Is building a small, concentrated solar power facility to boost the output of a unit currently fired by coal a good or bad thing from an environmental perspective?
The Grand Canyon chapter of the Sierra Club is grappling with that very question as Tucson Electric Power prepares to build the “Sundt Solar Boost” project alongside Sundt Unit 4, a 45-year-old, 173-MW dual-fuel unit in Tucson now fired by coal. The $7 million CSP project, which is expected to begin commercial operation by February 2013, will produce enough steam on sunny days to generate 5 MW in Unit 4’s boiler.
“Obviously there’s some good in what TEP is doing,” Sandy Barr, the Sierra Club chapter’s director, said in an interview. “It would have been much better, though, if it weren’t attached to a coal plant,” particularly one dating from the 1960s, she said.
Barr expressed concern that, by investing in an add-on to Sundt Unit 4, TEP is likely planning to continue operating the fossil unit for some time.
TEP spokesman Joseph Barrios noted that Sundt Unit 4 had been burning natural gas until two years ago. “We were looking for ways to boost the capacity of the unit and decided [the CSP add-on] would be a good demonstration project.”
Barrios said that while TEP has extensive experience with solar photovoltaic facilities, “we don’t have solar thermal” capacity but would like to test it. Like other utilities in Arizona, TEP also needs to gradually expand its use of renewables to comply with the state’s renewable portfolio standard and its 15%-by-2025 mandate.
“The decision to install the CSP system wasn’t intended as a way to extend the life of Unit 4,” Barrios said. “It was intended as a way to improve [the unit’s] productivity.” He noted that while TEP has no immediate plans for new or replacement units at Sundt, it has looked into the potential for building gas-fired combined-cycle capacity. CSP could also work with that kind of plant, Barrios said.
The Sundt Solar Boost project will employ AREVA Solar’s Compact Linear Fresnel Reflector solar steam generators. TEP said that the output of the CSP add-on is expected to reduce annual coal use at Sundt Unit 4 by 3,600 tons, and to avoid to annual release of about 8,500 tons of carbon dioxide. If the plant reverted to natural gas-firing, the CSP facility would reduce annual gas use by 46 million cubic feet, and avoid the annual release of 4,600 tons of CO2.
–Housley Carr