COMPETITIVE SOLAR TECHNOLOGIES

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1 COMPETITIVE SOLAR TECHNOLOGIES June 25, 2008 The eventual market will be driven by the levelized cost of energy. At this early development stage, competition is measured on the basis of technology and system costs. There are two proven competing technologies, crystalline silicon and thin film cadmium telluride (CdTe). Assuming equivalent levels of automation (see page 12), and that bifacial PV cells can be made with the same cost and performance as monofacial PV sells, a FT-CPC installation produces lower cost power than either conventional multi-crystalline PV modules or the new thin film PV collectors. Competitive technical strategies Strategies are measured by outcomes. It is not possible to prove the eventual success of a strategy, and more than one strategy may produce the desired outcome. One needs to believe. One strategy is to first focus on high cell performance then reduce costs. Existing PV panels evolved in this manner. The difficulty with this performance first strategy is that costs are embedded in the concept an may not come down enough to be competitive. An exemplar is SunPower s 21% production efficient SP-210. Developers built a product around mono-crystalline PV cells. Today the market for this elegant higher cost module is residential construction where area is at a premium and buyers are concerned about esthetics. Another example of performance first is 3D tracking PV concentrators. It will be difficult to reduce tracking, cooling and O&M costs down to the point where the technology is cost competitive. Over the years the market found that it can achieve moderately lower $/W p by evolving away from 20% efficient mono crystalline cells to lower cost 15% efficient multi crystalline cells. This has led to the modules that dominate the market today. A second strategy is to first focus on module producibility, then increase performance. The difficulty here is that efficiencies may remain low and system costs (module + installation) increase because of the larger number of panels needed to meet a given load. This second strategy is exemplified by Evergreen Solar Inc s string ribbon panel. Multi crystalline silicon is grown as a ribbon from melt rather than cut from cast boules. Today there seems to be little $/W difference between Evergreen Solar and the rest of the market. p FirstSolar and Nanosolar also follow this producibility first strategy. First Solar has achieved impressive $/Wp at the module level. Costs at the system level including installation are less impressive. Data from Nanosolar is not yet available. 1

2 The third strategy is the basis for this business venture: Provide the lowest cost energy by using static concentrators to replace expensive PV cells with inexpensive reflectors. Exploit the best available PV cell technology. This strategy is durable in that the business commits to static concentrators but not a particular PV cell technology. The PV cells are the best technology available at a given time. There is a balance between cost and performance. The best technology will be higher efficiency, though not at excessively higher cost. Silicon PV The industry standard today is first generation PV with multi crystalline solar cells cut from cast ingots (figure 1). A Solarbuzz survey counts 60 crystalline silicon solar cell manufacturers. In another survey, Solarbuzz lists 46 PV module brands world wide. The Solarbuzz market survey concludes that the average selling prices (ASP) in May 2008 was $4.81 /Wp. ASPs have increased slightly since 2004 when they were $4.35 /Wp. This Solarbuzz survey includes both large and small volume retail. Assuming 30% operating margins, a $4.81/Wp ASP translates into a cost of $3.70 /Wp. The silicon PV module market is certainly competitive, there is not much distinction between products. Costs remain high because of tight silicon supplies. There has been a shortage of solar grade PV wafers Figure 1 Multi-crystalline silicon module caused by limited wafer production capacity. This has kept wafer prices high. The shortage is being resolved today with huge polycrystalline production capacity coming on line in China. Wafer prices should decline significantly. High quality mono-crystalline silicon is a candidate PV cell technology for static concentrators. 2

