Solar power to enhance green roofs

BY GEOFF WILSON

Solar power is poised for a rapid decline in costs that will make it a mainstream power option in the next few years, according to a new assessment by the Worldwatch Institute in Washington, D.C, and the Prometheus Institute in Cambridge, Massachusetts.

This reduction of costs can be expected to energise a joint harness approach to green roofs and photovoltaics.

When he was in Australia last February, Steven Peck, President of Green Roofs for Healthy Cities-North America , predicted that Australian solar researchers had the opportunity to become a world leaders in solar power and green roof combinations, once cost reductions had been made in photvoltaic technology.

That opportunity appeared about to arrive, courtesy of China….

Worldwatch reported on May 22 that global production of solar photovoltaic (PV) cells, which turn sunlight directly into electricity, had risen sixfold since 2000 and grew 41% in 2006 alone. Although grid-connected solar capacity still provided less than 1% of the world’s electricity, it increased nearly 50% in 2006, to 5,000 megawatts, propelled by booming markets in Germany and Japan. Spain is likely to join the big leagues in 2007, and the United States soon thereafter.

Worldwatch said: “This growth, while dramatic, has been constrained by a shortage of manufacturing capacity for purified polysilicon, the same material that oes into semiconductor chips. But the situation will be reversed in the next two years as more than a dozen companies in Europe, China, Japan, and the United States bring on unprecedented levels of production capacity. In 2006, for the first time, more than half the world’s polysilicon was used to produce solar PV cells.

“Combined with technology advances, the increase in polysilicon supply will bring costs down rapidly-by more than 40% in the next three years, according to Prometheus estimates.

“Solar energy is the world’s most plentiful energy resource, and the challenge has been tapping it cost-effectively and efficiently,” said Janet Sawin, a senior researcher at Worldwatch, who authored the update.

“We are now seeing two major trends that will accelerate the growth of PV: the development of advanced technologies, and the emergence of China as a low-cost producer.” she said.

The biggest surprise in 2006, according to Worldwatch, was the dramatic growth in PV production in China. Last year, China passed the United States, which first developed modern solar cell technology at Bell Labs in New Jersey in the 1950s, to become the world’s third largest producer of the cells-trailing only Germany and Japan.

China’s leading PV manufacturer, Suntech Power, climbed from the world’s eighth largest producer in 2005 to fourth in 2006, and PVs have made the company’s CEO one of his nation’s wealthiest citizens. Experts consulted by Worldwatch believe that China, with its growing need for energy, large work force, and strong industrial base, could drive dramatic reductions in PV prices in the next few years, helping to make solar competitive with conventional power even without subsidies.

“To say that Chinese PV producers plan to expand production rapidly in the year ahead would be an understatement,” says Travis Bradford, President of the Prometheus Institute. “They have raised billions from international IPOs to build capacity and increase scale with the goal of driving down costs. Four Chinese IPOs are expected to come to market this month alone,” he said.

Worldwatch said supply shortages had led manufacturers to find ways to use polysilicon more efficiently, and had accelerated introduction of new technologies that did not rely on purified silicon and were inherently less expensive to manufacture. So-called thin film cells could be made from amorphous silicon and other low-cost materials. Companies developing these technologies had recently become the darlings of Silicon Valley venture capitalists.

Although in the past, thin film cells had not been efficient enough to compete with conventional cells, today over a dozen companies-including Miasole, Nanosolar, and Ovonics- were competing to scale up production of low-cost solar modules that could be churned out like rolls of plastic.

“The conventional energy industry will be surprised by how quickly solar PV becomes mainstream-cheap enough to provide carbon-free electricity on rooftops, while also meeting the energy needs of hundreds of millions of poor people who currently lack electricity,” Ms Sawin of Worldwatch said..

Note to Editors: To obtain the full Vital Signs Update on solar power, or to interview the author, contact Darcey Rakestraw at drakestrawATworldwatch.org or phone Washington DC 202-452-1992 x 517.

Green roofs can improve photovoltaic efficiency

A rather silly contest occurred in London in April 2007. It was been between the advocates of green roofs and the industry behind photovoltaic panels for electrical power generation from rooftops. Each was competing for roof space priority.

As the photo above from Germany well shows, the two can co-exist on a rooftop. Indeed, the green roof can improve photovoltaic efficiency by reducing the ambient temperature, and the photovoltaic array can help protect the green roof from damage of gusting winds.

Not many people know that photovoltaic arrays have an efficiency drop as ambient temperatures on a rooftop climb steadily during a hot day.

According to an analysis by officers of the Queensland Department of Public Works, at their current state of development photovoltaic arrays are still not economically viable in urban environments. Their figuring runs like this:

“Photovoltaic panels are priced at A$10 per Watt (excluding GST). So a one kilowatt panel will have a purchase cost of around AU$10,000. With installation, the cost comes up to around $14,000. (For comparison, a coal-fired power station produces electricity at a cost of around $1,500 per kilowatt). Nevertheless photovoltaic panels do have a place in remote locations where the cost of providing or upgrading the mains electricity grid can be substantial.

“Practicability is a further issue. The same one kilowatt panel discussed above will cover an area of 12 square meters, and should have a northerly orientation for optimum performance. The one kilowatt output is a maximum rating that varies with the orientation of the panel relative to the sun, the amount of cloud cover, and the temperature (with output dropping off as the temperature climbs above 25°C.

“With commercial office buildings requiring electricity in the range of megawatts, a photovoltaic array would have to extend over an area of several thousand square meters in order to provide, say, 50% percent of such a building’s power requirements during daylight hours”.

The Queensland Department of Public Works’ has been engaged in research involving the use of photovoltaic panels and interactive inverters that enable surplus electricity for the solar panels to be fed into the main electricity grid.

The Department has designed, constructed and installed three prototype systems that are currently undergoing testing. A full report will be published soon in Urban Agriculture Online.