Cost Analysis of Solar Reflective Hard-Coat Materials Deposited by Ion-Beam-Assisted Deposition

Abstract

Commercialization of concentrating solar power (CSP) technologies require the development of advanced reflector materials that are low cost and maintain high specular reflectance for extended lifetimes under severe outdoor environments. During the past nine years, the National Renewable Energy Laboratory (NREL) has funded Science Applications International Corporation (SAIC) in McLean, Virginia, to develop a promising low-cost advanced solar reflective material (ASRM) combining the best of both thin-glass and silvered-polymer reflectors. The alumina Al2O3 coating is deposited by ion-beam-assisted physical vapor deposition (IBAD). Materials undergoing testing demonstrate excellent durability under accelerated and outdoor weathering. To help commercialize the technology, NREL had a cost analysis performed incorporating realistic web coating assumptions and the technical improvements made in the ASRM. The biggest process cost items are the alumina and machine burden (which collects the cost of the building and office staff). The switch from a polyethylene terethaphalate (PET) to a steel substrate for the ASRM is a significant contributor to the cost. The cost of high-purity alumina should drop from $400 to $200/kg when purchased in 20 kg quantities. Alumina deposition rate then becomes the critical cost driver. In a previous study, deposition rates above 100 nm/s were not examined, but deposition rates greater than 100 nm/s are being used routinely for thin alumina coatings deposited on commercial web-coaters as barrier coatings. In addition, multiple (2–3) Al2O3 IBAD zones can be used in one roll-coating machine to deposit thicker alumina at a lower web speed. This means that with increasing deposition rate and/or multiple zones, the total production cost of the SAIC ASRM with 1 μm thick Al2O3 on PET will meet both the 1992 cost goal of $10.76/m2$1/ft2 and the equivalent cost goal of $13.79/m2$1.31/ft2 when the 1992 cost goal is corrected for inflation. There is a minimum deposition rate needed to reach the cost goal and a maximum deposition rate related to the number of zones after which no significant cost gains are observed. These asymptotic total production costs are $8.06/m2($7.39/m2 excluding substrate) for a large commercial web-coating company and $7.62/m2($6.94/m2 excluding substrate) for a smaller company. As can be seen by these numbers, the $10.76/m2 cost goal can be reached, but the cost of the substrate is still a major consideration. In addition, the width of the web was increased from 600 to 1200 mm, which decreased the asymptotic total production costs. The results of the cost analysis will be described.

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“…for building costs, $0.08/kWh electricity cost, 1.8 per cent (of all other expenses) general overhead, 90 per cent yield, 90 per cent tool uptime, 90 per cent labour productivity and a five year straight line depreciation. These process descriptors are comparable to other published cost models for thin film deposition (Kennedy and Swisher, 2005). In addition, the use of 256 nozzles was assumed, since this upgrade was in progress by Litrex at that time.…”