Phase 1, in which I charge my EV with PV

I'd like to charge my EV directly with solar during the day. I use about 8kWh/day in my EV M-F, so ideally the system could add about that much (perhaps sized 20% higher to account for inverter inefficiency and AC/DC losses in the car's charger).

I have ~4.5 solar equivalent hours where I live, so it seems like I could get by with roughly 2-3kW of solar panels. I could do it at 120V/12A/~1.4kWh, or 240V/12A/2.9kWh.

I'm mostly doing this to learn, have fun, and to provide my EV with cleaner power than what the utility provides; I'm under no illusion that the ROI is going to be attractive. The system will not be grid-tied (at least not in the initial iteration that I'm thinking of). No batteries, just solar PV driving the inverter and charging the car while the sun shines -- supplemented by utility power when the solar watts are inadequate. Maybe I'll add batteries one day when they're cheaper, to make the system more flexible.

I'm leaning toward the EG4 6000XP, but I'm open to other options. One thing I don't like about the 6000XP is that it can't combine the solar power with utility power, it can only detect when the solar power isn't enough for the load, at which point it just switches over entirely to utility power. Is that correct? I would prefer an inverter that just draws the amount of utility power to make up the deficit, but I'm not aware of one that's available in the sub-$1,500 range (which is my preference).

I assume I'll have to deal with grounding at some point...and I've read enough about how that works with the 6000XP to know that I have no idea what I'm doing there yet. But there's time to learn.

Any words of wisdom, caution, or otherwise as I embark on this project?

Did you make a list of related threads on this forum and others that you have used for research so far? So we can understand where the gaps are in your understanding?

The less buffer battery you have the more complex of a control problem you will have, since if your EV onboard charger draws more than your battery less solar can supply the inverter will shut off and the system needs to reset. Zero battery buffer requires finding a battery less inverter and having the wherewithal to debug and make work a system sometimes running on knife’s edge of feasibility and without custom control software to compensate for no buffer

You could argue that a 2.5kWh battery for $700 liberating you from such complexity is a bargain for a one off bespoke system.

This may not actually be as big a deal in practice because a low power EVSE limit might just reset after a few minutes of hemming and hawwing after clouds

While the battery-less solar to EV charging requires some engineering tradeoffs… Grounding is pretty easy (only a few right ways to do it, they are all cheap and no thinking needed once you know who to listen to) and involves no control theory or power electronics, just bond N-G in either 6000XP or dedicated panel feeding from it and bond G to your house ground. Assuming you are aware that this setup is not allowed to bridge onto grid power without a more complex grounding setup.

I belive the eg4 3k can supplement grid power.

zanydroid said:

Did you make a list of related threads on this forum and others that you have used for research so far? So we can understand where the gaps are in your understanding?

The less buffer battery you have the more complex of a control problem you will have, since if your EV onboard charger draws more than your battery less solar can supply the inverter will shut off and the system needs to reset. Zero battery buffer requires finding a battery less inverter and having the wherewithal to debug and make work a system sometimes running on knife’s edge of feasibility and without custom control software to compensate for no buffer

You could argue that a 2.5kWh battery for $700 liberating you from such complexity is a bargain for a one off bespoke system.

This may not actually be as big a deal in practice because a low power EVSE limit might just reset after a few minutes of hemming and hawwing after clouds

While the battery-less solar to EV charging requires some engineering tradeoffs… Grounding is pretty easy (only a few right ways to do it, they are all cheap and no thinking needed once you know who to listen to) and involves no control theory or power electronics, just bond N-G in either 6000XP or dedicated panel feeding from it and bond G to your house ground. Assuming you are aware that this setup is not allowed to bridge onto grid power without a more complex grounding setup.

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Hi @zanydroid -- I appreciate your reply. I'm just now getting a chance to respond.

I haven't made a list exactly, but I've spent quite a bit of time reading through threads here (and elsewhere) that discuss different approaches to EV charging. In fact, I've been in a state of analysis paralysis for quite a while -- many months.

Most of the approaches I've read about involve batteries...which is probably a good clue that having some battery in the system is not a bad idea. As you say, a battery simplifies the problem. I was hoping there was a budget non-battery inverter that could spare me from the control complexity by cleverly and nearly-instantaneously mixing utility power with the available PV power. Now I'm not so sure that's the case.

I would be willing to consider a small amount of battery in the short term. In the longer term, I would be willing to consider much more battery capacity, and use it in a dual-purpose way to provide power to my house during a utility outage. I'm reluctant to do so right now because 1) I want to spend a relatively small amount in my "getting feet wet" stage, and 2) battery prices have been falling pretty sharply, and I don't want to catch a falling knife. My life would probably be a lot simpler if I would just suck it up and buy something like the EG4 WallMount.

