Rooftop solar, especially when leased, is much more expensive than grid-scale solar, plus carbon savings are less. Economies of scale for big solar produce electricity cheaper and with less carbon. And unless a rooftop solar system has battery storage, it won’t help in a power outage.
The savings from utility-scale solar are considerable.
“Most of the environmental and social benefits provided by PV systems can be achieved at a much lower total cost at utility-scale than at residential-scale,” is how the study puts it.
“The biggest two takeaways were surprising,” Fox-Penner said. “The generation cost per solar MWh purchased is half as large for utility-scale solar as for rooftop solar. And per MW of solar installed, the carbon savings and the fuel savings from a MW of utility-scale PV are 50% larger.”
Utility-scale solar offers higher capacity factors and significant economies of scale, Crossborder concludes. But rooftop offers location at the point of end-use, reliability benefits (especially when paired with storage), societal and customer choice benefits, and lower cost to customers than green pricing programs.
The supposed resilience of rooftop solar doesn’t exist yet because they automatically shut off when there is an outage (to prevent power going back up the lines when repairs are happening.) Batteries will help. Even so, they generally won’t power a house at full power or for more than a few hours.
Rooftop solar offers the potential of greater resilience for the homeowner against outages, he said. It is only a potential advantage because most rooftop solar systems, as currently installed, automatically shut down when the grid goes out “to protect workers and to meet fire protection requirements.”
Rooftop solar still provides many benefits. However, big can almost always produce something cheaper than small.