3 Thin film CdTe Cadmium Telluride (CdTe) is a second generation thin film PV cell technology. This technology has received attention by the press because First Solar, Inc. has achieved of noticeably lower $/W p costs at the module level. First Solar module costs are reported to be $1.23 /W. What the hype overlooks is that the customer in interested in system level energy cost - /kwh. Lower efficiency means more panels need to be installed to provide the same power. Half the efficiency doubles the installation cost. First Solar does not target the residential market because of its high installation cost. Their target is large scale utility installations where installation costs are low and low module costs give them an advantage over other technologies. Thin film technologies There are a number of thin film technologies that follow the strategy of producibility first. CIGS or copper-indium-gallium-selenide is a materials set used by Nanosolar. Amorphous silicon is another. Most of these technologies fall into the low efficiency category as does CdTe. Some of them like amorphous silicon degrade with time. There are 22 companies selling various forms of amorphous silicon cells and two companies in addition to Nanosolar manufacturing CIGS cells. rd 3 generation technologies Technologies that do not rely on traditional p-n junctions include: quantum dots, nanotubes, photoelectrochemical, polymer, nanocrystal, and die sensitive solar cells are still in the research phase. 3D PV concentrator In the industry, the phrase concentrated PV generally refers to high concentration tracking PV concentrators (Figure 2). Two axis tracking increases the solar resource by 35%. The optics work OK so long as the system is pointed precisely. However the cost of servosystems, mechanical structure, maintenance and cooling the solar cells is a difficult if not impossible cost burden. Figure 3 shows a polar tracker with flat panels, similar structures are investigated for 2 axis trackers with lense type PV concentrators. p Figure 2 PV lens concentrator 3

4 Figure 3 single axis tracker Figure 4 Solar power tower Solar thermal tower The solar power tower concept, figure 4, was investigated in the 1980s. Heat collected at the top of the tower is used to power turbines to generate electricity. One of the lessons learned form the 1980s was that optical scattering caused by dust and dirt collection on the heliostat mirrors results in serious optical losses. Since the mirrors are second surface reflectors, the heliostat experiences double scattering, once as the light passes through the air-glass interface on the way to the reflector, once as reflected light passes back through the glass-air interface. Optical efficiency can drop by 15% within two days after cleaning, and gets worse still with time. Solar thermal troughs Solar thermal parabolic troughs, figure 5, suffer from a number of problems. Like power towers, scattering losses are significant. Tracking is sill required although it is simpler single axis tracking. Transporting the heated fluid over considerable distances back to a central generators results in costs and thermal losses. Thermal losses make it difficult to get high enough temperatures for efficient turbine operations. The market has not yet proven solar thermal systems to be competitive with PV panels. Figure 5 Parabolic trough concentrator 4

5 Other static concentrators We are aware of one other company pursuing static ideal concentrators. The Stellaris Corp. Lowell Mass has a patent application (US2008/ A1) March 6, That application is focused on a monofacial plat type ideal concentrator fabricated from plastic. That application is directed at using a fluid to optically couple but mechanically decouple the solar cell from the plastic rod. While there are a number of practical difficulties with the Stellaris concept they are looking in the right direction system cost potential The FT-CPC in a 2x static configuration will be compared with its to closest proven competitors. As before, the year 2012 is taken as the base year allowing visible technology to scaled for automated production FirstSolar s thin film CdTe is the low module cost leader and the most serious visible competitive technology. In 2007 FirstSolar claims their average production cost to be $1.23/W p. Through a combination of production efficiencies and performance improvements, FirstSolar expects cost performance to improve at the rate of 10%/year which suggests module costs of $0.83/W p at the beginning of Page 12 developed a module cost comparison between SunPower and the 2x static concentrator. Those same numbers are used here to build a 2012 system cost comparison. The 2x static cost/performance estimates are closely tied to the SunPower collector and the assumption that cell conversion efficiency would be the same (20%) and PV cell cost would be the same. No effort has been made to optimize the PV cell to suit the static concentrator. Installation cost was developed bottom up for a large field installation where the cost of land was $4,000/acre. First Solar, with half the efficiency, was assumed to have double the installation cost. The installation assumed DC power as the product for all systems. The result is presented in figure 6. At the module level, the 2x static configuration is close to the thin film collector. But the 2x static should have double the efficiency hence half the installation cost. This results in a significant cost advantage at the system level. Based on the assumptions made, the 2x Figure 6 Competitive cost/performance estimates static system would provide the lowest cost PV energy. 5