July 8th, 2012 by James Ayre
Solar thermal power is, for the most part, unrestricted by materials availability, according to new research from the Chalmers University of Technology.
There are still a few minor issues left, though, such as finding a replacement for the silver in mirrors.
With growing international export restrictions on rare earth metals, and diminishing availability, the dependency that some renewable technologies have on scarce materials has gained attention.
Some of the main players in the wind and solar industries have been attempting to greatly limit their use of restricted elements, such as indium, or rare earth metals. There has also been a growing notion within the solar industry that Concentrating Solar Power (CSP) should likely be built using mainly commonplace commodities like glass and steel.
The new research from, Chalmers University of Technology, has investigated, in great detail, the material issues for CSP. Their primary conclusion is that “CSP does indeed seem to be largely unrestricted, viewing the material requirements compared to the global reserves. In theory, enough solar plants could be built to cover — at the very least — five times the current global electricity demand.”
The report also brings to light some of the problems that are likely to challenge the industry in the future. The main issue is that silver is likely to be in short supply in the coming decades even without additional industrial demand; as of now, silver is extensively used in CSP for reflecting surfaces. To remain cost competitive, CSP mirror manufacturers will likely have to look at other reflective surface materials, such as aluminium.
“The prospects for strong growth for CSP over the next few decades seem good, but would cause a stir on the global commodity markets,” says Dr Erik Pihl, lead author of the scientific article.
“Following a Greenpeace/IEA SolarPACES/ESTELA growth scenario where CSP reaches 8000 TWh/year in 2050, the solar plants would consume up to 50-120% of today’s yearly nitrate salt production, and 5-15% of several common materials such as glass, nickel, magnesium and molybdenum.”
“The report has used data directly from plant manufacturers Cobra and eSolar for trough and tower plants. These plants have somewhat different characteristics when it comes to material use.”
“Parabolic trough plants tend to use a lot of concrete and iron, while the concept of small heliostat tower plants has a higher use of aluminium and stainless steel,” says Erik Pihl. “The common design of a parabolic trough plant also requires more molten salt per MW than a salt-receiver tower plant, even when the former has fewer storage hours. That means that trough plants appear slightly more sensitive than tower plants to possible salt production bottlenecks, unless other storage techniques can be employed.”
Pihl thinks that as we go for higher steam temperatures and increased plant efficiency, we should expect to see material demands for plants decreasing.
“We see that clearly when comparing a mature design to a novel concept. That does not automatically mean that all material restriction problems will be solved. We might trade a large use of common materials for small quantities of scarce elements. It comes down to what alloys we use in pipes, receivers and turbines.”
“Higher temperatures means more use of high quality steels, but alloy materials such as molybdenum and niobium have restrictions in both stock and production.”
“There might be enough for CSP alone, but there are many other uses,” says Erik Pihl. “That could be a problem in the more distant future. In the short term, substituting silver and increasing nitrate salt production should be the first priority.”
Source: Chalmers University of Technology
Image Credits: Erik Pihl
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