It is virtually impossible even for experienced experts to
visually tell the difference between a high quality solar
panel and a low quality one.

Key Quality Attributes

  • Thickness and quality of the glass
  • Grade of aluminum used in the frame
  • Quality of the EVA (Ethylene Vinyl Acetate) used to
    encapsulate and protect the solar cells
  • Durability of the diodes and junction box
  • Quality and efficiency of the solar cells

Many shoppers tend to favor brand names they are familiar
with from other household appliances.  However, some of
the lowest rated solar panels on the market are
manufactured by some recognized brand names.  

Request factory or government documents to back any
product claims.  Look for the manufacturer’s stock symbol,
sponsoring government entity or manufacturing facility
address.  A reputable manufacturer with a solid warranty
policy will at least stand by the product.


PTC / STC ratio of at least 89.5%


STC Rating  (Standard Test Conditions)
Standardized test performed by the factory (frequently
referred to as Factory Test Conditions)
If the factory test proved that a panel produces 500 watts,
that number will be printed on the factory label.

Below are the Standard Test Conditions required for testing.

  • STC – 1,000 Watts per square meter solar irradiance???
  • 25 degrees C cell temperature
  • Air mass equal to 1.5
  • ASTM G173-03 standard spectrum
  • PVUSA (Photovoltaics for Utility Scale Applications)

PTC Rating (PVUSA Test Conditions)

  • PVUSA test conditions were developed to compare PV
  • PTC of 1,000 watts per square meter solar irradiance
  • 20 degrees C air temperature
  • Wind Speed of 1 meter per second (at 10 meters above
    ground level)
  • Higher PTC rating equates to better performance.

PTC rating is normally lower than the STC rating, but the test
conditions reflect more realistic solar and climactic
conditions.  The PTC rating is generally recognized as the
most reliable measure of PV output.  

Resources: There are numerous online resources, including
the State of California website which show the rating of
most solar panels.

PTC / STC Ratio

  • Divide the PTC rating by the STC rating.
  • Example: A solar panel with a PTC rating of 180 and an
    STC rating of 200 would have a ratio of 90%.
  • In many states, tax credits are higher based on better
    performing equipment.


  • Criteria:  No higher than a 3% Negative Tolerance
  • Verification: Manufacturers specification sheet
  • Negative Tolerance rating of a solar panel is the amount
    of power that a solar panel can be “off specification”.  
  • Example: A 500W solar panel with a 5% negative
    tolerance rating may provide as low as 95% of the
  • In other words, if you purchased a 500 Watt panel it may
    produce only 475 Watts.  This would still be considered
    adequate by that manufacturer’s standards to pass their
    testing and inspection and still label it as a 500 Watt
  • It’s analogous to an auto manufacturer claiming that a
    product will get 40 miles per gallon but under real world
    driving conditions it never seems to get there.

CEC Efficiency Rating (California Energy Commission)

Inverter efficiency directly correlates to the financial
payback.  The lower the efficiency the lower the amount of
energy the system will produce.  Higher efficiency also
earns higher tax credits or rebates in most states.

Minimum Criteria: 94.5%



Minimum Criteria: 13.2%
Verification: Manufacturer’s Specification Sheet

Efficiency is often misinterpreted.  Basically, the higher the
efficiency the smaller the solar panel.  If you have the
space, a larger panel may actually be more economical and
deliver the same amount of energy.  A more efficient panel
may have a minor advantage when operating under low
light conditions.  It is more important to refer back to the
overall efficiency of the system – including the solar panels
and the conversion efficiency rating of the inverter.


Criteria: $3.94 per watt (equipment only) for an average 4kW
The higher the system wattage, the lower the price per watt
should be.

Verification: Request written quote from seller

Calculating Price Per Watt

  • Divide the price of the system by the total wattage.
  • A 5.0 kilowatt system priced at $20,000 would have a
    price per watt of $4.00 per watt.  
  • A 5kW system sold for $25,000 would have a price-per-
    watt of $5.00.
  • All other things being equal, (same component
    manufacturers, quality etc) obviously the $4.00 per watt
    would be a better investment.


Key Attributes:

  • Design
  • Materials
  • Thickness

Request sample of the mounting system and specifications

Minimum: 6105-T5 Aluminum Extrusion
Some manufacturers use thinner gauge aluminum mounting
rails.  These require more holes drilled in the roof for
additional mounting points to provide the rigidity needed to
secure the panels.

It is relatively easy to compare the aluminum rails by laying
one on the ground and putting your weight on it.  If it cannot
support your weight it is probably not strong enough to
secure your system for the next several years.

Request the specific brand and model of the mounting
system as well as the warranty.  This is an important
component.  Do not accept generic terms -- ask for the
manufacturer and the specific model number.

Some sellers have attempted to package name-brand
manufactured solar panels and inverters with cheap,
inferior mounting racks.  On the surface it may appear to be
a good buy, however, compromising the quality of the
mounting system could endanger your entire investment.  


  • Make sure the equipment is UL tested and approved.
  • If it is not UL approved, it cannot legally be installed on
    an occupied dwelling
  • Non UL approved equipment is NOT eligible for state tax
    credits or rebates.


