Charging your EV off solar panels

[blitzracing]

Sounds like a great idea, so armed with a 3.5kw solar array and an electric mini lets see what we can do. I have a car charger as part of the solar inverter, that is described as charge on solar or excess solar only. This theory presents an interesting problem, as your charge current to the car is fixed at a preset current (around 6 amps) at mains voltage for a trickle charge. This is where the problem lies, as unlike charging a DC battery with a solar panel where you can vary the charge current according to available voltage, its all or nothing on car charger. This means in real terms the solar panel has to produce at least 2kW to start the car charging, whilst if the solar output goes to 3.5kw you are still stuck at 6 amps, so the rest gets dumped back into the grid if you don't use it. Likewise if the solar output drops below 2 kw the inverter will have to start pulling current from the mains to maintain the 6 amps , which is a pain if you are not in a hurry to charge the car, as there will be more power when the sun is brighter.

My temporary fix is a big semiconductor relay switched off a separate solar panel that only turns on the "mains" to the car when the sun is bright enough to produce 2kw or over. There is quite large hysteresis on the relay input so that you don't glitch the car charger as clouds go past the sun so it can drop to 1.6kw and simply pull 400 watts of the grid when needed as the best I can do. Im waiting for the manufacturer of the charger to configure it, but I don't see any way around this basic problem without back up batteries to charge the car.

Any one else tried solar charging?

[bearman68]

I'm assuming your unit is grid tied? -Why don't you just plug the car into the mains. When it's sunny it will use solar, and when it isn't it will use grid. If you wanted to get more sophisticated, a simple timer would be adequate, and maximise the solar usage. It will work in this manner very easily, without further work or additional control.

[blitzracing]

In think all I can do is skim of power above 2kw for the car on the solar switch, so dull days below 2 kw will be a complete waste of time if not backed up with mains. Its not a big issue as I can get off peak at 5p a unit anyway. If you look at just the power available from solar, a 3.5kw array will give you about 1000 miles motoring a month in the summer, but as you cant seem to use a variable current / voltage regime, I doubt you will get a 1/4 of that.

[dvs_dave]

Direct solar charging makes no sense as it means you have to have your car charging very slowly throughout the day, which is when you actually need to be using the thing, so very impractical.

Charging your EV overnight when grid power is super cheap and you don’t need to use the car is really the only solar usage profile that makes sense. That way all your excess solar energy gets fed into the grid at a premium rate during the day, offsetting the cost of charging the car at night.

Failing that, the only other alternative is to have onsite battery storage for your solar. However that’s very expensive, and questionable from an overall efficiency standpoint. Charging batteries, to then charge another battery, etc. Not the smartest use of energy.

[bearman68]

blitzracing said:

In think all I can do is skim of power above 2kw for the car on the solar switch, so dull days below 2 kw will be a complete waste of time if not backed up with mains. Its not a big issue as I can get off peak at 5p a unit anyway. If you look at just the power available from solar, a 3.5kw array will give you about 1000 miles motoring a month in the summer, but as you cant seem to use a variable current / voltage regime, I doubt you will get a 1/4 of that.

My experience (not of car charging but I can't see that this load will be any different), is that the load will run at X kwh, and the meter will turn at X-Y kwh, where Y is the solar input. Check out your meter. This would be the simplest and most efficient use of power. I do a similar thing for my hot water heating, but for hot water, the heater is adjusted so X=Y.

[modeller]

There are various commercial solar linked chargers available which can vary the current (from 6A to 16A) , such as Zappi.
There is also this .. which is an open source project: https://shop.openenergymonitor.com/openevse-wifi-e...

[gangzoom]

dvs_dave said:

Failing that, the only other alternative is to have onsite battery storage for your solar. However that’s very expensive, and questionable from an overall efficiency standpoint. Charging batteries, to then charge another battery, etc. Not the smartest use of energy.

For May and June when we had excessive solar and it was filling up our PowerWall by early afternoon I used the PowerWall + solar to charge the car.

The PowerWall seems to be able to use a mixture of gird, solar and itself to managed demand from the house.



We don't get paid for metered export so I would plug the car in when I got home around 5pm, add about 10-15% SOC using a mixture of tailed solar + PowerWall stored electricity. When we had sun in May and June it essentially reduced our grid electricity usage to zero.

Ofcourse you need sun for any of this to work, but I'm thinking of adding another 4KW of panels to our existing 4KW system if we can access the 'green' house grant.

