct solar radiation. (See Figures

5 and 6). Most systems are oriented either

east-west or north-south with single-axis

tracking during the day. East-west orientation is better in winter and more constant

throughout the year, while north-south 

orientation is better in summer and provides

greater annual output. The systems are programmed to turn the collectors upside down

at night or during high winds to reduce

stress on the structure and help keep the

mirrors clean.

Because they transmit structural stress

from wind loading and require large areas

for installation, parabolic-trough collectors

are usually ground mounted. IST is developing a smaller, lower-profile version of its

collector system that will be more suitable

for roof mounting, but its standard troughs

are 20 feet by 7.5 feet (6.1 meters by

2.3 meters). IST typically installs sets of

either 16 troughs (4 rows of 4 for 2400

square feet of collector) or 24 troughs 

(4 rows of 6 for 3600 square feet of collector). Each set can run on a single-drivemotor tracking system. These installations

require about 6,000 and 9,000 square feet

(557 and 836 square meters), respectively,

of level or slightly south-facing, unshaded

space with the latter being the smallest size

generally viable project. The collector system should be fenced and within 1000 feet

of the conventional water heater for the

building where the water is being used (the

closer the better). Parabolic-trough systems

will usually be installed by the manufacturer. IST generally assembles the collectors

onsite or nearby.

Federal-Sector

Potential

Technology-Screening Process

The FTA series targets technologies that

appear to have significant untapped Federalsector potential and for which some Federal

installation experience exists. Many of the

12

02279806m

Parabolic troughs

Controller

Sunlight

sensor

Solar pump

Thermal

storage

Hot water pump

Chilled water to

air conditioning system

One or

two-stage

absorption

chiller

Cooling

water

Heater

Figure 10. Schematic of trough cooling system.

02279806m
FTAs are about new technologies identified

through advertisements in the Commerce

Business Daily and trade journals and

through direct correspondence soliciting

technology ideas. Those technologies are

then evaluated in terms of potential energy,

cost, and environmental benefits to the 

Federal sector.

Parabolic-trough solar water heating was

included in the New Technology Demonstration Program because this renewable

energy technology has obvious energy, cost,

and environmental benefits and has substantial untapped potential in the Federal sector.

IST is officially designated by DOE as an

energy service company qualified for ESPC

contracts. Additionally, the IDIQ contract

with IST substantially simplifies procuring

this technology. (The thermal performance

of IST's parabolic-trough systems was independently measured by Sandia National

Laboratories and reported in Sandia Report

SAND94-1117).

Estimated Market Potential

In FY 1995 the Federal government

spent $3.6 billion on energy costs for buildings—75% on electricity, 12% on natural

gas, 6% on fuel oil, and 8% on other forms

of energy. An estimated 12% of energy use

for buildings is for water heating. Assuming

a similar percentage for Federal facilities

suggests that Federal water heating costs

about $432 million per year.

The FEMP Tracks database of Federal

facilities lists 16 prisons, 87 hospitals, and

147 housing complexes that are located

within Southwestern or other states where

there are probably adequate solar resources

for parabolic troughs and that are large

enough that they would likely benefit from a

parabolic-trough system (Table 3).

Laboratory Perspective

Although only a few parabolic-trough solar

water-heating systems have been installed so

far, the technology is well developed and

has been clearly demonstrated. The National

Renewable Energy Laboratory and Sandia

National Laboratories helped develop the

technology, and as mentioned earlier, Sandia

measured its performance. FEMP and the

two laboratories have worked closely with

IST to identify good opportunities to apply

the technology at Federal facilities. The two

laboratories also supported past efforts to

use parabolic-trough heating for electrical

generation and industrial process water and

continue to work on solar thermal electrical

generation.

Cost-shared, collaborative technology

development testing and evaluation projects

with NREL and Sandia have allowed IST 

to greatly improve the performance of 

parabolic-trough collector technology.

Solgel antireflective coating for the glass

enclosure surrounding the receiver tube is

made by IST under license from Sandia

National Laboratories. ECP-305+® silvered

polymer reflector film was developed under

a collaborative project between NREL and

the 3M Company and was tested and 

evaluated by IST. Both of these improvements enhance energy capture. For example,

the system installed in 1996 for the Jefferson

County Detention Facility in Golden,

Colorado, which features these enhancements, delivers about 38% more energy 

per surface area of collector than the one

installed in 1990 at the California Correctional Institute at Tehachapi, which is not

enhanced. Using these new technologies,

however, only increases costs by about 10%.

IST has also begun using a black-nickelbased selective-absorption coating for the

receiver tube. Both costs and 

13

Sandia National Laboratories/PIX06068 

Figure 11. Gould Electronics of Chandler, Arizona, has had its parabolic-trough 

collector system since 1982. An example of use of oil for heat transfer for highertemperature uses, the system provides process water for copper foil production.

Prisons of Hospitals of Housing complexes of more than

more than more than 100,000 sq. ft. or more than 10,000 sq. ft.

State 25,000 sq. ft. 25,000 sq. ft. and 5,000 sq. ft. per building

Arizona 2 14 16

California 5 24 67

Colorado 2 6 9

Hawaii 0 1 5

New Mexico 0 11 12

Nevada 1 3 4

Puerto Rico 0 1 0

Texas 6 23 26

Utah 0 1 5

Wyoming 0 3 3

Total 16 87 147

Source: FEMP Tracks database

Table 3. Federal Facilities of Size and Location to be Likely

Candidates for Parabolic-Trough Systems
environmental concerns with manufacture

and disposal are less for this coating than

for previously used black-chrome coatings.

Application

The two most important factors in determining economic feasibility for any solar

water-heating system are the cost of building the system and the cost of operating

conventional water-heating systems. Parabolictrough collectors, in particular, require high

direct normal solar radiation, high hot-water

use levels, continuous hot-water use, and in

the case of use for air-conditioning, a long

cooling season. Therefore, parabolic-trough

solar water-heating or air-conditioning systems could benefit many hospitals, prisons,

barracks, and other Federal facilities in the

southwestern United States.

Federal facilities have two options available for procuring a parabolic-trough solar

water-heating system. The traditional option

is directly purchasing the system. A simplified procurement and budgeting option is

using ESPCs, as provided for in IST's IDIQ

contract.

Application Screening

In either case, the first step toward determining if a solar water-heating system

would be viable for a facility (or facilities)

is to assess the hot-water needs. How much

hot water at what temperature do the various

facilities use (or are new facilities expected

to use), on what kind of schedule? How

much does it cost for the energy to heat that

water? Could costs be reduced with a more

efficient conventional water heater? What

options are there for reducing hot-water 

use or lowering the temperature of water

provided? 

The next step is to obtain a preliminary

estimate of whether solar water heating 

will be cost effective. The FEMP Federal

Renewables Program at the National

Renewable Energy Laboratory has developed a computer program entitled Federal

Renewable Energy Screening Assistant

(FRESA) that can make such a preliminary

assessment. See the How Do You Figure

sidebar for a list of the necessary information. IST can provide a similar rough assessment specific to using parabolic-trough

collectors.

In order to directly purchase a parabolictrough-collector solar water-heating or airconditioning system, a positive FRESA

assessment should be followed up with a

formal feasibility study, including life-cycle

cost analysis (Appendix D) in accordance

with 10 CFR 436A and a request for proposals. A simpler economic criteria than

life-cycle cost analysis is the payback

period— the time it would take for energy

cost savings to repay the investment cost.

Executive Order 12902 directs that agencies

shall build any energy-saving project with a

simple payback of less than 10 years. This

is 

generally a more rigorous criterium than

life-cycle cost analysis, so there will be

many projects with positive life-cycle cost

analysis but with greater than 10-year simple payback. These may also be built, but

Executive Order 12902 would not apply.

Assuming a payback of less than 15 years

and a system life of 30 years, one can

expect 15 years or more of "free energy."

If, however, a project is built under

ESPC, as IST's IDIQ contract allows, it is

not necessary to do formal cost analysis or

14

How Do You Figure?

To obtain a preliminary analysis of whether solar water heating would be cost effective for a facility, use the Federal Renewable Energy Screening Assistant (FRESA)

software package. It’s available from the Federal Renewables Program at the National

Renewable Energy Laboratory (NREL). (See Federal Program Contacts.) Federal

Renewables Program staff can also do the analysis, if provided the following data:

• Hot-water use in gallons per day

• Fuel type and cost

• Zip code

• Incoming cold-water temperature

• Outgoing hot-water supply temperature

• Area of southern exposure roof or nearby grounds available for system

• Tilt and direction of roof area. 

One can do a rough calculation before asking for FRESA or a more detailed F-Chart

analysis. Divide 51.4 by the solar insolation for the area (single-axis tracking in kilowatt-hours per square meter per day as given in Appendix A). This should provide the

number of years it would take for the system to pay for itself based on an installed

cost of $22 per square foot.

The FRESA system does include solar resource data based on your zip code, but to

obtain comprehensive solar resource data request the NREL Solar Radiation Data

Manual for Flat-Plate and Concentrating Collectors or the CDROM of the National

Solar Radiation Data Base (Appendix A).

To estimate hot-water use, check the hot-water-use records; install a meter and track

usage; or project demand based on average use for various facilities as found in the

American Society of Heating, Refrigerating and Air-Conditioning Engineers' Handbook

of Applications. Typical usage per day per occupant in gallons is 20–30 for housing,

30 for hospitals or prisons, 5 for dining facilities, and 3 for other uses.

To determine incoming water temperature, which may vary considerably with the season, call the water utility or check the supply with a thermometer. In some instances,

the average annual air temperature also roughly indicates water supply temperature.

These temperatures are important because solar water heating is more efficient when

incoming water temperatures are lower (less heat loss to the environment); whereas,

cold air temperatures reduce efficiency.

To calculate system output information more rigorously than the preliminary analysis

provided by FRESA, use a computer program such as F-chart, or consult with

Federal Renewables Program staff or a solar water-heating system supplier.

The optimum size for collectors and storage will depend on fuel cost, available solar

resource, and the hot-water use pattern, but expect capacity on a good summer 

day to roughly match usage. The resulting system should meet about half of annual

demand. Precise optimization of system size will require both a calculation of output

and an evaluation of system economics.

To evaluate the economics of a contemplated system in detail, use the FEMP

Life-Cycle Costing Handbook and associated BLCC software, available by calling the

FEMP Help Desk. (See Federal Program Contacts.) One can also consult with the

Federal Renewables Program or a private engineer.
request competitive bids. To pursue ESPC

financing under the IDIQ, simply provide

IST staff with the necessary information and

they will determine whether it would be

economically advantageous for them to

build the system or—as they have for all

their installations thus far—convince a third

party to finance the project. To save on limited travel funds, IST personnel will usually

do a preliminary assessment by telephone to

determine whether economics are promising

enough for them to further investigate the

project and whether a DORFP should be

done. They will look for the following 

positive factors.

• Expensive utility rates for conventional

water heating—about $6/MBtu or more

(2¢/kWh of electricity, 60¢ per therm of

natural gas, 55¢ per gallon of propane, or

83¢ per gallon of fuel oil; average energy

costs for Federal facilities in FY 1995

were 6.1¢/kWh of electricity, 35¢ per

therm of natural gas, 64¢ per gallon of

propane, and 60¢ per gallon of fuel oil,

according to a FEMP survey)

• High direct normal solar radiation—

4 kWh per square meter or more, location in the three or two highest bands,

respectively, in Figures 5 or 6 on 

pages 6 and 7.

• High levels of hot-water use—10,000 gallons per day or more; or a long cooling

season of 9 months or longer

• Continuous facility use—preferably

7 days per week, 52 weeks per year

• Adequate unshaded space for the collector field

• For air-conditioning, inability to tolerate

system shutdown during a power failure.

Certainly, it is not always necessary to

meet each of these criteria. Furthermore, a

very high indication in one area, such as

energy costs, could overshadow counterindications in another area. Lower sunshine

levels or hot-water use might suggest alternative solar water-heating technologies.

Where to Apply

This technology is best applied at:

(1) Hospitals

(2) Other large health care facilities such 

as large clinics

(3) Military and civilian detention facilities

(4) Food preparation and service facilities

(5) Dormitories and barracks

(6) Laundries

(7) Central plants for district heating or 

water-heating systems

(8) Operation and maintenance (O&M) 

facilities, such as for transportation 

vehicles and equipment, requiring large 

volumes of hot water

(9) Production or assembly facilities 

requiring large amounts of hot water 

(e.g., munitions facilities) 

(10) Gymnasiums and recreation facilities 

with heated, indoor swimming pools

(11) Bachelor officer quarters and guest 

residential facilities

(12) Any other facility requiring large 

amounts of hot water on a continuous 

basis or otherwise meeting most of 

the criteria listed in “Application 

Screening.”

What to Avoid

If purchasing a system or seeking an

ESPC project, one should be aware of certain considerations. No one of these situations would preclude a project, but be sure

to inform IST staff about:

• Areas particularly prone to very severe

weather—high winds, tornados, hail

storms or hurricanes—or to vandalism

• Areas with unusually high dust or dirt

loads in the air

• Particularly mineral-rich water supply

(can foul the heat exchanger and the rest

of potable loop—less of a problem for

troughs than for other solar water-heating

systems)

• Facilities facing possible closure or

reduction in hot-water or air-conditioning

use

• Missed opportunities to make a parabolictrough project more economically attractive by adopting water conservation

measures, switching fuels, or installing

more efficient conventional water heaters

as part of the project. (The IDIQ does

allow such measures to be incorporated

into and financed as part of a trough 

project and IST will investigate their

inclusion.)

• Situations where a conventional energy

source is expected to become available

that is significantly less expensive than

that currently used

• Situations where the space dedicated to

the collector field could later be needed

for building expansion

• Oversizing the system so full capacity is

not always used (if not an ESPC)

• Lack of commitment to system maintenance (if not an ESPC).

Equipment Integration

Integrating the parabolic-trough collector

system into the existing hot-water system 

is simply a matter of adding a line routing

the cold intake water through the heat

exchanger in the thermal storage tank on 

its way to the existing conventional water

heater. Prisons with security perimeters

might need to penetrate a wall to do this.

The collector field requires electrical connections for the pump and the tracking system. Valves are included for the intake and

outflow of the fluid loop and one is added

on the old line direct to the water heater,

making it easy to bypass the parabolictrough system if ever necessary. 

Maintenance Impact

Parabolic-trough collector systems

require somewhat more maintenance than

most nonconcentrating solar water-heating

or other renewable energy or energy 

efficiency installations. Because hightemperature and high-pressure fluid is

involved, they should be monitored regularly. Also, the mirror surfaces should be

washed every few months. Consequently,

although facility staff could easily take on

these duties, the system installers usually

also maintain the system. Under an ESPC,

this is standard practice.

The mirror surfaces will degrade slowly

with time and may need replacement after

about 15 years. The pumps and tracking

equipment should last for the life of the project, but the pump seals will likely need to

be replaced after about 10 years and the

tracking equipment controls may need

replacement as soon as 10 years or as late 

as 30 years.

Because the solar collector system

reduces the amount of time that the conventional hot-water heater operates, the heater

should last longer. There is no other real

impact on existing equipment.

Equipment Warranties 

If IST sells a system, they guarantee 

the general collector system for 5 years; 

individual components such as pumps carry

whatever warranty the manufacturer provides. Note that under an ESPC, replace15
ment responsibility rests totally with the

installer and the facility pays only for

energy delivered.

Codes and Standards 

Other than local building and plumbing

codes, there are no special standards that

parabolic-trough solar water-heating systems need to comply with. In certain jurisdictions, codes could require double-walled

heat exchangers or nontoxic antifreeze,

but the system design IST usually uses is

already double-walled. IST prefers to use 

an ethylene glycol/water solution as the 

heat transfer fluid, but can easily substitute

nontoxic propylene glycol. If a facility does

not already have one, it might need to add 

a material safety data sheet for ethylene 

glycol.

Costs

Parabolic-trough system installation costs

will vary considerably with circumstances

for particular projects. IST quotes costs on

an individual basis. Costs per unit will,

however, generally be higher for smaller

projects and lower for larger projects. Costs

for three completed projects ranged from

$21 to $32 per square foot of collector and

$101 to $135/MBtu of energy per year 

($24 to $43 per square foot and $113 to

$204/MBtu per year in 1997 dollars). New

technology that IST is now using costs

about 10% more but produces about onethird more energy. Two new projects cost

$29 and $36 per square foot of collector 

and $101 and $132/MBtu per year. The

larger of these projects, however, was 

oversized with unusually large storage to

accommodate local utility peak pricing for

electricity, so a large new project is quite

likely to have lower costs than these.

Under an ESPC contract, the facility

does not pay for the project cost, but instead

pays for the resulting utility bill savings. 

A flowmeter on the intake and temperature

gauges on intake and outflow are connected

to a Btu meter that calculates energy delivered. If the facility has concerns about the

energy delivery calculation, FEMP/NREL can

set up an independent verification system

for initial system operation.

The IDIQ contract directs establishment

of an annual energy use baseline for the

facility and projection of energy cost savings. Monthly billing is based on projected

energy delivery and fixed energy costs

agreed on in the delivery order. Otherwise,

billing could be directly based

on the Btu meter, at fixed or

current energy prices.

(Including improvements such

as energy conservation measures or replacement of the

conventional water heater, in

addition to the parabolic-trough

collector system, may require

additional billing arrangements.)

Utility and

Government Incentives

and Support

Utility company incentives

for demand reduction and load

management can be an important non-Federal source of

financial assistance. Demandside management (DSM) activities, such as promoting solar

water-heating systems, can save

a utility from investing in system expansions or help them

comply with air quality programs. Some incentive programs are designed for residential

customers, but others also apply to or are

specifically designed for commercial facilities, including Federal buildings. Federal

facilities may also negotiate specific incentives for larger projects beyond the scope of

standard programs or in cases where standard programs do not exist.