As far as my gaps in understanding, they are many and large. Conceptually I can rough out the big pieces, determine an appropriate number of panels to support my intended usage, figure out how to mount and wire them, and make a bunch of PV cables with MC4 connectors. I don't think I'll have too much difficulty figuring out how to wire a load center from my inverter, installing a 60A breaker or whatever, and wiring that either directly to my EVSE or to a 14-50 outlet. Where things start to get fuzzy is...well, in plenty of areas:


All of the above (and more) is why I've been stuck in analysis paralysis. My post on this forum was my way to try to get things kickstarted so I can hopefully get started on building something this summer.

TLDR.

If you are basically trying to make a stand alone EV charging station, you can.

You will need batteries.

Shopping list:
Enough PV for the 4 hours you state, to give you juice for the day, add at least 10% to your load ot get the amount of PV
Inverter. If you are going 120 volt, any will do, as long as it connects to the battery.
Battery(ies), I'd get 2 Lifepower4 or the like.

Mr Butterfingers said:

Most of the approaches I've read about involve batteries...which is probably a good clue that having some battery in the system is not a bad idea. As you say, a battery simplifies the problem. I was hoping there was a budget non-battery inverter that could spare me from the control complexity by cleverly and nearly-instantaneously mixing utility power with the available PV power. Now I'm not so sure that's the case.

Click to expand...

So, there definitely exists AIO that can do Solar-Utility mode (and you can look for a batteryless). But these by default will not blend utility with inverter. That is not allowed without either being naughty or with an interconnection agreement. These switch between grid and load in an all-or-nothing fashion. I don't think you can use a double conversion setup either to blend it without writing custom code. (double conversion being taking AC, converting it to DC, and then putting the on the same DC bus as the MPPT and modulating the power share as appropriate in real time. I have not seen this architecture, presumably b/c if you have the money to pay for this much hardware, you also have the money to buy an interconnection agreement and appropriate tier AC blending inverter. Or because the demand is so low nobody deigns to implement & sell it). AC blending is an advanced feature, you need a multiplus or better. $1500 for a 230V EU version that is not legal to grid connect in the US, but is capable of AC load sharing. I don't know if it's capable of battery-less operation (IE, the AC blending things are niche, and battery-less are a niche, the combination can be a unicorn).

Mr Butterfingers said:

I would be willing to consider a small amount of battery in the short term.

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On r/evcharging, I remember talking to someone that used a pretty small buffer battery. For a simple EVSE with static charging rate, you would size the inverter to the discharge power of the battery, and the MPPT+solar to probably 1.5-2x the discharge power. And the inverter matched to the EVSE charge rate. This way if there is plenty of sun the MPPT has enough power to satisfy the buffer battery and the EV. (You should go look for other posts or endlessphere posts for someone who has actually implemented it, vs shooting from the hip).

24V would be a good choice for ~3kW charging rate, in the sense that you can scale down the system better than 48V (unless smaller 48V batteries from reputable companies are readily available now).

Dynamic direct from solar charging feels more like an undergrad or masters capstone project in complexity (3-6 months of work of real development). I would imagine they would flex on their classmates with going with as small of a buffer battery as possible, without any resetting.

Mr Butterfingers said:

- Inverters. I'm aware of a handful of popular inverters, like the 6000XP, which would likely serve the purpose I have in mind. But even there I don't have a great handle on everything. For example, I assumed that the 6000XP would seamlessly combine utility power and PV power, but that does not appear to be the case.

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It won't because it's an AIO off grid inverter. It's not allowed to blend in the AC domain. And as said earlier blending in the DC domain is not common.

Mr Butterfingers said:

- If I have a battery, will something like the 6000XP be able to seamlessly prioritize PV input going to the load, and supplement with battery when needed/as needed? Or will my EVSE draw from the battery, and the 6000XP will charge from the battery with solar as it's available? Or does it even matter?

Click to expand...

This is called Solar Battery priority mode. It is a standard AIO feature. If you want more intuition you can look for one of the power architecture schematics posted here and get confidence that this is doable. The way it would work is, the DC from the MPPT and battery will eventually converge (potentially after some voltage conversion steps) at the input to the inverter.

Mr Butterfingers said:

- The nuts-and-bolts part of a solar install: the appropriate type of wire to use in different places (I think I'm OK on the PV wire side), what type of conduit to use, and how to get wires from outside my garage to inside of my garage where the inverter would probably live. Do I mount a combiner box on the outside of my garage, and have the wires enter the garage from a hole in the back of the combiner box? Or do I run a conduit from outside up through a hole in the soffit, then down to a combiner box (or directly to the inverter) inside the garage? Or would the inverter prefer to live in my basement where the temperature and humidity are more steady? If it's in my basement, how do I run wire/conduit through my basement foundation wall?- Grounding requirements, as I mentioned before. You said it's pretty simple, but I read at least one long and confusing thread on this forum about it, and afterward I felt even less confident that I understood things.- In the event I get something other than a 6000XP, it seems likely I'll have to add breakers/disconnects/fuses, and I'd have to educate myself on all those things. One of the reasons the 6000XP is appealing to me is because all of that stuff is integrated, and I don't have to source a bunch of extra pieces and figure out a safe and not-ugly way to mount everything.

