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We have solar panels but don’t earn anything from the export - got the panels installed for free amd can use the electric, but the installers get the export tariff

how practical is it to mostly/fully charge with solar? Assuming I have the car on the drive 3-4 days per week and I only have 8 panels(no idea what watt). Is there a limit below which the car won’t charge or can you happily trickle tiny amounts in?
 

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At a guess, 8 panels @ 250W each is 2 kW Max. That's facing due south, aimed straight at the sun on a perfect day in June. If they're like mine, facing due East at 20 degree shallow angle, you're more likely to see 1.5 kW max.
I have 16x250W panels facing East so that gets 3kW max, but I've boosted it with 1kW of south-facing panels on garden shed roof, so the best I ever see is 4kW on that perfect day. But over the course of that perfect day, they make 30 kWh. So I try hard to charge my EV on days like that, often on granny EVSE set to 6A.

6A is the lowest that charging can take place at. So call it 1.5 kW, maybe 1.4 kW if voltage <250V.

Typically my house draws about 250W when "idling", so there's the fridge-freezer, router, telephone, telly + recorder on standby, a few other bits, so if you're the same, you could easily be exporting 1kW on a good summer day. So that's 2/3 of what your EV wil trickle-charge at. Some EVs have a "reduced charging current" switch so the car only takes 6A, and some granny EVSEs have selector button to tell it to only offer 6A to the car, which the car must obey not exceed. Screwfix granny EVSE will offer 10A, can't be switched to 6A, so you'd need the car to have the ability to limit, or evconnectors.com granny EVSEs can be set to 6A, so any EV will be limited on that EVSE. But you pay more for the option!

So I'd say yes, go for it! Anything you put into the EV from solar is that much less grid power you're paying for!

I'm about to start designing & making an interceptor-module, which will get inserted into my Rolec dumb EVSE that just offers 32A at the moment. This module will talk over radio to another module that's measuring power being exported from the house. If that's more than 6A worth, it will tell the EVSE module how much current it can offer the car, so this will track the sunshine, and shut down charging for a few mins if the kettle goes on etc. Once that's working, I'll make even better use of my panels. The current the EVSE offers goes from 6A upwards, infinitely smoothly, to whatever's the max, usually 32A, and whatever value the EVSE offers the car, the car must react and adjust in about 5 seconds. So real-time solar tracking is perfectly doable.
 

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Lets assume you have 8x250watt= 2kw panels so even on the best of sunny summer days for say 1hr in the middle of the day that is what you could produce. A lot of EVs will not charge below 10A =2.4kw and even if they could charge at 6A it is not worth the bother. However that is not to say that you cannot MOSTLY charge your EV in summer. You could do this manually if at home or get a smart charger which would take what your panels are producing and add grid leccy to top up but i would just stick to manual and charge using the "granny cable" which the car will probably come with.

I would suggest that a better ie cheaper way to use this free leccy is to get a solar diverter to heat your hot water if you have an immersion heater and a tank. If you have a smart meter then you should charge the car at night on cheap TOU( time of use) tariffs such as Octopus Go.
 

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I'm about to start designing & making an interceptor-module, which will get inserted into my Rolec dumb EVSE that just offers 32A at the moment. This module will talk over radio to another module that's measuring power being exported from the house. If that's more than 6A worth, it will tell the EVSE module how much current it can offer the car, so this will track the sunshine, and shut down charging for a few mins if the kettle goes on etc. Once that's working, I'll make even better use of my panels. The current the EVSE offers goes from 6A upwards, infinitely smoothly, to whatever's the max, usually 32A, and whatever value the EVSE offers the car, the car must react and adjust in about 5 seconds. So real-time solar tracking is perfectly doable.
There's already an open source project that can pretty much do this already. See EV Charging
If you've not seen it already it's worth checking out. Might save wheel reinventing.
 

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There's already an open source project that can pretty much do this already. See EV Charging
If you've not seen it already it's worth checking out. Might save wheel reinventing.
Thx, yes, am aware of that. But I think that replaces the entire ECU with their own one? And there's a lot of webby stuff happening. I'm aiming to make a simple piece of kit that I can add into existing dumb EVSE. I just might get some kind of app on Android/iPhone, would need to co-opt my son to build that!, but again it may only have a small built-in screen + buttons to do the menu choices. And partly it's an exercise to keep my remaining grey cells working ...
 

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... A lot of EVs will not charge below 10A =2.4kw and even if they could charge at 6A it is not worth the bother...
That so? Agreed that Zoes have a reputation for not being efficient when charging at low currents. My ID.3 manages 90-93% efficiency at 6A, exactly the same as at 10A & at 32A, as far as I can measure. And supposedly a lot of EVs are using the same charging modules sourced from whoever, so I'd expect most EVs to be well-behaved at 6A.

.. I would suggest that a better ie cheaper way to use this free leccy is to get a solar diverter to heat your hot water if you have an immersion heater and a tank.
Agreed, I have Solic 2000 & it's been great! Paid for itself within 2 years, bought it 5 years ago. Boiler is generally off from April through September as the solar gives us all the HW we need.
But no use if you have a Combi boiler!

This summer I now have a EV rather than PHEV to fill, so expecting a lot more solar leccy to go into the car. Whether we still get enough HW from the Solic scooping up the leftovers, I don't know!

This is the kind of thing I might build into my solar-controller for Rolec, program it to monitor house import/export as usual, but use an occasional short test-charge of say 1 minute at 3kW to work out whether the HW is hot or not! Here's how that would work!

Solic will grab up to 3kW to heat the immersion, so when it's running I see 0W exported. Actually the reading varies between 20W imported & 20W exported, there's a bit of noise, but arounf 0W average-ish.

Suppose the house is exporting 0 kW.
If HW is already hot, the Solic won't be diverting anything, so I start the test charge at 3kW. I'm expecting to see 3kW now being imported from Grid. I see this happen, so I now know the water's hot, and there's nothing available to charge the car. Perhaps its cloudy and all th eleccy's used already.

But now suppose the water's cold. Solic is, unknown to me, using 3kW to heat it up, and okW is being exported. 3kW is therefore the total panel production (assuming house draws 0W for now as a simplification). I start my test charge at 3kW, the Solic sees momentary 3kW import, and shuts down, so house in importing 0kW. I now know the Solic's active, so the decision is, do I want HW asap at 3kW, with no car charging, or do I want the car charging at 1.5 kW and 1.5 kW being diverted to HW? Or some other balance, like 2kW to car & 1kW to HW?

All sorts of choices are then available, and I think that I'd choose to prioritise HW heating, as it would be a disaster to have only cold available when wife takes her bath! So with a bit of cunning test-charging, it's possible to infer the state of the HW diverter! Maybe I can even work out the total amount of kWh the Solic's used today, and when that's suitably large, I can de-prioritise it and charge the car a bit.
 
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