What Is Renewable Energy

Renewable energy is a source of power which is replenished naturally, such as solar, wind or biomass. In 2005, about 13% of global primary, or raw, energy comes from renewables, of which most is from traditional biomass like wood-burning.

Hydropower is the second largest renewable source, supplying 2-3%, while modern renewable technologies such as solar, wind, marine and geothermal collectively produce less than 1% of the total world energy demand.

Solar

Solar Photovoltaic (PV) systems convert radiation from the sun into electricity. PV will work in any weather so long as there is daylight - the greater the intensity of sunlight on the PV panels, the more electricity is generated. Research is ongoing in solar technology, and efficiency is expected to increase substantially (current PV is approximately 15% efficient) as developments such as solar thermal energy generation (STEG) are brought into the mainstream.

Despite our infamous weather, the average UK home could generate 50-60% of its electricity needs from PV panels installed on the house rooftop.

Wind

Wind turbines harness the power contained within a moving mass of air. The rotation of the blades causes the shaft of the turbine to rotate inside a generator, producing electricity. The greater the speed of the wind, the more power is produced and as wind speed increases with height, turbines are normally sited on a tall mast.

Biomass

Biomass is only considered renewable because it can be replaced at the same rate as which it is used (by growing trees for example). Biomass includes two main categories: woody (forest residues and energy crops like willow) and non-woody (animal waste and high energy crops like rapeseed).

Biofuels

Biofuels are derived from biomass and are used in vehicles as a blend with conventional fuel. Petrol vehicles can be modified to take a blend of 85% bioethanol and 15% petrol, while diesel vehicles generally accept 5% biodiesel and 95% mineral diesel. Some manufacturers, such as Volkswagen Germany, cover their diesel engines to run on 100% biodiesel.

It should be noted that 100% biodiesel engines are not carbon neutral - life cycle assessments show that first generation biofuels can save up to 60% carbon emissions, while second generation biofuels can save up to 80%.

Recently, biofuels have gained headlines in the form of disputes over land-use. Italy and Mexico have both seen that increased use of land for biofuels inevitably leads to lower crop-production, sparking protests over the price of pasta or corn flour.

The UK has set a target for biofuels under the Renewable Transport Fuel Obligation, which requires 5% of all fuel sold by 2010 to come from renewable sources.