Hydropower in Arkansas

Electricity production in Arkansas is similar by source to the rest of the country. For Arkansas, the percentages are coal, 47 percent, nuclear 25 percent, natural gas 15 percent; and hydroelectric, 10 percent. Sustainable sources such as wind and solar electric represent only a fraction of a percent.

An ideal power source would be sustainable, clean and available when needed in the amounts needed. Hydroelectric energy production comes close to this ideal.

Facilities range in size from the generators at Remmel Dam on Lake Catherine with a 9.3 megawatt capacity to the dam at Bull Shoals with 380 megawatts. The dam on Lake Dardanelle comes in second with a capacity of 161 megawatts. Total hydropower in Arkansas is 1,374 megawatts from 15 facilities.

Discussions about energy supplies can get terribly muddled without a clear understanding of three terms: power, energy and capacity factor. Power is the ability to do work, energy is the actual work done and capacity factor is the amount of time actually doing the work.

An example may be helpful. The generators on Lake Dardanelle have a rating of 161 megawatts (power). When the generators run at this rate for one hour, they will produce 161 megawatt-hours (energy). To get the maximum possible annual energy produced, simply multiply by the number of hours in a year.

But they don’t run all the time. Too much water due to heavy upstream rainfall, or too little water, or even varying demands limit the amount of time the dam is generating (capacity factor). The average capacity factor for hydropower in Arkansas is about .47. This means on an annual basis, hydroelectric facilities produce about 47 percent of the energy theoretically possible.

Capacity factors for other energy sources for comparison are about 90 percent for nuclear and 17 percent for solar electric systems. A high capacity factor is not necessarily good, nor a low one bad as the important thing is matching supply with demand. A large reservoir like Bull Shoals is valuable as both long term and short term energy storage. Water accumulates during the winter when there is lower demand for electricity and then is released on hot afternoons in the summer to generate power “on demand.”

The ability to rapidly increase power production is important to meet peak demands. On the other hand, nuclear power reactors are better at providing base load power due to the fact that they run best a full power and are not capable of powering up and down to meet variable loads.

Hydropower is not a perfect solution due to several drawbacks. To be economically practical, they need to be large; therefore, large amounts of land are put underwater. More than 5 million people were displaced by the construction of the Three Gorges Dam in China. The remains of an unusual resort community called Monte Ne lies submerged under Beaver Lake. Occasional mechanical failures of dams have had catastrophic results, and reservoirs have limited lifetimes due to silt accumulation which ultimately limits power production.

Virtually all suitable sites for hydropower in Arkansas have been used. The last battle for a large reservoir, at Gilbert, resulted in the creation of the Buffalo National River. It is over 135 miles and the first federally protected river with the highest bluff and the tallest waterfall between the Rockies and the Appalachians.

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