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Solar charged, portable, battery-powered charger

Discussion in 'Model S: Battery & Charging' started by hughconn, Apr 1, 2014.

  1. hughconn

    hughconn Member

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    I built something that I hoped would be able to charge my Tesla while parked at work. I have a solar panel attached to a 12 volt battery attached to a 2000 watt inverter. The result is I produce 120 volts 12 amp juice. I thought that this would be sufficient to recharge the Tesla as if it was plugged into a normal 120 volt US home outlet. If so, I would get 3 miles per hour and after 9-10 hours at work almost replace the juice used to drive to work. But, of course it is not working.

    At first my inverter was under powered and the green light on the remote charger was red (not enough power). Upgraded to a 2000 watt inverter. With a 2000 watt inverter I get the green glow on the charger, but the car starts to charge then stops. The car shows 119/120 volts and 12 amps. Am I not pulling enough amps to feed the Tesla? Remember the Star Trek episode where the alien creature was sucking the juice from the enterprise and draining all the power? My situation reminds me of this. Only I apparently do not have enough juice to feed the beast.

    So, do I need an even bigger inverter 3000 watt? Or do I need more than 1 battery to generate adequate juice? Or am I chasing a dream and this just won't ever work?

    Now for the obvious remarks: Why not just plug in at work? Not near an outlet. Why bother if you have enough juice left to drive home? It's the challenge, my friend! Don't you have anything better to spend your free time and money on? Apparently not!

    Constructive feedback welcome.:biggrin:
     
  2. Raffy.Roma

    Raffy.Roma Active Member

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    Actually it's my dream to build a portable solar power system useful to charge the Model S. Maybe that some TMC Members could build such a system?

    IMO it's difficult because you need big solar panels to get enough power to charge the Model S. But maybe a solution could be found anyway to build a portable solar power system to charge the Model S?
     
  3. rjcbox

    rjcbox Member

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    Having solar for the home, I know the output from the panels is never constant. Different angles of the sun throughout the days, slight overcast, a larger cloud cluster goes by, etc. Even w/ apparently perfect conditions, my second-to-second meter output readings fluctuate constantly. On the other hand, your standard AC output is fairly constant. Maybe you need a very steady feed of juice which the portable system cannot produce.
     
  4. miimura

    miimura Active Member

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    Try monitoring the voltage and current going into the DC side of the inverter. Also, consider the size of the battery in Watt-Hours and the power from the solar panel(s) and the power going into the inverter.

    From the sounds of it, you may have as much as 1,700 Watts going into the DC side of the inverter, given about 85% efficiency. You would need 7 250 watt panels at rated power (which only happens in perfect conditions) to keep up with that. A large lead acid car battery might have 1200 watt-hours if discharged slowly, less if drained in an hour.

    Is this worth it to get just a couple kWh into your Tesla?
     
  5. VolkerP

    VolkerP EU Model S P-37

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    Did you try to lower the charging current in the Model S? 12A is max for the 120V NEMA 5-15 adapter.
    It would be good to know the solar generator capacity in W and the capacity of your 12V battery in Ah of your portable system.

    I calculated 10sq m (~100sq ft) of solar modules to replenish the energy of a 10 mile commute during one day. I dream of a DC charging mode where the model S just sucks up the watts of a solar canopy.
     
  6. mnx

    mnx 2013 P85

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    #6 mnx, Apr 2, 2014
    Last edited: Apr 2, 2014
    How big are the cables connecting the battery to the inverter? FWIW 12 amps @ 120V would be 120 amps @ 12V!!!

    FWIW I'd use at least 2AWG wire to connect the battery to the inverter.
     
  7. tezco

    tezco Sig P85

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    You would need a much larger battery bank if you plan to store any of your solar output. Otherwise you will discharge a single 12V in a matter of minutes at a discharge rate of 120 Amps (and that is assuming 100% efficiency converting the juice in the battery back to 120V).
     
  8. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    #8 FlasherZ, Apr 2, 2014
    Last edited: Apr 2, 2014
    A few more things are needed... does the UMC flash any red lights when the car stops charging? What color is the car's LED ring, what messages are seen when it stops?

    I can think of a few things that might be the culprit - you picked up on one in another thread, that the Tesla does not seem to like isolated / non-bonded power sources (except in Norway, where they make a special UMC). When you use an inverter or a generator, this can be an issue. In some cases, you can solve this by bonding ground to neutral in the inverter -- HOWEVER, you must consult the inverter instructions or contact the inverter manufacturer! Sometimes, the inverter's design can create serious problems for bonding, if they ground the case to the DC negative input.

    The Tesla could be seeing wacky voltage fluctuations, it will refuse to charge on some generators for this reason. There are ways of solving this -- batteries, giant caps on the DC side, etc.

    As mentioned, wire size is important, you'll need heavy cables to support the DC draw.

