Advice needed for at-home all-solar EV charger

[WhiteBusLady]

Hi, I'm new to this forum and have questions. I lived completely off grid for 15+ years, boondocking in a homemade motorhome. I have recently built and now occupy a completely off-grid house. I want to build a stand-alone Tier2 charging system for an EV (still shopping, will probably be an eSprinter though Zevo400 might also do).

I need to be able to charge a 100+ kwh battery. 24 ~400W panels will do the job, power-wise. (Is okay that it will take 3-4 days in December). I can get used panels, I have plenty of open space. My concern is the hardware to connect the car to the array. My knowledge is out of date and the vehicles sound full of fancy software.

Superficially, it sounds simple. I should be able to install a controller, an inverter that handles 240v, and a Tier 2 adapter to suit whatever vehicle I buy. Most of the vehicles charge at specific rates, e.g. 9kW for home-based Tier 2. But irl, my panels will produce from 0 to (24 x 400) = ~7kW max, varying with the sun. Is this variability ok? I'm used to 3kW to 4kW inverters. Can I get 10kW? Are they huge and expensive? Are there special considerations for this application?

Is there any way I can do a direct DC connection and skip the inverter? I have no need for fancy software to optimize flow between multiple sources like utility power vs my panels. Public utility hookup is not an option. (And my house system is just about right for the house with 6 panels and two 3kWh batteries in series - not nearly enough to charge a vehicle.)

I recently bought an EcoFlow solar generator. Everything I need for home backup power except the panel itself is in this single box that is almost the same size as a single golf cart battery. Fantastic improvement in technology in less that 20 years! Is there an all-in-one solution for my panel-based EV charging station?

 

[fuzzmunky415]

Welcome WBL!
Divide and conquer....
Concept itself is simple, but the devil is in the details. That's where we shine, knowledge from all across the spectrum (some even on the spectrum lol) awaits on this forum to get you to decision points towards your goal. Enjoy your new university.

 

[WhiteBusLady]

Typo correction to original post: max theoretical power = 24 x 400 = 9.6kW but actual measured power on Dec 22 (solstice) suggests no more than 24 x 300 = 7.2kW, if that.

 

[crossy]

Hi WBL and welcome to the madhouse. As @fuzzmunky415 notes this forum is probably the most friendly and broadly experienced forum of its kind in the known universe.

We (mostly) don't bite and the only stupid question is the one that goes unasked!!

I'm definitely no expert on EV charging and while I've noticed there are a few direct solar=>EV solutions out there, they do seem to share one important property, they are definitely not cheap

It's not just power (kW) you need, it is energy (kWh). You need to determine just how much energy you're going to need on a daily basis, you're not likely to need to fully re-charge your 100kWh vehicle every day (or are you?). Then you can size your system.

I suspect you're going to need more panels than you anticipate (we always do) but that's what the various solar calculators are for

As a real-world example.

We have 23kWp of panels, on our best recent day we made about 82kWh. Peak output from the array on that day was about 14kW (see the graph below), note that we can export to the grid once our batteries are full. I expect that to increase over the next couple of months before the rains (and clouds) arrive.

But, we are in a rather sunny tropical location.

Do note that our arrays are not ideally tilted and we have some shading from the house and Madam's precious mango trees with which I do not dare to mess despite my looking like a ruddy mango at the end of the fruiting season, it's the bananas that start then ...

 

[upnorthandpersonal]

Your post can be here, or general solar/battery for example. Let me know if you want to change the title of the post.

 

[WhiteBusLady]

Hi WBL and welcome to the madhouse. As @fuzzmunky415 notes this forum is probably the most friendly and broadly experienced forum of its kind in the known universe.

We (mostly) don't bite and the only stupid question is the one that goes unasked!!

I'm definitely no expert on EV charging and while I've noticed there are a few direct solar=>EV solutions out there, they do seem to share one important property, they are definitely not cheap

It's not just power (kW) you need, it is energy (kWh). You need to determine just how much energy you're going to need on a daily basis, you're not likely to need to fully re-charge your 100kWh vehicle every day (or are you?). Then you can size your system.

I suspect you're going to need more panels than you anticipate (we always do) but that's what the various solar calculators are for

As a real-world example.

We have 23kWp of panels, on our best recent day we made about 82kWh. Peak output from the array on that day was about 14kW (see the graph below), note that we can export to the grid once our batteries are full. I expect that to increase over the next couple of months before the rains (and clouds) arrive.

