Solar Panels on an Electric Car

I love electric cars. Ever since a friend let me drive his Tesla, well I have been hooked. Sure Tesla is a luxury car, but still the concept is great. I have made solar cells as an under graduate in electrical engineering, so I am educated somewhat on the subject. In places like the US southwest, solar makes a lot of sense, but less so in the snowy areas. I’m rather enthuiastic about Energy Vault’s technology where they use crains to store electricity. I really hope they can make it work.

Regardless of my enthuiasm for electric technology this post is really about a new car that Toyota is testing. The idea htey have is to put a lot of solar panels on a car to help it get some free power from the sun to extend your range.

There are a couple of things that I am very excited about that they have changed in this test vehicle as compared to versions they have released in the past. There are a few things that I think the article got wrong, and there are a few things that I am unclear on. All of which I will discuss.

Now you might be asking how does this connect to FIRE, well, the idea is that the solar panels may ultimately give you enogh power to have you not need to manually charge the batteries most days, if ever. It’s brillaint if you can handle how ugly it looks. I am all for utility, but I am one who loves the sleek lines of a pretty car. I am not immune to that sales pitch, unfortunately, but as long as I am aware of it, it mostly manifests itself in my regular habit of cleaning up my car.

So let’s talk about this article finally. Toyota’s release has some more data that is more tech and goes into more detail. I’m going to go one at a time at the major points and caveats in the two documents

What Toyota did was to plaster across the whole top of the vehicle new triple gate solar cells which essentially have 3 cells in one each tuned to pick up one particular color of light. This gets you more efficency; they are quoting 34%. That’s great; it’s the limit of what single gate solar cells can do. Everything you buy today is single gate and retail is getting you like 20 – 22% efficency; meaning 20% of the light hitting the cell gets converted to electricity with the rest going into heat or being relfected.

My first problem is that trigate cells are currently very expensive and not worth the price difference. Maybe Sharp has solved that problem, but they don’t go into that. I have to remember that electricity is cheap, so this only is a good idea if it’s cheaper than plugging it into the wall regardless of how excited about the idea I am. Problem number two is where do you live. Here in the NYC area where I live, we get a fairly large amount of snow each winter, and it’s against the law to leave that snow on the roof of your car. We all use brooms and the like to get the snow off. These panels will need to be durable to take that abuse without scratching and thus lowering the panel efficency if they plan to sell it to use northners.

Another concern I have is that they put the cells on the rear window. That’s rather not street legal here in the US, and I think it’s a safe bet that it’s not legal anywhere else. I suppose you could have it as like a blanket that you could put on the car when you’re not driving. I have a small panel that I hooked up to a fan to help cool my car on hot summer days like today, and that helps keep my car cooler. I’ll explain how that works and how cheap it is to make if you want to know; hint $20. Anyway for my little panel the risk of theft is low, but in a place like Manhattan, I’d be concerned about it. If it’s part of the car, that’s a different story.

The next point is that the car can get about a maximum of 44.5km range per day if the car is stationary or about 56.3km per day if it’s moving. First question is why. neither article clearly states the reason, but the Toyota relase explains it in such a way as to make me think that the reason is that the solar panels put out so much power that the battery can’t take it all. So if you are driving during the peak solar output, noonish, then you will get some extra power as that extra power will go directly to the motors and systems you are using.

Those 44km are 27 miles and the 56km is about 35 miles. According to the US DOT, the average American drives about 37 miles per day. Somehow I do not think that is a considence. Now the Toyota link adds the saveat that the rage estimates come from averaging the last 10 years in a particular district in Japan which accounts for weather and the like. The latitude for that place is the same, more or less, as LA to Atlanta in the US. So again, us northerners would get less, and since LA is drier than Japan, they’d get a bit better range in LA. Check this map from the USGS to see what I mean in more detail. Still, most Americans would be able to get most of their daily driving miles for the cost of those extra solar panels. That’s pretty cool. Imagine not having to waste time charing up most days. I know my wife would love that. She hates getting gas for some reason. Keep in mind the rear window is covered in cells, and that is not legal, but is in all the images. That would lower the range significantly assuming that I am correct about that not being street legal. I could be wrong on that.

There are no details about costs, when the car would be released, or anything else than that. This is a test vehicle after all, and not a production model. Still, this is promising, and like all tech, very, cool. My hope is that this is green squared; good for your wallet and for the environoment, as both matter to me.

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