The Hawaiian Electric Company, for

example, has a commercial and industrial

user rebate program that pays $125/kWh

capacity reduction of evening peak usage

plus 5¢/kWh for 1 year's production by

solar projects displacing electric water heating. The Lakeland (Florida) Department of

Electric and Water Utilities has started a

program—which it expects to be adopted

statewide—in which the department acts

very much like an energy service company.

The utility installs metered solar water

heaters on a lease basis and charges the customer for the energy delivered. During the

5 years of operation of a Sacramento

Municipal Utility District incentive program, more than 3000 solar water heaters

were installed. On the one hand, anticipated

utility industry restructuring may cut back

on DSM programs such as these, but on the

other, it may encourage utilities to spin off

energy service companies specifically set up

to design and install energy efficiency and

renewable energy projects.

Although Federal facilities can accept

utility rebates, they cannot take advantage of

tax credits or incentives, so the following

does not apply to Federal facilities that 

purchase a parabolic-trough system outright.

Even with an ESPC project, the facility 

cannot use tax credits or incentives, but the

installing company or third-party investor

may be able to. Tax incentives can therefore

be very important for parabolic-trough systems installed as ESPC projects. Because of

such incentives, it is not unusual for ESPC

projects to be financially attractive to the

system installer or third-party investor even

if it would be economically marginal for the

Federal facility to purchase the system. (See

case studies on pages 17 and 18.) System

cost and the cost of competing conventional

water heating will always be the dominant

factors, but if those factors make the margins close, tax incentives may make projects

financially feasible.

The Federal government currently provides a 10% business energy tax credit for

purchase of solar and geothermal energy

equipment (Section 1916 of the Energy

Policy Act of 1992; 26 USC 48). Also,

26 USC 168 allows for accelerated depreciation of solar energy property investments —

5 years instead of 20 years. These two

incentives can be quite significant to a thirdparty investor with a high tax bill. A hypo16 Russ Hewett, NREL/PIX05649

Figure 12. Simple connections to intake and outflow

temperature gauges and an intake flowmeter allow 

this Btu meter to quite accurately report how much

energy has been delivered by a parabolic-trough 

collector system.
thetical example on the Solar Energy

Industries Association Internet Web site

(http://www.seia.org/legdepre.htm) 

calculates the resulting combined savings as

more than 40%.

Similarly, more than half the states and

some local governments do provide incentives for solar thermal collector or solar cell

system purchases. The State of Hawaii currently allows a 35% tax credit for solar projects for commercial buildings. Total tax

credits for projects there can cut installation

cost almost in half for a third-party investor

in an ESPC project, and accelerated depreciation can add further savings. Other examples include an Arizona 6% loan program

for renewable energy and energy efficiency

equipment acquisition and a Texas corporate

income tax deduction for solar energy

equipment acquisition. A good source of

information on state incentives is a DOENorth Carolina State University Internet

web site: http://www-solar.mck.ncsu.edu/

dsirexls.htm.

Additional Considerations

On the negative side, the facility loses

use of the land occupied by the collector

field. On the positive side, because the conventional water heater is used less, polluting

and global warming air emissions are

reduced (on site for gas or oil heaters; at 

the power plant for electric heaters).

Technology

Performance

IST has installed parabolic-trough solar

water-heating systems for three state or

local prisons and one local indoor-pool

recreation center. All were installed on a

payment-for-energy-savings basis. The following is based on discussions with operators of a city pool in Colorado that has had 

a parabolic-trough collector system since

1985, a county jail in Colorado with a 

system since 1986, and a state prison in

California with a system since 1990. A new

system at another county jail in Colorado

has only been operating a short time. 

Field Experience

Facility managers indicated that the 

parabolic-trough collector systems were

largely "transparent" to them and their staff.

That is, they did not know all that much

about the collectors, and said staff just knew

that they were there and working. The existence of the system has no particular impact

on their daily operations. Maintenance 

is minimal and performed by IST. 

Down-time is minimal. One system was

down for 2 months after a backhoe broke

the delivery line to the facility and the facility delayed repair. Another system was

down for 3 weeks with a hose problem

when IST personnel were tied up on another

project. The third project had about 5% of

the reflectors damaged by a freak wind

storm, but IST had the system back up

within a week. Very deep snow occasionally

interferes with the tracking systems.

Because the conventional water-heating 

system is still in place, system downtime

causes no service disruption. Under an

ESPC, facilities are also fully protected

from any downtime because payments are

based either on annual energy audits or

directly on energy delivery meters.

Facility managers were generally quite

impressed with how well the systems operated and with the service provided for the

systems. The extent of the energy cost savings they were getting was not always that

clear to them, but they thought projects were

delivering about what was projected. Staff

for the recreation center indicated that they

are now considering expanding the center or

building a new parking lot and that the collector field location could turn out to limit

available options for those projects. There

were no problems with vandalism of the

collector fields, even when near heavy traffic by school-age children, nor were there

problems with impacts on birds or 

animals.

Energy Savings

The three projects each produce about

what was projected, about 200,000 Btu per

year per square foot of collector. All three

displace natural gas use. Assuming backup

water-heater efficiency of 75%, this means

they save about 267,000 Btu (200,000/.75)

of natural gas per year per square foot of

collector. (New projects incorporating

improved technology are about onethird more efficient for production of about

267,000 Btu per square foot, displacing

about 356,000 Btu of gas per square foot 

of collector. [See Laboratory Perspective on

page 13]) For the California prison—a very

large facility with a district heating system—the parabolic-trough system was built

without storage and only large enough to

displace 10% of total natural gas use for hot

water and space heating. But for the other

two projects, as they would for most facilities, the parabolic-trough system substitutes

for about half of the conventional energy

that would otherwise be used for water heating. One new project is sized to provide

80% of water-heating energy, but the larger

system and storage size for that project is

justified by a need to avoid high time-of-day

peak pricing by the local electric utility.

Maintenance, Environmental,

and Other Impacts

Managers noted very little impact on

their operations or on their facilities.

Maintenance of the parabolic-trough systems is all handled by IST under the Super

ESPC and the systems have no impact on

other systems except extending the life 

of conventional water-heating equipment 

by reducing its use.

Every unit of energy delivered by the

solar collector directly eliminates conventional energy use—and the associated pollution and global warming impacts. Because

of the inherent efficiency loss in heating

water with conventional fuels, the environmental benefits of substituting parabolictrough solar water heating for natural gas,

propane, or fuel oil are actually about one

and two-thirds times as great as the amount

of energy provided (assuming a 60%-

efficient heater) and about three times as

great when substituting for electric water

heating (assuming 30%- to 40%-efficient

electric production at the power plant). 

Case Study 1 —

Adams County

Detention Facility,

Brighton, Colorado

The Adams County Detention Facility 

in Brighton, Colorado (about 30 miles

[48 kilometers] northeast of Denver), was

originally designed for about 500 inmates

but is currently housing more than 800. The

facility uses an average of about 18,000 gallons (68,000 liters) of hot water per day 

for kitchen, shower, laundry, and sanitation

facilities. The facility's existing waterheating system included six natural-gasfired boilers.

In 1986, IST installed a 6000-square-foot

(555-square-meter) parabolic-trough collec17
tor system, together with a 5000-gallon

(19,000-liter), nonpressurized, stainlesssteel thermal storage tank, on a paymentfor-energy-savings basis. IST expanded the

system to 7200 square feet (669 square

meters) of collector in 1988 in response to

increased hot-water use resulting from

increased inmate population. The parabolictrough system preheats the water supply to

five of the six boilers and thereby provides

about 40% (1400 million of 3500 MBtus per

year) of the energy required by the prison

for water heating. 

The parabolic troughs heat the transfer

fluid (ethylene glycol mixture) to as much

as 256 ̊F (124 ̊C). Whenever the amount of

direct sunlight is above a set threshold, the

circulating pump turns on, sending the

heated antifreeze mixture through a coppercoil heat exchanger in the storage tank,

heating that water to as much as 185 ̊F

(85 ̊C).

The system has operated continuously

since 1987 except for a 2-month period after

the line from the collector field to the facility was broken by a backhoe during a construction project. Deep snows occasionally

keep the tracking system from working and

the system automatically shuts down during

high winds. IST personnel clean the reflectors and check the system for leaks two or

three times per year. The system's operation

has little impact on facility personnel who

know that it is there and how to turn it off if

anything should ever go wrong. Otherwise

they have nothing to do with it.

The Adams County Detention Facility

system is owned and operated by third-party

investors. The investors contracted with IST

to design and construct the system. Initial

cost of the system was $218,400 but a

$40,000 state "buy-down" subsidy reduced

the price to $178,400 and the investors benefitted $21,840 from a 10% tax credit. The

owners are responsible (with guidance from

IST) for major repairs or renovations and

pay IST to operate and maintain the system.

Adams County pays the owners for the heat

provided by the system—based on readings

from a Btu meter at the facility—at a discount from the current rate they pay for natural gas. The county spends about $200 per

month less for the combination of the trough

system plus utility bills than it would without the solar collector system.

The system has been operating for more

than 10 years. Because the facility's backup

conventional boilers are 70% efficient, the

1400 MBtus per year of solar energy provided by the parabolic-trough system saves

2000 MBtus of gas per year—enough

energy for total energy consumption by

more than 20 households. The total 

reduction in natural gas consumption thus

far is about 20 billion Btus. Over the life of

the project, approximately 50 billion fewer

Btus of natural gas (equivalent to about

370,000 gallons of fuel oil) will be burned,

with associated savings in pollution and

greenhouse gas emission. 

As can be seen from the added notes to

the life-cycle cost calculations in Appendix

E, the Adams County system would not

have been economically viable at the full

cost of $218,400. At the state-subsidized

cost of $178,400, however, the parabolictrough system yields discounted cost savings of about $29,000 over the life of the

project. As can be seen from the cash flow

calculation in Appendix F, however, the tax

benefits of 10% investment credit plus

accelerated depreciation that are available to

the private investors who funded the project

provide substantial additional savings. The

investors are able to pass on about $200 per

month savings to the facility and still get 

a 6% return on their investment, despite

lower than anticipated natural gas costs. The

county has already saved nearly $24,000;

projected savings for the 25-year life of the

project, based on actual natural gas costs for

the first 10 years and 3% escalation for the

future, are $58,000.

The 10-year operating history of the parabolic-trough solar water-heating system for

the Adams County Detention Facility shows

clearly that the technology works, and that

with installation on a payment-for-energysavings basis, operation posed no burden on

the facility or on facility staff. The cost calculations for the project show that subsidies

can provide the difference to make a project

economically viable and that the tax benefits

to a private funder can be very important.

The project's economic history and lessfavorable-than-anticipated return for the

investors also shows that one cannot count

too heavily on conventional energy prices

rising (something not done under the IDIQ).

From the facility's perspective, however, this

reinforces the fact that payment for savings

is a guaranteed-win situation, regardless of

whether energy prices rise or fall.

Case Study 2 —

Federal Correctional

Institution, Phoenix,

Arizona

Located about 10 miles (16 kilometers)

north of Phoenix, Arizona, the Federal

Correctional Institution (FCI-Phoenix) is a

18

Warren Gretz, NREL/PIX00327

Figure 13. Parabolic-trough solar water-heating system for Adams County Detention

Facility, Brighton, Colorado.
medium-security prison for males. It opened

in 1985 and was designed for about 500

inmates but is currently housing about 1200.

With five two-story housing units and a

kitchen/laundry building, the facility 

uses an average of about 21,000 gallons

(79,494 liters) of hot water per day for

kitchen, shower, laundry, and sanitation

needs. The facility now uses electricity for

all of its hot-water heating (current cost

6.2¢/kWh) and other utility needs. It does

not have access to natural gas and propane

was considered a safety concern in the

prison setting.

IST has an ESPC contract, which was

negotiated prior to the new IDIQ, to build

and install a parabolic-trough solar waterheating system for FCI-Phoenix. The

designed system includes 18,000 square feet

(1672 square meters) of parabolic-trough

solar collectors to be located inside a fenced

enclosure of about 1.2 acres (0.5 hectare). A

21,000-gallon (79,494-liter) thermal energy

storage tank will be located adjacent to the

solar field. This larger-than-typical storage

will allow the system to meet a projected

82% of the facility’s hot-water needs and

also meet most of the morning peak demand

at FCI-Phoenix—which will reduce charges

from the utility. An incoming cold-water

supply line is routed to a copper-coil heat

exchanger in the thermal storage tank and

then through insulated underground piping

to seven buildings. The solar-heated water is

tempered down to 140 ̊F (60 ̊C) when necessary and then serves as preheated incoming water for the existing electric water

heaters in each building.

The system will include 120 parabolictrough collectors built by IST. Each 150-

square-foot (14-square-meter) collector

(20 feet by 7.5 feet [6.1 meters by 2.3 meters])

will have an aluminized acrylic reflective

surface mounted on a steel trough. The system is modular and the enclosure will have

excess space, so the system can be easily

expanded. The system will be controlled by

one Honeywell Fluxline master start-up and

field controller and four Honeywell local

sun-tracking controllers. Four three-phase

electric motors with jack/cable drive will

actually turn the collectors. Water will be

delivered to and from the collectors in insulated two-layer, flexible stainless-steel

hoses. IST will fabricate the nonpressurized

stainless-steel thermal energy storage tank.

The parabolic-trough collector system 

for FCI-Phoenix is designed to provide

4923 MBtu per year of energy for domestic

water heating, displacing electric water

heating. (The electricity saved is about the

amount 150 people would use for all purposes.) Because electric power plants only

convert about one-third of fossil-fuel 

energy to electricity, and electric water

heaters are about 95% efficient, the fossilfuel combustion saved will be about 

15 billion Btu per year. As indicated in

Appendix G, the 28 million kWh saved over

the life of the project will eliminate more

than 80,000 kilograms of nitrogen oxides

and nearly 100,000 kilograms of sulfur

dioxide pollution plus 27 million kilograms

of carbon dioxide greenhouse gas emissions.

Life-cycle cost analysis for the FCIPhoenix project is shown in Appendix G,

and cash-flow analysis for the facility and

for the investors is shown in Appendix H.

The project has excellent economics, with

life-cycle energy savings nearly twice the

cost of the project and an 8-year simple payback. These figures reflect the favorable

impacts of a good solar resource and a large

facility, but also show how high conventional energy costs make a parabolic-trough

system economically attractive. The utility

in this case does not have a peak pricing

system per se, but the case does show how

time-of-day or highest-demand pricing systems can make renewable energy systems

more attractive—particularly systems that

meet more of the demand.

Construction of the parabolic-trough 

project for FCI-Phoenix will begin in early

1998, so lessons learned for the facility are

limited so far. Even though ESPC was used

on this project, finalizing the contract and

commencing installation took longer than

anticipated. This suggests the importance of

lining up investors ahead of time and being

aware of the regulations involved in dealing

with Federal agencies and in setting up 

business in a new state.

The Technology in

Perspective

Parabolic-trough solar water heating is 

a proven technology that can play a significant role in reducing conventional energy

use at Federal facilities in the Southwest or

other areas with high direct-beam solar radiation. Facilities such as prisons, hospitals,

and military barracks with large, constant

water use loads are particularly good candidates. As with any alternative energy technology, the primary economic factors will

be the cost of the system and the cost of

conventional energy. Facilities dependent on

high-cost water heating are definitely more

likely to find parabolic-trough solar waterheating systems economically attractive.

The technology for domestic water 

heating with parabolic-trough collectors 

was advanced considerably by highertemperature systems built in the 1980s for

steam electric generation. Although the

company that built those systems is no

longer in business, the systems are all still

operating, demonstrating the technology’s

technical merits and durability of the technology. Only one company, IST, is currently

manufacturing parabolic-trough collectors

for solar water-heating systems, but that

company has an excellent track record, having built several effective systems—all at

government facilities and all operating quite

well.

Just as importantly from a Federal-facility perspective, IST has an IDIQ contract

with FEMP for installing parabolic-trough

water-heating systems at any Federal facility

where a system would be appropriate. The

near future of parabolic-trough water heating will be as much a reflection of the

attractiveness of ESPC financing as of the

technology itself. The IDIQ greatly facilitates the procurement process. Once the 

system is in place, there is essentially no

burden on the facility. The energy service

company conducts all operation and maintenance and facility staff need not do anything

extra. ESPC requires no funding from the

facility and guarantees the facility savings.

Virtually the only risk to the facility would

be the inconvenience of removing the 

parabolic-trough system should it not work

adequately. ESPC financing also enables 

the energy service company or third-party

investor to exploit tax credits and accelerated depreciation—and pass on benefits to

the facility—that would not be available 

to a facility purchasing a system.

The FEMP Federal Renewables Program at the National Renewable Energy

Laboratory can quickly assess whether solar

water heating is likely to be economically

attractive for a Federal facility with a minimum of information. The potential for

application at rural Federal facilities in the

Southwest, which are more likely to have

high energy costs and a high solar resource,

is quite good.

19
Dramatic technological breakthroughs to

make parabolic-trough solar water heating

economically attractive in areas with less

sun or for facilities that have low-cost conventional energy available are unlikely.

Incremental improvements in mirror and

absorber coatings, however, are quite likely,

and will make parabolic troughs increasingly efficient for the situations where 

they already are attractive. Any major cost

reductions would come from economies of

scale associated with substantially increased

sales volume. This in turn would depend on 

market acceptance, subsidies, or an increase

in conventional energy prices.

