Alex Robbins is contributing editor at Telegraph Cars where, as well as responding to readers’ queries, he also contributes reviews of new and used cars, together with articles on buying and selling.
His knowledge of the used car market informs his many buying guides relating to the best buys in particular sectors, with an emphasis on value for money. Every week he will answer your questions on buying and selling, as well as solving your car problems, whether consumer or mechanical.
Do you have a motoring dilemma you’d like our expert to solve? For consumer and used car advice, or car faults, email CarsAdvice@telegraph.co.uk and include your subscriber number. This week’s question …
It’s that time of year when I spend a lot of time looking for a parking space in the shade. It occurs to me that that’s a waste of solar energy. Why has no one produced a car with a solar panel on the roof to top up the battery?
Actually, they have – the first-generation Nissan Leaf was available with a small solar panel mounted at the top of the boot lid. But while the Leaf was electric, the solar panel didn’t charge the main drive battery – instead, it acted like a trickle charger, keeping the 12V battery topped up and thus lightening (ever so slightly) the load on the drive battery while the vehicle was in motion.
Nissan wasn’t the only manufacturer to toy with the technology. Toyota offered a proper solar panel on the roof of the Prius Plug-In. However, this really demonstrated why solar panels don’t work all that well in automotive applications. So low was the rate of charge it produced that to charge even the Prius’s relatively small drive battery would have taken 10 days using the solar panel alone, and then only with the car parked in full sunshine.
Given that the panel was an optional extra costing £ 1,500, few buyers took it up. And that fact rather explains why solar panels have never caught on for electric cars, either – the cost-benefit ratio simply isn’t in their favor.
Why not use one on petrol or diesel cars to top up their starter batteries, then? Well, put simply, it shouldn’t be needed if the alternator is doing its job properly. And if the car is to be left for a long time, that’s the purpose of a trickle charger – it wouldn’t be worth going to the expense of fitting solar panels just for these rather rare occasions.
However, one area in which solar panels can work well is on a camper van, feeding the leisure battery. Volkswagen offers solar panels as an option on some of its campers, while several aftermarket suppliers offer kits for other models. So-equipped and with the right weather, campers can run their electrical equipment off-grid – which is not just a more environmentally friendly solution, but also removes the need to find a campsite with an electric hook-up.