Is there such a thing as TOO MUCH PV on your roof?

Published on October 27, 2017

My view: NO.

The State of California, however, has another view, revealed through planned changes to our venerable energy code, Title 24 Part 6.

Around a decade ago the State set “big, bold” goals for all new homes to be ZNE by 2020 (also, for all new commercial buildings to be ZNE by 2030). However, in the intervening years since those goals were established, a few devils have been found amidst the details. One such Aha is that, while conceptually having a home produce enough energy to supply its own needs on an annual basis makes perfect sense, at high rates of adoption this presents some grid-level challenges. Specifically, most of the renewable energy production will come from rooftop photovoltaics on sunny afternoons … hmmm … but that’s not when most of the demand occurs! The demand peak occurs later in the day, when people come home and start to cook, tinker with their thermostats, etc. This imbalance is illustrated in the rapidly-becoming-famous “duck curve” graph.

So now there’s concern about “grid harmonization,” and the State is indicating that future versions of the energy code will limit “excess” PV and/or require that it be countered by onsite energy storage to address this imbalance. Even now, “excess” solar energy production is effectively discouraged by utility rate structures that ensure you will never see good value for PV capacity above and beyond your own annual electricity load — not even when it’s there to compensate for natural gas use, for example.

Paradoxically, the State has also acknowledged that as it moves to higher levels of clean energy (via increases in the renewable portfolio standard, or RPS), in the next couple of decades most of the new renewable energy supply will come from PVs. A bit of a disconnect?

Notably absent from presentations on State plans to address the “duck curve” are discussions of providing UTILITY-LEVEL energy storage. While eager to point out that PV is more economical at utility scale (true), they don’t seem to be nearly so quick to comment on whether it might be equally more economical to provide energy storage at utility scale (that seems likely to be true, no?!). This seems an obvious omission and should be added to the public discourse, promptly.

Also absent from the blithe comments about how, really, we should be looking to install utility-scale PV rather than putting it on all the little rooftops, is any observation about the massive ecological impacts associated with utility-scale solar developments.

My vision for a clean energy future includes a diversity of solutions, with solar on rooftops both small and large, wherever it is productive. Just as nature is not efficient, but rather smart, simple economics are not the final determinant of what makes sense. What makes sense is to preserve wilderness for all its uniquely important values, and limit the footprint of intrusive human developments such as solar farms to the greatest extent possible.

Reflections here provoked by some of the presentations at this week’s excellent Symposium on Zero Net Energy Buildings and Beyond, presented by the Emerging Technologies Coordinating Council. My thanks to all of the organizers and speakers for your contributions!

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