Check the manufacturer’s warranty policy and get it in
The information we have collected is designed to help you find the right system for your needs, identify the best prices
and best value, and reduce your payback period and improve your overall Return on Investment.

Solar involves high tech products and it is recommended that you talk to an experienced expert It is also important that
you educate yourself on basic solar technology so that you are equipped to make intelligent decisions for the best
equipment to meet your requirements.
Bringing you a prosperous future where energy is clean, abundant, reliable, and affordable

A Consumer’s Guide
Get Your Power from the Sun

Bringing you a prosperous future where energy is clean, abundant, reliable, and affordable
A Consumer’s Guide



What is a solar electric or photovoltaic system? . . . . . . . . . . . . . . . .2
Are incentives available to help reduce the cost? . . . . . . . . . . . . . . . .3

Investing in a PV system

Why should you buy a PV system? . . . . . . . . . . . . . . . . . . . . . . . . . . .5
Is your home or business a good place for a PV system? . . . . . . . . . .5
How big should your PV system be, and what features
should it have? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
How much will you save with your PV system? . . . . . . . . . . . . . . . . .8
How much does a PV system cost? . . . . . . . . . . . . . . . . . . . . . . . . . . .8
How can you finance the cost of your PV system? . . . . . . . . . . . . . .9

Selecting a PV provider

Who sells and installs PV systems? . . . . . . . . . . . . . . . . . . . . . . . . . .11
How do you choose among PV providers? . . . . . . . . . . . . . . . . . . . .11
How do you choose among competing bids? . . . . . . . . . . . . . . . . . .12
Is the lowest price the “best deal”? . . . . . . . . . . . . . . . . . . . . . . . . . .13

Before connecting a PV system to the grid

What should you know about permits? . . . . . . . . . . . . . . . . . . . . . .14
What should you know about insurance? . . . . . . . . . . . . . . . . . . . .14
How do you get an interconnection agreement? . . . . . . . . . . . . . . .14
How do you get a net-metering agreement? . . . . . . . . . . . . . . . . . . .15
What should you know about utility and inspection sign-off? . . . .16
What should you know about warranties? . . . . . . . . . . . . . . . . . . . .16

Getting help . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

Cover photo: This PV system, integrated into an awning over the
back porch of a home in California, generates electricity while

shading the family's outdoor activities. (Courtesy of AstroPower/PIX12345)

Photo opposite: These PV modules are light and flexible, which
makes them suitable for roofing shingles.

This Consumer’s Guide is based on a state-specific guide written
by Tom Starrs and Howard Wenger for the California Energy
Commission, which was supported, in part, by the National
Renewable Energy Laboratory in Golden, Colorado.

Get Your Power from theSun

Are you thinking about buying a solar electric system for your home or business?
If so, this booklet provides some basic information that can help you.

Solar electric systems, which are also called photovoltaic or PV systems,
are reliable and pollution-free. They make use of a renewable source of energy—
the sun. And PV systems for homes and businesses are becoming more
affordable all the time.

PV works best in an energy-efficient building. So, adding insulation and energy-
efficient lighting, appliances, and windows is a good idea, to reduce your
home’s overall electricity use before you install a PV system.

To make PV systems even more affordable, several states offer financial incentives
through solar rebates and other programs. Some utilities have net metering
programs, which further enhance the economics of PV. Net metering
means that when your PV system generates more power than you need, the
excess goes to the utility grid and the meter runs backward. This allows you
to receive full retail value for the power that your PV system generates.

This booklet can guide you through the process of buying a solar electric system.
It is not a technical guide to designing or installing a system—for that
information, we recommend consulting an experienced PV system designer
or supplier.

A PV system can be a substantial investment. As with any investment, careful
planning will help you make the right decisions for your home or business.

Warren Gretz, NREL/PIX06283


What is a solar electric or
photovoltaic system?

Photovoltaic (PV) systems convert
sunlight directly to electricity. They
work any time the sun is shining,
but more electricity is produced
when the sunlight is more intense
and strikes the PV modules directly
(as when rays of sunlight are perpendicular
to the PV modules). Unlike
solar thermal systems for heating
water, PV does not use the sun's
heat to make electricity. Instead,
electrons freed by the interaction
of sunlight with semiconductor
materials in PV cells are captured
in an electric current.

PV allows you to produce electricity—
without noise or air pollution—from
a clean, renewable resource. A PV
system never runs out of fuel, and it
won't increase U.S. oil imports. Many
PV system components are manufactured
right here in the United States.
These characteristics could make PV

technology the U.S. energy source
of choice for the 21st century.

The basic building block of PV technology
is the solar “cell.” Multiple
PV cells are connected to form a PV
“module,” the smallest PV component
sold commercially. Modules
range in power output from about
10 watts to 300 watts. A PV system
connected or “tied” to the utility
grid has these components:

• One or more PV modules, which
are connected to an inverter
• The inverter, which converts the
system's direct-current (DC) electricity
to alternating current (AC)
• Batteries (optional) to provide
energy storage or backup power
in case of a power interruption
or outage on the grid.
AC electricity is compatible with
the utility grid. It powers our lights,
appliances, computers, and televisions.