But, we are in a rather sunny tropical location.

Do note that our arrays are not ideally tilted and we have some shading from the house and Madam's precious mango trees with which I do not dare to mess despite my looking like a ruddy mango at the end of the fruiting season, it's the bananas that start then ...


View attachment 284235

Most of this has already been addressed: 24-400W panels is enough. Will provide at least 24kWh per day, most days, in December even if tilted only 10 degrees. This is a real-life number based on my current house panels measured on Dec 22. That will fill 100kWh battery in four days. That is enough. I need to drive 160 miles once or twice a month, and 1 mile once a week. Anything beyond the 160 miles would be a major, one-off trip that would require commercial charging along the way. There will be a few, but have no impact on this home design because I won't be home to use it <grin>.

Not cheap: "cheap" is a relative term. I'm going to be spending $75,000 on the vehicle (I have narrowed it down to three choices) and with my current driving pattern will save at least $20,000 in 10 years at today's gasoline and diesel prices. $2000-$3000 in solar hardware is small compared to $95,000, and I would need to pay for the Tier 2 wall unit and 240v wiring for any EV based on either solar or utility power source no matter what house I live in. The big difference is the inverter - do I really need one? Or can I just use a controller to feed the a DC connection? If yes, what does that DC connection look like?

 

[WhiteBusLady]

Your post can be here, or general solar/battery for example. Let me know if you want to change the title of the post.

New title: Advice needed for at-home all-solar EV charger
This should make it clear that I am actively soliciting advice.
New location: How about moving to the general solar/battery forum? Maybe it would receive more attention from the serious techies.

Thanks for the help!

 

[crossy]

Back in May 2024 Entelligent announced and started taking pre-orders for a direct solar DC-DC EV charger for up to about 12.5kW the TCLEV T1 EV charger. Just add panels!

It would be ideal for your purposes and the target price was an affordable 2,500 USD.

Enteligent Accepting Pre-Orders for World’s First DC-to-DC Solar EV Charger

Enteligent Inc., developer of solar-powered electric vehicle service equipment (EVSE) and solar power optimization technologies, is acc...

www.nacleanenergy.com

Unfortunately, the link to pre-order is now dead and the Entelligent site now only has a much larger commercial level charger

Evidently the market was just too niche

Others are offering "Solar EV chargers" but these all are intended to integrate with an existing domestic solar power system although at least one does promise DC-DC charging.

 

[WhiteBusLady]

Drat!

Am I on the right track to be looking at the panel - controller - inverter setup?

What companies are the currently considered the best controller / inverter suppliers?

I depended on Alt-e for several years and don't know who to turn to now.

 

[crossy]

Yeah, I reckon it's going to be an inverter-based system.

The problem is the variable nature of solar and the difficulty of dynamically changing the car charge rate, you'd likely need a battery to bridge over the breaks when an annoying cloud got in the way.

There are a couple of EV charging threads on here so it's worth having a quick poke around the forum for suggestions.

We've gone the "brute force and ignorance" route with 90kWh of LiFePO4, 22kWp of panels and 20kW of inverters (we power our whole home and Madam is not a low-energy lady), the packs are usually full by about lunch time so the afternoon output is potentially wasted. We can just plug in an EV, set it to charge at 5kW (or more on a sunny afternoon) and we're gold.

EDIT It may still be worth talking to Enteligent, I don't see a price for their "commercial" charger, but you never know. What's the worst that can happen

 

[WhiteBusLady]

Thanks! for your quick replies. I'm starting to get a bad feeling about this, just as I have found what might be the right vehicle.

I was told early on that EVs could accept variable input. That I could set up a Tier 2 outlet and if only 3-4 kW was coming in early and late in the day that it would still charge, just slowly. Is that not true? Must I set it for a certain rate that must be constant all day?

I was assuming the car was the battery. Unless the price of batteries has tanked there is no way I can justify buying several.

I'm pretty stubborn, but I don't know enough about this to push my way through to a solution. I'll let it sit here on the forum for a few days and see what happens. Hopefully someone who knows exactly how the cars themselves charge can suggest a solution.

 

[WhiteBusLady]

and I will also follow up with Enteligent. Again, thanks.

