Hydropower is the oldest source of electricity, with the world’s first commercial power plant powered by hydro started operating in Wisconsin, USA in 1882. (The world’s first coal power plant started operations in 1890).
While hydro power brings to mind large dams and massive turbines, there are also smaller versions of hydro power plants, those that operate at less than 10 MW, and today there are select regions where even micro and pico hydro power plants are running, with capacities at less than 10 kW! However, the lion’s share of hydro power installed capacity and generation are from large hydro power plants, some of which run to over 1000 MW, with China’s Three Gorges Hydro power project having a massive capacity of 22,500 MW.
Globally, hydro power has a massive 1.3 TW (1300 GW) of installed capacity, with well over 90% of this contributed by large hydro power. Small hydro power plants contribute about 80 GW global capacity. Hydro power generates about 4500 TWh of power every year, about 17% of total power generated from all sources making it the largest renewable source of power, by far.
Most forms of hydro power plants are well established technologies including small and micro hydro power generation. The only prominent sector of terrestrial hydro power generation that is still evolving is hydrokinetic power generation, which relies on generating power from the flow of water (kinetic) rather than the fall of water (potential). If one were to consider ocean-based power generation too under hydro power, almost all ocean-based power sources - tidal, wave, ocean thermal and osmotic - contribute very little to the overall power production currently and technologies for some of them like wave, ocean thermal and osmotic pressure based power generation are still evolving.
150 countries worldwide produce electricity from hydropower, though the extent of use varies significantly between these countries. For hydro power to contribute significantly to a country’s electricity needs, the region needs to have certain geographical characteristics. In addition to the presence of water flows, they also need appropriate geological features such as a fall of water from a reasonable height for run-of-river hydro or locations where large dams can be constructed for reservoir-based hydro power. Micro and pico hydro projects need to have small rivulets running in the neighbourhood.
Hydro power is renewable, is low cost, and can provide power at reasonably high capacity factors, up to about 60%. The key challenge with hydro power, especially large hydro power, is the environmental harm and social displacements resulting from large reservoir construction. Such negative consequences have resulted in opposition from both environmentalists and social activists, leading to long lead times for all types of hydro power projects - small or large.
Innovations in terrestrial hydro power in the 2020-2030 period are likely in modular hydropower systems, run of river and damless hydro electric projects, hydrokinetics, small hydroelectric turbines, more efficient turbines and in the use of digital technologies to increase operational efficiencies and more effective maintenance of hydro power plants. Ocean-based hydro projects - especially wave & tidal projects - are also likely to witness significant innovations and explorations, though these are likely to be confined to select geographies.
The carbon footprint of hydropower plants is a bit contentious. While many studies put the CO2 emissions at about 25 g CO2eq/kWh, there are others that give higher estimates. Some studies also suggest that there are significant CH4 emissions from hydro power operations as a result of organic matter decay in anaerobic conditions in the reservoirs.
Taking a conservative approach and assuming the total hydro power carbon footprint to be about half that of natural power generation (about 150 g/kWh), a 1.3 TW of installed capacity that supplies about 17% of total global electricity consumption of about 27,000 TWh implies savings of about 2.5 billion tons of CO2 emissions per annum when compared to conventional thermal power (coal and natural gas) - effectively, every kW of hydro power installed can offset about 2 tons of CO2 per annum.
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