Solar to Battery EV Charger

[premierautomotive]

Hi DIY Solar Forum,

Thank you all firstly for being so open and supportive to newcomers like myself in the solar arena. I wanted to ask you all for your help in the planning of a system, that is exclusively for use to charge an EV vehicle. The plan is simple, but with anything solar, has many nuances that I'm not sure I fully understand, and ask for your help and suggestions in building out such a system.

I would like to receive PV power through panels, around 2-3kw capacity of panels, to directly charge a battery (5 or 10kw), which can then in turn have just a single connection to any standard EV vehicle charger.

My understanding is, the inverter capacity would determine the maximum power that the vehicle could charge at. Most vehicle home chargers are rated at 7.6kw charge speed single-phase, so a 8kw inverter should do the trick. The point of the system is for it to be an affordable alternative as compared to refueling from the grid, and definitely in comparison to fossil fuel costs, having a payback period of 2-5 years (depending if comparing to fuel costs or grid energy costs).

The car drives on average around 30km every day, and using a reverse conversion of kwh/100km, if the car model is consuming 15.5kw/100km, a 5kw battery should suffice. Should you over capacity this, so there is always 20% juice left, for battery life reasons?

Regarding the inverter, although 8kw is what would be recommended, I believe a 6kw system capacity is OK for our purpose, as that additional 1.6kw isn't going to make too much of a difference while charging in the evening, when idle at home, so a 6kw system can be acceptable, if the only difference is charge speed (it would mean a few minutes more in charge time based on the car km use specified above). In terms of inverter selection, we are using the same electricity split-phase setup as the US does, but I wondered whether since the application of this inverter is just for one purpose, would a off-grid inverter (cheaper) be OK to use? After reading many reviews and posts here, we really like the Deye systems for hybrid-split phase, but it seems unnecessary for this specific application? Am I right in the assumption that a off-grid inverter 6kw capacity that has PV input and battery storage functionality would be OK for our purpose? We are specifically looking at the Growatt SPF 6000 ES Plus model, spec sheet attached, but any suggestions you might have are welcome.

For the PV Panels, we plan to use Astronergy 620w panels, specs also attached.

For the batteries, we are considering to use Amy whom is famous on this forum for good and reliable well priced batteries, pre-built from their factory.

For the EV charger, we plan to use this Beny Charger, spec sheet also attached.

Questions
-Are my assumptions mentioned above of inverter correct?
-Will around 4-6 panels be appropriate for this inverter, as I had a bit of difficulty planning out the voltage voc calculation and chaining/paralleling the PV connections, as well as the isc short circuit capacity, some help here would be appreciated.
-Should you buy over capacity of batteries, as they should not drain below 20%, so eg if we need 5kw daily, its better to buy ~6.3kw of batteries so as not to drain the batteries completely and only up to 20%? Similarly if requiring 10kw, its better to buy 13kw batteries?
-Is this general idea smart to do, as you charge daily, rather than cycling the full battery of the EV, you are only constantly recharging the little bit you use everyday. Will it affect the battery life much of the vehicle by doing this?
-What would be required for example if you wanted to charge the vehicle in the daytime, directly from the sun, bypassing the battery? What inverter functionality would be required in this regard?
-I believe we do not need hybrid connectivity for this system, as it is much cheaper to just get a 2nd additional charger that is connected via breaker to the grid, in case the system is down or no sun for a few days.
- We get around 5 hours sun daily, year round, where I am.

Thanks everyone,
Appreciate your help.

 

[sunshine_eggo]

Some other considerations:

1. Inverters are at peak efficiency around 30% rated, e.g., 6000W inverter is at peak DC-AC efficiency at around 2000W.
2. If only charging ~5kWh/day, what's the rush? Does it need to be done in an hour?
3. Is 5 hours sun/day actual or solar equivalent hours? Given your location, I would assume equivalent unless you have shading.

Questions
-Are my assumptions mentioned above of inverter correct?

Mostly. For reliability, you don't want to run an inverter at 100%.

-Will around 4-6 panels be appropriate for this inverter, as I had a bit of difficulty planning out the voltage voc calculation and chaining/paralleling the PV connections, as well as the isc short circuit capacity, some help here would be appreciated.

If #3 is solar equivalent hours, if you're considering 2500-3700W of PV, you have the potential to harvest 12.5-18.5kWh/day

-Should you buy over capacity of batteries, as they should not drain below 20%, so eg if we need 5kw daily, its better to buy ~6.3kw of batteries so as not to drain the batteries completely and only up to 20%? Similarly if requiring 10kw, its better to buy 13kw batteries?

Extra battery capacity is never bad.

-Is this general idea smart to do, as you charge daily, rather than cycling the full battery of the EV, you are only constantly recharging the little bit you use everyday. Will it affect the battery life much of the vehicle by doing this?