Home Power/

Residential grid-connected PV system

Special appliances that run directly
on DC power are available, but they
can be expensive.

Before you decide to buy a PV system,
there are some things to consider:

First, PV produces power intermittently
because it works only when
the sun is shining. This is not a problem
for PV systems connected to the
utility grid, because any additional
electricity required is automatically
delivered to you by your utility. In
the case of non-grid, or stand-alone,
PV systems, batteries can be purchased
to store energy for later use.

Second, if you live near existing
power lines, PV-generated electricity
is usually more expensive than conventional
utility-supplied electricity.
Although PV now costs less than
1% of what it did in the 1970s, the
amortized price over the life of the
system is still about 25 cents per
kilowatt-hour. This is double to
quadruple what most people pay for
electricity from their utilities. A solar
rebate program and net metering can
help make PV more affordable, but
they can't match today's price for
utility electricity in most cases.

Finally, unlike the electricity you
purchase monthly from a utility, PV
power requires a high initial investment.
This means that buying a PV
system is like paying years of electric
bills up front. Your monthly electric
bills will go down, but the initial
expense of PV may be significant.
By financing your PV system, you
can spread the cost over many years,
and rebates can also lighten your
financial load.

Are incentives available to
help reduce the cost?

Yes, many states offer incentives.
For specific information, call one of
the contacts listed under “Getting
Help” at the end of this booklet.
Another excellent source is the
National Database of State Incentives
for Renewable Energy (DSIRE).
Prepared by the North Carolina Solar
Center, this database contains information
on financial and regulatory
incentives that promote renewable
energy technologies.

Net Metering—In more than 35
states, customers who own PV systems
can benefit from laws and
regulations that require “net” electric
meter reading. The customer is billed
for the net electricity purchased from
the utility over the entire billing
period—that is, the difference
between the electricity coming from
the power grid and the electricity
generated by the PV system. Through
net metering, the customer obtains
the full retail electricity rate—rather
than the much lower wholesale
rate—for kilowatt-hours of PV-produced
electricity sent to the utility
power grid. The benefits of net
metering to consumers are especially
significant in areas such as Hawaii
and New York, which have high
retail electric rates. Utilities also
benefit because the solar-generated
energy often coincides with their
periods of “peak” demand for

Property and Sales Tax—Tax
incentives may include a sales tax
exemption on the PV system purchase,
a property tax exemption,
or state personal income-tax credits,

PV awnings such as this one in California provide both
electricity and shade.
PV awnings such as this one in California provide both
electricity and shade.
all of which provide an economic
benefit to consumers by lowering
high capital costs. The U.S. government
also provides financial support
for PV technology through a tax
credit for commercial uses of solar
energy. This energy investment credit
provides businesses (but not individuals
or utilities) with a 10% tax credit
and 5-year accelerated depreciation
for the cost of equipment used to
generate solar electricity.

Buy-Down—Rebates and buy-
downs, typically based on the rated
power of the system, help to defray
high capital costs and to create
competitive, sustainable market

growth. In the United States, the

U.S. Department of Energy has been
involved in a program known as
TEAM-UP, or Technology Experience
to Accelerate Markets in Utility
Photovoltaics. Through this program,
some 80 utilities in 40 states have
installed more than 7 megawatts
of grid-connected PV; supplier buy-
downs and consumer rebates range
between $2 and $4 per watt.
Residential Energy Rate—This
is the average retail residential rate
for energy from utilities, in cents
per kilowatt-hour. Check your utility
bill for your actual rate.

Investing in a PV system

Why should you buy a PV

People decide to buy PV systems for
a variety of reasons. Some people
want to help preserve the Earth's
finite fossil-fuel resources and reduce
air pollution. Others want to invest
in an energy-producing improvement
to their property. Some people
like the security of reducing the
amount of electricity they buy from
their utility because it makes them
less vulnerable to future price
increases. And some people just
appreciate the independence that
a PV system provides.

If you plan to build a home away
from an established utility service,
inquire about the cost of installing
a utility line. Often, the cost of
extending conventional power to
your residence is higher than the
cost of a solar option.

Whatever your reason, solar energy
is widely thought to be the energy
source of choice for the future, and
you may be able to take advantage
of a state-sponsored program to help
make it your energy choice for today
and tomorrow.

Is your home or business a
good place for a PV system?

Can you locate your system
so it works well?

A well-designed PV system needs
clear and unobstructed access to the
sun's rays for most or all of the day,
throughout the year. You can make
an initial assessment yourself. If the

location looks promising, your PV
provider can determine whether your
home or business can effectively use
a PV system.

The orientation of your PV system
(the compass direction that your system
faces) affects its performance. In
the United States, the sun is always
in the southern half of the sky but is
higher in the summer and lower in
the winter. Usually, the best location
for a PV system is a south-facing
roof, but roofs that face east or west
may also be acceptable. Flat roofs
also work well for solar electric systems,
because PV modules can be
mounted flat on the roof facing the
sky or bolted on frames tilted toward
the south at an optimal angle. They
can also be attached directly to the
roof as “PV shingles.”

If a rooftop can't be used, your solar
modules can also be placed on the
ground, either on a fixed mount or
a “tracking” mount that follows the
sun to orient the PV modules. Other
options (often used in multifamily
or commercial applications) include
mounting structures that create covered
parking, or that provide shade
as window awnings.