The difficulty of competing with conventional energy water heating prices is the

only major roadblock to extensive use of

parabolic-trough solar water heating at

Federal facilities that meet the criteria for

good project candidates. From the standpoints of technological feasibility, compatibility with existing facilities, conventional

energy use reduction, and pollution and 

climate-change-gas emission reduction, the

outlook is quite good. The technology is

more limited geographically to areas of high

solar resource and to larger facilities than

are other solar water-heating technologies,

but the economics are better. With the IDIQ

contract, Federal facilities that are good 

candidates for the technology really should

investigate it. There is no cost and little

effort required of the facility to find out if 

a parabolic-trough system is feasible. If one

is feasible, the facility can reap at least

modest cost savings along with substantial

energy savings. Even where the economic

payoff is small, parabolic-trough projects

are of great value because of the added 

benefits of reducing pollution and climatechange emissions by reducing fossil-fuel

combustion. Federal facilities also need to

comply with Executive Order 12902 and can

play a valuable role by setting good renewable energy use examples.

Manufacturers of

Parabolic-Trough

Collectors 

Industrial Solar Technology Corporation

4420 McIntyre Street

Golden, CO 80403

(303) 279-8108 (Ken May or Randy Gee)

(303) 279-8107 (fax) 

indsolar@msn.com

To our knowledge this is the only company currently making parabolic-trough

solar collectors or installing parabolictrough water-heating systems. Another 

company that has occasionally made troughs

for its own ice-making systems is listed

below with absorption cooling manufacturers. To see if new companies have entered

the field, check the Thomas Register or call

the FEMP Federal Renewables Program.

(See Federal Program Contacts.) The Solar

Energy Industries Association membership

and the Interstate Renewable Energy

Council's Procurement Guide for Renewable

Energy Systems are also good sources of

manufacturers.

Manufacturers of

Indirect-Fired

Absorption Cooling

Systems

American Yazaki Corporation

10-ton single-effect

13740 Omega Road

Dallas, TX 75244

(972) 385-8725 (Trevor Judd)

Carrier Corporation

100–680-ton single-effect

100–1700-ton double-effect

P.O. Box 4808

Syracuse, NY 13221

(315) 432-7152 (Douglas Rector)

Dunham-Bush, Inc.

100–425-ton single-effect

100–1400-ton double-effect

101 Burgess Road

Harrisonburg, VA 22801

(540) 434-0711 (Daryl Showalter)

Energy Concepts Company

refrigeration/ice making/high-efficiency

cooling

627 Rangely Avenue

Annapolis, MD 21401

(410) 266-6521 (Don Erikson)

McQuay International

100–1500-ton double-effect

P.O. Box 2510

Staunton, VA 24402

(540) 248-9557 (John Alcott)

The Trane Company

100–660-ton single-effect

380–1150-ton double-effect

3600 Pammel Creek Road

La Crosse, WI 54601-7599

(608) 797-3369 (Mike Thompson)

York International Corporation

120–1377-ton single-effect

120–1500-ton double-effect

P.O. Box 1592

York, PA 17405-1592

(717) 771-6386 (Dante Ferrente)

These manufacturers were identified

from literature of and correspondence 

with the American Gas Cooling Center,

1515 Wilson Blvd., Arlington, VA 22209,

(703) 841-8409; check with them or the

Thomas Register to see if other companies

are now making indirect-fired absorption

cooling equipment that might be suitable 

for use in conjunction with parabolic-trough

collector systems.

Federal Program

Contacts

Federal Energy Management Program 

(FEMP)

Help Desk: (800) 566-2877

FEMP@tmn.com

FEMP Federal Renewables Program (at the 

National Renewable Energy Laboratory

[NREL])

1617 Cole Boulevard 

Golden, CO 80401-3393

(303) 384-7509

nancy_carlisle@nrel.gov

U.S. Department of Energy (DOE), Golden 

Field Office, contracting officer for IDIQ 

contracts

Beth Peterman (303) 275-4719

20
Who is Using the

Technology

Federal Sites

Federal Correctional Institution-Phoenix,

Phoenix, Arizona, area

4923 million Btu/yr domestic hot water,

construction initiated 1998

FCI-Phoenix

37900 North 45th Avenue

Phoenix, AZ 85207

U.S. Army Yuma Proving Ground, Yuma,

Arizona

8,970 million Btu/yr absorption cooling,

space heating, and domestic hot water,

installed 1979, refurbished 1986

Jack Nixon (602) 328-2198

Mail Code STEYP-EH-P

Director of Engineering and Housing

U.S. Army Yuma Proving Ground

Yuma, AZ 85365-9104

Non-Federal Sites

Adams County Detention Facility, Brighton,

Colorado

1400 million Btu/yr domestic hot water,

installed 1986

Rob Neiman (303) 654-1850, x 3335

Maintenance Supervisor for Facility

Management

150 N. 19th Avenue

Brighton, CO 80601

California Correctional Institution at 

Tehachapi, California

6000 million Btu/yr domestic hot water,

installed 1990

Harry Franey (916) 327-1134

Energy Manager

California Department of Corrections

P.O. Box 94283

Sacramento, CA 94283

Paul Beck Recreation Center, Aurora,

Colorado

569 million Btu/yr indoor swimming pool 

heating and domestic hot water, installed 

1985

Richard Abrahams (303) 361-2995

Recreation Services

City of Aurora

14949 E. Alameda

Aurora, CO 80012

Jefferson County Detention Facility,

Golden, Colorado

2100 million Btu/yr domestic hot water,

installed 1996

Anne Panza (303) 271-5026

Jefferson County Detention Facility

200 Jefferson County Parkway

Golden, CO 80401

For Further

Information

Government Agency Technology

Transfer Literature

Dudley, V.E.; Evans, L.R.; Matthews, C.W.

(1995). Test Results Industrial Solar

Technology Parabolic Trough Solar

Collector. SAND94-1117. Albuquerque,

NM: Sandia National Laboratories; 137 p.

Federal Energy Management Program.

(1996). Program Overview: Energy Savings

Performance Contracting. Washington,

D.C.: Federal Energy Management

Program; 2 p.

Federal Energy Management Program.

(1996). Solar Water Heating Federal

Technology Alert. Washington, D.C.: Federal

Energy Management Program; 44 p.

Federal Energy Management Program.

(1997). What’s New in Federal Energy

Management: Measurement and Verification

Guidelines for Energy Savings Performance

Contracting. Washington, D.C.: Federal

Energy Management Program; 2 p.

FRESA. Software that evaluates the costeffectiveness of solar water heating.

Available from Andy Walker at the Federal

Renewables Project at the National

Renewable Energy Laboratory, Golden,

Colorado (303) 384-7531.

Hewett, R.; Gee, R.C.; May, E.K. (1991).

Solar Process Heat Technology in Action:

The Process Hot Water System at the

California Correctional Institution at

Tehachapi. NREL/TP-253-4624. Golden,

CO: National Renewable Energy

Laboratory; 4 p.

Marion, W.; Wilcox, S. (1994). Solar

Radiation Data Manual for Flat-Plate and

Concentrating Collectors. NREL/TP-463-

5607. Golden, CO: National Renewable

Energy Laboratory; 252 p.

United States Department of Energy

(Golden Field Office)/Industrial Solar

Technology Corporation. (September 30,

1996). "Indefinite Delivery/Indefinite

Quantity Type Contract for Energy Savings

Performance Contract Services to Install

Line Focussing, Parabolic Trough Solar

Collector and Related Systems in Federal

Facilities, by Performance on Delivery

Orders Issued Against the Contract." 

91 p. Available from Beth Peterman at 

(303) 275-4719.

Other References

American Gas Cooling Center. (1995).

Natural Gas Cooling Equipment Guide.

Arlington, Va.: American Gas Cooling

Center; 160 p. (703) 841-8409.

Gee, R.C. (1996). "Parabolic Trough

Collectors for Industrial and Commercial

Applications." 19th World Energy

Engineering Conference Proceedings,

Atlanta, Georgia, November 6-8, 1996. 

pp. 267-271.

Gee, R.C.; May, E.K. (1993). "A Seven Year

Operation and Performance History of a

Parabolic Trough Collector System." ASME

International Solar Energy Conference

Proceedings, Washington, D.C., April 4-9,

1993. pp. 309-313.

Solar Energy Industries Association. (1995).

Catalog of Successfully Operating Solar

Process Heat Systems. Washington, D.C.:

Solar Energy Industries Association; 44 p.

21
22

Appendixes

Appendix A: Available Solar Radiation for Selected National Solar Radiation Data Base Stations

Appendix B: Data Necessary for Evaluating Parabolic-Trough Solar Water-Heating Systems

Appendix C: Absorption Cooling Technology

Appendix D: Federal Life-Cycle Costing Procedures and the BLCC Software 

Appendix E: Adams County Detention Facility Case Study: NIST BLCC Comparative Economic 

Analysis 

Appendix F: Adams County Detention Facility Case Study: ESPC Economic Analysis 

Appendix G: Federal Correctional Institution—Phoenix Case Study: NIST BLCC Comparative 

Economic Analysis 

Appendix H: Federal Correctional Institution—Phoenix Case Study: ESPC Economic Analysis
23

Appendix A: Available Solar Radiation for Selected

National Solar Radiation Data Base Stations

(Greater than 4.0 kWh/m2/day Direct-Beam Radiation for Horizontal Single-Axis Tracking Systems)

[Data excerpted with permission from Solar Radiation Data Manual for Flat-Plate and Concentrating Collectors (1994) 

National Renewable Energy Laboratory (NREL/TP-463-5607)]

Direct Beam Solar Radiation for Concentrating Collectors (kWh/m2/day), Uncertainty ±8%

Tracker Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec Year

Flagstaff, 1-Axis, E-W Average 4.4 4.4 4.4 5.1 5.7 6.3 4.4 4.3 4.6 4.9 4.6 4.3 4.8

Arizona Horiz Axis Min/Max 2.5/6.0 2.9/6.0 2.7/6.4 3.8/6.1 4.2/6.8 4.7/7.7 2.8/6.0 2.3/5.6 3.4/6.4 2.5/6.3 2.6/6.1 2.3/5.7 2.9/5.3

1-Axis, N-S Average 3.6 4.4 5.4 6.9 7.9 8.6 6.0 5.9 6.0 5.4 4.1 3.4 5.6

Horiz Axis Min/Max 2.1/5.0 2.8/5.9 3.3/7.8 5.1/8.4 5.8/9.4 6.3/10.3 3.7/8.1 3.3/7.7 4.4/8.4 2.7/6.9 2.2/5.4 1.8/4.5 4.6/6.2

Phoenix, 1-Axis, E-W Average 4.2 4.6 4.8 5.7 6.4 6.8 5.6 5.3 5.2 5.0 4.5 4.1 5.2

Arizona Horiz Axis Min/Max 3.0/5.4 3.0/5.9 3.4/6.3 4.8/7.1 5.2/7.1 6.0/7.5 4.5/6.7 4.4/6.3 4.1/6.3 3.5/6.0 2.6/5.8 2.5/5.8 4.5/5.6

1-Axis, N-S Average 3.4 4.6 5.8 7.6 8.5 8.9 7.2 7.0 6.5 5.4 4.0 3.2 6.0

Horiz Axis Min/Max 2.4/4.5 2.8/5.9 4.0/7.7 6.5/9.8 7.0/9.7 7.9/10.0 5.7/8.8 5.6/8.4 5.1/8.1 3.6/6.6 2.2/5.1 1.8/4.5 5.2/6.5

Prescott, 1-Axis, E-W Average 4.4 4.5 4.5 5.4 6.1 6.8 5.0 4.7 5.0 5.2 4.8 4.4 5.1

Arizona Horiz Axis Min/Max 2.8/5.8 2.8/6.0 2.8/6.4 4.0/6.4 5.0/6.9 5.3/7.4 3.8/6.3 3.1/5.9 3.9/6.7 3.0/6.4 2.8/6.2 2.5/5.7 4.3/5.8

1-Axis, N-S Average 3.7 4.5 5.6 7.3 8.3 9.1 6.7 6.4 6.5 5.7 4.2 3.4 6.0

Horiz Axis Min/Max 2.3/4.8 2.8/6.1 3.5/8.1 5.5/8.9 6.9/9.5 7.2/10.1 5.1/8.6 4.4/8.1 4.9/8.9 3.2/7.1 2.5/5.5 2.0/4.4 5.1/6.8

Tucson, 1-Axis, E-W Average 4.7 5.0 5.1 5.9 6.5 6.7 5.0 5.0 5.1 5.3 5.0 4.5 5.3

Arizona Horiz Axis Min/Max 3.1/6.0 3.8/6.3 3.6/6.5 4.8/6.9 5.4/7.1 5.3/7.7 4.2/6.0 3.8/5.9 4.3/6.3 4.0/6.4 3.0/6.0 3.1/5.9 4.7/5.7

1-Axis, N-S Average 4.0 5.1 6.2 8.0 8.8 8.9 6.5 6.6 6.6 5.9 4.5 3.6 6.2

Horiz Axis Min/Max 2.6/5.2 3.8/6.6 4.4/8.1 6.5/9.5 7.4/9.6 6.9/10.4 5.4/7.8 5.0/7.9 5.4/8.2 4.4/7.2 2.6/5.5 2.5/4.8 5.4/6.8

Bakersfield, 1-Axis, E-W Average 2.1 2.9 3.5 4.5 5.6 6.5 6.5 5.9 5.2 4.4 3.0 2.0 4.3

California Horiz Axis Min/Max 0.6/3.8 1.4/4.2 1.8/5.1 2.5/5.5 4.6/6.6 5.7/7.1 5.6/7.3 4.5/6.6 3.7/6.1 3.3/5.2 1.6/4.0 0.9/3.9 3.5/4.8

1-Axis, N-S Average 1.6 2.7 4.0 5.8 7.5 8.6 8.7 7.9 6.5 4.6 2.5 1.5 5.2

Horiz Axis Min/Max 0.5/3.0 1.3/3.9 2.1/5.9 3.2/7.2 6.0/8.8 7.5/9.5 7.3/9.9 5.8/8.9 4.6/7.7 3.4/5.5 1.3/3.3 0.7/2.9 4.1/5.6

Daggett, 1-Axis, E-W Average 4.5 4.7 5.0 5.7 6.5 7.1 6.6 6.2 5.9 5.5 4.9 4.6 5.6

California Horiz Axis Min/Max 2.9/5.8 3.0/6.2 3.9/6.5 4.4/6.8 5.6/7.0 6.1/7.8 4.6/7.6 4.6/7.2 4.2/6.8 4.1/6.3 3.4/5.9 3.5/5.6 4.8/6.0

1-Axis, N-S Average 3.7 4.6 6.1 7.7 8.7 9.6 8.8 8.4 7.5 6.0 4.3 3.5 6.6

Horiz Axis Min/Max 2.4/4.7 2.8/6.2 4.7/8.1 5.8/9.1 7.6/9.5 8.2/10.4 6.0/10.4 6.0/9.9 5.1/9.0 4.3/6.9 2.9/5.2 2.6/4.3 5.6/7.1

Fresno, 1-Axis, E-W Average 1.8 2.7 3.6 4.6 5.7 6.4 6.6 5.9 5.1 4.3 2.7 1.7 4.3

California Horiz Axis Min/Max 0.5/3.4 1.7/4.4 2.0/5.2 2.7/5.9 4.4/6.8 4.6/7.4 5.7/7.3 4.2/6.7 4.0/5.9 2.9/5.0 1.2/4.0 0.5/3.8 3.2/4.8

1-Axis, N-S Average 1.3 2.5 4.1 5.9 7.6 8.4 8.8 7.8 6.3 4.3 2.2 1.2 5.1

Horiz Axis Min/Max 0.4/2.6 1.5/4.1 2.1/6.0 3.6/7.9 5.8/9.0 5.8/10.0 7.2/9.9 5.2/9.0 4.8/7.4 2.8/5.2 0.9/3.3 0.4/2.7 3.7/5.8

Long Beach, 1-Axis, E-W Average 3.2 3.3 3.5 4.1 4.0 4.2 5.2 4.8 4.0 3.7 3.5 3.2 3.9

California Horiz Axis Min/Max 2.0/4.6 2.1/4.9 2.6/5.1 3.2/5.5 2.7/5.1 2.0/5.4 4.1/5.9 3.9/5.5 2.2/4.8 2.6/4.5 2.5/4.3 1.8/4.2 3.3/4.3

1-Axis, N-S Average 2.6 3.2 4.1 5.3 5.2 5.4 6.6 6.2 4.8 3.8 2.9 2.4 4.4

Horiz Axis Min/Max 1.6/3.7 1.9/4.7 3.0/6.0 4.0/7.1 3.5/6.6 2.7/7.0 5.1\7.6 5.1/7.0 2.7/5.8 2.8/4.7 2.1/3.7 1.4/3.2 3.7/4.7
24

Direct Beam Solar Radiation for Concentrating Collectors (kWh/m2/day), Uncertainty ±8%

Tracker Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec Year

Los Angeles, 1-Axis, E-W Average 3.2 3.4 3.6 4.1 3.9 3.9 4.8 4.5 3.8 3.6 3.5 3.2 3.8

California Horiz Axis Min/Max 2.0/4.5 1.9/5.0 2.4/4.9 3.3/5.4 3.0/5.1 2.4/5.3 3.7/6.1 4.0/5.3 2.2/4.8 2.8/4.4 2.3/4.7 1.8/4.1 3.4/4.2

1-Axis, N-S Average 2.6 3.2 4.1 5.3 5.0 5.0 6.1 5.7 4.6 3.7 2.9 2.4 4.2

Horiz Axis Min/Max 1.6/3.6 1.8/4.8 2.8/5.8 4.2/7.0 3.7/6.6 3.2/6.9 4.6/8.0 4.9/6.8 2.7/5.8 2.9/4.5 1.9/4.0 1.3/3.1 3.8/4.7

