What is the difference between DC-powered and AC-powered solar water pumps?

DC-powered pumps run on direct current, which means the solar power (which is also direct current) does not need to be converted to AC-power. DC-powered pumps are generally 20-40% more efficient than AC-powered pumps. Due to the current low cost of solar panels, however, this difference in efficiency is not as important as it used to be. There are also pumps which can use both DC as well as AC power as their input.