Alternative power sources: pros and cons

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Large hydroelectric plants typically have a capacity of 300-400 megawatts

(TIME.com Europe) -- As Europe grapples with a fuel crisis, what are the alternative power sources?

Advantages: A proven technology for electricity production, capable of generating large amounts of power. Large hydroelectric plants typically have a capacity of 300-400 megawatts. It's also entirely renewable with no CO2 emissions. Disadvantages: Public-environmental opinion has turned against hydroelectric plants and the dams they require. Potential sites in Europe have mostly been used already. Projects to use the remaining sites would run into strong local opposition. Even smaller hydroelectric plants cause some damage to the landscape.

Current contribution: 13% of electricity production Forecast for 2010: 12.4%

The energy output of wind turbines is proportional to wind speed

Advantages: Entirely renewable with no CO2 emissions. Existing technology is already relatively high-output and affordable -- individual machines with 2-3 megawatt capacity are being developed for offshore applications.

Disadvantages: Not everywhere is suitable. With output proportional to wind speed, wind turbines only make sense in coastal areas and on high ridges. Wind is not a constant energy source, so wind energy supplements rather than replaces fossil or nuclear sources. Unsightly and noisy.

Current contribution: 0.2% Forecast for 2010: 2.8%

Advantages: Renewable with no CO2 emissions. Contrary to popular belief, PV modules can convert diffused light as well as direct sunlight into electricity so they could be used from northern Europe to the Mediterranean, although they're more productive -- and so cheaper -- with more sunlight.

Disadvantages: Cost is exceptionally high, although prices are starting to come down. They require a large surface area and high-capacity plants would only be viable in southern Europe.

Current contribution: 0.03% Forecast for 2010: 0.1%

Advantages: Highly efficient. They could generate significant quantities of electricity without CO2 emissions and could replace internal combustion engines in cars -- a major source of greenhouse gases.

Disadvantages: Prohibitively expensive and still dependent on fossil fuels to produce the hydrogen they require.

Current contribution: 0% Forecast for 2010: 0%

Advantages: Proven technology and plentiful sources in waste products from agriculture, forestry and food processing. It is renewable and is not dependent on fossil fuels. Gases produced could be used in combined-cycle plants. Surrounding forests can act as sinks for CO2 emissions.

Disadvantages: Burning biomass creates polluting gases and liquid waste. At large plants it's economically feasible to install technology to recycle and process the wastes, but there are still doubts about the ecological impact of smaller biomass plants. Collecting, transporting and storing biomass is expensive.

Current contribution: .95% Forecast for 2010: 8%

Advantages: Highly efficient and cheap. Plentiful resources still exist within Europe.

Disadvantages: Major producer of greenhouse gases and a cause of acid rain. It also liberates radioactive elements within coal in quantities higher than properly operated nuclear power plants, but well below minimum levels tolerated by EU states.

Current contribution: 31% Forecast for 2010: 25%

Advantages: Widely available, easily transported and efficient. CO2 emissions are far lower than other fossil sources.

Disadvantages: Gas reserves will be exhausted well before reserves of coal run out. Most of Europe's gas comes from Russia and Algeria making it vulnerable to unpredictable political events.

Current contribution: 12% Forecast for 2010: 22%