The sunny side of solar power

Though inclined to find fault with the concept of using the sun as a source of electricity, William Nuttall is coming round to thinking it has a lot of potential compared with other renewables.

When I discuss renewable energy with friends the conversation nearly always turns to solar power.

Often I find myself saying that its prospects in the UK are poor. I can see the disappointment on their faces and I quickly realise that I have said the wrong thing. It is not just that I should be less forthright.

I should also remember that, of all the renewables, solar power is the one most likely to benefit from new inventions and dramatic breakthroughs. As soon as I have voiced my initial scepticism my thoughts turn to the fact that the technology has great potential.

For the UK solar power means solar photovoltaics and the direct conversion of light into electricity. Part of my negativity comes from the fact that semiconductor solar cells are very expensive to make when compared to the cost of the electricity they produce.

Moreover, they produce electricity precisely when we do not need it. What the UK needs are environmentally benign sources of electricity for cold dark evenings in January when electricity demands are highest. Unless we become an air-conditioned society, with the balance of electricity demand shifted towards summer days, then it seems unlikely that widespread use of solar cells will be sensible.

At present, domestic consumers with solar cells benefit not only from government subsidies, but also from a simplistic electricity billing and metering system. Domestic electricity tariffs do not fluctuate hour by hour, but are averaged over months and quarters. In principle solar homes can take grid electricity that is among the most expensive to produce, but only pay at a lower rate defined by average demand.

This situation is complicated by the fact that typically the first 225kWh (or roughly 40 per cent of standard domestic use) is more expensive than later electricity units.

Solar power enthusiasts stress that domestic solar users should be able to sell their surplus electricity back to the grid. But how should the price they are paid compare with the real costs of electricity at that instant? Also what conventional generation should be throttled back as a consequence? These are some of the real economic and environmental issues.

As my Massachusetts Institute of Technology colleague Steve Connors points out, when thinking of electricity one must beware the dangers of averaged numbers.

Much of my lack of enthusiasm for conventional solar cells comes from the fact that currently the industry relies upon silicon and other inorganic semiconductors. The semiconductor industry makes economic sense when producing tiny and high-value microprocessors, but solar installations must cover many square metres.

Despite attempts to develop higher technology approaches, single crystal silicon continues to dominate solar cell production. I concede that capital costs of single crystal silicon systems have dropped significantly in recent years, largely as a result of incremental improvements in manufacturing, but such cells still suffer from the fact that it takes years to generate back the electricity required to manufacture them.

Notwithstanding steady improvements in the silicon situation, my optimism for solar power really rises when I start to think about discoveries that have started to emerge from the laboratory in the past two decades. Solar cells do not have to be made by the intensive physical processing of inorganic semiconductors. They can be made of plastic using bulk liquid chemistry. These polymer photovoltaics have the potential to be enormously cheaper than their semiconductor competitors. Rather than emerging from the clean rooms of a semiconductor plant, I imagine them coming off giant rollers as plastic sheets not unlike newspaper presses. The drawbacks of polymer photovoltaics are their low electrical production efficiencies and the need to carefully encapsulate the delicate chemicals involved so as to ensure long-term reliability.

Neither of these limitations, however, seems fundamentally insuperable.

I have heard talk of the day when research into self-organising systems, such as liquid crystals, will allow us to paint our houses with a liquid photovoltaic that organises itself into an effective solar cell.

Researchers worldwide are already working on the underpinning science. When I think of one day painting my house to make it one big iridescent solar panel, or of wrapping it in plastic sheet like a Christmas artwork, I realise that I am tapping into the radical side of solar technology. This is where the fun and the promise really lie. Already solar cells are no longer thought of as simply sources of electricity. They are aesthetic objects fundamental to modern architecture. Prestige office buildings are frequently clad in extremely expensive materials such as marble or stainless steel. Solar cells are already attractive and practical competitors for such architectural applications.

On reflection I turn away from my hasty myopic opinion and concede that solar power has much to offer our built environment. I am enthused by the creative potential of a field that is bringing together experts from such diverse disciplines as condensed matter physics and architecture.

William Nuttall is director of the MPhil in technology policy at Cambridge University.