National Renewable Energy Laboratory 

Innovation for Our Energy Future 

A national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

NREL is operated by Midwest Research Institute ● Battelle Contract No. DE-AC36-99-GO10337 

Solar Secure Schools: 

Strategies and Guidelines 

October 2004 — April 2005 

G.W. Braun 

En-Strat Associates 

Darnestown, Maryland 

P.F. Varadi 

PV Enterprises Inc. 

Chevy Chase, Maryland 

Subcontract Report 

NREL/SR-520-38435 

January 2006 
Solar Secure Schools: 

Strategies and Guidelines 

October 2004 — April 2005 

G.W. Braun 

En-Strat Associates 

Darnestown, Maryland 

P.F. Varadi 

PV Enterprises Inc. 

Chevy Chase, Maryland 

NREL Technical Monitor: J. Thornton 

Prepared under Subcontract No. AEI-4-44238-01 

Subcontract Report 

NREL/SR-520-38435 

January 2006 

National Renewable Energy Laboratory 

1617 Cole Boulevard, Golden, Colorado 80401-3393 

303-275-3000 • www.nrel.gov 

Operated for the U.S. Department of Energy 

Office of Energy Efficiency and Renewable Energy 

by Midwest Research Institute • Battelle 

Contract No. DE-AC36-99-GO10337
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Table of Contents 

Executive Summary.................................................................................................................................... 1 

Introduction................................................................................................................................................. 2 

What Are Energy Secure Schools? ......................................................................................................... 2 

Are Energy Secure Schools Technically Feasible? ................................................................................ 3 

How Can Solar Power Make Schools Energy Secure?........................................................................... 3 

Basic Solar Secure School System Functionality ....................................................................................... 4 

Scale Economies..................................................................................................................................... 4 

Peak Power Demand............................................................................................................................... 4 

Energy Use.............................................................................................................................................. 5 

Engineering: Are Energy Secure Schools Technically Feasible?............................................................... 5 

Current Technical Solutions: Full Energy Security................................................................................ 5 

Current Technical Solutions: Limited Energy Security.......................................................................... 6 

Future Technical Solutions: Full Energy Security.................................................................................. 7 

Economics: Are Energy Secure Schools Affordable? ................................................................................ 7 

School-Based Solar Power System Affordability................................................................................... 8 

System installed cost........................................................................................................................... 8 

Avoided grid electricity purchases...................................................................................................... 9 

Deciding How to Manage Electricity Price Risk.................................................................................. 10 

Economic Value of Solar Secure Power............................................................................................... 11 

Is Solar Secure Power Affordable?....................................................................................................... 12 

Policy: Will U.S. Schools be Energy Secure? .......................................................................................... 14 

Recommended Strategy for Solar Secure Schools................................................................................ 15

Appendix A: Energy Secure Schools—Technology, Economic, and Policy Considerations (previous 

work under NREL subcontract AEI-4-44238-01) .................................................................................... 16 

Appendix B: Plug-In Hybrid School Buses for Future Solar Secure Schools.......................................... 23 

Appendix C: Should Our Schools Be Energy Secure? A Guide for Decision Makers............................. 24 

Appendix D: Illustration of Load Leveling by a Commercial Rooftop Solar Power System .................. 29 

i 
Executive Summary 

On-grid applications of solar power have eclipsed traditional grid-independent applications in recent years. As a 

result, the overall solar power market has grown consistently by around 30% per year, and the global solar 

industry’s annual sales are in the $10 billion range. Most on-grid solar power applications use the roofs of homes 

and commercial buildings as platforms; meanwhile, in the United States, large numbers of scale model solar 

power systems are being deployed at schools by electric utilities for promotional and educational purposes. 

Can school-based solar power systems provide more tangible value? In 2002, the U.S. Department of Energy and 

the National Renewable Energy Laboratory envisioned a national network of solar-powered, school-based 

emergency centers. A previous report1

 considered the technological, economic, and policy considerations of this 

initiative and identified the need for financing strategies and decision tools for school boards and administrators. 

Schools are used routinely in sheltering vulnerable populations during and after major disasters such as 

hurricanes, terror attacks, and local and regional grid failures. The previous report concluded that shelters 

operating without power are neither healthy nor safe. An “energy secure school” would be protected against grid 

and natural gas supply disruptions, and a “solar secure school” would be insulated from significant unplanned 

increases in its annual energy bill. 

Solar secure schools are not only technically feasible but also economically justified when grid electricity prices 

are high and volatile or schools are shut down by grid power outages more than once every 10 years. Solar power 

prices and grid electricity prices are trending strongly in opposite directions, so solar secure schools soon will be 

an attractive cost control and public safety strategy in most states. 

The present effort has produced a simple step-by-step process that school officials can use to assess their energy 

security options. The solar power industry, in cooperation with federal and state clean energy R&D programs, 

should emphasize development of products that allow seamless, plug-and-play integration of basic solar secure 

school subsystems, including power conversion and energy storage. The ultimate plug-and-play option for solar 

secure schools may be the “plug-in hybrid” school bus, providing prepaid plug-and-play energy storage that has 

the important advantages of being portable and essentially maintenance free. 

Options are emerging to solve the capital budget allocation problem. School budgets, both capital and operating, 

are typically strained; a third of all school construction and renovation bond issues are rejected by voters. Solar 

service companies are emerging that offer attractive solar electricity prices and take full long-term responsibility 

for operation and maintenance of school-based solar power in return for use of the school roofs as solar power 

array mounting platforms. 

Solar electricity prices offer the additional attraction of being fixed for a decade or two, during which grid 

electricity prices will continue to escalate unpredictably with the price of fossil fuels. More aggressively managed 

school districts will be able to maximize electricity cost savings by self-financing their solar power needs, 

especially in states that adopt preferential “feed-in” tariffs that guarantee long-term purchase prices for solar 

electricity fed into the grid. Such long-term solar electricity purchase arrangements greatly facilitate access to 

low-interest private financing of solar power systems and are, therefore, already widely employed in European 

countries. 

 

1

 See Appendix A for a summary of the full report. 

1 
Introduction 

School-based solar power systems can be upgraded to deliver emergency power when the grid is down for 

extended periods. Other emergency generation solutions (e.g., fuel-based emergency generators or grid-charged 

energy storage) have costs in the same range and are limited by their fuel or electricity storage capacity, among 

other drawbacks. In 2004, the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) 

initiated a project to develop guidelines and design specifications for low-cost, prepackaged photovoltaic (PV) 

solar power systems on schools to enable the schools to be used as community emergency centers. The first phase 

of this work pointed to several key steps toward a national network of energy secure schools, including the 

following: 

 Recognizing PV/battery hybrid options in applicable guidelines and standards 

 Developing and disseminating decision tools for school boards, school business managers, and facility 

managers, along with procurement guidelines and technical specifications to support deployment 

 Providing technical demonstrations of basic system sizes and configurations for upgrading school-based solar 

power systems for emergency power purposes 

 Designing incentives specifically to encourage early consideration of school-based solar power systems and 

related reliability upgrades 

 Initiating collaborative R&D to provide technology base support and focus industry attention on new 

products necessary to make schools energy secure in the most cost-effective manner 

 Raising awareness of the role solar power will play in the future energy supply mix and solar power’s ability 

to meet critical energy needs when fuel supplies and electricity infrastructure are disrupted. 

As important as they are, these matters are moot unless strategies are in place to evaluate and finance solar power 

on schools and maximize its energy security benefits. Applying such strategies with the help of the guidelines and 

specifications envisioned by NREL will result in energy secure schools. This report outlines the strategies and 

provides general guidance and specifications for use by school boards and administrators. 

What Are Energy Secure Schools? 

Energy security is a term originally applied in a national context; it referred to vulnerability to disruption in 

supplies of imported fuel. The oil shocks of the 1970s raised concern about energy security and led to President 

Nixon’s “Project Independence” and the creation of a strategic petroleum reserve. More recently, the United 

States began importing liquefied natural gas as well as oil, while global demand for oil and natural gas has 

increased against a backdrop of war and terrorism affecting fuel-rich regions. The Northeast U.S. blackout of 

2003 and comparable grid disruptions in other industrial countries served as reminders that energy security 

depends on electricity infrastructure as well as fuel supply. 

The expansion of critical loads through the addition of electricity-dependent technologies, including computers, 

has highlighted the dependence of organizations and facilities on reliable power. In the wake of recent blackouts 

and security scares, some cities are now pressing facility executives to have backup generation available to power 

more than just safety and security systems, e.g., for operational continuity of low-rise structures such as schools. 

This is a legitimate dimension of the original concept of energy security. 

The concept of energy security can be expanded further by considering price. Energy supplies are not secure if 

they become unaffordable. The legitimacy of this aspect is underscored by the California electricity crisis, during 

which retail grid electricity prices were essentially unstable and threatened regional economies and electricity 

customers. By restructuring the U.S. natural gas and electricity industries to introduce competition and promote 

economic efficiency, regulators also have made the industries less responsible for energy security and less able to 

deliver it. 

2 
Schools are affected by all dimensions of energy security, from the effects of global fuel price instability to local 

energy infrastructure disruptions and local utility price trends and swings. Of all energy users, schools are among 

the most vulnerable to energy insecurity. Without electricity, schools are not safe for work or study. With no way 

of generating extra revenues to pay for unexpected costs, schools must cut programs and staff when energy bills 

rise unexpectedly.2

 

Typically, some schools in each community are designated as emergency shelters. Emergency shelter operation in 

the wake of disasters usually coincides with short-term or extended grid failure. In a previous report3

 it was 

established that emergency shelters operating without power are neither healthy nor safe. An energy secure school 

would be protected from grid and natural gas supply disruptions and insulated from significant unplanned 

increases in its annual energy bill. 

Are Energy Secure Schools Technically Feasible? 

To qualify as energy secure, schools must have stable energy costs and the ability to operate normally when 

external energy supply is disrupted. U.S. energy consumers, including schools, have enjoyed relatively stable 

energy costs throughout most of the 20th century. The technologies that made this possible are still available, and 

new options such as solar power are now available as well. Technically mature on-site power systems are now 

options where operational continuity during short-term loss of external energy supply is a critical need. On-site 

solutions include fuel-based emergency generators and battery-based uninterruptible power systems (UPS). 

Properly sized, installed, and maintained, these on-site solutions work well to buffer energy users from grid 

outages ranging from less than a second to a few hours with UPS and even up to a few days with emergency 

generators with dedicated or uninterruptible fuel supplies. However, they have the basic disadvantage of 

depending on external sources of electricity or fuel, for recharging in the case of UPS and for extended operation 

in the case of emergency generators. By contrast, the technical maturity and reliability of terrestrial solar power 

systems is now well established, as is the preference for solar power in off-grid applications requiring long-term 

uninterruptible power. For these reasons, and others,4

 where solar power can be justified economically it should 

be configured not just to supply bulk electricity but also to ensure the supply of electricity when local grid 

operation is disrupted for extended periods. 

