What is the carbon footprint of renewable electricity?

As part of an analysis of the carbon footprint of nuclear power, Keith Barnham notes the footprint of renewables. The british Climate change commission (CCC) has recommended any new power stations should not exceeed 50 gCO2/kWh.

When comparing the carbon footprints of electricity-generating technologies, we need to take into account carbon dioxide emitted in all stages in the life of the generator and its fuel. Such a study is called a life cycle analysis (LCA).

There are other gases such as methane that are more dangerous greenhouse gases than carbon dioxide. The most reliable LCAs take all greenhouse gases into account and present equivalent carbon dioxide emissions.

In a recent paper in Energy Policy, Daniel Nugent and Benjamin Sovacool critically reviewed the published LCAs of renewable electricity generators. All the renewable technologies came in below the 50 gCO2/kWh limit.

The lowest was large-scale hydropower with a carbon footprint one fifth of the CCC limit (10 gCO2/kWh). A close second was biogas electricity from anaerobic digestion (11 gCO2/kWh). The mean figure for wind energy is 34 gCO2/kWh, and solar PV comes in a shade under the 50g limit, at 49.9 gCO2/kWh. Bear in mind that rapidly evolving PV technology means that this last figure is contantly falling.

It’s a lot more difficult to do the calculation for nuclear power, because of the concentration of uranium affects the energy to enrich; the costs of decommissioning (dismantling and waste disposal) are poorly known. Barnham’s article goes into more detail about the wide range of estimates and their assumptions.