Concentrated solar power on demand

Abstract

A concentrating solar power system is presented which uses hillside mounted heliostats to direct sunlight into a volumetric absorption molten salt receiver with integral storage. The concentrated sunlight penetrates and is absorbed by molten salt in the receiver through a depth of 4–5 m, making the system insensitive to the passage of clouds. The receiver volume also acts as the thermal storage volume eliminating the need for secondary hot and cold salt storage tanks. A small aperture and refractory-lined domed roof reduce losses to the environment and reflect thermal radiation back into the pond. Hot salt is pumped from the top of the tank through a steam generator and then returned to the bottom of the tank. An insulated barrier plate is positioned within the tank to provide a physical and thermal barrier between the thermally stratified layers, maintaining hot and cold salt volumes required for continuous operation. As a result, high temperature thermal energy can be provided 24/7 or at any desired time.

The amount of storage required depends on local needs and economic conditions. About 2500 m[superscript 3] of nitrate salt is needed to operate a 4 MW[subscript e] steam turbine 24/7 (7 h sunshine, 17 h storage), and with modest heliostat field oversizing to accumulate energy, the system could operate for an additional 24 h (1 cloudy day). Alternatively, this same storage volume can supply a 50 MWe turbine for 3.25 h without additional solar input. Cosine effect losses associated with hillside heliostats beaming light downwards to the receiver are offset by the elimination of a tower and separate hot and cold storage tanks and their associated pumping systems. Reduced system complexity also reduces variable costs. Using the NREL Solar Advisor program, the system is estimated to realize cost-competitive levelized production costs of electricity.