How Can Solar Power Make Schools Energy Secure? 

A previous report5

 explained that a school with a PV array of any size on its roof can be upgraded by adding 

energy storage and appropriate power conversion and control equipment so that, when the grid goes down, at least 

some building circuits and critical equipment remain operable. The economics of basic solar power systems and 

the costs of an appropriate energy security upgrade were outlined, but technical choices and specifications—i.e., 

 

2

 For example, “Everett School District (Washington) cut its electricity consumption 12 percent in 2000 but still had a nearly 

100 percent increase in power costs. To pay the bill, it cut the school budget by $1 million, equal to annual spending for 

textbooks or the salaries of 15 teachers.” Source: Hardin, B. (March 1, 2005). “Utility Exposes Enron Greed at its Core.” 

Washington Post. 3

 Braun, G.W.; Varadi, P.F; Thornton, J. (In review). Energy Secure Schools: Technology, Economic and Policy 

Considerations. National Renewable Energy Laboratory. 4

 For example, underground fuel storage for emergency generators is subject to regulatory requirements pertaining to spill 

containment, release detection and response, tank abandonment and removal, and so forth. Source: University of Maryland 

Department of Environmental Safety (May 2003). Underground Storage Tanks: Motor Fuel, Used Oil And Emergency 

Generators USTs. Safety Fact Sheet, www.des.umd.edu/compliance/factsheet/undergroundtanks.html. 5

 Braun, G.W.; Varadi, P.F; Thornton, J. (In review). Energy Secure Schools: Technology, Economic and Policy 

Considerations. National Renewable Energy Laboratory. 

3 
“how can solar power make schools energy secure?”—were not discussed. Today’s answer and tomorrow’s 

answer will differ. The menu of relevant energy storage choices will continue to expand. Meanwhile, solar power 

equipment costs will continue to drop, even as fossil fuel prices continue to escalate, driving the price of grid 

electricity steadily higher. 

Basic Solar Secure School System Functionality 

The basic solar secure school system must do the following: 

 Offset grid electricity purchases, especially when grid electricity prices are high 

 Provide emergency power sufficient to support routine school operations during a grid outage of any 

duration. 

Sizing of the basic solar secure school system is driven by three factors: 

 Economies of scale of the basic solar power system 

 The school’s nominal peak power demand and daily energy use in normal operation 

 The school’s energy use when operating to conserve electricity without limiting operation. 

Efforts are also underway to use demonstration-scale solar power systems for educational purposes. 

Scale Economies 

Commercial rooftop solar power project costs depend on project scale. Solar power modules are a major cost 

driver for any solar power system, and collector array cost typically scales directly with system size. However, 

other cost elements, including DC-to-AC power conversion equipment, project development, engineering, and 

installation fees, do not scale directly with system rating. The result is that small-scale solar power systems can 

cost 50%–100% more per installed kW than large ground-based or commercial rooftop systems.6

 Table 1 suggests 

that there are significant economies of scale even in the range of sizes that would significantly reduce or avoid 

grid electricity charges entirely. In the near future, size may be the difference between school-based solar power 

that is affordable and solar power lifecycle costs that exceed the cost of avoided grid electricity purchases. 

Accordingly, the basic school-based solar power system should be sized to make full use of suitable roof area. For 

typical U.S. elementary, middle, and high schools, this entails rooftop solar power arrays with ratings of 100–500 

kW. 

Table 1. Scale Effects on Commercial Rooftop Solar Power System Costs 

System Size (kWac) 10-50 50-150 150-500 500-1,000

Installed Cost - Low (1) 7,500 6,750 6,450 6,250

Installed Cost - High (2) 9,000 7,750 7,100 6,500

Notes:

1. The low end of the cost range is based on experience of nationally active companies offering solar service to 

low-rise commercial building owners in the United States. 

2. The high end of the range includes allowances for special site preparation, engineering, etc., and other 

contingencies driven by local requirements and conditions. 

$/kWac

Peak Power Demand 

During emergency operation, a school-based solar power system can be made functionally equivalent to natural 

gas fueled emergency generators already being deployed in some schools. The emergency generators specified for 

 

6

 The majority of current school-based systems are at the high end of this range because they involve small, customized 

installations and equipment purchased through distributors and local dealers. 

4 
Montgomery County, Maryland, public schools are capable of carrying loads of 30–100 kW depending on 

whether the school is an elementary school (small), middle school (medium), or high school (large). They are 

fueled with natural gas from separate, uninterruptible natural gas lines. A solar power system will be able to 

support a few hours of operation at full load on an average day. Depending on the season, its actual peak output 

during a typical day may not approach its annual peak output. Because of this, and because part of the energy 

delivered by the solar power array must be stored for use earlier and later in the day, the solar power system 

should have a peak output approximately three times the above-specified loads, i.e., 100–300 kW, depending on 

the type of school. 

Energy Use 

A school’s energy use during normal operation will result in a load factor of 50% or less, depending on the type 

of school and the season. At a 50% load factor, a school with a peak demand of 100 kW would consume 1,200 

kWh daily. A 300-kW solar power system would deliver roughly this amount on average over a year depending 

on location. Assuming roughly half of the daily energy use could be served directly from the solar power array, 

energy storage capacity must be minimally capable of storing the other half for delivery earlier and later in the 

day. This suggests storage system sizing of 3–6 kWh per kW of rated solar power system output. For example, a 

storage system for a 300-kW solar power system roughly should be sized to store 900–1,800 kWh of electricity. 

Not all of the charging electricity is recovered as useful electricity when a battery is discharged. Up to 30% is lost 

to power conversion inefficiencies and other loss mechanisms. However, a UPS battery would be fully charged 

when a grid outage occurred, and the solar power system would only need to replenish daily use during an 

extended grid outage; thus, round trip efficiency, although technically important, is not economically important. 

Engineering: Are Energy Secure Schools Technically Feasible? 

Current Technical Solutions: Full Energy Security 

There are significant numbers of medium to large (30 kW to several MW) grid-tied solar power systems in 

operation, particularly in Europe and California. Experience to date with this scale of solar power has 

demonstrated a strong market preference for packaged solutions. However, there are no packaged grid-interactive 

system offerings at this scale that also come with energy storage. Solar power system integrators are technically 

qualified to design and build large systems incorporating battery energy storage, but their related experience is 

limited, mostly to large, stand-alone (off-grid) PV/battery hybrid systems or smaller, grid-tied PV/battery hybrid 

applications. Custom engineering would be required for large, grid-tied PV/battery hybrid systems. For this 

reason, equipment and installation costs for large, grid-tied PV/hybrid systems likely would be elevated, 

especially if the basic solar power system is installed first and later upgraded and reconfigured to provide energy 

security. One key factor driving customization costs is the lack of off-the-shelf power conversion units with 

ratings exceeding 5 kW that also meet the following specifications: 

 Capability for battery charging from the solar power array or the grid 

 Capability for AC power generation from multiple DC sources, i.e., batteries and the PV array 

 Capability for two modes of AC power generation: 

o Grid-tied from the PV array (normal) 

o Grid-isolated from the PV array, the battery, or both (emergency). 

Once such units are available, capturing the full economic benefit of a large, grid-tied PV/battery hybrid system 

will in many cases require a third mode, i.e., grid-tied from the PV array, the battery, or both for peak shaving 

purposes. 

5 
Technology and components to fill the abovementioned gaps in current packaged solar power system offerings 

are available from two sources: the UPS industry and the emergency generator industry. An important caveat: 

highly engineered equipment intended for a specific purpose must be applied to other purposes with considerable 

care, even when the application is permissible without voiding product warranties. 

 

Large-scale UPS offered by several manufacturers can be a suitable complement to the basic solar power system. 

They are available over a wide range of power ratings, battery capacities, and battery types and interactivity. Their 

costs range widely from relatively low-cost systems capable only of operating in a grid-isolated mode to those 

providing seamless automatic transfer of loads between UPS and grid. 

In combining off-the-shelf UPS equipment with solar power systems, there is still one gap to be filled, arising 

from the fact that the controls and inverters supplied as a part of UPS include no provision for battery charging 

from a DC source such as a solar power array. Various configuration options are possible to fill this gap, but 

suitably large PV charge control products are either unavailable or in very limited production; power ratings of 

charge control components for typical off-grid PV/battery hybrid systems are well below the peak output of an 

economically optimal school-based solar power system. 

In summary, the product development gap facing energy secure schools is modest: mature and readily available 

power conversion products to integrate, operate, and optimize the interplay between large solar power arrays, 

large battery banks, and the grid are not yet available, and there is as yet little market pull to encourage investment 

in new product offerings. Most significantly, the national R&D programs addressing solar power technology and 

battery energy storage technology are not addressing, individually or collaboratively, the need for plug-and-play 

functionality for all elements of battery-coupled, grid-tied solar power systems. National solar programs in the 

United States and elsewhere are driven by a vision of solar power as a bulk energy source, not as an enabler of 

fully energy secure buildings. This can change, and the first step would appear to be the creation of a technology 

and deployment roadmap that recognizes and exploits the symbiosis of solar power and energy storage. Examples 

of the economic optimization opportunities involved were highlighted by Hoff, et al.7

Current Technical Solutions: Limited Energy Security 

Presently, significant numbers of schools are being equipped with small-scale (hundreds at 1–10 kW) or mediumscale (tens at 10–50 kW) solar power arrays and grid feed-in inverters. These installations are funded via targeted 

grants and rebates typically available for a year or two in a given utility service area. They can be upgraded to 

provide back-up power during grid outages by adding batteries and an off-the-shelf 1–5 kW “battery-based” 

inverter of the sort available from at least two U.S. inverter manufacturers and their distributors.8

 For applications 

larger than 5 kW, it is possible to deploy multiple power conversion units each powered by a portion of a large 

solar power array and a large battery bank. With investment in custom engineering and site electrical work, 

multiple circuits within a school can be kept energized for emergency purposes, even if solar power system and 

battery capacities are insufficient to support normal operations.9

 

The prospect for sustainable deployment of such sub-optimally-sized solar power systems on schools in the 

United States is limited. More readily accessible markets are currently available to the U.S. solar power industry, 

and school maintenance and renovation budgets typically do not have the flexibility to pay for energy security 

 

7

 Hoff, T.E.; Perez, R.; Margolis, R.M. (2005). “Maximizing the Value of Customer-Sited PV Systems Using Storage and 

Controls.” Clean Power Research, www.clean-power.com/research/customerPV/OutageProtection_ASES_2005.pdf. 8

 Brief descriptions of several leading grid-tied PV inverters are provided in the following article: Schwartz, J. (April/May 

2005). “What’s Going On – The Grid?” Home Power Magazine. 9

 A demonstration of this strategy has been proposed for modification of part of the Odyssey Charter School in Palm Bay, 

Florida, to serve as an energy secure community shelter. Source: Young, W. Private Communication. Florida Solar Energy 

Center. 

