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Carbon capture and storage (CCS) electricity revealed to be high environmental impact

Posted on by Craig Jones

The UK is legally committed to reducing greenhouse gas (GHG) emissions by 80% between 1990 and 2050. This is a considerable challenge and all sectors have a valuable part to play. To be achieved the electricity sector is expected to have an almost complete decarbonisation and it’s clear to see why. Electricity generation contributes around 30% to the UKs GHG emissions and being a highly centralised system it’s an obvious target for reduction. 

However, future electricity demand is predicted to rise from an increasing population, higher demand for electric vehicles and heat pumps, and from a future tipping point that could facilitate a ‘dash for electricity’ – at the point when electricity becomes lower carbon than using natural gas. As a result the carbon footprint of each kilowatt hour of electricity needs to reduce 95% by 2050. That said, the Committee on Climate Change consider the decarbonisation of electricity as the most cost effective strategy to meeting the UK carbon budgets.

To achieve such a challenging target the UK needs to rely on a mixture of proven low carbon generation technologies such as nuclear, wind, solar and biomass. But we also have considerable hopes pinned on the development of carbon capture and storage (CCS) technologies. CCS is often expected to capture 90% of the GHG emissions from coal and gas fired generators. But what are the implications of this, and will carbon capture and storage really allow us to meet a 90% reduction in our GHG emissions? 

Let’s start by looking at our current supply of electricity. In 2011 gas provided 40% of our electricity generation, coal 30%, nuclear 19%, renewable 9.4% and other fuels provided 2.5%. Natural gas and coal therefore provided 70% of our electricity needs.  It’s therefore clear to see why so many hopes are pinned on the success of carbon capture and storage technologies. 

A paper published in the journal Energy Policy, by Dr Craig Jones, Circular Ecology, and Professor Geoff Hammond, University of Bath, has assessed the environmental implications of a changing UK electricity system. The assessment takes a bigger picture perspective by using an integrated approach to assess the impact of future electricity pathways on a ‘whole systems’ basis. Whilst most of our attention is traditionally on direct emissions, i.e. released at the power station, this approach steps back and looks at the wider energy system. In fact, it traces activities all the way back to the extraction of fuels and materials from the earth. This is the carbon footprint, or sometimes called consumption based emissions at a national level. It’s a topic that’s slowly gaining recognition at Government level. Consumption based reporting is on DECC’s radar following an enquiry in 2012 by the House of Commons Select Committee on Energy and Climate Change and by implementing this approach surprising insights into the impacts of our energy system were discovered. 
 

Carbon Capture and Storage (CCS) can’t deliver as promised

The article found that carbon capture and storage couldn’t deliver a 90% reduction in the emissions of a power station on a whole systems basis. In fact a reduction of 70% was more likely – which is a significant shortfall. A key finding was the importance of the upstream emissions of fuel production. In particular fugitive methane emissions are released in coal mining and gas pipelining operations. Methane is 25 times more potent as a greenhouse gas than carbon dioxide and therefore even a small emission can provide a notable contribution to the carbon footprint. This contributed a surprising amount to results because upstream emissions aren’t captured in CCS technologies. This is of particular importance to coal fired electricity generation, which has much lower generation efficiency than gas. A lower efficiency means more coal is needed and therefore more upstream methane emissions.

However, just as prominent was the fuel penalty of a CCS installation, which is often considered to be around 15-20 % (extra fuel requirement). This adds further to the lower generation efficiency of coal fired electricity, which in turn increases upstream methane emissions. In fact, when upstream emissions are also considered carbon capture and storage may only deliver a 70 % reduction in GHG emissions for coal fired generation. Currently, coal-fired electricity was found to release 1.09 kg CO2e per kWh of electricity delivered to the UK consumer. This was predicted to fall to 0.31 kg CO2e per kWh with CCS technologies. This is far short from the hopes of a 90 % GHG reduction.

