California is the biggest state for residential solar in the country. The state has also supported residential solar with the $2.2 billion California Solar Initiative (CSI), which many have thought was at least in part responsible for the growth of home solar in the state. A new study from Vanderbilt University, funded in part by the Department of Energy, found that other factors, like the spread of solar leases and the influence of neighbors may have had more of an impact on the growth of solar in the state.
“Despite the fact that policy makers have paid overwhelming attention to increasing the economic benefits by reducing costs to get people to adopt solar technology, our analysis indicates that this has much less effect than generally perceived,” said Assistant Professor of Computer Science Yevgeniy Vorobeychik. “That is what the data is telling us.”
The study points out that California has installed more than 245,000 residential systems since 2007. During that period—particularly in the past few years—the cost of solar panels has plummeted and the number of companies installing solar in California has increased as more people have shown interest in going solar and have gone solar.
To narrow the study Vorobeychik and doctoral student Haifeng Zhang narrowed the research to rooftop solar installations from May 2007 to April 2013 in San Diego County. They had detailed information on 8,500 projects in the country over the period, including system size, cost, incentive granted and more.
“The problem with assessing the success of programs like CSI is that you need to compare them with what would have happened in the same world without the incentives,” Vorobeychik said. “Of course, that is impossible, so you need to use techniques, like the our data-driven agent-based modeling methodology, that analyze the data and make predictions on how it would behave under different circumstances.”
They analyzed data from May 2007 to April 2011 to determine relative importance economic benefit and peer influence to homeowners’ decisions to go solar. They tested the model’s accuracy by predicting the pattern of adoption from May 2011 to April 2013, according to Vanderbilt.
The researchers tested the model using eight different scenarios with varying incentive levels. They said they found little difference in adoption rates whether or not there was a subsidy. However, the availability of leasing programs as well as the number of people in the neighborhood with solar were bigger influencers on the growth of solar in a neighborhood.
The research also showed that using the same amount of money that CSI has but in an incentive program designed to provide systems to low-income household: "At little or no cost would have done more to stimulate the adoption of rooftop solar systems than the incentive-based approach that the initiative used," Vanderbilt stated.
The researchers collaborated with Joshua Letchford and Kiran Lakkaraju at Sandia National Laboratories. It is described in the Proceedings of the 14th International Conference on Autonomous Agents and Multiagent Systems and is scheduled for publication in May.Tweet