6 
upgrades of school-based solar power systems. Accordingly, more detail regarding how to consider and specify 

energy security upgrades for these systems is not offered here. Generally, the most favorable scenario for funding 

such upgrades is to include them in local mitigation strategies for which budgets typically become available 

within a year or so after a disaster strikes.10 

Special cases deserving attention in the context of disaster preparedness have been covered in a previous report.11

States that designate and equip schools as public crisis centers and disaster relief shelters should consider 

upgrading existing solar power system arrays on these schools to supply critical loads during extended population 

sheltering operations. Special consideration should be given to schools designated as “special needs” shelters, i.e., 

shelters intended for medical care of elderly or chronically ill persons. Proper care of chronic illnesses, for 

example, typically relies on equipment powered by electricity, e.g., for dialysis and treatments of chronic 

respiratory ailments. 

Future Technical Solutions: Full Energy Security 

In the longer term, an emerging option for large, school-based solar power systems is the use of “plug-in” hybrid 

electric vehicles (HEVs) as portable energy storage systems during extended grid outages.12 Appendix B 

discusses how plug-in HEVs can facilitate fully solar secure schools. For example, fleet vehicles are envisioned as 

an early plug-in HEV market; hybrid school buses could include their own sun-powered battery charger. 

The most important aspect of the connection between HEVs and energy secure schools may be the size of the 

market for HEVs and the technology investment it justifies. The HEV market is real, and the market forces 

driving it are rapidly gathering. Oil prices have peaked again and are now the subject of Congressional concern.13

Gasoline prices have pushed beyond $2 per gallon in the United States, and many urban areas of the United States 

and elsewhere face daunting public health issues related to vehicle emissions. HEVs have imbedded battery 

storage. They come with or can be readily equipped with the power conversion and control equipment needed to 

accept energy from a solar power array, store it, and deliver it on demand to a building or any AC circuit within a 

building. This readily realized potential creates a new route on our nation’s overall technology roadmap. Such a 

route bypasses the issues that have limited deployment of on-grid energy storage in the past. Specifically, lowmaintenance, safely enclosed batteries in HEVs overcome the main obstacles to on-site stationary battery systems, 

i.e., high initial cost of equipment used only in emergencies, requirements for routine maintenance and periodic 

battery replacement, and special attention to ensure personnel safety. 

Economics: Are Energy Secure Schools Affordable? 

The affordability of energy secure schools depends on the cost and economic value of the basic solar power 

system as well as the incremental cost and value of enhanced capability ensuring operational continuity during 

 

10 The local mitigation strategy (LMS) is a plan that seeks to reduce or eliminate damage due to storms or other disasters 

before they occur. For example, in Florida, the primary mechanism in the development and implementation of the LMS is the 

LMS Committee. The LMS Committee is made up of various county, state, and municipal officials as well as representatives 

from private and nonprofit agencies. Working together to represent all interests in the community, the LMS Committee 

identifies potential mitigation projects (e.g., retrofitting existing buildings for use as hurricane shelters), prioritizes such 

projects, and, together with officials from the State Department of Community Affairs, oversees their completion. Limited 

grant funding is made available from the State of Florida, with the goal of reducing potential economic losses by building 

disaster-resistant communities. Source: Young, W. Private Communication. Florida Solar Energy Center. 11 Braun, G.W.; Varadi, P.F; Thornton, J. (In review). Energy Secure Schools: Technology, Economic and Policy 

Considerations. National Renewable Energy Laboratory. 12 Hakim, D. (April 2, 2005). “Hybrid-Car Tinkerers Scoff at No-Plug-In Rule.” New York Times. 13 Bartlett, R. (March 14, 2005). “Peak Oil Presentation to the U.S. Congress [Video].” C-SPAN, 

www.energybulletin.net/5080.html. 

7 
extended grid outages. For illustrative purposes, this section compares generic costs and values for a range of 

assumptions that may be valid for U.S. schools over the next decade. Actual costs and values, however, will not 

only change with each passing year but also will vary from school to school, depending on school size, location, 

grid electricity costs, vulnerability to extended grid outages, and plans and provisions for use as community 

emergency shelters. The guidelines provided in Appendix C are intended to help school officials combine 

information from their own operating experience with the following generic cost information to determine 

whether investments in solar secure schools are prudent. 

Operational continuity requires a source of electricity roughly equivalent to the local grid during periods when the 

grid is disrupted for extended periods. A relatively large solar power system is required for this purpose. Its cost 

cannot be justified based on the energy it delivers during emergencies, so its affordability must be assessed based 

on whether the electricity purchases from the grid that it offsets are worth the investment. 

School-Based Solar Power System Affordability 

The basic parameters of commercial rooftop solar power economics and finance are installed cost and annual 

electricity production (i.e., avoided grid electricity purchases). 

System installed cost 

Installed cost depends on local construction costs and solar competencies of local engineers and contractors. More 

importantly, it depends on array mounting and orientation details as well as overall project scale and timing. Scale 

dependency and timing aspects are roughly quantified in the following tables. Basic solar power system installed 

costs currently vary from as low as $6,000/kWac for large school-based systems to as much as $9,000/kWac for 

smaller retrofit systems on schools in the 10–50 kWac range. The latter systems, while unable to support full 

school operations on an ongoing basis, can be configured to power critical loads when the local grid is out of 

service. System costs are expected to continue on the well-established downward path based on technology 

improvements and economies of higher-volume component manufacturing. Table 2 summarizes the outlook for 

solar power costs by making simplifying assumptions about system size, cost of capital, and rate of equipment 

cost reduction. The table shows the effect of conservative assumptions about expected equipment price trends, 

e.g., annual average price reductions in the 5% range consistent with historical experience. It shows that, 

depending on solar resource quality and cost of capital, solar power costs are already in the range of economic 

competitiveness or will be within the next 10 years in most cases. Meanwhile, the cost of upgrading the basic 

solar power system with enough battery capacity to store half the system’s average daily output adds only 5%–

15% to the system cost. 

8 
Table 2. Current and Projected Solar Power Costs, 2005–2015 

2005 2010 2015

Resource Quality Capital Charge

kWh/kW %/year

2,000 $0.33 $0.25 $0.20

1,200 $0.54 $0.42 $0.33

2,000 $0.16 $0.13 $0.10

1,200 $0.27 $0.21 $0.17

2005 2010 2015

Resource Quality Subsystem

kWh/kW

Solar Power $1,950 $1,500 $1,200

2,000 $200 $200 $200

1,600 $160 $160 $160

1,200 $120 $120 $120

Assumptions: 

2005$

300-kWac solar power system

2005 installed cost = $6.50/Wac

Cost reductions @ 5%/year

Installed battery cost = $200/kWh

Battery Storage

5

10

Energy Cost 

Installed Cost 

($/kWh)

($ x 1,000)

Avoided grid electricity purchases

In the commercial rooftop solar power economic model, avoided electricity purchases represent a cost saving 

attributable to the solar power system, a form of virtual revenue. Commercial electricity prices vary regionally but 

are typically the sum of multiple components captured in the form of “fixed charges,” reflecting the cost of 

operating the utility system on a continuous basis, “fuel charges,” reflecting the cost of fuel burned in power 

plants, and “demand charges,” reflecting the incremental cost of meeting demand during higher-use periods. 

Currently, U.S. commercial building owners pay an annual average rate of around $0.1/kWh, which includes base 

energy generation and delivery charges as low as $0.05/kWh and incremental additional charges as high as 

$0.20/kWh during peak demand periods. Actual average electricity prices applicable to schools are presented in 

Table 3 for states where disasters or power grid disruptions have affected school operations in recent years. There 

is significant variation, notably Hawaii’s prices ranging 50% above the national average, reflecting the state’s oil 

dependence and limited investment in renewable energy. In locations where utilities experience a peak demand in 

the summer daytime hours, avoided costs attributable to a commercial rooftop PV system will be higher than in 

other locations because of the good match between solar electricity delivery and building energy use. Such a good 

match is illustrated in Appendix D. 

9 
Table 3. Historical Grid Electricity Costs for Commercial Customers, 1999–200314 

California Florida Hawaii Maryland New Jersey New York

Year

1999 10.05 6.22 12.74 6.82 9.74 11.19

2000 10.25 6.25 14.81 6.55 9.14 12.65

2001 12.49 7.08 14.81 6.42 9.19 12.98

2002 13.22 6.64 14.11 6.09 8.87 12.46

2003 12.19 7.13 15.02 6.95 9.25 12.93

2004 (2) 9.04

Mean 11.64 6.66 14.30 7.01 9.24 12.44

Range 3.17 0.91 2.28 2.95 0.55 1.74

Range - % of mean 27% 14% 16% 42% 6% 14%

Volatility index (1) 5% 3% 3% 8% 1% 3%

Cents/kWh

Notes: 

1. The volatility index is calculated by determining the maximum, minimum, and average 

electricity prices for each of the preceding 5 years and dividing the difference between the 

maximum and minimum by five times the average. The index is a rough measure of the expected 

future annual percentage change. 

2. 2004 Maryland prices are assumed to be 30% above 2003, based on published rate increase 

summaries by PEPCO.

Table 3 includes a measure of price variation among states and price volatility, quantified by determining the 

maximum, minimum, and average electricity prices for the preceding 5 years and dividing the difference between 

the maximum and minimum by the average. The use of data from 2003 and earlier may in some cases understate 

the volatility index in general and especially for states emerging from electric utility restructuring. For example, 

the volatility index for Maryland would be in the same range as for other states if pre-2003 data were used to 

calculate it, but using 2004 data provides a strikingly different perspective. 

This seeming anomaly can be explained simply. During the recent wave of restructuring across the United States, 

a typical approach was to freeze the bulk energy component of retail electricity prices during a 4- or 5-year 

“transition period,” creating a period of price stability typically followed by major electricity rate increases. For 

example, in Washington, D.C., and its Maryland suburbs, Pepco’s fixed price generation component of bills for 

commercial customers in Pepco's service territory expired on July 1, 2004. As a result, small commercial 

customers’ total bills increased approximately 13%, medium-sized commercial customers’ (e.g. schools) bills 

increased approximately 25%–30%, and large commercial customers’ bills increased approximately 48%–57%. 

Pepco attributes these increases to a 112% increase in the price of coal since 2000 and to significant increases in 

other power plant fuels as well (e.g., natural gas). In these and other states, the prevailing pattern of expanding 

electric generation capacity by adding natural gas fueled power plants, combined with recent upward swings in 

wholesale natural gas prices, has also driven significant recent increases in retail electricity prices.

