Coal is cheap, abundant, and responsible for about 40 per cent of the world’s electricity generation. That’s a problem, because it also has some of the highest greenhouse gas emissions of any energy source. It’s no wonder a technology that could allow the world to continue burning coal – but cleanly – is being met with some excitement, then.

Writing in the Telegraph at the end of last year, Algy Cluff, chief executive of energy company Cluff Natural Resources, said ‘underground coal gasification’ could “provide a vital energy solution and produce abundant and cheap gas for generations”. The technology briefly put its head above the parapet again today, as the BBC asked whether it be “the clean energy of the future”.

The prospect has certainly piqued the government’s interest, with energy minister Michael Fallon establishing a working group to explore its feasibility.

But is it too good to be true? We explore underground coal gasification’s prospects and try to separate the theory from the reality.

What is underground coal gasification?

Underground coal gasification (UCG) involves drilling down into coal – normally deep underground – then igniting it. The resulting gas then runs up another borehole and is collected on the surface, as the diagram below shows:

Once the gas is collected, companies can use it to run power stations, or convert it into transport fuel. Carbon capture and storage (CCS) technology can be added, reducing the process’ emissions, and making it relatively ‘clean’.

As such, the government now sees the “exciting potential” of UCG as means to generate abundant, domestically-sourced, ostensibly fairly low carbon power in the UK, the Telegraph reported.

So, what are UCG’s prospects in the UK?

200 years of coal

UCG is normally conducted onshore, as in the picture above, but new ‘horizontal drilling’ technology means it could now be possible to get at hard to reach offshore coal seams.

But could it really provide energy for 200 years, as the Telegraph claimed?

The Telegraph cited British Geological Survey (BGS) research which suggests there could be as much as 17 billion tonnes of coal located off Britain’s shores. It says that could be enough to provide energy for 289 years, based on 2004 consumption levels.

But that’s assuming all the resources can all be accessed and can are fit to undergo UCG. BGS analyst, Nigel Smith, tells us there are still a lot of unknowns.

He says that while horizontal drilling technology does make it easier to access offshore coal resources, it’s still not clear where suitable coal seams might be located. He acknowledges that some areas which BGS identified as potential UCG locations “could be quite controversial”.

Even in areas where there is existing data, Smith says there’s “quite a bit of work to do” to gather data, with some places still being a total blindspot. Companies will need to drill more boreholes to get a better idea of where suitable coal seams are, he says – which takes time and investment.

There could also be public opposition to UCG, just as there has been to shale gas in recent months, further slowing progress. Though Julie Lauder from industry group, the Underground Coal Gasification Association, says because the UK is predominantly looking at using UCG offshore, this could be less of an obstacle to the industry.

The technology is already dividing opinion, despite only being in its infancy, however. Lauder says the process is akin to scaling up the coal fires some people have in their front rooms. Campaign group, Frack Off, sees it somewhat differently, however. It warns the process would create what it describes as “hell on earth”, as it involves sparking large fires deep underground.

Once the technical and social obstacles are considered, it’s very hard to estimate exactly how much coal could end up being gasified.

Emissions

UCG could be a low carbon form of power generation if CCS technology – which is currently unproven on a large scale – was added. That in turn affects the technical and economic viability of the projects.

As the Climate Change Act legally obliges the government to reduce the UK’s emissions by 80 per cent by 2050, the onus will be on the UCG industry to prove the low emissions technology works. If it can’t show UCG with CCS is viable, it’s questionable whether or not the projects would be allowed to proceed.

Michael Blinderman, director of Ergo Exergy Technologies which develops UCG equipment, estimates that UCG power plants with CCS could emit 26 per cent less carbon dioxide than some natural gas generators. His calculations suggest UCG gas could emit as little as 380 grams of carbon dioxide per kilowatt hour of electricity generated.

That’s pretty good going compared to other fossil fuels, though it’s still more than nuclear and renewables, as the chart below shows:

Source: Intergovernmental Panel on Climate Change, Special Report on Renewable Energy Sources and Climate Change Mitigation

But CCS is yet to be proven on a large scale.

The government has just given  £1 billion of funding to kick start research programmes, and the Environment Agency  requires any UCG power plant to have CCS fitted, but it’s unclear when such projects could become a reality. And if the UCG gas gets turned into transport fuel, companies don’t have to fit any CCS technology – making it much more carbon intensive.

Questions also remain over where the carbon could be stored, if it’s captured. About 30 per cent of the captured carbon dioxide could be pumped back into the coal chamber, Lauder tells us – but that still leaves 60 per cent to store.

The BBC summarises the issue well:

“The problem, of course, is that the [UCG] process depends entirely on wider efforts to develop CCS, efforts that have, so far, singularly failed to find a solution.”

So while UCG could be made into a low carbon form of power generation with the addition of CCS technology, it’s unclear when the technology will exist to make that a realistic prospect.