Solar-to-work conversion from meteorological data

Abstract

The aim of this paper is to develop an algorithm able of determining the exergy or maximum work (GHIX) that can be extracted from solar global horizontal irradiance (GHI). A theoretical device made of a radiation absorber-emitter slab, connected to a temperature Ta heat reservoir, to a work extractor that operates in connection with a low temperature TL = Tamb heat reservoir, is exposed to an annual typical meteorological sun, made-up of hourly data, from five cities in Uruguay. The slab to be impinged by GHI has to be heated to the optimum high temperature Ta, so to become the hot reservoir for the thermal cyclic motor that will produce maximum work GHIX. Two alternative procedures are being used in making the year's hourly optimum Ta series; maximize the work production or minimize the entropy production, equivalent to minimize the exergy annihilation. Exergy factor GHIX/GHI results in a weak logarithmic function of GHI and in a weak geo-reference-dependence, for Uruguay. Annual exergy factor in all five cities in Uruguay belong to the interval (0.814<GHIX/GHI<0.819) with average (0.816). Agreement exists with similar measurements from other places found in the literature.