This paper discusses the performance limits of heat engines exchanging heat
radiatively with a hot source while in thermal contact with a cold sink.
Starting from solar energy conversion models, we derive power-versus-efficiency
upper bounds for both reciprocal and nonreciprocal radiative heat engines. We
find that nonreciprocal engines may allow significantly better performance than
reciprocal ones, particularly for low emitter temperatures or when operating
close to Carnot efficiency. The results give valuable guidelines for the design
and optimization of thermophotovoltaic systems.Comment: 6 pages, 5 figure