Sacramento, 1-Axis, E-W Average 1.8 2.6 3.4 4.3 5.5 6.2 6.6 5.8 5.2 4.1 2.5 1.7 4.1

California Horiz Axis Min/Max 0.7/3.0 1.2/4.6 1.8/5.3 2.1/5.4 4.0/6.5 4.9/7.3 5.6/7.1 4.7/6.6 3.8/5.8 3.2/4.8 1.1/4.1 0.6/3.6 3.4/4.6

1-Axis, N-S Average 1.3 2.4 3.8 5.6 7.3 8.3 8.8 7.7 6.3 4.1 2.0 1.2 4.9

Horiz Axis Min/Max 0.5/2.2 1.0/4.2 2.0/6.1 2.8/7.0 5.3/8.7 6.4/9.8 7.4/9.6 6.3/8.8 4.4/7.2 3.1/4.9 0.9/3.2 0.4/2.5 4.1/5.3

San Diego, 1-Axis, E-W Average 3.8 3.8 3.9 4.3 3.9 4.0 4.9 4.8 4.2 4.1 4.0 3.8 4.1

California Horiz Axis Min/Max 2.4/4.9 2.5/5.1 2.9/5.3 3.4/5.5 2.5/5.2 1.8/5.7 2.9/5.8 3.8/5.6 1.9/5.2 3.0/5.2 2.7/5.2 2.5/4.8 3.6/4.5

1-Axis, N-S Average 3.1 3.8 4.6 5.6 4.9 5.0 6.2 6.1 5.1 4.4 3.6 3.0 4.6

Horiz Axis Min/Max 2.0/4.1 2.3/5.1 3.4/6.3 4.3/7.1 3.1/6.8 2.3/7.3 3.6/7.4 4.7/7.2 2.3/6.3 3.2/5.5 2.4/4.6 2.0/3.8 3.9/5.0

San Francisco, 1-Axis, E-W Average 2.5 2.8 3.3 4.0 4.7 5.1 5.5 4.9 4.6 3.9 2.8 2.5 3.9

California Horiz Axis Min/Max 1.6/3.5 1.5/4.9 1.9/5.2 2.4/5.2 3.3/5.7 3.6/6.3 4.9/6.4 3.7/6.1 3.3/5.6 2.6/5.0 1.8/3.9 1.1/3.9 3.2/4.2

1-Axis, N-S Average 1.9 2.5 3.8 5.2 6.1 6.5 7.1 6.3 5.4 3.9 2.3 1.8 4.4

Horiz Axis Min/Max 1.2/2.6 1.3/4.6 2.1/6.0 3.1/6.7 4.2/7.5 4.6/8.3 6.2/8.3 4.7/8.0 4.0/6.8 2.5/5.0 1.5/3.2 0.8/2.8 3.7/4.7

Santa Maria, 1-Axis, E-W Average 3.6 3.8 4.0 4.5 4.9 5.3 5.6 5.2 4.6 4.3 3.9 3.7 4.5

California Horiz Axis Min/Max 2.1/4.9 2.1/5.0 2.3/5.7 3.0/5.7 2.9/6.2 3.6/6.4 4.6/6.4 4.1/5.9 3.2/5.6 3.2/5.2 2.6/5.2 2.6/5.0 3.6/5.0

1-Axis, N-S Average 2.9 3.6 4.6 5.9 6.4 6.8 7.1 6.5 5.5 4.5 3.4 2.8 5.0

Horiz Axis Min/Max 1.6/3.9 2.0/4.8 2.7/6.7 4.0/7.5 3.8/8.2 4.5/8.3 5.7/8.3 5.0/7.5 3.7/7.0 3.3/5.5 2.2/4.5 2.0/3.8 4.1/5.5

Alamosa, 1-Axis, E-W Average 4.8 5.0 4.7 5.0 5.4 6.2 5.5 5.0 5.1 5.2 4.8 4.6 5.1

Colorado Horiz Axis Min/Max 3.5/5.7 3.8/6.0 3.3/5.7 3.3/5.9 4.3/6.3 5.1/7.4 4.7/6.9 4.0/5.9 3.5/6.3 2.8/6.4 3.5/5.8 3.2/5.6 4.4/5.7

1-Axis, N-S Average 3.7 4.8 5.7 6.9 7.4 8.4 7.4 6.7 6.5 5.5 4.0 3.4 5.9

Horiz Axis Min/Max 2.6/4.6 3.6/5.9 3.8/6.9 4.6/8.3 5.8/8.8 6.9/9.9 6.2/9.4 5.4/8.1 4.2/8.0 3.0/7.0 2.8/4.9 2.3/4.2 5.0/6.6

Boulder, 1-Axis, E-W Average 3.5 3.7 3.7 4.0 4.2 5.0 4.9 4.5 4.4 4.3 3.6 3.4 4.1

Colorado Horiz Axis Min/Max 2.3/4.6 2.8/4.5 2.1/4.8 2.9/5.0 2.9/5.7 3.5/6.4 3.8/6.1 3.4/5.4 2.8/5.5 2.5/5.2 2.7/4.7 2.0/4.3 3.4/4.5

1-Axis, N-S Average 2.6 3.4 4.2 5.3 5.6 6.6 6.5 6.0 5.4 4.3 2.8 2.3 4.6

Horiz Axis Min/Max 1.6/3.4 2.5/4.2 2.2/5.7 3.6/6.4 3.8/7.6 4.8/8.5 4.8/8.1 4.5/7.1 3.4/6.7 2.4/5.3 2.2/3.6 1.3/3.0 3.7/5.1

Colorado Spgs, 1-Axis, E-W Average 3.9 4.0 3.9 4.2 4.2 5.1 4.8 4.5 4.4 4.5 3.9 3.8 4.3

Colorado Horiz Axis Min/Max 2.5/5.0 3.1/4.7 2.2/5.2 2.8/5.3 3.1/5.4 3.8/6.4 4.0/6.1 3.4/5.5 3.0/5.6 2.6/5.7 2.9/5.1 2.4/4.8 3.6/4.7

1-Axis, N-S Average 2.9 3.7 4.5 5.6 5.7 6.8 6.4 6.0 5.5 4.7 3.2 2.7 4.8

Horiz Axis Min/Max 1.8/3.8 2.8/4.5 2.4/6.0 3.7/7.1 4.2/7.4 5.1/8.5 5.2/8.1 4.4/7.4 3.6/7.1 2.6/5.9 2.3/4.2 1.6/3.5 4.1/5.3

Eagle, 1-Axis, E-W Average 3.1 3.6 3.5 4.0 4.4 5.4 5.1 4.6 4.5 4.3 3.3 3.1 4.1

Colorado Horiz Axis Min/Max 2.0/5.2 2.6/4.6 2.3/4.5 3.1/4.9 3.2/5.5 4.5/7.1 4.3/6.1 3.3/5.7 2.8/5.4 2.5/5.6 1.7/4.8 1.4/4.3 3.6/4.5

1-Axis, N-S Average 2.3 3.2 4.1 5.3 6.0 7.3 6.9 6.2 5.6 4.4 2.6 2.1 4.7

Horiz Axis Min/Max 1.4/3.9 2.3/4.3 2.5/5.1 4.1/6.6 4.3/7.6 6.0/9.6 5.8/8.4 4.3/7.8 3.3/7.0 2.5/5.7 1.4/3.8 0.9/3.0 4.1/5.1

Grand Junction, 1-Axis, E-W Average 3.3 3.7 3.7 4.3 5.0 5.9 5.5 5.1 4.9 4.5 3.6 3.4 4.4

Colorado Horiz Axis Min/Max 1.9/5.3 2.3/5.2 1.8/4.9 3.2/5.4 3.5/6.0 4.3/7.6 4.8/6.2 3.7/5.8 3.0/5.9 2.6/5.6 2.1/5.2 1.2/4.7 3.3/4.9

1-Axis, N-S Average 2.5 3.4 4.3 5.7 6.7 7.9 7.4 6.7 6.2 4.6 2.9 2.3 5.1

Horiz Axis Min/Max 1.5/4.0 2.0/4.9 1.9/5.7 4.0/7.2 4.5/8.2 5.6/10.2 6.3/8.2 4.7/7.9 3.7/7.3 2.5/5.8 1.6/4.2 0.8/3.3 3.7/5.6
25

Direct Beam Solar Radiation for Concentrating Collectors (kWh/m2/day), Uncertainty ±8%

Tracker Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec Year

Pueblo, 1-Axis, E-W Average 4.0 4.2 4.2 4.6 4.8 5.7 5.5 5.1 4.8 4.8 4.1 3.9 4.6

Colorado Horiz Axis Min/Max 2.6/4.9 3.1/5.1 2.5/5.1 3.3/5.4 3.8/5.9 4.6/7.0 4.4/6.5 4.2/6.0 3.6/5.8 2.8/5.8 3.0/5.3 2.7/5.0 4.1/5.1

1-Axis, N-S Average 3.1 3.9 4.9 6.1 6.4 7.5 7.2 6.6 5.9 4.9 3.3 2.8 5.2

Horiz Axis Min/Max 1.9/3.8 2.9/4.8 2.8/6.1 4.3/7.3 4.9/8.0 6.0/9.3 5.7/8.7 5.4/7.9 4.4/7.4 2.9/6.1 2.5/4.4 1.9/3.6 4.6/5.7

Key West, 1-Axis, E-W Average 3.8 4.1 4.3 4.5 4.1 3.6 3.5 3.4 3.1 3.5 3.6 3.7 3.8

Florida Horiz Axis Min/Max 2.3/4.9 2.7/5.1 2.9/5.3 3.6/5.5 2.8/4.7 2.5/4.5 2.9/4.0 2.8/3.9 2.4/3.7 2.4/4.5 2.5/4.5 2.6/4.7 3.3/4.1

1-Axis, N-S Average 3.6 4.4 5.3 6.0 5.3 4.5 4.5 4.3 3.9 3.9 3.5 3.3 4.4

Horiz Axis Min/Max 2.1/4.6 2.8/5.6 3.5/6.7 4.7/7.5 3.6/6.2 3.1/5.7 3.6/5.1 3.6/5.0 3.0/4.7 2.8/5.1 2.4/4.4 2.3/4.3 3.8/4.8

Tampa, 1-Axis, E-W Average 3.3 3.6 3.8 4.3 4.1 3.4 3.1 3.0 2.9 3.5 3.5 3.4 3.5

Florida Horiz Axis Min/Max 1.9/4.6 2.4/4.8 2.6/4.8 3.5/5.3 3.1/5.0 2.2/4.6 2.3/3.9 2.0/4.0 2.0/3.7 2.0/4.4 2.3/4.6 2.2/4.5 2.8/4.1

1-Axis, N-S Average 3.0 3.7 4.7 5.7 5.4 4.4 4.0 3.9 3.6 3.9 3.3 2.9 4.0

Horiz Axis Min/Max 1.6/4.1 2.4/5.1 3.2/5.9 4.7/7.1 4.1/6.7 2.8/5.9 3.0/5.0 2.7/5.3 2.5/4.8 2.3/4.9 2.2/4.3 1.8/3.9 3.2/4.7

Honolulu, 1-Axis, E-W Average 3.5 3.8 3.7 3.6 4.1 4.4 4.6 4.4 4.1 3.8 3.5 3.5 3.9

Hawaii Horiz Axis Min/Max 2.2/4.8 2.1/4.8 2.3/4.8 2.5/4.7 3.0/5.1 3.9/5.2 3.8/5.3 3.3/5.3 3.2/4.7 2.9/4.5 2.3/4.4 2.2/4.4 3.2/4.3

1-Axis, N-S Average 3.5 4.3 4.7 4.9 5.5 5.7 6.0 6.0 5.5 4.5 3.6 3.3 4.8

Horiz Axis Min/Max 2.1/4.7 2.4/5.5 2.9/6.2 3.3/6.4 3.9/6.9 5.0/6.8 5.0/7.0 4.4/7.1 4.3/6.3 3.5/5.5 2.3/4.4 2.0/4.2 3.9/5.3

Kahului, 1-Axis, E-W Average 4.0 4.1 4.0 4.0 4.6 5.1 5.1 4.9 4.7 4.3 4.0 4.1 4.4

Hawaii Horiz Axis Min/Max 2.5/5.7 2.3/5.6 2.1/5.5 2.4/5.3 3.3/5.7 4.2/6.6 3.8/6.1 3.7/5.9 3.8/5.4 3.2/5.5 2.4/5.3 2.8/5.3 3.6/5.0

1-Axis, N-S Average 4.0 4.7 5.2 5.4 6.2 6.7 6.7 6.7 6.3 5.2 4.2 3.9 5.4

Horiz Axis Min/Max 2.5/5.7 2.5/6.4 2.7/7.3 3.2/7.2 4.3/7.8 5.4/8.8 5.1/8.1 4.9/8.2 5.2/7.4 3.8/6.7 2.5/5.6 2.7/5.1 4.4/6.2

Lihue, 1-Axis, E-W Average 3.3 3.4 3.1 3.0 3.7 3.9 3.8 3.9 3.9 3.5 3.0 3.2 3.5

Hawaii Horiz Axis Min/Max 1.7/4.7 1.4/4.9 1.4/5.0 2.0/4.1 2.6/4.8 2.7/5.7 2.6/4.9 2.7/4.8 2.7/4.7 2.6/4.3 1.6/4.2 1.7/4.8 2.8/4.1

1-Axis, N-S Average 3.2 3.8 3.9 4.0 4.8 5.0 4.9 5.1 5.1 4.1 3.0 3.0 4.2

Horiz Axis Min/Max 1.6/4.6 1.6/5.6 1.6/6.3 2.6/5.4 3.3/6.3 3.4/7.4 3.3/6.3 3.5/6.5 3.5/6.0 3.0/5.0 1.6/4.2 1.6/4.5 3.3/4.9

Boise, 1-Axis, E-W Average 1.7 2.4 3.0 3.8 4.7 5.5 6.4 5.6 5.0 4.0 2.2 1.7 3.8

Idaho Horiz Axis Min/Max 0.4/2.8 1.0/3.9 1.8/4.5 1.8/5.2 3.1/5.9 3.4/6.9 5.1/7.6 3.9/7.0 3.3/6.4 2.6/5.7 0.9/3.6 0.6/3.4 3.3/4.3

1-Axis, N-S Average 1.1 2.1 3.4 4.9 6.3 7.3 8.7 7.5 6.1 3.9 1.6 1.1 4.5

Horiz Axis Min/Max 0.3/1.9 0.9/3.4 1.9/5.1 2.4/6.7 4.2/8.0 4.5/9.2 6.8/10.4 5.1/9.4 4.0/7.9 2.5/5.4 0.7/2.6 0.4/2.1 3.8/5.0

Pocatello, 1-Axis, E-W Average 1.7 2.4 2.9 3.5 4.3 5.3 6.0 5.2 4.7 3.9 2.1 1.7 3.6

Idaho Horiz Axis Min/Max 0.8/3.4 1.4/3.8 1.5/4.2 2.1/5.3 2.8/5.9 3.5/6.7 4.9/7.2 3.5/6.5 3.4/6.2 2.7/5.4 1.0/3.8 0.5/3.0 3.0/4.2

1-Axis, N-S Average 1.2 2.1 3.3 4.5 5.7 7.0 8.0 7.0 5.7 3.9 1.6 1.1 4.3

Horiz Axis Min/Max 0.6/2.4 1.2/3.4 1.6/4.6 2.7/6.9 3.9/7.9 4.6/9.0 6.4/9.7 4.6/8.7 4.0/7.7 2.6/5.3 0.7/2.8 0.3/1.9 3.5/4.9

Dodge City, 1-Axis, E-W Average 3.7 3.8 3.8 4.2 4.3 5.1 5.2 4.5 4.1 4.1 3.5 3.4 4.1

Kansas Horiz Axis Min/Max 2.1/5.4 2.2/5.3 2.0/5.0 2.9/5.2 3.1/5.6 3.5/6.5 3.9/6.0 3.3/5.8 2.3/5.0 2.1/5.6 2.1/5.1 1.9/5.0 3.4/4.7

1-Axis, N-S Average 2.8 3.6 4.4 5.5 5.8 6.6 6.8 6.0 5.0 4.2 2.9 2.5 4.7

Horiz Axis Min/Max 1.6/4.2 2.0/4.9 2.2/5.7 3.8/6.7 4.0/7.6 4.6/8.6 5.2/7.9 4.3/7.5 2.9/6.1 2.2/5.7 1.8/4.2 1.4/3.7 3.9/5.2

Goodland, 1-Axis, E-W Average 3.6 3.7 3.7 4.2 4.3 5.4 5.4 4.9 4.4 4.4 3.6 3.5 4.2

Kansas Horiz Axis Min/Max 2.5/4.8 2.7/4.6 2.3/4.8 3.1/5.3 3.3/5.7 3.8/7.0 4.3/6.7 3.9/6.2 2.5/5.5 2.0/5.7 2.4/4.8 2.8/4.4 3.7/4.7

1-Axis, N-S Average 2.7 3.4 4.3 5.5 5.8 7.1 7.1 6.4 5.4 4.4 2.9 2.4 4.8

Horiz Axis Min/Max 1.9/3.6 2.5/4.3 2.5/5.6 4.1/7.1 4.5/7.6 4.9/9.2 5.7/9.0 5.1/8.2 3.1/6.8 2.1/5.9 1.9/3.8 1.9/3.2 4.2/5.3
26

Direct Beam Solar Radiation for Concentrating Collectors (kWh/m2/day), Uncertainty ±8%