Having battery storage had really transformed the effectiveness of our solar PV panels. The fact we get paid an assumed 50% export traiff on FIT when we are now actually exporting sub 1% is the icing on the cake .

Edited by gangzoom on Tuesday 14th July 07:39

[gangzoom]

dvs_dave said:

Direct solar charging makes no sense as it means you have to have your car charging very slowly throughout the day, which is when you actually need to be using the thing, so very impractical.

Without been able to store day time solar your quite right, this was our last day of proper sun in June. My wife was actually at home and even with the battery starting at 5% SOC by 4pm it was completely full, and solar energy was been directed to the hot water system. I than got home around 5pm and plugged in the car to charge. We ended up with net grid usage of 1kWh that day, but if we didn't have a battery it would have been an export value of around 15kWh even after heating up the hot water.

If you want to maximise local solar generation you need a home battery storage system, if that makes any financial sense is a different question all together.

[snowy]

This sounds a plausible way forward to remove the need for a lot of infrastructure, Nano coil tech

https://energy.mit.edu/wp-content/uploads/2015/05/...

[blitzracing]

modeller said:

There are various commercial solar linked chargers available which can vary the current (from 6A to 16A) , such as Zappi.
There is also this .. which is an open source project: https://shop.openenergymonitor.com/openevse-wifi-e...

Here in lays the problem- how can the charger control the current, it would need to be a variable voltage supply and the cars electronics expects 230 volts? You can certainly program the cars intake current, but in my case this only goes down to 6 amps. All I can see you doing is match the charger current to what the car is programmed to take.

[Dave Hedgehog]

i would love to get solar and some battery storage, its very cool tech, but it makes no financial sense with green tarrifs charging 5p/kwh overnight, looking at 30 years RoI

[blueacid]

blitzracing said:

Here in lays the problem- how can the charger control the current, it would need to be a variable voltage supply and the cars electronics expects 230 volts? You can certainly program the cars intake current, but in my case this only goes down to 6 amps. All I can see you doing is match the charger current to what the car is programmed to take.

So you're actually on the right lines here - the 'granny' chargers which allow you to select from 6A/8A/10A are pretty generic. When type 2 charging, in many cases (there are some exceptions) the vehicle can have its maximum current limit flexed from 32A right down to 1.6A (or in some cases even 0A and then back up again). There are many more steps than the three of 6/8/10 that granny chargers have.
If the vehicle can pause and resume charging too, that's even more useful. And it's this method that chargers like the zappi and ohme use.
The charger isn't doing any of this actual work for itself, it's not like a dimmer-switch fitted inline with a light bulb, it instead sends data to the car via the signal pins, and then the car's charger chooses how fast (or not) to charge based on the data it's told.

[FlossyThePig]

Dave Hedgehog said:

i would love to get solar and some battery storage, its very cool tech, but it makes no financial sense with green tarrifs charging 5p/kwh overnight, looking at 30 years RoI

Next door neighbour had solar panels installed a few years ago. The FIT payments have covered the installation cost after 8 years. FIT is no more but has been replaced by SEG (paid for surplus exported to the grid). I'm just switching to the outgoingOctopus tariff so should get some credit against my bill. SWMBO is more aware of the benefit of the array and has said things like "It's sunny so I'll turn on the washing machine now".

Batteries are expensive, especially if the make starts with a T. However there are times when you can get paid to charge them.

For those interested in charging a car from your roof have a look at some of the videos Nigel at https://www.youtube.com/c/TheEVPuzzle/videos has made.

[anonymous-user]

https://nakedsolar.co.uk/ev-pv/

[blitzracing]

blueacid said:

So you're actually on the right lines here - the 'granny' chargers which allow you to select from 6A/8A/10A are pretty generic. When type 2 charging, in many cases (there are some exceptions) the vehicle can have its maximum current limit flexed from 32A right down to 1.6A (or in some cases even 0A and then back up again). There are many more steps than the three of 6/8/10 that granny chargers have.
If the vehicle can pause and resume charging too, that's even more useful. And it's this method that chargers like the zappi and ohme use.
The charger isn't doing any of this actual work for itself, it's not like a dimmer-switch fitted inline with a light bulb, it instead sends data to the car via the signal pins, and then the car's charger chooses how fast (or not) to charge based on the data it's told.

So there is hope- its a SolarEdge charger, lets see what it can do. I have a fault at the moment logged with them as the configuration software does not appear to be enabled, so I cant set up the charger, it simply charges at solar plus mains to reach the 6KW the car is set to.

