**5.1 Hydroelectric (hydropower) energy**

Hydroelectricity (hydropower) is generated by the gravitational flow of water through the turbine attached to a generator. Most of the hydropower is created from water stored in a reservoir with a wide dam. The largest hydropower plant in China is currently in operation with 22.5 gigawatt (GW). The rising portion of hydroelectricity is created by water flowing down the river straight through the turbine or by water flowing via the pipes and the turbine near the spur of the river before returning to the river, and this form of hydroelectricity is called run-of-the-river hydropower. Advantage of it is that vast areas of land are not submerged behind a dam, but on the other hand, a smaller volume is valuable for storage [18].

Environmental impact relies in some cases on eliminating the likelihood of carbonic acid gas release during power generation. It has been found that areas with hydropower potential that value more highly to utilize the sources of power that depend on fossil fuels emit up to four times more the quantity of greenhouse emission than necessary [19]. This suggests that hydropower production does indeed have the power to cut back greenhouse emissions.

Increased opportunities for hydropower would also result from changes in how electricity markets are run. Sub-hourly scheduling tries to encourage greater participation and compensation for flexibility. Hydropower may be compensated for forward market scheduling. Independent System Operators (ISOs) arranging hydropower resources across several hours or days would also enable hydropower optimization in the context of other resources. This "fixed-schedule" method might boost plant earnings by 63–77%. Why? Because the existing market structure advantages fossil fuel producers with time-independent output. They may burn fuel to create power at any time of day or night. Pumped hydropower or energy-limited hydropower does not have this benefit and must instead guess the lowest cost time to "refuel" and the greatest price time to sell.