Minimizing depth of discharge maximizes battery life. daily charging of the small amount used will likely result in longer life than charging less frequently at higher rates.

-What would be required for example if you wanted to charge the vehicle in the daytime, directly from the sun, bypassing the battery? What inverter functionality would be required in this regard?

Simply turn on the charger. The PV would provide whatever loads it can and draw additional from the battery (or charge the battery if surplus PV). Clouds will destroy production, so you need enough battery to keep the charger from cycling charging on/off due to passing clouds.

-I believe we do not need hybrid connectivity for this system, as it is much cheaper to just get a 2nd additional charger that is connected via breaker to the grid, in case the system is down or no sun for a few days.

Hybrid is a misleading term. You do not need one that is "grid interactive" that can interface and provide surplus power. An inverter/charger that can DRAW from the grid in the event that PV or battery is insufficient is an option with the Growatt you mentioned.

 

[premierautomotive]

Some other considerations:

1. Inverters are at peak efficiency around 30% rated, e.g., 6000W inverter is at peak DC-AC efficiency at around 2000W.

Hi bud, thanks for replying. I had a bit of difficulty understanding this point. So that means, it would be best to operate the charger at 2000w max output? As I also read the peak efficiency of the inverter in the specs is 93%, is that referring to something else? Is the 2000w a suggested max output so the inverters life is not affected? In that case for us, a more appropriate size of inverter would be something like 20K watts?

1. If only charging ~5kWh/day, what's the rush? Does it need to be done in an hour?

No rush at all, but it would be best if its as close to the peak charging capacity of the car.

1. Is 5 hours sun/day actual or solar equivalent hours? Given your location, I would assume equivalent unless you have shading.

Yes, correct, solar equivalent hours.

Mostly. For reliability, you don't want to run an inverter at 100%.

I understand, by how much is it recommended to oversize the inverter usually, or is it dependent on model to model? Would you know any inverters that meet such requirements that we could look into, but are reasonably priced?

If #3 is solar equivalent hours, if you're considering 2500-3700W of PV, you have the potential to harvest 12.5-18.5kWh/day

Yes, for the 5kw battery for example, I believe just 1-1.25KWp of panels would be enough, so maybe 2-3 panels. My concern was the minimums that a inverter would need to begin operating.

Extra battery capacity is never bad.

Understood!

Minimizing depth of discharge maximizes battery life. daily charging of the small amount used will likely result in longer life than charging less frequently at higher rates.

That makes a lot of sense, battery technology and the information you find is quite varied and a bit confusing, as I have read/seen some people saying you should use the full cycle of the battery, then charge, or not to charge daily, as it reduces the batteries' life.

Simply turn on the charger. The PV would provide whatever loads it can and draw additional from the battery (or charge the battery if surplus PV). Clouds will destroy production, so you need enough battery to keep the charger from cycling charging on/off due to passing clouds.



Hybrid is a misleading term. You do not need one that is "grid interactive" that can interface and provide surplus power. An inverter/charger that can DRAW from the grid in the event that PV or battery is insufficient is an option with the Growatt you mentioned.

Understood, in this case then I would not need to add a second EV charger that is regularly connected to the grid, this inverter could do the job to just provide the energy in case of no battery/no sun.

Thanks for all your help!

 

[sunshine_eggo]

Hi bud, thanks for replying. I had a bit of difficulty understanding this point. So that means, it would be best to operate the charger at 2000w max output? As I also read the peak efficiency of the inverter in the specs is 93%, is that referring to something else? Is the 2000w a suggested max output so the inverters life is not affected? In that case for us, a more appropriate size of inverter would be something like 20K watts?

You'll see that 93% efficient at about 2000W on a 6000W inverter. Below 2000W, it drops off and can be truly terrible at low power (50-100W) and it slowly drops off above that to probably about 85% @ 100%.

No rush at all, but it would be best if its as close to the peak charging capacity of the car.

Why best? Charging a battery faster is more stressful than lower current charging. The only reason to charge fast is because you need to drive it ASAP. If there's no hurry to drive, the ideal charge to be to complete the charge shortly before you need to drive. For example: You get home at 6pm and don't need to drive again until 7am. The least stressful charge would be to charge at a lower rate over the 13 hours. This shouldn't necessarily be a goal, but I'm trying to convey a concept.

Yes, for the 5kw battery for example, I believe just 1-1.25KWp of panels would be enough, so maybe 2-3 panels. My concern was the minimums that a inverter would need to begin operating.

The minimums are typically driven by MPPT operating voltage. You want your array Vmp above the minimum MPPT voltage.

That makes a lot of sense, battery technology and the information you find is quite varied and a bit confusing, as I have read/seen some people saying you should use the full cycle of the battery, then charge, or not to charge daily, as it reduces the batteries' life.