Deciding How to Manage Electricity Price Risk 

As discussed in the preceding paragraph, grid electricity suppliers are subject to major cost uncertainties, 

particularly related to their fuel and wholesale electricity purchases. Therefore, they typically will not guarantee 

stable forward pricing unless forced to do so by their regulators. Even then, the guarantee period is typically 5 

years or less. Future electricity costs are much more difficult to forecast than in the past because in many cases a 

major portion of a school’s electricity bill is no longer subject to economic regulation. For example, a school 

system in Everett, Washington, experienced a 100% increase in its annual electricity bill during the recent 

 

14 Energy Information Administration, www.eia.doe.gov/cneaf/electricity/epa/average_price_state.xls. 

10 
California electricity crisis and responded by cutting its electricity use by 12% and its school budget by $1 

million. 

In general, schools have no way of securing stable electricity prices from their usual suppliers (i.e., electric 

utilities) because the utilities themselves are subject to increasing cost volatility. The best step a school system 

can take is to assess the likelihood and level of grid electricity price volatility using analysis of the sort illustrated 

in Table 3, and then review price stabilization options, including solar power. Table 4 uses the volatility index 

calculation illustrated in Table 3 to indicate which price stabilization option might be appropriate in a particular 

situation. For example, applying Table 4 to the price volatility information in Table 3 suggests that Maryland’s 

8% price volatility is in the unacceptable range. Depending on 2004 data for other states, at least one other state, 

California, can at best claim minimum price stability. Major school districts in California are doing exactly what 

the guidance in Table 4 suggests: evaluating long-term solar electricity purchases now. 

Table 4. School Energy Price Stability Levels 

Energy Cost Stability 

Level Indicators Stabilization Options

Maximum Stable grid electricity prices 

(volatility index < 2%)

Secure long-term grid electricity 

supply contract if available

Intermediate Variable grid electricity prices 

(volatility index 2-4%)

Evaluate energy efficiency 

investments having < 5-year 

simple payback now

Minimum Highly variable grid electricity 

prices (volatility index 4-6%) 

Evaluate solar electricity 

purchase within next 5 years

Unacceptable Unstable grid electricity prices 

(volatility index > 6%)

Evaluate long-term solar 

electricity purchase now

Note: The volatility index is calculated by determining the maximum, minimum, and average 

electricity prices for each of the preceding 5 years and dividing the difference between maximum 

and minimum by the average. 

Economic Value of Solar Secure Power 

For ethical and liability reasons, the private sector has become much more attentive in recent years to providing a 

safe work environment for employees. Safety has become a top priority for many major corporations and is 

equally important for children and teachers. Recognizing the safety and operational continuity value of reliable 

electricity, some school systems equip their buildings with emergency generators. Although many do not, with 

more and more critical automated systems dependent on electricity, it is reasonable to expect full back-up power 

capability for schools to become the standard rather than the exception as it is now. How long it will take to reach 

a tipping point in this direction is unknown. Looking only at the direct economic cost to a school system of 

sending students home when the power goes out or closing schools until power is restored, the cost of emergency 

power may be difficult to justify. Calculating the indirect cost to the local economy of the ripple effect (both 

safety and economic) of a community reallocating its resources to care for children while its schools are 

unexpectedly closed, might give a different answer. For purposes of rough analysis, the cost of operating the 

school can be used as an indicator of the economic value of operating the school. 

It is well known that the grid is interruptible. What is not well known is that grid power reliability varies 

substantially even within the same utility service area, i.e., some electricity customers experience frequent or 

extended outages and others do not. The substantial variation in grid reliability depends on technical factors 

typically invisible to a school district and its facility managers. These include the general age and condition of 

regional and local transmission and distribution infrastructure, funding and technical adequacy of related 

maintenance programs, circuit and equipment loadings, vulnerability to damage by accidents and storms, and, 

11 
most significant and least understood, levels of redundancy and ability to switch loads from one substation or 

feeder to another. Typically, reliability “is what it is” unless the grid customer is willing to consider paying for 

equipment upgrades, redundant connections, or both. These options typically provide improved but not full 

energy security, and their cost is often prohibitive, leading commercial customers to weigh the cost of business 

downtime against the cost of installing on-site back-up power sources. 

Schools could do the same if they had a way to go about it. Considering general levels of energy security and their 

rough costs is a good place to start. The following discussion outlines these basic considerations. Using this 

information, Appendix C, Part 2 provides a step-by-step method of determining the need for uninterruptible 

electricity for a particular school and the best means to provide it. Such simple and generic guidelines can be used 

for basic assessment purposes to start the process. Typically, school energy and facility managers have the 

experience and expertise to conduct the more detailed analysis required to weigh specific options, or local 

consultants and professional engineers are available to provide it. 

Is Solar Secure Power Affordable? 

The basic parameters of solar-extended back-up power economics are the cost of energy storage and related 

equipment and the avoided cost of shutting down a school when grid electricity service is lost. First, in 

considering the affordability of solar secure power, other potentially more economical ways of providing 

uninterruptible energy, including emergency generators fueled by dedicated and uninterrupted sources of natural 

gas, should be considered. Second, levels of emergency energy security should be identified, which depend on 

choices made by school boards based on local conditions, state policies, and economic considerations. To 

simplify the matter, multiple levels of targeted operational continuity security can be identified. The maximum 

level provides for full operation of the school based on a dedicated uninterruptible source. The minimum level 

provides for use of the school as a population shelter in emergencies based on a dedicated uninterruptible source 

capable of powering critical loads only. Other levels can be specified between these two extremes. 

The average daily electricity production of a school-based solar power system can be determined by dividing its 

average annual electricity production by 365. Assuming the solar power system is sized to supply most of the 

school’s average net electricity consumption, a battery system should be sized to store a minimum of 50% of the 

full average daily DC output of the solar power array. UPS costs vary widely depending on their size and 

functionality, but battery capacity is a primary cost driver. For generic analysis purposes, the cost of battery 

energy storage for coupling with large rooftop solar power systems is assumed to be approximately $200/kWh. 

Using these simplifying assumptions, Table 5 summarizes strategies and options for ensuring various levels of 

operational continuity as well as the rough per pupil cost of implementing these options. 

12 
Table 5. Strategy, Options, and Costs of Operational Continuity 

Operational Continuity 

Security Level Strategy Options Cost 

(per pupil)

Emergency generator (> 25 kW) fueled by 

uninterruptible natural gas $50-100

Energy storage (> 25 kW) with solar 

recharge capability

$50-100

Emergency generator (> 25 kW) fueled by 

interruptible natural gas or diesel fuel $25-50

Energy storage (> 25 kW) with limited solar 

recharge capability

< $50

Emergency generator (< 25 kW) fueled by 

uninterruptible natural gas < $50

Energy storage (< 25 kW) with solar 

recharge capability

$15-25

Limited Partial

Emergency power for critical 

loads limited by fuel availability 

or battery capacity

Emergency generator (< 25 kW) fueled by 

interruptible natural gas or diesel fuel $15-25

Assumptions: 

Solar power system output = 1,600 kWh/kW

Installed battery cost = $200/kWh

10-kW and 100-kW emergency generators @ $300-$1,000/kW depending on size, fuel, and fuel storage

Unlimited uninterruptible power

Emergency power limited by fuel 

availability or battery capacity

Unlimited emergency power for 

critical loads

Unlimited Full

Limited Full

Unlimited Partial

Per pupil costs in Table 5 can be compared with per pupil benefits. Commercial businesses typically know or can 

easily calculate what the cost of a lost day of operation is and invest in on-site back-up power according to its cost 

in relation to revenue loss potential. Schools do not lose revenue when they shut down, but disruption in their 

operation adversely affects the local economy and may expose local and state education departments to 

unbudgeted costs. The school’s daily operating cost provides an indicator, if not an accurate measure, of the 

overall economic impact of extended, unplanned school shutdowns. Per pupil spending in the United States 

averaged $8,019 per student in the 2002/2003 school year and varied from less than $5,000 to more than 

$13,000.15 The number of legally mandated class days in a school year is assumed to be around 180. 

Using these simplifying assumptions, Table 6 compares the cost of solar extended back-up power with the order 

of magnitude economic impact of school shutdowns using per pupil cost as a surrogate cost. A key factor in such 

crude analysis is the value of operational continuity. 

Table 6 suggests a favorable benefit/cost ratio for scenarios involving more than one power-loss-related school 

shutdown per decade. Experience in Maryland, Florida, and other states suggests that shutdowns of the nature 

experienced in connection with major weather events may happen multiple times in a decade and last days or even 

weeks; the conservatism involved in assuming an average 1-day shutdown may offset the lack of conservatism 

involved in assuming an economic impact equal to the cost of a day of educational operations. For decisionmaking purposes, the analysis illustrated in Table 6 should be applied using case-specific information rather than 

national averages and nominal costs. 

 

 

15 Richmond, E. (March 18, 2005). “Nevada 47th in Per-Pupil Funding.” Las Vegas Sun. 

13 
Table 6. Benefits and Costs of Full Uninterruptible Back-up Power for Schools 

Outage-Related 

Shutdowns per 

Decade (1)

Daily Per Pupil Cost 

of Educational 

Operations (2)

Per Pupil Unlimited 

Full Uninterruptible 

Power Cost (3) Benefit/Cost Ratio

1 $60 $75 0.8

3 $60 $75 2.4

10 $60 $75 8

Notes:

1. Average 1-day shutdown duration.

2. Mean U.S. per per pupil spending; value of operational continuity assumed equal to cost of operation. 

3. Mean of full uninterruptible power cost range from Table 5.

Policy: Will U.S. Schools be Energy Secure? 

This is a question that will be decided by school boards and college and university administrators, public and 

private, state and local. Federal, state, and local emergency management organizations and their private partners 

(e.g., the American Red Cross) also have a major stake in the outcome, but at present they have no direct input to 

the design and energy management of the schools they rely on when disaster strikes. 

There are no insurmountable technical obstacles to creating a national network of energy secure schools even 

now, and important enabling technologies (e.g., HEVs) are becoming available. The opportunity to save money 

while improving energy security is already being exploited in some significant cases. This opportunity clearly will 

expand as the cost of fuels and grid electricity increases and solar power costs continue to drop. 

The most natural response to the opportunity is not available. Utilities operating local grids in the United States do 

not, for a variety of valid business reasons, invest in energy supply facilities on customer premises, even when 

their regulators permit or encourage such investment. An alternative solution that exploits tax-exempt public 

financing mechanisms is needed. 

