THE CONVENTIONAL IMAGE of solar power is multiple photovoltaic panels stuck on a roof. But there is also another approach, one that is much closer to the conventional, centralised-utility model of electric power generation. Concentrator technology stems from the recognition that sunlight is a dilute resource.
Using mirrors that track the Sun to concentrate solar light, much as kids use a magnifying glass to burn paper, you can focus the Sun's rays into a beam that is powerful enough to melt steel. Concentrators can be either photovoltaic, generating electricity directly, or solar thermal, generating heat to drive steam turbines [see 'Ways to catch rays', p75].
As with every other solar technology, concentrators are not new. Invented in the late 1970s, they have undergone a long, painful apprenticeship as developers learned how to deal with problems like eroding mirrors and tracking devices that became jammed with dirt.
Now, at the height of the silicon shortage, concentrator firms have unexpectedly become the darlings of venture capitalists. At Solar Power 2006, the concentrator session was standing room only. "We were all amazed," recalls Mints, "because that's usually the session you go into if you want to take a nap."
Interest is particularly keen in Australia following an ambitious announcement in October 2006 by Melbourne-based concentrator specialist Solar Systems. The firm plans to build in northwest Victoria what will be — by an order of magnitude — the largest photovoltaic power plant in the world. State and federal governments are providing A$125 million for the 154 MW plant. The private sector is expected to provide up to a further A$295 million.
Solar Systems has already demonstrated the effectiveness of its concentrator technology with four community-sized stations, providing power to remote Aboriginal communities around Alice Springs. The stations consist of a cluster of 14 metre-wide tracking dishes, each mounted with 112 curved mirrors.
The mirrors reflect the light — concentrated 500 times — onto an array of solar cells mounted at the focal point of the dish. High-performance proprietary heat sinks, integrated on the back of the cells, keep them cool enough to touch.
During daylight hours, the solar stations replace diesel-driven generators, saving A$1,000-worth of fuel a day and eliminating polluting greenhouse emissions. Each station generates enough electricity to power a thousand local homes.
To achieve such high performance, Solar Systems uses the most efficient photovoltaic cells available. These are made by Spectrolab, a Los Angeles-based subsidiary of Boeing; and they are not made from silicon but from multiple layers of compound semiconductors like gallium arsenide. Normally used to power satellites, Spectrolab's cells offer efficiencies of up to 35 per cent, and are expected to top 40 per cent by the end of the decade.
Of course, such cells are much more expensive than their silicon counterparts but, as Solar Systems' technical director John Lasich explains, you don't need many of them. A module the size of a mobile phone can produce enough juice to run a house, putting out 1,500 times more power than a standard photovoltaic panel of the same size.