Is your site free from shading by
trees, nearby buildings, or other

To make the best use of your PV system,
the PV modules must have a
clear “view” of the sun for most or
all of the day—unobstructed by trees,
roof gables, chimneys, buildings, and
other features of your home and the

surrounding landscape. Some potential
sites for your PV system may
be bright and sunny during certain
times of the day, but shaded during
other times. Such shading may substantially
reduce the amount of electricity
that your system will produce.
To be eligible for some rebates, your
system must be unshaded between
certain hours during certain times of
the year. Some states have laws that
establish your right to protect your
solar access through the creation of
a “solar easement.” Your PV provider
can help you determine whether
your site is suitable for a solar
electric system.

Does your roof or property
contain a large enough area
for the PV system?

The amount of space that a PV
system needs depends on the size
of the system you purchase. Some
residential systems require as little
as 50 square feet (for a small “starter”
system), but others could need as
much as 1,000 square feet.
Commercial systems are typically
even larger. If your location limits
the size of your system, you may
want to install one that uses more
efficient PV modules. Greater efficiency
means that the module needs
less surface area to convert sunlight
into a given amount of electric
power. PV modules are available
in a range of types, and some offer
more efficiency per square foot
than others do (see table on the
next page). Although the efficiency
(percent of sunlight converted to
electricity) varies with the different
types of PV modules available today,
higher efficiency modules typically

cost more. System sizing, discussed
later in this booklet, should also be
discussed with your PV provider.

What kind of roof do you have,
and what is its condition?

Some types of roofs are simpler and
cheaper to work with, but a PV system
can be installed on any type.
Typically, roofs with composition
shingles are the easiest to work with,
and those with slate are the most
difficult. In any case, an experienced
solar installer will know how to
work on all types and can use roofing
techniques that eliminate any
possibility of leaks. Ask your PV
provider how the PV system affects
your roof warranty.

If your roof is older and needs to be
replaced in the near future, you may
want to replace it at the time the PV
system is installed to avoid the cost
of removing and reinstalling your
PV system. PV panels often can be
integrated into the roof itself, and
some modules are actually designed
as three-tab shingles or raised-seam
metal roof sections. One benefit of
these systems is their ability to offset
the cost of roof materials.

How big should your PV
system be, and what features
should it have?

To begin, consider what portion of
your current electricity needs you
would like your PV system to meet.
For example, suppose that you would
like to meet 50% of your electricity
needs with your PV system. You
could work with your PV provider
to examine past electric bills and

determine the size of the PV system
needed to achieve that goal.

You can contact your utility and
request the total electricity usage,
measured in kilowatt-hours, for your
household or business over the past
12 months (or consult your electric
bills if you save them). Ask your PV
provider how much your new PV
system will produce per year (also
measured in kilowatt-hours) and
compare that number to your annual
electricity usage (called demand) to
get an idea of how much you will
save. In the next section, we'll provide
more information on estimating
how much you will save.

Some solar rebate programs are
capped at a certain dollar amount.
Therefore, a solar electric system
that matches this cap maximizes
the benefit of the solar rebate.

To qualify for net metering in some
service territories, your PV system
must have a peak generating capacity
that is typically not more 10 kilowatts
(10,000 watts), although this
peak may differ from state to state.
Also, utilities have different provisions
for buying excess electricity

produced by your system on an
annual basis (see the section on net
metering). Finally, customers eligible
for net metering vary from utility to
utility; for example, net metering
could be allowed for residential customers
only, commercial customers
only, or both.

One optional feature to consider is
a battery system to provide energy
storage (for stand-alone systems) or
backup power in case of a utility
power outage (for grid-connected
systems). Batteries add value to your
system, but at an increased price.

As a rule, the cost per kilowatt-hour
goes down as you increase the size
of the system. For example, many
inverters are sized for systems up to
5 kilowatts, so even if your PV array
is smaller (say, 3 kilowatts), you may
have to buy the same size of inverter.
Labor costs for a small system may
be nearly as much as those for a large
system, so you are likely to get a better
price for installing a 2-kilowatt
system all at once, rather than
installing 1 kilowatt each year for
two years.

Roof Area Needed in Square Feet (shown in Bold Type)
PV Module
Efficiency (%) PV Capacity Rating (Watts)
100 250 500 1,000 2,000 4,000 10,000
4 30 75 150 300 600 1,200 3,000
8 15 38 75 150 300 600 1,500
12 10 25 50 100 200 400 1,000
16 8 20 40 80 160 320 800
For example, to generate 2,000 watts from a 12%-efficient system, you need 200 square feet of
roof area.

How much will you save
with your PV system?

The value of your PV system's electricity
depends on how much you
pay for electricity now and how
much your utility will pay you for
any excess power that you generate.
If your utility offers net metering
(and so pays the full retail price for
your excess electricity), you and your
utility will pay the same price for
each other's electricity. You can use
the calculation box on the next page
to roughly estimate how much electricity
your PV system will produce
and how much that electricity will
be worth. Actual energy production
from your PV system will vary by up
to 20% from these figures, depending
on your geographic location, the
angle and orientation of your system,
the quality of the components, and
the quality of the installation.

