California's range of incentives for rooftop solar has been less effective than hoped, but putting that same amount of money into free solar for the state's poorest residents could give the state more solar for its buck.
That's according to researchers at Nashville's Vanderbilt University, who examined the results of the $2.2 billion California Solar Initiative (CSI) in a paper scheduled for publication next month. CSI provides rebates to encourage the installation of rooftop solar systems in California, and is at least partly responsible for California's explosion in solar power generating capacity, with more than 2,300 megawatts of rooftop solar in the state these days.
But CSI could have done better, say the researchers. The increasing popularity of solar leasing companies has limited the effectiveness of CSI's per-watt rebate incentives to the point where it's hard to tell whether they actually encourage any homeowners to go solar. A far better use of that $2.2 billion, says the study, would be to provide free or extremely low cost rooftop solar for less-affluent Californians. That switch would mean a lot more solar gets built faster, with all the attendant climate and employment benefits that go along with rooftop solar installation.
The study, to be published in May in the imposingly named journal Proceedings of the 14th International Conference on Autonomous Agents and Multiagent Systems, was performed by Vanderbilt doctoral student Haifeng Zhang and Assistant Professor of Computer Science Yevgeniy Vorobeychik, along with Joshua Letchford and Kiran Lakkaraju of Sandia National Laboratories.
In the study, the researchers considered data from 8,500 new solar projects installed in San Diego County between 2007 and 2011. They collected data on system cost and size, home and lot size, whether the system was leased or bought outright, amount of incentives used, and so forth. They then used that data to create a model to describe the effect of the incentives on solar adoption, which they then ground-truthed by using the model to predict local solar installations from 2011 through 2013.
One reason CSI's incentives haven't been as effective as one might hope, according to Vorobeychik et al, is that they've essentially become part of the income stream for solar leasing companies, who rarely pass the rebates on to their retail customers. That means that while those rebates may keep solar leasing companies afloat, they don't play much of a role in individual property owners' decisions whether to go solar.
The researchers modeled rooftop solar adoption rates with a range of CSI-style subsidies and found that given the prevalence of solar leasing and a few other factors, the effect of increased rebates on actual new installations was, in the words of Vanderbilt's David Salisbury, "extremely modest."
What would work better? According to the study, using a phenomenon called "peer influence" stood a much better chance of persuading Californians to install solar on their rooftops. That just means that people whose friends and neighbors are installing solar are more likely to do so themselves, as long as those friends and neighbors have good things to report about the experience.
And it's hard to imagine what might prompt better peer reviews than a solar system that not only cuts your electric bill, but which you get for free -- or close to it.
To quote Vanderbilt's David Salisbury:
Vorobeychik and his colleagues explored the impact of scaling up a small existing CSI program that gives solar systems to low-income families for little or no cost. They determined that an optimal program of this type could result in significantly greater adoption compared to the incentive approach. In addition, they found that its relative advantage increased at higher budget levels.
In other words, Vorobeychik and his colleagues predict that the more cash California puts into CSI's low-income solar subsidy program, the more watts of new solar the state would get per dollar.
Kind of nice to know that targeting our solar subsidy money toward the people who need the most help could also make the most difference in the state's carbon footprint.
A final note: The study didn't compare per-watt efficiency of an expanded CSI-style low income solar program with state and federal subsidies to large corporations' utility-scale solar projects. Someone should really do that, because it would be pretty interesting.