California’s Rooftop Solar Initiative

Came across an article in the Sacramento Bee last week that was somewhat critical of California’s moves to require all new build houses to include rooftop solar panels.

If I understood correctly, the concerns appeared to be:

1. Residential rooftop solar is not the most cost effective way to generate renewable electricity
2. The additional electricity coming during the middle of the day will result in problems for system operators

I believe that, while these concerns may be valid if one chooses to look just at rooftop solar in isolation, there are other developments that will mitigate these concerns.

Cost Effective

While it may well be true that more smaller installations is less cost effective than a utility scale solar farm would be, there are other advantages. Installation costs will likely reduce as the volume increases, continuing the trend that sees solar installations getting cheaper. The distributed nature of the system can also be an advantage, especially in a state that suffers from unpredictable natural disasters. Of course, current interconnection policies tend to bar standalone use of the panels when the grid power is lost, but that can be changed.

Energy Storage

The second item is already something that homeowners are addressing, especially in areas like Alameda where the net metering pricing has gone away. Local storage systems, like Tesla’s Powerwall batteries will reduce the amount of excess power fed to grid during the middle of the day; instead it will be stored locally for use by the home owner in the evening (reducing the load on the grid during one of its normal peak periods).

In addition to permanent batteries. there is also significant interest in vehicle-to-grid (V2G) solutions, where excess power from an EV’s battery can be fed back into the grid during that peak period, and then replenished again later.

Given the right interconnection policies, these batteries, whether permanently in the home or in an EV, may be recharged overnight from excess wind energy, taking advantage of lower tariffs and helping smooth the load on the network, getting them ready to assist with the early morning peak again.

Utility Scale Storage

In addition to batteries in homes and EVs, having excess solar power during the day from rooftop systems may mean utilities need to consider investment in their own energy storage solutions. This may be large scale battery systems, of the type we’ve seen Tesla installing for utilities, or it may be other types of system like pumped water or the novel Gravitricity idea of using a weight suspended in a disused mine shaft, or similar deep hole in the ground.

In Conclusion

My conclusion is that, while residential rooftop solar alone may be less effective, having more of it in place as part of a larger system of renewable energy generation, storage and distribution will be a big advantage for California. It also doesn’t, and shouldn’t, impact industrial/commercial rooftop solar installations.

The state’s utilities may need to plan for more distributed energy storage & less utility scale solar, leaving the solar generation to end users. Their generation budgets are likely better spent on wind farms, which are less practical in residential settings, and provide power at times when solar may not be available, or tidal systems which need to be operated by a utility. New budgets for utility scale storage systems as well as systems to manage distributed residential batteries and V2G systems will also be needed as part of the overall plan.