Wind energy is one renewable energy technology developed successfully by mechanical engineers. In the 1970s, wind systems and PV systems started out on nearly the same footing: only a few experimental systems for each were installed around the world. Today, there are roughly 10 times more wind energy systems than PV systems installed—50,000 MW of wind systems versus 5,000 MW of PV systems. Why were wind energy technologies able to surpass PV systems? One reason was that wind developers were able to quickly demonstrate economies of production just as a market opportunity appeared. The state of California offered long-term standard-offer contracts from 1985 to 1989 to purchase the electricity over 20 years from large-scale renewable energy projects. These long-term contracts were similar in many ways to the successful European feed-in tariffs. Solar concentrators producing heat to drive electric generators—called concentrating solar power (CSP) systems— also took advantage of the California opportunity; almost 400 MW of CSP systems were installed in the 1980s, and they have been generating solar electricity ever since then. Fabrication facilities are relatively inexpensive for both wind and CSP systems when compared with PV manufacturing facilities. Wind production facilities resemble automobile assembly lines.9
PV production facilities, although not as complex or costly as those of the inte-grated-circuit industry processing semiconductor silicon, still cost roughly 10 times more than wind production facilities. For early investors, this is an important issue. Consider the investment choice. Crystalline silicon and amorphous thin-film flat-plate PV production facilities both cost about $100 million or more for 100 MW per year manufacturing plants.10,11 A wind production facility of the same size might cost $10 million for the same annual production. Investment in production facilities for new technologies entails significant risk, and the lower risk for investing in wind facilities was one reason investors provided funds for large 1,000 MW wind projects in the 1980s. PV was not able to demonstrate the economies of production quickly enough to take advantage of the small window of opportunity provided by California's standard-offer contracts. In the 1980s, the very-high-efficiency solar cells needed by CPV systems were still in the research laboratory.
The California market incentives helped wind and CSP developers and investors move their technologies forward, reducing cost and acquiring valuable operational experience that improved reliability. Wind engineers developed their qualifications standards during this same period; like early PV technologies, wind systems often suffered from poor reliability until their certification standards were established and required in the marketplace.
Some noteworthy similarities exist between wind energy systems and CPV systems.9 They both employ relatively common materials, particularly steel. Wind system costs are typically less than $1 per watt; they depend mainly on the cost of steel, whereas flat-plate PV is linked to the availability and cost of expensive semiconductor silicon. But solar concentrator structures are also amenable to an auto-assembly type of production (see Fig. 5), and CPV developers estimate CPV production facility costs are much closer to those of wind systems than to those of flat-plate PV production facilities. In early EPRI cost studies, CPV production facility costs were estimated (on the same costing basis as the crystalline and amorphous silicon facilities) to be about $28 million for a 100 MW per year installation—about one-quarter the cost of the conventional silicon PV facilities.10 These lower investment costs can lead to a faster scale-up of manufacturing facilities because investor risk is relatively smaller than the risks entailed in investing in conventional PV production facilities.
Further, cost studies in Spain and Israel estimate CPV installed system costs will, like wind systems costs, finish below $ 1 per watt when gigawatt levels of CPV production are reached.7,12 Both CPV and wind energy technologies are modular, like flat-plate PV modules, but the sizes are different. Wind units are now megawatts in size whereas CPV units range from kilowatts to tens of kilowatts. Flat-plate PV
modules are usually less than 100 watts. And, obviously, both wind and CPV systems have moving parts, yet moving parts have not limited the success of wind systems. Finally, wind systems first penetrated the energy marketplace in sites with very high and steady winds, whereas CPV systems will almost certainly enter markets in locations with considerable sunlight and almost no clouds, similar to the climates of the southwestern United States, Spain, Australia, and Israel.
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