Fortunately, a promising solution is emerging. In certain states, and even nationally, there is sufficient solar power 

market activity to attract new ventures focused on providing “solar service,” which includes financing. This 

means that a school district, having identified solar power as an element of its energy security strategy, could have 

the benefit of solar secure schools without diverting scarce capital budgets for the purpose. The San Diego 

Unified School District in California is doing just that. Working with Los Angeles-based Solar Integrated 

Technologies, the district is re-roofing 15 schools and three administrative buildings with roof-integrated solar 

power panels. Solar Integrated Technologies will install 1 million square feet of solar power arrays and maintain 

them at no cost to the district for 20 years. Leveraging state solar power rebates, the firm will sell the energy these 

roofs produce to the district at about half the cost now paid to San Diego Gas & Electric. The district anticipates 

$6.9 million in total cost savings over 20 years.16

School districts able to allocate capital to capture operating cost savings will be able to maximize electricity cost 

savings by self-financing their solar power needs, especially in states that adopt preferential “feed-in” tariffs that 

guarantee long-term purchase prices for solar electricity fed into the grid. Such long-term solar electricity 

purchase arrangements greatly facilitate access to low-interest private financing of solar power systems and are, 

therefore, already widely employed in European countries.

 

16 Louv, R. (March 22, 2005). “Solar Schools Help Shape Our Future.” San Diego Union-Tribune. 

14 
Recommended Strategy for Solar Secure Schools 

How can the most U.S. schools become energy secure as soon as possible? First, decision makers in the 

educational community must understand energy security issues well enough to make good decisions. 

Accordingly, the information summarized in this report and elsewhere has been used to create a simple step-bystep process that school officials can use routinely to assess their energy security options (Appendix C). Second, 

this process must be actively disseminated, e.g., by the U.S. Department of Energy and NREL. 

Third, product-engineering gaps must be filled and new, more conveniently usable and cost-effective technologies 

brought into play. The importance of energy secure schools to public safety and education costs justifies creating 

a technology roadmap that addresses technology gaps and opportunities and focuses industry attention on product 

and market needs. The U.S. Department of Energy has spearheaded development of technology roadmaps in 

recent years; a small, focused effort of this sort should target solar secure schools. 

Finally, policies tend to reflect business as usual. Energy secure schools are a future need, not a current reality. 

Modest adjustments in current policy are required and should be considered: 

 

 How can consideration of cost-effective measures to increase the energy security of schools be encouraged? 

 How can existing solar power incentive programs encourage upgrades of solar power systems to provide 

operational continuity during extended grid outages? 

 What new approaches are needed to attract low-cost capital to school-based solar power system financing? 

Energy secure schools need policy champions at the state level. Multiple national organizations (e.g., 

organizations of school administrators and school board members) could take the lead in the policy arena. 

15 
Appendix A: Energy Secure Schools—Technology, Economic, and Policy Considerations 

(previous work under NREL subcontract AEI-4-44238-01) 

Gerald W. Braun 

En-Strat Associates 

14801 Braemar Crescent Way 

Darnestown, MD 20878 

e-mail: gbraun12@comcast.net

Peter F. Varadi 

PV Enterprises Inc. 

4620 N. Park Ave. #1606W 

Chevy Chase, MD 20815 

e-mail: pvaradi@aol.com

John Thornton 

National Renewable Energy Laboratory 

1617 Cole Blvd. 

Golden, CO 80401-3393 

e-mail: john_thornton@nrel.gov

ABSTRACT

School-based solar electricity systems can be upgraded to 

deliver emergency power when the grid is down for 

extended periods. Other emergency generation solutions 

(e.g., fuel-based emergency generators or grid-charged 

energy storage) have costs in the same range and are limited 

by their fuel or electricity storage capacity, among other 

drawbacks. In 2004, the U.S. Department of Energy’s 

National Renewable Energy Laboratory initiated a project to 

develop guidelines and design specifications for low-cost, 

prepackaged photovoltaic (PV) systems on schools to enable 

the schools to be used as community emergency centers. 

Results to date are presented, including the following: 

 Current practice and relevant federal, state, and other 

criteria, standards, and guidelines pertaining to the use 

of schools as community emergency centers 

 Experience with school-based shelter operations and 

power needs during recent disasters and implications 

for PV system sizing and configuration 

 Relevant deployment scenarios, design concepts, and 

costs. 

1. INTRODUCTION

Over the next few years there will be a proliferation of gridconnected photovoltaic (PV) systems installed in schools 

across the United States. This trend has already started; 800 

school-based PV systems will be operating by 2006, 

including large rooftop arrays made economically attractive 

by combining state clean energy rebates with other 

incentives. Continued deployment will be driven by the fact 

that schools operate during daytime hours when solar 

electricity is produced and also by projected PV cost 

reductions, escalating fuel and grid electricity costs, and 

steps to curtail greenhouse gas production and educate 

children regarding responsible energy use. This creates an 

unprecedented opportunity to make the nation’s schools 

energy secure and suitable for use as community emergency 

centers. 

2. SCHOOL-BASED EMERGENCY CENTERS

Disasters happen. Among other consequences, they disrupt 

grid power for extended periods. Meanwhile, our society 

relies increasingly on grid electricity for health, safety, and 

convenience. Extended loss of grid power over a wide 

geographic area threatens public health and safety. 

Vulnerabilities increase as populations age, building 

automation becomes more prevalent, and grid-powered 

medical treatments (e.g., dialysis) are more widely applied. 

Power reliability measures (e.g., emergency generators and 

uninterruptible power supplies) are sized and configured to 

avoid loss of critical functions during power interruptions of 

less than a second to a few hours. However, when disaster 

strikes, grid power can be disrupted for much longer 

periods. Table 1 provides examples from the recent 

hurricane season in Florida. According to the American Red 

Cross, 21 of 50 states are vulnerable to similar hurricanerelated consequences. Grid outages continuing after stored 

fuel and electricity run out can transform a modern building 

from a marvel of integrated operation into a threat to health 

and safety. 

16 
TABLE 1. 2004 HURRICANE-RELATED CASES AND 

CONSEQUENCES IN FLORIDA1

Case Consequences 

Hurricane Frances – 

Florida Statewide 

200,000 people spent Saturday 

night in 407 evacuation shelters 

Hurricane Frances – 

Palm Beach County 

Schools 

$300,000 loss of fresh and 

frozen food 

Hurricane Frances – 

Flagler County Schools 

Two of three school-based 

general shelters without power 

Hurricane Jeanne – Polk 

County 

73 of 122 schools without 

electricity; 2-3 weeks of classes 

cancelled 

Hurricane Charley – 

Charlotte County 

Power outages of up to 2 

weeks; schools closed for 4 

weeks; power outage affected 

gas stations, impacting portable 

generator fuel supply 

Hurricane Frances and 

Jeanne – St. Lucie 

County 

14 shelters with emergency 

generators with 3-day fuel 

capacity; all were used for both 

hurricanes for as long as 3 

weeks; some had no grid power 

for 7 days; some emergency 

generators failed 

Hurricanes Frances and 

Jeanne – Pinellas County 

Power outages of up to 1 week; 

Port of Tampa closed, creating 

major fuel supply problem 

To provide emergency shelter, a building must have power 

for its security and communication systems, emergency 

lighting, medical equipment, food storage, ventilation, and 

even heating and cooling during weather extremes. 

Accordingly, buildings used in emergencies should be 

“energy secure,” i.e., they should have reliable power for at 

least some of their internal systems. They need it during 

normal operations, but the need becomes critical when 

disaster strikes. The longer the period of emergency 

operation, the more critical the need for emergency power 

becomes. 

School buildings are the primary local emergency shelter 

option for people ordered or choosing to evacuate “at risk” 

areas. Schools are also used to shelter evacuees from 

buildings that have become uninhabitable due to grid 

outages. In its Design Guide for Improving School Safety in 

Earthquakes, Floods and High Winds, the Federal 

Emergency Management Agency simply states that “schools 

intended for use as shelters and/or emergency response after 

a (wind) storm should be equipped with an emergency 

generator.”1

 

3. UNMET NEED FOR ENERGY SECURE SCHOOLS

A case could be made that all schools should be energy 

secure. However, most schools are not. Even those used as 

evacuation shelters typically are not. Emergency generators 

are not an ideal solution; they require expert maintenance 

and operation to remain reliable. They are noisy, 

aggravating the trauma of disaster refugees, and provisions 

for long-term fuel storage raise additional environmental 

and safety concerns. Though recommended, they are legally 

and technically optional in most cases. Other cheaper but 

less reliable strategies are used, e.g., planning to bus 

evacuees to shelters still receiving grid power or equipping 

some schools for connection to a portable generator that 

may be delivered by relief organizations. 

4. PV-POWERED SCHOOLS

Exploiting PV-powered schools is a better solution in many 

cases. Public schools are a natural application for on-grid 

solar electricity. They draw electricity from the grid mostly 

during daylight hours when electricity prices rise to 

$0.20/kWh and higher. They typically have ample unused 

roof space that can be covered with solar arrays, and the 

insulating effect of the arrays can reduce heat gain through 

the roof, thereby reducing electricity use for space 

conditioning. Schools are built to last, having typical 

operating lifetimes of 50–100 years. Further, school 

property is not taxed. Thus, a capital item such as a solar 

power system can be financed over decades based on the 

proceeds of low-yield, tax-free bonds. Finally, the operating 

cost of a solar power system is minimal and does not vary 

from year to year. Its output reduces grid power costs that 

escalate and are subject to uncontrolled upward spikes that 

can impact educational program budgets. 

 

Within 5 years, school-based PV systems will be costeffective, even without incentives, across a broad range of 

southern U.S. states and will be especially cost-effective in 

the Sun Belt and states offering incentives for solar 

electricity. Table 2 summarizes the current outlook for costeffective school-based PV systems, specifically: 

 Large school-based solar electricity systems are more 

cost-effective than smaller ones and have installed costs (in 

2005) that are marginally cost-effective without incentives 

in areas having excellent solar resources, i.e., the true Sun 

Belt areas of the U.S. southwest. They will have similar 

economics across a broad swath of southern states in 2010 

based on expected cost reductions. 

 Smaller school-based solar electricity systems may 

be deployed where larger systems are still uneconomic; they 

will pay back part of their initial cost during their economic 

life. Cost subsidies like those offered in California and New 

Jersey may be required to encourage their consideration.

