Solar thermal: The other solar energy

EL SEGUNDO: While most of the focus in the solar world is on Photovoltaic (PV) power, the fastest-growing segment of the solar market is actually the solar thermal market, which will expand by a factor of 37 from 2009 to 2014, compared to just a sixfold rise for PV during the same period, according to iSuppli Corp.

Solar thermal, or Concentrated Solar Power (CSP), is undergoing a boom, as newly installed capacity explodes.

Annual global CSP installations are projected to reach 10.8 Gigawatts (GW) in 2014, up from just 0.29GW in 2009. In contrast, PV installations will amount to 45.2GW in 2014, up from 7.0GW in 2009.

The figure presents iSuppli’s forecast of annual global solar installations by technology type, contrasting the growth of PV and CSP.Source: iSuppli, USA

Collecting the sun
PV employs arrays of cells that convert the sun’s radiation into direct current electricity. On the other hand, solar thermal uses mirrors to reflect the sun’s heat energy onto collectors filled with fluids or gases. This energy is then used to heat water and, in turn, drive a steam turbine to generate electricity. One type, the dish system, doesn’t use steam turbine but rather a Stirling engine that creates mechanical motion to operate an electrical generator.

The most popular type is a parabolic trough version that heats a tube of synthetic oil, which is pumped through a heat exchanger to create water steam that drives a turbine electricity generator. Other types include a tower configuration with flat mirrors that reflect to a central tower collector as well as versions that use a
Fresnel lens to amplify the sun’s effect.

Another type, called a chimney, doesn’t use water or fluids but employs convection air currents to suck air in through turbine fans at the bottom of a tower surrounded by a greenhouse-like apron of glass.

CSP plants also are beginning to store the sun’s heat energy for release to steam generators at night. Forms of molten salt and graphite lead the list of storage alternatives for slowly releasing heat.

CSP market vs. tower and dish technology
“The market for CSP is currently limited, with two countries--the United States and Spain—dominating project deployments so far,” said Greg Sheppard, chief development officer at iSuppli. “About 10 projects are online at present, but by the end of 2011 the number of projects will grow to 40 with another 100 in the planning phase from 30 vendors. North Africa, China, and Australia are the next high-growth regions.

“CSP stakeholders also believe 2010 is the year when the technology could really gain traction in the market, even though companies are looking at land rights acquisitions—which progress on a much slower scale than technology evolution—while also examining water use, wildlife impact and power transmission issues that could prove to be bottlenecks for some countries, including the United States.”

Parabolic CSP might be the dominant approach at the moment, but iSuppli believes tower and dish technology will catch up in the next few years.

Solar One
An example of the CSP model is The Nevada Solar One facility, which is majority owned and operated by Acciona, responsible for generating enough electricity to power 14,000 homes in the Las Vegas area.

The plant, the biggest solar facility in the world when it opened in 2007, can produce up to 75 Megawatts (MW). It is built on 400 acres and employs 182,000 mirrors that heat oil-based liquid to more than 750 degrees Fahrenheit. The liquid’s heat is then transferred to steam and drives a turbine system, which is supplied by Siemens.

If more of these facilities crop up, and should the timetable for CSP be on target, another technology in the move to green energy may be at hand—one that could reduce the market’s dependency on traditional methods of generating electricity.

Source: iSuppli, USA