- Shale gas ranks between the fourth and eighth relative to other electricity options.
- To become the most sustainable option, large improvements would be needed.
- This includes a 329-fold reduction in environmental impacts.
- A 16-fold increase in employment would also be needed.
- An electricity mix with less rather than more shale gas is more sustainable.
Jasmin Cooper, Laurence Stamford, Adisa Azapagi
School of Chemical Engineering and Analytical Science, The University of Manchester, The Mill, Room C16, Sackville Street, Manchester M13 9PL, UK
Received 13 September 2017 Accepted 13 November 2017
Many countries are considering exploitation of shale gas but its overall sustainability is currently unclear. Previous studies focused mainly on environmental aspects of shale gas, largely in the US, with scant information on socio-economic aspects. To address this knowledge gap, this paper integrates for the first time environmental, economic and social aspects of shale gas to evaluate its overall sustainability.
The focus is on the UK which is on the cusp of developing a shale gas industry. Shale gas is compared to other electricity options for the current situation and future scenarios up to the year 2030 to investigate whether it can contribute towards a more sustainable electricity mix in the UK. The results obtained through multi-criteria decision analysis suggest that, when equal importance is assumed for each of the three sustainability aspects shale gas ranks seventh out of nine electricity options, with wind and solar PV being the best and coal the worst options. However, it outranks biomass and hydropower.
Changing the importance of the sustainability aspects widely, the ranking of shale gas ranges between fourth and eighth. For shale gas to become the most sustainable option of those assessed, large improvements would be needed, including a 329-fold reduction in environmental impacts and 16 times higher employment, along with simultaneous large changes (up to 10,000 times) in the importance assigned to each criterion. Similar changes would be needed if it were to be comparable to conventional or liquefied natural gas, biomass, nuclear or hydropower.
The results also suggest that a future electricity mix (2030) would be more sustainable with a lower rather than a higher share of shale gas. These results serve to inform UK policy makers, industry and non-governmental organisations. They will also be of interest to other countries considering exploitation of shale gas.
Exploitation of shale gas is a contentious topic in many countries. At present, shale gas is exploited at a large scale only in the US, with other nations considering its development (Cooper et al., 2016). The UK is at the cusp of starting exploitation, with the government and industry keen to develop a shale gas industry, but with a strong opposition from numerous stakeholders, including non-governmental organisations, local residents and activists (Gosden, 2017, Johnston, 2017, Ward, 2017).
The impacts on the environment are the main argument against the exploitation of shale gas while the supporters highlight improved national energy security and economic development as key aspects in its favour (House of Lords, 2014, Moore et al., 2014). Some of these sustainability aspects have been considered previously by the authors (Cooper et al., 2014, Cooper, 2017), but evaluated environmental, economic and social aspects in isolation of each other. This work builds on that research by integrating all three dimensions to assess the overall sustainability of shale gas in the UK using multi-criteria decision analysis (MCDA). The main goals of this study are:
- to assess the overall sustainability of shale gas relative to other electricity options in the UK, including other fossil alternatives, renewables and nuclear power; and
- to investigate how its deployment could affect the sustainability of a future UK electricity mix, taking into account different levels of shale gas penetration.
In total, 18 sustainability indicators are considered, of which 11 are environmental, three economic and four social. While there have been numerous other studies on the sustainability of shale gas, they are almost exclusively based in the US and tend to focus on environmental aspects, typically considering only one or a limited number of impact categories; for an extensive review, see Cooper et al. (2016). Therefore, as far as we are aware, this is the first study internationally to provide an integrated assessment of shale gas and to compare it other electricity options.
The methods used in the study are outlined in the next section. The results are presented and discussed in Section 3 and conclusions are drawn in Section 4.
The environmental and economic sustainability assessments have been carried out using life cycle assessment (LCA) and life cycle costing (LCC), respectively; social sustainability has been evaluated by developing relevant social sustainability indicators. A brief overview of these is given below, followed by a description of the MCDA method used.
