Alternative energy sources, especially with regard to air emissions. The likely life-cycle emissions (taking into account fuel cultivation, harvesting, collection, transportation and processing, as well as power plant construction, operation and decommissioning) from main renewable energy technologies and conventional electricity generation are shown in Tables 2 and 3.
The results are purely indicative but show the variations and relative differences between the various fuel inputs. Life-cycle emissions from renewable energy use are small compared with those from fossil fuel plants. The studies upon which the figures are based did not examine nuclear energy.
Though nuclear power generation does have a major environmental impact, it releases no sulphur dioxide (SO2) or nitrogen oxides (NOx) and little carbon dioxide (CO2). Its life cycle emissions of these gases falls within the ranges shown for non-hydroelectric renewable energy.
Table 2. Life cycle air emissions from renewable energy (g/kWh)
|Current Practice||Future Practice||Small Scale||Large Scale||Photovoltaic||Thermal Electric|
Table 3. Life cycle air emissions from conventional electricity generation in the United Kingdom
|Best Practice*||Flue Gas|
& Low NOx
* Not representative of state-of-the-art technology. ETSU Report No. R-88,“Full Fuel Cycle Atmospheric Emissions and Global Warming Impacts from UK Electricity Generation”, HMSO, London.
Renewable energy entails a number of other potential environmental impacts. On the negative side, renewable energy can make large tracts of land unusable for competing uses, disrupt marine life, bird life and flora/fauna, and produce visual and noise pollution. Generally though, these potential environmental impacts are site-specific and there are a number of ways to minimise the effects, which are usually small and reversible. There are environmental benefits from renewables other than reduction of greenhouse gas and other air emissions. For example, hydroelectric schemes can improve water supplies and facilitate reclamation of degraded land and habitat.
The use of bioenergy can have many environmental benefits if the resource is produced and used in a sustainable way. If the land from which bioenergy is produced is replanted, bioenergy is used sustainably and the carbon released will be recycled into the next generation of growing plants. The extent to which bioenergy can displace net emissions of CO2, will depend on the efficiency with which it can be produced and used. Bioenergy plants have lower emissions of SO2 than do coal and oil plants, but they may produce more particulate matter.
These emissions are controllable but they increase generating costs. The environmental and social effects of large-scale hydropower are site specific and are the subject of much controversy. Large-scale projects may disturb local ecosystems, reduce biological diversity or modify water quality. They may also cause socio-economic damage by displacing local populations. A number of projects in developing countries have been stalled or scaled down for these reasons; obtaining loans from international lending institutions and banks for major projects has become more difficult. Although these ill effects can be managed and mitigated to some degree, they may affect the future of hydropower in general.
Mini- and micro-hydro systems have relatively modest and localised effects on the environment, but their kWh cost is generally higher. Hydro-power emits some greenhouse gases on a life-cycle basis (especially methane generated by decaying bioenergy in reservoirs), but in most cases far less than the burning of fossil fuels.
Geothermal plants may release gaseous emissions into the atmosphere during their operation. These gases are mainly carbon dioxide and hydrogen sulphide with traces of ammonia, hydrogen, nitrogen, methane, radon, and the volatile species of boron, arsenic and mercury.
This could slow the future development of geothermal resources. Emissions can be managed through strict regulations and by control methods used by the geothermal industry to meet these regulatory requirements.
Hydrogen sulphide abatement systems reduce environmental damage but are costly to install. Wind-power generation has very low emissions on a life cycle basis, but has a number of environmental effects that may limit its potential.
The most important effects on the environment
Wind turbines must be in exposed areas and are therefore highly visible. They are considered unsightly by some people, and concerns have increased with the larger size of new generation turbines.
Wind turbines produce aerodynamic noise, from air passing over the blades and mechanical noise from the moving parts of the turbine, especially the gearbox. Better designs have reduced noise, and research continues. Wind farms developed far from highly populated areas are, by definition, less offensive.
Wind turbines may scatter electromagnetic signals causing interference to communication systems. Appropriate siting (avoiding military zones or airports) can minimise this impact.
Birds get killed when they collide with the rotating blades of a turbine. Migratory species are at higher risk than resident species. Siting the turbines away from migratory routes reduces the impact.