Tracker Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec Year

Wichita, 1-Axis, E-W Average 3.2 3.2 3.3 3.6 3.8 4.5 4.7 4.3 3.7 3.7 3.1 3.0 3.7

Kansas Horiz Axis Min/Max 1.6/5.1 1.8/4.5 1.7/4.5 2.5/5.1 2.9/5.1 3.3/5.7 3.8/6.2 3.0/5.5 1.9/5.3 2.0/5.0 2.0/4.7 1.9/4.8 3.1/4.3

1-Axis, N-S Average 2.5 3.0 3.8 4.7 5.1 5.9 6.3 5.7 4.5 3.8 2.5 2.1 4.2

Horiz Axis Min/Max 1.2/4.0 1.7/4.2 2.0/5.2 3.2/6.7 4.0/6.9 4.3/7.6 5.0/8.2 3.9/7.4 2.4/6.5 2.0/5.2 1.6/3.8 1.4/3.5 3.6/4.9

Billings, 1-Axis, E-W Average 2.3 2.7 3.1 3.4 3.9 4.8 5.6 5.1 4.1 3.5 2.5 2.2 3.6

Montana Horiz Axis Min/Max 1.2/3.6 1.8/3.9 2.0/4.5 2.4/4.8 2.7/5.0 3.5/6.3 4.2/6.5 4.1/6.3 2.3/5.7 2.3/4.4 1.7/3.4 1.5/3.1 3.0/4.0

1-Axis, N-S Average 1.4 2.2 3.3 4.3 5.2 6.4 7.4 6.7 4.9 3.3 1.8 1.3 4.0

Horiz Axis Min/Max 0.8/2.3 1.5/3.2 2.1/4.8 3.1/6.3 3.7/6.6 4.6/8.4 5.4/8.6 5.3/8.4 2.7/6.8 2.1/4.2 1.2/2.5 0.8/1.8 3.3/4.5

Miles City, 1-Axis, E-W Average 2.3 2.7 3.1 3.4 3.9 4.9 5.5 5.0 4.0 3.4 2.4 2.1 3.6

Montana Horiz Axis Min/Max 1.2/3.2 2.0/3.9 2.0/4.5 1.7/4.9 2.7/5.3 2.7/6.4 4.4/6.5 4.0/6.1 2.1/5.2 2.2/4.3 1.5/3.2 1.4/3.3 3.0/4.2

1-Axis, N-S Average 1.4 2.2 3.3 4.4 5.2 6.5 7.4 6.5 4.8 3.1 1.7 1.2 4.0

Horiz Axis Min/Max 0.7/2.1 1.6/3.2 2.1/4.7 2.2/6.4 3.7/7.0 3.5/8.4 5.9/8.8 5.1/8.1 2.5/6.3 2.0/4.0 1.0/2.3 0.8/1.9 3.3/4.7

Grand Island, 1-Axis, E-W Average 3.2 3.2 3.3 3.7 3.9 4.8 4.9 4.4 3.8 3.7 2.9 2.8 3.7

Nebraska Horiz Axis Min/Max 1.5/4.5 1.9/4.1 1.7/5.1 2.0/4.8 2.3/5.1 3.3/5.8 3.7/6.0 2.9/5.4 2.1/5.3 2.3/4.9 1.8/4.1 2.1/3.7 2.9/4.2

1-Axis, N-S Average 2.3 2.8 3.7 4.8 5.2 6.3 6.5 5.8 4.7 3.7 2.3 1.9 4.2

Horiz Axis Min/Max 1.0/3.3 1.5/3.8 1.8/5.7 2.6/6.4 3.1/6.8 4.4/7.7 4.9/8.0 3.8/7.2 2.6/6.5 2.3/4.9 1.3/3.1 1.4/2.5 3.4/4.7

North Platte, 1-Axis, E-W Average 3.1 3.2 3.3 3.7 3.9 4.9 5.0 4.5 4.0 3.8 3.0 3.0 3.8

Nebraska Horiz Axis Min/Max 1.7/4.6 2.1/4.1 1.9/4.7 2.5/4.7 2.6/5.3 3.5/5.9 4.0/5.8 3.3/5.8 2.3/5.4 2.0/4.9 1.7/4.0 2.0/4.1 3.1/4.2

1-Axis, N-S Average 2.2 2.9 3.7 4.9 5.2 6.4 6.6 5.9 4.8 3.8 2.3 2.0 4.2

Horiz Axis Min/Max 1.1/3.3 1.8/3.7 2.0/5.4 3.2/6.3 3.5/7.1 4.5/7.8 5.1/7.7 4.3/7.6 2.8/6.7 1.9/4.9 1.3/3.0 1.3/2.8 3.4/4.6

Scottsbluff, 1-Axis, E-W Average 3.0 3.3 3.3 3.6 3.9 5.0 5.4 4.9 4.3 3.9 3.0 3.0 3.9

Nebraska Horiz Axis Min/Max 2.2/4.0 2.7/4.4 2.4/4.5 2.8/4.9 2.9/4.9 3.7/5.9 4.7/5.9 4.0/5.8 3.0/5.5 2.4/4.8 2.2/3.9 2.2/4.2 3.5/4.2

1-Axis, N-S Average 2.1 3.0 3.7 4.7 5.2 6.6 7.0 6.4 5.2 3.8 2.3 1.9 4.3

Horiz Axis Min/Max 1.4/2.9 2.3/4.0 2.6/5.0 3.5/6.4 3.8/6.5 4.7/7.8 6.1/7.8 5.0/7.6 3.5/6.8 2.4/4.9 1.7/3.0 1.4/2.8 3.9/4.7

Albuquerque, 1-Axis, E-W Average 4.5 4.6 4.6 5.3 5.9 6.3 5.5 5.2 4.9 5.1 4.6 4.4 5.1

New Mexico Horiz Axis Min/Max 3.1/5.8 3.0/5.7 3.0/6.2 4.3/6.1 4.7/7.1 5.3/7.4 4.3/6.4 3.7/6.0 3.9/6.2 3.3/6.5 2.8/5.9 2.6/5.7 4.3/5.5

1-Axis, N-S Average 3.7 4.6 5.6 7.2 8.0 8.4 7.2 6.7 6.2 5.4 4.0 3.4 5.9

Horiz Axis Min/Max 2.5/4.8 3.0/5.7 3.4/7.6 5.7/8.4 6.1/9.7 6.8/10.0 5.4/8.4 4.7/7.9 4.7/7.9 3.4/7.2 2.4/5.2 2.0/4.5 4.8/6.4

Tucumcari, 1-Axis, E-W Average 4.1 4.3 4.4 4.9 5.1 5.6 5.3 4.8 4.5 4.7 4.2 4.1 4.7

New Mexico Horiz Axis Min/Max 2.6/5.4 3.1/5.4 3.1/5.4 4.0/5.8 4.2/6.1 4.4/6.7 4.4/6.1 4.1/6.1 3.8/5.8 3.3/6.2 2.5/5.2 2.4/5.7 4.1/5.1

1-Axis, N-S Average 3.3 4.2 5.2 6.6 6.8 7.4 6.9 6.3 5.7 5.1 3.7 3.1 5.4

Horiz Axis Min/Max 2.1/4.4 3.0/5.4 3.6/6.4 5.2/7.8 5.6/8.2 5.6/8.9 5.7/8.2 5.4/8.3 4.6/7.3 3.5/6.7 2.1/4.5 1.8/4.4 4.7/5.9

Elko, 1-Axis, E-W Average 2.8 3.1 3.2 3.6 4.4 5.4 6.0 5.4 5.1 4.4 3.0 2.8 4.1

Nevada Horiz Axis Min/Max 1.7/4.2 1.8/5.0 1.9/4.2 2.0/5.1 2.5/6.0 3.5/7.0 4.9/7.9 3.7/6.5 3.1/6.8 3.2/5.5 1.7/4.7 1.0/4.7 3.5/4.5

1-Axis, N-S Average 2.1 2.8 3.7 4.8 5.9 7.2 8.1 7.3 6.3 4.5 2.3 1.9 4.8

Horiz Axis Min/Max 1.2/3.1 1.6/4.6 2.2/4.9 2.7/6.7 3.4/8.1 4.8/9.5 6.5/10.7 5.0/8.9 3.8/8.6 3.2/5.7 1.3/3.7 0.6/3.2 4.0/5.3

Ely, 1-Axis, E-W Average 3.6 3.8 3.7 4.2 4.6 5.7 5.7 5.1 5.2 4.7 3.7 3.5 4.5

Nevada Horiz Axis Min/Max 2.4/4.8 2.3/5.7 2.3/5.0 2.7/5.7 3.0/5.8 4.1/7.0 4.2/7.3 3.5/6.9 2.8/6.4 3.5/5.8 2.1/5.0 1.2/5.3 3.5/5.0

1-Axis, N-S Average 2.7 3.5 4.4 5.5 6.3 7.7 7.8 7.0 6.5 4.8 3.0 2.5 5.1

Horiz Axis Min/Max 1.6/3.6 2.1/5.4 2.5/5.9 3.4/7.7 4.3/8.0 5.4/9.5 5.5/9.9 4.9/9.4 3.5/8.4 3.5/5.9 1.6/4.1 0.8/3.7 4.1/5.6
27

Direct Beam Solar Radiation for Concentrating Collectors (kWh/m2/day), Uncertainty ±8%

Tracker Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec Year

Las Vegas, 1-Axis, E-W Average 4.3 4.5 4.8 5.5 6.1 6.8 6.1 5.8 5.6 5.3 4.6 4.3 5.3

Nevada Horiz Axis Min/Max 2.7/5.7 3.0/5.8 3.8/6.3 4.1/6.4 5.2/7.1 5.7/7.6 4.4/7.1 4.4/6.9 4.0/6.6 3.5/6.1 3.1/5.7 2.7/5.3 4.5/5.8

1-Axis, N-S Average 3.4 4.4 5.7 7.4 8.2 9.1 8.2 7.8 7.1 5.6 3.9 3.2 6.2

Horiz Axis Min/Max 2.1/4.6 2.8/5.7 4.2/7.7 5.5/8.7 7.0/9.6 7.5/10.3 5.5/9.6 5.8/9.4 4.9/8.5 3.7/6.5 2.5/4.9 1.9/4.0 5.2/6.7

Reno, 1-Axis, E-W Average 3.2 3.5 3.9 4.4 5.2 6.0 6.6 5.9 5.4 4.8 3.4 3.1 4.6

Nevada Horiz Axis Min/Max 1.8/5.1 2.0/5.6 2.1/5.8 2.7/6.1 3.5/6.3 4.6/7.2 5.3/7.7 4.2/6.9 3.5/6.9 3.7/5.6 2.0/5.0 1.5/4.8 3.6/5.2

1-Axis, N-S Average 2.3 3.2 4.5 5.8 7.0 8.0 8.8 7.9 6.8 4.9 2.7 2.2 5.4

Horiz Axis Min/Max 1.3/3.8 1.8/5.2 2.3/6.8 3.5/8.1 4.8/8.5 6.1/9.7 7.1/10.3 5.6/9.4 4.2/8.8 3.7/5.7 1.6/4.1 1.0/3.4 4.2/6.0

Tonopah, 1-Axis, E-W Average 4.0 4.1 4.3 4.8 5.3 6.3 6.4 5.8 5.6 5.2 4.1 3.9 5.0

Nevada Horiz Axis Min/Max 2.5/5.6 2.5/5.9 2.7/5.7 3.0/6.0 4.0/6.4 5.1/7.6 5.0/7.9 4.3//6.9 3.2/6.8 3.9/5.9 3.0/5.7 2.4/5.5 4.0/5.5

1-Axis, N-S Average 3.1 3.9 5.1 6.4 7.2 8.4 8.6 7.8 7.1 5.4 3.4 2.9 5.8

Horiz Axis Min/Max 1.9/4.3 2.2/5.7 3.2/6.9 4.0/8.0 5.4/8.8 6.8/10.2 6.5/10.7 5.8/9.5 4.0/8.8 4.2/6.3 2.4/4.7 1.7/4.0 4.7/6.3

Winnemucca, 1-Axis, E-W Average 2.8 3.0 3.3 3.8 4.6 5.6 6.3 5.6 5.2 4.4 2.9 2.7 4.2

Nevada Horiz Axis Min/Max 1.1/4.5 1.6/5.2 2.0/4.7 1.8/5.0 2.7/6.0 3.6/7.1 5.2/7.5 3.6/6.8 3.8/6.9 3.3/5.8 1.3/4.6 0.8/4.7 3.6/4.8

1-Axis, N-S Average 2.0 2.7 3.8 5.1 6.2 7.4 8.5 7.5 6.5 4.5 2.3 1.8 4.9

Horiz Axis Min/Max 0.8/3.3 1.4/4.8 2.3/5.4 2.3/6.6 3.7/8.2 4.9/9.5 6.9/10.2 4.9/9.4 4.6/8.8 3.2/5.9 1.0/3.5 0.5/3.2 4.2/5.5

Oklahoma City, 1-Axis, E-W Average 3.4 3.4 3.5 3.9 3.9 4.5 4.9 4.4 3.7 3.8 3.3 3.2 3.8

Oklahoma Horiz Axis Min/Max 1.6/5.0 1.9/4.7 2.0/4.9 2.9/5.2 3.0/4.9 3.5/5.6 3.0/6.3 3.5/5.4 2.3/4.9 2.4/5.1 1.9/4.9 1.9/4.6 3.3/4.3

1-Axis, N-S Average 2.7 3.3 4.2 5.1 5.2 5.9 6.5 5.9 4.7 4.1 2.8 2.4 4.4

Horiz Axis Min/Max 1.3/4.0 1.8/4.6 2.2/5.7 3.7/6.9 3.9/6.5 4.6/7.4 4.1/8.4 4.7/7.3 2.9/6.2 2.4/5.4 1.7/4.2 1.5/3.5 3.8/4.9

Burns, 1-Axis, E-W Average 1.9 2.4 2.9 3.5 4.4 5.1 6.2 5.5 4.8 3.8 2.0 1.8 3.7

Oregon Horiz Axis Min/Max 0.9/3.1 0.8/4.4 1.6/4.0 1.9/5.2 2.7/5.5 3.8/6.6 5.3/7.1 3.3/6.9 3.5/6.1 2.3/5.5 0.6/3.9 0.9/3.4 3.2/4.3

1-Axis, N-S Average 1.3 2.1 3.2 4.6 5.9 6.9 8.3 7.3 5.9 3.7 1.5 1.1 4.3

Horiz Axis Min/Max 0.6/2.1 0.6/3.8 1.7/4.4 2.6/6.6 3.7/7.4 5.1/8.9 7.2/9.6 4.4/9.4 4.3/7.6 2.3/5.3 0.5/2.9 0.5/2.2 3.7/5.0

Medford, 1-Axis, E-W Average 1.3 2.1 2.7 3.5 4.5 5.4 6.5 5.6 4.8 3.4 1.3 1.0 3.5

Oregon Horiz Axis Min/Max 0.4/2.7 0.7/3.6 1.2/4.2 2.2/4.9 3.2/5.8 4.0/7.0 4.9/7.4 3.6/7.1 3.5/6.2 1.7/5.0 0.6/2.5 0.3/1.9 2.6/3.9

1-Axis, N-S Average 0.9 1.7 2.9 4.4 6.0 7.1 8.7 7.3 5.7 3.2 1.0 0.6 4.2

Horiz Axis Min/Max 0.3/1.9 0.5/3.1 1.2/4.6 2.6/6.3 4.1/7.8 5.1/9.3 6.4/10.0 4.6/9.6 4.1/7.7 1.6/4.8 0.4/1.8 0.2/1.2 3.1/4.5

Redmond, 1-Axis, E-W Average 1.9 2.3 2.9 3.5 4.4 5.2 6.2 5.4 4.7 3.6 2.0 1.8 3.7

Oregon Horiz Axis Min/Max 1.3/3.3 1.1/3.8 1.9/4.5 2.1/4.8 2.7/5.4 3.7/6.4 4.6/7.7 3.8/6.8 3.1/6.1 2.1/5.2 1.2/3.3 0.8/3.2 3.0/4.2

1-Axis, N-S Average 1.3 1.9 3.2 4.5 5.9 6.9 8.3 7.2 5.6 3.5 1.5 1.1 4.3

Horiz Axis Min/Max 0.8/2.2 0.9/3.2 2.0/4.7 2.8/6.1 3.7/7.2 4.9/8.6 5.9/10.5 5.0/9.1 3.8/7.5 1.9/4.9 0.9/2.4 0.5/2.0 3.4/4.8

San Juan, 1-Axis, E-W Average 3.5 3.5 3.7 3.7 3.2 3.6 3.6 3.5 3.2 3.1 3.2 3.2 3.4

Puerto Rico Horiz Axis Min/Max 2.8/4.3 2.9/4.2 2.9/4.3 2.6/4.5 1.6/4.3 2.6/4.8 2.9/4.3 2.5/4.4 2.4/4.0 2.2/4.1 2.0/4.5 2.2/4.8 2.9/4.0

1-Axis, N-S Average 3.5 4.0 4.8 4.9 4.1 4.5 4.6 4.6 4.2 3.7 3.3 3.0 4.1

Horiz Axis Min/Max 2.8/4.3 3.2/4.8 3.6/5.6 3.4/6.1 2.1/5.5 3.3/6.2 3.7/5.6 3.3/5.9 3.1/5.4 2.6/4.9 2.0/4.6 2.1/4.7 3.5/4.8

Rapid City, 1-Axis, E-W Average 2.8 3.1 3.3 3.6 4.0 4.8 5.1 4.9 4.3 3.8 2.9 2.7 3.8

