U.S. Department of Energy Energy Efficiency and Renewable Energy

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February 28, 2013
Q.

Hello, I'm a student doing a project on solar energy. I'm looking to get more information about my topic and just had a few questions.

  1. What are the environmental benefits of using solar power as a main energy source?
  2. I live in Virginia, where the weather varies quite often. Would you recommend using solar panels on my home?
  3. How much maintenance do solar energy panels require?
  4. How many solar panels are needed to provide power or hot water for an average home and what would be the total cost for the project?
SunShot Solar Outreach Partnership

The SunShot Solar Outreach Partnership has been tasked with helping accelerate adoption of photovoltaic (PV) solar at the local level by providing timely and actionable information to local governments.

A.

Whether you are referring to solar photovoltaic (PV), concentrated solar power (CSP), or solar heating and cooling technologies, solar energy provides numerous environmental benefits. Most of the environmental benefits are derived from avoiding emissions from fossil-based sources of energy. On average, PV technologies have an energy payback time of two years, meaning it only takes two years for solar PV modules to produce the equivalent energy that was used to manufacture them. In addition to its environmental benefits, studies show solar energy offers a host of other long-term societal benefits, including the avoided cost to ratepayers from reduced electricity transmission congestion, enhanced grid security through near point power usage, supporting local electrical and constructions workers, and the increased public tax-base to the local communities where solar and solar companies are located.

As you can see in the map from the U.S. National Renewable Energy Laboratory (NREL), the solar resource, a measure of the sunlight's intensity, in Virginia is near the average for the country at around 4.6 kWh/m2/day. With a properly installed and oriented PV system, a Virginia homeowner can produce a significant portion of their electric load from their roof space.  Germany is the world's leading installer of solar even though it has a similar solar resource to Alaska. But the strength of the solar resource is not the only determining factor on whether one should invest in solar. Your local electricty price also influences how much money you will save by using solar energy. Nevertheless, the solar resource in Virginia is more than adequate for solar energy to work for you.

A residential solar PV installation requires very little maintenance since most PV modules are warrantied for over 25 years and the inverters are warrantied for over 10 years. Typically, your contract with the installer will detail who is responsible for system maintenance. These types of services could include replacing the inverters once or twice over the life of the PV modules, clearing the modules of any debris that might impair their performance, and ensuring there aren't any catastrophic failures that knock the PV system offline.  

An average U.S. home uses approximately 11,496 kWh per year. To determine how large a PV system you need in Virginia to produce an equivalent amount of power with solar, we can look at the map from NREL. Using the provided measurement of 4.6 kWh/m2/day, we multiply that by 365 days to get 1679 kWh/m2/yr. By dividing this number by 1000 watts – the amount of sunlight on a square meter at noon under clear sky – we arrive at 1.7 kWh/W/yr. If we divide this number into the number of kilowatts used by the average home in a year we see that we need a solar installation of approximately 6.8 kW in size to produce an equivalent amount of power. Using the latest data published in GTM/SEIA's Solar Market Insight: Q3 2012 report, we see that the average installed residential PV system cost is $5.21/W. A 6.8 kW system would therefore cost about $35,000. Fortunately, there are numerous State and Federal tax credits, as well as incentives from many utilities, that help lower this cost. All of these incentives can be found through the Database of State Incentives for Renewable Energy (DSIRE).

Should you like to learn more about residential solar and solar energy technology, visit the Small Solar Electric Systems page on the Department of Energy's website.

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