Click to expand...

These things are all pretty well understood. It's probably easier for people if you give the questions to them pictorially with photos rather than wall of text.

It's probably easier to force yourself to pick a feasible/safe option and then make iterative changes on it vs having the entire set of free parameters floating around driving yourself nuts.

It's probably easier for people to engage if you force yourself to simplify the description and parameter space. I know, it's hard, my first few posts here were walls of text with some dense analysis.

For some of those construction questions, you can make a separate thread here or on an electrical DIY forum, maybe even simplified to a toy example, to get ideas on how to make a particular kind of conduit run work. This is ofc subject to going down a dumb path in the overall project plan because of XY problem, but at least you make it easy for respondents to participate and you learn something.

The inverter/battery is just wear item / entertainment stuff to me. IMO the $1500 +$800 cost of a 6000XP and buffer battery is in the noise of grand scheme of my edutainment toys, as long as it's safe and doesn't explode, I don't care where it is installed. The LFP battery certainly can light up. For some people on this forum, $5K, $10K are nbd for this.

For grounding, I dunno. You have to figure out your learning style and capability of filtering out technical nonsense (of which there is a lot in grounding) while you don't know much. One valid learning style is finding a trustworthy sunbae to just tell you the way it is. There's much more complex technical stuff I've had to master or pretend to understand as a practicing (non-electrical) engineer.

There are ways to mitigate messed up ground bonding (EG add output GFCI and either accept the potential for a problem in the portion of the system before the GFCI, or somehow "double insulate" it in an electrical safety and fire safety sense). For me, after exploring some bad ideas / hacks around it, I understand the correct way better.

millsan1 said:

TLDR.

Click to expand...

Touché.

millsan1 said:

If you are basically trying to make a stand alone EV charging station, you can.

You will need batteries.

Shopping list:
Enough PV for the 4 hours you state, to give you juice for the day, add at least 10% to your load ot get the amount of PV
Inverter. If you are going 120 volt, any will do, as long as it connects to the battery.
Battery(ies), I'd get 2 Lifepower4 or the like.

Click to expand...

Thank you!

zanydroid said:

24V would be a good choice for ~3kW charging rate, in the sense that you can scale down the system better than 48V (unless smaller 48V batteries from reputable companies are readily available now).

Click to expand...

If I go with batteries, then I think I want to go with 48V from the start. Mostly because I'd eventually like to use the same system for whole-house backup (via L14-30 inlet w/ interlock that I already have wired to my main panel). Is there a problem using ~3kWh + 6000XP to charge something like the EG4 14.3kWh Wallmount battery?

zanydroid said:

It won't because it's an AIO off grid inverter. It's not allowed to blend in the AC domain. And as said earlier blending in the DC domain is not common.

Click to expand...

Thanks for this. I've read that the 6000XP and others can be wired with grid input as passthrough AC (and/or using the AC to charge the battery), and I naively assumed there was more sophistication going on -- AC blending.

zanydroid said:

This is called Solar Battery priority mode. It is a standard AIO feature. If you want more intuition you can look for one of the power architecture schematics posted here and get confidence that this is doable. The way it would work is, the DC from the MPPT and battery will eventually converge (potentially after some voltage conversion steps) at the input to the inverter.

Click to expand...

Perfect, I can go off and research that. I've been a little fuzzy on some of the terminology/features in the AIO's, and this will help with my understanding.

zanydroid said:

These things are all pretty well understood. It's probably easier for people if you give the questions to them pictorially with photos rather than wall of text.

It's probably easier to force yourself to pick a feasible/safe option and then make iterative changes on it vs having the entire set of free parameters floating around driving yourself nuts.

It's probably easier for people to engage if you force yourself to simplify the description and parameter space. I know, it's hard, my first few posts here were walls of text with some dense analysis.

Click to expand...

Ok, I think you get me. I knew when I was typing my posts that it was way too long and that I'd inevitably get a 'TLDR' (it arrived even sooner than I expected). I was wary of holding all my cards and then having to play them piecemeal as people asked of my plan, "Did you think about ___?". So all cards on the table. I knew that wouldn't play well with most, but thank you for reminding me!

I really appreciate your thoughtful reply. I'll go off and read/think some more.

