Ideal heat engine receives heat at a high temperature and loses heat at a low temperature. In the case of our satellite, keep in mind that the heat received at a high temperature comes as a sum of two parts: a positive portion of heat due to the absorption of the solar radiation, and a negative portion due to the hot surface of the satellite emitting its own thermal radiation. It is interesting to notice: in solar panels, the photons themselves play the role of the working gas of the heat engine; the and photons arrive at the very high temperature of the solar surface; the efficiency of the solar panels can be very high because the entropy is received by the heat engine at the solar temperature. In our case, however, there is a big loss (an increase) of entropy at the moment when photons at the solar temperature are absorbed by the satellite at a much lower temperature.
Please submit the solution to this problem via e-mail to physcs.cup@gmail.com. The next hint for the Problem 5 will be published at 13:00 GMT, 17th April 2022, together with the next updates of the intermediate results.