Building Technologies Program

Energy effi ciency and solar energy technologies 

can result in zero net energy consumption from 

nonrenewable sources

During times of peak demand, a near zero energy home generates more 

power than it uses and reduces power demand on the utility provider. In a 

Florida study, a prototype near zero energy home outperforms a conventional 

model by providing most of its own power needs throughout the year.
The two homes were built in 

Lakeland, Florida, in the spring 

of 1998. They were constructed 

by the same builder and had 

identical compass orientations 

and fl oor plans (2,425 square 

feet). The energy use of both 

homes was monitored from April 

1998 to June 2002.

The objective was to test the 

feasibility of constructing a new 

single-family residence that was 

engineered to reduce the home’s 

energy loads to an absolute minimum so that most 

of the cooling, water heating, and other daytime 

electrical needs could be met by the solar systems. 

The near zero energy home included a number 

of features and engineering elements that were 

designed to minimize cooling loads, especially in 

Performance Features

Control Home

• Gray/brown asphalt shingle roof 

with 1.5-foot overhangs 

• R-30 attic insulation

• R-4 wall insulation on interior of 

concrete block walls

• Single-glazed windows with 

aluminum frames

• R-6 ducts located in attic 

• Standard electric appliances 

(range, water heater, refrigerator, 

and dryer)

• Standard incandescent lighting 

(30 recessed-can lights)

• Standard-effi ciency, 4-ton, SEER 

10 (seasonal energy effi ciency 

ratio) heat pump (a typical air 

conditioner in Florida).

Near Zero Energy Home

• 2-kW solar water heater

• 4-kW utility-interactive PV 

system

• White-tile roof with 3-foot 

overhangs

• R-30 attic insulation 

• R-10 exterior insulation over 

concrete block system 

• Advanced solar-control doubleglazed windows 

• Oversized, interior-mounted 

ducts

• High-effi ciency refrigerator 

• High-effi ciency compact 

fl uorescent lighting

• Programmable thermostat 

• Downsized SEER 15.0, variablespeed, 2-ton air conditioner with 

fi eld-verifi ed cooling-coil air fl ow.

Conducting 

the Test

A bird’s-eye view of both homes 

The completed control and near zero energy homes in the Windwood Hills development of Lakeland, Florida.

From July 2001 to June 2002, the 

occupied near zero energy home 

consumed only 2,150 kilowatt-hours 

(kWh) of utility-grid power for all its 

electrical needs. This compares to 

21,240 kWh used by the control home 

(unoccupied for 1.5 months). Energy 

effi ciency along with solar generation 

reduced the energy use of the near 

zero energy home compared to a 

conventional identical home by 90%. 

Energy Bottom Line 

for 2001–2002 

Control Home

Near Zero Energy Home 

late afternoon during the utility’s peak period of 

electrical demand. As a research project, the goal 

was to see how much energy and peak demand 

could be saved in the near zero energy home 

compared to the standard or “control” home.

The energy savings picture (for cooling): The estimated percentage of energy 

savings attributed to each measure used in the near zero energy home.

The energy savings picture (for cooling): The estimated percentage of energy 
Bringing you a prosperous future where energy is clean, abundant, reliable, and affordable 

Another innovative feature is the refl ective 

white-tile roof on the near zero energy home 

versus the locally popular gray/brown asphalt 

shingles on the control home. Both homes 

have R-30 fi berglass insulation in the attic. 

But records from June 18, 1998, a peak 

utility day, point up the differences. The attic 

temperature in the control house rose quickly 

in the afternoon to reach a maximum of 138°F, 

The traditional wide roof overhang of old-style 

Florida homes is seldom used these days, on 

the assumption that air-conditioning takes 

care of cooling needs. But why make the air 

conditioner work harder and cost more to operate 

than it should? The near zero energy home’s 

3-foot roof overhang (versus 1.5 feet for the 

control) produces twice as much shade, which 

is especially benefi cial for controlling solar gain 

(heat buildup) on walls and windows.

while the near zero energy home’s attic reached 

only 100°F, about the same as the outside air 

temperature.

Exterior insulation (R-10 value) thermally 

encases the near zero energy home. This allows 

the masonry to be pre-cooled during daytime 

hours when the sun is shining brightly and the 

photovoltaic (PV) system output is at maximum 

power. The pre-cooled concrete walls help maintain 

indoor comfort into the late afternoon and evening.

The near zero energy home’s windows, which 

account for almost one-fi fth of the energy 

savings (for cooling), were selected 

for both appearance and thermal 

effectiveness. The advanced 

solar-control windows are 

spectrally selective. This means 

that they transmit much of the 

light in the visible portion of 

the solar spectrum, but limit 

transmission in the infrared and 

ultraviolet portions (which overheat 

and fade interior materials).