17 
TABLE 2. NET KWH COSTS FOR SCHOOL- BASED PV

Poor Resource - 20 kW systems - 2005 (6) 2005 2010 2015 2020 2025 2030

Cost - $/kWh (2)(3) 0.4 0.4 0.4 0.4 0.4 0.4

Avoided Cost - $/kWh (4) 0.10 0.12 0.13 0.16 0.18 0.21

Net Cost - $/kWh (1) 0.30 0.28 0.27 0.24 0.22 0.19

Excellent Resource - 200 kW system - 2005 (5)

Cost - $/kWh (2)(3) 0.15 0.15 0.15 0.15 0.15 0.15

Avoided Cost - $/kWh (4) 0.10 0.12 0.13 0.16 0.18 0.21

Net Cost - $/kWh (1) 0.05 0.03 0.02 -0.01 -0.03 -0.06

Good Resource - 200 kW system - 2010 (5) 

Cost - $/kWh (2)(3) 0.15 0.15 0.15 0.15 0.15

Avoided Cost - $/kWh (4) 0.12 0.13 0.16 0.18 0.21

Net Cost - $/kWh (1) 0.03 0.02 -0.01 -0.03 -0.06

Notes:

1. All costs in 2005$.

2. Public bond financing, no incentives, annual capital charge rate = 5%.

3. Poor, good, and excellent resources: 1,000, 1,500, and 2,000 kWh/kW.

4. Real grid electricity annual cost escalation = 3%.

5. Single 200-kW system at $6,000/kW installed in 2005 and $4,500/kW installed in 2010. 

6. Ten identical packaged 20-kW systems at $8,000/kW installed in 2005.

Although sustainable or “green” design is an emerging 

standard for new school construction, marginal costeffectiveness is typically not a sufficient condition for 

investments in solar energy systems. Capital budgets for 

public schools must be approved directly by local voters, 

making it problematic to set aside a portion of such funds 

for discretionary energy-related investments whose costs are 

recaptured over decades, not years. 

So, in spite of the economic factors cited above favoring 

solar electricity systems on schools, actual deployment in 

the near term likely will depend on the availability of 

appropriate economic incentives and other policies that 

differentiate or decouple energy infrastructure investments 

from educational infrastructure investments. Policies are 

needed that avoid forcing school boards to choose between 

low and stable lifecycle energy costs and near-term school 

construction and renovation needs. 

 

This is easier said than done. The most natural solution is 

not available. Utilities operating local grids in the United 

States do not, for a variety of valid business reasons, invest 

in energy supply facilities on customer premises, even when 

their regulators permit or encourage such investment. An 

alternative solution is needed that exploits tax-exempt 

public financing mechanisms. 

5. DISASTERS AND BACK-UP POWER 

There is no shortage of information and guidance related to 

preparing for disasters and emergencies. Given the many 

life-and-death issues confronting emergency managers and 

responders, most publications give scant attention to the 

issue of power continuity and typically provide no guidance 

regarding the equipment involved or strategies for its 

installation and operation. On the other hand, emergency 

management personnel consistently say that, during an 

actual emergency, lack of back-up power adversely affects 

important aspects of emergency and sheltering operations. 

For example, local emergency managers point out the 

following occurrences during disaster conditions: 

 Portable generator availability is typically limited and 

subject to competing demands; available portable 

generators are dispatched to disaster-stricken areas to serve 

the highest public safety needs, which may not include 

mass care. Also, the resources needed to ensure proper, safe 

hook-up may not come with the portable generator. 

 Permanent fuel-based generators rely on stored fuel 

or sources of fuel that are often compromised by the event 

that created the emergency. For example, weather disasters 

can result in extended disruption of gasoline and diesel fuel 

deliveries, and natural gas infrastructure may be shut down 

for public safety reasons in the aftermath of earthquakes. 

Fuel-based generators require routine maintenance, and their 

noisy operation adds to the stress of nearby human 

populations coping with the trauma of the disaster. 

 Battery-based uninterruptible power systems (UPS) 

typically have sufficient capacity to carry over critical loads 

for one to several hours, after which the loads must be 

switched over to other back-up power sources. Evacuation 

shelters, by contrast, often remain in operation for several 

days or even a week or longer. For this reason and for other 

operational considerations, UPS are less likely than 

generators to be the choice for facility-wide back-up power. 

18 
6. MAKING PV-POWERED SCHOOLS ENERGY 

SECURE

In relation to the abovementioned range of current options, a 

UPS capable of being recharged by a PV array has major 

benefits. Instead of a battery bank charged from the grid and 

useful only as long as its charge lasts, stored energy is 

replenished daily and can be drawn on until grid power is 

restored. Historically, solar/battery hybrids have been the 

preferred solution for applications requiring highly reliable 

power independent of the grid, including some for which the 

grid is close by but less cost-effective.2

 

Battery bank sizing for PV-powered energy secure schools 

will consider critical loads and energy consumption during 

mass care operations as well as collateral applications, such 

as the following: 

 Powering resumption of educational operations. In 

the wake of hurricanes and other disasters, large areas are 

without power, sometimes for weeks. Schools remain closed 

even after evacuees leave. PV-charged UPS would permit 

more timely resumption of classes and school activities than 

would otherwise be possible in these cases. 

 Mitigating black-out and brown-out impacts. When 

the local grid is overloaded, grid operators disconnect loads 

and/or reduce system voltage to limit power flows. The 

availability of stored energy connected to the local grid that 

could be dispatched during such conditions would be 

valuable to the utility and the community it serves.3

 Avoiding unplanned school evacuations and 

shutdowns. Depending on UPS capability, the need to 

evacuate or shut down a school when grid power is lost 

could be avoided. For example, at least three severe weather 

events, including ice storms, severe thunderstorms, and 

hurricane-related winds, have occurred in the Washington, 

D.C., suburbs in the past several years. These resulted in 

large swaths of urban and suburban areas being without 

power for 2–3 days or more while utility crews from out of 

state helped restore downed power lines. Montgomery 

County (Maryland) schools have emergency generators for 

use in such emergencies, but most schools in most other 

parts of the United States do not. Under similar conditions 

they must shut down and await restoration of grid power. 

7. ENERGY SECURE SCHOOL DEPLOYMENT 

SCENARIOS, DESIGN CONCEPTS, AND COSTS

A number of design goals are possible for the basic PV 

installation. Their feasibility depends on the following: 

 Type of project (new school or renovation) 

 Availability and limitations on incentives 

 Grid electricity costs and reliability 

 Building load profiles and energy use 

 Local solar industry competencies. 

A number of design goals are also possible for adding solarenhanced back-up power capability; generally, the goal 

should be to take full advantage of the batteryreplenishment capability of the PV array. The feasibility of 

such goals depends on the following: 

 Whether the school qualifies or will be upgraded to 

qualify for mass care uses 

 Type and capability of existing back-up power 

provisions 

 Power demand of equipment used during extended 

emergencies. 

Beyond these considerations, loads to be served in extended 

emergencies only can be identified generically based on 

expected minimum and nominal daily emergency power 

generation. Operational strategies and procedures for 

limiting demand to the highest priority daily needs should 

be developed in advance. Regarding sizing, there are three 

basic scenarios to consider: 

 Where solar electricity is already cost-effective.

Where solar electricity is cost-effective for school rooftop 

applications, the regional and local solar industry will likely 

have acquired appropriate experience. Schools will be 

equipped with the largest possible solar array, which, based 

on the roof area of typical public elementary and high 

schools will have a peak output in the 150–500 kW range. 

For example, two schools in northern New Jersey are being 

equipped with 180- and 360-kW systems. Figure 1 shows a 

portion of the smaller installed array. In such cases, battery 

storage ideally will be sized relative to the capability of the 

array to keep it charged during periods when it is the 

school’s only power source.

Figure 1. Rooftop PV array on Bayonne, NJ high school 

 Where solar electricity system sizes are limited by 

available incentive funds. Where the economic feasibility 

of solar electricity depends on limited pools of public 

funding, smaller PV arrays may be deployed in sizes of 10–

30 kW, or roughly 10% of the fully cost-effective range 

19 
above. For example, approximately 30 schools in California 

are being equipped with systems in the 20–30 kW range.4

 In 

such cases, battery storage can be sized according to the 

requirements of specific loads that must be carried for a 

school to function as a special needs shelter in an 

emergency, i.e., loads related to the safety and medical care 

of elderly or disabled people evacuated from homes, 

assisted living facilities, nursing homes, or hospitals. 

 Where solar electricity systems have been installed 

for educational or public relations purposes and are too 

small (i.e., < 5 kW) to power a full range of critical loads.

For example, more than 500 schools in the United States are 

hosting PV systems in the 1–5 kW range that are being paid 

for by local utilities or state clean energy funds for purposes 

of increasing awareness of renewable energy or to enhance 

the public’s perception of the donor. Typically, these 

systems are configured to feed small amounts of electricity 

directly into the local grid, essentially bypassing school 

building circuits. These installations represent an 

opportunity to enhance the school’s operational capabilities 

during power outages by, for example, using them to power 

battery-charging stations for emergency lighting, computer 

systems, and other UPS batteries that are discharged in the 

early hours of an extended grid outage. 

Design concepts responsive to the above scenarios and to 

the other considerations mentioned are summarized 

parametrically in Table 3. They should be considered in 

reference to the cost of other solutions. An alternative to 

upgrading an existing or new solar electricity system to 

serve critical loads in an emergency is to install a diesel 

generator. The average retail cost of an emergency 

generator rated between 10–100 kW is around $400–$700 

per kW, but this does not include long-term fuel storage, 

automatic electrical interface equipment, or installation and 

commissioning.5

 Portable emergency generators with 

limited onboard fuel storage are available at retail for as 

little as a few hundred dollars per kW. Permanent 

installations that include industrial-quality generators, 3 or 

more days worth of fuel storage, and provisions for 

automatic power transfer typically cost several hundred to 

more than a thousand dollars per kW depending on their 

size. The most economical size is a few hundred kW; 

smaller and larger installations cost more. 

Table 3 puts the cost of upgrading a school-based PV 

system in perspective as follows: 

 The cost of secure energy from an existing PV 

installation (i.e. < $1,500/kW) can be in the same range 

as the cost of secure energy from permanent fuel-based 

emergency generators having adequate fuel storage to 

remain in operation for more than a few days. 

 A PV system reliability upgrade will be more costeffective in powering specific critical loads essentially 

indefinitely. It will be significantly less cost-effective 

where the requirement is to power all loads, both 

critical and non-critical, for only a few hours. 

Thus, the worst-case duration of the expected emergency 

and its effect on fuel supply may be decisive factors. 

Disasters that affect large areas and involve extended 

recovery operations can disrupt fuel supplies, thereby 

rendering fuel-based emergency generators ineffective after 

their onboard storage is depleted. 

TABLE 3. DEPLOYMENT SCENARIOS, DESIGN CONCEPTS, AND COSTS FOR PERMANENT INSTALLATIONS

Peak 

Output 

(kW)

Area 

(square 

meters)

Installed 

Cost ($K)

GridconnectInstalled 

Cost ($K)

Peak 

Output 

(kW)

Energy 

Storage 

(kWh)

Installed 

Cost ($K) Inverter

Installed 

Cost ($K) 

Energy 

($K) 

Secure 

Energy 

($K)

Total 

($K)

200 2,000 1,050

Grid feedin 

inverter

150 125 1,000 238 UPS (1) 40 1,200 278 1,478

20 200 113

Grid feedin 

inverter

20 12.5 100 24 Dual 

mode (2) 6 133 30 162

5 50 31

Dualmode 

inverter

6 5 25 7 N/A (3) 0 38 7 44

Notes:

1. Off-line standby UPS product, new or refurbished, either part of original installation or retrofit.

2. Inverter retrofit - cost of the original inverter credited against the cost of a dual-mode replacement.

3. Assume dual-mode inverter is part of original installation.

4. Based on typical current costs of included subsystems.

Cost Summary (4) Inverter

Rooftop PV System

Power Conv.

