SOLAR ELECTRIC

Connecting Your Solar Electric System to the

Utility Grid

A Winning Combination—Design, Efficiency, and Solar Technology

In the past, most homes with solar electric

systems were not connected to the local utili-

ty grid. It made sense to install solar electric

systems in areas without easy assess to the

power grid, where the option of extending a

power line from the grid might cost tens of

thousands of dollars.

In recent years, however, the number of

solar-powered homes connected to the local

utility grid has increased dramatically. These

“grid-connected” buildings have solar elec-

tric panels or “modules” that provide some

or even most of their power, while still being

connected to the local utility.

Owners of grid-connected homes can

choose to supply a portion of their energy

with solar energy, using the utility for power

during the night or on cloudy days. Because

of the up-front costs of installing a solar

electric system, many of these homeowners

initially install systems that meet about one-

quarter to one-half of their energy use.

Net metering

Grid-connected systems generally use a

billing process called “net metering” or “net

billing.” In this process, any energy generat-

ed by the solar modules that your home does

not use immediately is sent to the utility grid.

However, when the solar electric system is

producing less power than is needed, you

can draw additional power from the grid. If

your system is connected to the grid through

a single electric meter, your meter can actual-

ly run backwards as you contribute excess

energy to the utility. The excess electricity is

being credited to you at the same retail rate

as the electricity you use from the utility.

Your utility may require the use of two

meters—one that meters your consumption

of energy from the grid and the other that

meters your contribution to the grid. In this

case, your solar-generated excess energy

could be credited at the retail rate or possi-

bly at a lower wholesale rate, depending on

the utility.

In addition, some utilities bill their cus-

tomers according to a “time-of-use” rate

system. Under this system, customers are

billed at a higher rate during certain times

of the day, such as during the sunniest day-

time hours of summer when air conditioners

are working at their peak. If this is the case

with your utility, you may be able to “trade”

your excess energy to the utility at these

same rates. You can therefore benefit from

the fact that your solar electric modules

produce the most power during those sunny

summer days. When you need power from

the utility during the off-peak periods, such

as in the evening, the rate is usually lower.

If you choose to have a grid-connected

solar electric system, and your system pro-

duces enough energy in any given month so

that you do not have to draw from the grid,

you may still receive a small monthly bill. This

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Solar electric systems

sometimes produce more

electricity than your home

needs. This extra electricity is

either stored in batteries or

fed into the utility grid.

Homeowners can be given

credit by their local power

companies for the electricity

produced at their homes

through "net metering"

programs.

SOLAR ELECTRIC

is because many utilities charge monthly fees

for meter reading. Again, check with your

local utility.

Connecting to the grid

One of the most important steps in pur-

chasing a grid-connected solar electric system

is choosing a provider with experience. A

good provider will also have a properly

licensed electrical contractor, have enough

years of experience to have demonstrated an

ability to work with customers, and be able

to compete effectively with other firms.

A good provider should be familiar with

your local utility’s regulations on intercon-

nection requirements. If your provider is not

familiar with these requirements, check with

your local utility, state energy office, or state

or local Public Utility Commission for details.

Your solar electric provider should supply

you with everything you need to run your

system, including a specific type of inverter

for grid-connected systems, batteries (if you

want backup power), and a special electric

meter. As mentioned already, some utilities

require you to have one electric meter that

runs both forward and backward. Other utili-

ties require two separate meters: one for

incoming power you receive, and one for

power you generate that goes back into the

system. These meters are sometimes paid for

by the utility, but may be part of your

provider’s price for the system.

As part of the installation of your solar

electric system, you will need to sign an

interconnection agreement with the utility

company. Your solar electric provider may be

able to handle the negotiations and paper-

work with the utility, but this contractual

agreement is between you and your local

utility. Be sure to read the fine print in this

agreement, which may differ considerably

from one utility to another. It could range

from a short one-page statement to a

lengthy booklet. In either case, the fine print

may contain references to liability issues that

you will want to fully understand before

signing the contract.

Also, be sure to speak with your home-

owner’s insurance provider, because the solar

electric system itself will need to be added

to your policy. In many cases, you may have

to add a rider to your policy for the grid-

connected system.

More information

Contact your local utility for more infor-

mation about its particular practices. The

general customer service representatives may

not be familiar with net metering, so several

phone calls may be necessary to find the

correct contact person. Your solar electric

provider should also have more information.

To learn about local incentives in your

area, go to the national Database of State

Incentives for Renewable Energy (www.

dsireusa.org). This Web site also includes

rules, regulations, and policies for many

areas across the nation.

The U.S. Department of Energy’s Energy

Efficiency and Renewable Energy Network

(EREN) has compiled a list of state energy

contacts (see www.eren.doe.gov/state_energy).

These contacts may be able to assist you

with problems you may be having with your

local utility.

Produced for the

U.S. Department of Energy

by the National Renewable

Energy Laboratory, a DOE

national laboratory

DOE/GO-102002-1594

July 2002

Printed with a renewable-source ink on

paper containing at least 50% wastepaper,

including 20% postconsumer waste

This house in coastal Maine

generates its own electricity

from a 4.25-kilowatt solar

electric system beautifully

integrated into the rooftop.

Through a net-metering

agreement with Central

Maine Power, excess solar

electricity is sent to the utility

grid, effectively spinning the

utility meter backward. The

homeowners get this power

back in an even exchange at

night and during periods of

minimal sun.

This home in Virginia is powered by a 6-kW,

grid-connected solar-electric system and is

being monitored by NREL’s Center for

Buildings and Thermal Systems.