The results of the LCA, LCC and social sustainability assessment are summarised in Table 1, based on the previous work by the authors (Cooper et al., 2014, Cooper, 2017); for definitions of the indicators, see Table S1 in the Supporting Information (SI). In addition to shale gas, the following electricity options are also considered: conventional gas, liquefied natural gas (LNG), coal, nuclear, hydro, wind, solar photovoltaics (PV) and biomass. These options have been chosen as they are currently used in the UK and are expected to play a role in a future electricity mix.
Table 1. Sustainability indicators and their estimated values for different electricity optionsa.
Both the current electricity mix and future scenarios are considered. As commercial production of shale gas is not expected in the UK until post-2020 (Lewis et al., 2014), the year 2030 has been selected for the evaluation of a future electricity mix. Two 2030 electricity scenarios are considered: one with low penetration of shale gas (1%) and another with the highest possible contribution (8%) to the mix; for details, see Table 2. The results of the LCA, LCC and social sustainability assessment for the current and future electricity mixes are given in Table 3 (Cooper et al., 2014, Cooper, 2017).
Table 2. Current electricity mix and future scenariosa.
Table 3. Sustainability indicators and their estimated values for the current electricity mix and future scenarios (Cooper et al., 2014, Cooper, 2017).
Multi-criteria decision analysis
The Simple Multi-attribute Rating Technique (SMART) method has been chosen for the MCDA in this work because it is relatively simple to implement and can accommodate a large number of criteria and alternatives being considered. SMART involves the following steps (Edwards, 1977):
- identification of the options to be compared;
- identification of the decision criteria;
- scoring of the criteria in the order of importance (increasing from a score of 10 for the lowest importance onwards) and estimation of their weights of importance;
- rating of the options on a scale of 0 (worst) to 1 (best);
- estimation of the overall scores and ranking of the options on a scale from 0 (worst) to 1 (best); and
- identification of the best option.
The MCDA has been carried out using the Web-HIPRE tool (Mustajoki and Hamalainen, 2000) based on the decision tree in Fig. 1. Following the SMART methodology, the sustainability aspects and indicators have been weighted based on their assumed relative importance and the options rated based on their performance for each indicator (see Table 1) using value factions. Two types of value functions – linear and exponential – have been applied to investigate the effect on the overall ranking of the options and gauge the robustness of the results. The calculated weightings and ratings have then been used to estimate the overall sustainability score – the option with the highest value is considered the most sustainable and vice versa. For further details on the SMART methodology, see Section S1 in the SI.
Fig. 1. MCDA decision hierarchy, showing the sustainability aspects, indicators and electricity options considered in the analysis.
[Goal: i) to assess the overall sustainability of shale gas relative to the other electricity options in the UK; ii) to find out how its deployment could affect the sustainability of a future UK electricity mix. Indicators: ADPe: abiotic depletion of elements; ADPf: abiotic depletion of fossil fuels; AP: acidification potential; EP: eutrophication potential; FAETP: freshwater aquatic ecotoxicity; GWP: global warming potential; HTP: human toxicity potential; MAETP: marine aquatic ecotoxicity potential; ODP: ozone depletion potential; POCP: photochemical oxidant creation potential; TETP: terrestrial ecotoxicity potential; LCOE: levelised costs of electricity; DE: direct employment; WI: worker injuries; PSI: public support index; DFS: diversity of fuel supply].
Two MCDA models have been constructed in Web-HIPRE, one comparing shale gas with the other electricity options and another comparing the present and future electricity mixes. The former is based on the data summarised in Table 1; the data for the second MCDA model can be found in Table 2, Table 3.
In the base case, it is assumed that all three sustainability aspects (environmental, economic and social) are equally important, assigning each a weighting of 0.33; the effects of changing the importance of the aspects have been assessed through extensive sensitivity analyses. A further analysis has also been carried out to find out to what extent the weightings would need to change for shale gas to emerge as the most sustainable option overall, or to be comparable with conventional gas, LNG, renewables or nuclear power. The required improvements in the performance of shale gas for different sustainability indicators have also been considered.
