Life Cycle Assessment of Renewable Energy Sources and Energy Networks

Decarbonisation of electricity supplies requires an understanding of where CO₂ emissions arise across the life cycle of electricity generation, transmission and distribution as well as demand. For electricity generation, emissions from burning fossil fuels during operation are well-known but there are also emissions that arise indirectly during extraction and processing of materials, construction, maintenance and decommissioning. This means that 'low carbon' technologies like renewables and nuclear are not entirely carbon-free. Work at IES has been applying life cycle assessment (LCA) methods to assess the energy consumption and CO₂ emissions of a range of new renewable technologies as well as transmission and distribution networks. These include micro-wind turbines, wave energy converters and tidal current turbines.

Detailed life cycle stages analysed for the Pelamis wave energy converter [1]
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Carbon Audits of Marine Energy Converters

In separate studies we have analysed the life cycle energy and CO₂ emissions for several marine energy converters:

• Pelamis wave energy converter manufactured by Pelamis Wave Power (formerly Ocean Power Delivery) [1] and
• Marine Current Turbine Ltd's Seagen tidal current turbine [2].

Micro-generation is being promoted to lower CO₂ emissions by replacing grid electricity with production from domestic generators. One concern over this drive is that the use of smaller plant could lead to the loss of economies of scale. In part this relates to cost but also life cycle embodied energy and CO₂ emissions. IES conducted a life cycle audit for the SWIFT, a 1.5 kW rooftop-mounted, micro-wind turbine, manufacturered by Edinburgh-based Renewable Devices. The analysis shows that the energy intensity and CO₂ emissions compare well with large wind turbines and are significantly lower than fossil-fuelled generation [3].

Carbon Audit of the National Grid in Great Britain

Using a 40-year period and assuming a static generation mix it shows that the carbon emissions of the transmission network are around 11gCO₂/kWh of electricity transmitted. Operational emissions account for 96% of this with transmission losses alone totalling 85%. Other significant contributors are sulphur hexafluoride (SF₆) emissions while the embodied CO₂ of the raw materials within the network infrastructure itself represents a modest 3%. While reductions in the carbon intensity of the generation mix is largely outside the control of transmission companies, investment decisions informed by whole-life cycle carbon assessments of network design could balance higher financial and carbon ‘capital’ costs of larger conductors with lower transmission losses and CO₂ emissions over the network lifetime [4].

A similar analysis is being conducted for the 33 kV distribution system in the north of Scotland [5] - details will appear soon.

Key Publications

The full range of papers relating to climate change and its impact on renewables is available from my publications page. Key work includes:

[1] R.P.M. Parker, G.P. Harrison and J.P. Chick, 'Energy and carbon audit of an offshore wave energy converter', Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 221 (8), December 2007, 1119-1130. Recipient of the 2007 Arthur Charles Main Award for best paper on a power industries subject published by the Institution of Mechanical Engineers (IMechE).

[2] C. A. Douglas, G. P. Harrison and J. P. Chick, 'Life cycle assessment of the Seagen marine current turbine', Proceedings of the Institution of Mechanical Engineers, Part M: Engineering for the Maritime Environment, 222 (M1), February 2008, 1-12.

[3] R. K. Rankine, J. P. Chick and G. P. Harrison, 'Energy and carbon audit of a rooftop wind turbine', Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 220 (7), 2006, pp. 643-654.

[4] G. P. Harrison, E. J. Mclean, S. Karamanlis and L. F. Ochoa, 'Life Cycle Assessment of the Transmission Network in Great Britain', Energy Policy, in press. Available here.

[5] C. McConville and G. P. Harrison, 'Energy and carbon audit of a 33 kV medium voltage distribution system in Scotland', in preparation.

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LCA related publications