Generally low head turbines are going to be of the reaction type. The water passing through a reaction turbine loses its energy, or pressure, as it passes the turbine blades. The turbine must be encased in a pressurized housing, and fully submerged in water. This is different from an impulse turbine which changes the velocity of the water. Water is directed at the blades of an impulse turbine with a high velocity nozzle, and the velocity of the water turns the blades. An impulse turbine can be open to the air, and only needs a casing to control splash. All turbine types can be classified into one of these two groups.
Figure 1: Types of Hydropower turbines
The turbines are listed from higher head to lower head. The turbines highlighted with red are considered low head turbines, and examples of these turbines are discussed in this report.
The two conditions that are used to choose the appropriate turbine for a site are head and flow rate. The head is measured as the vertical distance between the highest and lowest water surface, minus any losses that occur through that drop (such as pipe friction). The flow rate is a measure of all of the water that will be passing through the turbine. Turbines can generally operate through a range of flow rates, but the size of that range varies with turbine type. Also the efficiency of the turbine lowers as the flow rate varies from the designed flow rate. This is something to consider when choosing a turbine for a site. It is possible that the best turbine may not utilize all of the flow available at high flow, so that the range can also cover the low flow periods. A detailed analysis of the flow over time will need to be performed to choose a turbine that is best suited for a site. The power produced by a site can be estimated using the following equation, where head is in feet and flow is in cubic feet per second.
This equation can provide an estimate of the power available at a site, either high or low head, but the turbine manufacturer should be contacted regarding the efficiency of a particular turbine, and how that efficiency may vary with flow rate.
Turbine selection charts can be used as a starting point to determine which turbine may be applicable to a particular site. The ranges shown are approximate, and the turbine manufacturer should be contacted to verify that the turbine is appropriate for the site’s specific conditions. The turbines may operate within the whole range shown, but the efficiency may decrease as you approach the corners or edges of the range. Please use these charts as a starting point and a visual approximatation of the range of turbine applicability. This is also not an exhaustive listing of all turbines available. These are the turbines that we believe will be appropriate in Colorado’s irrigation infrastructure for sites in the low head range, between 5 and 30 feet. For clarity the charts have been divided into two subranges.
Following this text there is a link to each of the turbines or manufacturers shown in the tables below.
Figure 2: Very Low Head range turbine selection chart
Figure 3: Low Head range turbine selection chart
Ossberger - Cross Flow Turbine http://www.hts-inc.com/ossbergerturbines.html
Energy Systems and Design LH1000 http://www.microhydropower.com/
Power Pal http://www.powerpal.com
Canyon Hydro - Kaplan Turbine www.canyonhydro.com
Toshiba International - Hydro-eKIDS www.tic.toshiba.com.au/hydro-ekids__8482_
Ossberger Canada - Moveable Power House http://www.hsi-hydro.com/cd/
Mavel - MicroTurbines www.mavel.cz
Voith Hydro - Mini Hydro www.us.voithhydro.com/vh_en_pas_small_hydro.htm
Voith Hydro - Eco Flow Turbine www.koessler.com
Andritz Hydro - Kaplan Turbines www.andritz.com
Gilkes - Francis Turbine www.gilkes.com
Clean Power AS - Turbinator http://www.cleanpower.no/Home.aspx
Very Low Head Turbine (VLH) www.vlh-turbine.com
Natel Energy - Hydroengine www.natelenergy.com
HydroCoil Power www.hydrocoilpower.com
Ritz-Atro Hydrodynamic Screw Turbine www.ritz-atro.de
3 Helix Power - Archimedean Screw http://www.3helixpower.com/
Alternative Hydro Solutions - Darrieus Water Turbine www.althydrosolutions.com
New Energy Corp - EnCrrent Power Generation System http://newenergycorp.ca
HydroVolts - www.hydrovolts.com
Elephant Butte Irrgation District http://www.ebid-nm.org/
Water Vortex Power Plant http://www.zotloeterer.com/our_company.php