Block’s Indicator of Sustainable Growth

by Ray Block

When Arthur J Goldman, the founder of Luz abandoned the parabolic trough for his new start up BrightSource Energy, the dominant feature is a 143-metre central power tower.

On top of the tower, 1600 double tracking heliostats (small mirrors) reflect sunlight on to a boiler to produce high temperature steam.

The company has contracts with the two largest utilities in California- PGE and SCE to deliver 2.6 GW of solar power from 2013 onward. It will start with a 100 MW unit at Ivanpah, with construction commencing in 2010. A new company Ivanpah Solar, bringing in the large specialist construction group Bechtel, as an equity partner will later be expanded to 440 MW, with the addition of three further solar plants.

BrightSource also intends to install 900 MW of solar power at Coyote Springs, Nevada, largely to fulfil contract agreements with the Californian utilities. Other expansion plans are for solar plants in Arizona and New Mexico.

With a much smaller area of land and less water usage, the power tower has cost advantages over the solar trough, and the energy efficiency can be as high as 34 per cent. But there is one major difficulty still to be overcome. The Andasol plants in Spain are fitted with thermal storage capability of 7.5 hours, which allows the operators of the power grid to rely on the solar plant to deliver power for at least two hours, irrespective of the cloud cover. BrightSource doesn’t have thermal storage capability at this stage.

Another company using the power tower concept is eSolar. Little more than two years old, founder Bill Gross, an entrepreneur in computer software has moved very quickly into CSP, with a power tower concept and thousands of small flat mirrors similar to BrightSource. A man in a hurry, Gross’ company already opened a demonstration plant in August 2009 with capacity of 5 MW in Lancaster, CA to prove that the technology produces cost effective electricity, and can be replicated.

The main cost of the plant is the steel and the actuator for controlling the small flat modular mirrors. The steel holds the mirror in shape without distorting, to stay in a perfect parabola. “Because we use a one square meter mirror, we use half the steel of a solar trough,” says Gross.

The eSolar system has computer controlled 24,000 individual mirrors, all pointing in slightly different directions to project on one spot, with each mirror having its own microprocessor to control movement. Software is made up of 50 people in a company of 135 staff. Bill Gross estimates that the build and install cost of a modular 46 MW plant will be between $2.50 and $3 per watt.

eSollar has inked in contracts for 245 MW with SCE in Southern California and one of 92 MW with El Paso Electric in New Mexico. This is quite modest compared to the latest step announced in January 20l0.

A deal with China Shandong Penglai Electric, brings eSolar into the big time. Involved is an almost certain technology transfer involving 2 GW of solar power in a $5 billion deal. The project will start off with 92 MW, with development starting in 2010.The magnitude of the whole contract is exceptional, given that the eSolar basic plant design is for 46 MW of generating capacity.

The Irish renewable energy investment company, NTR, which bought control of SES Systems and its sister company Tessera Solar in 2008 for $100 million has moved forward quickly, with an initial 1.5 MW plant in Peoria Arizona, and a 27 MW plant in San Antonio Texas, involving a 20 year power purchase agreement with CPS Energy.

SES, formerly Stirling Energy Systems, with a then struggling capital base had saddled itself in 2005 with big Californian contracts. These comprise the 900 MW Imperial Valley 1 and 2, and the 850 MW Calico 1 and 2 purchase power agreement in Southern California, with San Diego Gas & Electric and SCE. There have been difficulties with environmental lobby groups holding up regulatory approvals.

It is ironic that the SES technology is the most economic of all CSP systems in the amount of land utilised and in water usage. Yet the Calico project in the Mojave Desert, if it were to gain regulatory approval would still require 34,000 solar dishes, each 40ft high and 38ft wide on 8,230 acres.

The SES CSP system doesn’t have a parabolic trough, or a power tower. But the SunCatcher solar power collection dishes, which has been re-designed with the research of Sandia National Labs’ National Solar Test Facility is now ready for commercial production. Although, there is no capability for thermal storage, it may become a winner in some markets.

The modular SunCatcher uses precision mirrors attached to a parabolic dish to focus the sun’s rays onto a receiver, which transmits the heat to a Stirling engine. The engine is a sealed system filled with hydrogen. As the gas heats and cools, its pressure rises and falls. The change in pressure drives the piston inside the engine, producing mechanical power, which in turn drives a generator to make electricity.

The new SunCatcher is much lighter than the original model, it is round instead of rectangular to allow for more efficient use of steel, has improved optics, there are 60 per cent fewer engine parts, and fewer mirrors- 40 instead of 80. Automobile manufacturing techniques have been used. To reduce costs, the reflective mirrors are formed into a parabolic shape using stamped sheet metal.

Sandia National Labs test measurement of solar to grid conversion efficiency of the SES system made in February 2008 was 31.25 per cent.