PG&E in its 2020 ERRA Forecast Proceeding testimony wrote “however, BTM DG [behind the meter distributed generation] has a limited impact to the annual system peak as customer-owned solar photovoltaic (PV) generation is minimal during the peak hour of 7 p.m.” Uh, how does PG&E know that customer-owned solar doesn’t contribute to reducing the system peak if PG&E does not meter that generation?

PG&E actually has it wrong. Customer-owned solar has in fact reduced the former pre-solar peak that used to occur between 2 and 4 p.m. The metered load that PG&E can see, which is customer usage minus solar output (BTM DG), has shifted its apparent peak from 4 p.m. to 7 p.m.–3 hours. The graphic above illustrates how this shift has occurred. (PG&E produced a similar chart of its 2016 loads in its TOU rate rulemaking.) So BTM DG has had a profound impact on the annual system peak.