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Posted 7/14/2014

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By Sean McBride
Corporate Communications

Earlier this year, the Charleston District’s St. Stephen Powerhouse hydropower units hit 999,999 megawatt hours (MWH) produced on the plant revenue meter. Why is that significant? Because there is no 1,000,000 on the meter, so it rolled over back to zero.

The St. Stephen Powerhouse began operations in 1985 and this was just the sixth time that this mark has been reached. Previously, the mark was reached in 1990, 1993, 1997, 2003 and 2006.

Over the lifespan of the project, the facility has produced an average of 566 MWH per day. If you did the math, that would mean that the meter would roll over just less than every five years. But, as the numbers show, one million MWH occurs with varying frequency. That’s because there were many years when there wasn’t enough water flowing from the upstate, down the Santee River, through the Rediversion Canal and through the powerhouse generators to produce as many MWH.

“The number of MWH produced is directly related to how much water flows through the turbine-generators,” said Jim Carter, operations project manager. “2013 was a great year for generation, due to lots of water, but for a while before that, there was hardly any water.”

For comparison, in 2013, the powerhouse produced 354,411 MWH, which hadn’t been produced in the previous three and a half years combined. The reason this is significant relates to the cost of power to Santee Cooper, the power company that is supplied by the hydropower that is produced by the St. Stephen Powerhouse.

“When Santee Cooper gets power from us, they get it at low cost, because hydropower is very cost-efficient,” said Carter. “When they can’t get it from us, they have to get it from a more expensive source. Hydropower is basically a free energy source. Natural gas is the lowest cost replacement power when compared to coal or nuclear, but hydropower is the most environmentally friendly and low-cost overall.”

The St. Stephen Powerhouse typically produces enough MWH to power 40,000 homes on the Santee Cooper power grid. That number is based on the average kilowatt hours used by a home per year versus what is produced by the powerhouse. But the value of energy produced at the powerhouse goes beyond just power. The powerhouse was built as part of the Cooper River Rediversion Project, which diverted water flow and saves taxpayers $13-18 million per year in dredging costs in Charleston Harbor from reduced sedimentation flow through the Cooper River.

In 2035, the Charleston District is scheduled to hand control of the St. Stephen Powerhouse over to Santee Cooper as part of the original 50-year agreement that was signed. But before then, expect to see the MWH meter roll over several more times.

civil works hydropower st. stephen