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Fuenkli

E Vehicle charging with PV

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I am considering buying an e vehicle and would like to charge it at home using a PV system. I want to do this to reduce my carbon foot print and because is my hoppy. So the cost (within reason) is not the main issue how to proceed.  I have a CoCT signed off 4.4kWp/4.6kVA/14kWh lithium battery hybrid GTI system on a single phase 60A grid supply. The system is just big enough to cover my present energy demand. If I want to charge an e vehicle I would need more PV generation capacity. What would be my options? I am already on the legal limit with my GT system so it would probably have to be an off grid solution. What do you suggest? There is lots of roof space available to install panels.

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Where will the vehicle stand most of the time? If you are commuting then home charging from pv wont provide power at the right time of day.

What are the charging amps and voltages required?

Edited by DeepBass9

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1 hour ago, DeepBass9 said:

Where will the vehicle stand most of the time? If you are commuting then home charging from pv wont provide power at the right time of day.

What are the charging amps and voltages required?

the car will usually be at home during the day. I am retired and use the vehicle only for shopping and leisure in and around Cape Town. I am not very familiar with the charging systems for e vehicles. I think they all have high current DC as well as on board low current (for home charging) 220V AC charging capabilities.  I do on average about 10'000km/year. Considering that a small e vehicle is using about 20kWh/100km I would require about 2500kWh/year to charge the car. I would be happy if I could cover 80% of this with my PV system. The car will not be used every day so a 5kWp system would probably be sufficient. Because the system has to be off grid (hopefully without batteries) the charging current would have to be adapted based on the available PV output.  

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Maybe my experience as a novel electric vehicle owner will be useful to you.

I bought a BMW i3 approximately two months ago. Many reasons for that: my old car was getting on in years, I wanted to reduce my carbon footprint, I wanted to make better use of my solar generating capacity and who can resist the lure of a new big toy... Definitely not a money saving endeavour as yet, but then a hobby does cost.

Thus far I am very happy with the car - a completely new driving experience. I am really enjoying it.

I run a grid tied/  hybrid solar system (SMA Sunnyboy + Sunny Island) together with 16 kWh of BlueNova batteries. I in fact added an extra 8 kWh to help me charge my vehicle. I have 3.96 kWp of solar panels on the roof. That is near the limit of what I can accommodate in a relatively north facing direction.

Being single my daily consumption ran around 8 to 10 kWh prior to having the electric vehicle (I have converted to a solar geyser, gas hob, LED lighting, low-power pool pump et cetera). I could therefore definitely produce more electricity than I was consuming and I wanted to put this electricity to good use.

I am at work most of the day, so am actually not able to charge with solar directly except over weekends or if I'm lucky enough to get home before the sun has set. Luckily, my daily commute is around 20 km only. That means I only have to recharge the battery by approximately 2 to 5 kWh on a daily basis, depending if I do any other trips. (It is up and down the mountain!) 

I am also very lucky in that the shopping centre very near my house (literally two minutes down the road) has recently installed a DC fast charger. I therefore always have a backup option if I need to get the battery full quickly or return from a long trip with an empty battery. Daily charging I manage from stored battery capacity or do over the weekend when I'm at home.

The BMW can be programmed to charge immediately or to charge later at set times that you can select. You can also vary the charging current. The standard charger supplied with the vehicle charges at a current of  10 A. You can reduce that I think to a minimum of around 6 to 8 A. With second party chargers you can charge up to 15 A from a standard plug. If you want faster charging rates you need to invest in a wall box or similar equipment. That is of course if you use electricity from the grid. With a standard solar setup I think you will be limited to the slower charging rates (with the current of around 8 to 10 amp) as you will otherwise require a lot of panels and very large inverted to produce for instance 10 kW of power. That of course means that if the battery is completely empty it will take you a very long time to charge.

I schedule charging for the early morning hours when there are no other competing demands on the electrical supply. The inverter and batteries can happily supply the required current. This works very well for me and I leave home with a 100% charged battery every morning. Thus far I am simply using the charger supplied with the car and have not felt the need to upgrade to a faster solution, especially since I do have the DC charging backup.

