Solar cells take a leaf from the lotus's book
If you want to squeeze more electricity from your solar cells, try keeping them clean for a start. The Mars rovers, Spirit and Opportunity, know all about that: their power is significantly diminished when layers of dust build up on their solar panels, which can only be removed by a fortuitous gust of wind. Here on Earth we have the advantage of rain and dew, which can facilitate the removal of dirt and dust, allowing more light to be absorbed and converted into electricity.
Researchers at Georgia Tech in the United States have developed a method for producing silicon surfaces which can keep themselves clean by causing water to bead up and roll off, carrying away dirt and dust in the process1. The surfaces also possess the added benefit of low reflectivity. Both of these are attractive qualities in any system designed to capture as much light as possible, such as photo-voltaic cells for solar power.
The key to repelling water is to reduce the contact between the droplets and the surface, in the same way that a lotus leaf sheds water. The researchers accomplished this by using a combination of chemical etching and vacuum deposition, to produce a silicon surface comprised of micron sized pyramid structures and nanometre sized features, so the final product has a dual roughness to it.
By reducing the build-up of dirt, the photo-voltaic material beneath the surface can absorb more light and the system will also require less maintenance. Even in arid areas, dew can form on surfaces and will have the same potential to remove dirt.
The textured surface also absorbs more light than if it was planar, effectively trapping the light and increasing its chances of being absorbed into the material.
One concern is the fragility of the surface, because in practice it will have to withstand some degree of mechanical wear. Bird droppings, for example, might need to removed by abrasive cleaners, and debris brought by the wind might pose a risk for damage.
Any improvements in efficiency have to be balanced against the cost of the process that affords those benefits and the working lifetime of the product. But if this surface treatment can yield just a few percent improvement in the efficiency of solar to electricity generation, the costs may well warrant it.
Articles published in the Optical Future's blog are licensed under a Creative Commons Attribution-Non-Commercial 2.5 Canada License.