Reliability Upgrade

PV Array Battery Storage

20 
8. STEPS TOWARD A NATIONAL 

NETWORK OF ENERGY SECURE 

SCHOOLS

Several steps should be taken to ensure that solar 

electricity is used to best effect in support of 

U.S. public schools and their collateral use as 

mass care centers in disaster situations: 

 Standards. PV/battery hybrid emergency 

power options should be addressed in standards 

and selection criteria for crisis and mass care 

centers. 

 Technical Demonstrations. Procurement 

guidelines and technical specifications are also 

needed, as well as demonstration projects to 

validate them; options for upgrading schoolbased PV systems for emergency power 

purposes must be demonstrated so that proper 

comparisons with existing solutions can be made 

by school officials and emergency managers. 

 Decision Tools. School boards, school 

designers, and school business managers need 

guidelines and quantitative information to help 

decide if solar electricity is the right choice and 

to maximize its functional and economic 

benefits. A strategy and resource guide for this 

purpose should be developed and disseminated. 

 Incentives. Separate measures are needed to 

encourage school-based PV systems and related 

reliability upgrades, e.g., loans that can be repaid 

by school boards based on avoided grid power 

purchases. Incentives should also be provided to 

schools investing in solar to encourage 

consideration of reliability upgrades, e.g., where 

a state clean energy fund is offering rebates for a 

portion of the initial cost of a PV system, the 

state and the Federal Emergency Management 

Agency (FEMA) could collaborate to provide a 

similar rebate for a reliability upgrade.7

 

 R&D. Until now, there has been little 

demand for large battery-coupled PV systems for 

grid-connected buildings. Relevant battery and 

power conversion technology is widely used in 

other commercial applications; however, vendors 

typically have little or no experience with solar 

electricity applications of their products. A 

collaborative R&D initiative would be an 

appropriate response to the need for sustained 

industry attention. 

 Awareness. There is a need for greater 

awareness of the role solar electricity will play in 

the future energy mix and especially of the 

opportunity to exploit its collateral potential as 

an emergency power source. Outreach to the 

public education and emergency management 

communities could be based on a model Energy 

Secure Schools program in a specific state 

coordinated among emergency management, 

education, and energy agencies as well as the 

American Red Cross. Relevant federal agencies 

should consider offering planning grants to 

encourage development and implementation of 

such a model program. 

9. COUNTING THE COSTS

It is possible to roughly estimate the scope and 

cost of a national network of energy secure 

schools.8 It would involve the deployment of 

2,000–3,000 MW of solar electricity systems on 

approximately 20,000 schools at a cost of $10–

$15 billion over 10 years. In the context of 

current industry capability, this is ambitious but 

feasible: global PV equipment shipments are 

nearly 1,000 MW per year and growing at 30% 

annually. 

Eighty percent of this cost is attributable to 

energy production that offsets purchases from 

the grid; even without incentives, it will be 

recovered via avoided grid electricity purchases 

over 10–20 years, depending on the average 

annual rate of grid electricity price escalation. 

The remaining 20% ($2–$3 billion) would be the 

public cost of energy secure public crisis centers. 

It must be weighed against lifesaving and mass 

care benefits as well as the value of buffering the 

effects of grid outages during normal school 

operations. 

10. ACKNOWLEDGEMENTS

This paper is based on research conducted by 

En-Strat Associates under NREL subcontract 

AEI-4-44238-01. 

11. REFERENCES

1

 From various sources including personal faceto-face interviews with local emergency 

management and school officials in Florida 

counties affected by three 2004 hurricanes, 

including Charlotte, Pinellas, Polk, and St. 

Lucie. 

2

 Federal Emergency Management Agency. 

FEMA 424: Design Guide for Improving School 

21
Safety in Earthquakes, Floods, and High Winds. 

January 2004. 

3

 Varadi, P.; Braun, G. “Security PV.” 

Renewable Energy World; September–October 

2003. 

4

 Perez, R.; Collins, B. “Solar Energy Security.” 

Refocus; July/August 2004; p. 24–26. 5

 California Energy Commission. Solar Schools 

Program. 

www.consumerenergycenter.org/solar_schools/p

rogram.html 6

Fraser, H.; Johnson, J. Standby Electric 

Generators for Emergency Farm Use. Ontario 

Ministry of Agriculture, Food and Rural Affairs; 

May 1999; 

www.gov.on.ca/OMAFRA/english/engineer/fact

s/99-005.htm. 7

 Whereas most U.S. PV incentives are indexed 

to array output, legislatures abroad (e.g., in 

Germany) are considering incentives for PVcoupled energy storage. 

8

A national system of PV-powered public crisis 

centers was proposed by the U.S. Department of 

Energy in 2002. See Plympton, P.; Thornton J. 

"Solar Schools as Community Emergency 

Centers." SOLAR 2002; Reno, NV; June 15–20, 

2002. The current scope and cost are consistent 

with the U.S. Department of Energy’s original 

estimate. 

22
Appendix B: Plug-In Hybrid School Buses for Future Solar Secure Schools 

Plug-in HEVs are hybrid cars with enhanced battery capacity. As the term suggests, plug-in 

HEVs—which look and perform much like "regular" cars—can be plugged in to a 120-volt outlet 

(e.g., each night at home or during the workday at a parking garage) and “fueled” from electricity 

sources, including the local grid or a rooftop solar power system. Plug-in HEVs are thus able to 

run on stored electricity for much of a typical day's driving, up to 60 miles per charge depending 

on the size of the battery, which is far beyond the average U.S. commute. When the charge is 

used up, the vehicle automatically switches to running on the fuel in its fuel tank. A plug-in HEV 

with a 60-mile range operating on battery power would have a battery capacity of 15–30 kWh 

depending on its category; the high end of the range would correspond to a heavy vehicle such as 

an SUV. 

Plug-in HEVs operating on grid power stored in onboard batteries would have equivalent fuel 

costs well under $1/gallon and an emissions profile roughly half that of a conventionally fueled 

vehicle. Electric utilities are interested in promoting plug-in HEVs for purposes of revenue 

enhancement, local pollution mitigation, and the potential to use the combined storage capacity of 

numerous plugged-in HEVs to store cheap off-peak energy for potential use in meeting system 

peaks. Preliminary thinking regarding deployment suggests an initial stage involving fleet 

vehicles operated by local governments and school districts.17 

A school district’s school bus fleet would be an appropriate application for plug-in HEVs. The 

buses are operated during daytime hours over a limited range and could be “refueled” at night 

with low-cost, off-peak electricity from the local grid and from roof-mounted solar power 

modules. Based on the dimensions of a typical school bus, the roof-integrated solar power system 

would have a peak capacity of 1–2 kW and would be capable of delivering an average of 5–10 

kWh to a hybrid bus battery daily. 

It makes sense to integrate current thinking about plug-in HEVs and energy secure schools. 

Doing so suggests a scenario involving the use of plug-in hybrid school buses in combination 

with school-based solar power systems to keep the schools operating during extended grid 

outages. It is even imaginable that the plug-in HEVs could be “fueled” by the school-based solar 

power systems and also provide limited capability to avoid purchases of grid electricity during 

high-cost peak-demand periods. 

Further study and, more importantly, experience will be required to determine how schools can 

exploit the combination of solar power and plug-in HEVs to cut operating costs. It is beyond the 

scope of this report to predict the rate or pattern of adoption of HEVs in the United States, but 

even modest adoption rates could easily keep pace with the parallel deployment of solar power 

systems. For example, with a battery capacity of 50 kWh each, 10 plug-in hybrid school buses 

could be refueled using a 100-kW school-based solar power system producing a daily average of 

500 kWh. This daily average is typical of U.S. Sun Belt states. 

 

17 Duncan, R. (February 16, 2005). “Gas-Optional Vehicles (Plug-In Hybrids).” Austin Energy. Informal 

presentation to ACORE. 

23
Appendix C: Should Our Schools Be Energy Secure? A Guide for Decision Makers 

Purpose 

Strategic questions of school energy security must be answered by school boards and school 

administrators. School boards typically do not concern themselves with energy matters, so they 

need a simple methodology for answering the questions. 

As discussed above, costs of U.S. electric service vary significantly from location to location and 

are subject to varying volatility based on generation mix, economic regulation, and so forth. 

Reliability of electric service is subject to even greater variation, and the diverse approaches to 

deregulation among the states may lead to even greater variation in the future. Meanwhile, local 

and regional grids differ significantly in terms of the disasters to which they are vulnerable and in 

the economic capacity of local and regional grid operators to pay for the levels of redundancy, 

equipment capacity margins, and preventive maintenance that were accepted standards across the 

U.S. industry in former times. 

Because energy security has two dimensions—cost stabilization and emergency preparation—the 

methodology must address both. Part 1 of the following guidelines is intended to help define a 

strategy to stabilize energy costs. Part 2 is intended to help create a strategy to avoid operational 

disruption and unsafe conditions. The method used in both cases recognizes the lack of credible 

future forecasts and uses available historical information to quantify relevant trends. 

Analysis 

Part 1: Energy Cost Stabilization 

Background 

Investigation of the economic costs and benefits of school-based solar power systems in the 

United States leads to the following conclusions: 

 Large school-based solar electricity systems have installed costs such that they are now (in 

2005) marginally cost-effective without incentives only in areas having excellent solar 

resources (i.e., the true Sun Belt areas of the U.S. southwest) and will have similar economics 

across a broad swath of southern states by 2010, based on expected cost reductions. 

 Smaller school-based solar electricity systems that may be deployed where larger systems are 

still uneconomic will only pay back part of their initial cost during their economic life, so cost 

subsidies in the range currently offered in California and New Jersey may be required to 

encourage their consideration. 

Electricity prices in recent years have become more volatile with a strong upward trend. The 

more important factor is volatility. Costs that can be reasonably forecasted are manageable. Big 

energy cost surprises can cause serious problems. Every school district knows its annual 

operating cost and the portion of it that relates to its electricity use. Some districts and schools are 

able to pay special attention to controlling energy costs, but it is not realistic to suggest that a 

school district undertake complicated economic analysis to determine if solar power makes 

economic sense. A simpler step-by-step approach is as follows: 

24
Step 1: Determine current electricity costs. Average grid electricity prices paid by schools are 

$0.05–$0.15 per kWh and can be computed by simply dividing a school’s annual electricity bill 

by its annual electricity use in kWh. If the price is close to or above $0.10/kWh, go to Step 2. 