Also, you may not get full retail
value for excess electricity produced
by your system on an annual basis,
even if your utility does offer net
metering. Be sure to discuss these
issues with your PV provider. Request
a written estimate of the average
annual energy production from the
PV system. However, even if an estimate
is accurate for an average year,
actual electricity production will
fluctuate from year to year because
of natural variations in weather
and climate.

If your utility does not offer net
metering, you can still use the calculation
box to determine the amount
of electricity your system will
produce. However, this is not as
straightforward, because the excess

electricity will not be worth as much
as the electricity you actually use.
You may earn only 2 cents per
kilowatt-hour—or less than half the
retail rate—for your excess power.

PV systems produce most of their
electricity during the middle of the
day, when residential electric loads
tend to be small. If your utility does
not offer net metering, you may
want to size your system to avoid
generating electricity significantly
beyond your actual needs.

How much does a PV
system cost?

No single answer applies in every
case. But a solar rebate and other
incentives can always reduce the
cost. Your price depends on a number
of factors, including whether
your home is under construction and
whether PV is integrated into the
roof or mounted on top of an existing
roof. The price also depends on
the PV system rating, manufacturer,
retailer, and installer.

The size of your system may be the
most significant factor in any measurement
of costs versus benefits.
Small, single-PV-panel systems with
built-in inverters that produce about
75 watts may cost around $900
installed, or $12 per watt. These
small systems offset only a small
fraction of your electricity bill. A
2-kilowatt system that meets nearly
all the needs of a very energy-
efficient home could cost $16,000
to $20,000 installed, or $8 to $10 per
watt. At the high end, a 5-kilowatt
system that completely meets the
energy needs of many conventional

Calculating Electricity Bill Savings for a Net-Metered PV System

Determine the system's size in kilowatts (kW). A reasonable range is from
1 to 5 kW. This value is the “kW of PV” input for the equations below.

Based on your geographic location, select the energy production factor
from the map below for the “kWh/kW-year” input for the equations.
Energy from the PV system = (kW of PV) x (kWh/kW-year) = kWh/year

Divide this number by 12 if you want to determine your monthly energy reduction.

Energy bills savings = (kWh/year) x (Residential Rate)/
100 = $/year saved

(Residential Rate in this above equation should be in dollars per kWh; for example,
a rate of 10 cents per kWh is input as $0.10/kWh.)

For example, a 2-kW system in Denver, CO, at a residential energy rate of
$0.07/kWh will save about $266 per year: 1,900 kWh/kW-year x $0.07/kWh
x 2 kW = $266/year.

homes can cost $30,000 to $40,000
installed, or $6 to $8 per watt. These
prices are rough estimates; your
costs depend on your system's configuration,
your equipment options,
and other factors. Your local PV
providers can give you more accurate
estimates or bids.

Note: The uncertainty of the
contoured values is generally ±10%.
In mountainous and other areas of
complex terrain, the uncertainty may
be higher.

How can you finance the cost
of your PV system?

When it comes to financing the cost
of purchasing and installing your
PV system, there are some special
programs particular to financing
solar and other renewable energy

This 20-kilowatt PV system produces electricity for the common
areas of a shopping center in Cambridge, Massachusetts.
Schott Applied Power Corp./PIX08808 This 20-kilowatt PV system produces electricity for the
areas of a shopping center in Cambridge, Massachusetts.
Schott Applied Power Corp./PIX08808
investments. But most of the
options will be familiar to you.

The best way to finance PV systems
for homes is through a mortgage
loan. Mortgage financing options
include your primary mortgage; a
second mortgage, such as a U.S.
Department of Housing and Urban
Development (HUD) Title 1 loan; or
a home-equity loan that is secured
by your property. There are two
advantages to mortgage financing.
First, mortgage financing usually provides
longer terms and lower interest
rates than other loans, such as conventional
bank loans. Second, the
interest paid on a mortgage loan is
generally deductible on your federal
taxes (subject to certain conditions).
If you buy the PV system for your
home at the same time that you
build, buy, or refinance the home,
adding the cost of the PV system to
your mortgage loan is likely to be

relatively simple. It is also one way
to avoid additional loan application
forms and fees.

If mortgage financing is not available,
look for other sources of financing,
such as conventional bank
loans. Seek the best possible combination
of low rate and long term.
This allows you to amortize your PV
system as inexpensively as possible.
Because your PV system is a long-
term investment, the terms and
conditions of your financing are
likely to be the most important
factor in determining the effective
price of your PV-generated power.

PV systems for businesses are probably
best financed through a company's
existing sources of funds for
capital purchases—such as Small
Business Administration loans or
conventional bank loans.

Selecting a PV provider

Who sells and installs PV

In some areas, finding a PV provider
can be as simple as picking up the
telephone directory and looking
under “Solar Energy Equipment and
Systems—Dealers.” However, many
of the listings are solar water-heating
companies and many companies
might not be experienced in PV system
design or installation. Similarly,
many electrical contractors, although
proficient in typical electrical contracting
work, might not have expertise
in PV or residential roof-mounting
techniques. How do you identify solar
electric system providers? Here are
several suggestions.

