Off-Grid EV Charging

There are plenty of reasons to install solar panels on one’s home. Reducing electric bills, reducing carbon footprint, or simply being in a location without electric service are all fairly common. While some of those might be true for [Dominic], he had another motivating factor. He wanted to install a charger for his electric vehicles but upgrading the electric service at his house would have been prohibitively expensive. So rather than dig up a bunch of his neighbors’ gardens to run a new service wire in he built this off-grid setup instead.

Hooking up solar panels to a battery and charge controller is usually not too hard, but getting enough energy to charge an EV out of a system all at once is more challenging. The system is based on several 550W solar modules which all charge a lithium iron phosphate battery. The battery can output 100 A DC at 48 V which gives more than enough power to charge an EV. However there were some problems getting this much power through an inverter. His first choice let out the magic smoke when it was connected, and it wasn’t until he settled on a Growatt inverter capable of outputting 3.5 kW that the system really started to take shape.

All of this is fairly straightforward, but there’s an extra touch here that makes this project noteworthy. [Dominic] wanted to balance incoming power from the photovoltaic system to the current demands from the EVs to put less strain on the battery. An ESP32 was programmed to only send as much power to the EVs as the solar system is producing at any given time, and also includes some extra logic to make sure the battery doesn’t drain itself from the idle power requirements of the inverter. Right now the system works well but the true test will be when it goes through its first winter. Even though solar panels are more efficient at colder temperatures, if the amount of sunlight or the angle of the panels aren’t ideal there is generally much less production.

40 thoughts on “Off-Grid EV Charging

  1. I’ve been doing this for decades; but my setup is pretty basic.

    When grid power is available, the PV panels feed a Microsine or Enphase microinverter, which pushes power back into the AC line. My EV’s charger than uses AC power to charge its batteries.

    When grid power is not available, the PV panels are simply switched to an individual battery in my EV’s pack. My pack was built with 12v lead-acid batteries, so an off-the-shelf MPPT tracker could charge them. I built a Battery Balancer that used relays to read the voltage of each 12v battery, and select the lowest one to be charged. Every 15 minutes, it checked again to see which battery was now the lowest, and charged it.

      1. This was in a 1980 Lectric Leopard (a converted Renault LeCar; also called the R5). The original pack was sixteen 6v batteries. I converted it to ten 12v batteries, then 15 8v batteries. I’m currently converting it to use 42 3.2v CALB lithium cells.

  2. I have been off grid solar for two years with a Growatt 5KW inverter and a pair of 5KWh lithium iron phosphate batteries. This has been far more reliable than living in the city. Zero power outages, because I’m in control and failure is minimized. But I do have multiple backups for everything!

    1. At a guess AC is more generally useful and the parts are available off the shelf. DC would be more efficient but I don’t know of any low power cheap DC chargers, even the small units for garages are ~40kw.

  3. Ground based systems are popular here (43N) and are preferred by the codes office. If you want more constant power year round, panels should be more vertical than ‘average’. I’ve been solar-preheating DHW for 40 years and put the collector on a vertical wall. In midsummer I have no problem. In January, still works pretty good except for that week or two of gray skies. If they were on the 5-in-12 roof I’d spend too much time clearing the snow but not getting much sun.

  4. “The battery can output 100 A DC at 48 V which gives more than enough power to charge an EV. ”

    I mean, you need an inverter to raise the voltage to a level where the battery can charge, right?

      1. While the battery may be able to create the current needed, it can only do so for a very short time. The 4.8 kW battery represents less than 10% of what’s needed to charge most cars. It’s good for about 20 miles of range.

  5. Battery powered vehicles are simply gimmicks! Overpriced n overrated! Just another fad that will be gone very soon! Climate change is natural n not man made n we are carbon based life forms! The more carbon the better! There’s no way to have an infrastructure to support even just a couple hundred thousand of these gimmicks without blackouts! Gasoline powered vehicles will never be replaced by WoKeism! If you’re brainwashed enough to believe all the fake news hot air propaganda then you are truly a brainwashed Libtard! Electricity is mostly made by burning fossil fuels! Your fantasy of windmills n solar panels are a pipedream beyond the measure of reality!

      1. Lets see a set of solar panels costs about 50 k, 25 % efficient on the best day to charge an overpriced vehicle which is a fire hazard. Insurance is going up because they have no trained people to fix a fender bender which may have compromised the battery and nowhere to recycle them. If you want electricity you have to boil water, simple as that.

    1. I’m not sure if you’re being sarcastic Mugen but some of your statements have already been proven false by countries making the transition. The UK is up to ~650k fully electric vehicles with no blackouts. Roughly 50% of electricity comes from green sources. Those numbers are improving all the time.

        1. About Co2 emissions, in spite of all the technical progress, more houses, cars, etc that ha been made in the past the Co2 emissions, 6,500 million metric tons today is the same (roughly) as 1970.

