Interview: How can we get cheaper power from the sun?

Nanotechnology offers new ways to make solar power cost efficient. Dr Hele Savin, a World Economic Forum Young Scientist, is interviewed about how this breakthrough is changing the energy industry, as well as the advantages and frustrations of working closely with industry.

You’re working on research to improve the efficiency of photovoltaic cells, making it more cost-effective to generate electricity from the sun. How are you doing that?

Most photovoltaic cells are made from silicon. It’s a relatively cheap raw material, as it comes from rocks and sand, but it always has lots of impurities. Purifying it is very expensive, and impossible to achieve completely. What we’re trying to do is make photovoltaic cells work better with higher levels of impurities, by using nanotechnology to manipulate the defects in the silicon.

The dirtier the silicon it’s possible to use in PV cells, the cheaper they will be to produce.

Without getting into too many technicalities, can you explain how it’s possible to use nanotechnology to manipulate defects in silicon?

Here are a couple of examples. One of the hypotheses we’re working on comes from my background in electronic engineering, where copper impurities in silicon can be extremely harmful to the workings of transistors and sensors. My previous work in microelectronics was on addressing this problem by using light to make the copper defects in silicon electrically active.

We suspect that the reaction between sunlight and copper impurities in silicon might be one reason why PV cells lose some efficiency over time – the copper starts to move around and form clumps, degrading the performance of the cell. We’re looking at tackling that by creating using a negative charge at the surface of the silicon to attract copper ions, which should stop them from clumping.

Another thing we’re doing is manipulating the surface of the silicon to minimize sunlight reflection – obviously, the more sunlight is reflected, the less is available to be converted into electricity. Instead of the familiar blue colour of PV cells, incidentally, this approach makes them completely black.

And what kind of efficiency gains are you achieving?

We’re currently at around 20% efficiency. But really, that’s the wrong question. It’s meaningless to discuss efficiency without also considering the cost of manufacturing.

For example, the world record for all photovoltaic technologies at the moment is 44.7% efficiency, but this technology is completely different to what I’m working on – it uses many different materials layered on top of each other, each of them absorbing light at a different wavelength. So it’s much more efficient, but it’s also much more expensive.

There will be some applications where that kind of balance of expense and efficiency is what you need – when you have a small area available to generate electricity, for example. But where you have bigger surface areas to work with, it makes more sense to cover them with cells that are somewhat less efficient but a good deal cheaper. Euros per watt, or dollars per watt, is the benchmark.

And, as with your work on reducing copper clumping, retaining efficiency over time must also be a consideration.

Yes – but even though we’re working on stability, actually PV cells are already very stable. You’ll get 30-40 years out of current technologies, and in most cases they’ll still be functional after more than 50 years.

Some other researchers are currently working on alternative kinds of PV technologies, based on organic materials, which are extremely cheap but where durability is the constraining factor – they last only a few days, or at most months. Who knows if it might be possible to increase their lifespan in the future? For now, though, silicon is the dominant technology for achieving the optimal balance of manufacturing cost, durability and efficiency.

How closely do you collaborate with industry in your research?

Very closely, and that’s both a benefit and a frustration. It’s a benefit because we get to try out our ideas straight away on an industrial scale. The manufacturers we’re working with are obviously keen to get any edge they can on their competitors quickly as possible, so we can move ahead quickly with testing our hypotheses and scaling up the ideas that work.

For an academic, that’s very motivating and rewarding. When you’re working on something very new and experimental, it can be years before there’s even a possibility of commercialisation. But with our work, we can see it getting into the marketplace very rapidly.

Working closely with manufacturers is also very helpful in terms of getting feedback about what’s feasible and not feasible on an industrial scale. For example, some of the processes used to address impurities in silicon involve toxic gases, which we’re trying to find alternatives to. Manufacturers can tell us quickly whether something that works in the lab will be possible in a factory. And they can evaluate costs much more easily than we can.

And what about the frustration?

The frustration comes because we can’t always make our discoveries available to the public. As an academic your ideal is always to be able to publish, to make knowledge available to everyone to make the world a better place. But obviously the manufacturers who are providing our funding prefer to keep breakthroughs to themselves.

So we always have to find a balance. Sometimes it’s possible to patent discoveries, but often what we discover are improvements in processes of production rather than the product itself. And these are things the manufacturers who fund us don’t want to patent because it’d be impossible to go into their competitors’ factories to check if they’re breaking the patent, as you can by looking at their products. So in these cases, the knowledge is kept private, as a trade secret.

Is there no potential to find a funding model where this kind of research is supported by an industry group comprising a wide range of manufacturers, on the understanding that findings become public knowledge?

That’s an ideal situation and something universities are trying to achieve. But the PV industry is so competitive, with such tight margins, that it’d be challenging to bring all the manufacturers together.

What is the role for government in solar technology?

I think the most useful role governments can play is making sure people who make decisions have access to the latest knowledge. Some countries do this a lot better than others. In Germany, for example, it’s easy to get set up to become a producer of solar power. In some other countries, information is harder to come by and there’s  lots of paperwork.

What solar technology is suitable differs greatly between countries and applications, and the academic research can be so specialised it’s difficult for outsiders to get an overview of what the alternatives are. That’s one valuable contribution of World Economic Forum events, as in general we lack forums for scientists to discuss with politicians.

Finally, does the future for solar energy generation lie primarily in homeowners putting PV cells on the roof, or micropower plants serving communities, or vast installations in deserts that are capable of powering entire nations?

All of the above – there’s a place for each of them. In many places the price of solar power is already competitive with fossil fuel-based ways of generating electricity, and there is still a great deal of scope for researchers to make advances in various forms of PV technology. It’s only a question of time before solar power takes the lead in global energy production.

Author: Hele Savin is assistant professor at the Micro and Nanosciences Department, Aalto University, Finland.

Image: A worker inspects solar panels at a solar Dunhuang, 950km (590 miles) northwest of Lanzhou, Gansu Province. REUTERS/Carlos Barria