• Check the Source Guide for renewable
energy businesses (including
PV) by name, product type, business
type, and location: http://energy.
• Contact the Solar Energy Industries
Association (SEIA) at 202-628-7745
for a list of solar service providers.
• Contact your utility company
to see which vendors it might
• Conduct a search on the Internet.
Reputable, professional contractors
with experience in PV systems are
the best choice for the actual

How do you choose among
PV providers?

Compile a list of prospective PV
providers. (Those closest to you

should have the lowest travel costs).
Contact these providers and find out
what products and services they offer.
The following questions may give you
a good sense of their capabilities:

Has the company installed grid-
connected PV systems? If not,
has it installed grid-independent
(or stand-alone) PV systems?

Experience in installing grid-
connected systems is valuable
because some elements of the installation—
particularly interconnection
with the local utility—are unique
to these systems. Because grid-
connected systems are relatively
uncommon, however, most contractors
with PV experience have worked
only on stand-alone systems. So,
they have experience with all aspects
of PV system installation except
connection with the utility grid.
However, a competent company
with PV experience should not be
eliminated just because it has not
yet installed grid-connected PV.
Experience with off-grid systems is
valuable, because grid-independent
systems are more technically complex
than grid-tied systems.

How many years of experience
does the company have installing
PV systems?

This issue speaks for itself: A contractor
who has been in business a long
time probably understands how to
work with customers and to compete
effectively with other firms.

Is the company properly licensed?

PV systems should be installed by
an appropriately licensed contractor.
This usually means that either the
installer or a subcontractor has an
electrical contractor's license. Your
State Electrical Board can tell you
whether a contractor has a valid
electrician's license. Local building
departments might also require that
the installer have a general contractor's
license. Call the city or county
you live in for additional information
on licensing.

A solar rebate program may require
that, in addition to being properly
licensed, installers must demonstrate
that they have special knowledge
about installing PV systems. This special
knowledge may be demonstrated
in one of the following ways:

• Possession of a solar contractor
specialty license, issued by a local
building jurisdiction, that recognizes—
through testing or other
means—special knowledge of PV
• Certification in PV systems by a
group such as the state chapter
• A letter from the PV system manufacturer
stating that the installer
has the experience and training
needed to install the system
Does the company have any
pending or active judgments
or liens against it?

As with any project that requires a
contractor, due diligence is recommended.
Your state electrical board

can tell you about any judgments or
complaints against a state-licensed
electrician. Consumers should call
the city and county they live in for
information on how to evaluate contractors.
The Better Business Bureau
is another source of information.

How do you choose among
competing bids?

If you decide to get more than one
bid for the installation of your PV
system (always a good idea), make
sure that all bids are made on the
same basis. For example, a bid for a
system mounted on the ground is
usually very different from another
bid for a rooftop system.

Similarly, some PV modules generate
more electricity per square foot than
others. Bids should clearly state the
maximum generating capacity of the
system (measured in watts or kilowatts).
If possible, have the bids specify
the system capacity in “AC watts”
under a standard set of test conditions,
or specify the output of the
system at the inverter.

Also request an estimate of the
amount of energy that the system
will produce on an annual basis
(measured in kilowatt-hours).
Because the amount of energy
depends on the amount of sun-
light—which varies by location, season,
and year to year—it’s unlikely
the contractor will quote a specific
figure, but a range of ±20% is realistic.
Bids also should include the total
cost of getting the PV system up and
running, including hardware, installation,
connection to the grid, permitting,
sales tax, and warranty.

Your warranty is a very important
factor for evaluating bids. A solar
rebate program may require that
systems be covered by a two-year
parts-and-labor written installation
warranty, for example, in addition
to any manufacturers' warranties on
specific components. The installer
may offer longer warranties. Also, ask
yourself, “Will this company stand
behind the full-system warranty for
the next two years?”

Is the lowest price the “best

It might not be. You generally get
what you pay for, and it's possible
that a low price could be a sign of
inexperience. Companies that plan
to stay in business must charge
enough for their products and
services to cover their costs, plus a
fair profit margin. Therefore, price
should not be the only consideration,
and quality should probably
rank high on the list.

A home in the woods of New
Hampshire had too much shade
to use PV on the roof. The
solution was installing a
freestanding PV array.
Alan Ford/PIX09507

Before connecting a PV system to the grid

What should you know about

If you live where a homeowners association
must approve a solar electric
system, you or your PV provider may
need to submit your plans. You’ll
need approval before you begin
installing your PV system. However,
some state laws stipulate that you
have the right to install a solar
electric system on your home.

You will probably need to obtain permits
from your city or county building
department. These include a building
permit, an electrical permit, or both.
Typically, your PV provider will take
care of this, rolling the price of the
permits into the overall system price.

However, in some cases, your PV
provider may not know how much
time or money will be involved in
“pulling” a permit. If so, this task
may be priced on a time-and-materials
basis, particularly if additional
drawings or calculations must be
provided to the permitting agency.
In any case, make sure the permitting
costs and responsibilities are
addressed at the start with your PV
provider before installation begins.

