Now that you have determined net head and design flow of your stream, it’s time to think about the kind of turbine that is best suited to your site. Specifically, the turbine is the piece of the hydropower system that collects the energy input; it’s the interface between the water in the penstock and the shaft connected to the power generator. Turbines are different from water wheels of old because water is delivered at high pressure and velocity through a nozzle that focuses a jet of water onto the runner. The runner rotates to transfer energy to the generator power shaft. Different turbines have different types of runners, and the turbine’s housing design is integrated with the runner in terms of how the water impacts and reacts with the runner and flows through the turbine and down into the tailrace. Choosing a Turbine Choice of the best turbine design for your site depends upon the site’s characteristics, as well as the head and flow. Most small hydro systems employ direct drive between the runner and the generator, meaning that there are no efficiency robbing belts, gears, or pulleys. Belts and pulleys may be required in larger systems so that both the turbine and generator can run at their respective optimal speeds.
Hydropower Resources
There are many local, state, and federal guidelines and laws surrounding the use of water, water rights, and alteration of streams and wetlands. Due diligence is required to identify all of the legal issues that apply to your site. For larger, grid-tied hydro systems, you will need to look into licensing, permitting, design specifications, and fees that may be required. Here are some places to start your research (see Resources for websites):
• The Environmental Protection Agency’s Clean Water Act Section 401 Water Quality Certificate provides guidance on water quality standards that may be required by your state for projects that impact streams or wetlands.
• The Federal Energy Regulatory Commission’s responsibilities include licensing of new or existing power generation projects and oversight of all ongoing project operations, including dam safety inspections and environmental monitoring.
• The U. S. Army Corps of Engineers has jurisdiction over most U. S. waterways and wetlands, and offers some useful design guides.
There are two basic approaches to small-scale hydro turbines, categorized by how they capture the energy in water. You may have a very small stream with a very high head that creates lots of pressure but perhaps relatively little flow. Or you may have access to a river meandering through your property, powerful and high-flowing but without much head. Each situation requires a specific approach to capturing the available resource, and each turbine can be customized by the manufacturer, and by your control of the water flow hitting the turbine, for best efficiency at a specific site.
Impulse Turbines
Impulse turbines work well in situations with high water pressure (head) and low-to-medium water flow. Impulse turbines are not submersed in water; they operate in the air and receive water from an inlet pipe, sending it through one or more nozzles to create a focused, high-velocity spray. Additional nozzles may be used to increase the power output, but this can be achieved only when there is enough supporting water volume. The water jet(s) hits the runner’s paddles, causing it to spin. Two common (and similar) turbine designs use Pelton and Turgo runners. These runners have a number of cups around the perimeter to catch the jet of water. A good example of an impulse turbine is the alternator-based micro-hydro generator made by Harris Hydro. Beneath the housing is a Peltonwheel runner connected to the shaft of the alternator. These micro-hydro systems can produce up to 2,000 watts of DC power, depending on the water flow rate, pressure, and output voltage. Useful power output starts at 25 feet of head and a water flow rate of 15 gpm, a configuration that will yield about 25 watts of power.
Hydropower Resources
There are many local, state, and federal guidelines and laws surrounding the use of water, water rights, and alteration of streams and wetlands. Due diligence is required to identify all of the legal issues that apply to your site. For larger, grid-tied hydro systems, you will need to look into licensing, permitting, design specifications, and fees that may be required. Here are some places to start your research (see Resources for websites):
• The Environmental Protection Agency’s Clean Water Act Section 401 Water Quality Certificate provides guidance on water quality standards that may be required by your state for projects that impact streams or wetlands.
• The Federal Energy Regulatory Commission’s responsibilities include licensing of new or existing power generation projects and oversight of all ongoing project operations, including dam safety inspections and environmental monitoring.
• The U. S. Army Corps of Engineers has jurisdiction over most U. S. waterways and wetlands, and offers some useful design guides.
There are two basic approaches to small-scale hydro turbines, categorized by how they capture the energy in water. You may have a very small stream with a very high head that creates lots of pressure but perhaps relatively little flow. Or you may have access to a river meandering through your property, powerful and high-flowing but without much head. Each situation requires a specific approach to capturing the available resource, and each turbine can be customized by the manufacturer, and by your control of the water flow hitting the turbine, for best efficiency at a specific site.
Impulse Turbines
Impulse turbines work well in situations with high water pressure (head) and low-to-medium water flow. Impulse turbines are not submersed in water; they operate in the air and receive water from an inlet pipe, sending it through one or more nozzles to create a focused, high-velocity spray. Additional nozzles may be used to increase the power output, but this can be achieved only when there is enough supporting water volume. The water jet(s) hits the runner’s paddles, causing it to spin. Two common (and similar) turbine designs use Pelton and Turgo runners. These runners have a number of cups around the perimeter to catch the jet of water. A good example of an impulse turbine is the alternator-based micro-hydro generator made by Harris Hydro. Beneath the housing is a Peltonwheel runner connected to the shaft of the alternator. These micro-hydro systems can produce up to 2,000 watts of DC power, depending on the water flow rate, pressure, and output voltage. Useful power output starts at 25 feet of head and a water flow rate of 15 gpm, a configuration that will yield about 25 watts of power.
Crossflow Turbines
A crossflow turbine is a sort of modified impulse
turbine where water flows in high volume and
with low pressure through a large opening, rather
than through small, high-pressure nozzles. Water
passes over the runner blades in a somewhat
similar fashion to a water wheel.
