House hunters are more likely to pay a higher price if their preferred home comes equipped with a photovoltaic solar power system, according to a recent study.

On average, buyers will are willing to pay $15,000 for a standard 3.75-kilowatt photovoltaic system than they would pay for a comparable home without this system. This amounts to about $4 per watt.

This finding was published in a study entitled "Selling into the Sun: Price Premium Analysis of a Multi-State Dataset of Solar Homes." The principal authors, Ben Hoen and Ryan Wiser, are researchers at the Lawrence Berkeley National Laboratory. Other university researchers and real estate appraisers also contributed to the study, which was prepared for the Solar Energy Technologies Office, part of the Department of Energy's Office of Energy Efficiency and Renewable Energy.

The study analyzed 22,822 home sales in eight states between 2002 and 2013. Of these homes, 3,951 were equipped with photovoltaic systems. The study says this is more than twice the number of homes with photovoltaic systems analyzed in previous studies, and that the time period of the research happened to coincide with three different market conditions: a housing boom, a crash, and a recovery.

"As solar photovoltaic systems become an increasingly common feature of U.S. homes, the ability to value homes with these systems appropriately will become increasingly important," the report concludes.

The report says buyers are consistently willing to pay more for photovoltaic systems across a variety of states, home types, and market conditions for both housing and renewable energy systems. The benefit was slightly greater in California homes, but this was not a statistically significant difference since it was consistent with lower net costs and income estimates in other states.

The willingness of buyers to pay more for photovoltaic systems also remained consistent even as the gross costs of these systems decreased and the housing market crashed and began to recover during the study period. Researchers said this finding indicates that photovoltaic value remains robust in a variety of housing conditions and that net cost of the system - which includes government or utility incentives - rather than the gross cost is the more important factor in the housing market.

In contrast to previous studies on the topic, there was relatively little difference in the added value of photovoltaic systems between new and existing homes. The authors say part of this result may be due to the exclusion of sales in the "very high" price range and the prevalence of more recent sales. However, they also note that there is some evidence of discounting for photovoltaic systems on new homes.

A "green cachet" is thought to exist for some homes, meaning that buyers would be willing to pay a certain additional amount for a photovoltaic system of any size. However, the size also appears to make buyers more willing to pay incrementally higher costs for larger systems.

The study says additional research would be required to determine the effect of depreciation on older photovoltaic systems and the subsequent effect on home values. The study says that for the first decade, the market appears to depreciate the systems at a rate exceeding the rate of efficiency losses and straight-line depreciation over the life of the system.

In addition, the report concludes that other analysis should focus on leased photovoltaic systems, since these make up a growing portion of photovoltaic sales for residential use. The study also says it would be beneficial to cover a wider variety of states and see how values compare in areas with a bounty of photovoltaic homes and areas where fewer homes with photovoltaic systems are on the market.

The report says that an increasing number of American homes are using photovoltaic systems, with more than half a million systems installed across the country. A total of 42,000 systems were installed in the second quarter of 2014, a fourfold increase over the second quarter of 2010. The growth has been spurred in part by the decreasing expense of installing a photovoltaic system and also by the expansion of inexpensive options such as leased systems and zero money down financing.

The Department of Energy has also launched a SunShot Initiative, seeking to make the cost of solar energy competitive with other electricity production methods, or six cents a kilowatt hour, by 2020. The department says solar systems currently account for less than 0.5 percent of energy production, but could provide 27 percent by 2050 if solar energy becomes competitive.

Solar energy costs are well on the way to becoming more competitive, according to the Department of Energy. Between 2010 and 2013, the cost fell from 21.4 cents per kilowatt hour to 11.2 cents per kilowatt hour.

Real estate professionals have also been working to figure out how to calculate the value of renewable energy systems in homes. The Appraisal Institute, a professional organization of home appraisers, recently established the Residential Green and Energy Efficient Addendum. This form seeks to help appraisers identify and value the green features of a home.