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Professional Engineering 15 January 1997

Cut-price deal to catch the sun

Michael Kenward reports

WOULD you enter a lottery where the prize is a chance to add £300 or more a year to the cost of your electricity? Twelve thousand Japanese households did just that last year. Only 2,000 won the subsidy the lottery gave them for a new solar roof to provide electricity to their homes.

The government subsidy, a part of a Japanese attempt to emit carbon dioxide levels, pays for part of the cost of a solar roof, up to just £2,500. By installing a solar roof, the houses can expect to save between £400 and £450 a year on their electricity bills. Over the life of the roofs, a house owner could save up to £9,000, but this is less than half the initial cost of purchase and installation.

Undaunted, this year as many as 9,000 Japanese families could seize the chance to tear up money for the sake of the environment.

In the long term, Canon, the cameras-to-copiers company, hopes to bring down the cost of solar electricity so there is no need for a subsidy. The company plans to do this by exploiting technology developed for its photocopiers.

Canon has adapted materials that it developed for copiers to produce comparatively cheap flexible solar panels. The company has also patented manufacturing techniques for continuous production of solar cells.

A typical domestic solar roof produces about 3,700kWh of electricity a day, enough to meet the needs of a family of four. In Japan the idea is not to store electricity for use when there is no sunlight. Instead, the government obliges electricity utilities to buy surplus electricity from home owners Each house has two meters, one for incoming electricity and one for power sent out into the grid.

Even with this ability to sell power, solar electricity is uneconomic. For home owners to break even over the life of a solar roof, the set-up cost has be less than £13,000, says Eiichi Kondo, head of the Canon Ecology Research and Development Center, near Kyoto. This is where Canon hopes its new technology will pay off.

Photovoltaic cells catch light and generate electricity. Existing cells are made out of silicon crystals left over from producing electronic chips. This limits the supply of crystalline solar cells. Kondo, who failed in his own bid for the government's solar subsidy, says crystalline silicon takes four to seven years to pay back the energy that goes into making them.

Crystal silicon also restricts the design of solar panels. Devised first to provide electricity for spacecraft, crystal silicon solar cells are made of small pieces sandwiched between sheets of glass. This restricts how cells can fit on to a roof.

Canon's breakthrough is that its cells are made of non-crystalline or amorphous silicon. The company developed its expertise in this material to make light-sensitive drums for photocopying machines. Amorphous silicon needs much less energy than crystals to produce, and pays this back in around 14 months.

Canon's construction method also means its solar panels weigh less than half as much as conventional cells.

One problem is that amorphous silicon is only half as efficient as crystalline silicon at turning sunlight into electricity, so far, but it can be mounted on to more manageable materials. Canon puts amorphous silicon on to thin and flexible sheets of steel and then coats them with plastic. The new solar cells can be designed to look like ordinary roofing material and need no special skills for installation.

While solar cells will never cost less than ordinary roofing, there is at least a chance that amorphous silicon will give some people a competitively priced electricity supply.

Canon, which has only recently started commercial production of the cells, is confident their cost will fall. The company started marketing the cells in Europe at the end of 1996.

"We believe we can make solar cells cheapest with amorphous silicon," says Kondo. Canon is the only company that sells solar cells built around this technology.

Canon admits its production line, at a factory near Kyoto that also makes computer printers, is more of a demonstration plant than a fully fledged factory. Each month it produces solar cells that can generate 2.5MWh electricity.

It now has to scrap about 20% of the cells it produces. "We still have various problems. Manual assembly means people make mistakes," says Kondo. He hopes to rapidly reduce wastage to less then 5% and the aim is to develop automated assembly to replace manual production.

In the first six months of panel sales, more than 100 homes were fitted with them. The company has also supplied panels for schools and municipal buildings.

The cells have also gone on trial in Mexico and Indonesia. There the idea is to bring electricity to communities that are not linked to the electricity grid.

Canon has invested some £100 million in solar cell technology over the past decade. It has yet to make any money from the business. Fujio Mitterai, the company's president, expects to move into profit some time after the year 2000.

The company hopes to win a large share of the market in Japan, where the government wants 400MW of solar cells installed by the year 2000, and 4,600MW by 2010. This could create a market worth around £1 billion for cells alone in 2000 and £6 billion in 2010.

© 1997

Michael Kenward ©2000 Last changed 07 February 2008