There is no battery technology that truly benefits from full depth discharges, though NiMH and NiCd can benefit from occasional full depth discharges. There's also other considerations. Using only 5% of your capacity and charging 95% to 100% every day isn't necessarily a great idea. as charging to 100% can be more stressful. Charging from 80-85% per day would be preferred over 95-100% every day to reduce charging stress.

If the vehicle has a LFP battery, it will benefit from periodic charging to 100% to retain cell balance. If NMC, there's never really a need to go to 100%.

Understood, in this case then I would not need to add a second EV charger that is regularly connected to the grid, this inverter could do the job to just provide the energy in case of no battery/no sun.

Yes. Most inverter/charger/AiO units can use grid for pass through and charging purposes when PV is insufficient.

 

[Doggydogworld]

A few commercial "chargers" (actually EVSEs, the AC charger is inside the car) are designed to work with grid-tied solar. Here's one from SolarEdge that works with their inverters. Emporia and Zappi also have units. There are also systems designed to operate completely off-grid, but most are commercial and expensive. The PairTree is an self-contained unit that can be moved to a new location pretty easily.

Regarding the inverter, although 8kw is what would be recommended, I believe a 6kw system capacity is OK for our purpose

Your Beny EVSE says output can be throttled down all the way to 6A (roughly 1.4 kW of continuous power). So in theory you could set it around 8A in normal usage to get optimum efficiency from a 6 kW / 240V inverter and set it at 20-25A if you're in a hurry and need to max the inverter out. You could also save money with an even smaller 240V inverter, say 3 kW, and the 6A setting.

-Will around 4-6 panels be appropriate for this inverter,

4 panels in series is 223 Voc, 184Vmp and 14 Isc
6 panels in series is 335 Voc, 276Vmp and 14 Isc

The MPPT in your Growatt needs at least 120V, which both configurations easily provide even on hot days. Both are also well below the max 500Voc and 100A Isc. So this looks OK.

-Should you buy over capacity of batteries, as they should not drain below 20%,

Yes, 20% is a good minimum SOC for daily LFP cycling. 50% for lead-acid.

-Is this general idea smart to do, as you charge daily, rather than cycling the full battery of the EV, you are only constantly recharging the little bit you use everyday. Will it affect the battery life much of the vehicle by doing this?

EVs with LFP batteries need to be charged to 100% every week or so. EVs with NMC batteries should not be charged to 100% unless necessary. I believe NMC life is maximized if you stay within 40-60% SOC, but most people daily charge to 80 or 90% without issue.

-What would be required for example if you wanted to charge the vehicle in the daytime, directly from the sun, bypassing the battery? What inverter functionality would be required in this regard?

Your Growatt should handle this fine. If you always charge in the daytime it'd be nice to find an MPPT that DC charges your EV battery directly and do away with the inverter and stationary battery. Unfortunately the only MPPTs that do this seem to be expensive commercial units.

As it is, the least expensive option for daytime charging is probably 3 and a ~2 kW 120V all-in-one hooked to a 12V lead-acid battery for buffering only. If the car typically stays plugged in 10+ daytime hours you could get 80-90% of the benefit for a fraction of the cost. Especially since the car can drive a few cloudy days with no charging at all.

-I believe we do not need hybrid connectivity for this system, as it is much cheaper to just get a 2nd additional charger that is connected via breaker to the grid,

Why even get a 2nd EVSE? If it's cloudy just unplug the Beny from the Growatt and plug it into the wall outlet. I'm assuming the Beny has a plug, if not other EVSEs do.

 

[premierautomotive]

You'll see that 93% efficient at about 2000W on a 6000W inverter. Below 2000W, it drops off and can be truly terrible at low power (50-100W) and it slowly drops off above that to probably about 85% @ 100%.

Ah I understood, yes I saw a video also of someone infact using the 6000w growatt model, and ran it at 20A draw, and it shutoff because of overheating/gave an error. This one below if you're interested to see it:

Why best? Charging a battery faster is more stressful than lower current charging. The only reason to charge fast is because you need to drive it ASAP. If there's no hurry to drive, the ideal charge to be to complete the charge shortly before you need to drive. For example: You get home at 6pm and don't need to drive again until 7am. The least stressful charge would be to charge at a lower rate over the 13 hours. This shouldn't necessarily be a goal, but I'm trying to convey a concept.

That is correct, i suspect this worry is because of the initial range anxiety that comes with owning an EV, but you are right in the sense that slow charge is better and really there will never really be a case where you need all the juice and quickly where I am.

The minimums are typically driven by MPPT operating voltage. You want your array Vmp above the minimum MPPT voltage.

