still inadequate, though recently much improved. CONAES is in agreement with the general assessment provided in the recent study of photovoltaics by the American Physical Society, which suggests that market penetration is unlikely to exceed 1 percent before the year 2000, and advocates the exploratory development approach in preference to the mass-production strategy.22

Solar Thermal Conversion The most heavily financed system for generating electricity with thermal energy from the sun is the solar tower concept, with arrays of mirrors focusing sunlight on a boiler at the top of a tower. Although this concept appears technically feasible, there is insufficient information for reliable cost estimates. Projected costs appear to lie in the range of 5–10 times the current bus-bar cost of electricity if storage costs are included. Because so much of the cost is embodied in structural materials such as concrete and steel, which represent well-developed technologies for which large cost reductions are unlikely, reducing costs will be difficult. A 10-MWe pilot plant is being constructed in Barstow, California. Photovoltaic conversion probably offers greater long-term promise and potential for improvement.*

Wind Power Wind generators constitute a form of solar energy that is already economic for a few sites and markets. However, integration of this highly variable power source into utility grids could increase total generating costs if a great deal of backup capacity were required, When used in small amounts, however, wind generators can save fuel without requiring additional capacity. Economic uses might be found in utility districts that have a high proportion of hydroelectric generating capacity, or extensive pumped hydroelectric storage, either of which could accommodate the variations in wind power output.

Sites for wind generation are limited by wind conditions and scenic considerations. The amount of land required per unit of electrical capacity is much larger than for most other forms of solar energy (although land used for wind generation is of course not completely excluded from other uses). Interference with communications can also be a problem, because television and microwave signals are reflected by the moving surfaces of wind turbines. A major environmental impact is likely to be from access roads for maintenance and construction and from electrical interconnections of numerous units.

The most immediate prospect for wind technology would be to develop a diversified design and manufacturing effort directed generally at


Statement 1–45, by J.P.Holdren: So do solar pond collectors driving low-temperature heat engines.

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