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Simplified solar charging for Model 3

Discussion in 'Model 3: Battery & Charging' started by Bobrrr, Jul 17, 2019.

  1. Bobrrr

    Bobrrr Member

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    Mar 6, 2014
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    Orange County CA
    I am planning on keeping my Model 3 at a second home where I only drive it on alternating weekends. The home is a condo with a long (200 feet+) run from my meter to my carport. Including permits, I estimate that the cost of running power conduit and placing a 120V outlet at my carport would be about $2,000. A 240V 14/50 NEMA outlet would cost more and would be overkill for my situation.

    As an alternative, I was thinking I might be able to install a solar panel on the flat carport roof and use that power to charge my M3 battery during the 10 day intervals while I am away. I am in California with good sun most of the year.

    Any advice on the feasibility and cost of doing this would be super helpful. Thanks!
     
  2. pdx_m3s

    pdx_m3s Member

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    I believe you would need some sort of battery/storage to act as a load buffer between the highly variable solar panel output and what the onboard charger is drawing. You’re essentially building a very simple “off the grid” setup, which requires storage.
     
    • Like x 1
  3. Enginerd

    Enginerd Member

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    You'd probably have to size the system to provide at least say 15A continuously for a decent period of time. For a standard 120V outlet, you can dial down the Tesla charge current on the charging screen, but I can't remember how low you can go. I have a hobbyist-sized battery + 100W solar setup I use for charging mower batteries, etc. With essentially an oversized 100Ah car battery and a 120V 1500W (peak) inverter, I can't pull 15A even briefly, let alone continuously. So my dream of charging the car during a zombie apocalypse is just out of reach. Part of that sizing involves some really stout wires between the battery and inverter, and minimizing the length. I think I have #00 wires, but only 6" long. Sounds like you might still come in under the electrician's estimate though.
     
  4. ZOMGVTEK

    ZOMGVTEK Member

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    It's possible, and you could likely do it with no storage. However the costs to have a stable 15A/120V outlet would far exceed $2k in parts. Probably in the neighborhood of 4-5K in parts and labor would likely be at least as much. You'd need to have considerable overkill to have high confidence that the output would be stable as the car has no feedback and would stop charging if power dropped for any period of time. Storage would make this a bit more stable, but pose other challenges and add considerable cost and complexity on its own.

    Either way, this system would be a whole lot more sensible if it was grid tied so the excess power isn't useless. But if you didn't need to charge more than say 40 miles a day, id say 10K is a good ballpark, installed. The panels are cheap, but racking and install is generally quite costly. Unless you don't drive and are willing to charge at 5A or some absurd rate, I don't see this being sensible.
     
  5. Bobrrr

    Bobrrr Member

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    Thanks to the 3 of you for very useful comments. Based on your input, I'm going to get quotes to run either a 120v or 240v line from my meter and see if I can get it done at a reasonable price.
     
  6. swaltner

    swaltner Active Member

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    Yep, you’ll spend way more on an off-grid solar system than just burying a line.

    Definitely look for 240v options if you’re trenching already. The only cost delta is really the wire, which would be $1/ft. If a 120v install costs $2,000, a 240v/50a install “should” be $2,250.
     
  7. ZOMGVTEK

    ZOMGVTEK Member

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    You can run a 240V 15A 6-15 for maybe $20 over a 5-15 standard outlet 120V outlet. If it’s 200’+ though, you’re going to want to oversize the conductor or else there’s gonna be some nasty voltage drop under load. #10 is probably the smallest conductor I’d run. A NEMA 6-20 plug would get you down the road just fine. Way better than a 5-15 that’s painfully slow. You don’t need a 50A circuit, but the physical costs of the materials are not all that substantial depending on the area and if it’s run in conduit or not.
     
  8. PulseWidth

    PulseWidth New Member

    Joined:
    Jun 11, 2019
    Messages:
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    Location:
    San Francisco Bay Area
    I am attempting just this, but it will cost quite a bit. As part of a home upgrade to solar (9.57 kW system), I will be installing 2 (LG RESU10H) batteries with two StorEdge inverters as part of a grid-tied system. The batteries are to help keep the house running on a "critical loads" panel during power outages (of which we have had a lot of here in SF East Bay) and in preparation of PG&E outages during fire season.

    I haven't completed the install, but if folks are interested, I can follow up with my system and experience once it is fully operational. I plan on using my JuiceBox Pro 40 to regulate my charging times to peak solar output and sufficiently low amperage to only use our own self generated power. Of course this is theoretical and we'll see what the real-world results are here in a few weeks.
     
    • Love x 1
  9. Phlier

    Phlier Bluebird

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    I think you'll find that there would be a very large audience here, interested in following you through the entire process start to finish.

    As much information, video, etc. that you could provide would be eaten up by a lot of us. :)
     

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