An Introduction

The purpose of the Hydropower Section of this website is to provide a Primer on medium and small hydropower (up to hundreds of kW or low MW capacity). We hope that at the conclusion of reading this material, you will have a basic understanding of how hydropower works, how you might decide if you have a potentially viable hydropower site, and what are the steps involved in planning and building a hydropower system (including environmental concerns, permissions, etc…).

This Primer will focus on systems of less than 10 MW capacity, and specifically on “run-of-river” types schemes where there is no appreciable storage of water behind dams. In many instances these schemes have no dams or weirs and use only the natural river fall. Because of this, “run-of-river” schemes tend to be much more environmentally friendly than large-scale hydropower systems.

Southeast Power Engineering uses the theories and procedures described on this web site for every project and combines that work with detailed economic analysis to help guarantee success.

If the reader wishes to go into greater depth than is provided in these pages there are a wealth of resources available on the Internet (some noted in our “LINKS” section).

What is covered in the Hydropower section

  • How does hydropower work
  • Typical hydropower system layout
  • Types of hydropower turbines (more details)
  • Environmental factors
  • Steps for developing a hydropower site

Why Hydropower

In 2007 the UK emitted 545.7 million tons of the greenhouse gas CO2 into the atmosphere. Nearly 40% of this gas was produced by the generation of electricity as is shown in the following graph of sources of CO2 in the UK.


The UK has made the commitment to reduce these CO2 emissions to less than 60% of the 1990 levels (589 million tons in 1990) by 2050 with significant progress made by 2020. Additionally, the UK will need around 30-35GW of new electricity generation capacity over the 20 years as many of the current coal and nuclear power stations, built in the 1960s and 1970s, reach the end of their lives and are set to close. Given the expected increase in energy needs in the UK by 2050, the reduction in CO2 from power plants in reality must be reduced by 90% from current levels.

One GWh of electric energy produced means a reduction of CO2 emissions by approximately 480 tonnes (or 1,058,218 lbs). This is the same as a power plant putting out an average of 114 kW of power.

So that is an argument for any CO2 free, renewable energy source.

Hydropower has a number of advantages over solar or wind power, the other two most common clean electricity sources.

  • High efficiency (70%-90%) which is more efficient than wind, wave, or solar power.
  • High capacity factor (typically greater than 50%), which compares to 10% for solar and 30% for wind.
    • Capacity factor is the ratio of ENERGY generated over a year to the ENERGY that would be produced if the system were at 100% all the time for that same year.
    • To illuminate this point, solar systems do not produce energy in the dark. Also during daylight, the light level is varying with time of day and with cloud cover.
  • Power output correlates with higher winter demand (water flows are typically higher in winter)
  • Slow time variation – varies over periods of hours or days and not in periods of minutes as wind and solar do.
  • Hydropower systems can be used where dams, weirs, or mills operated in the past to take advantage of any remaining infrastructure.
  • Robust, relatively simple technology that can last as long as 50 years or more. Small or medium hydropower; and specifically “run-of-river” hydropower has a low environmental impact.