Question: What do you think about the energy of the future?Dark matter?

Susan Cartwright answered on 14 Jun 2015:

Sadly, not dark matter: it may constitute about a quarter of the energy density of the universe, but there is no obvious way to harness it: whatever they are, dark matter particles are weakly interacting, which means that the vast majority of them whiz through the Earth as if it were empty space. If you can’t catch them, you can’t exploit them.

I think the energy of the future is likely to be much more prosaic: depending on how far in the future you want to go, a mixture of solar power, various types of water power (hydroelectric, tidal), wind, and probably nuclear, with the solar power percentage increasing as you go further into the future. This does, however, depend crucially on improvements in technology, specifically batteries. At the moment, both solar and wind power can’t provide more than a fairly small fraction of the energy needs of a country like the UK, because they don’t provide the power when you need it. The UK needs lighting at night, and heating during the winter, as well as industrial power 24h/day. Solar power doesn’t work very well at night, and it’s not very efficient during the winter either, because the Sun is so low in the sky. Wind power has similar problems: you can’t turn the wind on or off at will. So, in order to make efficient use of these methods of power generation, we need low-cost, high-performance power storage (the great advantage of fossil-fuel power stations is that you can turn them on and off to meet demand – for example, at half-time in the unlikely event that England are playing Germany in the world cup final, when 30 million people put the kettle on at exactly the same time). If this can be achieved, I think solar power will eventually become the power source of choice: it is widely available, potentially cheap, and plentiful.

If it can be achieved, nuclear fusion also has great potential as a future energy source, the joke being that it’s *always* a future energy source, regardless of the date at which the statement is made… Ideally, hydrogen fusion would be perfect: the fuel is essentially inexhaustible and the waste product – helium – benign. Unfortunately, practical nuclear fusion is far from this ideal: the only fusion reaction that looks tractable in the real world is deuterium-tritium, which does not have an inexhaustible fuel supply (tritium is radioactive, and has to be manufactured: supplies are very limited indeed), and does not have completely benign waste products: it makes neutrons, which can convert stable atoms into radioactive ones. It may be possible to overcome these problems – lining your fusion chamber with lithium can both absorb the neutrons and, better still, actually use them to make more tritium – but it’s a hard problem, and I’m not convinced it can be solved before the battery problem. Conventional nuclear power – fission – is much easier, but has such a toxic reputation that it’s probably not politically feasible (in my opinion much of this is more perception than fact, but perception is absolutely critical in this field – if proposing to build more nuclear power stations will lose you the election, you’re not going to do it).

I don’t think fossil fuels have a long-term future in power generation: they are a finite resource, and they contribute to global warming. Biofuels are a possibility, but the current version is an environmental nightmare, with rainforest being felled to make space for palm oil plantations, and in a world with a growing population it’s hard to justify growing plants for fuel and not food. Biofuels that use waste products of food crops – cereal stalks, for example, or used cooking oil – are worthwhile, but less efficient than solar power.