Direct Panel --> vehicle solar charging

[islandchick]

Hi, I have been lurking around the boards for quite a while, but haven't delved too heavily into it until lately. I was wondering if any of you smartypants engineering types has put together a trickle charger of sorts for your Tesla, a roll up or similarly portable panel to put on the roof of the car attached to a charging plug? For charging when you have to park outside for work or are otherwise kept from charging. I know it probably wouldn't do a lot, but since you're parked for all day anyway, why not use that UV for something instead of just damaging your paint.

 

[arg]

You can't charge on AC at less than 6A (720W if you do it at 120V, 1400W if you do it at 240V), so you need a substantial amount of panels to be able to do this, and you need at least a small battery or to be grid-tied to stabilise the voltage/current, given that with AC charging the car controls the charging rate (you can only tell it the maximum it can take). People with grid-tied or off-grid solar on their homes have done this (and there are a few commercial products) so as to charge at approximately the rate being generated by the solar and so avoid drawing from the grid. It doesn't really work for a few panels standalone.

In theory, DC charging gets around the minimum charge rate and lets the charge rate be controlled by the external charger so you don't need the batteries or grid-tie, but it's vastly more complex and if you try to do it with anything remotely off-the-shelf like starting with the CHAdeMO adapter, very expensive.

Also an issue with 'just a couple of panels' is that to charge at all the car's computers, cooling systems etc. all have to be powered up, so eating a couple of hundred watts before you even start - which means that with a small number of panels, hardly any (or a negative amount!) would actually end up as useful charge.

 

[islandchick]

Hmm. Darn. Got to be a way, but I see what you mean.

 

[ewoodrick]

I think that a 4x2 foot solar cell puts out about 100 watts. A 120V 15A circuit charges at about 1200 watts.

So, if you use the enormous 4x2 panel, at full power, it will take 2.5 hours to go a mile. If you could get 8 full power hours, then it would tend to cover a 2 mile commute. But in reality, that probably barely covers the phantom drain. And that's not one of the 1x1 ft small panels.

Some of the other EVs have had a solar cell, but they generally for running a small fan to circulate air, and I don't think that they even do it anymore, just not enough return for the cost. Especially when lots of people park in covered or shaded places.

 

[arg]

One thing you could usefully and quite easily do is use a modest size panel to keep the 12V battery topped up. That would allow you to park indefinitely without loss of charge from the main battery (assuming you are parked outdoors!).

 

[SSedan]

The load to run the computers and chargers seems to be quoted as 400watts.
Now DC to DC you might not need the chargers but you are going to need a way to get the voltage up.

I am not an elecical engineer or really know much about batteries either but I doubt you could charge a 400volt battery with 100-200watts at 12volts so likely some other sort of hardware that will consume some electricity making it usable.