South Dakota Horiz Axis Min/Max 1.8/3.8 2.0/3.9 2.4/4.4 2.7/5.2 2.9/5.1 3.6/6.1 4.6/5.7 4.1/5.8 2.5/5.6 2.7/4.7 1.9/3.7 1.8/3.8 3.4/4.3

1-Axis, N-S Average 1.9 2.6 3.6 4.6 5.3 6.4 6.8 6.4 5.1 3.6 2.1 1.7 4.2

Horiz Axis Min/Max 1.2/2.6 1.7/3.4 2.5/4.8 3.4/6.7 3.8/6.9 4.8/8.3 6.0/7.7 5.4/7.7 3.0/6.8 2.5/4.4 1.4/2.7 1.1/2.4 3.7/4.8
28

Direct Beam Solar Radiation for Concentrating Collectors (kWh/m2/day), Uncertainty ±8%

Tracker Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec Year

Abilene, 1-Axis, E-W Average 3.7 3.9 4.1 4.3 4.4 4.9 4.9 4.4 3.8 4.1 3.8 3.7 4.2

Texas Horiz Axis Min/Max 2.0/5.2 2.7/5.3 2.7/5.9 3.0/5.4 3.1/5.3 3.8/6.3 3.5/6.6 3.2/5.7 2.8/5.0 2.6/5.2 2.5/5.0 2.2/5.2 3.7/4.6

1-Axis, N-S Average 3.1 3.9 5.0 5.7 5.8 6.4 6.5 5.9 4.8 4.5 3.4 3.0 4.9

Horiz Axis Min/Max 1.7/4.4 2.8/5.4 3.2/7.2 4.1/7.3 4.2/7.1 5.1/8.3 4.6/8.8 4.2/7.8 3.5/6.5 2.9/5.7 2.3/4.5 1.8/4.2 4.3/5.4

Amarillo, 1-Axis, E-W Average 4.0 4.1 4.2 4.6 4.6 5.2 5.0 4.6 4.2 4.6 5.0 3.9 4.4

Texas Horiz Axis Min/Max 2.5/5.3 2.3/5.3 3.1/5.4 3.5/5.6 3.6/5.5 4.0/6.5 4.1/6.5 3.6/5.8 3.5/5.6 3.0/6.0 2.2/5.2 2.9/5.7 3.9/4.8

1-Axis, N-S Average 3.3 4.0 5.0 6.1 6.2 6.8 6.7 6.1 5.2 4.9 3.5 3.0 5.1

Horiz Axis Min/Max 2.0/4.3 2.2/5.3 3.5/6.4 4.7/7.5 4.9/7.4 5.2/8.6 5.3/8.6 4.7/7.9 4.5/7.0 3.2/6.5 2.0/4.5 1.7/4.4 4.5/5.4

Austin, 1-Axis, E-W Average 3.0 3.3 3.3 3.3 3.4 4.2 4.5 4.3 3.6 3.7 3.3 3.0 3.6

Texas Horiz Axis Min/Max 1.6/4.4 1.9/4.7 2.0/4.6 2.2/5.1 1.4/4.4 3.0/5.3 3.0/5.8 3.2/5.5 2.4/5.0 2.1/4.7 1.4/4.9 1.9/4.9 3.2/4.0

1-Axis, N-S Average 2.6 3.4 4.0 4.3 4.4 5.4 5.9 5.6 4.5 4.1 3.0 2.5 4.2

Horiz Axis Min/Max 1.4/3.9 2.0/4.9 2.4/5.6 2.9/6.7 1.9/5.7 3.9/6.9 3.9/7.7 4.1/7.2 2.9/6.4 2.2/5.3 1.4/4.5 1.5/4.1 3.7/4.7

El Paso, 1-Axis, E-W Average 4.5 4.9 5.2 5.6 6.1 6.3 5.2 4.8 4.7 4.9 4.7 4.4 5.1

Texas Horiz Axis Min/Max 3.0/5.9 3.4/6.3 3.3/6.6 4.3/6.4 5.2/7.3 4.9/7.6 4.2/6.1 3.9/5.9 3.7/5.6 3.7/6.2 2.7/5.8 2.8/5.5 4.6/5.6

1-Axis, N-S Average 3.8 5.0 6.3 7.6 8.2 8.2 6.8 6.4 5.9 5.4 4.2 3.6 6.0

Horiz Axis Min/Max 2.7/5.1 3.5/6.5 4.0/8.2 5.8/8.8 7.0/9.9 6.4/10.0 5.4/8.1 5.1/7.8 4.7/7.1 4.0/6.9 2.4/5.3 2.2/4.5 5.4/6.5

Fort Worth, 1-Axis, E-W Average 3.2 3.4 3.4 3.5 3.7 4.4 4.7 4.2 3.6 3.7 3.4 3.2 3.7

Texas Horiz Axis Min/Max 1.5/4.5 2.3/4.8 2.1/4.7 2.4/5.2 2.0/4.9 3.5/5.4 3.5/6.2 2.9/5.4 2.4/4.8 2.3/4.9 1.8/4.4 1.9/4.5 3.3/4.1

1-Axis, N-S Average 2.7 3.4 4.1 4.6 4.9 5.7 6.2 5.6 4.5 4.0 3.0 2.5 4.30

Horiz Axis Min/Max 1.2/3.8 2.3/4.7 2.5/5.7 3.2/6.8 2.7/6.5 4.5/7.2 4.7/8.3 3.8/7.4 3.0/6.1 2.5/5.3 1.7/4.0 1.5/3.5 3.8/4.7

Lubbock, 1-Axis, E-W Average 4.0 4.1 4.2 4.6 4.7 5.1 5.0 4.5 3.9 4.4 4.1 3.9 4.4

Texas Horiz Axis Min/Max 2.6/5.3 2.9/5.7 3.0/5.4 3.6/5.7 3.6/5.7 3.8/6.2 3.5/6.5 3.3/5.8 2.8/5.4 3.1/5.9 2.5/5.3 2.2/5.5 3.9/4.8

1-Axis, N-S Average 3.3 4.1 5.1 6.1 6.2 6.7 6.6 6.1 5.0 4.8 3.6 3.1 5.1

Horiz Axis Min/Max 2.1/4.4 2.8/5.7 3.6/6.5 4.7/7.6 4.8/7.6 5.0/8.1 4.7/8.7 4.3/7.8 3.5/7.0 3.3/6.5 2.2/4.7 1.7/4.3 4.5/5.5

Midland, 1-Axis, E-W Average 4.0 4.3 4.6 4.7 4.9 5.2 4.9 4.5 4.0 4.5 4.2 4.1 4.5

Texas Horiz Axis Min/Max 2.7/5.6 3.0/5.6 3.0/5.9 3.6/6.0 3.9/5.7 4.2/6.8 3.2/6.4 3.3/5.6 2.9/5.2 3.1/5.8 2.8/5.6 2.6/5.7 4.2/4.9

1-Axis, N-S Average 3.5 4.4 5.5 6.3 6.6 6.8 6.5 6.0 5.1 4.9 3.9 3.3 5.2

Horiz Axis Min/Max 2.3/4.8 3.0/5.7 3.5/7.2 4.7/8.1 5.2/7.7 5.3/8.9 4.2/8.6 4.5/7.6 3.6/6.8 3.3/6.5 2.5/5.1 2.1/4.6 4.9/5.7

San Angelo, 1-Axis, E-W Average 3.7 3.9 4.2 4.3 4.3 4.8 4.8 4.5 3.8 4.1 3.9 3.7 4.2

Texas Horiz Axis Min/Max 2.0/5.3 2.7/5.3 2.6/5.7 3.3/5.5 2.9/5.4 4.0/6.4 2.9/6.2 2.8/5.8 2.7/5.2 2.6/5.5 2.6/5.4 2.3/5.5 3.7/4.7

1-Axis, N-S Average 3.2 4.0 5.1 5.6 5.7 6.3 6.4 6.0 4.8 4.5 3.6 3.0 4.9

Horiz Axis Min/Max 1.7/4.6 2.7/5.3 3.2/7.0 4.2/7.4 3.7/7.2 5.2/8.4 3.8/8.4 3.8/7.8 3.4/6.8 2.9/6.1 2.4/5.0 1.8/4.4 4.3/5.5

San Antonio, 1-Axis, E-W Average 3.0 3.3 3.3 3.2 3.3 4.0 4.4 4.1 3.6 3.7 3.3 3.0 3.5

Texas Horiz Axis Min/Max 2.0/4.2 2.2/4.8 1.9/5.0 1.5/4.5 1.6/4.1 2.5/5.1 2.6/5.8 2.9/5.2 2.2/5.1 2.0/5.0 1.5/5.1 2.1/4.7 3.1/3.9

1-Axis, N-S Average 2.7 3.4 4.0 4.2 4.2 5.2 5.7 5.4 4.5 4.1 3.1 2.5 4.1

Horiz Axis Min/Max 1.7/3.8 2.3/5.0 2.3/6.1 1.9/6.0 2.1/5.3 3.1/6.7 3.3/7.6 3.8/6.8 2.8/6.4 2.2/5.7 1.5/4.8 1.7/4.0 3.6/4.6

Waco, 1-Axis, E-W Average 3.1 3.3 3.4 3.4 3.6 4.4 4.8 4.4 3.7 3.8 3.3 3.2 3.7

Texas Horiz Axis Min/Max 1.6/4.5 1.9/4.7 2.1/4.9 2.3/5.5 1.6/5.0 3.2/5.4 3.2/6.3 3.4/5.3 2.5/5.1 2.4/4.7 1.5/4.7 1.9/4.7 3.3/4.2

1-Axis, N-S Average 2.6 3.3 4.1 4.4 4.8 5.7 6.3 5.9 4.7 4.1 3.0 2.6 4.3

Horiz Axis Min/Max 1.4/3.9 2.0/4.8 2.5/6.0 3.0/7.3 2.1/6.6 4.2/7.1 4.3/8.4 4.5/7.2 3.2/6.6 2.6/5.1 1.4/4.3 1.6/3.8 3.8/4.9
29

Direct Beam Solar Radiation for Concentrating Collectors (kWh/m2/day), Uncertainty ±8%

Tracker Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec Year

Wichita Falls, 1-Axis, E-W Average 3.4 3.5 3.7 3.9 4.1 4.7 4.9 4.4 3.9 4.0 3.5 3.3 3.9

Texas Horiz Axis Min/Max 1.6/4.7 2.4/5.0 2.5/4.9 2.8/4.9 3.2/5.1 4.0/5.9 3.7/6.6 3.2/5.4 2.7/5.1 2.5/5.2 2.2/4.7 2.0/4.9 3.4/4.3

1-Axis, N-S Average 2.8 3.5 4.4 5.2 5.5 6.2 6.5 5.9 4.9 4.3 3.0 2.6 4.6

Horiz Axis Min/Max 1.3/3.9 2.4/5.1 3.0/5.8 3.6/6.6 4.2/6.7 5.3/7.8 4.8/8.8 4.2/7.4 3.4/6.6 2.7/5.6 1.8/4.2 1.5/3.8 4.0/5.1

Cedar City, 1-Axis, E-W Average 3.7 3.8 3.8 4.5 5.1 6.2 5.5 5.1 5.1 4.8 3.9 3.7 4.6

Utah Horiz Axis Min/Max 2.5/5.2 2.3/5.4 2.1/5.4 3.0/5.9 4.1/6.2 4.8/7.5 4.1/6.9 3.6/6.6 3.2/6.3 2.3/5.8 2.8/5.8 1.9/5.6 3.6/5.6

1-Axis, N-S Average 2.9 3.6 4.6 6.0 7.0 8.3 7.5 6.9 6.6 5.1 3.3 2.7 5.4

Horiz Axis Min/Max 2.0/4.1 2.0/5.2 2.6/6.5 4.1/7.9 5.6/8.5 6.3/10.1 5.5/9.4 4.8/9.0 4.0/8.1 2.5/6.1 2.3/4.9 1.4/4.1 4.2/6.5

Salt Lake City, 1-Axis, E-W Average 2.0 2.7 3.2 3.7 4.5 5.6 5.8 5.2 4.8 4.1 2.6 1.9 3.8

Utah Horiz Axis Min/Max 0.6/4.9 0.9/4.0 1.6/4.3 2.5/4.8 3.1/5.9 3.8/6.8 4.7/6.8 4.3/6.4 3.4/6.1 2.9/5.3 1.4/3.9 0.3/3.6 3.1/4.4

1-Axis, N-S Average 1.4 2.4 3.6 4.8 6.1 7.4 7.6 6.9 5.8 4.1 2.0 1.2 4.5

Horiz Axis Min/Max 0.5/2.8 0.9/3.5 1.7/4.9 3.3/6.2 4.1/8.0 5.0/9.2 6.3/9.1 5.5/8.6 4.1/7.5 2.7/5.4 1.1/3.0 0.2/2.4 3.6/5.1

Yakima, 1-Axis, E-W Average 1.4 2.2 3.0 3.5 4.4 5.0 5.8 5.2 4.5 3.4 1.7 1.3 3.5

Washington Horiz Axis Min/Max 0.6/2.5 0.4/3.4 1.9/4.0 2.3/4.6 2.9/5.4 3.6/6.5 4.6/6.9 3.9/6.6 2.9/5.8 1.9/4.3 0.9/2.5 0.6/2.5 3.1/3.8

1-Axis, N-S Average 0.9 1.8 3.2 4.5 5.9 6.6 7.8 6.8 5.3 3.1 1.2 0.8 4.0

Horiz Axis Min/Max 0.3/1.6 0.4/2.8 2.1/4.2 2.8/5.7 4.0/7.3 4.7/8.7 6.1/9.3 5.2/8.8 3.3/6.9 1.7/4.1 0.6/1.8 0.4/1.5 3.5/4.4

Casper, 1-Axis, E-W Average 3.1 3.4 3.5 3.6 4.1 5.2 5.5 5.1 4.5 3.9 3.1 2.9 4.0

Wyoming Horiz Axis Min/Max 2.2/4.2 2.4/4.5 2.4/4.5 2.7/5.1 2.8/5.1 3.5/6.3 4.7/6.3 3.6/5.9 3.1/5.8 2.6/5.1 2.3/3.7 2.2/4.1 3.3/4.4

1-Axis, N-S Average 2.1 3.0 3.9 4.7 5.5 6.9 7.3 6.8 5.5 3.8 2.3 1.9 4.5

Horiz Axis Min/Max 1.5/2.9 2.1/4.0 2.6/5.1 3.4/6.6 3.8/6.9 4.6/8.4 6.2/8.4 4.9/8.0 3.7/7.1 2.5/4.9 1.7/2.8 1.4/2.7 3.6/5.0

Cheyenne, 1-Axis, E-W Average 3.3 3.6 3.6 3.8 3.9 4.8 4.9 4.5 4.3 4.1 3.3 3.2 3.9

Wyoming Horiz Axis Min/Max 2.1/4.3 2.8/4.3 2.5/4.5 3.0/4.6 2.6/4.8 3.4/6.1 4.3/5.7 2.9/5.2 2.9/5.3 2.4/4.9 2.6/3.9 2.3/4.3 3.5/4.3

1-Axis, N-S Average 2.3 3.2 4.1 5.0 5.2 6.4 6.5 6.0 5.2 4.1 2.6 2.1 4.4

Horiz Axis Min/Max 1.7/3.1 2.5/3.9 2.7/5.3 4.0/6.1 3.5/6.5 4.5/8.2 5.7/7.6 3.8/7.0 3.5/6.6 2.4/4.9 2.0/3.1 1.5/2.9 3.9/4.9

Lander, 1-Axis, E-W Average 3.2 3.7 3.9 3.9 4.2 5.2 5.3 5.0 4.5 4.1 3.3 3.2 4.1

Wyoming Horiz Axis Min/Max 2.3/4.4 2.6/4.8 2.4/4.8 2.7/5.3 2.7/5.4 3.5/6.5 3.7/6.1 3.8/5.5 2.9/5.8 2.9/5.3 2.4/4.0 1.8/4.0 3.5/4.6

1-Axis, N-S Average 2.2 3.2 4.3 5.0 5.6 7.0 7.1 6.6 5.5 4.0 2.5 2.0 4.6

Horiz Axis Min/Max 1.5/3.1 2.1/4.2 2.5/5.4 3.5/6.9 3.5/7.3 4.7/8.7 4.6/8.2 4.9/7.5 3.5/7.2 2.8/5.2 1.8/3.0 1.1/2.6 3.8/5.1

Rock Springs, 1-Axis, E-W Average 3.0 3.4 3.6 3.8 4.4 5.3 5.4 5.0 4.7 4.2 3.1 2.9 4.1

Wyoming Horiz Axis Min/Max 2.1/4.2 2.2/4.3 2.1/4.4 2.7/4.9 3.0/5.6 4.0/6.6 4.5/6.3 3.6/6.0 2.9/6.1 2.8/5.3 2.2/4.3 1.5/3.9 3.2/4.5

1-Axis, N-S Average 2.1 3.0 4.0 5.0 5.9 7.2 7.3 6.7 5.8 4.2 2.4 1.9 4.6

Horiz Axis Min/Max 1.5/3.0 2.1/3.9 2.2/5.1 3.4/6.4 4.0/7.6 5.3/8.9 6.0/8.6 4.7/8.2 3.5/7.7 2.8/5.5 1.7/3.3 0.9/2.6 3.6/5.2

Sheridan, 1-Axis, E-W Average 2.3 2.7 3.1 3.4 3.7 4.7 5.3 4.8 4.1 3.4 2.5 2.3 3.5

Wyoming Horiz Axis Min/Max 1.1/3.5 2.2/4.1 2.2/4.2 2.5/5.2 2.7/4.8 3.3/6.1 4.1/6.3 4.0/6.0 2.3/5.3 2.4/4.4 1.8/3.6 1.4/3.1 3.0/4.0