 

[crossy]

Yeah, the car can accept variable charge rate, the EVSE tells it what's available and that's what the car takes. The issue is knowing what's available at any instant, that is a lot harder than one imagines. I have visions of monitoring the battery current and adjusting the EVSE dynamically to keep it near zero. That's one of those jobs that may get done one day, currently I'm tied up earning the odd crust.

That's why DC-DC is actually "easier" because you get direct access to the vehicle battery without all the in-car charging gubbins getting in the way. That said high-voltage, high-energy DC is very good at turning your electronics (or worse, you) into a blackened area and some magic-smoke.

I don't know how big or friendly Enteligent are, but if you can get to the developers there may be a dev/prototype unit gathering dust that you could "win". Despite that old adage, if you don't ask you don't get!

Do not give up, even if you're limited to using the granny-lead you can still charge.

The DIYSolarForum will not be defeated!!

 

[crossy]

@upnorthandpersonal please can we change the thread title and location as the nice lady asked?

 

[upnorthandpersonal]

@upnorthandpersonal please can we change the thread title and location as the nice lady asked?

Done.

 

[WhiteBusLady]

Too late for me*, but I finally found some workable-sounding ideas for a completely off-grid solar EV charging station. Each of them requires hardware beyond my current level of expertise, though I'm sure I could learn. Maybe this info will help someone else.

There are two approaches: Level 2 AC charger and Level 3 DC charger. I wanted to try L3 - I'm going from DC panels to DC battery - why put an inverter and more batteries in between? The key seems to be voltage. The suggestion is to use a step-up transformer to get from 48V solar array to 400V wall charger. https://www.larsonelectronics.com/p...FCvfuxjjKpmJNCOI9WhD0RdsJpwNgI2LffHi78SRXdjuj $9,000+. Too big to install myself. Too big to move if I have to move closer to town as I age. Too expensive for just one vehicle, low mileage.

L2 is more within my reach. But I was going to need way too many lithium or lead acid batteries to support a steady supply of power to the inverter, as well as a temperature-controlled shed to house them. A partial answer to that is a new-to-me type of inverter with a Smart Load feature - it automatically adjusts to your panel-side batteries in real time, including for passing clouds, I'm told. AG4 breakers were also mentioned, though I don't know what they are or what holds them.

Both of these options are impractical for me given the expense at my age (short amortization period), and the limited and decreasing amount of driving I already do.


*Another older post by someone else suggested an all-EV thread would be helpful. That would be where the following info belongs.

I finally bought a diesel Sprinter. Too many reasons against an EV:

• Only two vehicles fit both my size and range requirements: Mercedes e-Sprinter and Chevy BrightDrop.
• Off-grid charging station too expensive
• Off-grid charging station too slow. In December it would take 4 days (24-400W panels or 48 used aka cheap 220-250W) to charge enough to go back to town. I'd have to keep my old vehicle around for emergencies. Insurance, registration, maintenance, parts issues for 28yr old vehicle.
• Notice that a truly off-grid system can only charge during the day, not overnight. You cannot drive "to town" two days in a row.
• Currently only one commercial charging station, 75 mi away, not always working.
• 2024 Sprinter was $15,000 less than 2025 e-Sprinter and I saved another $10-15,000 on charging station. Not a complete showstopper by itself, but that much money and I still had to keep my old vehicle?

Why not hybrid:

• not many (any?) large hybrid or PHEV vehicles to choose from
• not enough all-electric range to matter (I drive one mile once/week, 100mi once/month and 150mi once/month. It is all or nothing - 1 mile to see neighbors or 50+ one-way miles to civilization)
• I'm guessing hybrids will be like early EVs - not long-term maintainable (10+ years?) due to phasing out for newest EVs with improved batteries

I feel like an environmental traitor. I expect many of the above reasons will be mitigated within the next 2-4 years. But I need a new vehicle *now* (mid-70's owner replacing 28-year-old vehicle).

 

[fuzzmunky415]

Too late for me*, but I finally found some workable-sounding ideas for a completely off-grid solar EV charging station. Each of them requires hardware beyond my current level of expertise, though I'm sure I could learn. Maybe this info will help someone else.

There are two approaches: Level 2 AC charger and Level 3 DC charger. I wanted to try L3 - I'm going from DC panels to DC battery - why put an inverter and more batteries in between? The key seems to be voltage. The suggestion is to use a step-up transformer to get from 48V solar array to 400V wall charger. https://www.larsonelectronics.com/p...FCvfuxjjKpmJNCOI9WhD0RdsJpwNgI2LffHi78SRXdjuj $9,000+. Too big to install myself. Too big to move if I have to move closer to town as I age. Too expensive for just one vehicle, low mileage.

