There are commercial off the shelf products coming for this. Enteligent is the one I am looking at most closely. The DCBEL one also has a high voltage DC input IIRC. There will be others soon too, now that ISO 15118-20 was finally published 6 months ago.
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I am power systems designer. I design power grids, specialising in solar/hydro/wind hybrid grids. I have built dozens of electric cars, conversions, and electric hot-rods over the years. I owned/operated an electric vehicle dealership for a number of years, but am 90% retired now. These days, the bulk of what I do is design and inspect hybrid power grids in yachts. I am old, and don't really want to work that hard anymore.
You are dead-on with rooftop solar companies, their focus is extremely narrow. Their product, their software, as soon as it gets out of their comfort zone, the solar installers in the PNW tell the customer to call me.
There are a half-dozen entities that I know of that are working on interesting products for solar + EV. Having sat at the design table for a couple of them, there is an over-reaching problem that most are trying to overcome: just plain rooftop solar + regular old EVSE is too good. It is like trying to invent a wheel that is more round. Let me explain...
I have plain old rooftop grid-tied solar on one of my homes. I also have EVSEs (4 of them). In my state, power credit is 1/1, so the grid acts as a perfect battery. I say perfect because if I put a KW into it, I get a lossless KW out of it. Because rooftop solar is site-usage-first, any power I am producing goes into my car first. If the car needs more, I can pull out of my grid "battery", to be replaced to the grid after I unplug my car. I get to do this for free. There is inverter loss, but it is quite small. A DC direct system will remove some of the loss, but nowhere near enough to justify the cost of building such a system (in the designs I have been involved in). The added complexity and dedicated components end up being a Rube Goldberg machine.
So by default, any solar you produce on your roof will go into your car first, this is a good thing. But what if you don't want to use any grid power in your car, and shut down the charger if there is not enough solar to charge it? That is a simple matter of grid-gating, and only running your EVSE when the gate is in the positive flow mode. Ideally, the EVSE would also try to throttle to use whatever is available. Wall is making an EVSE that does just that, and I like it a lot.
This brings us back to the question of solar DC/DC charging. Because of all of the above it is viewed by most engineers as being a novelty; a fun way to do it differently, but not having a real market.
That said, as soon as somebody builds one, I will buy it. I like novelties.
The BMS must be able to control the charging and the rate, or you risk damage to your pack. For this reason, if the incoming charge is not controllable, the vehicle will rightly shut it down. Unless you are going to bypass the BMS and the system controller on the vehicle (proprietary and closed), you have to handshake with the vehicle for it to accept the control and then the charge. "Cheap MPPT controllers" are obviously not going to provide any of this.
One of the reasons that modern EV batteries have a long life expectancy is the rigid controls they are equipped with. Bypassing these (like bypassing the safeguards to tie in a parallel towed battery) could dramatically affect the life of your 131KW pack.
Have you done a price check on replacing one of those?
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