Code requirements for PV systems
vary somewhat from one jurisdiction
to the next, but most are based on
the National Electrical Code (NEC).
Article 690 in the NEC spells out
requirements for designing and
installing safe, reliable, code-compliant
PV systems. Because most local
requirements are based on the NEC,
your building inspector is likely to

rely on Article 690 for guidance in
determining whether your PV system
has been properly designed and
installed. If you are one of the first
people in your community to install
a grid-connected PV system, your
local building department may not
have experience in approving one
of these systems. If this is the case,
you and your PV provider can speed
the process by working closely with
building officials to bring them up
to speed on the technology.

What should you know about

For grid-connected PV systems, your
electric utility will require that you
enter into an interconnection agreement
(see also the next section).
Usually, these agreements set forth the
minimum insurance requirements to
keep in force. If you are buying a PV
system for your home, your standard
homeowner’s insurance policy is
usually adequate to meet the utility’s
requirements. However, if insurance
coverage becomes an issue, contact
one of the groups listed in the Getting
Help section.

How do you get an
interconnection agreement?

Connecting your PV system to the
utility grid will require an interconnection
agreement and a purchase
and sale agreement. Federal law and
some state public utility commission
regulations require utilities to supply
you with an interconnection agreement.
Some utilities have developed

simplified, standardized interconnection
agreements for small-scale PV

The interconnection agreement specifies
the terms and conditions under
which your system will be connected
to the utility grid. These include your
obligation to obtain permits and insurance,
maintain the system in good
working order, and operate it safely.
The purchase and sale agreement specifies
the metering arrangements, the
payment for any excess generation,
and any other related issues.

The language in these contracts
should be simple, straightforward,
and easy to understand. If you are
unclear about your obligations under
these agreements, contact the utility
or your electrical service provider for
clarification. If your questions are
not answered adequately, contact
one of the groups in the Getting
Help section.

National standards for utility interconnection
of PV systems are being
adopted by many local utilities. The
most important of these standards
focuses on inverters. Traditionally,
inverters simply converted the DC
electricity generated by PV modules
to the AC electricity we use in our
homes. More recently, inverters have
evolved into remarkably sophisticated
devices to manage and condition
power. Many new inverters contain
all the protective relays, disconnects,
and other components necessary to
meet the most stringent national
standards. Two of these standards are
particularly relevant:

• Institute of Electrical and Electronic
Engineers, P929: Recommended
Practice for Utility Interface of

Photovoltaic Systems. Institute of

Electrical and Electronic Engineers,

Inc., New York, NY (1998).

• Underwriters Laboratories, UL
Subject 1741: Standard for Static
Inverters and Charge Controllers for
Use in Photovoltaic Power Systems
(First Edition). Underwriters

Laboratories, Inc., Northbrook, IL

(December 1997).

You don’t need to fully understand
these standards, but your PV provider
and utility should. It is your obligation
to make sure that your PV
provider uses equipment that complies
with the relevant standards,
however, so be sure to discuss this

How do you get a net-
metering agreement?

Some utilities offer customers with
PV systems the option to net meter
the excess power generated by the
PV system. As noted, this means that
when the PV system generates more
power than the household can use,
the utility pays the full retail price
for this power in an even swap as the
electric meter spins backward, and
your PV power goes into the grid.

Net metering allows eligible customers
with PV systems to connect
to the grid with their existing single
meter. Almost all standard utility
meters can measure the flow of
energy in either direction. The meter
spins forward when electricity is
flowing from the utility into the
building and spins backward when
power is flowing from the building
to the utility.

For example, in one utility program,
customers are billed monthly for the
“net” energy consumed. If the customer’s
net consumption is negative
in any month (i.e., the PV system
produces more energy than the customer
uses), the balance is credited
to subsequent months. Once a year,
on the anniversary of the effective
date of the interconnection agreement,
the utility pays the customer
for any negative balance at its wholesale
or “avoided cost” for energy,
which may be quite small, perhaps
less than 2 cents per kilowatt-hour.

Net metering allows customers to get
more value from the energy they
generate. It also simplifies both the
metering process (by eliminating the
need for a second meter) and the
accounting process (by eliminating
the need for monthly payments from
your utility). Be sure to ask your
utility about its policy regarding
net metering.

Under the federal Public Utility
Regulatory Policies Act (PURPA), utilities
must allow you to interconnect
your PV system. They must also buy
any excess electricity you generate,
beyond what you use in your home or
business. If your utility does not offer
net metering, it will probably require
you to use two meters: one to measure
the flow of electricity into the building,
the other to measure the flow of
electricity out of the building. If net
metering is not available, the utility
will pay you only a wholesale rate for
your excess electricity. This provides a
strong incentive to use all the electricity
you generate so that it offsets electricity
you would otherwise have to
purchase at the higher retail rate. This
may be a factor in how you optimize

the system size, because you may want
to limit generating excess electricity.
Such a “dual metering” arrangement is
the norm for industrial customers who
generate their own power.

What should you know about
utility and inspection sign-off?

After your new PV system is
installed, it must be inspected and
“signed off” by the local permitting
agency (usually a building or electrical
inspector) and most likely by
the electric utility with which you
entered into an interconnection
agreement. Inspectors may require
your PV provider to make corrections
(which is fairly common in the construction
business). A copy of the
building permit showing the final
inspection sign-off may be required
to qualify for a solar rebate program.

