Chinese solar-panel manufacturers dominate the industry, but a new way of making an exotic type of crystalline silicon might benefit solar companies outside of China that have designs that take advantage of the material.
GT Advanced Technologies, one of world’s biggest suppliers of furnaces for turning silicon into large crystalline cubes that can then be sliced to make wafers for solar cells, recently announced two advanced technologies for making crystalline silicon. The new approaches significantly lower the cost of making high-end crystalline silicon for highly efficient solar cells.
The first technology, which GT calls Monocast, can be applied as a retrofit to existing furnaces, making it possible to produce monocrystalline silicon using the same equipment now used to make lower quality multicrystalline silicon. It will be available early next year. Several other manufacturers are developing similar technology.
It’s the second technology, which the company calls HiCz, that could have a bigger long-term impact. It cuts the cost of making a type of monocrystalline silicon that is leavened with trace amounts of phosphorous, which further boosts a panel’s efficiency. This type of silicon is currently used in only 10 percent of solar panels because of its high cost, but could gain a bigger share of the market as a result of the cost savings (up to 40 percent) from GT’s technology. The technology will be available next year.
A standard solar panel, made of multicrystalline silicon, might generate 230 watts in full sunlight. A panel the same size made of monocrystalline silicon could generate 245 watts. But phosphorous-doped monocrystalline silicon (also called n-type monocrystalline) enables a type of solar panel that generates 320 watts, a huge leap in performance.
Most Chinese solar manufacturers have focused on multicrystalline silicon solar panels. Companies such as U.S.-based Sunpower have focused on the advanced monocrystalline panels, and have designed cells to exploit its properties. Such companies will benefit as the HiCz technique developed by GT Advanced Technologies becomes more common.
“There’s a potential shift in the market,” says Vikram Singh, general manager for the photovoltaic division at GT Advanced Technologies. He says some western companies could become more competitive because they have technologies to take advantage of the materials.
Several other companies are developing technologies similar to Monocast, including solar-panel makers in China, such as Suntech and the Dutch equipment maker ALD.
The HiCz technology can be considered the next step on the way to higher-efficiency solar cells. It can be used to make monocrystalline silicon, even the phosphorous-doped type, for about the same cost as the Monocast technology. HiCz could allow a leap from cells that convert 16 to 18 percent of the energy in sunlight into electricity to ones that can convert 22 to 24 percent, thus decreasing the cost per watt of solar power. But it can’t be retrofitted to existing equipment, which could slow its adoption.
The conventional way to make monocrystalline silicon is to introduce a seed crystal into a pool of molten silicon and slowly draw it out—as you do, it forms a large tube-shaped chunk of silicon called a boule, in which all of the atoms are lined up in the same orientation. This is usually done in a batch process, but the HiCz process makes it possible to continuously feed in raw silicon to the melt, along with whatever trace elements are needed to give it the desired electronic properties. The continuous process is more productive, which means fewer machines are needed, reducing costs. It also produces high yields when introducing materials including trace elements such as gallium and phosphorous. GT estimates the process can reduce the costs of making monocrystalline solar by between 20 and 40 percent.
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