This efficiency describes the performance of the sunlight to electricity conversion and does not implement the efficiency of the storage subsystem. This value is consequently independent of the orbit and gives the actual efficiency of a system operating in an eternal sun orbit. This holds true for both a photovoltaic and a solar dynamic system. Typical values, which were derived from the Space Station Freedom design and technology status, are shown in Table 1. The sun-to-user efficiency of the solar dynamic option is in the order of three times higher than for the photovoltaic system. If we include the storage subsystem in our consideration and ask for the continuous electrical power output per collector area in kWe/m2 then this value depends on the orbit altitude, i.e. on the eclipse time. For the Space Station orbit the solar dynamic system becomes even more attractive with a specific continuous electrical power output four times higher than the one of the photovoltaic system, Table 1. This has two reasons: • the efficiency of the latent heat storage is higher compared to the Ni-Cd batteries of the photovoltaic system • generally it is advantageous to store energy before converting it, because then the losses of the storage have not to be taken from the valuable converted part of the energy.
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