Question

High cost and low efficiency are the disadvantages of solar energy. Then then how can it be used in artificial satellites and space probes?

Answer 1

As mentioned above even though it has these disadvantages, the solar energy is only on of the few available in space and therfore it is used in satellites.
Yes new sources such as photovoltaic energy is being developed but still as solar energy is present in abundance, it is preferred

Hope this helps