Which among the following options cannot be done by solar power?

Solar power can be used for space heating (through solar thermal collectors or passive solar design), water heating (solar water heaters are common worldwide), and various other applications. However, navigation (using GPS, maps, or celestial navigation to determine position and direction) is not directly powered by solar energy - it requires electronic systems, satellites, or manual methods. While solar panels can power navigation equipment, the process of navigation itself is not an application of solar power. The question asks what cannot be done BY solar power (as an energy source), making navigation the correct answer.