Interior-mounted, oversized ducts positioned 

within the air-conditioned space as opposed 

to the hot attic are used in the near 

zero energy home to great advantage. 

Tests at the Florida Solar Energy Center 

(FSEC) showed that heat transfer to the 

duct system can rob the air conditioner 

of as much as one-third of its cooling 

capacity during the hottest hours. 

Oversizing the ducts allows high air fl ow and 

low friction loss (previously shown to provide 

as much as a 12% improvement in cooling 

effi ciency at essentially no extra cost).

High-effi ciency appliances and lighting further 

minimize the near zero energy home’s electrical 

load. These appliances and lighting also release 

less heat into the home while operating, which 

decreases the cooling load that must be met 

by the air-conditioning system. The smaller 

appliance, lighting, and air-conditioning loads 

mean less PV capacity is required to meet the 

home’s total electrical load.

A programmable thermostat is set so that the 

indoor temperature is allowed to increase 

overnight and while the house is unoccupied. 

This decreases the number of hours per day 

Breaking Out the Savings

For illustration purposes, some features of the near zero 

energy home have been relocated (versus actual).
appliance. The small system (half the size of 

that in the control home) is highly unusual for 

such a large home in Lakeland, Florida, but it’s 

performing to expectations. In addition, the unit’s 

cooling coil air fl ow was fi eld-verifi ed at the near 

zero energy home, which involved using a fl ow 

hood to adjust the fan speed of the variablespeed air handler. Installers who neglect this 

crucial step commonly cost the system a 

10% drop in operating effi ciency. 

the air conditioner operates. Running the air 

conditioner less reduces the total electricity 

consumption and lowers utility costs.

The solar water heating system supplies most 

of the hot water for occupant needs. Its energy 

output is equivalent to that of a 2-kW PV system.

The combination of effi ciency features reduces the 

cooling loads so that a downsized air conditioner 

suffi ces. Here too, FSEC chose a high-effi ciency 

About the Solar Systems

was specifi ed. One was located on the southfacing roof, which is generally the preferred 

placement for a PV system. The other was 

located on the west-facing roof, because this orientation provides more PV power during the hot 

afternoons, when the utility experiences its peak 

demand period. Reducing demand at this time of 

day is particularly valuable to the utility. The PV 

system is grid-interactive. It produces DC power 

that is converted to AC and then fed directly into 

the local utility distribution system. The City of 

Lakeland’s municipal utility, Lakeland Electric, 

owns the PV system and allowed unprecedented 

connection of a residential PV system to the 

utility grid.

The solar water heating system is a typical 

Florida direct circulation system with a 2-kW 

solar collector, an 80-gallon storage tank, and a 

PV-powered pump. This FSEC-approved system 

supplies most of the home’s hot water, which 

is the largest residential energy use in Florida 

after air-conditioning. The solar water heater also 

eliminates any electrical requirements during hot 

summer afternoons—the utility’s peak period of 

electrical demand.

The PV system was sized to provide power that 

would offset as much of the household load as 

possible. Based on the predicted load for a peak 

day, a 4-kW PV array (split into two subarrays) 

Energy Effi ciency Enhances 

Solar Technology

It’s important to note that a solar technology 

system will not save energy. People invest 

in solar technology because it’s an energy 

producer—one that releases no noxious 

gases into the air and that can minimize or 

eliminate monthly utility bills. And, when solar technologies are combined with energy 

effi ciency measures, their investment value 

is magnifi ed. 

Here’s where energy effi ciency factors in: as 

a home’s energy effi ciency increases, solar 

technology can offset more of the utility bill. 

This makes it a better investment, because 

the solar technology power stretches 

further. In the Florida case, building energy 

effi ciency into the near zero energy home 

and sizing and locating the solar technology system correctly resulted in the solar 

technology system offsetting about 85% of 

all annual grid electricity needs.

Of course, purchasing the solar technology 

system and installing certain energy effi ciency 

measures incurs up-front costs. But in many 

cases, these costs can be recouped over time 

by the savings on the monthly energy bill. 

What works in Florida can work just as well 

in other parts of the country. The energy 

effi ciency measures and solar technology 

confi gurations will vary locally, but energy 

effi ciency can improve the value of the solar Near zero energy home’s roof and windows beat the heat technology resource anywhere.

Comparison of the infrared 

appearance of west-facing 

windows of both homes 

in the afternoon. The 

near zero energy home’s 

windows accounted for 

almost one-fi fth of the energy savings (for cooling).

What If?

A quarter-million people move to Florida 

each year and build more than 100,000 

new homes, so the demand for electrical 

energy increases proportionally. Imagine 

the scenario if all those new homes were 

built like the near zero energy home (rather 

than the control home). How big a difference 

would this make?