Mr Butterfingers said:

If I go with batteries, then I think I want to go with 48V from the start. Mostly because I'd eventually like to use the same system for whole-house backup (via L14-30 inlet w/ interlock that I already have wired to my main panel). Is there a problem using ~3kWh + 6000XP to charge something like the EG4 14.3kWh Wallmount battery?

Click to expand...

The problem is potentially UL9540 compliance. The wallmount batteries are only UL9540 pair certified with 18kpv (maybe de jure under LuxPower brand name and control number). Now, if you aren't cycling power through it continuously, maybe it's not considered an ESS, therefore is exempt from UL9540.

Here is one (non-authoritative but from important rules agency)

"An energy storage system is defined in the 2022 Energy Code as one or more devices assembled together to store electrical energy and supply electrical energy to selected loads at a future time."

And Energy Code may not be the specific code that requires 9540. I know Residential Code requires it. So perhaps the definition embedded in that is the one to go off.


The other way to address UL9540 concern is, if you will never grid tie it, then the POCO is less likely to confirm that the setup is fully code compliant. If you put up solar panels, and they're reported to POCO or AHJ, even if off grid, an inspection may get triggered due to some sequence of events starting from the report (and the report could be from a neighbor or a linesperson)

I primarily charge from battery-less grid tied solar. I set my charging rate depending on the weather or inverter output, I bought one of those 6/8/10/15a adjustable AC chargers from ebay. I have a 5kw inverter with 6.6kw pv (max legal residential system for my region). On clear days I'm producing 4-5kw from 9am so a charging rate of 15a/3.4kw works great.

I can also charge using a separate off grid system when the grid goes down, I have 2x Victron 100/20's & a 150/35 providing a maximum theoretical output of 3.8kw (4.5kw of pv) so setting a charge rate of 10a/2.4kw on a clear day works well without stressing anything.

Yes speaking of XY problem it wasn’t clear why non grid tie was a goal in the OP. In California even without net metering, grid tie one time soft cost overhead comprise $145 (POCO) + one times plans cost (possibly $0 if in a system type and location that is compatible with SolarApp+) + permit fees ($50-100 in AHJs that waive them for clean energy projects)

Can’t beat $145 with any battery buffer.

Grid tie equipment (like a Growatt grid tie or hybrid) is comparable cost to the current crop of split phase AIOs anyway.

zanydroid said:

Yes speaking of XY problem it wasn’t clear why non grid tie was a goal in the OP. In California even without net metering, grid tie one time soft cost overhead comprise $145 (POCO) + one times plans cost (possibly $0 if in a system type and location that is compatible with SolarApp+) + permit fees ($50-100 in AHJs that waive them for clean energy projects)

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I'm under the assumption that dealing with the local bureaucrats for permits/inspections, as well as the utility company, would represent a significant amount of overhead -- if not in dollars, then in time and aggravation. Maybe my assumption is wrong.

Also, in my first iteration I was planning on building mobile ground mounts that I can move 1-2 times a day to maximize solar exposure. I don't think any such system would be approved for grid-tie.

Mr Butterfingers said:

I'm under the assumption that dealing with the local bureaucrats for permits/inspections, as well as the utility company, would represent a significant amount of overhead -- if not in dollars, then in time and aggravation. Maybe my assumption is wrong.

Click to expand...

Well often what happens here is people anchor on one answer based on their assumptions (which are philosophically oriented), and a common one is underestimating the ROI of paying the cost of going on grid (bending the knee and doing it the way they want). Because it's very hard/impossible for off-grid to beat 1:1 net metering if available, even before factoring in the initial investment/ongoing maintenance cost (which includes labor) for a given level of reliability.

I don't mind dealing with them as much, and I put the time into figuring it out. Also no ground mount space in suburbs here so I had to go with more roof mount. You can check how it is in your location, I think most of New England is fine.

Yeah they're not going to approve mobile mounts, it's unlikely they'll meet wind resistance limits.

zanydroid said:

Well often what happens here is people anchor on one answer based on their assumptions (which are philosophically oriented), and a common one is underestimating the ROI of paying the cost of going on grid (bending the knee and doing it the way they want). Because it's very hard/impossible for off-grid to beat 1:1 net metering if available, even before factoring in the initial investment/ongoing maintenance cost (which includes labor) for a given level of reliability.

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We're 0.75:1 where I live (meh), and the town's permit fee is $50 (yay). As you say grid-tie makes the most ROI sense. I should probably further educate myself on what it would take to do things in an inspectable way, and just suck it up and put some panels on my garage. I'm not going up on my 3-story 12/12 roof, period. But I think I can handle DIY on my 9/12 garage roof. Plus any leaks would be apparent and not nearly as catastrophic as a leak above my finished attic living space.