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Hello,
I'm new to the forum and considering to buy the Volkswagen E-Up or Skoda Citigo-e in the next months.

Since I'm kind of green power enthusiast (but also a noob for diy electric stuff) I was wondering if in theory you could add a solar panel to the roof of the car to get a little charge while the car is parked somewhere under the sun? Let's suppose I would put a 250W panel so that if it gets 4 hours of maximum sunlight it will deliver up to 1KW of charge to the battery so this would add around 8km of range to the car.

Let's not consider the price part (if it's convenient or not) would it be possible to actually charge? The voltage I believe for this cell is 30v, is it possible to convert DC 30v to AC 120/220V and sent it to the outside charger to imitate a slow home outlet? Would it even charge at such a low amperage?

Has anyone tried it or thought about it?
 

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2020 BMW i3S 120Ah BEV
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I think the car will require a minimum of 1.2kw to actually bother charging, and it won't be acceptable for the sun to drop behind a cloud and have it drop below that output. And I'm not convinced you can get that amount of current from a car-sized panel. Your only possible method would be to charge another battery slowly and use that to boost the car when it has sufficient charge, but honestly I think all you'd learn from that would be that it's not worthwhile because of weight, etc.
 

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I think the car will require a minimum of 1.2kw to actually bother charging, and it won't be acceptable for the sun to drop behind a cloud and have it drop below that output. And I'm not convinced you can get that amount of current from a car-sized panel. Your only possible method would be to charge another battery slowly and use that to boost the car when it has sufficient charge, but honestly I think all you'd learn from that would be that it's not worthwhile because of weight, etc.
Yep pretty much sums it up. It has been done:
But really not worth it.
 

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Discussion Starter #4
I guess it does sum it up. But what if could be charged at around 100W, would that be possible? To even get 1km of additional range?
 

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The problem is that none of the commercially available EVs are setup to receive such a low level of charge. There's no reason in principle that you couldn't design a BMS to add small amounts of charge to the battery. However, it will be a negligible amount of charge.

If you could squeeze say 2kW of high density panels onto an electric campervan or minibus then there might be 'mileage' in it. If I was designing an EV then I would make sure it could accept a DC trickle charge from a modular string of solar panels and integrate some into the roof but also allow additional panels to be plugged in.
 

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I guess it does sum it up. But what if could be charged at around 100W, would that be possible? To even get 1km of additional range?
Not without hacking directly into the DC high voltage connections of the battery, and using an inefficient DC:DC converter to take your solar panel output up to the cars battery voltage. The car will probably also be quite upset at stray current going into the battery while "off".

If you want to add power to the car while "on", the parasitic loss (from DRLs, the dashboard, engine ECU, battery BMS, and anything else on the 12v system) will potentially be higher than the 200w your panel is generating.

If you want to use the cars actual charger, the minimum it will take is 6 amps. If you're lucky the car would work happily on 120v rather than 240v, but that is still 720 watts. Hence the need for a buffer battery and charging in bursts.
 

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Best just to get solar on your house.
 

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Better off building a solar charger for the 12V battery: with no alternator, the energy in that has to come from the HV battery. If you can keep that charged, that's a small power draw that's reduced.

Nissan used to offer one, but for the extra weight and cost it's probably not worth it.
 

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Discussion Starter #10
Why do you think that the built in charger only accepts currents from 5A and not below even if it would take weeks?
Is it because it's gonna damage the battery or something?
 

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If you get solar on your house roof and a 6 amp charger for the car, you'll be chargng for free providing the panels are delivering at least 1.6 kW If the sun goes in reducing the power available, the charge will continue with the balance coming off the mains supply.
The video linked to above doesn't show any of the technicals involved. I'm not convinced it was truly charging from that array.. I'd rather the Chadmo port have a Chademo capability rather than that (but that's a Leaf, not a VW or a Skoda.)
 

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If you get solar on your house roof and a 6 amp charger for the car, you'll be chargng for free providing the panels are delivering at least 1.6 kW If the sun goes in reducing the power available, the charge will continue with the balance coming off the mains supply.
The video linked to above doesn't show any of the technicals involved. I'm not convinced it was truly charging from that array.. I'd rather the Chadmo port have a Chademo capability rather than that (but that's a Leaf, not a VW or a Skoda.)
It wasn't charging from the panels directly, there's some lead acids and a 2kw inverter under the bonnet, which the panels charge.
 

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Why do you think that the built in charger only accepts currents from 5A and not below even if it would take weeks?
Is it because it's gonna damage the battery or something?
It's the lowest value that a charger can advertise in the J1772 specification, so while the charger maybe could go lower there's no way to request it to do so without some kind of hardware or software modification.
 

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.. .and has been stated before attempting to switch on all the required circuits to activate the charge session would likely take more than 100W anyway, which leaves barely any for charging the HV batteries, particularly once you take into account the DC-AC-DC conversion chain with losses along the way.

You just have to accept that transport, moving a ton or two of metal around with people in it, requires a HUGE amount of energy; and trickle charging such huge batteries with such low currents is just a complete waste of energy. You would likely never even recover the energy that was used to make the panels and components to convert it into usable transport kwh in the entire lifetime of a setup like this, and that's even if you got it working in the first place.
 

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Discussion Starter #15
I see, so the minimum to make it work is the get a >1kwh solar setup or add a battery in between?
 

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Just focus on trickle charging the 12v battery, which in effect is then saving the HV battery from having to top it up.
 

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I see, so the minimum to make it work is the get a >1kwh solar setup or add a battery in between?
In the UK you will rarely achieve 5A at 230 volts from a 1kW solar set-up and would need at least 2kW of panels to achieve this on a regular basis. You haven't said where you are planning on doing this but I notice your showing a Hungarian IP so are presumably also 230v - it is possible with the correct EVSE to charge at a lower voltage (say 120v in the USA) and hence achieve the 5A required at a lower wattage and hence fewer panels but it would be painfully slow.
Adding a battery in between adds to the round trip losses so you lose that way as well.
 
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