BIGGER, CHEAPER SUN

CSP innovation: Technologies that crash the cost barrier; Several companies are breaking ground with new technologies that promise to drive down costs and boost efficiency
Rajesh Chhabara, 1 April 2010 (CSP Today)

"A number of innovative technologies are being developed and tested with the aim of improving efficiency, while driving down construction and operational costs of concentrated solar power plants.

"…Masdar, Abu Dhabi’s multi-faceted renewable energy initiative, turned CSP on its head with the announcement of its ‘Beam Down’ technology…[R]eversing conventional solar tower technologies, where scores of mirrors on the ground direct the solar radiation onto a receiver at the top of a tower to heat a heat transfer fluid to generate steam, Masdar’s beam down layout inverts the process…Flat mirrors placed on the ground reflect the solar radiation on to another set of mirrors, called secondary mirrors, on top of the tower, which in turn directs the radiation to a concave receiver- a liquid filled cylinder- at the base of the tower. Eliminating the need to pump heat transfer fluid up to the top of the tower enables the beam down process to bypass an energy intensive – and costly – process."

The Masdar beam-down solar power tower. (click to enlarge)

"Improving on the beam down prototype developed many years ago by the Weizmann Institute in Israel, which used a monolithic mirror at the top of the tower to redirect sun energy to a receiver on the ground, the Masdar project uses a set of 48 mirrors with a reflectivity of 98%…While the extra set of mirrors reduces cost efficiency by around 15 to 20 percent, this efficiency-loss is more than offset by removing the need to pump the fluid…Like other Masdar renewable energy projects developed for the region, the beam down process is aimed at creating power for cooling. A key challenge is presented by the UAE’s proximity to both the desert and the coast. High humidity before and after the sunset causes condensation on the mirrors, while strong wind causes the sand to stick to the mirrors, reducing reflectivity…

"The need to drive down the cost of CSP is driving several other initiatives. Early this year, the aluminium manufacturer Alcoa partnered with the National Renewable Research Laboratory (NREL) in the US to jointly test a new parabolic trough system that uses highly reflective aluminium mirrors in place of the conventional glass mirrors…[A]n all aluminium solar field can reduce the cost of a CSP project by 20% on account of lower installation costs…[T]he aluminium mirrors can be mass-produced, resulting in further cost saving due to economies of scale. Aluminium is also more sustainable, given that it can be repeatedly recycled…Alcoa expects the commercial production of aluminium troughs to begin in two-three years…"

Rendering of the HelioFocus device. (click to enlarge)

"In Israel, HelioFocus says it has developed a solar thermal system that significantly reduces the amount of land required to build a CSP plant. The system will be a six-story high parabolic dish, which will concentrate the solar radiation onto an optical receiver placed at the centre. The receiver will convert the concentrated radiation into hot air with temperatures reaching up to 1000 Celsius. The hot air will then be channelled to drive a gas turbine…The vertical design of the HelioFocus structure [also] removes the need to have a flat ground…

"Australia-based Solar Fusion Power has developed low cost wire braced heliostats to collect heat from solar radiation and uses calcium hydride as a storage medium instead of molten salt…Solar Fusion says the system can achieve 50% conversion efficiency compared with 20% efficiency that conventional CSP plants can reach. The cost reduction is achieved through higher efficiency and low cost of storage system…Tyco Flow Control has developed a mechanism that uses molten salt…for transferring heat instead of conventionally used oil. Tyco developed a pipe that is wrapped with a heat tracing cable to keep…the salt from freezing…Iberdrola is currently experimenting with this device…[M]ost of these technologies however have yet to be tested…"