Step 2: Determine the scale of future electricity price increases. Using historical price 

information, an electric price “volatility index” can be calculated simply by repeating Step 1 for 

each of the five previous years, determining the difference between highest and lowest average 

cost during the period, and dividing by the lowest cost. Table C-1 illustrates the calculation for 

selected states. 

Table C-1. Historical Grid Electricity Costs, 1999–200318

California Florida Hawaii Maryland New Jersey New York

Year

1999 10.05 6.22 12.74 6.82 9.74 11.19

2000 10.25 6.25 14.81 6.55 9.14 12.65

2001 12.49 7.08 14.81 6.42 9.19 12.98

2002 13.22 6.64 14.11 6.09 8.87 12.46

2003 12.19 7.13 15.02 6.95 9.25 12.93

2004 (2) 9.04

Mean 11.64 6.66 14.30 7.01 9.24 12.44

Range 3.17 0.91 2.28 2.95 0.55 1.74

Range - % of mean 27% 14% 16% 42% 6% 14%

Volatility index (1) 5% 3% 3% 8% 1% 3%

Cents/kWh

Notes: 

1. The volatility index is calculated by determining the maximum, minimum, and average 

electricity prices for each of the preceding 5 years and dividing the difference between the 

maximum and minimum by five times the average. The index is a rough measure of the expected 

future annual percentage change. 

2. 2004 Maryland prices are assumed to be 30% above 2003, based on published rate increase 

summaries by PEPCO.

 

Step 3: Determine a reference price for future grid electricity purchases. Calculate a nominal 

average grid electricity price for the next 10 years by multiplying the average current price from 

Step 1 using the following formula: 

 Average 10-year electricity price = current price x [1 + 2 x (volatility index)] 

Step 4: Solicit competitive bids for solar power “service” (i.e., the equivalent of grid power 

service), monthly billing for electricity from solar power systems mounted on a school’s roof but 

financed and operated by a private company. Companies offering such service can be identified 

by searching the web using key words such as “solar” and “finance.” The bids will typically lock 

in a price for solar electricity 10–20 years into the future. From these bids, determine the best 

available solar electricity price (cost per kWh delivered) for the next 10 years. 

Step 5: Evaluate the bids in relation to grid electricity prices. If the 10-year average solar 

electricity price is in the same range as the nominal 10-year average grid electricity price, 

contracting to purchase solar electricity is a prudent choice, especially if arrangements can be 

 

18 Energy Information Administration, www.eia.doe.gov/cneaf/electricity/epa/average_price_state.xls. 

25
made to extend the fixed-price solar electricity purchase period beyond 10 years or take over 

ownership of the solar electricity system at the end of the power contract period. 

Step 6 (optional): Determine if self-financing of a solar power system would result in significant 

cost savings. Energy services companies are able to structure power project financing to take 

advantage of tax incentives and so forth, but public agencies such as school districts have the 

advantage of access to low-interest, long-term, tax-exempt debt financing ideally suited to lowrisk capital projects having a relatively long economic life. If self-financing is feasible, it’s 

advantages can be weighed by soliciting turnkey bids for nominal 300, 150, and 100 kW solar 

power systems, depending on the school’s size (i.e., for high, middle, and elementary schools, 

respectively). Nominal sizes are provided here for scoping purposes. The recommended size for 

schools in a particular system or area is a matter of professional judgment based primarily on 

expected peak demand in normal operation and whether full operation of heating and cooling 

systems is critically important to educational operations. State energy offices and independent 

groups with knowledge of applicable programs, incentives, and restrictions should be called on 

for assistance in identifying potential bidders and preparing uncomplicated letter solicitations. 

Part 2: Emergency Energy Security 

Background 

The affordability of energy secure schools is not a strictly economic question and cannot be 

answered with precision. There are two key factors in answering the question: safety and 

operational continuity. For ethical and liability reasons, the private sector has become much more 

attentive in recent years to providing a safe work environment for employees. Safety has become 

a top priority for many major corporations and is equally important for children and teachers. 

Recognizing the safety and operational continuity value of reliable electricity, some school 

systems equip their buildings with emergency generators. Although many do not, with more and 

more critical automated systems dependent on electricity, it is reasonable to expect full back-up 

power capability for schools to become the standard rather than the exception as it is now. How 

long it will take to reach a tipping point in this direction is unknown. Looking only at the direct 

economic cost to a school system of sending students home when the power goes out or closing 

schools until power is restored, the cost of emergency power may be difficult to justify. 

Calculating the indirect cost to the local economy of the ripple effect (both safety and economic) 

of a community reallocating its resources to care for children while its schools are unexpectedly 

closed, might give a different answer. For purposes of rough analysis, the cost of operating the 

school can be used as an indicator of the economic value of operating the school. 

It is well known that the grid is interruptible. What is not well known is that grid power reliability 

varies substantially even within the same utility service area, i.e., some electricity customers 

experience frequent or extended outages and others do not. The substantial variation in grid 

reliability depends on technical factors typically invisible to a school district and its facility 

managers. These include the general age and condition of regional and local transmission and 

distribution infrastructure, funding and technical adequacy of related maintenance programs, 

circuit and equipment loadings, vulnerability to damage by accidents and storms, and, most 

significant and least understood, levels of redundancy and ability to switch loads from one 

substation or feeder to another. Typically, reliability “is what it is” unless the grid customer is 

willing to consider paying for equipment upgrades, redundant connections, or both. These options 

typically provide improved but not full energy security, and their cost is often prohibitive, leading 

commercial customers to weigh the cost of business downtime against the cost of installing onsite back-up power sources. 

26
Schools could do the same if they had a way to go about it. Although schools and school districts 

typically lack the expertise to assess the impact of energy industry trends that may affect their 

vulnerability to future grid disruptions, their facilities staff will know how many grid disruptions 

have affected their operations in recent years and can apply this experience to assess the 

economic value of back-up power relative to its cost. The following simple step-by-step approach 

is suggested for first-stage analysis. Typically, school energy and facility managers have the 

experience and expertise to conduct the more detailed analysis required to weigh specific options, 

or local consultants and professional engineers are available to provide it. 

Step 1: Test the school’s vulnerability to grid outages. Determine the number of grid outages 

affecting the school in the most recent decade that required evacuating the school or rendered it 

unable to hold classes on a regularly scheduled school day. Estimate the number of days school 

operations were so affected. 

Step 2: Compute the average daily cost of school operation by dividing the annual cost per 

student by the number of days of the legally mandated school year and multiplying by the number 

of students. 

Step 3: Roughly estimate nominal economic value of back-up power over the next 10 years by 

multiplying the results of Step 1 and Step 2. If the result exceeds $30,000 for an elementary 

school, $50,000 for a middle school, or $100,000 for a high school, go to Step 4. 

Step 4: If the school has natural gas service, check with the local natural gas utility to determine 

if it can guarantee an uninterruptible supply of natural gas for emergency power purposes and 

compensate the school district if the uninterruptible supply is not available when needed, i.e., 

during a grid outage. 

 

Step 5: If the natural gas utility can guarantee uninterruptible service, request assistance from the 

utility in identifying sources of natural gas fueled emergency generators. Request quotes for 

installation and hook-up of appropriately sized generators: 100 kW for high schools, 50 kW for 

middle schools, and 30 kW for elementary schools. 

Step 6: If the natural gas utility cannot guarantee uninterruptible service, and if the school is 

equipped with a rooftop solar power array, determine its average daily electricity production by 

dividing the solar power array’s average annual DC electricity output by 365. A battery system 

should be sized to store a minimum of 50% of the full average daily DC output of the solar power 

array. 

Step 7: If the solar power system’s average daily production is less than the school’s average 

daily energy use, determine the most critical circuits to remain energized during an extended grid 

outage, and request design/install bids for standard, grid-isolated UPS equipment, with battery 

storage capacity consistent with Step 6, provisions to charge it alternately from the grid or the 

solar power array, and peak output consistent with the nominal loadings of the selected circuits. 

Step 8: If the school is not equipped with a solar power array, determine the maximum potential 

output of a solar power array that could be installed when economically feasible. Follow the 

guidelines in Step 7 in procuring and installing UPS equipment for interim use in supporting 

normal school operations to the extent possible during a limited grid outage of a day or less and 

for later integration with a solar power array. 

27
Note: With any form of emergency generation, the option exists to configure it to adjust and 

optimize the school’s pattern of grid electricity use, e.g., to draw electricity from the grid at 

favorable prices, minimize demand charges, take advantage of favorable rates utilities offer to 

customers willing to reduce use or be disconnected during high demand periods, and so forth. 

Consideration of such options is appropriate if solar power and/or emergency generation or major 

UPS equipment is installed or planned. However, the best options will be highly site and utility 

specific; involve specific costs, operational constraints, and maintenance requirements; and 

should in most cases be defined and evaluated with the assistance of properly qualified 

engineering consultants.19 

 

19 For a discussion of related issues, see Audin, L. (February 2005). “Showcase: 

Power.” Building Operating Management, www.facilitiesnet.com/bom/article.asp?id=2568. 

 

28
Appendix D: Illustration of Load Leveling by a Commercial Rooftop Solar Power 

System20

 

 

20 Merrill, L. (Nov/Dec 2003). “Solar Power Rising.” Distributed Energy. 

29
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4. TITLE AND SUBTITLE

Solar Secure Schools: Strategies and Guidelines 

5c. PROGRAM ELEMENT NUMBER

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PVC6-8101 

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En-Strat Associates 

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14. ABSTRACT (Maximum 200 Words)

Large numbers of solar power systems are being deployed at U.S. schools. Schools are used routinely in sheltering 

vulnerable populations during and after major disasters. An “energy secure school” would be protected against grid 

and natural gas supply disruptions, and a “solar secure school” would be insulated from significant unplanned 

increases in its annual energy bill. Solar secure schools are not only technically feasible but also economically 

justified when grid electricity prices are high and volatile or schools are shut down by grid power outages more than 

once every 10 years. Solar power prices and grid electricity prices are trending strongly in opposite directions, so 

solar secure schools soon will be an attractive cost control and public safety strategy in most states. The present 

effort has produced a simple step-by-step process that school officials can use to assess energy security options. 

15. SUBJECT TERMS

solar; pv; photovoltaics; energy security; schools; plug-in hybrids 

16. SECURITY CLASSIFICATION OF: 19a. NAME OF RESPONSIBLE PERSON 

a. REPORT 

Unclassified 

b. ABSTRACT 

Unclassified

c. THIS PAGE 

Unclassified

17. LIMITATION 

OF ABSTRACT

UL 

18. NUMBER 

OF PAGES 

19b. TELEPHONE NUMBER (Include area code)

Standard Form 298 (Rev. 8/98) 

Prescribed by ANSI Std. Z39.18