Reducing Big Problem With Little Hydro Plants

Hydropower will never be the complete answer to emissions-free energy production in the U.S., but a strong case can be made for it becoming a useful part of the answer.
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The leading cause of climate change today is the burning of fossil fuels related to energy production. Numerous proposals to reduce greenhouse gas emissions have included implementing cap-and-trade markets, applying carbon taxes and encouraging research and development into promising new energy production technologies such as fuel cells, ocean power and ethanol. We are currently at the vanguard of discovering which of these methods will prove fruitful, politically palatable and cost-effective.

As we proceed, it is worthwhile to continue exploring all of our available options, to help diversify avenues of approach into this difficult and pressing problem.

Another approach to reducing greenhouse gas emissions, therefore, involves more actively switching to proven renewable technologies in the production of electricity and reducing the use of fossil fuels in electricity production.

This is the main objective of the Renewable Portfolio Standards being passed in many states across the U.S. In 2003 only three states had passed legislation implementing renewable portfolio standards, but by 2007 the number had grown to 28, and the U.S. House of Representatives introduced legislation to implement a federal-level RPS at 15 percent of electricity generation.

Renewable alternatives to fossil fuel use include solar, wind, geothermal, biomass and hydroelectric power.

Currently, hydroelectric power is far and away the main renewable in use, satisfying two-thirds of all renewable electricity production in the United States. A proven technology, its benefits reach beyond just emissions-free electric power. Entirely domestic, hydropower relies on no foreign imports for production, it is decentralized and it has excellent reliability and energy-efficiency properties.

Not without its detractions, of course, hydropower does affect fishery resources and river ecosystems. Often underemphasized, however, is that there are gradations of hydropower production, and “small” or “micro” hydropower systems have extremely minimal impacts on river ecosystems. The exact definitions vary, but small hydropower plants are generally considered those that generate between 30 megawatts and one megawatt of power, and micro hydropower systems are those that produce enough power to supply a small village or town: less than one megawatt.

In the early 1990s the Department of Energy began a concerted effort to assess the total amount of undeveloped hydropower resources within the United States, part of a larger national energy strategy to identify all available energy resources within the U.S. In 1998 the first report — based on a compilation of previously identified developable sites, with the source data coming from existing state- and federal-level databases — came out, concentrating on conventional (i.e., large) hydropower capacity development.

Understanding that environmental concerns limited the development of much of this potential, the next report, which came out in 2004, concentrated on sites with potential for smaller-scale development. The unique assessment method used in the study identified both previously known sites and new ones, combining digital elevation models with geographic information system tools to estimate the power potential of a mathematical analog of every natural stream segment in the country.

This gross power “potential” was re-evaluated in 2006. The figure fell as a result of removing sites in land protected from development by federal statutes and policies or because of known environmental sensitivities. The remaining power potential, referred to as gross power “available,” still amounts to more than 275,000 megawatts of capacity, distributed across the United States.

Next, the 2006 report identified all “available” resources by their feasibility. The practical feasibility of development at each site was based on three criteria: site accessibility, load or transmission proximity, and land-use and environmental sensitivities that would make development unlikely (according to data from the Conservation Biology Institute).

Finally, the ultimate estimates of the power potential at each site were based on a rigorously environmentally “friendly” development model. The model consisted of a “penstock” running parallel to the stream, culminating in a powerhouse where the “tailwater” — after turning the turbine to create electricity — returned the working flow to the stream. No dams or impoundments of any kind that would obstruct the watercourse or form a reservoir were assumed in the estimates. The model also made sure to never utilize more than half the water flow of the waterway for electricity generation and limited penstock lengths.

Table 1 displays the results of these conservative analyses, presenting for each state the small and micro “potential,” “available” and “friendly” gross power numbers. Clearly, a large potential exists for small and micro hydropower development. Even if we concentrate on just the friendly hydropower resources, the numbers imply increased hydropower resources of nearly 60,000 megawatts — a 75 percent increase from current renewable hydropower production levels. Western states dominate in friendly gross power, as they do with potential gross power, but smaller resources are still located in every state in the country.

Search Table 1 below. Source: Dept. of Energy data

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Table 2 translates these totals into carbon emissions saved. Assuming that any additional hydropower developed would essentially be in lieu of electricity generated with carbon emissions, the conversion process from megawatts potential produced to emissions saved is conducted in three steps. First, megawatt capacity is translated into kilowatt-hours produced. Then, an estimate is made of the pounds of emissions avoided per kilowatt-hour of electricity generated through hydropower. Finally, the pounds of emissions are multiplied by the measure of kilowatt-hours produced and then are converted to metric tons to produce the final “emissions” saved estimates (measured as millions of carbon emissions per metric ton).

Search Table 2 below. Source: Dept. of Energy data

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The results show that small, friendly hydropower production can contribute significantly to decreased emissions production. Compared to 2003 emissions per state (the final column in Table 2), hydropower has the potential to reduce emissions by nearly a third in at least 18 states.

But what about all those big, “unfriendly” dams already built? There’s a future for them, too.

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