Minimum power requirement for charging from home solar panels

[Badger]

I will shortly be picking up a newish Enyaq 80 Sportline. I am trying to go green.

I currently have a 4kW home solar panel system that generates on a cloudy day between 1.0 - 1.2kWhr back to the grid.

I understand there is a minimum power requirement to charge an EV battery of 1.4kW. If this is correct, on winter or cloudy days, I will not be able to charge my car until my net generation exceeds 1.4kW (solar panel output minus household usage). Hence I will be generating <1.4kW to the grid rather than to my car battery.

A few questions:

• Is my understanding on the minimum power setting correct and why is this necessary?
• Is this a Skoda imposed power limitation or the EV charger manufacturer limitation?
• Can either minimal power setting be reduced to allow me to charge the car battery when I am generating enough to export to the grid, eg. say above 100W?

Finally, I am considering buying a Mappi 2 EV charger as they are reported to be good for managing solar panel outputs. Are there other chargers which have a lower minimum power that are compatible with solar generation?

Many thanks in anticipation.

[ChangoMutney]

We have a Zappi v2 but no car yet. The Zappi 2 does seem to handle solar very effectively from looking at the Manual to make sure you get the most out of what you have installed.

[orrery]

The minimum power is set by the standards probably due to the signalling protocol between charge-point and car, as far as I know. I've never seen charging at less that 6 amps/1.44kW. So, yes, you need clear of that to start charging if you are not to import anything.

You can use the additional power that can't be used to charge the car in an immersion heater diverter to heat your water. My immersion diverter seems to co-exist happily with the Hypervolt car charger - heating the water first (as it can use a few hundred watts), then charging the car.

[Ouvavou]

I have a Zappi and no car (yet) also. I also don’t have solar but I’m gettting 5kw installed in a few weeks which will definitely be before the car arrives! The Zappi has a eco+ Mode that will use all available solar but, if that drips below 1.4kw, will use the grid to keep the charge going. I’m assuming it will only use grid power to balance up to the 1.4kw and not over - I think this will be the mode of choice for me in daylight hours in winter.

[RichR]

I think orrery has the reason for that 6A (1.4kW) figure. There are various things that happen when you plug an AC connector into an EV (Type 1 or Type 2) as defined in the SAE J1772 standard. The first thing is that there's a resistor in the plug that indicates to the car what the maximum current that can be handled by the cable is - this is defined for 13A, 20A, 32A and 70A (63A if 3 phase). So the car must never pull more than this value in order to protect the cable. Next there is PWM signal from the EVSE to inform the car what it is capable of outputting. This is defined for 6A (10%) to 30A (50%) continuous in the standard. Again, the car must draw no more than this value in order not to damage the device supplying the power.

For example a standard 7.2kW PodPoint wallbox would put out the signal to say it can provide 30A, and if a 32A cable is used, that'd indicate it's capable of 32A. The car would then would be able to determine from the current state of the battery how much it can use to charge it, and be able to use up to 30A (6.9kW) if it wants to. If you're using a three pin mains plug granny charger, that'll tell the car it can't use more than 10A - 2.3kW.

So there is no provision in the standard for a supply to say it can supply less than 6A. In practice it's possible that if the PWM ratio is under 10% (the ratio for 6A), the car's BMU might understand it and limit the current, but as it's not in the standard there's no guarantee. I would assume that the Zappi EVSE if told it can only use solar, and there is less than 6A (1.4kW) available, it would simply disconnect the supply to the car.

[ComicGeek]

I charge my 80 at both work (which has a 4 kWp PV system) and at home (which has a 4 kWp PV system plus battery storage).

I have a Project EV charger at both, which in theory has PV capability and monitors the export rate from the house through a CT clamp. In Eco mode mine charges at a set 6A plus whatever the export rate is - in Eco+ mode it only uses the export rate, but only when this is over 6A (I have never got this Eco+ mode to work properly).

In reality, and after playing around with it for some time, I tend to just charge at work whenever it's sunny at 7 kW without the PV mode - at least I know that it's partly free, and it would take blooming ages to charge at 6A! It's a company car, so needs to be available for people to use.

At home I charge at night time only using a cheap rate, which I also use to partly charge the home battery, and then top up the home battery with excess PV generation during the day. There's no point in using the battery to charge the car directly due to the various losses involved, but I can run the rest of the house from the battery most days.

[orrery]

I would assume that the Zappi EVSE if told it can only use solar, and there is less than 6A (1.4kW) available, it would simply disconnect the supply to the car.

I presume that car can use less than 6 amps, even whilst the charge point is advertising a higher value, such as for balancing the cells.

[RichR]

Yes, that is correct. If you watch on a smart meter what happens when it gets near the target SOC, it drops right down to just a few hundred Watts. I guess it might be interesting to mock up an EVSE and supply maybe a 5% PWM signal and see what happens - but it might be different depending on the make of the car, so probably not meaningful.

[Badger]

Many thanks for helping to clarify the situation.

[white67]

Just caught this thread, I agree with ComicGeek - you really need a battery if you want to capture all your solar power.

I'm fortunate to have installed a Powerwall late last year which I'd use if I didn't have free juice at work. So I charge the car (7kW) there when it's stationary.
My solar is also 4kWp and on a good day (Glasgow) so far this year I'm getting 15kW total.

With a full PW battery I reckon I would struggle to feed the car with a meaningful amount after deducting home use, which is surprisingly high even with a small household. (Electric cooking!!)

That said I should be topping 20kW soon, but it's still a way to go to get to even a 1/2 charge on my Enyaq 60. For only part of the year when the sun is useful.

I'd suggest you go to the Energy Savings Trust to see if there are any incentives for a battery if you're interested. A lot of paperwork but I'm happy with my PW and Enyaq.

Hope this helps.