Low-tech Magazine: Solar powered cars

If racing cars can drive on solar energy, then why do normal cars still need fossil fuels?

Around 30 cars race 3,000 kilometres across the Australian continent in the “World Solar Challenge”. Solar cars are electric vehicles that generate their own electricity, by means of around 6 m² of solar panels installed on their bodywork, and a series of linked up batteries that serve as a fuel tank. If we want the car to survive in the longer term, it should become slower and lighter again, trimmed to the efficiency of solar panels and batteries. (Picture: Venturi Astrolab)

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Solar cars can absorb the rise and fall of solar energy by adapting their speed.

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In the first edition of the contest, twenty years ago, the average speed of the winner was 67 kilometres an hour (42 mph). Two years ago, in the previous edition, the speed rose to almost 103 kilometres an hour (64 mph). This time the solar cars, driving in normal traffic, were warned to stick to the speed limits.

Why don’t normal cars drive on solar energy? Clearly, the technology is available. A first reason is that most countries receive less solar energy than Australia. If the solar cars were to reach the same speeds in Western Europe or the northern United States, they should be equipped with twice as many solar panels.

Nocturnal drives

The energy efficiency of solar panels increases with an average of 0.5 percent a year, so the solar cars now taking part in the race will only reach the same performance elsewhere in 20 years time. Night-time is a second problem. Long nocturnal drives are ruled out because of the impossibility to refuel.

The unreliability of solar energy, however, is not the main reason why our cars still drive on fossil energy. The problem of the night could be bypassed by recharging electricity in a fuel station. If that electricity is produced by windmills, we still have zero-emission cars. If the electricity is produced by fossil fuels or nuclear energy, we don’t. But even in that case the environmental damage of cars falls dramatically, since most driving occurs during the day. Fuel stations that deliver electricity (no new technology is needed for that) are also a solution on dark days.

It's a sunny day

Also a lower performance in speed is not insurmountable, on the contrary. The speed of cars could be dependent on the weather: on sunny days we can drive faster (or further) than on a grey day. That might sound ridiculous, but it is an answer to the fickleness of solar energy that constitutes a challenge for traditional electricity production. Solar cars can absorb the rise and fall of solar energy by adapting their speed.

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A racing car on solar energy weighs just over 200 kilograms and consumes as much energy as a vacuum cleaner. Compared to that, our cars are mastodons.

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The main reason why we still drive on petrol is the design of present-day cars. Solar racing cars every year become more feathery, while our automobiles every year become bigger, heavier, faster and more powerful. Engines have become much more economical, but those gains always get swallowed by more weight, more power, a higher performance and extra electronics.

Vacuum cleaner

If all the gains of more economical motors had been put into a lower fuel usage, today’s cars would hardly use any energy at all. This does not only concern phenomena like the Hummer. A Volkswagen Polo today is bigger and heavier than a Volkswagen Golf in the beginning of the eighties.

A racing car on solar energy weighs just over 200 kilograms and consumes as much energy as a vacuum cleaner. Compared to that, our cars are mastodons. Nevertheless, both vehicles attain their design goals: transporting a human body. The majority of the population is not interested in a car with a maximum speed of 200 kilometres an hour (125 mph). Yet everyone gets it, even when buying the smallest and slowest model.

According to the car manufacturers, the ever increasing weight is a consequence of always increasing safety measures. Yet, a better adjustment of the different car models to each other (the crash compatibility) and the lowering of the maximum speed would have at least a similar positive effect on road safety.

Tesla Roadster

In recent years, car manufacturers introduced (prototypes of) electrical vehicles that have the same performance as a sports car with a combustion motor. These models steer the eco-technology in the wrong direction. It’s the high performance that is the problem. Electrical sports cars have to be recharged, and that energy is mostly generated by fossil fuels.

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There is no point in placing solar panels on the bodywork of a car unless the performance of the vehicle goes down.

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If we want the car to survive in the longer term, it should become slower and lighter again, trimmed to the efficiency of solar panels and batteries. There is no point in placing solar panels on the bodywork of a car unless the performance of the vehicle goes down. Otherwise the technology will be used to meet a not yet existing demand, like cooling the interior of the car while parked (an application that is already on the market).

Maximum speed

Until now, the only manufacturer that recognizes this, is the manufacturer of the Venturi Astrolab (picture intro). This car, which will be introduced on the market at the start of 2008, combines lightweight materials originating from the racing industry with a modest performance, like a maximum speed of 120 kilometres an hour (75 mph).

An important point to make is that solar cars should be more durable, or that the solar panels will be re-used when the car is taken off the road. If not, we will never make good the energy expense of producing them.

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