An Advance in Low Head Hydro Technology Opens New Sites for Potential Electricity Generation

This entry is the latest in a Worldwatch blog series on innovations in the climate and energy world.

Natel's SLH turbine, courtesy of

According to BP’s Statistical Review of World Energy for 2011, global hydropower consumption set an all-time high by growing 5.3 percent in 2010, led by China and Canada. The 2010 International Energy Outlook, developed by the U.S. Energy Information Administration, projects that renewable energy will be the fastest growing source of electricity through 2035, 53 percent of which will be hydropower (mostly in non-OECD nations). But in the United States—the world’s second largest consumer of electricity—hydropower potential is almost fully tapped, and the future of energy is in natural gas and other renewables.

Isn’t it?

A recent innovation by Natel, a California-based engineering firm, can produce power from ‘low head’ dams and other existing structures. ‘Head’ is a measurement of water pressure and at dams the head is often proportional to the height of the water behind the dam. By increasing the height of the water level behind them, dams increase the force of the falling water on the turbines within the dam, thereby increasing electrical generation capacity. Low head dams are less than 30 feet tall and typically have generators smaller than 10 megawatts (MW), whereas high head dams are over 500 feet tall and have generators of 30 MW or more. However, even a low head dam could generate up to 200 MW if there were a large enough rate of water flow and enough turbines.

Dams store water as a source of fast, reliable, and zero-emission energy generation, and they can serve as a baseload source of electricity to link with variable wind and solar generation. Large dams produce a lot of power but often are expensive, have lengthy construction times, and significantly alter riparian ecosystems. A low-head hydropower system like the one Natel has designed can be placed on existing water management structures including reservoirs, irrigation canals, municipal water systems, wastewater treatment plants, and other industrial water systems. This makes the environmental impact of this innovation relatively minimal, although fish passages or riverbank habitats must still be considered during installation.

One Natel turbine, called the SLH, can provide power ranging from six kilowatts to two megawatts. The SLH design is strikingly different from conventional low head turbines in that each SLH module has a series of horizontally oriented curved blades, similar to a ladder, that are connected to a chain. As the entering water forces the blades to spin, the chain spins a shaft which powers an electric generator. The SLH blades move like a conveyor belt or the caterpillar tracks on a tank, whereas other low head turbines are shaped like boat propellers, screws or wheels.

The SLH turbine operates at a wide range of pressures and water flows, has a relatively high hydraulic efficiency of 80 percent, and is priced competitively with other types of low-head turbines. The SLH has been specifically designed for existing water management structures, simplifying the installation and maintenance procedures. The integrated electrical components allow for operators to program the generator and connect to the grid with relative ease. The turbine housing can be easily removed for maintenance, and allows fish and debris to pass through without damage.

Does it pass the laugh test?

Definitely. Natel installed its first commercial system— a 10 kW generator that operates on a head of 9 feet — in December 2009 at an irrigation ditch in Buckeye, Arizona. The company has launched a few other pilot projects, and five more projects are scheduled for completion by the end of 2011.

How scalable is it?

Very – only 3 percent of the existing 80,000 dams in the United States are used to generate power. 40,000 of these dams are less than 25 feet tall and therefore suitable only for low head hydro. A 2004 DOE report identified 10,100 additional undeveloped sites across the U.S. that would be suitable for low head hydropower (between 5 and 20 feet tall, not in wilderness or other excluded areas, and within one mile of both roads and power transmission infrastructure).

What does it bring to the table?

The DOE reports that currently low head hydro generates only 14,000 GWh of power annually, while the 10,100 undeveloped sites could potentially produce 622,000. As a comparison, the U.S. currently produces 250,000 GWh of hydropower each year and consumes about 3,750,000 GWh of electricity in total. Judging by these figures, the U.S. could meet a large percentage of its electricity demand (without developing any new dam sites or on-site greenhouse gas emissions) by installing low head hydropower on the 40,000 existing man-made structures eligible for such development.

What is the biggest obstacle to success?

Due to the precision required in manufacturing, costs for conventional turbines hover at around $3,000/kW and around $1,700/kW for the SLH. This high price point hinders the low head hydropower industry. For undeveloped sites, earthwork, structural engineering, and other project costs may also be substantial, further reducing the return on investment. Natel claims that the SLH could cost $1,000/kW and a project could have a payback period of under seven years if the turbines were produced at a commercial scale.

How close is it to commercialization?

The federal government is pushing low head hydropower towards commercialization. Natel received a Small Business Innovation Research grant from the Department of Energy to cut the cost of low head hydromachinery. Congress also passed the Hydropower Improvement Act in March, which Senator Murkowski (R-AK) says “emphasizes the need to improve efficiency at existing facilities and to tap into the hydropower potential at existing non-powered dams.” Bipartisan legislation that could earn a production tax credit for hydropower is currently in the House of Representatives.

The final word(s):

There is enormous potential for supplying clean energy and creating jobs by installing low head hydro throughout the U.S. Installing the turbines first on existing water management structures makes the most sense both financially and environmentally. If federal support can bring down costs of low head turbines as they have for wind and solar, innovations like low head hydropower can become a key component of our renewable energy future.

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