Opportunities and risks associated with normal operation
The table evaluates the opportunities and risks of renewable energies compared with conventional power generation during normal, trouble-free operation. Green fields represent positive features, red fields negative ones. Remarks on the various criteria:
Electricity production costs
The cost of electricity from photovoltaic and fuel cells is still very high compared with electricity from all other sources. These two methods are of interest above all in places where they are not competing with other forms of power generation. Examples: remote houses not connected to the grid or mobile equipment like campers or yachts.
Unpredictable fluctuations
In order to be able to cover power requirements constantly and so guarantee security of supply, grid operators must make provision for unpredictable fluctuations in the amount of electricity available. This is done by running backup power plants at the same time. The ecological advantage of alternative power generation is hence somewhat qualified (cf. p. 21). This applies in particular to wind power, because the actual wind resource may, for a time at least, vary considerably from the anticipated or average resource.
Emissions during manufacture and construction
During the construction of large hydroelectric power plants, emissions are significantly higher than during the construction of other renewable energy power plants. This is due to the production of cement and the large earth-moving operations required for the dam. The construction of solar chimney power plants also involves emissions during the production of cement for the chimney and the manufacture of glass for the roof area.
Emissions during operation
During operation, renewable energies are "unbeatable" as far as emissions are concerned. In relation to the power generated, coal power plants emit the most pollutants – the amount depending on the flue-gas treatment measures adopted. Even in the case of optimum flue-gas treatment, considerable amounts of CO2 are released into the environment. This is also true of gas power plants.
Geographical extent of environmental impact
The greatest environmental impact of wind farms comes from their noise emissions and the visual disturbances caused by their rotating blades. The problems of storing radioactive waste from nuclear power plants are confined to the storage site and its immediate surroundings. The construction of hydroelectric power plants usually has a major impact on the natural surroundings. The situation with conventional thermal power plants is quite different: they contribute to global climate change through their CO2 emissions.
Treatment and storage of waste
The difficulties surrounding the disposal of waste from nuclear power plants are well known. Highly radioactive materials are transported – over long distances in some cases – to reprocessing plants or final storage sites. Nuclear waste has to be stored in a way that guarantees it is safely confined for 10,000 years. Coal power plants produce large amounts of ash, which has to be disposed of.