How would the footprint of a shale gas operation compare with the footprint of other ways of delivering a similar quantity of energy?
There are many dimensions to a "footprint". In this blog post, I'll look at land area, vertical height, and vehicle movements.
I'll compare a shale gas pad (which might produce 0.9 billion cubic metres of gas over 25 years) with a 174-MW wind farm and a 380-MW solar park, both of which would deliver roughly 9.5 TWh of electricity over 25 years – the same amount of energy as the chemical energy in 0.9 billion cubic metres of gas.
In this table I've highlighted in green the "winning" energy source for each of the footprint metrics.
|Shale gas pad
174 MW capacity
380 MW capacity
|Energy delivered over 25 years
|Number of tall things
|1 drilling rig
|Land area occupied by hardware, foundations, or access roads
|Land area of the whole facility
|Area from which the facility can be seen
|3800 (or 7600*)
The total land area of the facility is smallest for the shale gas pad, and largest for the wind farm. The land area actually occupied by stuff is smallest for the shale gas pad, and largest for the solar park – the wind farm has lots of empty land between the turbines, which can be used for other purposes.
In terms of visual intrusion, the wind turbines are the tallest, and could be seen from a land area of between 52 and 170 square km, depending how they are laid out. (To roughly estimate an area of visual influence, I computed the land area within which the drilling rig or a wind turbine would be higher than 3 degrees above the horizon, assuming a flat landscape.) By this measure, the shale gas pad creates the least visual intrusion. Moreover, the drilling rig might be in place for only the first few years of operations at the shale gas pad. The solar panels are the least tall, but the solar facility occupies 450 times as much land area as the shale gas pad. (I've assumed that the wind farm and solar parks wouldn't require any additional "intrusive" electricity pylons.)
When it comes to truck movements, all three energy facilities require lots! I've assumed that solar panels are delivered at a rate of 800 (originally 400*) panels per truck; for the wind farm, my estimate is dominated by the delivery of materials for foundations and roads at 30 tonnes per truck; the estimates for the shale gas pad are from DECC's recent Strategic Environmental Assessment and from the Institute of Directors' report "Getting Shale Gas Working". The shale gas pad might require the fewest truck movements, if all water is piped to and from the site. But if water for the fracking is trucked to and from the site, then the shale-gas facility would require the most truck movements.
What can we take from these numbers? Well, perhaps unsurprisingly, there is no silver bullet – no energy source with all-round small environmental impact. If society wants to use energy, it must get its energy from somewhere, and all sources have their costs and risks. I advocate deliberative conversations in which the public discuss the whole energy system and look at all the options.
Thanks to Jenny Moore, Martin Meadows, and James Davey for helpful discussions.
Comments and clarifications
All estimates are for energy production facilities located in the UK. The estimate of energy produced from a shale gas pad is highly uncertain, since there are no data for actual shale gas production in the UK.
The comparison in the table is based on deeming 1 kWh of electrical output from the wind to be 'equivalent' to 1 kWh of chemical energy in the form of gas. This is the conventional equivalence used for example in DUKES and in Sustainable Energy - without the hot air. The following differences between the energy sources should be noted.
- The three sources of power have different profiles of power generation. On an annual scale, a single shale gas well produces most power when it is newly fractured, whereas a wind-farm produces a relatively constant average power over its life. On an hour-by-hour scale, the gas from the well is dispatchable – its flow can be turned up and down at will – whereas the power from a wind-farm is intermittent.
- In a world in which the only conceivable use for gas is making electricity in a power station with an efficiency of about 50%, one might prefer to deem each 1 kWh of gas as 'equivalent' to just 0.5 kWh of electricity.
- On the other hand, in a world that values gas highly relative to electricity that is generated at times when the wind blows, one might imagine planning (as Germany is said to be planning) to use electricity from wind-farms to synthesize methane (with an efficiency of 38-48%); then one might deem each 1 kWh of wind-electricity as being 'equivalent' to 0.38-0.48 kWh of gas.
- If one wished to make a comparison in which both power sources are constrained to have very low carbon emissions, the shale-gas well must be accompanied by other assets. For example, if the gas is sent to a power station that performs carbon capture and storage, the gas-to-carbon-free-electricity efficiency might be about 42%, and the land area for the power station and the carbon transport and storage infrastructure should be included; assuming that these assets have an area-to-power ratio of 100 ha per GW(e), each 43.4-MW gas well (which would yield 18.2 MW of electricity) would require an extra 1.82 ha of land, which roughly doubles the 2-ha land area mentioned in the table.
My estimate for vehicle movements for large wind-farms is based on Farr wind-farm. I'm sure there is considerable variation from project to project, and I would welcome more data. For the number of truck movements required for a wind farm, I reckoned there would be about 870 movements to bring in the turbines themselves [counting an in-bound and out-bound trip as two movements], and significantly more movements to bring in the materials for roads and concrete for foundations. Some of these materials may be mined from quarries located on the wind-farm, which would then involve no vehicle movements on public roads; based on Farr wind-farm (where three quarters of the road materials were sourced on site) [sorry, I don't have a link for this fact], the road building would require 2774 vehicle movements for a 174-MW windfarm, and the foundations would require another 4140 or so – in total, about 7800 vehicle movements.