Solar panels normally use the sun to generate power. They are increasingly seen as a possible solution for energy shortages in the developing world, but solar cells could have other uses. They can recycle waste light energy from artificial lights (a process known as ‘light harvesting’) which sounds like a great idea for parts of the world where we leave our lights on for too long. At the moment there are a few reasons why we don’t currently see this technology every day. Watch this space, though, because the sun may be rising on a new wave of solar panel-powered devices.
When considering using a solar panel to harvest waste light, you need to weigh up the cost of producing them vs. the amount of energy it will actually produce. Solar panels can recycle waste light, but the efficiency is often poor because most wasted light is relatively dispersed and low in energy. In the majority of situations, the energy harvested would be so small that it would make little sense to transport it back into mains power.
There are, however, examples of people using small, low cost solar cells to power pocket appliances (which are increasingly common due to advances in microchip technology). On a small scale, light harvesting can be cost effective and convenient and, in some instances, the need for batteries (and the need to regularly charge them) may be removed altogether. If you want an example of this then look no further than solar-powered pocket calculators, which in 1990 made up 10% of the entire solar panel market.
Nowadays, solar powered appliances are becoming more sophisticated. The company GCell, for example, makes a special type of solar cell that works well in dim light with a relatively cheap manufacturing process (see www.gcell.com for an excellent video). GCell can therefore offer solar powered portable keyboards for your phone or tablet and a solar powered backpack to charge your electronics on the go.
Innovations in light harvesting are being made but, for now, their uses are limited to low energy appliances. The poor efficiency of today’s solar panels stop them from being used to glean energy from street lights: they would harvest so little that it would make almost no difference to its total power consumption. It has, however, been suggested that light harvesting could be used to store energy for a low-energy emergency lighting system in streetlights.
Overall, as solar cells become more efficient and cheaper to make, and electronic devices become more energy efficient, light harvesting should become more common. Hopefully light-powered portable devices may not only save energy but also making our lives easier. It might just mean that we need to let your smartphone do some sunbathing once in a while!
by Kane Heard
Minnaert, B. and Veelaert, P., (2014). A Proposal for Typical Light Sources for the Characterization of Indoor Photovoltaic Application. Energies,7 (3): 1500-1516.
Girish, T. E., (2006). Some suggestions for photovoltaic power generation using artificial light illumination. Solar Energy Materials & Solar Cells, 90: 2569-2571.