    The power factor isn't perfect on a charger power supply, so your inverter will need to be up to the task for continuous loads. Many "2000W" inverters are really ~1200-1500W continuous, with peak of 2000W. To consider power factor and other items, you'll need to make sure your inverter is capable of at least 1800 VA continuous operation for that 12A @ 120V charging.
     
  9. swaltner

    swaltner Member

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    Not quite portable, but EV ARCâ„¢ : is a commercial product that does this. 9 solar panels (2.3 kW solar array) with a large on-board battery to store the power that is generated. Obviously at a price of $40k, this is in a different ball park from what you're talking about, but is likely along the lines of what you would be looking for to solve the discharge issues on a single lead acid battery. The reason this commercial product makes sense is that there isn't a need to trench and tear up your parking lot. The trenching and other installation costs can eat you alive on installs, especially at commercial sites.
     
  10. hughconn

    hughconn Member

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    Turns out most inverters generate voltage with a modified sine wave, and the Tesla's sensitive electronics seek pure sine wave voltage. So the inverter needs to be a pure sine wave type. Further, to draw 120 volts at 15 amps for minimum of 5 hours would require a battery pack (marine type deep cycle) of around 6-12 volt batteries and 3 full-sized solar panels to feed them while being drawn on by the inverter. My set-up used only 1 battery and it would be fully drawn in around 20 minutes, not quite 1 mile of re-charge for the Model S. That's where I draw the line. It becomes too unwieldy and is certainly not portable with that configuration. Maybe in 5 years or so the practicality will make more sense. In the end, it is really really not practical - at least today. Thanks for the posts and notes.

    However, perhaps for a Volt or a Leaf it might be...
     
  11. Raffy.Roma

    Raffy.Roma Active Member

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    Anyway this thread has been very interesting. Meet you on this thread in 5 years.
     
  12. zdre

    zdre 40kWh Model S P6415

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    I really thought this was an April Fool's joke
     
  13. tezco

    tezco Sig P85

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    Yes, and in the dead of winter a lot of that 120V will be going directly into the pack heaters to keep the battery warm enough for optimal charging, and therefore not not giving you a single mile of driving re-charge.
    I've got 32 x 325 watt PV panels up on my garage roof, which is enough to keep up with my 30A charging rate on sunny days in the dead of winter from about 11am to 2pm; otherwise I'm drawing at least partially from the grid. You would really need a carport covered with panels to make the project fly.
     
  14. jyinger

    jyinger Member

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    I am considering solar panels on the roof our our house to feed Tessie. Have any of you had Solar City or Verengo install solar panels? Other solar panel companies? Has it reduced your monthly $$ to Edison?
     
  15. Chipper

    Chipper Active Member

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    I just had 10kW worth put on my roof. It was just finalized last week and commissioned by the electric company. I would loved to have had Solar City do the work, but they do not operate in Tennessee or even neighboring Georgia so I used a local company, SolarTech and they were fantastic! SolarTech tells me that the 10kW system will most likely meet ALL my electric needs (including the Tesla). Based on what I have produced so far--BTW watching the electric meter run crazy fast backwards is a HOOT!!--I believe SolarTech is correct.
     
  16. tga

    tga Active Member

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    Make sure to do your homework before signing a contract. There are 3 ways finance the system:

    1. Outright purchase (cash or financed). You own the system and receive all the tax credits, incentives, etc.
    2. Power Purchase Agreement. The installer owns the system and receives all the tax credits, incentives, etc. You pay per kWh used (essentially, you are buying electricity from the installer vs the local utility).
    3. Lease. The installer owns the system and receives all the tax credits, incentives, etc. You pay a flat monthly rate to finance the system.
    AFAIK, SolarCity only does PPA's, and Verengo does leases (I think). Depending on where you live and the incentives available in your state, and how the lease/PPA is structured, #1 may be a better deal long term. There are financing programs available that can get you a customer-owned system with no upfront cost.

    DSIRE is a good site for researching the incentives in your area: http://www.dsireusa.org/

    I went with #1 (a 9kW purchased system). I live in Mass, in an area fed by a municipal utility (ie, town-owned power plant). Our utility does not allow leases or PPA's. All grid-tied systems must be owned by the customer. We also don't get net metering; they pay us the wholesale price for power fed to the grid (ie, "generation charge" only - $0.08/kWh) and charge retail for power drawn from the grid (generation+distribution - $0.17/kWh). In MA, only investor-owned utilities are required to do net metering; municipals are not required to.
     
  17. rlang59

    rlang59 Member

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    SolarCity does PPA, lease, and sells systems.
     
  18. tga

    tga Active Member

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    I found lots of references to PPA's and leases on SolarCity's site, but nothing about outright sales. But since I've already got a system, I'll admit I got bored quickly and gave up. :wink:

    BTW, it looks like Verengo also does PPA's.
     

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