Data quality assessment
A data quality assessment has been carried out to evaluate the overall quality of the data used in the study and, through that, the validity of the results. A pedigree matrix, typically used in LCA (Althaus et al., 2007, Weidema et al., 2013), has been applied for these purposes. The pedigree matrix rates data quality on the following six criteria on a scale from 1 (high) to 5 (low): reliability, completeness, temporal correlation, geographical correlation, technological correlation and sample size. For further details, see Table S2 in the SI.
The data have been rated for each of the above criteria and averaged for each sustainability aspect, using the results from LCA, LCC and social sustainability assessment, respectively. The ratings have then been added up to calculate the overall data quality score for each sustainability aspect, ranging between 6 and 30 as follows:
- 6 to 12: high quality;
- > 12 to 18: medium quality;
- > 18 to 24: medium-low quality; and
- > 24: low quality.
This section first compares the overall sustainability of shale gas with the other electricity options. This includes a sensitivity analysis and the improvements in the life cycle of shale gas electricity that would be required to improve its overall ranking. This is followed by a comparison of the current electricity mix with the future scenarios and, finally, by the assessment of data quality.
Sustainability of shale gas compared to other electricity options
The results in Fig. 2 indicate that, if the environmental, economic and social aspects are equally important, the best options are wind and solar PV with scores of 0.79 and 0.78 (linear value function; LVF) and 0.90 (exponential; EVF) while the worst is coal with 0.39 (LVF) and 0.54 (EVF). Shale gas ranks seventh out of nine options for both value functions, scoring 0.64 and 0.69, respectively. The best and the worst options are unaffected by the type of the value function used but the order of some other options changes.
For example, hydroelectricity ranks fifth for the LVF and eighth for the EVF, while biomass ranks eighth for the LVF and sixth for the EVF. This is because the LVF does not take into account the magnitude of the difference in values of different indicators (for these, see Figs. S1 and S2 in the SI). For instance, while biomass scores poorly for six out of 11 environmental indicators and for two out of three economic indicators, it is still much better (up to two orders of magnitude) than the worst option for each indicator (see Table 1). Thus, using the EVF, which takes this into account, is arguably more appropriate.
Fig. 2. Ranking of the electricity options assuming equal weightings for the sustainability aspects and indicators.
As can be seen in Fig. 2, the environmental aspect contributes the most towards the overall score for shale gas (38% for the LVF and 43% for the EVF), followed by the social (30% and 33%) and finally the economic aspect (26% and 29%). Similar contributions are found for most other options. The exception is coal where the social dimension is dominant (41% and 48%) and the environmental has a small influence overall (16% and 18%).
The sensitivity analysis explores how the ranking of the options changes when one of the three sustainability aspects is prioritised over the other two. In each case, the weightings for each aspect have been changed in turn until the ranking of the best or worst option changed. The equal importance of each sustainability indicator remains unchanged throughout. These results are discussed in turn in the next sections.
If the environmental aspect is assumed more important than the other two, wind and solar PV remain the best options until the weighting for the environmental aspect is seven times higher for the LVF and 31.5 times for the EVF (Fig. 3a&b). At and above these weightings, hydropower is the most sustainable option, followed closely by wind while solar PV drops to the seventh (LVF) and eighth place (EVF). Shale gas is ranked, respectively, sixth, followed closely by solar PV, and fourth, being only marginally better than nuclear and conventional gas. For both value functions and all the options, the main contributor to the overall sustainability score is the environmental aspect, which is to be expected given its high assumed importance.
Fig. 3. Ranking of the electricity options assuming different importance of the environmental aspect.
