Providing large-scale electricity demand with photovoltaics and molten-salt storage
Résumé
A strategy for feasibly and affordably achieving high electrical grid penetration (24 h/day, 365 days/yr) from electricity produced by large-scale low-cost photovoltaic (PV) systems is proposed and evaluated. It is based on oversizing PV plants without storage beyond meeting their peak daytime demand, and storing the excess energy as high-temperature heat in molten salts, from which high-efficiency steam turbines can be driven. Grid penetration levels of ~80-95% can be realized with storage capacities of only ~12 hours of average electricity demand. The feasibility reflects a striking difference between economic and thermodynamic factors. The recent dramatic decrease in PV costs more than compensates for the efficiency penalty. All components are off-the-shelf, mass-produced technologies. Hence the proposal is ready for immediate implementation. First, the thermodynamic arguments for the size and performance of such systems are reviewed. Then it is shown that the cost of electricity would be competitive with that of conventional power plants, and far better than using lithium-ion batteries. The geographic decoupling of PV fields from the storage facilities and turbines permits greater decentralization of PV fields and/or more centralization of larger storage facilities and power blocks. Because PVs collect and convert diffuse solar radiation, they are viable for areas with high global, but not direct, solar radiation, where concentrating solar thermal power plants are not feasible. It is also shown that none of the system components constitutes a limited resource. This also applies to future scenarios of much greater electricity use linked to the global transition to all-electric vehicles.
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