Optimization of a Point-Focusing, Distributed Receiver Solar Thermal Electric System

Abstract

This paper presents an approach to optimization of a solar concept which employs solar-to-electric power conversion at the focus of parabolic dish concentrators. Modularity is obtained through the use of multiple concentrators to achieve the desired power level (up to 10MW); the system is connected to an electric utility grid but is capable of operation in a stand-alone mode. The power conversion subsystem is packaged into a single assembly which includes (1) a cavity receiver, (2) thermal transport hardware, (3) a heat engine and (4) a synchronous a-c generator. In the example presented, the baseline heat engine is a Stirling cycle power plant and the receiver is a high temperature (∼800°C) sodium pool boiler; thermal transport is provided by a short pipe with the dual function of delivering sodium vapor to the engine heater head and returning liquid condensate to the boiler. The optimization procedure is presented through a series of trade studies, which include the results of optical/thermal analyses and individual subsystem trades. The optical/thermal analyses include the effect of concentrator rim angle, surface slope error, pointing error, geometric concentration ratio and pertinent cavity parameters including shape, temperature and inner surface radiation properties. For the concentrator, the effects pf slope error, rim angle and diameter on unit cost (dollars/m2 of aperture) are presented as part of an overall cost analysis which generates total system life-cycle energy cost as the optimization parameter. Alternate closed-cycle and open-cycle Brayton engines and organic Rankine engines are considered to show the influence of the optimization process, and various storage techniques are evaluated, including batteries, flywheels and hybrid-engine operations.