When the importance of the environmental aspect is reduced by 2.8 times for the LVF, solar PV outranks wind as the best option and shale gas is ranked sixth, marginally better than biomass and hydroelectricity (Fig. 3c). For the EFV (Fig. 3d), the importance of this aspect has to be 2.7 times lower than of the other two dimensions of sustainability for the rankings to change; solar PV is still the best option but hydro is now the least sustainable, together with coal and followed closely by shale gas in the seventh place. In both cases, the economic and social aspects have a similar contribution, dominating the overall sustainability scores, while the contribution of the environmental aspect is small, again as expected, given its assumed low priority.
Wind and solar PV remain the best options until the weighting of the economic aspect is 23 times higher for the LVF and 2.5 times for the EVF (Fig. 4a&b). At and above these weightings, solar PV is still the best option but hydro becomes the least sustainable, followed closely by coal. It is interesting to note that for the LVF, wind drops to the fifth place (Fig. 4a) because of its poor performance in levelised and capital costs. Shale gas is ranked sixth for the LVF and seventh for the EVF.
Fig. 4. Ranking of the electricity options assuming different importance of the economic aspect.
On the other hand, if the economic aspect is assumed to be the least important, the rankings remain the same until it is 49.5 times less important. In that case, hydro is the most sustainable option jointly with wind for the LVF (Fig. 4c); shale gas is in the seventh place. For the EVF, wind overtakes solar PV as the most sustainable option when the importance of the economic aspect is reduced by 4.5 times (Fig. 4d).
The ranking of the options changes when the social aspect is 12.3 times more important than the other two for the LVF and 11 times for the EVF at which point LNG becomes the least sustainable option, narrowly behind coal (Fig. 5a&b). Shale gas ranks seventh for both value functions, following nuclear power; for the EVF, it is only marginally better than coal and LNG.
Fig. 5. Ranking of the electricity options assuming different importance of the social aspect.
When the importance of the social aspect is reduced by 24.5 times for the EVF, LNG becomes the most sustainable option, being only slightly better than wind, nuclear, solar PV and conventional gas (Fig. 5c). Coal remains the least sustainable option and shale gas is ranked seventh. For the LVF, there is no change in the rankings with a reduction in the importance of the social aspect.
Changes needed for shale gas to become the most sustainable option
This section aims to determine what would be required for shale gas to become the most sustainable option among those considered in this study. First, multiple indicators are considered simultaneously for each sustainability aspect before looking at the individual indicators.
Multiple sustainability indicators and aspects
Based on its performance in different sustainability aspects and indicators (Table 1), and not considering any improvements in the sustainability, there are only two scenarios in which shale gas would become the top-ranking option (jointly with some others). These are as follows:
- joint best with LNG and conventional gas if the capital cost is 1000–10,000 times more important than the other economic indicators and, simultaneously, the economic aspect is 1000 times more important than the other two aspects; and
- joint best with conventional gas and nuclear if the importance of worker injuries is 1000 times higher than of the other social indicators and, at the same time, the importance of the social aspect is 1000 times greater than of the other two.
For the remaining indicators, shale gas can never be the best option unless its performance is improved considerably. For example, a 40%–70% improvement is needed in all the indicators for shale gas to become the most sustainable option, jointly with wind and solar PV (Table 4). If the performance is improved in one sustainability aspect at a time, even larger improvements are needed. For the environmental aspect, a 100-fold reduction in the environmental impacts is required and this aspect has to be 3.8–23 times more important than the other two.
For the economic aspect, a large reduction (50% to 20 times) in costs is needed, together with an increase in the importance of this aspect (up to 2.5 times) for shale gas to be the best option, together with solar PV. However, for greater reductions to all cost indicators (see Table 4), no changes in the importance of the economic aspect are needed. Improvements in the social indicators are only applicable to employment and public support, which must be improved by at least 16 and 13 times, respectively, for shale gas to emerge as the top option (Table 4). Thus, based on these results, it is highly unlikely that shale gas would be the most sustainable option among those assessed here.