Tuesday, March 29, 2011

Hydro Potential U.S.A.

Yesterday’s post made me aware that I’d never before mentioned hydro-electric power on this blog before, although it interests me a great deal. As mentioned, we obtain 6 percent of our electric power from hydro plants. I got to wondering how many such plants we have—and whether or not a nice map may be available. Thanks to the Department of Energy, I found this wondrous map here.

The map shows all existing hydro-power plants as little yellow squares. The legend, which shows areas (in purple) unsuitable for hydro power because of federal laws or policies prohibit such facilities, also shows areas which have a potential for future use (in brown). That category is labeled “high head/low power.” In trying to understand that, I gained some insight into how hydro-power is classified.

The word head refers to the height achievable for water to drop from one level to the other. A high head means greater than 500 feet, a low head less than 500 feet. The height we’re talking about here needs to be geological, thus due to the mountainous character of a region. That is why the brown areas correspond to such regions in the United States. Masses of water must be contained, and a man-made “head,” thus a reservoir resting on monstrous concrete pillars, would be too costly.

The word power refers to electrical capacity an area is capable of generating, measured in megawatts (MW). This measure is an indirect way of speaking about the amount of water available. The more water, the greater the power potential. A high power is 1 MW or greater; a low power is less than 1 MW.

MW refers to a capacity to generate power all at once, thus without reference to time. Turn it on, and its turbines put out that amount immediately. The flow of energy, the actual output, is designated by kilowatts per hour (kWh). In 2008 the U.S. generation was 4.156.7 billion kWh.

Based on the above, hydro plants are classified as High/High, High/Low, Low/High, and Low/Low. The brown area on the map (never mind DEA’s use of the word orange) represent areas where drop distances are 500 feet or greater but the water available is such that power potential is less than 1 MW. DEA’s selection of this midlevel potential is because the High/High situations have been mostly exhausted already. To look at the top category, here is a tabulation of the top five hydro-power sites in the United States sorted by capacity.

Some notes to this table:
  • Coolee, Bath County, and Hoover would be classified as High Head/High Power whereas Niagara and John Day would be classified as Low Head/High Power.
  • The actual height of Niagara Falls (the natural phenomenon) is 167 feet. The head in the power facility at Niagara Falls is achieved by diverting water from the river to another point.
  • The Bath County, Virginia facility is pumped storage, meaning that water is held in two reservoirs, one high, one below the power station. In periods of high power demand, water is released to generate power. In periods of low demand (late at night), the water is pumped back to the high reservoir.
  • The Hoover Dam is on the border between Arizona and Nevada.
What the DEA map tells me is that we do still have a lot of potential—but to exploit it we need to build many, many small plants—until the brown regions turn yellow. The Chinese have a saying: Yellow is the Middle Way—thus it is the route we must find to avoid both Scylla and Charybdis. (If that last phrase puzzles you, look here.)

1 comment:

  1. Hydro power is not without it's problems.

    Even with fish ladders and other mitigation strategy, a dam and hydro plant significantly impacts the viability of Salmonids like trout, salmon and graylings.

    Changes to the thermal profile of the rivers have significant impact to the Klamath, Dechutes, Sacramento and Colombia.