My one concern with a totally off grid solution with no battery (and I am definitely no expert) is whether the car's charging system will be happy with a fluctuating power delivery as is often the case with solar production. I am worried that the charging may be interrupted due to  the software in the car detecting what it interprets as a grid error when your solar output drops from a passing cloud. Either you would need to use a very low charging current so that your production always exceeds the demand during charging (but then you are basically throwing a lot of potential power away) or you may need to have a system with a relatively small battery that can supplement and keep the power delivery steady.

I know that a fair number of consumers in Europe are using solar for charging, but my understanding is that it is mainly in the setting of a grid tied solution. This will of course guarantee a steady delivery of power to the car during the charging process.

Just my experiences and thoughts.

 

 

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2 hours ago, South Easter said:

Maybe my experience as a novel electric vehicle owner will be useful to you.

thank you very much for the reply. It is so cool that you have an EV you enjoy and that you can charge it with your PV system.  I envy you 🙂.  Unfortunately I do not have any surplus PV power (thanks to our politicians). I think you are right that it is not possible to charge an EV with an off grid system without batteries ☹️. So what do I do? I can think of three options:

1. convert to house to a 3 phase grid supply and increase the PV system to the required size (+- 10kWp) to accommodate my higher consumption with an EV.

2. keep the single phase 4.4kWp existing grid tied system and add an 5kWp off grid system with batteries.

3. ditch Eskom and go totally off grid

What do you think? 

 

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On 2020/01/10 at 5:20 PM, Fuenkli said:

I am considering buying an e vehicle and would like to charge it at home using a PV system. I want to do this to reduce my carbon foot print and because is my hoppy. So the cost (within reason) is not the main issue how to proceed.  I have a CoCT signed off 4.4kWp/4.6kVA/14kWh lithium battery hybrid GTI system on a single phase 60A grid supply. The system is just big enough to cover my present energy demand. If I want to charge an e vehicle I would need more PV generation capacity. What would be my options? I am already on the legal limit with my GT system so it would probably have to be an off grid solution. What do you suggest? There is lots of roof space available to install panels.

Hi @Fuenkli

I have a wallbox for EV charging that's being powered by the off-grid PV installation:https://powerforum.co.za/topic/2322-youdas-off-grid-lab/page/2/?tab=comments#comment-58507
So, it's doable, but there are few obstacles and therefore I would say that the off-grid route is really not the best one:

EV charging needs a nice and firm 230V AC source. 230V x 6A is the absolute minimum. 230V x 32A (cca 7kW)is optimal for most of the onboard EV chargers. Some cars have a 3-phase onboard charger, but luckily every EV is able to work with a single-phase AC too. So, you need to have roughly 8-10kW single phase off-grid inverter and a large array of solar panels.

You CAN utilize a weak 3kW inverter, if you limit the charging current (all wallboxes can be configured like that), but that does not make a sense, as it would take weeks to recharge the car's battery after a long trip.

Second trouble is, that the inverter has to deliver a steady AC power to the wallbox, regardless of how much sun is shining. IF there's less sun, the inverter can't simply lower it's AC output power. So, the missing power has to be drawn from the grid (cheap) or from a huge battery bank (expensive). The only workaround is to track the PV production in the realtime and everytime it drops, instruct the wallbox to tell the car to lower the charging current. The EVSE protocol is ready for this and the communication between the EV and the wallbox is utilizing a simple PWM signal. But as far as I know, there are no wallboxes on the market that are supporting direct communication with the off-grid PV inverters. Reason is simple - there's not enough demand on the market for such solution.

