Renewable energy generation of electricity is advocated as a means of reducing carbon dioxide emissions associated with the generation from fossil fuels. Whilst it is true that renewable sources do not generate significant carbon dioxide whilst producing electricity, as with fossil-fuelled plants they do embody significant emissions in their materials of construction. The "full-chain" environmental impacts of wind, hydro, solarthermal and photovoltaic conversion are quite different and the likely trend in future reduction of embodied energy of next generation systems reflects the relative maturity of each technology. There has been much recent development of solar thermal electricity generation options for which there is a wide divergence in embodied CO2 emissions.