Off-grid car charging - a mad idea

Chris_5339762

This is all theoretical at the moment and there maybe a stupid reason why this can't happen, but here's my current silly idea.

To all intents and purposes, you're limited to a 6kW solar system under the new ESB NC6 regulations - unless you want to pay them loads of money. That isn't enough to reliably power an electric car at any time of the year, as you need a lot more than a 6kWp system to get yourself anything decent during winter.

My roof has 12 panels on it which can generate about 5.5kW peak - limited by our 3kW inverter plus a nice 5kWh battery. Scaling that up, in theory to give you about 20kW peak in the summer would be about 48 panels. That would roughly cover the top garden of my house in terms of ground mounts. As you typically get about 1/10th to 1/5th of that in the winter in the clouds, you'd still get about 2 - 3kW in general during January. It would do the job for the slow months.

Obviously you wouldn't want this to connect to the ESB in any way, so could you just hook this lot up to a 20kW inverter and then into say, a 3 phase Zappi. That would then merrily and completely charge a high capacity electric car at just about any time of the year. Your fuel bill would drop to zero with a medium size investment (I have no idea how much this lot would cost, but for a self install it wouldn't be awful).

I can hear you shouting dump loads, and of course you could dig a pit, fill it with sand and have a dump load into immersion heaters in the sand. But you'd also just cover the panels when you're not using them. Easy. Perhaps sliding garage doors over them or something like that. You wouldn't be out of the house when the car is charging, and you just unplug the system when you do go for a walk so it doesn't spend a long time charged and dumping power. Basically, you'd just plug it in when you need it, and stay in the house when its in use. In the summer, 20kW should charge the high capacity electric cars in about 4 hrs. This seems like a reasonable sweet spot too.

Perhaps you'd need a 3kW battery or something on the inverter to load balance and smooth things a little bit, but my novice head can't see anything diasterously wrong with this idea. Yes, there'd be a small amount of manual adjustment here, but provided the whole lot isn't grid tied, then there should be no problem from the ESB side. Perhaps from the general safety or sanity side, but we'd ignore that for the moment. The whole idea is that this system would NEVER be used to power the house or connect with the grid in any way.

On the other hand, this hasn't been done here as far as I know and smarter people than me must have considered it. Any ideas from the clever people on this forum on improvements to this idea, or why I really really really shouldn't do such a thing?

10-10-20

Dump loads aren't needed for solar, only wind really. If there is no load on the inverter then the panels stop producing.

The concept is fine except for it's simplicity. I mean that to say that there is nothing stopping you from creating a 20kW solar array and 3P inverter, except that it's a huge price to pay to only charge an EV battery. Plus, it doesn't have an autonomy as it's almost fully dependent on having the EV plugged in as you'll loose the available energy when the car is unavailable. The tiny 3kWh battery will be worthless as it will be topped up in a matter of an hour or so and it will only contribute a small percentage to the EV battery.

But you're effectively highlighting a significant gap in the mini-generation market as the NC7 process is not transparent and isn't conducive to homeowners with large amounts of roof-space.

I'd like to think that there is a solution to this coming down the road - a type of a shared scalable battery, multiple MPPT inputs and super-hybrid-inverter with two inverters - one for the grid at 5.7kW and the other for the house. That way you could continuously export onto the grid at 5.7kW while also driving the house loads off the second. Maybe it already exists...?

graememk

Need to get your head around kWp(peak/panel), kW(power) and kWh(energy)

That isn't enough to reliably power an electric car at any time of the year, as you need a lot more than a 6kWp system to get yourself anything decent during winter.

Just want to clear something up, In the summer its plenty to charge the car with, and then if you oversize panels to say 8-9kwp on a 6kw inverter that really stretches your time out to charge the car. But the car has to be home. But in winter, it will be hard to not run a generator to charge the car!

to build a system like that you basically generate your own grid, eg a victron quattro or something, a big battery, and charge controllers. The key to off grid is a lot of batteries, that is the buffer.

Andy In off grid garage [yes in Australia] once he gets out of winter charges his car from his batteries/solar.

There is a loophole re the NC6, You can connect anything you want to the DC side of your battery, or size of battery.. or number of off grid inverters to said battery.

Lots of solar, Lots of batteries!

the_amazing_raisin

Yeah pretty much every MPPT out there will just regulate the panels to the demand, if there's no demand then panels are just open circuit

Right, in terms of what you can achieve, I'd recommend looking at the thread below (yes I'm shamelessly plugging my own thread 😂)

https://www.boards.ie/discussion/2058294549/im-driving-on-sunshine-whooah

I'm starting to record my EV driving data every month to see how much free driving I'm getting

Now my system is grid tied and obviously feeds the house's needs before the car. You're proposing what is effectively a dedicated system, so you could potentially achieve more

A couple of thoughts however:

First, charging an EV off solar is great but you're offsetting the cheapest electricity in terms of cost per kWh. Every kWh I feed into my house is worth 2kWh into the car, so it's a much better saving to power the house and avoid that day rate

Second, a lot depends on your habits. If you're at home most of the day then you can make the most of solar charging. If you're out and about a lot then you'll miss out on the sunshine. So if there's something else you can use the electricity for then that could be worthwhile as a second diverter

Third, you'll need to trick the Zappi somehow to make it work the way you want. It needs to sense electricity going to the grid to start charging the car. No grid means nothing to sense, and I don't think there's a mode of the Zappi which really supports this

Maybe one idea would be to have an electric heater as your "grid" and the panels just load it with as much power as they can produce. The Zappi will then see the power going to the heater and start charging the car

Fourth, it seems like a very expensive idea for the savings. I presume you'll be doing a lot of the work DIY, but even so it'll be a big investment, so is it worth the cost? I definitely wouldn't bother going for 3 phase because that means you need a very expensive 3 phase inverter (or 3 inverters). Stick with single phase and oversize the panels to what the inverter MPPTs will allow

the_amazing_raisin

https://www.boards.ie/discussion/comment/120978773#Comment_120978773

Systems like that already exist, I know Victron inverters can limit feed in and you can select the max amount and even the behaviour

I think Sunsynk can do it as well. I thought Solis could too but I don't have one so can't confirm

unkel

It costs about €300 to charge up an EV doing average 16k km for the year using nightrate

Is it wise to spend €20k so you can do it for free? 😂

Buffman

I know someone with a similar setup as you describe. Keep it simple though, no need to over complicate it.

Any properly designed system will be able to regulate itself when there's no load so no need to worry about dumping anything (hence why 'open circuit' figures are so important with design), and with a large battery to keep topped up that shouldn't be much of an issue.

Basically an array with an MPPT/Inverter setup with a decent sized battery. A cheap 'dumb' car charger that doesn't care if it's on the grid on not as long as it's getting power, or even the granny charger will do in a pinch. I don't see why you'd need a Zappi as you don't need to monitor grid or solar output to do what you require and it would just be an expensive complication.