No show stoppers for concentrating solar power

July 4, 2012, Chalmers University of Technology
Parabolic trough collectors at the PSA, Plataforma Solar de Almeria, experimental facilities in Spain. Concentrated sunlight heats up a synthetic oil in the pipes at the focus of the troughs. Photo: Erik Pihl

( -- A recently published study confirms that solar thermal power is largely unrestricted by materials availability. There are, however, some issues that the industry needs to look into soon, like replacing silver in mirrors.

In the wake of Chinese export restrictions on rare earth metals, the dependence of some on scarce materials has gained attention. Several players in the wind and PV industry are struggling to get away from excessive use of restricted elements, such as or . Meanwhile, there has been a shared notion amongst solar scientists and industry that (CSP) should “probably” be less restricted, being built mainly on commonplace commodities like steel and glass.

A recently published study from Chalmers University of Technology has gone into the details on material issues for CSP. The main conclusion is that CSP does indeed seem to be largely unrestricted, viewing the material requirements compared to the global reserves. In theory, enough solar could be built to cover – at the very least – five times the current global electricity demand.

However, the report also highlights some issues that are likely to pose challenges to the industry. The main point of concern is that silver, today extensively used for reflecting surfaces, will most likely be in short supply in the coming decades even without demand from a booming CSP industry. CSP mirror manufacturers might have to look at other reflective surface materials, such as aluminium, to secure cost competitiveness.

“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.”

Erik Pihl believes that we can expect to see material demands for plants decreasing as we go for higher steam temperatures and increased plant efficiency.

“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 . 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.”

The full article “Material Constraints for Concentrating Solar Thermal Power” has been published in Energy.

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5 / 5 (1) Jul 04, 2012
One of the key advantages I notice about solar boilers is that the simple, even "primitive" nature of the fundamental designs and technologies actually makes them less expensive and more resilient in the real world than many "higher tech" options.

As an over simplified example, if you want to COOK food for nearly free, you could scarcely do better than to get a Fresnel lens and a mirror on a clear summer day. That back yard barbecue, such as today, is typically done on a sunny day, with a grill with gas or charcoal fuel, well the fact is solar ovens or fesnel lenses can cook the food just as well, and at ZERO carbon footprint, with no fuel cost at all.

On the Greenpowerscience channel on youtube, Dan and Denise boiled their noodles and cooked their sauce with a Fresnel lens.

I've always wanted to try this, though they need safety measures to protect children, just don't use them with children around, and they cost a bit to start, but hey, it's free energy...
not rated yet Jul 04, 2012
Why silver? Astronomers have used Al on their mirrors for a long time. Thermal solar allows easy storage for baseload use, PV solar doesn't. Salt shortages? Really?

@Lurker: you don't need a fresnel for a solar cooker. Cardboard, Al foil, and a sheet of glass will do it. Focusing solar cookers are almost as easy.

not rated yet Jul 04, 2012

The best use for CSP is home, building units that can make, use both electricity and waste heat. Since they are saving, making retail prices their payback is faster than utility would.

Plus these use less material/kw and more eff.

There are many other mirror materials than silver plus max temps are much lower with water as the working and heat transfer fluid in home/building units.
not rated yet Jul 05, 2012
Why silver? Astronomers have used Al on their mirrors for a long time. Thermal solar allows easy storage for baseload use, PV solar doesn't. Salt shortages? Really?

I wasn't even aware they were using salts in the trough boilers. I though that was just the tower boilers. That actually doesn't seem to make a lot of sense, since they use vacuum tube insulation anyway, why wouldn't they just use water directly?
not rated yet Aug 13, 2012
With regard to the salt, both designs in the paper use thermal storage to provide near-baseload operation. There is no shortage of salt, but a bottleneck in extraction and manufacturing capability.

With regards to the silver; the possibility for using aluminium is discussed in the paper. Key difference is the reflection and light spectrum. Aluminium in mirrors would necessitate a collector area some 4-8% larger and thus a much higher silver price to be a cost effective substitution.

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