Energy conservation makes the most sense when it also saves money.

Europe is far ahead of the U.S. in gasoline mileage because it slaps taxes on big cars and trucks, big engines, gasoline and parking spaces for big vehicles. European cars average 43 miles per gallon compared with 29.3 m.p.g. for cars sold in the U.S., not counting our trucks and sport-utility vehicles.

China is far ahead of the U.S. in solar power because, it saw solar as a cheap solution for heating water in sinks and showers. With 30 million solar households, China has become a leading solar panel-maker.

High energy prices are making solar power more cost-effective in the U.S. Also, the 2005 Energy Policy Act gives consumers a tax credit of up to $2,000 on the cost of qualifying solar systems installed before 2008.

The California Public Service Commission voted to pay out $2.9 billion in rebates for the purchase of solar panels over the next 10 years. Venture capital firms are investing heavily in this technology, and big business is embracing it too.

A Wal-Mart Stores Inc. test store near Dallas has solar panels integrated into the garden center's canopy, the roof of the entry vestibules and several other areas. Wal-Mart intends over the next three years to cut energy use in stores by 30 percent.

U.S. firms in this fragmented business are relatively small; their shares are volatile and carry risk. The annual industry growth rate of more than 30 percent since 2000 still represents less than 0.1 percent of the world energy market. Yet demand for solar panels is growing, with waiting lists in some areas.

Three higher-visibility firms receive consensus analyst "buy" ratings, according to Thomson Financial:

- Evergreen Solar Inc. of Marlboro, Mass., develops, manufactures and markets solar-power products for electric power worldwide.

- SunPower Corp., Sunnyvale, Calif., designs, manufactures and sells solar cells, solar panels and inverters that convert sunlight to electricity.

- Energy Conversion Devices Inc., Rochester Hills, Mich., designs and sells thin-film solar-cell products, nickel metal hydride batteries and memory devices.