Don’t let the sun go down

Ever since the General Motors’ carSunraycer won the inaugural 1987 world solar challenge, many people have beenintrigued by the prospect of a viable solar car.   A car that runs on freeenergy from the sun without the need to stop and refuel would be sure to turn afew heads.   But the reality then, as now, is that such a car could not be builtwith available technology.   Drawbacks include the weight of the batteries thatwould be required, the low efficiency of cost-effective solar panels, and thefact that solar panels on moving vehicles are not constantly exposed to thesun.   While we may see solar panels extending the range of rechargeable electriccars in the near future, pure solar-powered cars remain the domain ofhobbyists.

Solar power may still help reduce ourreliance on fossil fuels in other ways.   Solar water heating systems are anexample. They trap the sun’s energy directly as heat and so can be cheaper tobuild and install than panels that generate electricity.   However in somelocations their payback period is too long for them to be an economicallysensible investment, although government subsidies can swing the cost-benefitbalance.

Generating electricity from the sun is alittle more complex than trapping heat directly, and the high cost ofsilicon-based solar panels means that very few households have moved beyondwater 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 ofresources and thus been quite costly.   The cost of batteries can also makesolar energy an expensive way to power a house, but some retailers will let youhave a grid connection that operates both ways.   This is paid for by way of aprice wedge between what they pay you when you pump power into the grid and whatthey 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 theup-front cost wasn’t so high.

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

Dye-sensitised cells (or DSCs for short) area completely new way of turning sunlight into electricity.   They work in asimilar manner to photosynthesis in plants.   DSCs have been widely tipped toeventually replace silicon-based cells in most applications, although they do havetheir 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% ofthe sun’s energy under peak conditions, compared to about 15% in a typicalsilicon cell.   This may sound about as useful as a fridge in Antarctica, butthe real advantage of DSCs is that they are very cheap to manufacture.

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

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

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

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