Technical Summary

A typical run-of-river small hydropower plant is illustrated in the figure below.  Water is removed from a river at an intake structure, which may be a simple canal outlet as shown, or a small diversion may be required to redirect water into a canal leading to a forebay.  The canals can often be several kilometers in length and may even involve a tunnel.  At the forebay, or headworks, the water goes into a penstock, or large pipe, leading to the powerhouse where the hydro turbines are located.  After passing through the turbines, the water travels through a tailrace to re-enter the river.

There are several issues that are inherent to many small hydropower stations.  First, the scale of electricity production is small, and the cost for design, engineering, and project financing can be high relative to the overall cost of the project.  Second, there is often no reservoir, and the station output is dependent on the water flow in the river, and that can vary significantly between the high water seasons and the low water seasons.

Resource Assessment

In the US, the Idaho National Engineering and Environmental Laboratory maintains a database of hydropower resources for each state.  These State Resource Assessment Reports have identified 5,677 sites in the United States with undeveloped capacity of about 30,000 MW.  The database summarizes the hydropower capacity for the state, and lists the hydropower capacity alphabetically by River Basin, with the stream name/plant name arranged alphabetically under each river basin.  The database also lists these sites numerically by FERC number, and provides a page on each site, listing all the environmental factors, KW capacity, location, owner's name, etc.

Cost and Performance

The capital cost for most small hydropower projects ranges from $1700 to 2300/kW.  Costs are very site-specific, and careful investigation of the hydrological resource, the geology and civil works requirements, and the electro-mechanical equipment requirements are needed to develop an accurate cost estimate. 

Operating and maintenance costs are typically quite low and range between  0.4  and 0.5 US cost/kWh for small hydropower facilities with capacity factors in the range of 40 to 50%.   The operating life of most facilities is over 50 years.