Connecting solar panels to your electric car

One aspect of environmentally friendly driving which is becoming more and more popular is the introduction of solar panels to electric vehicles. These are very environmentally friendly, very efficient and basically allow you to recharge your batteries while driving. The potential savings are enormous but how do you fit solar panels to your existing electric car?

Do you have experience of fitting solar panels to your car? Do you have any tips or advice for somebody looking to do this?

I have a friend in Canada who stays in a seasonal community over the summer. He added panels to his golf cart to recharge. Here is a video about it…

[ame=]Solar powered golf cart - YouTube[/ame]

Hi LuvMyTJ

That is a very interesting video - thanks for that.



With the 3 panels in series the voltage goes up but not the amps. So if he’s getting about 2.5 amps at 36 volts, it will take 40 hours of direct sunlight to charge from 50% SOC to full charge with those panels.

If he lives in sunny Arizona, he might make that 40 hours of 2.5 amp charging in a week but if he’s in cloudy New England it’ll take 10 days of sun to go from 50% SOC to fully charged.

People seldom “do the math” with these projects… But it makes them feel good anyway. To really make solar charging useful, you would need to generate enough amp/hours to produce 50% of your battery’s amp/hour capacity in a single day’s sunshine. For a 200 amp/hour battery pack that’s 100 amp/hours. In New England we get around 4.2 hours per day insolation so you’d need 100/4.2 or 23.8 amps from the solar panels for 4.2 hours (which actually takes into account a full day’s sunshine).

OK, so doing the math we find that’s around 1 KW of solar panels. Few electric vehicles have enough room on their roofs for that many panels. Even the best panels are only around 200 watts and they’re HUGE!!!

Until a major breakthrough in solar panel efficiency takes place, we’re stuck with the 12% to 15% efficient panels available today. Ideally, 1 square meter of Earth at the equator receives approximately 1 KW of sunlight at noon. If you get 4.2 equivalent hours of insolation on average, 1 square meter of 12% efficient solar panels makes 12% of 4.2 hours or about 50 watt/hours per square meter per day. That’s not a lot when the typical golf cart battery pack holds 7.2 KW/Hr of energy. That’s equivalent to needing 144 square meters of solar panels.

I can see a long train of trailers covered with solar panels to make enough power to never have to plug into the wall…

Hi Bob

Many thanks for the update on solar panels and the calculations which make very interesting reading indeed. I think you are correct in your assumption that many people do not understand what is required to make solar panels as efficient and as useful as possible although your calculations certainly put the situation into context.

Do you think we’re making any progress with regards to more efficient solar panels? Will they ever be a viable addition to electric vehicles or perhaps in their own time, an alternative?

There’s a lot of “wishful thinking” when it comes to solar panels. The Sun-Race they have every year or two had some interesting vehicles. They use only a couple hundred watts to move down the road and are totally covered with high efficiency panels.

Even if we could turn 100% of the sunlight falling on a panel to electricity it would still take more panels than the size of the vehicles could carry within their footprint for a useful size/speed/range EV. So I don’t think we’ll ever get to the point where on-board solar charging will become a reality except for occasional-use vehicles which sit for long periods unused.

One good way of utilizing solar energy to run an electric vehicle is to have your charging station solar powered. You can bank the sun’s energy either in batteries or onto the grid and then take it back out to recharge your electric vehicle. That’s the only thing that makes any sense at all. In my opinion putting solar panels on the roof of your EV is just being a show-off. It doesn’t really add significantly to the range or reduce charging costs.

Hi Bob

In your opinion, when do you think electric vehicles will “crack” the mass market?

Personally I dont think lies and untruths about EVs or the worldwide economy have helped the situation so far.

When the next quantum leap in battery technology arrives; then we’ll start to see more electric vehicles. Right now you can’t recharge an EV as fast as you can fill your gas tank so that’s the major stumbling block. Another, less important factor, is range. EVs can deal with under 100 mile range since you have your own “gas station” at home or work with a handy plug.

But if you could go 100 miles and pull into a recharge station, then be on your way in 5 minutes or less, I’d say the electric vehicle would be here to stay.

“Cambridge Crude” is one possible technology that, if perfected and developed commercially, could solve the charge-time problem. It’s still vapor-ware at the moment though. Although it “works”, it’s not ready for prime-time by any means.
‘Cambridge Crude’: New MIT Battery Design Could Be Breakthrough

Hi Bob

Thanks for the link, I will take a look at that when I get a moment.

I also note your comments regarding battery technology and the fact that investment in electric vehicle technology has far outstripped investment in this area so far. However, times seem to be changing, more finance is being pointed towards improving battery technology and recent comments, financial assistance and sales forecasts by the Chinese authorities have made people sit up and listen.

While the move to mass market may not be just around the corner, there are many who believe that 2013 could be a very important year for the industry.

See this thread regarding fast charging technology I posted a few days ago…

Also, my buddy with the panels on his cart were never meant to fully charge his car, just add to it. He is a tinkerer and loves to experiment. He has other videos where he designed a rain catching system to water his garden & lawn. Utilities in Canada are very expensive.

Hi LuvMyTJ

Many thanks for the interesting link (which I will look at in more detail later) and your comments. There are many interesting angles to look at regarding the electric car industry.