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Hydropower


Over the last fifty years, a vast number of Americans have reaped the benefits of hydropower.  Hydropower, or electricity produced from moving water, does not produce solid, liquid, or gaseous pollutants, and  it is renewable as water is considered an inexhaustible resource.  The Hoover Dam, Niagara Power Plant, and their large and small relatives are responsible for contributing more than 90% of all the renewable electric energy produced in the United States . 

Large-scale hydropower, or systems producing over 30 megawatts, are what often come to mind when one thinks of this power source.  Hydropower systems such as Hoover Dam, the powerhouse for Las Vegas and parts of California, function by backing up a river within a canyon to create a deep, slow-moving body of water behind a concrete dam.  The force of water being let out through the dam, either at a constant rate or certain times of the day or seasons of the year, generates electricity that is sent to remote regions via a power lines.  Other large dam systems generate energy through a process of moving water from different elevations within a multi-dam system.

However clean, such hydroelectric systems are not truly environmentally-friendly.   Large-scale hydropower has serious consequences for native species, local lifestyles, and landscape.  Large dams in the Pacific Northwest have hindered salmon migrations and adversely affected the salmon population, archeologically and anthropologically valuable canyons have been flooded along the Colorado River in the West, and hundreds of residents have been displaced in the flooding that following building a large dam.  The following environmental effects can have drastic, documented consequences upon river species and ecosystems:

  • disruptions to river water temperature and composition,
  • barring species? migrations routes, and
  • changes to natural river flow and intensity (including peak flood seasons).

The Low-Impact Alternatives

Green Energy Ohio and many other environmental groups around the nation advocate small-scale hydropower, or systems under 30 megawatts.  Related systems are mini hydro and micro hydro home-scale systems, which produce up to 1 megawatt and 100 kilowatts, respectively. An average micro-hydro turbine can produce anywhere from 1 kWh (1,000 watt-hours) to 30 kWh per day.  Without particular energy-efficiency measures, the average American home uses 10 - 15kWh of energy per day.

The Green-e certification program analyses different types of hydropower. Generally, only small hydro (dams 30 megawatts or less) and LIH facilities qualify. The Low Impact Hydropower Institute certifies dams as truly low-impact by studying the total environmental impacts of a particular hydropower dam.  The Low Impact Hydropower Institute has created a Low Impact Hydropower Certification program to identify and reward efforts by dam owners to minimize the impacts of their hydropower dams. The program certifies hydropower facilities with impacts that are low compared to other hydropower facilities based on eight environmental criteria:
1. river flows
2. water quality
3. fish passage and protection
4. watershed protection
5. threatened & endangered species protection
6. cultural resource protection
7. recreation
8. facilities recommended for removal

What it looks like

Hydro systems have smaller battery banks than their output would suggest. With a constant flow of water, these systems only need to compensate for the occasional demand stress on the system.  Conversely, solar and wind systems store power for windless or cloudy weather.

How it works

Standard micro-hydro systems are made of the following key components:

  • Penstock, the pipeline carrying water from source to turbine.
  • Turbine, which transforms the energy of the flowing water into rotational energy.
  • Alternator or generator, which transforms the energy of motion into electricity.
  • Regulator, which either controls the electricity produced by the generator, or reroutes excess energy.
  • Wiring delivering the electricity to either the power grid, home, or storage batteries.
  • Batteries (optional) to store the electricity.
  • Inverter (on DC-producing systems) to convert the electricity to the standard AC current used in the home.

A key component of the system's functionality is the height and pressure of falling water, known as "head." Head is a function of the height of the fall and the characteristics of the channel, and can be calculated by a professional, or on your own using the techniques mentioned in the "Steps to Micro-Hydro" section.  The higher the head, the less water needed to produce power, and the smaller, cheaper, and more efficient equipment can be used in your system.  A "high head" site typically has a height of over 10 feet, whereas shorter drops are referred to as "low head." Sites with drops of less than 2 feet may not support a system.

The power available at a site is the product of the flow volume and head.  Flow volume is measured in cubic feet per second (cfs) or gallons per minute (gpm), one cubic foot equaling 7.48 gallons.

Run-of-the-river plants can be designed using large flow rates with low head or small flow rates with high head.

Drop-in-the-creek generators are options for sites with low head (1 - 2 feet) and high volume.

