Don’t let the sun go down
Fri 17 Jul 2009 by Nigel Pinkerton.

Ever since the General Motors’ car Sunraycer won the inaugural 1987 world solar challenge, many people have been intrigued by the prospect of a viable solar car.   A car that runs on free energy from the sun without the need to stop and refuel would be sure to turn a few heads.   But the reality then, as now, is that such a car could not be built with available technology.   Drawbacks include the weight of the batteries that would be required, the low efficiency of cost-effective solar panels, and the fact that solar panels on moving vehicles are not constantly exposed to the sun.   While we may see solar panels extending the range of rechargeable electric cars in the near future, pure solar-powered cars remain the domain of hobbyists.

Solar power may still help reduce our reliance on fossil fuels in other ways.   Solar water heating systems are an example. They trap the sun’s energy directly as heat and so can be cheaper to build and install than panels that generate electricity.   However in some locations their payback period is too long for them to be an economically sensible investment, although government subsidies can swing the cost-benefit balance.

Generating electricity from the sun is a little more complex than trapping heat directly, and the high cost of silicon-based solar panels means that very few households have moved beyond water heating in their use of solar energy.   The sun’s energy may be free, but building the panels needed to capture this energy has typically required a lot of resources and thus been quite costly.   The cost of batteries can also make solar energy an expensive way to power a house, but some retailers will let you have a grid connection that operates both ways.   This is paid for by way of a price wedge between what they pay you when you pump power into the grid and what they charge when you draw power from the grid.   But batteries or no batteries, it goes without saying that more households would be using solar panels if the up-front cost wasn’t so high.

Most solar panels in use today are silicon-based, and the cost of producing such panels makes it difficult for solar energy to compete with fossil fuel or hydro generation.   But an alternative to heavy, expensive silicon panels is already in the latter stages of development, and cutting edge research in the area has been undertaken at New Zealand’s own Massey University.

Dye-sensitised cells (or DSCs for short) area completely new way of turning sunlight into electricity.   They work in a similar manner to photosynthesis in plants.   DSCs have been widely tipped to eventually replace silicon-based cells in most applications, although they do have their drawbacks as they are currently less efficient than silicon-based cells.  Massey’s research has produced dyes that are expected to capture at least 7% of the sun’s energy under peak conditions, compared to about 15% in a typical silicon cell.   This may sound about as useful as a fridge in Antarctica, but the real advantage of DSCs is that they are very cheap to manufacture.

Dyesol, the company that has the rights to commercialise Massey’s research, claims that the actual cost of producing a watt of electricity is many times lower when using DSCs.   Promoters have talked about production costs being as low as a tenth of the cost of silicon-based solar panels.   Even if this turns out to be optimistic, the cost per watt of electricity promises to be much more competitive than silicon-based cells.   The lower energy input required in the manufacturing process promises to make the total environmental impact of solar energy lower.   Research has also suggested that the overall performance of DSCs may be better than peak efficiency ratings suggest.   This is because DSCs perform relatively well in low-light conditions such as cloudy days or early in the morning.

The average household would still require a large area of solar cells to generate a practical amount of power.   But the large roof area of most New Zealand homes is ideal for this form of solar generation.   The technology can also be incorporated into tinted windows or other building materials to generate electricity.

Solar energy is the ultimate renewable resource, and dye-sensitised cells offer an alternative to expensive silicon.  As well as the environmental benefits, having a greater proportion of households generating their own power would reduce the need for large networks of pylons and other infrastructure.   Practical solar-powered cars may still be the stuff of dreams, but DSC solar panels could become a common sight on roof tops in the future.   If the dye’s turn out to be half as good as promoters claim, I’ll be the first to convert my unproductive roof area.

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