Hydroelectricity is electricity generated by hydro-power from the gravitational force of falling or flowing water. it is the most widely used form of renewable energy, accounting for nearly twenty percent of global electricity generation. why hasn't hydroelectricity replaced more traditional sources of electricity? a) it requires a lot of workers. b) there are very high maintenance costs. eliminate c) hydroelectricity is not very reliable energy. d) construction of a hydro-power plant is very expensive.