New solar cells see the light
A new generation of more efficient solar cells is on the horizon.
Today’s solar cells have an efficiency of 17 per cent, where 100 per cent means that all the energy from sunlight is converted to electricity. There are two types of solar cells, known as first- and second-generation cells. The most important difference between the two is the production price. First-generation cells are built of single crystals of silicon, and are expensive to produce,while the production of secondgeneration cells is far less expensive. The drawback of second-generation cells is that they sacrifice efficiency for cost, as compared to firstgeneration cells. However, because the cost is so much lower, the price per produced watt is also reduced.
Now, a new project at NTNU is taking part in the search for third-generation solar cells. Associate Professor Turid Worren is head of a project that will make a test model of the solar cells by the end of the year. The efficiency of the new cells should be beyond anything that has been produced in Norway to date.
LITTLE INTEREST SO FAR
“Theoretically, we might reach efficiencies of 60 per cent or higher. In practice we hope for 40 per cent efficiency at the start. Even at that level, the energy efficiency will be 2 to 3 times higher than today’s solar cells”,Worren says.
NTNU is the only institution in Norway where this kind of research is conducted. Worldwide, just a few groups are working on this new type of solar cell; otherwise, interest in the field has been limited.Worren says fossil fuels are to blame.
“I am convinced that a new generation of solar cells would have been available already, if not for cheap fossil energy”, she says.
The new solar cells are based on what are called ‘quantum dots’. All solar cells use semiconductors to absorb sunlight, but today’s cells are unable to absorb very much of the infrared heat radiation from the sun. The new solar cells being developed have pyramid-shaped semiconductor dots in addition to conventional semiconductors. These dots absorb a portion of the infrared light that the other parts of the solar cells do not capture.
The project uses new technologies and is partly financed by NTNU’s Nanolab. The longterm goal is to produce solar cells using this new technology.
“Using these kinds of solar cells, we could build solar cell power plants in sunny places in the developing world.At our latitudes, the most realistic use of this technology would be to cover buildings with aesthetic building elements that integrate solar cells”, Worren explains. People would accept this approach if the cells were decorative enough,Worren says. “Solar cells can be beautiful, and a good alternative to decorative stone and window glass”, she says.
On a worldwide basis, the installation of new solar cell plants (measured as the amount of energy produced) increased by 63 per cent from 2003 to 2004, with much of the increase due to political involvement. It is estimated that by 2010, the number of solar cell plants will have tripled compared to 2004. In Norway, solar cells are mainly used for mountain cottages and lighthouses, where it can be difficult to connect to the power grid.
“If we could cover 0.3 per cent of Norway’s land area with solar cell plants, we could produce 120 terawatt hours, which corresponds to our entire electricity consumption in 2002”, Worren says.
“That means that it is physically possible to handle Norway’s total energy consumption with power from solar cells, but that is neither necessary nor desirable. One alternative could be to produce just one per cent of Norway’s electricity consumption using solar cells. That would correspond to a solar cell area of some 90,000 roofs, each measuring 100 square metres”, she says.
Another factor that makes the production of more efficient solar cells interesting is the lack of raw materials for the current technology. Most solar cells have an active portion made of a thin wafer of silicon. The solar cell industry is currently experiencing a silicon shortage. The search for other ways to produce silicon has begun, but increased efficiency in silicon use will also be an important component of solar cell production.
By Tore Oksholen