This Q&A is part of the Guardian's ultimate climate change FAQ
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guardian.co.uk, Monday 26 September 2011 10.40 BST
The Gemasolar 15 MW solar power tower plant that uses molten salt technologies for receiving and storing energy. Its 16-hour molten salt storage system can deliver power around the clock. It runs the equivalent of 6570 full hours out of 8769 total. Gemasolar is owned by Torresol Energy and has been completed in May 2011. Photograph: Markel Redondo/Greenpeace
The majority of the world's man-made carbon emissions are released by the burning fossil fuels to create electricity, heat or motion. This means that it will almost certainly be impossible to reduce greenhouse gas concentrations to sustainable levels unless large quantities of low-carbon energy can be brought on-stream to substitute for fossil fuels.
The two main sources of low-carbon energy are renewables – which includes categories such as solar, wind, hydro, biomass and marine energy – and nuclear. In terms of total primary energy supply (i.e. raw energy created), data for 2008 suggest that fossil fuels provided around 85%, nuclear contributed around 2% and renewables provided around 13%. The renewables contribution breaks down by technology as follows:
Biomass (wood, etc): 10.2%
Wind: 0.2%
Hydropower: 2.3%
Marine: 0.0002%
Geothermal: 0.1%
Solar: 0.1%
In terms of final energy consumption (i.e. the energy consumed by end-users), the contribution of low-carbon sources is slightly higher.That's because a large proportion of the energy produced from fossil fuels is wasted as heat during the conversion to electricity. One estimate for the year 2009 put the contribution of renewables to final energy consumption at 19% and nuclear at 2.9%.
Some renewable energy technologies – including solar and wind – are growing in total capacity very quickly. However, the proportion of total energy that comes from low-carbon sources in the coming years and decades will depend not just on the roll-out of renewables and nuclear, but also on total energy consumption, which without regulation at the global level could continue to grow, cancelling out the emissions savings of low-carbon sources.
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