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.
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
Homes Off The Grid</p>