Dynamic Charging Feature for off-grid charging

Dynamic Charging Feature for off-grid charging


I plan to go off-grid at some point in the enearer future. By then I will have a MS and this is where the dynamic charging would come in handy.

As the output of the solar power system varies second by second it would be ideal if the ampage of the loading would be adjusted to pull just as much as the solar array produces. The problem with a fixed loading flow would be that either too much or too little would be pulled from the system and that the battry bank of the house would have to ballance the loading.

So ideal would be a feature where the house system could be linked with the Tesla app or some other form of communication to adjust second by second the load pulled into the MS to ballance the off grid system.

I know the fewest people are looking to go off-grid. But nevertheless even with a future grid that is smart and changes prices for power on an hourly or half-hourly basis this would make sense to minimize the cost of charging.

tes-s | 17. juli 2013

How about a current-limiting circuit for your HPWC or outlet you connect your charging cable to? Dynamically adjust the current available based on excess solar capacity.

Earl and Nagin ... | 17. juli 2013

The J-1772 charging standard has the ability to tell the EV what maximum current it can draw. It seems like it should be possible for a PV inverter to dynamically set the max current the car can draw based on solar production available. I don't know anyone who has done this and I'm too lazy/busy right now to look into it myself.
I'd love to hear of such a thing, so I can charge my car during power outages.
With CA forcing our power provider to buy our PV production at high Time-Of-Use prices, we're much better off being on-grid most of the time where we are buying low (charging at night) and selling high (producing solar electricity during the day).

GeekEV | 17. juli 2013

I'm no electrical engineer, but this doesn't seem to be necessary, unless your goal is to reserve some power for the rest of the house. You can't draw more power than is available, so even if the car is looking for 40A but only 30A is available, you'll only get 30A. The only time something like that would be a problem is if you're actually able to draw 40A but only wired for 30A. You'll burn up your wires.

Can an EE out there confirm?

Alex K | 17. juli 2013

@ GeekEV | JULY 17, 2013: You can't draw more power than is available, so even if the car is looking for 40A but only 30A is available, you'll only get 30A.

That's not true unless there is a special current limiting circuit installed, which most homes or business don't have. The car can theoretically draw whatever current it wants. What's stoping it is the communication between it and the wall connector (UMC/HPWC/EVSE). The Model S uses the J1772 protocol (but not the connector) which informs the car of the maximum current to draw.