Off-Grid Charging

Off-Grid Charging

I currently live off-grid and this is my set-up

5.400Kwh Solar (peaking at 6200Kwh)
70KWh Battery bank
I can Invert 4.4kw continuous(wanted to upgrade to 8.8Kw)

almost every morning my battery bank is at 100% State of Charge around 9:30-10:30am and the rest of the day my solar is doing nothing which is fine for charging my future Tesla Model 3.

Here is my problem, instead of upgrading to a second Inverter in parallel I was hoping I could divert the solar 150VDC to charge the Tesla with an adapter of sorts.
This way I'm not passing the DC through my Battery bank then Inverted it to 240VAC(2x120VAC) which the car would change again to DC with the on-board charger.

Does one exist? I am not grid connected so most so called "PV to EV" machines wont work because they still use AC I believe.

Note: My charge controller already has a built in relay switch that I can program to open/close with the State of Charge of my home battery bank, this way it could activate some sort of diverter to power a DC Charger?

hammer @OR-US | 26 april 2019

Even if there were a direct DC adapter ala Supercharging you'd need 350-400v, 150V isn't going to cut it. | 26 april 2019

Its' even more complex, the voltage required to charge the pack using DC has to be very tightly regulated and changes as the battery charges. Plugging in a solar (even one closer to the needed 350-400v), would cause one of two things:

1) When a cloud goes over the solar panels and the voltage dips, the battey would inject power into the solar cell array and likely fry them.

2) When the solar panels provide more voltage than desired, the battery will be destroyed and may catch on fire.

Bad idea on so many levels. Better to convert to AC, and let the car's internal AC-DC properly regulate the voltage and currents to what the battery safely needs.

andy.connor.e | 26 april 2019

This is why you do not put solar directly into your car. You need a "middle man" or a battery to store it in, that will give you a stable regulated output.

tommyfournier | 26 april 2019

Thanks a bunch for the comments,

your right hammer @OR-US that's exactly what I'm looking for ala mini supercharger, cant the voltage be easily boosted to 400v? buck-booster..

If not then I might need to find another adapter that can take my PV DC and invert to AC so I don't draw from my battery bank unnecessarily, but as mentioned with the clouds may still be a problem?

All this came about because I have a pre-conceived notion that it will degrade my Home battery bank faster having all that extra power going "through", Am I crazy in thinking this? use the plates faster

I have 24 x 2v 1450amp/h batteries all in series to make one 48v bank..lead acid type.

keep in mind I only want to activate the plug when my home SOC reaches 100%.

andy.connor.e | 26 april 2019

You can always step up the voltage from 48 to 350-400. But the voltage:current ratio will require quite a substantial amount of current out of the battery. You would be drawing 208A across all your battery cells, which is almost as much as a car would draw when starting its engine. I dont think that kind of current would be good for your battery health.

You really need a higher voltage out of the cell. You could hook up 500 phone charger banks up in series, but the voltage on those outputs are only 5V. Really, i dont think you have a high enough voltage for your application. 48V is plenty for general house appliance power, but not for fast EV charging.

Earl and Nagin ... | 26 april 2019

A buck-booster is essentially an inverter followed by a switching regulator in one package. While, perhaps not as efficient as a custom one, your solar to household AC plus the household AC to Battery DC in the Tesla is essentially a buck-booster.
Yes, using your Home battery bank batteries with your solar to charge the EV will degrade them somewhat if you charge your EV when the sun isn't putting out the full amount you're charging from. If you only charge at 3.6 kW (~ 15 amps at 240v) when the sun is shining or after your SoC reaches 100%, you'll probably put less load on your home battery.
If you do a lot of driving during the day, you'll undoubtedly want to upgrade your solar system to account for the additional energy needs of your EV and, perhaps, to enable charging at greater than 3.6 kW (only ~12 miles per hour).

tommyfournier | 26 april 2019

Andy.connor.e I was saying to step-up my solar array's 150VDC to 400VDC bypassing batteries, at 400VDC I'd still get 13.5 amps giving me a 5-6kw charge when the sun is out, but it may not work without the batteries. because the clouds might change incoming voltage, although the voltage from panels should not change much just the amperage which should not be an issue I presume.

Earl and Nagin, If I go the home-power route I'm definitely adding another 4400watt inverter in parallel letting me charge around 6-7kw easily. I would need to check what my batteries are rated for amps out Andy.connor.e mentioned...

Luckily I don't have the car waiting to be charged for another year if ti goes well, but I still need to figure out a proper solution...