October 30, 2016

Student blog: Visiting Saxapahaw Hydro Plant

Nicholas Institute for Environmental Policy Solutions

By Ted Herman - Master's of Environmental Management (MEM) / MBA student

Over the last ten years, interest has flooded into the investment of small hydro plants.  Companies like Cube Hydro, formed by Dr. Kristina Johnson (previously dean of Duke's Pratt School of Engineering), have showed up on the scene, creating portfolios of small hydro assets.

In October 2016, 20 Duke graduate students ventured 20 miles due west to Saxapahaw – a small old mill town on the Haw River, where a 1.6MW run-of-the-river facility now provides up to $3500 per day in revenue to its new owner, Gravity Renewables. The facility was built in 1938 with a grant from the Tennessee Valley Authority to provide power to the cotton mill and dye house, which has since been restored into a mixed-use facility, housing condominiums, the Haw River Farmhouse Ales Brewery, and the Haw River Ballroom. (Saxapahaw, it turns out, is a lovely little town.)

Operationally, the students were given an in-depth technical tour by the facility's only operator, Kevin, who's run the plant for the past eleven years. Kevin owns Turtle Run Farm just across the river and occasionally canoes to work.  (Kevin, it turns out, is a man of many talents; he's an electrician, a farmer, and invented the "use-yer-foot" portable sink.) Despite recent investments in software systems and automation controls, stepping into the generator house felt like stepping back in time. The wiring is all knob and tube style (which hasn't been used since the '50s) and the generators themselves were all original (nearly 80 years old!).

Requirements from the US Army Corps of Engineers stipulate the amount of water that must flow over the spillway at all times. Owing to the minimal flow of the Haw River on the day of our tour, only the 600kW generator was operating. 

Kevin gave us a rundown on his daily duties: on a "normal" day he spends the bulk of his time cleaning debris out of the pit and the head gates, but frequently there is work to be done elsewhere, mostly checking sensors and doing other physical work to keep things up to snuff. Since Gravity Renewables purchased it three years ago, significant investments have been made in the plant—most notably in modernizing its control systems, which now simplify Kevin's daily duties tremendously. From his description, it sounded akin to the transformation that took place in telephony: an operator's life was previously on their feet (actually, on roller skates) all day, and now the plant nearly runs itself with automated electrical switching. The plant is fully equipped with WiFi, and sends him text notifications if an alarm is triggered. With recent interest by the Federal Energy Regulatory Commission (FERC) in cybersecurity threats, the site underwent a full-day FERC audit not long ago, where he was questioned about nearly every aspect of the plant. 

MEM candidate Colin Walker took a neat slow motion video of the generators turning... which got me thinking... how much money does each revolution generate?  At $3500 per day at full capacity (1.6MW), that's $1312.50 for the small 600kW generator, and $2187.50 for the large 1MW generator.  The generators turn at 120rpm, or, 172,800 revolutions per day.  So, if the generators are running at full capacity, each revolution of the small generator yields 0.76 cents, and for the large generator, 1.27 cents.

Overall, these fortunate 20 Duke students learned a lot about the operation of a small hydro plant, and its role in North Carolina's power mix.  Many thanks to the Duke University Energy Initiative for supporting this trip, and to Gravity Renewables for hosting us!

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