[anonymous-user]

blueacid said:

blitzracing said:

Here in lays the problem- how can the charger control the current, it would need to be a variable voltage supply and the cars electronics expects 230 volts? You can certainly program the cars intake current, but in my case this only goes down to 6 amps. All I can see you doing is match the charger current to what the car is programmed to take.

So you're actually on the right lines here - the 'granny' chargers which allow you to select from 6A/8A/10A are pretty generic. When type 2 charging, in many cases (there are some exceptions) the vehicle can have its maximum current limit flexed from 32A right down to 1.6A (or in some cases even 0A and then back up again). There are many more steps than the three of 6/8/10 that granny chargers have.
If the vehicle can pause and resume charging too, that's even more useful. And it's this method that chargers like the zappi and ohme use.
The charger isn't doing any of this actual work for itself, it's not like a dimmer-switch fitted inline with a light bulb, it instead sends data to the car via the signal pins, and then the car's charger chooses how fast (or not) to charge based on the data it's told.

This ^^^ the "Type 2" charging port, uses a 240V (or 115v for those funny foreign places) nominal voltage, but the current that the OnBoard Charger (OBC) in the car actually pulls is controlled from the EVSE (Electric Vehicle Supply Equipment) the bit we call the "charger" but that actually isn't being just a simple ON/OFF relay in a posh box.

If you look at the Type 2 AC connector:



you will see 5 high current contacts, for 3 phases (L1, L2 & L3) for Earth, and for Neutral but also 2 smaller signalling contacts. Those contacts, called Promixity Pilot and Control Pilot use low voltage signals to allow the EVSE to tell the OBC exactly how much current it can pull from the supply. This is limited by things such as the supply to the EVSE, but also by the type and rating of cable between the EVSE and the vehicle.

The current that can be pulled is signalled by pulse width modulating the duty cycle of the CP signal, so EVSE's equipment can, and does (with the right EVSE), control the charging current right down to 0 amps if required!

[blitzracing]

This is what I was looking for, so the SolarEdge charger should be able to trickle charge only on Solar on days I dont use the car, whatever the output of the panels.

There is a comment here to say it can be done.

https://www.youtube.com/watch?v=A2lGkbooCXk

Ill update once I can get the software sorted.

Edited by blitzracing on Wednesday 15th July 09:31

[anonymous-user]

blitzracing said:

This is what I was looking for, so the SolarEdge charger should be able to trickle charge only on Solar on days I dont use the car, whatever the output of the panels.

There is a comment here to say it can be done.

https://www.youtube.com/watch?v=A2lGkbooCXk

Ill update once I can get the software sorted.

Edited by blitzracing on Wednesday 15th July 09:31

The limitation on lowest rate will be the lowest current at which the OBC (the bit in the car) can remain in 'continuous conduction' mode with saturated inductors, which is a geeky power electronics way of saying the car won't be able to charge all the way down to 0 amps! ime, most OBS wil however get down to around 1 or 2 amps, which is 240/480 watts, so your solar array is going to have to be able to generate that for it to work, but that's not outside the realms of possibility for a decent sized array in cloudy but bright weather

[robbieduncan]

Max_Torque said:

The limitation on lowest rate will be the lowest current at which the OBC (the bit in the car) can remain in 'continuous conduction' mode with saturated inductors, which is a geeky power electronics way of saying the car won't be able to charge all the way down to 0 amps! ime, most OBS wil however get down to around 1 or 2 amps, which is 240/480 watts, so your solar array is going to have to be able to generate that for it to work, but that's not outside the realms of possibility for a decent sized array in cloudy but bright weather

It's pretty cloudy here today. We have a 2.5kW system and it's still generating about 400W right now. A 4kW system should be able to get above 480W even on cloudy days in summer. Winter might be more of an issue

[kent_phil]

I don't think the Type-2 charging standard will allow charging below 1.2kw - hence why the zappi has two eco modes, one to top up when it is below the threshold and the other to pause until it is over again. Zappi gives you a % green energy status for each charge so you can monitor.

During the summer the charging off the solar works great for us, we have a 7kw array with 6kw inverter and a zappi - and probably don't pay anything to charge the cars from May to Sept and this has worked for the last three years for us.

The problem comes in the winter and as the sun settles lower on the horizon, on a peak summers day we can get about 53kwh of energy but on a dark mid-winter overcast and rainy day it has been as low as 1kwh.

I've just about made the man-maths work on a battery store with Octopus Agile / Outgoing Agile but it is tenuous - I'm hoping the new green energy grant will cover battery stores which will definitely cover the costs.