Broadband approach for the most energy efficient way of radiation-driven heating

The maximum efficiency of extracting work from thermal radiation energy has been intensely studied. However, a large part of the world's energy resources is actually used for heating rather than work production. Therefore, finding the most effective way of heating by using radiation energy is another problem of great practical interest, not often studied. Here, it is demonstrated that such a way involves heat extractors. A general broadband theory based on the first and second laws of thermodynamics and the model of deformed blackbody radiation is developed for radiation-driven heating systems. Particular cases are considered under the assumption of local thermal equilibrium. Application to solar radiation heating shows that the photothermal heating efficiency may be improved. During a winter clear sky day, solar radiation-driven heat extractors may provide, in the ideal case, several times more heat per unit collection surface area than traditional solar heating. When constructed with current technology, heat extractors with evacuated tube solar collectors oriented toward the Sun under low-concentrated radiation may provide between 106% and 118% more heat per unit collection surface area than traditional solar heating. For an improved (mature) heat extractor technology, this range of values increases to about 130% to 337%, depending on ambient temperature. This makes the problem of radiation heating efficiency important from a practical point of view.