USING THE SUN’S HEAT TWICE

CSP and CHP: A good fit?
Jason Deign, 21 October 2010 (CSP Today)

"…[With] expertise is combined heat and power (CHP) generation…the thermal fluid of a CSP [solar power] plant, when not being heated by the sun [such as when there is a temporary cloud cover], could be warmed by the jacket water and back-end exhaust heat from a CHP system set to run the turbines at part or full power…

"…[W]hether it would be worthwhile in practice would depend on relative gas and electricity export prices of the site…[It is] traditionally cost prohibitive…Whether the payback from the electricity gained will justify the cost of integrating CHP into a CSP site is currently unknown…"

schematic of CHP and how it is an advantage (click to enlarge)

"Certainly, [CHP for solar power plants] is not a notion that seems to have occurred to many others. Industrial groups contacted…such as Alstom and Bechtel, were not aware of activity in this area….[and Acciona Energy, a leading builder of solar power plants, has] not carried out any research in this area…

"… Spanish CHP industry body Cogen Spain…[has] no definite study on combining cogeneration and solar thermal…[and] has not considered starting these kinds of studies…[The idea is also new] for the Combined Heat and Power Association…[but a spokesman said it] could have benefits for both industries…"

There is no theoretical reason CHP can't be incorporated into this solar power plant schematic (click to enlarge)

"…[A] challenge that some analysts foresee is that in a CSP-CHP setup one of the main benefits of cogeneration—being able to provide low-temperature heat for other uses—would be lost…[because solar power plants are typically] in the middle of the desert, probably a long way from residential or commercial demand for heat…[Therefore,] some developers are now looking at industrial applications for waste solar thermal heat…

"…[O]ne developer, at least, is excited about putting CSP and CHP together…[as] a micro-CSP-powered CHP unit to provide electricity and heating for single buildings…Initially producing 1-2 kWe and 4-8 kWth, rising to 3 kWe and 12 kWth in production, the Digespo units are “based on a vision of a society which will be more multi-layered…a prototype operating at 65% to 70% efficiency [is expected to be] in place at the Hilton Hotel in Malta next June. While not quite [a] utility-scale application…it may at least go some way towards raising awareness of the potential for using CHP alongside CSP."