Most people think hydro power projects are all the same. When they hear hydro power, they think of massive dams and a massive power generation capacity.
Hydro power need not always mean large hydro power stations.
Renewable power is also being generated worldwide from much smaller power stations, through small hydro power plants.
Well, small hydro power, as the name itself says, refers to hydro power plants that are much smaller in scale than large hydro power plants.
While terminologies differ from one country to another, small hydro power plants usually denote hydro based power plants that are smaller than 25 MW, in many cases, only 1-5 MW in size.
Large hydro power plants could run to 100s of MWs, and in some select cases, to well over 1000 MW!
While many small hydro plants also use reservoirs as do large hydro plants (albeit on much smaller scales), a separate type of small hydro power plant called the Run of River small hydro power plant works with only a very small reservoir capacity. By cleverly locating the power plant such that there is a natural water fall (or in some cases diverting the river so there is a natural water fall), run of river systems generate power using little reservoir storage.
Owing to their smaller sizes as well as some of them not needing reservoirs and the associated infrastructure, small hydro power plants leave a much lower environmental footprint than large hydro power plants. These can hence be implemented much faster than the large ones. It is also feasible to locate these small hydro power plants in a larger number of locations compared to their larger versions.
However, the cumulative capacity added by small hydro power plants usually tend to be much lower than the cumulative capacity from large hydro power plants, owing to the massive individual capacities of the large plants compared to really small capacities for the smaller ones – in many cases, small hydro power plants are only a hundredth of the size of a large hydro power plant in the same region!
Interestingly, even though small hydro has a much smaller environmental footprint than does a large hydro power project, I have seen that in many countries, it still takes a considerable amount of time for small hydro projects to take off, mainly owing to the number of environmental clearances and approvals the developers need to obtain. In India (where I live), it could take 3-4 long years for a small hydro project to be commissioned, after the initial investment has been made.