L2 is more within my reach. But I was going to need way too many lithium or lead acid batteries to support a steady supply of power to the inverter, as well as a temperature-controlled shed to house them. A partial answer to that is a new-to-me type of inverter with a Smart Load feature - it automatically adjusts to your panel-side batteries in real time, including for passing clouds, I'm told. AG4 breakers were also mentioned, though I don't know what they are or what holds them.

Both of these options are impractical for me given the expense at my age (short amortization period), and the limited and decreasing amount of driving I already do.


*Another older post by someone else suggested an all-EV thread would be helpful. That would be where the following info belongs.

I finally bought a diesel Sprinter. Too many reasons against an EV:

• Only two vehicles fit both my size and range requirements: Mercedes e-Sprinter and Chevy BrightDrop.
• Off-grid charging station too expensive
• Off-grid charging station too slow. In December it would take 4 days (24-400W panels or 48 used aka cheap 220-250W) to charge enough to go back to town. I'd have to keep my old vehicle around for emergencies. Insurance, registration, maintenance, parts issues for 28yr old vehicle.
• Notice that a truly off-grid system can only charge during the day, not overnight. You cannot drive "to town" two days in a row.
• Currently only one commercial charging station, 75 mi away, not always working.
• 2024 Sprinter was $15,000 less than 2025 e-Sprinter and I saved another $10-15,000 on charging station. Not a complete showstopper by itself, but that much money and I still had to keep my old vehicle?

Why not hybrid:

• not many (any?) large hybrid or PHEV vehicles to choose from
• not enough all-electric range to matter (I drive one mile once/week, 100mi once/month and 150mi once/month. It is all or nothing - 1 mile to see neighbors or 50+ one-way miles to civilization)
• I'm guessing hybrids will be like early EVs - not long-term maintainable (10+ years?) due to phasing out for newest EVs with improved batteries

I feel like an environmental traitor. I expect many of the above reasons will be mitigated within the next 2-4 years. But I need a new vehicle *now* (mid-70's owner replacing 28-year-old vehicle).

Congratulations on your new Sprinter! Also thanks for mentioning the Chevy..had no idea of it's existence, could be a nice rig for camper conversion for short weekend getaways to the beach, country, etc.

Still hoping the new Ram Ramcharger will be the fit I'm looking for: tow capacity, PHEV if I want for short local, massive range when tank filled, possible solar battery bank for emergencies. Stellantis recently swapped the launch of the EV Ram with the Ramcharger, so I may see it before year end.

Funny that we develop so many boxes that need checking before pulling a trigger on a car or truck, when my mom used to choose a car because she liked the color.

 

[SolarForU2]

Currently I am putting up a PV array above our drive way leading to the garage, will have 9 x 440w panels, charging a small 200AH 48v Lifepo4 bank, via 2 DIY charge controllers. The bank connects to a 48v-230vac 3.5KW HF inverter, that can power the slow 2kw AC charger that came with the car.

A battery monitor will turn off the AC output if the battery volts drop too low on any one cell (2.95v), Thus in full or partial sun the bank supplies any load should passing cloud cover occur; this prevents the inverter dropping off during short duration cloud cover and having the cars HV relay switch on\off repeatedly.

Purchased most of the PV\batteries 2nd hand to keep costs down.

Cheers
Mike

 

[chateau_nomad]

Currently I am putting up a PV array above our drive way leading to the garage, will have 9 x 440w panels, charging a small 200AH 48v Lifepo4 bank, via 2 DIY charge controllers. The bank connects to a 48v-230vac 3.5KW HF inverter, that can power the slow 2kw AC charger that came with the car.

A battery monitor will turn off the AC output if the battery volts drop too low on any one cell (2.95v), Thus in full or partial sun the bank supplies any load should passing cloud cover occur; this prevents the inverter dropping off during short duration cloud cover and having the cars HV relay switch on\off repeatedly.

Purchased most of the PV\batteries 2nd hand to keep costs down.

Cheers
Mike

This sounds intriguing to me! I am also VERY interested in a "budget friendly" essentially unorthodox SUPPLEMENTAL EV charging solution.

