I don’t think it is all that much of a risk. Here are a couple of points to consider:
1 All of the residential pools right now are using fairly high and stable credit scores (680+ at least), so not anything like sub-prime.
2 People pay their electric bills before mortgage payments and car bills (smaller payments, and it is easier to shut off power than to foreclose or even repossess a car).
3 Much of the financial crisis was built on secondary instruments traded against asset backed securities – the basic idea of a pool of asset backed obligations doesn’t create the same kind of risk that the layers of derivatives in the mortgage crisis did.
As with any market if abused and manipulated into something altogether different than it’s shaping up to be would create some risk – similarly if the underlying credit risk slides deep into high risk credit – selling junk backed securities as asset backed equivalents still seems like a bad idea whether it is tied to real estate or solar – then there would be some risk, but that all seems awfully remote against the value of this evolving market.