Forecast: Sunny with a Chance of Curtailment

A while back, the DOE Solar Energy Technologies Office asked my colleague Wesley Cole to explore the implications of continuing declines in PV (and storage) prices on potential deployment. He led this study, which uses NREL’s ReEDS model and found least-cost expansion scenarios where the U.S. derives up to 55% of annual electricity from solar by 2050. ReEDS is great (and now open access), but it’s still “just” a capacity expansion model, so it doesn’t do chronological simulations and is thus limited in its ability to verify operational feasibility. So Bethany Frew led a follow-on study using a utility-grade dispatch model to look at some of these scenarios and test the usual metrics (dropped load, reserve violations, etc.). 

The result: our new paper, which looks at how the system would need to be operated at 55% PV penetration (with lots of storage) across all three U.S. interconnections. While the results align with what we’ve seen on smaller test systems, I think it provides a good perspective of the “new normal” under large-scale solar deployment: massive ramp rates and lots of economic curtailment. We didn’t simulate frequency response, but we had periods with very little synchronous generation (particularly in ERCOT), so this will keep the EEs employed designing grid-forming inverters. And, of course, we saw many hours of zero marginal prices to keep the market design folks busy, too. So, it’s certainly an exciting time to be in the grid integration space, with lots of interesting problems to solve.