If each home would save about 18,000 

kWh/year, the total savings for the 100,000 

homes would be 1.8 billion kWh. Based on 

Florida’s 2004 average cost of residential 

electricity ($0.09/kWh), this would save 

about $162 million per year in utility bills. 

Multiply these fi gures by all 50 states, and 

clearly the energy and air pollution savings 

in the United States would be astronomical. So dramatic, in fact, that it just doesn’t 

make sense to build a new home without 

incorporating energy effi ciency features.

Thermographic images of the roofs in both homes. 

The lower roof and attic heat gain into the near zero 

energy home reduces the demand for cooling.

More

Solar Heat

Transmitted

Less

Solar Heat

Transmitted

Heat Scale
A Tale of Two Houses

When all the numbers were in, the near zero energy 

home performed extremely well. The results for 

June 18, 1998—a day with the hottest daytime 

temperatures ever recorded in Lakeland, Florida, 

tell the story. During a 24-hour period, the near 

zero energy home used 72% less power from airconditioning than did the control home, even though 

the occupied near zero energy home maintained 

cooler indoor temperatures.

Over the day, the control home’s air conditioner 

consumed an average of 2,980 watts of power, 

while the near zero energy home’s 

air conditioner breezed along 

on 833 watts. When the 

power produced by the 

PV system was factored 

in, cooling the near zero 

energy home required 

only 199 watts of utilitysupplied power on that hot 

day in June. This is an astonishing 93% reduction 

compared to the control home.

The graph shows the difference between the 

average hourly energy demand of the control home 

and the near zero energy home from July 2001 to 

June 2002. The part of the curve that dips below 

the zero line indicates the times (~9:00 a.m. to 

~5:00 p.m.) when the near zero energy home 

produced more power than it required and supplied 

the excess to the utility grid. During the Florida 

utility peak period from 4:00 p.m. to 5:00 p.m., the 

control home had a typical demand of 2,400 watts 

compared to –200 watts for the near zero 

energy home.

Cooling Off under the Sun

Just imagine living in Florida and your 

fantasies might turn to swaying palms, fresh 

orange juice, and lots of air-conditioning. For 

most people, a summer spent in Florida’s 

heat and humidity would be unbearable 

without it.

So air-conditioning is a necessity. But it’s also 

a big energy drain that accounts for about 

35% of all electricity used in a typical Florida 

house. As the largest single source of energy 

consumption, a home’s air-conditioning load 

represents the biggest energy challenge. 

FSEC designed a project to answer this challenge. Two homes were built with the same 

fl oor plan on nearby lots. The difference was 

that one (the “control home”) conformed to 

local residential building practices, and the 

other (the “near zero energy home”) was 

designed with energy effi ciency in mind 

and solar technology systems 

on the roof. The homes were 

then monitored carefully 

for energy use.

The project’s designers 

were looking to answer 

two important questions: 

Could a home in a climate 

such as central Florida’s 

be engineered and built so 

effi ciently that a relatively small 

PV system would serve most of its cooling 

needs and even some of its daytime electrical 

needs? And would that home be as comfortable and appealing as 

the conventional 

model built 

alongside it?

The 

answer 

to both 

questions 

turned 

out to be a 

resounding 

“Yes!” And the 

test was especially rigorous, 

because it was begun during 

the summer of 1998–one 

of the hottest summers on 

record.

This news is important for city 

planners, architects, builders, 

and homeowners throughout the 

country. The solar/energy effi ciency 

combination worked so well in Florida that it 

can and should be tried in other parts of 

the country.
An electronic copy of this factsheet is 

available on the Building America Web 

site at www.buildingamerica.gov

Building America Program

George S. James • New Construction • 202-586-9472 • fax: 202-586-8134 • e-mail: George.James@ee.doe.gov

Terry Logee • Existing Homes • 202-586-1689 • fax: 202-586-4617 • e-mail: terry.logee@ee.doe.gov

Lew Pratsch • Integrated Onsite Power • 202-586-1512 • fax: 202-586-8185 • e-mail: Lew.Pratsch@hq.doe.gov

Building America Program • Offi ce of Building Technologies, EE-2J • U.S. Department of Energy • 1000 Independence Avenue, S.W. •

Washington, D.C. 20585-0121 • www.buildingamerica.gov

Building Industry Research Alliance (BIRA)

Robert Hammon • ConSol • 7407 Tam O’Shanter Drive #200 • Stockton, CA 95210-3370 • 209-473-5000 • fax: 209-474-0817 •

e-mail: Rob@consol.ws • www.bira.ws

Building Science Consortium (BSC)

