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PV vs. Solar Thermal

Distributed solar modules are gaining ground on concentrated solar thermal plants.

Fortnightly Magazine - July 2008

and the mechanisms to encourage and subsidize its development.

Another concern is the inherent variability of windpower. Integrating wind generation with the high-voltage transmission grid caused only minor concern when there wasn’t much of it, but now, with thousands of generators installed, transmission planners and operators face the challenge of how to integrate rapidly expanding windpower resources into the grid without jeopardizing transmission security and reliability. 1

The transmission system operators of California and Texas, two of the states with the largest windpower potential, have carried out studies on the cost of the infrastructure and ancillary services necessary to integrate wind with their generation resource portfolios. The studies have shown that, while feasible, the integration of large amounts of wind (perhaps as much as one-third of total installed capacity), especially where concentrated in a specific geographic area, comes at a cost—and that cost must be added to the direct cost of wind generation and interconnection. 2, 3

Solar on the Rise

As windpower continues growing toward its full potential, and transmission planners and regulators address integration issues, policymakers increasingly are focusing on solar power.

In the United States, the power industry has focused on solar thermal technology because it was perceived as more economically competitive than solar PV technologies. Parabolic-trough collector fields with oil-based heat transfer fluids have been successfully used to drive steam-turbine generating plants since the 1980s. The collector technology painstakingly has been improved and O&M costs dramatically reduced over 20-plus years of operational experience, and the lion’s share of proposed solar electric generation in the United States is based on this technology.

By contrast, policymakers in Europe made a significant commitment to solar power years ago, including PV. That commitment is especially apparent in Germany, where 20-year contracts and supportive feed-in tariff rates have signaled a long-term commitment to PV manufacturers, project developers, and the entire PV-plant supply chain. This has led to hundreds of megawatts of installed PV, and also allowed some PV manufacturers to improve their manufacturing processes and reap economies of scale by producing modules at declining prices. This in turn has produced a new model of grid-connected utility-scale solar PV—distributed central solar (DCS).

Additionally, DCS has benefited from the increasing efficiencies achieved by thin-film PV manufacturers, as well as realized economies of scale never achieved before.

For example, thin-film PV technologies based on cadmium-telluride (Cd-Te) have become much less costly than their better-known, silicon-based brethren. Although Cd-Te cells have lower conversion efficiencies than silicon-based cells, their costs are much lower. Some manufacturers of this PV technology already have committed to sales contracts with levelized costs around 12 cents/kWh over a 20-year term in the desert Southwest. 4

As a result of these innovations, solar power appears to be becoming a viable, large-scale source of renewable generation, after so many years of being considered the technology of the future. A recent article in Scientific American presented a vision of the solar future in which thousands of megawatts of concentrated solar power (CSP) and PV would meet almost 70 percent of the United States’ electric needs by