Parabolic trough reflectors: Does glass still have the cutting edge?

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1 Parabolic trough reflectors: Does glass still have the cutting edge? Posted by [1] on Jan 14, 2010 Are polymer and other lower-cost reflective materials about to break the early monopoly of curved glass in parabolic trough construction? By Toby Procter To date, glass has been the material of choice for large CSP installations. But recently a range of polymer and alloy alternatives have either already entered the CSP market, or are waiting in the wings. Bent glass manufacturers now face competition from the likes of ReflecTech and 3M, Patriot Solar Group and Germany s Alanod Solar. The initial cost-saving potential of polymers and other reflective trough coatings seem clear enough, extending beyond manufacturing cost advantages to the benefits of lightweight materials for transit to remote installation points, safety benefits, and relative ease of construction. ReflecTech, a wholly-owned subsidiary of CSP original equipment manufacturer, SkyFuel, says its mirror can be manufactured at a much lower cost than glass. The company says the advantage of ReflecTech film, which comprises multiple layers of polymer films with an inner layer of pure silver, is that the product is up to 60 percent lighter than glass. More importantly, it is unbreakable. Lighter and more durable trough material promises to reduce logistics and weight-related design, installation and maintenance costs. Bent glass manufacturer, Rioglass, says that for large-scale installations, the base price of tempered glass reflector panels is around ($42-45) per sq m.

2 When compared to ReflecTech s price ($18.84 per sq m, at volumes of sq m), the cost of ReflecTech s product is much lower. Even when you add the cost of a rigid substrate, such as aluminium sheet, at $9 per sq m, and protective edge tape, at $9 per roll (roughly $0.42/m2 for an LS2 size mirror of 2.20 sq m) the total volume cost is about $28.26/m2, percent less than glass. To date, ReflecTech has seven years real-time commercial use and 10 years worth of accelerated weather testing to demonstrate that it has less than 0.5 percent loss in reflectivity. Another key mover in the reflective film space is Minnesota-based 3M. Dan Chen, responsible for business development in 3M s Renewable Energy Division, says: If the CSP industry is to grow, costs need to sink dramatically, especially in the face of improvements in utility scale photovoltaic costs. 3M, targeting CSP and other solar clients in search of such advantages, has set itself a goal of reducing parabolic trough and mirror costs by 30 percent. The company has achieved a 94 percent total hemispherical reflectance (THR) reflective film for CSP application, with its Solar Mirror 1000 product. It has further prototypes in the pipeline for even higher performance films, with percent THR. In addition, 3M is working with Gossamer Space Frames, a parabolic trough frame company, to develop an integrated CSP solution. The company is also working with NREL to improve the product s durability, as well as its ease of application in trough assembly. The alloy advantage Polymer films are not the only contenders threatening to supplant glass for solar troughs. German manufacturer Alanod-Solar, says its nano-composite coated, anodised alloy Miro-Sun mirrors (with tailor-made space frames) provide comparable performance

3 and durability. It says they are substantially lighter and often cheaper than glass mirrors Recent measurements and accelerated weather testing data from both the NREL and the German Aerospace Centre (DLR) reveal that Alanod-Solar metal-based mirrors achieve competitive direct reflectivity. The metal-based mirrors also measure up in terms of durability. Accelerated tests revealed that over the equivalent of seven and a half years, their reflectivity declined between less than 1 and 2.3 percent. US-based Patriot Solar Group has also introduced an alloy alternative. The company uses a clear, acrylic plastic surface with an aluminum or zinc backing. The company states that its aluminium trough mirror is 94 percent reflective. If verified by NREL, it would more or less match Flabeg s performance quote for un-tempered glass, and 3M s for its Solar Mirror According to Patriot Solar Group, acrylic is lighter than glass, and, like polymer film on light alloy panels, is less labour-intensive. Furthermore, it says its acrylic product is up to 30 percent cheaper to manufacture and install. Research finds conflicting results However, recent research by the DLR throws into the question the fundamental advantages of both polymer and alloy alternatives. A DLR report, Optical Characterisation of Reflector Material for Concentrating Solar Power Technology, authored by Stephanie Meyen et al, demonstrated that silvered glass mirrors achieved direct and hemispherical reflectance of almost 94 percent. By contrast, polymer film with a silvered reflective layer only achieved comparable hemispherical reflectance, while its direct reflectance was about 5 percent lower.

4 In testing the comparative performance of aluminium and polymers, both the aluminium reflectors tested by DLR were outperformed by the unnamed polymer film tested. The DLR also carried out abrasion tests. Again, glass mirrors outperformed both polymer films and aluminium sheet. But the polymer manufacturers argue that any advantage is slight. 3M maintains that its Solar Mirror Film 1000 has been subjected to continuous outdoor testing at NREL since 1995 without losing more than 2 percent of its initial THR reflectance. RefleTech similarly argues that the test is misleading, and in no way comparable to actual installed conditions. Pointing to a study carried out by NREL, RefleTech contends that the specular (direct) reflectance for ReflecTech Mirror Film is comparable to glass, at 94 percent. Is bent glass still best? In any case, Jordi Villanueva of Abengoa subsidiary, Rioglass, argues that glass is still the only option of proven durability for installations exceeding 25MW with an expected standard 30-year life. Rioglass contends that polymer films suit only smaller installations with less serious durability requirements. Meanwhile, German competitor Flabeg, continues to develop new solar glass products, with a new EcoGuard low-iron float glass launched in A recent product launch by glass-bending equipment manufacturer, Glasstech, also provides further evidence that glass reflectors innings are not yet considered to be over. Existing evidence suggests that glass mirrors reflective performance may still have a slight advantage over their lightweight, lower cost counterparts.

5 Powered by TCPDF ( Published on New Energy Update Tracker ( But the hard proof may have to wait for real-life evidence of the accuracy of weathering and accelerated lifecycle tests on polymer films. Correction: The original article Parabolic trough reflectors: Does glass still have the cutting edge? published 14 th January 2010, made an incorrect price comparison between Reflectech's and Rioglass products. The original article suggested that the product prices were comparable. However, according to ReflecTech, ReflecTech's product is percent cheaper than that of Rioglass, when compared at relevant volume prices. The original article also incorrectly attributed ReflecTech s product to SkyFuel. In fact, ReflecTech is a wholly owned subsidiary of SkyFuel. To comment on this article, please contact: Toby Procter, freelance journalist at: tprocter@trendtracker.co.uk [2] Or contact the Editor, Rikki Stancich at: rstancich@gmail.com Links: [1] [2] mailto:tprocter@trendtracker.co.uk