Upper bound efficiency for thermal radiation energy conversion by using spectrally selective electrical, chemical and mechanical work extractors

The maximum work content factor K(U,i )(+)of the incoming thermal radiation energy depends on the temperatures of the radiation source, work extractor and environment, on the solid angle subtended by the radiation source, and on the spectrally averaged absorptance and emittance of the work extractor. The theory is applied to solar radiation as a particular case. The formula derived here for K-U ,i(+) is more accurate than well-known formulas from literature. The work extractor may provide work or not, depending on the averaged absorptance and emittance and radiation concentration. Solar thermal power plants based on plane blackbody collectors cannot provide work under unconcentrated solar radiation.