The Contagiousness of Solar Power

SolarCity Solar Power
Walter Schaefer, ERS, for Zondits. May 18, 2016

The recent rapid expansion of rooftop solar capacity in the United States has several well-documented causes, including falling system prices, generous (and extended1) subsidies, and innovative financing schemes. But can these factors alone explain a boom that has resulted in year-over-year growth rates between 60-70%2 and has led, by some estimates, to a new rooftop system being installed every four minutes3? The answer, according to SolarCity data as well as several independent studies, is no. The missing factor? The contagiousness of solar power.

Research has shown that installing a rooftop solar system on one’s home increases the likelihood that one’s neighbors will install their own panels. According to SolarCity, the nation’s largest solar system provider with a total of 230,000 installed systems, a third of its customers were referred by a friend or neighbor who also installed a system. This “neighbor effect” has been seen in communities around the country, from Hawaii to Colorado to Massachusetts, and it bodes well for solar system providers, as it stands to further reduce the cost of finding new customers and increase the rate of installation and visibility of solar photovoltaic systems.

The spread of solar in this manner – dubbed solar “contagion” – makes sense. Neighbors talk: those who have installed systems want to tell friends about the process and the benefits, while those who may or may not already have an interest in solar, are likely to be more receptive to hearing about the process directly from someone they know and trust. These first adopters serve as very effective “marketers” of solar technology, and solar providers are beginning to recognize that fact. SolarCity’s Solar Ambassador program, for example, offers rooftop owners $200 for each new customer they refer, in addition to offering a free month of solar electricity to the referred customer.


Solar power is contagious. These maps show how it spreads.

Vox, May 4, 2016

SolarCity, the largest solar installer in the United States, just published some fascinating data on this “contagion” effect. The company has installed 230,000 rooftop systems nationwide (often by allowing customers to lease panels rather than buy them upfront). It says fully one-third of customers were referred by a friend or neighbor.

SolarCity has also made some neat animations showing the “contagion” effect in action. Here’s Fort Collins and nearby Greeley, Colorado. The yellow dots show customers that came to SolarCity for installations. The green dots show installations that came about due to referrals:

Here’s an animation of rooftop solar going viral in Honolulu. As you can see, an initial wave of yellow dots usually brings a follow-up cluster of green referrals:

SolarCity
(SolarCity)

Here’s an animation of rooftop solar going viral in Honolulu. As you can see, an initial wave of yellow dots usually brings a follow-up cluster of green referrals:

SolarCity
(SolarCity)

Finally, here’s a map of the cities where the contagion effect is most pronounced. In Fort Collins, fully 69 percent of SolarCity’s installations came from referrals.

(SolarCity)
(SolarCity)
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  1. http://www.greentechmedia.com/articles/read/breaking-house-passes-1.1-trillion-spending-bill-with-renewable-energy-tax
  2. http://www.greentechmedia.com/articles/read/us-solar-market-sets-new-record-installing-7.3-gw-of-solar-pv-in-2015
  3. https://www.americanprogress.org/issues/green/report/2014/05/29/90551/rooftop-solar-adoption-in-emerging-residential-markets/