First question... how much do you have invested so far? This is important for a few reasons... let me explain:

I'm 70 years old and retired. We have a Chevy Bolt as daily driver which is always charged at home from our level-2 50 amp charge line. We NEVER use public commercial charging. Very low daily (local) mileage.

Our utility company recently announced a 15% to 20% increase in kWh. If I was in my 20's my roof would be covered in panels... which would be essentially a $30k investment. BUT... at 70 years old, that is NOT a wise investment.

What I'd like to do is something like the following:

10 - 400 watt solar panels on garage roof (southern exposure on hip roof)
Dedicated exclusively to EV charging... NO GRID TIE.

Inverter of sufficient size balanced between affordable and effective.

Enough battery to provide a buffer for the above mentioned cloud cover.

I reiterate... this would be supplemental only. I'm not expecting it to charge the EV battery from empty to full every day. I'm trying to get a ballpark starting budget to see if this is even worthwhile.

 

[42OhmsPA]

Bolt owner here. I bought mine after getting the solar addiction.
L2 charging at home is definitely doable.
I normally charge at 2.4KW but also charge up to 8KW.

At a minimum I'd start with a 10KW inverter, 4-5KW of panels and ~15KWh batteries.
There is a pile of info in my SRNE ASP parallel journey thread, some relevant some not.

Quick costs that come to mind.
~$1300 for AIO inverter, thanks to tariffs.
~$1500 for battery, if you build your own. (Double that if you aren't building your own).
~$2000 for panels and mounting if you find them locally.
~$750 for everything else; wire, fuses, breakers, conduit, tools, etc.

 

[Recovering EE]

Is your EVSE adjustable? Being able to turn it down to 8A at 120V or 240V would open up possibilities for a more modest inverter, along the lines of an EG4 6000XP. Many EVs come with a L1 EVSE (8A at 120V) that would likely fit the bill.

I recently put up 6.4kW of PV (3.2kW strings x 2), a 6000XP inverter and 28.6kWh of batteries (14.3kWh x 2). I've also got an L1/L2 EVSE that I can adjust all the way down to 720W output (6A at 120V). I charge two EVs with it, and because we are retired, we don't need many miles each day either. This off-grid system also feeds half my house, in the 'burbs.

If I was only charging one EV with this system, I'd easily get by with 5kW of PV and one 14.3kWh battery. You could time it to pull from the battery at night, but you'd probably need more battery.

With your proposed system, you could expect 24kWh out of such a system in Summer (4kW x 6Hrs), and 16kWh (4kW x 4Hrs) in Winter, depending on weather and latitude. Call it 20kWh, average. An EVSE pulling 8A at 120V is 960W (use 1kW, to make the math easier). If you put your EVSE on a timer from 6AM to 8PM it would put ~14kWh (1kW x 14Hrs) into your EV each day, and leave some in your battery to keep it happy. 14kWh should get you about 49 miles of range (14kWh x 3.5mi/kWh) from the Sun each day.

These are ballpark figures, of course. YMMV.

 

[chateau_nomad]

Thank both of you for the responses!! Sounds like maybe $6k - $7k for a doable setup?? And yes the tariff situation definitely muddies the waters. And yes the Bolt came with a 120v adapter plug... never used it.

I also appreciate the "napkin math"! I came close to buying the EG4 6000XP last fall... after watching one of Will's videos.

 

[time2roll]

Slow down the charging with a common 16A EVSE for the independent solar. Just under 4kW charging should work nicely with 6kW inverter. Probably close to 8-14kWh battery and as much solar as practical.

 

[Recovering EE]

Thank both of you for the responses!! Sounds like maybe $6k - $7k for a doable setup?? And yes the tariff situation definitely muddies the waters. And yes the Bolt came with a 120v adapter plug... never used it.

I also appreciate the "napkin math"! I came close to buying the EG4 6000XP last fall... after watching one of Will's videos.

Probably closer to $10k, now.

Depending on the year of your Bolt, that L1 EVSE *might* work at 240V, with a plug adapter. Then it would default to 12A at 240V, or 2.88kW. At 120V, the Bolt EVSE defaults to 8A at 120V, and you can change that to 12A at 120V, in a menu buried in the Infotainment screen. After 30 days, the charge rate drops back to 8A. (I have a '21 Bolt Premier, and '24 Ioniq 5 RWD LR LTD.)