Betsy Pettit • Building Science Consortium (BSC) • 70 Main Street • Westford, MA 01886 • 978-589-5100 • fax: 978-589-5103 •

e-mail: Betsy@buildingscience.com • www.buildingscience.com

Consortium for Advanced Residential Buildings (CARB)

Steven Winter • Steven Winter Associates, Inc. • 50 Washington Street • Norwalk, CT 06854 • 203-857-0200 • fax: 203-852-0741 •

e-mail: swinter@swinter.com • www.carb-swa.com

Davis Energy Group

David Springer • Davis Energy Group • 123 C Street • Davis, CA 95616 • 530-753-1100 • fax: 530-753-4125 •

e-mail: springer@davisenergy.com • deg@davisenergy.com • www.davisenergy.com/index.html

IBACOS Consortium

Brad Oberg • IBACOS Consortium • 2214 Liberty Avenue • Pittsburgh, PA 15222 • 412-765-3664 • fax: 412-765-3738 •

e-mail: boberg@ibacos.com • www.ibacos.com

Industrialized Housing Partnership (IHP)

Subrato Chandra • Florida Solar Energy Center • 1679 Clearlake Road • Cocoa, FL 32922 • 321-638-1412 • fax: 321-638-1439 •

e-mail: subrato@fsec.ucf.edu • www.baihp.org

National Association of Home Builders (NAHB) Research Center

Tom Kenney • National Association of Home Builders (NAHB) Research Center • 400 Prince George’s Boulevard •

Upper Marlboro, MD 20774 • 301-430-6246 • fax: 301-430-6180 • toll-free: 800-638-8556 • www.nahbrc.org/

National Renewable Energy Laboratory

Ren Anderson • 1617 Cole Boulevard, MS-2722 • Golden, CO 80401 • 303-384-7433 • fax: 303-384-7540 •

e-mail: ren_anderson@nrel.gov • www.nrel.gov

Tim Merrigan • 1617 Cole Boulevard, MS-2722 • Golden, CO 80401 • 303-384-7349 • fax: 303-384-7540 •

e-mail: tim_merrigan@nrel.gov • www.nrel.gov

Oak Ridge National Laboratory

Pat M. Love • P.O. Box 2008 • One Bethel Valley Road • Oak Ridge, TN 37831 • 865-574-4346 • fax: 865-574-9331 •

e-mail: lovepm@ornl.gov • www.ornl.gov

Produced for the U.S. Department of Energy (DOE) by the National Renewable Energy Laboratory, a DOE national laboratory.

May 2005 • DOE/GO-102005-2064

Printed with a renewable-source ink on paper containing at least 50% wastepaper, including 20% postconsumer waste.

A Strong Energy Portfolio

for a Strong America

Energy effi ciency and clean, renewable

energy will mean a stronger economy,

a cleaner environment, and greater

energy independence for America.

Working with a wide array of state,

community, industry, and university

partners, the U.S. Department of

Energy’s Offi ce of Energy Effi ciency

and Renewable Energy invests in a

diverse portfolio of energy technologies.

Research and Development

of Buildings

Our nation’s buildings consume more

energy than any other sector of the

U.S. economy, including transportation

and industry. Fortunately, the 

opportunities to reduce building energy 

use—and the associated environmental

impacts—are signifi cant.

DOE’s Building Technologies Program

works to improve the energy effi ciency

of our nation’s buildings through 

innovative new technologies and better

building practices. The program

focuses on two key areas:

• Emerging Technologies

Research and development of the 

next generation of energy-effi cient 

components, materials, and 

equipment

• Technology Integration

Integration of new technologies

with innovative building methods

to optimize building performance

and savings

For more information contact:

EERE Information Center

1-877-EERE-INF (1-877-337-3463)

www.eere.energy.gov

Project Participants

Florida Solar Energy Center

www.fsec.ucf.edu/

Sandia National Laboratories

www.sandia.gov/

Florida Energy Offi ce/Department of Environmental Protection

www.dep.state.fl .us/energy/fl a_energy/default.htm

Lakeland Electric

www.lakelandelectric.com/

For more information

Contact Danny Parker, Florida Solar Energy Center, 1679 Clearlake Rd., 

Cocoa, FL 32922; 407-638-1405 (voice); 407-638-1439 (fax); 

e-mail: dparker@fsec.ucf.edu.

Source Document

Field Evaluation of Effi cient Building Technology with Photovoltaic Power Production in New Florida Residential Housing, by Danny S. Parker, 

et al. The entire document is available online at www.fsec.ucf.edu/bldg/pubs/cr1044/index.htm

Rick Strawbridge, Inc.

863-646-9332 

Siemens/Hutton Communications

www.huttononline.com

Solar Source

www.solarsource.net/

The National Renewable Energy Laboratory

www.nrel.gov

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