So, for an off-grid EV charging, you will need:

  • 8-10kW off-grid inverter
  • 10+ kWp of panels
  • 10kWh+ of batteries
  • Wallbox that has an open programming API (for example OpenEVSE)
  • Programming skills to create a software interface between the inverter and the wallbox

On the other hand, there ARE wallboxes already available on the market that are able to throttle the EV charging power based on the PV production in the on-grid installations. Why? Because in the on-grid, they can use a simple current transformer to check the power export and adjust according to that in the realtime. A good example is ZAPPI:

https://myenergi.com/product/zappi/
https://www.youtube.com/watch?v=0EtegQfZQRw

image.png.d28a8139a87f271e7b00673995c41c62.png

 

Based on my experience, I would say that going the on-grid way is MUCH cheaper, quicker and generally straightforward when you plan to charge your EV with your PV.

1) In your case, the right solution would be to get a 3-phase house connection, get rid of existing 1-phase solar power plant and upgrade to a 3-phase solar, where the upper legal limit for home solar is 10kVA / 10kWp (in most of the countries). On top of it, install ZAPPI wallbox and you're all set.

2) Since I clearly understand the the solution #1 does not make economical sense, there's an alternative: Just add an on-grid inverter with its own panels to your existing installation. This works okay, via so-called AC coupling. Then, limit the grid feed-in of this new inverter to roughly 200W and install ZAPPI wallbox equipped with the current transformer. Whenever the wallbox will sense grid export, it will instruct the car to raise the charging power. Once the wallbox will see a drop in export, or even realize import from grid, it will instruct the car to lower the charging power or even pause it.

Solution #2 won't cost a fortune and will work like a charm. Also, it will not cause excessive export to the grid. On the other hand, don't even try to get CoCT on it, of course.

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I really can't add anymore to what Youda has said - I would classify myself as a novice who understands the basics but essentially still just wants things to work (and I someone else can make them work all the better). 

I get away with using my system for EV charging as I only need to do small top ups overnight. The slow charging rate then is not so problematic. I have accepted that I will use public charging for larger charges or if I need to top up quickly. There are three DC chargers I know of in Cape Town. They charge at 50 kw per hour (in Europe some chargers already do a lot more). One is in the Gardens Centre, another one at BMW Century City and the third is at Willowbridge (Tygervalley). They can charge an i3 from 0 to 80% in 30 minutes - you can fully charge while shopping. 

 

I like Youda's solution 2 but selling it to the CoCT officials will be very very hard as he says.... 

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@Youdathanks for the reply. Now I understand all the options I have with the pros and cons. I wish I could implement option 2 but the CoCT will never approve it and to do it illegally is a no no for me . I think my best strategy is to change the house to a 3 phase supply and install a much bigger PV system. It would also future proof the house for the time (hopefully soon 🙂) when it starts making financial sense to export the surplus power. I will now do the sums and then make a final decision.  Thanks again for your help.

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17 hours ago, South Easter said:

I have accepted that I will use public charging for larger charges or if I need to top up quickly

I agree this is another option but what about our carbon footprint? I think @plonksteronce calculated that charging an EV with dirty Eskom power actually increases your CO2 emissions compared to driving an internal combustion engine car 🤣

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20 minutes ago, Fuenkli said:

I think my best strategy is to change the house to a 3 phase supply and install a much bigger PV system.

Don't supply this as your stated reason for needing a bigger supply, you wont get one.

Bear in mind there is a fixed cost increase attached to a bigger supply as well.

I suggest you look at your billing structure, decide on the supply that suits your future expansion and budget.

Then dream up a fictitious reason for needing the very supply you want.

 

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21 hours ago, Fuenkli said:

2. keep the single phase 4.4kWp existing grid tied system and add an 5kWp off grid system with batteries.

You can use grid-tied charger to help charge the off-grid batteries. As long as it wasn't a bi-directional inverter/charger the off-grid system would still be considered off-grid.

What I am getting at is, there is still legally a way to use excess from your 4.4kWp by changing it to dc, which in turn can add to the 5kWp system.

 

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I take the point on the carbon footprint generated by using Eskom to charge - thus far I have managed to keep it to a minimum and estimate that more than 90% of charging was from solar. But it is still good to have a plan B

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