Off Grid Tesla Model 3 Charging

MPSTAPLES

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I've seen a number of threads concerning Tesla batteries, but I wanted to start a new thread that focuses specifically on the details of constructing an off-grid system for charging the model3. Will has a few youtubes about this, but I couldn't find anything definitive.

I should say that I'm a novice at this stuff. I put an off-grid on my shed that's working well. But that's about it. As I understand it, we should first know how much power is required for a Level 2 model 3 charge. I believe this is about 240v at 80amps -- around 17-19kW. I used Battle Born batteries for my previous project, and that seems to be working out (expensive). A 48v battery array seems reasonable, with a 24v set of panels in series to charge, and a couple of split phase inverters.

If someone could help me to zero in on this I would appreciate it. Although I would like to have Level 2 charging, I don't necessarily need to meet the 53 miles/hr (or whatever it is for typical grid-tie 240v charging), as long as it all works.

How many batteries would I need?
How many panels (24v, 200amp) to charge the batteries?

I can do the math, but I'm wondering about alternatives (not grid-tie) or different options.
 
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sunshine_eggo

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What is more important?

1) Charging speed
2) amount charged in a day

3) In either case, how many kWh do you want to charge in a given day?
 

MPSTAPLES

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What is more important?

1) Charging speed
2) amount charged in a day

3) In either case, how many kWh do you want to charge in a given day?

I could live with 4 or even 5 hours to fully charge. I never let the charge drop below 20%, and limit the high end to %80%. I'm not sure what the amount of charge would be for that. But I could live with a 4 hour charge time for that range.
 

sunshine_eggo

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I could live with 4 or even 5 hours to fully charge. I never let the charge drop below 20%, and limit the high end to %80%. I'm not sure what the amount of charge would be for that. But I could live with a 4 hour charge time for that range.

Does that mean you want to be able to charge the entire working range (60% total) in 4-5 hours?

How many kWh is that?
When do you want to charge?
 

lynhnn

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Let say you charge 80% from 20% = 60% of 75Kwh battery which is about 45Kwh. And given the lost about 10%, you will need 50Kwh to charge. If you are using 12v100ah BB which is 1.25kw each, you'll need 40 of them or more.
Now, if you need 5h to consume 50Kwh, that will come to 10Kwh inverter output. You'll need 240V split phase inverter (or 2 Victron inverters). You must use 48V battery bank. And to get 10,000w output, the current would be about 200 amp. That means you'll need battery cables of 3/0 gauge size or bigger to connect them.

Beside, to harvest 50Kwh per day, you'll need about 18Kw solar panels given good 4-6 hours of sun
 

wattmatters

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How many batteries would I need?
How many panels (24v, 200amp) to charge the batteries?

I can do the math, but I'm wondering about alternatives (not grid-tie) or different options.
Then you should do the maths.

It would be unusual to need to fully charge a Tesla every day. That would be a LOT of driving. A top up charge is more likely scenario.

Define how much capacity you really need to supply each day.
 

Ampster

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A quick rule of thumb I use for my Model 3 is 250 Watt hours per mile or four miles per kWh. Mine can charge at a maximum of 32 Amps which is 7.6 kW,
 

JoeHam

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A quick rule of thumb I use for my Model 3 is 250 Watt hours per mile or four miles per kWh. Mine can charge at a maximum of 32 Amps which is 7.6 kW,

Thanks for the real world numbers.

So, if someone drove 30 miles a day you would need a solar array that puts out 7.6 kW consistently for 4 hours a day.

I don’t see how the number of Battlebornes figures in here unless you want to charge at night which would add inefficiencies.

And your Tesla would need to be plugged in during peak sun hours in this basic example.
 

MPSTAPLES

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Unless doing this is just outrageously difficult, and Will seems to think it isn't, I can't imagine that there won't be a considerable call for off grid charging for EVs. I got screwed by the electrician who upgraded my electrical panel when I installed my home solar system. He did not allow for expansion, and I am pretty much out of luck for expanding my solar panels to charge my car. So, I'm either going to have to stick with PG&E and pay the true up, or go with an off grid setup to charge the car. I would love to do the latter. Would be a fun project.
 

MPSTAPLES

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Just read your post...before sending the one above. Hummmm... hadn't thought of just solar panels with no battery. Would need an inverter that did not require batteries, and enough panels to deliver 7 or 8 kW.
 

lynhnn

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Eventually you'll need a sizable battery bank and lots of solar panels. You'll need to cover winter time and raining days. Charging speed is not that important as the other two above. Charging the car during peak sun hours is good for testing out only and you will need to invest into the first two, again.
 

wattmatters

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I got screwed by the electrician who upgraded my electrical panel when I installed my home solar system. He did not allow for expansion
Sounds a bit harsh on the sparky. In what way were you screwed by them?

You only got screwed if you requested and paid for a panel to enable expansion and they did not do so.

As to adding more grid tied solar, assuming you have permission for that, adding a sub-panel to enable expansion would be fairly straightforward I'd have thought.

In any case, building an off-grid system is fun to do (sometimes) but has some limitations and different costs. Essentially you are swapping the grid for a home battery. And you'll need to have an extra distribution panel for it anyway.

Depending on how your export and import tariffs work, then you may be better just to stick with an expansion of your grid tied system. e.g. if you have 1:1 net metering then building off-grid system just to charge an EV makes little financial sense. Just put up more grid-tied solar.

If however you do not get credits for exporting excess energy, then off-grid can begin to make more economic sense, depending on the import tariffs and what times of day/night you are able to charge your car.

But if you want to build a home power backup system (e.g. if outages are common and energy security matters to you), or you just want to do it for fun, sure!

So, if someone drove 30 miles a day you would need a solar array that puts out 7.6 kW consistently for 4 hours a day.
If someone drives their EV 30 miles/day on average, then based on the consumption figures quoted, they's need 30 miles/day * 0.25 kWh/mile = 7.5kWh/day.

They don't need to generate 7.5kW of power, they just need to generate 7.5kWh of energy per day, on average. Or more to the point they need to deliver 7.5kWh/day, on average, to their EV. Allowing for energy efficiency losses along the way and let's call it 10kWh/day from solar PV.

But to cover the variability in solar PV output due to seasons, then you need to provide for such production during Winter. In NorCal in Winter you might get 2.5-3kWh/day per kW of solar PV (facing south on a reasonable tilt). So to get 10kWh/day in Winter you'll need ~3.5-4kW of solar PV.

Then you need somewhere to store than energy if the EV is not at home able to charge. This is where it gets trickier. Daily variability in weather means some days will produce more energy and some days less. So how many poor weather days do you want to provide coverage for?

Assuming you have fall back to grid charging (either at home or a public charger) then you don't really need to aim for 100% self powered, but I'd have thought you might want to aim for storing about 2 days worth of driving energy in a home battery. Say 20kWh give or take. If you get an extended rainy period, well you just suck it in from the grid instead.
 
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