Off Grid EV charging

[Miek]

I have a friend who's just bought a Tesla model 3 and wants to attempt to charge it 'Off Grid' using a PV car port. 

 

I can see it's possible to have a PV system with batteries and inverter to provide AC power to charge the car, BUT, 

Is it possible to charge and EV directly with the PV and inverter  but without any battery buffer on the PV side?

 

Assuming say you have 6kW of PV and an inverter capable of running off Grid AND without a battery bank. Will the charger accept a potentially fluctuating amount of power when for example a cloud passes by?

 

My feeling is that this won't work, but does anyone have any ideas to the contrary? 

 

I've not found much on line rearding this so any help would be much appreciated. 

 

 

[Jeremy Harris]

This will not work well with the Model 3, because Tesla have failed to implement charge control from a smart charge point.  It will work with most EVs, though, as the majority do implement the spec correctly.  It will work OK with other Tesla models, it's only the Model 3 that refuses to wake up and accept charge from a controlled charge point.

 

There are a few smart charge points that can control EV charging like this, although the range of charge current is limited by the specification to a minimum of 6 A, about 1.4 kW.  The Zappi is probably the best known that allows this sort of control.

 

DC charging isn't easy at home, as I don't think anyone makes the required DC connection units.  DC charging is normally reserved for rapid charging (50 kW and above usually).  The only practical option for home charging from PV at the moment is AC charging with a charge point like the Zappi, that has some form of PV charging capability (I say some form, as it's not 100% PV because of the 6 A lowest current limitation).

 

It may be that Tesla get around to fixing the Model 3 scheduled charging problem, although they have been aware of it for well over a year now and there's been no indication that they will fix it any time soon.

[Miek]

Thanks Jeremy, that's very helpful. 

 

So the model 3 can't be told what to do by a charger? that is annoying. 

 

Also the 6A lowest charging current is a bit of a hindrance on a smaller PV array.

 

It would be great if you could charge the car like a regular lead acid battery with a simple regulator and PV setup where any power, even I it's mA, is put into the battery. Wishful thinking...

 

[Jeremy Harris]

38 minutes ago, Miek said:

Thanks Jeremy, that's very helpful. 

 

So the model 3 can't be told what to do by a charger? that is annoying. 

 

Also the 6A lowest charging current is a bit of a hindrance on a smaller PV array.

 

It would be great if you could charge the car like a regular lead acid battery with a simple regulator and PV setup where any power, even I it's mA, is put into the battery. Wishful thinking...

 

 

 

I'm afraid so.  The Model 3 non-compliance is a real nuisance, as the last two cars I've had have had no problems at all with the charge point controlling the charge.

 

The 6 A minimum is  nuisance, but is reasonable, as the car onboard charger (for any EV) will tend to lose efficiency as the current decreases (just because a lot of the losses are fixed, and don't scale with current well).  As a general rule, the higher the AC charge current (within reason) the better the charger efficiency.