What it can do

Micro-hydro, like other forms of renewable energy, is a more environmentally-benign, and can be more reliable than traditional sources of power.  Systems that hook into a home or business provide a back-up source of power during outages.  Micro-hydro production also cumulates nicely over time, as power is generated 24 hours a day, under any weather conditions.  Homestead systems produces systems often produce enough power to run several refrigerators and space heaters.

How much it costs

On the right site, a hydropower system can cost as little as one-tenth the cost of a photovoltaic (solar power) system producing the same amount.

Steps to Micro-Hydro

These steps are intended to serve as a guideline only; you may find that your particular area has more, less, or different additions to this list.

1. Determine legal restrictions and requirements in your area.  Use and alternation of water systems are regulated in many areas of the country, regardless of whether or not they are on private property. Before you begin, you must consider how your work will alter wildlife habitat both on the site, near the stream, and down stream of your installation.  Will you be diverting water flow? Will you be disrupting habitat?  Depending on the land you are considering, you may need permits from the US Fish and Wildlife Service, the US Forest Service or Bureau of Land Management (if the land is federally owned).

Governmental points of contact for other permitting information and building
restrictions are your county engineer, state energy office, Federal Energy Regulatory
Commission and the US Army Corps of Engineers.

2. Determine head.  There are two types of head to consider, gross (or 'static') and net (or 'dynamic') head.  Gross head is the vertical distance between the penstock (the pipe that takes water from the stream) and where the water leaves the turbine.  Net head is the gross head, minus pressure losses due to friction and turbulence.  Minimizing length of, and turns in, the pipeline can prevent some losses to pressure.

To determine gross head, you can hire a professional to survey the site, or try the hose method.  With the hose method, two people work together to stretch a hose down the stream from the proposed penstock (intake pipeline) site.  With a funnel attached to the hose, Person A holds the funnel underwater to fill the hose.  Person B lifts the downstream end of the tube until water stops flowing from it.  The gross head is the vertical between Person B's end of the tube and the surface of the stream.   This process is repeated for the length of the stream between the proposed penstock site, and the proposed turbine site.  The sum of the measurements is a rough estimate of the gross head for the micro-hydropower site.

3. Determine water flow.  Your profession site surveyor will be able to calculate this information for you.  Otherwise, the US Geological Survey posts surface water flow data on their web site, and the county engineer, local water supplier, or flood control authorities may also be helpful in gathering this information.   On small streams, you may be able to measure the flow yourself using the bucket method.  Dam the stream to divert the water flow into a bucket, and time the rate at which the bucket fills.  Divide the number of gallons filled by the time to determine gallon-per-minute (or second) flow rate.  One cubic foot per second is equivalent to 448.8 gallons per minute.

4. Determining power.  The potential power for you site can be determined by multiplying:

Gross Head (feet) X Flow Rate (feet / per second) X System Efficiency (decimal value) X .085 (for calculations in American units) = Power (kW)

System efficiency ranges from 40% - 70%, with an average efficiency rating of 55% (.55).   Don't forget to consider seasonal deviations in your flow rate!

5. Determine economic feasibility.  One of the simplest ways to determine whether or not the project is economically feasible is to add up costs (developing, operating, and maintaining the site over the life of the system), and divide the amount by the system's productive capacity on your site. Compare this price-per-watt number with the costs of power from another source.   Net metering may also be an option for you, whereby excess power produced by your system would be fed back into the utility grid and credited to your account.

Low-impact hydro and Ohio

Belleville, Ohio

The City of Columbus operates O'Shaughnessy Dam, a low-impact hydropower installation on the Scioto River, at a head of 5.5 meters. The installation consists of two turbines spinning at 64.3 rpm.  Each turbine has an output capacity of 25.9 megawatts.  Photo below from the 2003 Central Ohio Solar Tour as participants view base of O'Shaughnessy Dam near turbine room.



More Information

US Department of Energy's Renewable Energy Clearinghouse: 1.800.363.3732 or www.eren.doe.gov.
 
Contributors and Works Consulted:

"Divided Over Dams." The American Experience, PBS, http://www.pbs.org/wgbh/amex/hoover/sfeature/damdivided.html.

Katya Chistik, Project Coordinator, Green Energy Ohio.

Ron Feltenberger, formerly Vice President and Hydro System Designer, Universal Electric Power.