The role of concentrated solar power with thermal energy storage in least-cost highly reliable electricity systems fully powered by variable renewable energy

Policies in the US increasingly stipulate the use of variable renewable energy sources, which must be able to meet electricity demand reliably and affordably despite variability. The value of grid services provided by additional marginal capacity and storage in existing grids is likely very different than their value in a 100% variable renewable electricity system under such policies. Consequently, the role of concentrated solar power (CSP) and thermal energy storage (TES) relative to photovoltaics (PV) and batteries has not been clearly evaluated or established for such highly reliable, 100% renewable systems. Electricity generation by CSP is currently more costly than by PV, but TES is much less costly than chemical battery storage. Herein, we analyze the role of CSP and TES compared to PV and batteries in an idealized least-cost solar/wind/storage electricity system using a macro-scale energy model with real-world historical demand and hourly weather data across the contiguous United States. We find that CSP does not compete directly with PV. Instead, TES competes with short-duration storage from batteries, with the coupled CSP+TES system providing reliability in the absence of other grid flexibility mechanisms. Without TES, little CSP generation is built in this system because CSP and PV have similar generation profiles, but PV is currently cheaper on a dollar-per-kWh basis than CSP. However, CSP with TES can provide grid flexibility in the modeled least-cost system under some circumstances due to the low cost of TES compared to batteries. Cost-sensitivity analysis shows that penetration of CSP with TES is primarily limited by high CSP generation costs. These results provide a framework for researchers and decision-makers to assess the role of CSP with TES in future electricity systems.