Are We Headed Toward a Green Bubble?

Cleantech Primer

Solar Power

How it works: Photovoltaic cells, in modules (solar panels) or thin film, convert sunlight to electricity. Solar thermal power uses sunlight to heat water, which turns to steam, which runs turbines.

Top companies: First Solar, Nanosolar, SunPower, United Solar Ovonic

Pros: Sunlight is free; state and federal subsidies available to users; works on individual roofs.

Cons: Sun only shines half the time, or less; systems are expensive--payback in reduced energy cost can take more than seven years; requires large amounts of land; dependent on silicon prices, which fluctuate.

Wind Power

How it works: Wind turns blades that power generators and produce electricity.

Top companies: General Electric, Nordex (Germany), Siemens (Germany), Vestas (Denmark)

Pros: Wind is free; European companies are bringing advanced technologies to the U.S.; electricity generated by wind can cost the same as coal or natural gas.

Cons: Wind is unreliable; requires large amounts of land; best winds blow in the least populated areas; requires backup power system.


How it works: Drills down into the earth's superheated core; the steam or hot water that escapes turns a turbine.

Top companies: C. Rokas SA (Greece), Ormat Technologies, Polaris Geothermal (Canada)

Pros: Available 24/7; requires less land than solar or wind; technology is inexpensive and easy to mass produce.

Cons: Geothermal reservoirs are hard to locate; drilling could cause earthquakes (A recent project in Switzerland was called off because of tremors).


How it works: Battery-powered electric motors to completely or partially (hybrid) power vehicles.

Top companies: General Motors (Volt), Tesla Motors, Toyota, Zero Motorcycles

Pros: Reduces or eliminates dependence on oil; cuts carbon emissions; less expensive to operate than internal combustion engines.

Cons: Batteries are large and expensive; range for all-electric cars is only 50 miles; requires system of recharging stations that electric grid may not be able to handle.


How it works: Agricultural products to power engines instead of fossil fuels.

Top companies: Archer Daniels Midland, Bunge Ltd., Novozymes (Denmark)

Pros: Cuts dependence on oil; conventional engines easy to convert; can use waste materials, including wood chips, restaurant oils or manure.

Cons: Conversion into energy is expensive; creates some pollution; can cut into world's food supply.

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Julie Bennett is a freelance writer.

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This article was originally published in the April 2010 print edition of Entrepreneur with the headline: Are We Headed Toward a Green Bubble?.

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