DG Technology Spotlight: Micro Hydropower

Small-scale and micro hydropower technologies are helping bring distributed electricity generation to remote areas around the world. The impacts on the environment are negligible and the economics are competitive. The worldwide market potential is fairly small in terms of overall megawatts (MWs) but for those locations without power today, a new micro-hydro system can make a tremendous difference in people's lives.

The International Small Hydro Atlas provides a nice definition of the various sizes of hydropower projects:

There is no International consensus on the definition of small hydropower. In Canada 'small' can refer to upper limit capacities of between 20 and 25 MW, in the United States 'small' can mean 30 MW, however, a value of up to 10 MW total capacity is becoming generally accepted. Small hydro can be further subdivided into mini hydro (usually defined as <500 kW) and micro hydro (<100 kW).

Hydropower - capturing and converting energy from flowing water - is currently the largest source of renewable power in the United States. Hydropower facilities generate about 10% of the nation's electricity consumption. The vast majority of the hydropower capacity (92 percent) is generated by large-scale hydro projects even though a vast majority (89 percent) of the hydropower dams would be considered a small-scale hydro project (~under 30 MW), according to the Low Impact Hydro Institute.

Unlike larger scale hydropower, Micro-hydro projects don't require a dam, only a barrier to impound or direct a sufficient and consistent amount of water into a pipe or channel leading to the turbine and generator. This type of hydro project is referred to as "run of the river." Wim Klunne's Micro Hydropower web portal offers dozens of case studies of existing projects.

In the past, dams for electricity were often built seemingly without much thought to the environmental impacts of the projects. Today, proposals for large-scale hydropower projects are controversial affairs. Micro hydro has none of the detrimental impacts that larger hydropower projects can have on the physical environment and on wildlife species.

Improvements in micro-hydropower technology indicate that economical electric production can be generated from heads (overall vertical drop) as little as 10 feet. One company, Nautilus Water Turbine, says that their micro hydro systems can operate efficiently and economically with heads as little as 2 feet.

Many renewable energy laws in the country allow small scale hydro to qualify as "green" electricity. However, the Low Impact Hydropower Institute (LIHI) points out that even small dams with small hydropower generators can be harmful to the environment and to river species. They've developed a certification program for hydropower projects that have minimized their overall impacts. Many of their certified projects have been smaller, run-of-the-river type power plants. LIHI has certified 16 projects across the United States and some utilities have indicated that they will seek certification of many more in the future as renewable energy green-tag markets mature.

In order to be certified by the Institute, a hydropower facility must meet criteria in the following eight areas: river flows; water quality; fish passage and protection; watershed protection; threatened and endangered species protection; cultural resource protection; recreation; facilities recommended for removal.

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