• Energy & Power

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



Can you locate your system so it works well?

A well-designed photovoltaic system needs clear and unobstructed access to the ’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 photovoltaic provider can determine whether your home or business can effectively use a photovoltaic system.

The orientation of your photovoltaic 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 photovoltaic system is a south-facing , but roofs that face east or west may also be acceptable. Flat roofs also work well for , because photovoltaic modules can be mounted flat on the facing the sky or bolted on frames tilted toward the south at an optimal angle. They can also be attached directly to the 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 photovoltaic 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 obstructions?

To make the best use of your photovoltaic system, the photovoltaic 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 photovoltaic 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 , 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 photovoltaic 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 photovoltaic system?

The amount of space that a photovoltaic 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 photovoltaic modules. Greater efficiency means that the module needs less surface area to convert into a given amount of electric . Photovoltaic modules are available in a range of types, and some offer more efficiency per square foot than others do. Although the efficiency (percent of converted to electricity) varies with the different types of photovoltaic modules available today, higher efficiency modules typically cost more. System sizing should also be discussed with your photovoltaic 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 photovoltaic 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 photovoltaic provider how the photovoltaic 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 photovoltaic system is installed to avoid the cost of removing and reinstalling your photovoltaic system. Photovoltaic 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 photovoltaic system be, and what features should it have?

Roof Area Needed in Square Feet (shown in Bold Type)
PV Module
Efficiency (%)
PV Capacity Rating (Watts)
100
250
500
1000
2000
4000
10,000
4
30
75
150
300
600
1200
3000
8
15
38
75
150
300
600
1500
12
10
25
50
100
200
400
1000
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.

To begin, consider what portion of your current electricity needs you would like your photovoltaic system to meet. For example, suppose that you would like to meet 50% of your electricity needs with your photovoltaic system. You could work with your photovoltaic provider to examine past electric bills and determine the size of the photovoltaic 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 photovoltaic provider how much your new photovoltaic 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 photovoltaic 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 5kilowatts, so even if your photovoltaic 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.