One of the big themes that we've been covering for a while is fracking' pumping in chemicals, sand and water to extract gas and oil trapped in shale. This process has already had a huge impact on America's energy costs, and it could eventually do the same here.
But there's another technology that could have equally large implications underground coal gasification (UCG). Supporters claim that UCG could enable us to extract clean energy from coal seams too deep to mine. What's more, it would do so with reduced carbon emissions and without the toxic by-products of conventional mines.
Best of all, it could also allow us to unlock the huge amount of coal at the bottom of the North Sea a trove that is already being compared to the discovery of North Sea oil.
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So how does it work and how could you potentially profit from it?
What is underground coal gasification?
Like fracking, UCG is not a new technology. In fact, Sir William Siemens (the brother of the founder of the German engineering firm) came up with the basic idea in 1868.
He believed that if you set fire to the coal in a mineshaft it would produce gas, which could then be collected, eliminating the need for manual extraction. The first serious tests were carried out in the Soviet Union in the 1930s. By the 1960s, five plants were using the process.
The discovery of more accessible natural gas supplies dampened interest. But researchers kept improving the techniques. As a result, the technology is now much more sophisticated.
Instead of digging a mineshaft and starting a fire (as fraught with potential problems as it sounds), the more modern take on UCG is to drill a hole into the seam and then inject oxygen and water to set it alight. The gas then exits through another hole.
As with shale gas, this process has its critics. The big concern is that if the pressure is too high, tar can be formed, which can get into the water supply. The other big worry is that the underground cavity created by the destruction of the coal could also collapse.
However, if the pressure is strictly controlled, then the amount of tar produced is relatively small, and will be filtered out by surrounding rocks. Tests carried out in Spain in the 1990s seem to vindicate this approach.
There are also benefits to this approach, according to the coal industry. Harmful vapours, such as sulphur dioxide, can be captured during the process and stored underground for less than the cost of conventional mining. The World Coal Association reckons that UCG could reduce levels of particulates (such as ash) released in mining by up to 50%. They also point out that toxic waste, such as mercury, is kept safely underground.
A final benefit is that the disruption above ground is far lower than any other form of mining.
As a result, several emerging countries are starting to buy into this technology. China's desire to secure its energy supply while reducing pollution has made it the leader in UCG, with more than 30 projects underway. India has also announced an ambitious scheme to tap into around 350bn tonnes of deep buried coal.
But it's not just developing countries who are taking advantage. Linc Energy has been running a site for over 14 years in Queensland, Australia. After a competitor accidentally discharged chemicals, the company was investigated by the state government but passed with flying colours.
In the US, meanwhile, conglomerate Peabody Energy has said that it will use UCG to reach coal reserves in Wyoming that are too expensive to reach with conventional technology.
Britain's new energy treasure trove - North Sea coal?
However, the biggest benefits could lie closer to home.
In the 1970s, the sale of drilling licences in the North Sea saw companies spend millions trying to discover the size and location of the oil reserves. Tycoon Algy Cluff and geologist Eric Craig led one of the biggest independent exploration teams.
While looking for oil, they found that the North Sea also had a huge amount of coal in the seabed. They estimated there was enough to power the whole of Europe for the next 2,000 years.
Even if you just count the coal on the edges of our coastlines, they reckoned there was about the equivalent of four billion barrels of oil a lot, in other words.
The problem was that the market was more interested in oil, and in any case, it was impossible to extract. But advances in UCG make such an ambitious project feasible.
Last year, the government granted 14 firms licences to start offshore drilling, plus grants in some cases to help with costs. The government also thinks that there could be 17 billion tonnes of coal on land.
It's high risk but it could be worth a punt
This is certainly not one for widows or orphans. Unlike shale oil and gas, UCG technology has not yet been widely adopted. Environmental concerns could derail the whole project. And as with any relatively new technology, something unexpected could happen.
But then, you could have said the same thing about shale gas four years ago. And the rewards could be immense if it does turn out to be feasible.
One company we're interested in is the micro-cap, Cluff Natural Resources (Aim: CLNR). This is a new consortium formed by Algy Cluff. It holds five licences to drill offshore in North Cumbria, Largo Bay (Fife), the Firth of Forth, Loughor Estuary (Wales) and Dee Estuary (Merseyside).
With no earnings, it's as risky as you could get, but given Cluff's reputation, it's worth considering as a play on a potentially very exciting technology.
By the way, if you haven't clued yourself up on fracking yet and how it could affect the UK, you should watch my colleague David Stevenson's video on the topic.
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