What should you know about

Warranties are key to ensuring that
your PV system will be repaired if
something should malfunction during
the warranty period. PV systems
eligible for some solar rebate programs
must carry a full (not “limited”)
two-year warranty, in addition
to any manufacturers’ warranties on
specific components. This warranty
should cover all parts and labor,
including the cost of removing any
defective component, shipping it to
the manufacturer, and reinstalling
the component after it is repaired
or replaced. The rebate program’s
two-year warranty requirement
supersedes any other warranty
limitations. In other words, even if
the manufacturer’s warranty on a
particular component is less than

two years, the system vendor must
provide you with a two-year warranty.
Similarly, even if the manufacturer’s
warranty is a limited warranty
that does not include the cost of
removing, shipping, and reinstalling
defective components, the system
vendor must cover these costs if
the retailer/vendor also installed
the system.

Be sure you know who is responsible
for honoring the various warranties
associated with your system—the
installer, the dealer, or the manufacturer.
The vendor should disclose the
warranty responsibility of each party.

Getting Help

Know the financial arrangements,
such as contractor's bonds, that
ensure the warranty will be honored.
(A warranty does not guarantee that
the company will remain in business).
Find out whom to contact
if there is a problem. Under some
solar rebate programs, vendors must
provide documentation on system
and component warranty coverage
and claims procedures. To avoid any
later misunderstandings, be sure to
read the warranty carefully and
review the terms and conditions
with your retailer/vendor.

For more information on solar electric
systems, please contact:

National Association of State Energy
Officials (NASEO)
1414 Prince Street
Suite 200
Alexandria, Virginia 22314
Phone: 703-299-8800 • Fax: 703-299-6208

Check the above Web site to find the
contact for your state energy office,
which typically promotes the development
and use of renewable energy
resources in your state. The office might
offer technical assistance, sponsor workshops
and forums, and provide general
information to resident energy consumers
on renewable energy resources
and applications.

National Association of Regulatory and
Utility Commissioners (NARUC)
1101 Vermont, N.W.
Suite 200
Washington, DC 20005
Phone: 202-898-2200 • Fax: 202-898-2213

This Web site has a listing of state
Public Utility Commissions that you
may contact.

Solar Energy Industries Association (SEIA)
1616 H Street, N.W., Suite 800
Washington, DC 20006
Phone: 202-628-7745 • Fax: 202-628-7779

The Solar Energy Industries Association
is the national trade association of the
solar industry. Many states have a state
chapter of the national SEIA organization,
which can be found on SEIA’s
Web site.

Other helpful Web sites

Solar Energy Technologies Program:

National Center for Photovoltaics:

Million Solar Roofs: www.millionsolarroofs.

Database of State Incentives for
Renewable Energy (DSIRE):

About the Office of Energy Efficiency and Renewable Energy

A Strong Energy Portfolio for a Strong America

Energy efficiency and clean, renewable energy will mean a stronger economy, a
cleaner environment, and greater energy independence for America. By investing in
technology breakthroughs today, our nation can look forward to a more resilient
economy and secure future.

Far-reaching technology changes will be essential to America's energy future.
Working with a wide array of state, community, industry, and university partners,
the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy
invests in a portfolio of energy technologies that will:

• Conserve energy in the residential, commercial, industrial, government, and transportation
• Increase and diversify energy supply, with a focus on renewable domestic sources
• Upgrade our national energy infrastructure
• Facilitate the emergence of hydrogen technologies as vital new "energy carriers."
The Opportunities

Biomass Program—Using domestic, plant-derived resources to meet our fuel,
power, and chemical needs
Building Technologies Program—Homes, schools, and businesses that use less
energy, cost less to operate, and, ultimately, generate as much power as they use
Distributed Energy & Electric Reliability Program—A more reliable energy
infrastructure and reduced need for new power plants
Federal Energy Management Program—Leading by example, saving energy
and taxpayer dollars in federal facilities
FreedomCAR & Vehicle Technologies Program—Less dependence on foreign
oil, and eventual transition to an emissions-free, petroleum-free vehicle
Geothermal Technologies Program—Tapping the Earth's energy to meet
our heat and power needs
Hydrogen, Fuel Cells & Infrastructure Technologies Program—Paving the
way toward a hydrogen economy and net-zero carbon energy future
Industrial Technologies Program—Boosting the productivity and competitiveness
of U.S. industry through improvements in energy and environmental performance
Solar Energy Technology Program—Utilizing the sun's natural energy to
generate electricity and provide water and space heating
Weatherization & Intergovernmental Program—Accelerating the use of today's
best energy-efficient and renewable technologies in homes, communities, and businesses
Wind & Hydropower Technologies Program—Harnessing America's abundant
natural resources for clean power generation

To learn more, visit

The National Renewable Energy Laboratory,
a DOE national laboratory, produced this Consumer’s Guide for:

U.S. Department of Energy
Office of Energy Efficiency and Renewable Energy
1000 Independence Avenue, S.W.
Washington, D.C. 20585
December 2003 • DOE/GO-102003-1844
solar buyers guide