1-Axis, N-S Average 1.5 2.3 3.3 4.4 5.0 6.3 7.1 6.4 4.9 3.3 1.8 1.4 4.0

Horiz Axis Min/Max 0.8/2.3 1.8/3.4 2.2/4.5 3.3/6.8 3.5/6.5 4.4/8.1 5.3/8.4 5.1/8.0 2.8/6.6 2.2/4.2 1.2/2.6 0.8/1.9 3.4/4.5
30

Seattle-Tacoma

Olympia

Yakima

Spokane

Astoria

Portland Salem

Eugene

Northbend

Medford

Redmond/

Bend

Pendleton

Burns Boise

Arcata Pocatello

Winnemucca

Elko

KalispellGreat Falls

Helena

Missoula

Cut Bank

Sacramento

San Francisco

Reno

Fresno

Ely

Tonopah

Salt Lake City

Cedar City

Las Vegas Bakersfield Santa Maria Daggett

Los Angeles

Long Beach

Flagstaff

Prescott

San Diego

Phoenix

Tucson

Barrow

Bettles

Kotaebuc

Nome Fairbanks

Big Delta

McGrath

St.Paul Island

Bethel

King Salmon

Tai Kii Ina

Gulkana

Anchorage

Kodiak

Annette

Yakutat

Cold Bay

Hilo

Kahului Honolulu

Lihue

El Paso MidlandOdessa

Lubbock

San Angelo

San Antonio

Austin

Abilene Fort Worth

Wichita Falls

Waco

Brownsville

Corpus Christi

Victoria

Houston

Port

Arthur

Lufkin

Albuquerque

Tucumcari

Amarillo

Grand

Junction

Alamosa

Eagle Boulder/

Denver

Colorado Springs

Pueblo

Goodland

Dodge City

Wichita

Topeka

Oklahoma City

Tulsa

Rock Springs

Lander

Cheyenne

Sheridan

Casper

Lewistown

Glasgow

Billings

Miles City

Minot

Bismarck Fargo

Rapid City

Pierre Huron

Sioux Falls

Scottsbluff Norfolk

Omaha

Grand Island

North Platte

Sioux City

Des Moines

Waterloo

Mason City

International

Falls

Duluth

St.Cloud

Minneapolis/ St.Paul

Rochester

Houghton

Sault Ste.Marie

Eau Claire

La Crosse

Green Bay

MadisonMilwaukee

Alpena

Traverse City

Muskegon

Grand

Rapids

Flint

Detroit

Lansing

Kansas City

Columbia

Springfield

Springfield

St.Louis

Rockford

Chicago

Peoria

Moline

Evansville

Indianapolis

South

BendFort

Wayne

Louisville

Lexington

Nashville

Memphis

Knoxville

Chattanooga

Fort Smith

Little Rock

Shreveport

Lake

Charles

Baton Rouge

New Orleans

Jackson

Meridian

Huntsville

Birmingham

Montogomery

Mobile

Key W

Tampa

Tallahassee/

Apalachicola Da

Jacksonvill

Macon

Columbus Savan

Atlanta

Greenville

Athens

Augusta

Colum

Asheville

Bristol 

Gree

Cincinnati

(Covington, KY)

Huntington

Dayton

Ro

Toledo

Mansfield

Charlest

Columbus 

Cleveland

Young

Akron- P

Canton

Roche

Buffalo

Erie

Br

Quillayute

Key: Primary Stations Secondary Stations

02279810m

Map showing the location of the 239 stations in the National Solar Radiation Data Base, the data of whic

calculate values for this appendix.
Appendix B: Data Necessary for Evaluating Parabolic-Trough

Solar Water-Heating Systems 

(Based, with a few additions and deletions, on checklists 1-2, 1-3, and 1-5 of ASHRAE's Active Solar Heating Systems Design Manual.

Copyright 1988 by the American Society of Heating, Refrigeration, and Air-Conditioning Engineers, Inc., Atlanta, Georgia. Reprinted by

permission)

A. Building hot-water requirements

1. Daily Load ________________ gal/day (L/day) maximum,

________________ gal/day (L/day) minimum

How determined? __________________________________________________

2. Daily use pattern __________________________________________________

3. Hot-water delivery temperature ______________%F (%C)

4. Load profile (list monthly hot-water load estimates, gallons [litres]):

Jan _______ Feb _______ Mar ______ Apr _______ May _______ Jun ______

Jul _______ Aug _______ Sep ___ ___ Oct _______ Nov _______ Dec ______

5. Total annual load ________________

B. Main heating system

1. Energy source: Gas _______ Electric ________ Oil ________ Steam _______

Cost _________

2. Hot-water heater/storage capacity ________________ gallon

Hot-water heater efficiency _______________

3. Hot-water circulation: Yes ________ No ________

4. Cold-water temperature ________%F (%C) maximum ________%F (%C) minimum

C. Building information

Date of construction ________________

Building name ___________________________________________________________

Location (including Zip code) ________________________________________________

1. Primary building use: _______________________________________________

2. Number of floors: ________________ Total floor area _______________ ft2 (m2)

3. Utilities available:

Natural gas ______________ Propane gas ____________ Fuel oil ___________ 

Electric: ________________ volt, ________________ phase, ___________ kW

4. Water quality: pH ________________ Dissolved solids ________________ ppm

D. Collector and storage locations

1. Area available for collectors _________ ft (m) (N/S) x _________ ft (m) (E/W)

Potential shading problems __________________________________________

Provide sketch showing shape and overall dimensions of potential collector locations and orientations with 

location and type of any obstructions of potential shading sources.

2. Potential storage location: Indoor ____________ Outdoor ____________

If indoor, available area ____________ ft (m) x ____________ ft (m);

Ceiling height ____________ ft (m)

Access to storage location: ____________ door sizes ____________ other

3. Potential mechanical equipment location: Indoor ____________ Outdoor ____________

If indoor, available area ____________ ft (m) x ____________ ft (m)

4. Approximate distance collector to heat exchanger or storage __________ ft (m) elev, ____________ ft (m) horizontal

5. Approximate distance heat exchanger to storage _________ ft (m) elevation _______ ft (m) horizontal

31
Appendix C: Absorption Cooling Technology

32

Single-Effect Absorption Chillers

Single-effect absorption-chiller systems consist of an evaporator, absorber, generator, separator, and condenser. They

operate as follows:

• The evaporator generates chilled water at 4 ̊–10 ̊C (40 ̊–50 ̊F) that is pumped to one or more air-conditioning units 

in the air distribution system of the building. Chilled water is produced when refrigerant water at very low pressure

extracts heat from the water to be chilled. As it absorbs heat, the refrigerant water vaporizes.

• The vaporized refrigerant water flows from the evaporator to the absorber. The absorber contains lithium bromide,

which is capable of absorbing large quantities of refrigerant vapor on contact. The refrigerant vapor is absorbed by

concentrated lithium bromide solution as it flows across the surface of the absorber coil.

• The diluted solution is preheated by a heat exchanger before being pumped to the generator. The generator boils

the dilute refrigerant/lithium bromide solution so that the refrigerant and lithium bromide can be separated and recovered for reuse. Solar flat-plate, evacuated-tube or parabolic-trough collectors are used to heat water to 76.7 ̊–98.9 ̊C

(170 ̊–210 ̊F), which is circulated through the generator to heat the refrigerant/lithium bromide solution. The solution

boils under low pressure. The refrigerant vapor is raised to a high temperature and pressure so that it can reject the

heat picked up in the

evaporator. When sunlight is insufficient or

unavailable to generate

thermal energy for the

generator, an auxiliary

electric, natural gas, or

steam subsystem is

used.

• The boiled solution is

then sent to the separator and into a condenser,

where it collects on the

surface of the cooling

coil. Heat is removed by

the cooling water and

rejected through a cooling tower. Refrigerant 

liquid accumulates in the

condenser and passes

into the evaporator, starting the cycle anew.

Separator

Lift pipe

Heat medium

(solar or gas)

Generator Heat exchanger

Absorber

Cooling water

Chilled water

Evaporator

Orifice

Condenser

Refrigerant vapor

Liquid refrigerant

Concentrated Lithium Bromide solution

Dilute Lithium Bromide/refrigerant solution

Chilled water

Cooling water

Heat medium (solar or gas)

Source: American Yazaki Corporation 02279801m
33

Double-Effect Absorption Chillers

Double-effect absorption-chiller systems use a high-temperature (HT) generator and a low-temperature (LT) generator

to improve the thermodynamic efficiency of the absorption cooling cycle.

• Operation of the evaporator and the absorber are the same as in the single-effect system.

• The diluted lithium bromide/refrigerant solution flows from the absorber into the HT generator. There, it is boiled

using thermal energy from solar collectors or an auxiliary subsystem. This drives the refrigerant vapor and semiconcentrated lithium bromide into the primary separator. From the separator, the lithium bromide solution flows to the

heat exchanger, where it is precooled before flowing into the LT generator.

• The hot refrigerant vapor flows from the primary separator to the LT generator, where it surrenders its heat to the

semiconcentrated lithium bromide solution. This decreases the temperature at which it enters the condenser to 

less than that of a

single-effect system.

Also, additional refrigerant is separated

from the lithium 

bromide in the secondary separator,

which further concentrates it.

• The concentrated

lithium bromide is

precooled by the 

heat exchanger

before flowing back

into the absorber.

The refrigerant vapor

flows to the condenser

where its heat is

removed by cooling

water and rejected

through a cooling 

tower. Refrigerant liquid

accumulates in the 

condenser and then

passes into the 

evaporator, starting 

the cycle over.

Primary

separator

Lift pipe

Thermal energy

(solar or auxiliary)

High-temperature

generator

Low-temperature

generator

Heat exchanger

Absorber

Cooling water

Chilled water

Evaporator

Orifice

Refrigerant Condenser

vapor

Liquid refrigerant

Concentrated Lithium Bromide solution

Dilute Lithium Bromide/refrigerant solution

Chilled water

Cooling water

Thermal energy

Source: American Yazaki Corporation 02279811m

Secondary

separator
Appendix D: Federal Life-Cycle Costing Procedures 

and the BLCC Software 

Federal agencies are required to evaluate energy-related investments on the basis of minimum life-cycle costs (LCC) (10 CFR Part 436).

A life-cycle cost evaluation computes the total long-run costs of a number of potential actions, and selects the action that minimizes the

long-run costs. When considering retrofits, sticking with the existing equipment is one potential action, often called the baseline condition.

The LCC of a potential investment is the present value of all of the costs associated with the investment over time.

The first step in calculating the LCC is to identify the costs. Installed Cost includes cost of materials purchased and the labor required 

to install them (for example, the price of an energy-efficient lighting fixture, plus cost of labor to install it). Energy cost includes annual

expenditures on energy to operate equipment. (For example, a lighting fixture that draws 100 watts and operates 2,000 hours annually

requires 200,000 watt-hours [200 kWh] annually. At an electricity price of $0.10/kWh, this fixture has an annual energy cost of $20.) 

Non-fuel Operation and Maintenance (O&M) includes annual expenditures on parts and activities required to operate equipment (for example, replacing burned-out lightbulbs). Replacement costs include expenditures to replace equipment upon failure (for example, replacing an

oil furnace when it is no longer usable).

Because LCC includes the cost of money, periodic and non-periodic O&M and equipment replacement costs, energy escalation rates,

and salvage value, it is usually expressed as a present value, which is evaluated by

LCC = PV (IC) + PV(EC) + PV (OM) + PV (REP)

where PV (x) denotes "present value of cost stream x",

IC is the installed cost,

EC is the annual energy cost,

OM is the annual non-energy cost, and

REP is the future replacement cost.

Net present value (NPV) is the difference between the LCCs of two investment alternatives, e.g., the LCC of an energy-saving or energycost reducing alternative and the LCC of the baseline equipment. If the alternative's LCC is less than baseline's LCC, the alternative is said

to have NPV, i.e., it is cost effective. NPV is thus given by

NPV = PV(EC0) - PV(EC1) + PV(OM0) - PV(OM1) + PV(REP0) - PV(REP1) - PV (IC)

or

NPV = PV(ECS) + PV (OMS) + PV(REPS) - PV (IC)

wheresubscript 0 denotes the baseline condition,

subscript 1 denotes the energy cost-saving measure,

IC is the installation cost of the alternative (the IC of the baseline is assumed to be zero),

ECS is the annual energy cost saving,

OMS is the annual non-energy O&M saving, and

REPS is the future replacement saving.

Levelized energy cost (LEC) is the break-even energy price (blended) at which a conservation, efficiency, renewable, or fuel-switching

measure becomes cost effective (NPV =

> 0). Thus, a project's LEC is given by

PV(LEC*EUS) = PV(OMS) + PV(REPS) - PV(IC)

where EUS is the annual energy use savings (energy units/year). Savings-to-investment ratio (SIR) is the total (PV) saving of a measure

divided by its installation cost:

SIR = (PV(ECS) + PV(OMS) + PV(REPS))/PV(IC)

Some of the tedious effort of LCC calculations can be avoided by using the BLCC software, developed by NIST. For copies of BLCC,

call the FEMP Help Desk at (800) 363-3732.

34
Appendix E: Adams County Detention Facility Case Study:

NIST BLCC Comparative Economic Analysis ******************************************************************************

* N I S T B L C C: COMPARATIVE ECONOMIC ANALYSIS (ver. 4.4-97 ) *

******************************************************************************

Project: Adams County Detention Facility in Brighton, Colorado

Basecase: Brighton-Gas Water Heating System—No Solar

Alternative: Brighton-Parabolic Trough Solar Water Heating System with Gas Backup

Principal Study Parameters 

—————————————-

Analysis Type: Federal Analysis—Energy Conservation Projects

Study Period: 25.00 Years (APR 1987 through MAR 2012)

Discount Rate: 3.4% Real (exclusive of general inflation)

Basecase LCC File: ACDFNOSO.LCC

Alternative LCC File: ACDFSOLR.LCC

Comparison of Present-Value Costs

Basecase: Alternative: Savings

Brighton-No Sol Brighton- from Alt.

with Solar

Initial Investment item(s): —————— —————— ——————

Capital Requirements as of Service Date $0 $178,400 -$178,400

————- ————- ————-

Subtotal $0 $178,400 -$178,400

Future Cost Items:

Annual and Other Recurring Costs $111,794 $45,986 $65,808

Energy-related Costs $353,493 $212,096 $141,397

————- ————- ————-

Subtotal $465,287 $258,082 $207,205

————- ————- —————-

Total Present Value of Life-Cycle Cost $465,287 $436,482 $28,805

(without state buydown) $465,287 $476,482 -$11,195

(with subsidy, but adjusted to reflect actual natural gas prices $401,851 $394,114 $7,737

for 1987–1997)

Net Savings from Alternative ‘Brighton-with Solar’ compared to Basecase ‘Brighton-No Solar’

Net Savings = P.V. of Noninvestment Savings $207,205

- Increased Total Investment $178,400

——————-

Net Savings: $28,805

Note: the SIR and AIRR computations include differential initial costs, capital replacement costs, and residual value (if any) 

as investment costs, per NIST Handbook 135 (Federal and MILCON analyses only).

