SciBar #26: Biotechnology in Solar Power

Solar power is actually sufficient to power the whole country. On a hot day (one where you'd burn in around an hour) we'd have enough electricity for an entire year if we could capture the sunlight from all over Britain for just ten minutes. If all south facing roofs in the country had solar panels, we would already be electricity self-sufficient. However panels aren't cheap, they have around a twelve-year payback time and most of the savings are from putting electricity back into the grid during daytime. What do we do at night?

Batteries are one option but these are not ideal. Instead, can we convert the sunlight into solar fuel? Then we can convert this fuel back into energy when we need it. Fuel fits in very well with our current infrastructure. For example, hydrogen is a very convenient fuel that we would be able to store at a petrol station.

Nature already does this - solar energy is converted into fuel. When humans eat food, the sugars and fats are our fuel. Our bodies take a lot of electrons out of this fuel, which converts it into carbon dioxide and water. If we could take out those electrons, then we'd have a current. Photosynthesis in plants works the other way round, starting with carbon dioxide and water but we still have the electrons.

There are four different techniques that are being looked into to get fuel from bio-technology:

1) Engineer algae/bacteria/plants
Change these at the genetic level to make hydrogen. The technology isn't quite there with this one yet - if all of the energy goes into hydrogen then the algae/bacteria/plants will die. It's also possible to grow algae, dry it out and then burn this bio-mass but this is incredibly inefficient.

Bacteria that create hydrogen only do so under stress, they don't want to lose their hydrogen. This is why they have to be genetically modified. How do we keep these bacteria doing un-natural things for us? How do we prevent them evolving back to the bacteria that they were before we modified them?

2) Convert agricultural "waste" into fuel
For example bio-diesel. However this starts to compete with food production so it's not ideal. It's also very inefficient - only 1.5% of the sun's energy that's gone into the plant comes out. Compare this to silicon solar panels, which operate at around 15% efficiency. The latest non-silicon panels can even get up to 30% but these are too expensive at the moment for mass use.

Crops such as grain leave a lot of inedible waste product. It contains a lot of cellulose. If we cleave up this long-chain polymer then we will be left with more useful sugars. The cut the cellulose up, genetically engineered enzymes are used but the engineering of these enzymes still hasn't been perfected yet.

It's also possible that we could use sewage. At the minute, we essentially burn it off to get clean water. The bacteria that are part of the process consume oxygen, but again if we could use a different bacteria that consumes protons to create hydrogen, then we’d have our fuel.

3) Bio-electrocatalysis
This is where we use a key enzyme in photosynthesis and sent electrons straight into a piece of metal to create electricity. This key enzyme, which contains the oxygen evolving centre, is responsible for this but it breaks apart when it’s used. In fact it only lasts for about thirty minutes and we can't repair it. Plants use a significant part of their energy just to repair it.

4) Artificial photosynthesis
This is moving from chemistry to biotechnology. Ideally we would this process to make methanol rather than hydrogen, which is easier to work with. As an interesting example, in one brand new line of research, scientist are attaching non-photosynthesising bacteria to nano-particles such as titanium-oxide to make them photosynthetic.

So, four options but none of them are quite there yet. Lars thinks that the fourth one is probably the one that will work as there has been a lot of progress made there recently. Biotechnology could soon be an important part of our energy mix.

SciBar returns to The Vat & Fiddle on Wednesday 31 August at 7.30pm

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