WASTEWATER FOR SOLAR PWR PLANTS

Waste not: Mohave Sun Power's solution for water scarcity
Rikki Stanich, 12 February 2010 (CSP Today)

"…[D]uring the stakeholder engagement phase of the [Mohave Sun Power 340MW Arizona concentrating solar power plant] planning procedure… concerns of local citizens and state agencies…[led the company to] the idea of using effluent from a nearby city’s wastewater treatment plant [for cooling]…

"…From an economic, environmental, and operational perspective, the use of wastewater for wet cooling presented a more viable option than that of groundwater extraction or dry cooling…The proposed Hualapai Valley Solar project will be sited on 4000 acres of private land in Mohave County, Arizona. It will use parabolic trough technology and will have thermal storage capacity. The project is scheduled to come online in late-2013…"

Artist's rendering of a parabolic trough solar power plant with thermal storage capability. The Hualapai Valley Solar project will be much bigger. (click to enlarge)

[Greg Bartlett, project director, Hualapai Valley Solar Project/managing director & co-founder, Mohave Sun Power:] "The project uses water for cooling, mirror washing, boiler makeup, potable uses, and other miscellaneous on-site uses, with the vast majority (approximately 90 percent) being used for cooling…Cooling water is used to condense the steam…to complete the steam cycle… [T]o re-use the cooling water, it must be cooled [by evaporation] so that it doesn't continuously increase in temperature…

"Although our project site was selected for its access to adequate, well-documented groundwater, we are pursuing the use of treated wastewater (effluent) as our primary source of cooling water…The city of Kingman is upgrading an existing wastewater treatment plant (WWTP), located approximately 20 miles from our project site…A majority of the output of the plant, the treated wastewater, is currently being evaporated in a large wetland area…"

The facts on power plant water use. (click to enlarge)

[Greg Bartlett, project director, Hualapai Valley Solar Project/managing director & co-founder, Mohave Sun Power:] "We intend to take delivery of the effluent at the boundary of the City's WWTP, and convey the wastewater to our project via a pipeline that we would finance. In addition, we would pay the City for the effluent, adding to the local economic benefits of our project…[T]he City could initially provide as much as 60-75 percent of our cooling water needs…[I]t is possible that we could use effluent for 100 percent of our cooling water needs within the first 5-10 years…The re-use of water…that is currently being evaporated (wasted), really fits into our vision of renewable energy…Public and governmental response has been very positive…

"Dry cooling systems cost more to build, and result in a [7-10%] higher cost to produce electricity…[D]ry cooling systems consume more electricity and make more noise (both a result of multiple, massive cooling fans), and they have more of a visual impact (due to much higher cooling towers…Equally significant, dry cooling produces less electricity for the grid and therefore offsets less greenhouse gas emissions…The re-use of wastewater is not a new concept, and all of the regulatory issues [are settled]…[F]or a solar plant that is best sited in hot, dry, remote areas, it is rare to find a city wastewater treatment plant located close by…This is a testament to our siting efforts…[but there] is no reason that every wet cooled thermal power plant could not use effluent…"