Nuclear fusion is famously an energy source that is 50 years away - and has been for the last 50 years. However, there has been a feeling of excitement in the sector recently - with numerous private enterprises attracting huge investment ($2.3 billion across 35 companies), and a flurry of news articles promoting it as a good investment - "It is time to bet big on fusion energy", "Nuclear fusion: why the race to harness the power of the sun just sped up".

So what is nuclear fusion, and should we all be rushing to sign up? Essentially, it is what keeps the sun burning - atoms, stripped of their electrons, are forced together, creating new elements and releasing energy in the process. The science is well understood - the tricky part is how to recreate that process when you don't have a 2000 trillion trillion tonne star in the laboratory to hold everything together. Instead, scientists use magnetic force, or small explosions to try and force everything together for long enough for fusion to take place.

The history of fusion has been mixed, and its this that provides the biggest warning against investment. ITER, which was meant to be the first proof-of-concept fusion power plant in France, started construction in 2007 and isn't expected to be operational until at least 2025, and the estimated cost of the project has risen from around $6bn to roughly $20-50bn - no-one seems quite clear on what the final figure will be. There have been numerous false alerts over the past 50 years - most notoriously, the announcement of cold fusion - and the claims of the newer breed of private fusion companies have often seemed over ambitious.

Despite that, however, fusion does seem to be tantalisingly close as a commercial opportunity. A recent experiment demonstrated that fusion could release more energy than it absorbed (although, for full disclosure, not yet more energy than the experiment required in total), and innovative technologies by companies such as First Light Fusion set out a plausible pathway to fusion based electricity generation within the 2020's.

So should we be investing in it? Ultimately, the commercial case is going to be driven by the ecological case - if scarcity of resources reduces the viability of existing power generation, whether that be artificial restrictions on the use of coal, or inherent limitations on the availability of rare earths for solar power, then a power generation technology such as fusion which has effectively unlimited fuel will ultimately be profitable - if it works. However; that is a very long game - in the short to medium term, it seems a safe bet that the price per unit of fusion generated energy will be well above that of fossil fuel, renewables or even nuclear fission. (Although I should point out at this stage that the nuclear waste from fusion is much less of an issue than for fission).

As such, the value of investments at the moment are supported by two things - government support for the technology, and public confidence that it will, eventually, be a game changer. Inherently a risky investment - but with the trend towards climate friendly policy, it could ultimately be a winner.