Thanks, yes learning more about this as I go, the person below clarified it also for me, which helps double check my maths on this

There is no battery technology that truly benefits from full depth discharges, though NiMH and NiCd can benefit from occasional full depth discharges. There's also other considerations. Using only 5% of your capacity and charging 95% to 100% every day isn't necessarily a great idea. as charging to 100% can be more stressful. Charging from 80-85% per day would be preferred over 95-100% every day to reduce charging stress.

If the vehicle has a LFP battery, it will benefit from periodic charging to 100% to retain cell balance. If NMC, there's never really a need to go to 100%.

I understand, what would you say would be "periodic", the other kind person below has replied about weekly to charge to 100%, I am just going to dig into this topic a bit more now to understand it better. Yes we plan to normally keep the EV charged to around 80-85%, drop down, and then charge it back up to 80-85% range for regular use, and then cycle periodically to 100% but try to line up reaching 100% and then immediate use, as I understand charging to 100% and keeping it idle there is also not good for the battery life of the vehicle.

Yes. Most inverter/charger/AiO units can use grid for pass through and charging purposes when PV is insufficient.

I understand this better now. Having dug in a bit more yesterday into this topic, I read a lot of information regarding the growatt 5000es model fiasco which aren't rated for US markets and similar to ours suggested above, the 6000 model. It seems the solution to using this isn't so clear cut and simple, and requires a transformer, and modifying the unit as well, to make it safe, which isn't guaranteed because the pcb can short due to movement or open arcs being created. Not sure if I totally followed along the entire discussion, but I wanted to ask you if you know that it would be safe if we just keep it disconnected from the grid permanently to avoid this issue? This was my understanding, that if it is used for a single device rated for the specific voltage use (in this case it matches up correctly) and not connected to the grid, it would be safe.

Thanks again for all your help!

 

[premierautomotive]

A few commercial "chargers" (actually EVSEs, the AC charger is inside the car) are designed to work with grid-tied solar. Here's one from SolarEdge that works with their inverters. Emporia and Zappi also have units. There are also systems designed to operate completely off-grid, but most are commercial and expensive. The PairTree is an self-contained unit that can be moved to a new location pretty easily.

Yes, thank you! We saw some of these setups but it seems the overall costs of this is quite high when buying from the brand names/complete setups, we were trying to DIY it to save some money!

Your Beny EVSE says output can be throttled down all the way to 6A (roughly 1.4 kW of continuous power). So in theory you could set it around 8A in normal usage to get optimum efficiency from a 6 kW / 240V inverter and set it at 20-25A if you're in a hurry and need to max the inverter out. You could also save money with an even smaller 240V inverter, say 3 kW, and the 6A setting.

Yes! I believe you can select the A output, so we should be able to control it to a trickle charge for normal use, and if we need to bump it up, then it is possible to do that, but I saw a setup on YT by chance that was very similar to ours, and it seems when fully loading the inverter it shuts off due to heat/throws up some errors. Video below if you are interested to see it also:

4 panels in series is 223 Voc, 184Vmp and 14 Isc
6 panels in series is 335 Voc, 276Vmp and 14 Isc

The MPPT in your Growatt needs at least 120V, which both configurations easily provide even on hot days. Both are also well below the max 500Voc and 100A Isc. So this looks OK.

Thank you so much for this!

Yes, 20% is a good minimum SOC for daily LFP cycling. 50% for lead-acid.

Understood

EVs with LFP batteries need to be charged to 100% every week or so. EVs with NMC batteries should not be charged to 100% unless necessary. I believe NMC life is maximized if you stay within 40-60% SOC, but most people daily charge to 80 or 90% without issue.

Wow, I did not know that the EV battery should be brought up to 100% weekly, I am going to study this a bit more as well. Our plan is to daily charge to 80-85% normal use, but I think I have to plan in taking it to 100% once a week in that case and then immediately using the vehicle after, so it can prolong the battery life, as I read you shouldn't charge to 100% and leave it idle too long, because that can damage the battery life expectancy also.

Your Growatt should handle this fine. If you always charge in the daytime it'd be nice to find an MPPT that DC charges your EV battery directly and do away with the inverter and stationary battery. Unfortunately the only MPPTs that do this seem to be expensive commercial units.

As it is, the least expensive option for daytime charging is probably 3 and a ~2 kW 120V all-in-one hooked to a 12V lead-acid battery for buffering only. If the car typically stays plugged in 10+ daytime hours you could get 80-90% of the benefit for a fraction of the cost. Especially since the car can drive a few cloudy days with no charging at all.

That's interesting, so far we were considering just using Lifepo4 cells, I'm going to look into this a bit further as well, appreciate it.

Why even get a 2nd EVSE? If it's cloudy just unplug the Beny from the Growatt and plug it into the wall outlet. I'm assuming the Beny has a plug, if not other EVSEs do.

Feel quite stupid for not considering this till you mentioned it, Duh, can just put the plugs next to each other and switch out when we want to use the grid.

Thanks so much for your help!