      1. “green sources” – ever looked into that?
        All sorts of things get called green.
        Importing wood chips from the USA over the ocean to Drax to burn is classed as green. Just ignore the fossil fuels burnt getting it there.
        Gas fired power stations in the UK are labelled as “low emission”.
        Cool aid much ?

        Now we need to invest in a massive upgrade of the electric grid, generation, storage solutions and all change over to electric cars.
        And who owns the UK energy sytem? hint: not the UK.
        Meanwhile we could make synthetic fuel offshore using existing infrastructure, and continue to burn an actual really honest “carbon neutral” fuel without spending billions on offshoring our carbon footprint to China to pretend we are so called green.
        The high the revolution that the UK apparently needs, politically: Strategic self sufficiency.
        So ask why we are doing this. And for whom.

        650K vehicles. Whoop de do. What about the rest?
        Approx 50 more nuclear power stations or equivilent to charge the rest, ignoring trucks and trains which operate off diesel fuel FYI.

        PS: It’s hilarious that my Telsa beats my twin turbo V10 off the line, but the noise isn’t quite the same.

    2. We have a couple of hundred thousand electrical vehicles in the country and still growing fast. The electrical grid is very reliable. Of course a low of work is done by the grid companies to keep up with the shift towards electrification, both supply and demand.

    3. Very well said. Wisdom evades many. While I find the technology itself cool and have built ebikes to sell and tinker with. I far prefer engines especially diesels as they’re better for the environment (not that I care since climate change is made up) but they’re efficient and cost less to run. I’d only go as far as a Toyota hybrid system because they use small cheap batteries and great for those who need an automatic transmission. As for me it’s manual transmissions.

    4. Wow. Talk about a bunch of rambling nonsense.

      “…we are carbon based life forms! The more carbon the better!”

      I’m not even sure how to approach this…. this is just… wow. This is the kind of nonsensical spin I expect from a politician or a sensationalist news host. You may as well be saying plants love CO2 so let’s remove all the oxygen from the air. More carbon, more better, am I right?

      “Electricity is mostly made by burning fossil fuels!”

      I know it’s easier to make claims than it is to do some actual research, but you really should look into things before rambling. While you are right that a simple majority of the electricity generated is produced by fossil fuels (in the US), a very considerable chunk is made from non-fossil sources. 40% as a matter of fact.

      If we broke that down into specific regions such as the Southwest Power Pool, it’s almost an even 50/50 split.

      “Your fantasy of windmills n solar panels are a pipedream beyond the measure of reality!”

      I’ll generally agree that going 100% renewable is a pipe dream. I don’t think anyone should seriously consider that feasible at this time. That being said, I see little reason not to offset fossil fuels as much as we reasonably can. Now the line drawn by “reasonable” is going to vary by the person, but I personally feel that the fact we’ve been able to offset 1/3 of our energy with wind in the SPP is worthy of praise. It’s not insignificant.

  6. I looked at this project page and the installation pictures are extremely scary. For this type of high voltage high current setup, the wiring needs to be much more professional than this janky mess of cables. This is a fire hazard waiting to happen, and no inspectors would approve of this. I understand this website is called HACKaday not JANKaday.

    One simple recommendation for Dominic would be to use some conduit feeding directly into each device (no loose wires), add some labels on each conduit pipe, and some safety/warning labels on the large switch, etc. This would cost at most an extra $50 and an hour or two of work. Save future Dominic some headaches, and prevent baby Dominic from electrocuting him/herself when they eventually enter that garage out of curiosity.

    1. I agree that it looks a bit hacky but electrically it is all fine. It is just the reality that you end up with a lot a cables (48V, mulitple 230V, Battery COMs, 2x RS485, 5V supply, demand switch, …) than run in parallel. They are all easily recognisable (48V battery cable is 50mm2, RS485 is 0,5mm2).

      I will hide all cables in an installation canals to make it look more pretty in the future.

    1. It is asinine that solar systems don’t have a DC outlet to directly charge vehicles. It seems inefficient and dumb to take DC, convert it to AC, and then back to DC to charge something.

      Furthermore, Tesla sells both solar systems and electric cars. And yet, to this day, they do not offer a bundle of the two. Buy both, and you can use the car as a battery in the event of grid failure.

  7. Nice idea Dominic, also saves the hassle of the grid connection certification & paperwork etc.

    Agree with giving it a tidy up.
    Think about sticking as much of the gear in metal cabinets as you can. Keeps it professional looking and helps stop chances of fire spreading.
    Id also be thinking about auto fire detection/ suppression.
    There’s no way I’d be wanting a big fat lithium battery in my house that’s for sure. Garage it is :-)

    The only batteries I’ve seen advertised with built in fire suppression are from solar edge.
    Incidentally they are dc/dc and they were selling dc/dc ev chargers before, but looks like they have a new version coming out soon… shame they are so expensive!

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