September 25, 2021

I, Science

The science magazine of Imperial College

By 2025, the UK Government has promised to halve carbon emissions. Clean energy looms large on the political agenda, granting science a lot of room to influence the direction of current and future energy policy.

But how much does science really have to say about clean energy? Time and again, we’ve heard the promises of wind and solar power fall flat as high costs and protesters get in the way; we’ve heard how hydrogen-powered cars will revolutionise the way we move; and we’ve heard about miracle energy cures like cold fusion, only to find out later that the results were unreliable and our trust in science was misplaced. So, what happened to our clean energy?


In nuclear reactors today, uranium fission (splitting into smaller parts) is used to produce energy. The total mass of the two nuclei formed in the decay is less than that of the original uranium, so there is extra energy left over that can be converted into electricity.

However, when compared with nuclear fusion – the process that keeps our Sun going – the energy yield from fission is tiny. One of the biggest challenges facing nuclear physicists is to find a nuclear fusion process that can be used and harnessed efficiently.

In nuclear fusion, two light nuclei are forced together at high enough energies to overcome the repulsion between them. The resulting nucleus has a smaller mass than the combined mass of the original nuclei; so again, energy is released – this time on a much bigger scale than the energy released in fission.

The most promising fusion reaction at the moment is that of deuterium (hydrogen with an extra neutron) and tritium (hydrogen with two extra neutrons). The deuterium-tritium reaction can produce enough energy to supply 676 U.S. citizens for a year – and that’s just using one molecule of each. The problem is that the fusion requires conditions of around 40 million Kelvin – a temperature that scientists are only just becoming able to reach.

Cold Fusion

In March 1989 two electrochemists, Martin Fleischmann and Stanley Pons, reported ‘cold fusion’ in an electrolysis experiment. They claimed that their experiment – where they’d used a palladium electrode submerged in heavy water to create electrolysis – produced excess heat and by-products typically found in nuclear reactions, such as neutrons and tritium.

Since the experiment involved little input energy, the results were termed ‘cold fusion’ – a process in which nuclear fusion could be produced using very small amounts of energy. It was a massive breakthrough in nuclear physics and in energy creation, suggesting that nuclear energy could be harvested at little expense and with abundant materials.

The media quickly snapped up the story and subsequently other scientists attempted to replicate the results. However, it soon became clear that the experiment could not be repeated, and the majority of the scientific community declared the results invalid, with only a few determined followers continuing to research the process.

Convincing evidence of cold fusion has yet to be found. Until then, we’re stuck with the more expensive and controversial nuclear fission processes found in reactors.

Wind and Solar Power

Unlike fusion, wind and solar power are actually commercially available: there’s the occasional massive wind turbine at the side of the motorway, or the occasional house with solar panels on top.

The key word here is ‘occasional’. Solar and wind power still have efficiency problems, particularly when the investment and land area needed are considered. The best places for wind farms, for example, need strong and reliable winds at an average of 25 km/h, found mainly in coastal areas (which are generally very expensive to build on) and flat, open plains. Not surprisingly, this rules out some pretty large areas of the UK – and even in some of the places that could hold wind farms, NIMBY (Not In My Backyard) protests from those who consider wind turbines an eyesore or too noisy have made it difficult for builds to go ahead.

Solar cell technology, too, is still in its infant stages. Solar power can be used as a supplement to some systems – for example, solar panels can heat water for household boiler systems – but the downside is that in winter, when you need heat and light the most, the solar panels are producing the least energy.

So while wind power might be useful for individuals who can put up with the noise, and solar power might be useful when the weather’s good, neither can really supply a consistent and unobtrusive energy supply as of yet. We’ve still got to wait a while before they can really provide competition to fossil fuel and nuclear power’s grip on the energy industry.

Hydrogen-powered Cars

A few years ago, hydrogen-powered cars were deemed to be the next big thing in the transport industry: reliable and totally clean to run. All the big car manufacturers were making prototypes. Pop down to the science museum, and you can see one such example, the Riversimple Urban car, in the Atmosphere gallery.

But we have yet to see these promised prototypes become commercially available. There are a few hydrogen cars on lease in Los Angeles, but only because there are also hydrogen refilling stations over there. And that’s the clincher, the reason that electric cars are winning out: hydrogen cars require billions of pounds worth of investment in new filling stations, while electric cars can simply be plugged into the grid.

Hydrogen and electric fuel cost about the same in terms of energy, too. Both rely on electricity: the electric car straight from the grid, while hydrogen is generally created from refining natural gas. So hydrogen cars’ claim to ‘clean’ fuel actually amounts to a reduction of 55% in greenhouse gas emissions, depending on where the electricity comes from: not much different to that of an electric car. Critics of hydrogen-powered cars have argued that it’s simpler to just put the energy directly into the car, rather than going through manufacturing and processing for hydrogen fuel.

Comparing the infrastructure costs, it’s then not really surprising that electric cars are winning the battle – looks like we’ll be seeing G-wiz cars around for a while before hydrogen gets a foot in the door.

So, maybe a few more years down the line, we’ll get the clean energy that we keep being promised: but for now, it’s still unreliable and noisy wind farms, inefficient solar power, radioactive nuclear power and carbon-intensive fossil fuels – what a choice!