One of the experiments on board is the U.S. Naval Research Laboratory’s Photovoltaic Radio-frequency Antenna Module, or PRAM, evaluating technology to transform solar power into radio frequency microwave energy. The energy, thus harnessed in space, could then be beamed down to earth. If successful and further developed, this energy source could also prove vital in future space missions, e.g. on the moon, on Mars, etc.
https://www.space.com/x-37b-military-space-plane-900-days-orbit