GLASS, PLASTICS, METALS & BIG SUN

Why glass is feeling the heat in the CSP reflector space; Plastics and metals could soon dominate the market for utility-scale CSP reflectors if glass manufacturers do not figure out a way to bring down costs.
Jason Deign, 11 February 2011 (CSP Today)

"…The fact the mirrors at the Californian desert [Solar Energy Generating Systems (SEGS)] installation have lasted since the 1980s has led to glass being venerated as the reflector material of choice in the industry. SEGS has become a byword for glass’s durability and efficiency in CSP applications…But perhaps not for long.

"One reason is that in recent years safety and pollution concerns in Europe and America have led to an increasing clampdown on the use of the copper or lead-based paints traditionally used to make mirrors [such as those at SEGS]…Manufacturers such as Flabeg and RioGlass have got around this by using unleaded paints. But these were designed for indoor applications and their performance in outdoor settings is unproven…"

The SEGS parabolic trough glass mirrors (click to enlarge)

"A second issue with glass stems from manufacturing costs…The crystal-clear low-iron glass needed for CSP plants only accounts for about 2% of production worldwide and involves a special manufacturing process, using low-iron sand, ultra-high temperatures and an oven that can take the heat and has been cleared of all impurities…

"…[Third, the expense involved with ovens] results in a high unit cost…If a manufacturer could run one of these ovens continuously for around nine months a year then it is possible they could bring the unit cost down to the level of standard ‘green’ glass…But right now there is simply not enough demand…[F]inally there is the manpower cost associated with assembling glass mirror arrays…[E]very mirror needs to be attached at four points and then properly aligned…[This means almost] half the cost of a collector field is in labour…"

Marred glass and an aluminum replacement sample (click to enlarge)

"Those pushing alternative reflector materials are naturally not shy about noting these cost challenges…Patriot Solar Group…advocates low-cost acrylic mirrors for small systems and anodised aluminium…for bigger applications…There are two other advantages to glass alternatives…breakability and…design flexibility…

"Despite all that, however, glass’s supremacy in CSP is far from over…[N]ew plants are [still] being made with glass mirrors…[E]ngineering, procurement and construction companies [and banks and investors] favour glass because [it is proven]…[but as] second or third-generation plants start appearing… unless glassmakers pull something else out of the hat…[the] race is on."