I'm an older guy with lots of electronics experience, some solar experience and 2 electric cars. I'm looking for help solving the following global environmental problem, starting with our own little problem:
> 1) I want to charge our Nissan Leaf and Tesla model 3 ONLY from the sun, and
> 2) I want to do this as efficiently as possible.
Sounds simple, and done-that-already, but it's not, unless I'm just wrong, it's not really got a solution yet.
Now in theory, and as simple as possible, this means the following setup:
1) Some solar panels,
2) One DC-DC converter*,
3) A battery charge controller to throttle up and down the converter, and
4) A car run by a traction battery.
- Here the converter needs to be the maximum power point type to most efficiently use the solar panels.
- Also to help minimize losses that every converter or inverter stage has, between the solar panels and the battery it would be best to have just one DC-to-DC converter. In practice, however, directly tapping and charging the high voltage DC traction battery is not very smart with an expensive car that is under warranty.
So moving to a more practical solution, I'm thinking of using the existing J1772 car charging ports (with the J1772 adapter to the Model 3), but to have my solar system smart enough to tell the cars how much solar power is available at any given moment so the car can track the solar production. This makes it so that when a cloud cuts the output of the panels, the car just takes what is available at that moment. And it means the car charges at the rate that we have sun that day, and no more. Yes, this adds one additional layer of inverter inefficiency, because now you first have a DC to AC converter from the solar array, and it then feeds an AC to DC converter and battery controller inside the car. But it also means not directly tapping into the high voltage DC of these car batteries, and also hopefully being able to use more off the shelf components.
Sounds simple. It's not. So far I've not found an off the shelf solution to this.
Here's are the ideas I have so far to accomplish this, DIY style:
* I already have purchased the J1772 specs, and can see that the pulse width can be programmed to tell the cars that can use that input how much current you want a J1772 car to draw. The trick is getting this available current from an off-grid solar array and then passing it to this J1772 interface.
* I have also found the design of a J1772 interface that could be modified here: Arduino EV J1772 Charging Station
What I'm still looking for is a good off-grid solar inverter that will tell me how much current is available, and then some way to have the Arduino read this information to convey that to the car via the J1772 controller.
So I guess my question is: has anyone else done this, or if not, how might you go about this, or is there an off the shelf solution somewhere. I haven't yet built the solar array, but am hoping to do that this summer (2021).
I've already seen these:
AT A MINIMUM, if I decide to be grid tied instead, I would like to be able to set the J1772 output current from information coming from our current solar output in amps, so as to NOT draw power from the grid to charge the cars if at all possible. The idea is that once we have enough sun then, and only then can we drive.