For comparison gas fired CCS generation was found to offer an 83% reduction in GHG emissions on a whole life basis. Gas-fired electricity currently releases 0.47 kg CO2e per kWh of electricity delivered to the UK consumer. This was predicted to fall to 0.08 kg CO2e per kWh with CCS technologies. Whilst the results for gas are more promising it should be noted that with depleting North Sea gas reserves the UK is looking abroad to provide more and more of its fossil fuels. This requires longer transport distances and longer gas pipelines, which in turn gives rise to more fugitive methane emissions for gas and its resulting GHG impact.
 

Wider Environmental Impacts of Carbon Capture and Storage

Naturally carbon isn’t the only environmental issue and it’s important to consider wider environmental impacts. This is where life cycle assessment (LCA) can help. LCA is a decision support ‘tool’ that can assess the environmental impact of up to 18 different environmental impact categories at once. For example, the impacts of human toxicity, soil acidification, fossil fuel depletion, land transformation and impacts on fresh and sea water resources, amongst others. Taking this approach a step further these results can be weighted into a single score, i.e. an ecopoint. Whilst this simplifies the interpretation of results it should be noted that weighing the relative importance of impacts will always have a level of subjectivity. This must be appreciated when looking at these results, but nonetheless in certain cases it remains a useful way of simplifying results. The method used here for the calculation of the ecopoints is called ReCiPe, which is a well used life cycle assessment method that was created by a collaboration of academic and industrial partners. The method contains built in weighting factors (which are usually determined by surveying experts) for each of its 18 environmental impact categories. A higher ecopoint score is seen as worse for the environment. In this study the baseline ecopoint index was considered as the grid average electricity from 1990, with an ecopoint score of 100.
 

Coal fired carbon capture and storage (CCS) has a higher impact than current gas fired electricity?

Using this approach an interesting result was discovered. On this basis coal fired carbon capture and storage is only expected to be 30 per cent lower environmental impact than current coal fired electricity generation (119 ecopoints to 85). Likewise gas fired CCS electricity is only expected to be 35 per cent lower environmental impact than current coal fired generation – 54 ecopoints to 35 ecopoints. 
 

However, the most striking result using this approach was that coal fired CCS is predicted to have a higher environmental impact than current gas fired generation – 85 ecopoints for Coal CCS to 54 ecopoints for current gas fired generation. This is significant and some of the key issues were increased depletion of fossil fuel reserves, human toxicity impacts and of course carbon footprint. It’s also interesting to see that current gas fired generation has a carbon footprint of 0.47 kg CO2e per kWh in comparison to coal CCS at 0.31 kg CO2e per kWh, which is just 35% lower than current gas generation. These results compare with the ecopoint score of average electricity in 2008 of 69 ecopoints. 

These results don’t look particularly promising for coal CCS from an environmental sustainability perspective, which is even higher environmental impact than the UK average electricity from 2008. This is unfortunate as coal is expected to become the world’s top energy source by 2017.

So what can we take from such analysis and what should we do about it? If we are to rely on carbon capture and storage as a future technology that will help us meet an 80% reduction in GHG emissions then we have to be careful that we don’t increase emissions elsewhere in the supply chain and that we don’t burden shift. We should be looking closer at fugitive methane emissions in coal mining and gas transmission and distribution. But we should also be asking what does coal CCS need to do to become a more attractive environmental proposition? To reduce the carbon footprint, and wider environmental impacts, of coal fired CCS will require considerable advances in the electrical efficiency of coal fired generators. Without such advances coal fired carbon capture and storage won’t offer as much environmental benefit as it first appears.

But this still leaves the question will coal fired CCS be able to offer any environmental gain? Please share your valuable opinion…

This article was originally published in Energy World (Energy Institute). 

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Reference to original journal paper: “The energy and environmental implications of UK more electric transition pathways: A whole systems perspective”, Energy Policy 52 (Jan 2013), pg 103–116, http://dx.doi.org/10.1016/j.enpol.2012.08.071 

Craig Jones

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