COOLING SOLAR POWER

CSP cooling options: Workarounds for water scarcity
27 August 2010 (CSP Today)

[Babul Patel, senior consultant, Nexant Inc.:] "When it comes to CSP planning, the biggest issue is the water resource, given that most CSP plants are located in arid areas. Permits and plans rely on access to and planned use of water…[It] can be a limiting factor…[A]lternatives for balance of plant and Rankine (steam) cycle cooling [are being tried]…With dry cooling an air-cooling condenser eliminates 90% of the water requirement…"

[Babul Patel, senior consultant, Nexant Inc.:] "The downside of air-cooled condensers is that on hot days [when the ambient air is too hot to cool the system], very poor performance…[lowers] the turbine’s efficiency and output during a period when you would expect it to be operating at highest efficiency…[Also,] the capital cost [for dry cooling] is [2.5 times ] higher than mechanical draft cooling towers [with water] but the operating cost is lower because you are not dealing with water - water treatment, and the discharge of waste water…"

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[Babul Patel, senior consultant, Nexant Inc.:] "The majority of that cost is the total cost of material…[and a CSP plant is] such a large surface area that there is no way to cut down the material cost…As we learn more about the layout and structure there are some cost savings, but these are miniscule compared to materials costs that are dependent on commodity prices."

[Babul Patel, senior consultant, Nexant Inc.:] "Engineers are looking at various [other] options. One is hybrid-cooling using a 25% capacity wet cooling tower and 100% capacity dry cooling…[T]he turbine steam exhaust is reverted to the wet cooling tower when ambient temperature rises…This option improves efficiency compared to a 100% dry cooling tower, and with little loss of capacity. The wet cooling tower is only used on hot days, so you would use only 10% of the water that would normally be required by a wet cooling tower…[It would be used] at around 90 degrees Fahrenheit / 32 degrees Celsius ambient temperature [about 40-60 days a year]…You still face the high capital cost outlay."

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[Babul Patel, senior consultant, Nexant Inc.:] "The Organic Rankine cycle [ORC] is another low temperature operating system using an organic compound which uses steam turbine exhaust to vaporize organic fluid that is used in another turbine cycle. It operates at lower temperature, but reduces the cooling load…as much as two-thirds…It’s a well-understood technology (it has been used in geo-thermal plants for years)…[Y]ou could piggyback the ORC on an existing system to increase the power generation of the plant and reduce the cooling requirement…[but] the return on investment is not attractive…[though] it is not [yet] clear as what the extra cost would be."

[Babul Patel, senior consultant, Nexant Inc.:] "Waste water is a viable option that is being looked at for several developments in California and Arizona…[where] the load centre and the CSP resource are in close proximity. In North Africa, on the other hand, most proposed sites are 50-100 miles from the coastal region, but most of the population is located near the coast…[Where there is] access to municipal water…costs are manageable…In the southwest US people are waking up to the fact that water is a very valuable resource…It is getting increasingly difficult to extract ground water for CSP…Most power plants are tending toward zero water discharge, where they have to treat and re-use water, which adds up to a significant capital and operating costs…[A] lot of new conventional (combined cycle and coal) plants [are being] permitted with zero liquid (water) discharge or ZLD…"