Light years ahead

Before the end of this month BP will formally inaugurate a new petrol station in Milton Keynes. From ground level, it will look little different from the company’s hundreds of other stations around the country. Seen from the air, however, the difference is obvious. The roof of the building is covered with photovoltaic panels, which […]

Before the end of this month BP will formally inaugurate a new petrol station in Milton Keynes. From ground level, it will look little different from the company’s hundreds of other stations around the country. Seen from the air, however, the difference is obvious.

The roof of the building is covered with photovoltaic panels, which convert light into electricity. The inauguration marks the completion of a pilot programme of 15 such solar-powered stations around the world, from Europe to Australia. The Milton Keynes project is the UK’s second; the first opened in Bedford last June.

The stations are more accurately described as solar assisted, rather than solar powered, because they are what are known as grid-connected projects, with solar electricity supplementing electricity from the National Grid.

‘Pure’ solar projects require considerable battery storage to maintain power supplies at night and during bad weather. There are many such schemes around the world providing electricity in remote locations, mainly for relatively low-power applications, such as village lighting, water pumping, telecommunications and cathodic protection systems for pipelines. But they do not make economic sense where a grid exists. ‘The problem would be the batteries,’ says Clive Sinnott, BP Solar’s project manager for the ‘Sunflower’ pilot scheme.

A grid-connected project is designed to reduce the amount of power drawn from the grid in times of peak demand. It also offers the potential to export power to the transmission system in times of low or no demand.

However, while this two-way interchange can work with grid-connected houses where the solar panels will be generating maximum power during the daytime when the house may be empty it does not with a facility like a petrol station, which has a constant 24-hour demand for lighting, refrigeration and heating/air conditioning.

Sinnott says the panels provide on average about 25% of the petrol station’s power needs, generating about 32,000kWh of electricity a year.

Each panel has 36 silicon wafer cells, which produce an electric current when struck by light. They are arranged in series to feed the cumulative current into a junction box at the back of the panel. BP’s patented Saturn panel technology has the most efficient conversion rate in the industry between 17% and 18% instead of 12 15% for conventional systems.

All the panels (250 on the larger projects) are connected to feed the direct current they produce into an inverter, which converts it into alternating current and synchronises the frequency to make it compatible with the grid.

The panels and inverter are expensive. Sinnott says the 250 panels for the station built by BP in Lisbon cost about $100,000. The inverters could cost a third of this again. At these prices, solar power cannot come close to competing with conventional generation. ‘If you did a hard economic case, about 30% of the installed cost is commercially viable,’ says Sinnott.

So why do it? The answer is that BP sees solar power as a big business of the future and the Sunflower programme is a testing ground. Sir John Browne, BP’s chief executive, has for the past two years been an advocate of solar power as one of the key technologies for alleviating global warming caused by carbon dioxide emissions (each kilowatt of solar generation saves 1 tonne of CO2 annually).

A target for turnover

BP Solar, which has four manufacturing plants around the world, has set itself the target of growing from a business worth about $100m a year today to one with a turnover of $1bn by 2007.

There is already a market for selling solar technology to firms which are prepared to pay a premium to enhance their green credentials. But BP is confident that the gap in generating cost will narrow as the price of fossil-fired power rises, through carbon taxes or other fiscal restraints, and that of solar power comes down. ‘I think BP would say we’re looking for a crossover in 10 years,’ says Sinnott.

The Sunflower programme is allowing BP to gain first-hand experience of how to cut the cost of solar installations. As contractors become familiar with the technology this opens up a big area for savings. There are now companies in all the countries involved which are prepared to bid for the work without factoring in massive risk margins for dealing with alien technology.

‘People were reluctant to get involved with it,’ says Brian Quinn, senior engineer on the project. ‘But all the technical people involved have now seen solar and we’re starting to build up a bank of experience. I think in three years the cost of installing a solar system will halve.’

Procurement manager Ken Sargeant says: ‘You’ve got to persuade people to do the work. It’s not like you just sit back and people walk in the door looking to do business with you.’

The programme has also shown BP how to make installations more efficient. For example, the panels have been mounted at an angle of 30 in Europe (slightly shallower nearer the equator) to optimise the amount of light they absorb. But this means there has to be a considerable gap between rows of panels to prevent one row from shading out the one behind it.

Laying the panels flat would reduce their individual efficiency, but hugely increase the output from a given surface area because nearly twice as many panels could be placed on it. Quinn says this configuration should increase the electrical output by 60%.

Technological advances offer a third avenue for reducing cost. The high-efficiency Saturn cells are made of 400 m thick silicon wafers, which constitute 60% of their cost. BP Solar is developing silicon-coated glass, with a silicon thickness of about 30 m, which would lend itself far more to automated production. There would be a loss in conversion efficiency, but Sinnott says this will be more than compensated for by a 40 50% cut in unit cost.

As the capital cost of solar projects comes down, the negligible operating costs will appear more attractive. There is no fuel cost, of course, and maintenance involves little more than cleaning the panels once a year. Panels erected 25 years ago are still working. ‘The panels will probably last longer than the petrol stations,’ says Sinnott.

BP Solar is reviewing the Sunflower programme, but Sinnott says the company will ‘certainly be doing more’ solar-assisted petrol stations this year, and he expects the sites to be 35% cheaper to develop.

Two new buildings at BP’s Sunbury site, where BP Solar is based, will also have grid-connected solar power. The first is scheduled for completion at the end of 1999 and the second in the first half of 2000.