Photovoltaics is a technology that converts radiant

light energy (photo) to electricity (voltaics). Photovoltaic (PV) cells are the basic building blocks of this

energy technology.

PV cells (also called solar cells) are made of semiconductor materials, most typically silicon. The amount

of electricity a PV cell produces depends on its size,

its conversion efficiency (see box on reverse), and

the intensity of the light source. Sunlight is the most

common source of the energy used by PV cells to

produce an electric current.

It takes just a few PV cells to produce enough electricity to power a small watch or solar calculator.

For more power, cells are connected together to

form larger units called modules. Modules, in turn,

are connected to form arrays, and arrays can be

interconnected to generate electricity for a large

load, such as a group of buildings. 

Single-crystal silicon is the most common semiconductor material used in making PV cells. Polycrystalline silicon, in the form of a thin film or coating 

on an inexpensive base of glass or plastic, is also

used, and PV modules can also be made of thin

films of amorphous (noncrystalline) silicon. Thin

films are usually less expensive to manufacture

because they require less silicon and the process is

less labor-intensive. PV devices are also being developed using combinations of other materials, such as 

cadmium, copper, indium, gallium, selenium, and

tellurium.

PV modules are typically installed on or near a

building or other structure. They can also be specially designed as an integral part of a building’s roof,

wall, skylight, or other element. This is called 

building-integrated PV or BIPV.

What are PV energy systems?

A PV energy system usually includes a module or

array and the structural hardware needed to install

it. The simplest PV systems generate DC electricity,

usually for a small load, when the sun is shining or

they are exposed to artificial light. More complex

systems include a power inverter that converts the

direct current (DC) generated by PV to alternating

current (AC), and batteries that store energy for use

at night or when the sun isn’t shining.

Today, PV is used primarily for cathodic (corrosion)

protection, traffic warning lights, water pumping

for irrigation and livestock, telecommunications,

security and lighting systems, resource monitoring, and electric load management. Many

of these uses are remote (or off-grid) power generation applications, not connected to utility power

lines. PV systems are already used in many off-grid 

applications in the Federal government, such as for

emergency call boxes near interstate highways.

When the electricity required for a Federal application exceeds the amount a PV system can supply, 

a conventional electric generator can be added to

create a hybrid PV/generator system. Wind systems

can also be added. PV systems actually have many

benefits:

• Portability—many kinds of PV systems can be

moved about easily.

• Reliability—they operate for long

periods with 

little maintenance.

• Low operating costs—the fuel 

is free and there are no (or few)

moving parts.

• Low environmental impact—

they are quiet and nonpolluting 

(no greenhouse gas emissions).

• Stand-alone capability—they

operate in remote areas far from

power lines.

• Modularity—power output can be

increased by adding more modules.

• Safety—they are not flammable

and meet National Electric Code

requirements.

• Versatility—they operate well in

almost any climate.

• Short lead time—prepackaged PV

systems are available, and utility

easements aren’t needed.

• Ease of installation—no heavy

construction equipment is required.

What are some opportunities for using PV in the

Federal government?

Photovoltaics is a good choice for remote applications in which the daily electric load falls somewhere between a few watt-hours and about

100 kilowatt-hours. Because it is nonpolluting, PV

Photovoltaics

Systems that Convert Sunlight to Electricity Can Meet Many Different Needs

FEDERAL ENERGY MANAGEMENT PROGRAM

Renewable

Energy

Technologies

for Federal

Facilities

U.S. Department

of Energy

Office of Energy

Efficiency and

Renewable Energy

Internet: http://www.eren.doe.gov/femp/

Sandia National Laboratories/PIX01472

PV-powered

security lighting

at Roosevelt

Lake in Arizona.
FEMP Help Desk:

800-DOE-EREC

(363-3732)

Internet:

http://www.eren.doe.

gov/femp

Produced for the 

U.S. Department 

of Energy by the

National Renewable

Energy Laboratory, 

a DOE national

laboratory

DOE/GO-10099-724

(a revision of

DOE/GO-10096-272)

September 1999

FEDERAL ENERGY MANAGEMENT PROGRAM

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

should definitely be considered for remote areas that

rely on fossil-fueled generators for electric power.

On a first-cost basis, the installed cost of a PV system can be less than the cost of utility service. But

PV may also be a good choice in areas where the

reliability of a power plant is questionable, or where

an agency is being charged high rates during peak

hours. 

The National Park Service has installed more than

450 PV systems, chiefly to provide power for

resource-monitoring equipment. These are some

additional, widely demonstrated, off-grid applications for PV:

• Lights for walkways, streets, highways, and 

common areas

• Residential uses (fans, lights, refrigerators) 

in remote areas

• Electricity for campgrounds, marinas, and 

offshore drilling platforms

• Equipment for weather stations and fire 

observation towers

• Communications equipment and facilities (e.g.,

emergency roadside phones, microwave repeater

stations)

• Cathodic (corrosion) protection for metal pipes

and similar objects

• Highway and warning signs, security systems,

transmission tower beacons

• Livestock watering pumps, irrigation systems,

and disinfection equipment

• Emergency power during times of crisis.

What is required?

Agencies should evaluate different PV systems 

on the basis of cost, system performance, system

reliability, and maintenance needs. These are some

additional requirements:

• Modules must face south and be unshaded; they

can be mounted on the application (e.g., a highway

sign), on a roof, or on the ground.

• Batteries are often needed to meet peak loads or

for nighttime use; they require periodic maintenance.

• Power inverters will be needed if the load requires

AC electricity.

What does a PV system cost?

To determine the economic feasibility of using a PV

system, agencies should consider these three main

factors:

• The size and nature of the load

• The availability of the solar resource

• The cost of alternative sources of power.

On a 20-year, life-cycle-cost basis, a remote PV system typically costs from 25¢–50¢ per kilowatt-hour.

In off-grid Federal applications, PV can be more

cost-effective than many alternatives. PV equipment

is available from companies listed on the General

Services Administration’s Federal Supply Schedule

(online, see http://www.gsa.gov/regions/7fss/7fx/

schedules). The Federal Energy Management

Program has developed specific Energy Savings

Performance Contracts (ESPCs) that assist Federal

agencies in obtaining PV systems (call the FEMP

Help Desk or one of the FEMP contacts below for

details).

For More Information

For additional information about PV and ESPCs,

contact:

Hal Post (PV)

Sandia National Laboratories

505-844-2154 

John Thornton (PV)

National Renewable Energy Laboratory

303-384-6469

Nancy Carlisle (FEMP Renewable Energy)

National Renewable Energy Laboratory

303-384-7509

Tatiana Strainic Muessel (FEMP Project Financing 

Team Leader)

U.S. Department of Energy

202-586-9230

What are the important terms?

Balance of system (BOS)—every element (and its associated costs) of 

a PV system except the modules themselves; this includes the design;

land and site preparation; installation; support structures; and power

conditioning, operation and maintenance, and storage equipment.

Break-even cost—the cost of a PV system at which the value of the

electricity it produces equals the cost of electricity from an alternative

source plus the delivery of this electricity to the site; a break-even 

distance is the distance a power line needs to be extended to match

the installation cost of a PV system.

Peak watt—the "rated" output of a cell, module, or system; the

amount of power a PV device produces when operating at 25°C 

during tests; the peak rating is usually determined during indoor

tests rather than outdoors.

PV conversion efficiency—the percentage of available sunlight converted to electricity by a PV module or cell; technically, the ratio of

electric power produced by a cell to the power of the sunlight striking

the cell.