Savings-to-Investment Ratio (SIR) For Alternative ‘Brighton-with Solar’ compared to Base Case ‘Brighton-No Solar’

P.V. of non-investment savings

SIR = ——————————————— = 1.16

Increased total investment

ADJUSTED INTERNAL RATE OF RETURN (AIRR) for Alternative ‘Brighton-with Solar’ compared to 

Base Case ‘Brighton-no Solar’ (Reinvestment Rate = 3.40%; Study Period = 25 years)

AIRR = 4.02%

Estimated Years to Payback:

Simple Payback occurs in year 17; 

Discounted Payback occurs in year 22 

35
ENERGY SAVINGS SUMMARY

Energy Units —— Average Annual Consumption ——- Life-Cycle

Type Basecase Alternative Savings Savings 

—————— ———— —————- —————- ————— —————

Natural Gas MBtu 5,000.0 3,000.0 2,000.0 50,000.0

EMISSIONS REDUCTION SUMMARY

Energy —— Average Annual Emissions ——- Life-Cycle

Type Basecase Alternative Savings Savings 

—————— —————- —————- ————— —————

Natural Gas:

CO2 (Mg): 264.1 158.4 105.6 2,640.7

SO2 (Kg): 1.0 0.6 0.4 10.5

NOx (Kg): 205.8 123.4 82.3 2,057.5

Total:

CO2 (Mg): 264.1 158.4 105.6 2,640.7

SO2 (Kg): 1.0 0.6 0.4 10.5

NOx (Kg): 205.8 123.4 82.3 2,057.5

c:\lcc\brighton.cmp

36
Appendix F: Adams County Detention Facility Case Study:

ESPC Economic Analysis 

CASE 3: ESCO OWNERSHIP OF THE SOLAR SYSTEM

(Gas Cost Data for the Period 1987 - 1997 Are Actual Gas Cost Rates as Provided by Public Service Company of Colorado)

SYSTEM: Parabolic Trough Solar System with Natural Gas Backup

SYSTEM INSTALLED COST (Gross): $218,400

SYSTEM INSTALLED COST (net of 10% tax credits and buydown by Colorado): $156,560

ANNUAL ENERGY REQUIREMENT(Million BTUs): 3500

Energy Requirement to Be Met by Gas(MMBTUs): 2100

BOILER EFFICIENCY: 70%

Annual Requirement for Gas(MMBTUs): 3000

Energy Requirement to Be Met by Solar 1400

Gas Savings Because of Solar (MMBTUs): 2000

Cost of Natural Gas in 1997 ($/MMBTU): 3.78

Gas Cost Inflation Rate 0.02

Starting O&M Cost: $600

Starting Insurance Cost $600

General Inflation Rate: 0.02

Discount Rate: 0.038

ANNUAL

VALUE REVENUE ANNUAL CUMUL- ANNUAL

GAS OF GAS FOR REVENUE GENERAL INSUR- NET ATIVE TAX

COST SAVINGS USER ($ FOR INFLATION O&M ANCE CAPITAL DEPRE- GROSS TAXES NET CASH NET CASH SAVINGS

YEAR RATE ($) SAVINGS) ESCO($) FACTOR COST COST COST CIATION INCOME (31%) INCOME FLOW FLOW ($)

1986 156560

1987 3.36 $6720 $2016 $4704 1.00 600 600 0 $7828 -4324 $0 $-4324 $7828 $7828 $1340

1988 3.06 $6120 $1836 $4284 1.03 615 615 0 $59493 -56439 $0 $-56439 $59493 $67321 $17496

1989 3.33 $6660 $1998 $4662 1.05 630 630 0 $35696 -32295 $0 $-32295 $35696 $103017 $10011

1990 2.83 $5660 $1698 $3962 1.08 646 646 0 $21417 -18747 $0 $-18747 $21417 $124434 $5812

1991 3.18 $6360 $1908 $4452 1.10 662 662 0 $17128 -14001 $0 $-14001 $17128 $141562 $4340

1992 2.99 $5980 $1794 $4186 1.13 679 679 0 $14998 -12170 $0 $-12170 $14998 $156560 $3773

1993 3.27 $6540 $1962 $4578 1.16 696 696 0 $0 3186 $988 $2199 $2199 $158759 $0

1994 3.56 $7120 $2136 $4984 1.19 713 713 0 $0 3558 $1103 $2455 $2455 $161213 $0

1995 3.48 $6960 $2088 $4872 1.22 731 731 0 $0 3410 $1057 $2353 $2353 $163566 $0

1996 2.95 $5900 $1770 $4130 1.25 749 749 0 $0 2631 $816 $1816 $1816 $165382 $0

1997 3.78 $7560 $2268 $5292 1.28 768 768 0 $0 3756 $1164 $2592 $2592 $167973 $0

1998 3.86 $7711 $2313 $5398 1.31 787 787 0 $0 3823 $1185 $2638 $2638 $170611 $0

1999 3.93 $7865 $2360 $5506 1.34 807 807 0 $0 3892 $1206 $2685 $2685 $173297 $0

2000 4.01 $8023 $2407 $5616 1.38 827 827 0 $0 3962 $1228 $2734 $2734 $176030 $0

2001 4.09 $8183 $2455 $5728 1.41 848 848 0 $0 4033 $1250 $2783 $2783 $178813 $0

2002 4.17 $8347 $2504 $5843 1.45 869 869 21840 $21840 -17735 $0 $-17735 $21840 $200653 $5498

2003 4.26 $8514 $2554 $5960 1.48 891 891 0 $0 4178 $1295 $2883 $2883 $203536 $0

2004 4.34 $8684 $2605 $6079 1.52 913 913 0 $0 4253 $1318 $2935 $2935 $206471 $0

2005 4.43 $8858 $2657 $6200 1.56 936 936 0 $0 4329 $1342 $2987 $2987 $209457 $0

2006 4.52 $9035 $2710 $6324 1.60 959 959 0 $0 4406 $1366 $3040 $3040 $212498 $0

2007 4.61 $9216 $2765 $6451 1.64 983 983 0 $0 4485 $1390 $3094 $3094 $215592 $0

2008 4.70 $9400 $2820 $6580 1.68 1008 1008 0 $0 4564 $1415 $3149 $3149 $218741 $0

2009 4.79 $9588 $2876 $6712 1.72 1033 1033 0 $0 4646 $1440 $3205 $3205 $221947 $0

2010 4.89 $9780 $2934 $6846 1.76 1059 1059 0 $0 4728 $1466 $3262 $3262 $225209 $0

2011 4.99 $9975 $2993 $6983 1.81 1085 1085 0 $0 4812 $1492 $3320 $3320 $228530 $0

TOTALS $194758 $58427 $136331 $20495 $178400 IRR: 6%

37
Appendix G: Federal Correctional Institution—Phoenix

Case Study: NIST BLCC Comparative Economic Analysis ******************************************************************************

* N I S T B L C C: COMPARATIVE ECONOMIC ANALYSIS (ver. 4.4-97 ) *

******************************************************************************

Project: FCI PHOENIX-SOLAR WATER HEATING

Basecase: Electric Resistance Water Heating System

Alternative: Parabolic Trough Solar Water Heating System with Electric Resistance Backup Subsystem

Principal Study Parameters 

—————————————-

Analysis Type: Federal Analysis—Energy Conservation Projects

Study Period: 20.00 Years (AUG 1997 through JUL 2017)

Discount Rate: 3.4% Real (exclusive of general inflation)

Basecase LCC File: FCINOSOL.LCC

Alternative LCC File: FCISOL.LCC

Comparison of Present-Value Costs

Base Case: Alternative: Savings

Electric Res. Parabolic from Alt.

System Trough

System

Initial Investment item(s): —————— —————— ——————

Capital Requirements as of Service Date $0 $650,000 -$650,000

—————- ————- —————-

Subtotal $0 $650,000 -$650,000

Future Cost Items:

Annual and Other Recurring Costs $143,419 $226,891 -$83,473

Energy-related Costs $1,528,397 $290,465 $1,237,932

Residual Value at End of Study $0 $0 $0

—————- ————- —————-

Subtotal $1,671,816 #517,356 $1,154,460

—————- ————- —————-

Total Present Value of Life-Cycle Cost $1,671,816 $1,167,356 $504,460

Net Savings from Alternative ‘Parabolic Trough System’ compared to Basecase ‘Electric Resistance System’

Net Savings = P.V. of Noninvestment Savings $1,154,460

- Increased Total Investment $650,000

——————-

Net Savings: $504,460

Note: the SIR and AIRR computations include differential initial costs, capital replacement costs, and residual value (if any) 

as investment costs, per NIST Handbook 135 (Federal and MILCON analyses only).

Savings-to-Investment Ratio (SIR) For Alternative ‘Phoenix-with Solar’ compared to Base Case ‘Phoenix-No Solar’

P.V. of non-investment savings

SIR = ——————————————— = 1.78

Increased total investment

Adjusted Internal Rate of Return (AIRR) for Alternative ‘Parabolic Trough System’ compared to 

Base Case ‘Electric Resistance System’ (Reinvestment Rate = 3.40%; Study Period = 20 years)

AIRR = 6.41%

Estimated Years to Payback:

Simple Payback occurs in year 8; 

Discounted Payback occurs in year 10 

38
ENERGY SAVINGS SUMMARY

Energy Units —— Average Annual Consumption ——- Life-Cycle

Type Basecase Alternative Savings Savings 

—————— ———— —————- —————- ————— ———————

Electricity kWh 1,768,000.0 336,000.0 1,432,000.0 28,640,000.0

EMISSIONS REDUCTION SUMMARY

Energy —— Average Annual Emissions ——- Life-Cycle

Type Basecase Alternative Savings Savings 

—————— —————- —————- ————— —————

Natural Gas:

CO2 (Mg): 1,713.8 325.7 1,388.1 27,762.4

SO2 (Kg): 5,971.3 1,134.8 4,836.5 96,729.9

NOx (Kg): 5,162.8 981.2 4,181.6 83,632.7

Total:

CO2 (Mg): 1,713.8 325.7 1,388.1 27,762.4

SO2 (Kg): 5,971.3 1,134.8 4,836.5 96,729.9

NOx (Kg): 5,162.8 981.2 4,181.6 83,632.7

c:\lcc\fciphoex.cmp

39
Appendix H: Federal Correctional Institution—Phoenix C

ESPC Economic Analysis 

SCENARIO: THE SOLAR SYSTEM IS OWNED AND OPERATED BY AN ESCOSYSTEM: Parabolic Trough Solar Water Heating System with Electric Resistance BackupSYSTEM INSTALLED COST (Gross): $650,000SYSTEM INSTALLED COST (net of 10% tax credits and buydown): $585,000ANNUAL ENERGY REQUIREMENT(kWh): 1768000SOLAR COLLECTOR AREA(sq ft): 18000ANNUAL ENERGY REQUIREMENT(kWh): 1432591AMOUNT OF SYST COST FINANCED: $585,000FIRST YR ELECTRICITY COST($/kWh): 0.062MORTGAGE: 18.5 years @ 9.5%ELECTRICITY COST INFLATION RATE: 3%ANNUAL MORTGAGE PAYMENT: $67,741GENERAL INFLATION RATE: 3%DISCOUNT RATE (Real): 3.40%Electricity Savings Going to ESCO (%): 90%FIRST YR INSURANCE COST($): $10,022

ANNUAL ANNUAL ANNUAL GOVERNMENT TOTAL

ELEC COST VALUE OF SAVINGS REVENUE PAYMENT AVAILABLE GENERAL GROSS 

YEAR INFLATION ELECTRICITY GOING to for and TAX CASH INFLATION O&M INSURANCE CAPITAL INTEREST LOAN DEPRE- ANNUAL 

NO. YEAR FACTOR SAVINGS GOVERNMENT ESCO($) CREDITS for ESCO FACTOR EXPENSE EXPENSE REPAYMENT EXPENSE BALANCE CIATION PROFIT 

0 1997 1.00 $0 $0 $0 $108191 1.00 $0 $0 $0 $0 $585000 1 1998 1.03 $45743 $4574 $41168 $0 $41168 1.03 $2318 $5161 $33871 $27788 $578917 $29250 -$23348 2 1999 1.06 $94230 $9423 $84807 $0 $84807 1.06 $4774 $10632 $67741 $54997 $566173 $222300 -$207897 3 2000 1.09 $97057 $9706 $87351 $0 $87351 1.09 $4917 $10951 $67741 $53786 $552219 $134550 -$116854 4 2001 1.13 $99968 $9997 $89972 $0 $89972 1.13 $5065 $11280 $67741 $52461 $536938 $81900 -$60734 5 2002 1.16 $102967 $10297 $92671 $0 $92671 1.16 $5217 $11618 $67741 $51009 $520206 $64350 -$39523 6 2003 1.19 $106056 $10606 $95451 $0 $95451 1.19 $5373 $11967 $67741 $49420 $501885 $52650 -$23959 7 2004 1.23 $109238 $10924 $98314 $0 $98314 1.23 $5534 $12326 $67741 $47679 $481823 $0 $32775 8 2005 1.27 $112515 $11252 $101264 $0 $101264 1.27 $5700 $12696 $67741 $45773 $459855 $0 $37095 9 2006 1.30 $115891 $11589 $104302 $0 $104302 1.30 $5871 $13076 $67741 $43686 $435801 $0 $41668 10 2007 1.34 $119368 $11937 $107431 $0 $107431 1.34 $6048 $13469 $67741 $41401 $409461 $0 $46513 11 2008 1.38 $122949 $12295 $110654 $0 $110654 1.38 $6229 $13873 $67741 $38899 $380618 $0 $51653 12 2009 1.43 $126637 $12664 $113973 $0 $113973 1.43 $6416 $14289 $67741 $36159 $349036 $0 $57110 13 2010 1.47 $130436 $13044 $117392 $0 $117392 1.47 $6608 $14718 $67741 $33158 $314454 $0 $62908 14 2011 1.51 $134349 $13435 $120914 $0 $120914 1.51 $6807 $15159 $67741 $29873 $276586 $0 $69075 15 2012 1.56 $138380 $13838 $124542 $0 $124542 1.56 $7011 $15614 $67741 $26276 $235120 $0 $75641 16 2013 1.60 $142531 $14253 $128278 $0 $128278 1.60 $7221 $16082 $67741 $22336 $189716 $0 $82638 17 2014 1.65 $146807 $14681 $132126 $0 $132126 1.65 $7438 $16565 $67741 $18023 $139998 $0 $90101 18 2015 1.70 $151211 $15121 $136090 $0 $136090 1.70 $7661 $17062 $67741 $13300 $85557 $0 $98068 19 2016 1.75 $155748 $15575 $140173 $0 $140173 1.75 $7891 $17574 $67741 $8128 $25943 $0 $106580 20 2017 1.81 $160420 $16062 $144378 $0 $144378 1.81 $8128 $18101 $67741 $0 $0 $0 $118150 TOTALS $241250 $2171251 $122227 $272212 $67741 $585000 $497659 

INTERNAL RATE OF RETURN FOR ESCO(%) 14% 

40
The Energy Policy Act of 1992, and

subsequent Executive Orders, mandate

that energy consumption in the Federal

sector be reduced by 30% from 1985

levels by the year 2005. To achieve 

this goal, the U.S. Department of

Energy’s Federal Energy Management

Program (FEMP) is sponsoring a 

series of programs to reduce energy

consumption at Federal installations

nationwide. One of these programs,

the New Technology Demonstration

Program (NTDP), is tasked to accelerate the introduction of energy-efficient

and renewable technologies into the

Federal sector and to improve the rate of

technology transfer.

As part of this effort FEMP, is 

sponsoring a series of Federal Technology Alerts (FTAs) that provide 

summary information on candidate

energy-saving technologies developed

and manufactured in the United States.

The technologies featured in the

Technology Alerts have already 

entered the market and have some 

experience but are not in general use 

in the Federal sector. Based on their

potential for energy, cost, and environmental benefits to the Federal sector,

the technologies are considered to be

leading candidates for immediate

Federal application.

The goal of the Technology Alerts 

is to improve the rate of technology

transfer of new energy-saving tech-nologies within the Federal sector and to

provide the right people in the field with

accurate, up-to-date information 

on the new technologies so that they 

can make educated judgments on

whether the technologies are suitable 

for their Federal sites.

Because the Technology Alerts are

cost-effective and timely to produce

(compared with awaiting the results 

of field demonstrations), they meet 

the short-term need of disseminating

information to a target audience in 

a timeframe that allows the rapid

deployment of the technologies—and

ultimately the saving of energy in the

Federal sector.

The information in the Technology

Alerts typically includes a description 

of the candidate technology; the 

results of its screening tests; a description of its performance, applications 

and field experience to date; a list of

potential suppliers; and important 

contact infor-mation. Attached 

appendixes provide supplemental 

information and example worksheets 

on the technology.

FEMP sponsors publication of the

Federal Technology Alerts to facilitate

information-sharing between manufacturers and government staff. While 

the technology featured promises significant Federal-sector savings, the

Technology Alerts do not constitute

FEMP’s endorsement of a particular

product, as FEMP has not independently verified performance data provided by manufacturers. Nor do 

the Federal Technology Alerts attempt

to chart market activity vis-a-vis the

technology featured. Readers should

note the publication date on the back

cover, and consider the Alert as an 

accurate picture of the technology and

its performance at the time of publication. Product innovations and the

entrance of new manufacturers or 

suppliers should be anticipated since 

the date of publication. FEMP 

encourages interested Federal energy

and facility managers to contact the

manufacturers and other Federal sites

directly, and to use the worksheets in

the Technology Alerts to aid in their

purchasing decisions.

Federal Energy Management Program

The Federal Government is the largest energy consumer in the nation. Annually, in its 500,000 buildings and 8,000 locations worldwide,

it uses nearly two quadrillion Btu (quads) of energy, costing over $11 billion. This represents 2.5% of all primary energy consumption in

the United States. The Federal Energy Management Program was established in 1974 to provide direction, guidance, and assistance to

Federal agencies in planning and implementing energy management programs that will improve the energy efficiency and fuel flexibility 

of the Federal infrastructure.

Over the years several Federal laws and Executive Orders have shaped FEMP's mission. These include the Energy Policy and Conservation Act of 1975; the National Energy Conservation and Policy Act of 1978; the Federal Energy Management Improvement Act of 1988;

and, most recently, Executive Order 12759 in 1991, the National Energy Policy Act of 1992 (EPACT), and Executive Order 12902 in 

1994.

FEMP is currently involved in a wide range of energy-assessment activities, including conducting New Technology Demonstrations, to hasten the penetration of energy-efficient technologies into the Federal marketplace.

This report was sponsored by the United States Government. Neither the United States nor any agency or contractor thereof, nor any of

their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness,

or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned

rights. Reference herein to any specific commercial product, process, or service by trade name, mark, manufacturer, or otherwise, does 

not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency or

contractor thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States

Government or any agency or contractor thereof.

About the Federal Technology Alerts
For More Information

FEMP Help Desk:

(800) 363-3732

International callers please use: (703) 287-8391

Web site: http://www.eren.doe.gov/femp/

General Contacts

Ted Collins

NTDP Program Manager

Federal Energy Management Program

U.S. Department of Energy

1000 Independence Avenue SW, EE-92

Washington, D.C. 20585

Phone: (202) 586-8017

e-mail: theodore.collins@ee.doe.gov

Steven A. Parker

Pacific Northwest National Laboratory

P.O. Box 999, Mail Stop K5-08

Richland, WA 99352

Phone: (509) 375-6366

e-mail: steven.parker@pnl.gov

Technical Contact

Russ Hewett, Mail Stop 2714

National Renewable Energy Laboratory

1617 Cole Boulevard

Golden, CO 80401

Phone: (303) 384-7463

Fax: (303) 384-7540

e-mail: russell_hewett@nrel.gov

Produced for the U.S. Department 

of Energy (DOE) by the National Renewable

Energy Laboratory,

a DOE national laboratory

DOE/GO-102000-0973

(A revision of DOE/GO-10098-485)

Revised January 2000

(Originally printed April 1998)

Printed with a renewable-source ink on 

paper containing at least 50% wastepaper, including 20%

postconsumer waste