TMC is an independent, primarily volunteer organization that relies on ad revenue to cover its operating costs. Please consider whitelisting TMC on your ad blocker or making a Paypal contribution here: paypal.me/SupportTMC

DC Charging of the Model S from a DC Home PV Solar Installation

Discussion in 'Charging Standards and Infrastructure' started by TonyWright, Nov 13, 2011.

  1. TonyWright

    TonyWright New Member

    Joined:
    Nov 13, 2011
    Messages:
    4
    Location:
    West Newbury, Massachusetts USA
    I have a 9 KW (40 panel) Grid tied PV Home Solar Installation that produces more power than I need for my home. We planned this on purpose to have excess power to charge a Tesla Model S. Of course I can set up a 240V AC charging station, but then I am converting DC from the panels to AC, and then, on board the Tesla, back again to DC, suffering significant power loss through two inverter conversions. It would seem pretty straightforward for the DC current from the panels to be gated through a solid state current controller to charge the Prius batteries directly without inverters. Does anyone know if Tesla or a third party will be manufacturing such a system. Similar systems may be already available for people with off-grid solar home installations that power lead acid battery storage banks.

    Especially in Europe or Japan with very high gasoline prices, I would think this approach really improves the economics of EV ownership. I would think solar city and Tesla would get together to write a lease agreement for tesla + Solar PV installation as a package!
     
  2. VolkerP

    VolkerP EU Model S P-37

    Joined:
    Jul 6, 2011
    Messages:
    2,455
    Location:
    Germany
    #2 VolkerP, Nov 13, 2011
    Last edited: Nov 13, 2011
    Hi Tony,

    charging from PV was discussed before here
    or in the TMC forum here and here.

    The baseline is, there is no economic point in this approach. If you got a lot of cash to burn, you might set up an off-grid / island system.
    Feeding DC to your batteries means, you either run out of sun before your car is full or you must dispose surplus energy. You need VERY big battery storage banks to balance production and consumption capacity for an electric car.
     
  3. Robert.Boston

    Robert.Boston Model S VIN P01536

    Joined:
    Oct 7, 2011
    Messages:
    7,842
    Location:
    Portland, Maine, USA
    Tony, you also need to look very closely at the value of Massachusetts "Solar Renewable Energy Credits." These are stupid-valuable (~40 cents/kWh), so you may be a whole lot better off financially selling your solar power to the grid and buying generic power to charge. This is just a bookkeeping transaction; your contribution to reducing pollution is unchanged regardless.
     
  4. TonyWright

    TonyWright New Member

    Joined:
    Nov 13, 2011
    Messages:
    4
    Location:
    West Newbury, Massachusetts USA
    Hi Volker,

    I already have a grid tied system so I can easily take the recommendations of the previous posts, But I see many one can buy a DC "charge controller" that is 93-98% efficient for charging home battery banks. Instead I suggest Tesla and PV companies supply a similar charge controller for shunting DC power direct to the Tesla when the sun is strong, thus avoiding two inverters at 0.85 x 0.85 = 72% efficiency. And to reply to Robert, I do have the SERC credit system in place. It is based on net metering so I diminish my credit if I charge from the grid.
     
  5. Lloyd

    Lloyd Active Member

    Joined:
    Jan 12, 2011
    Messages:
    4,886
    Location:
    San Luis Obispo, CA
    tony,

    If you are getting say 15 cents per KHW when your PV panels are producing and you are charging at night at say a cost of 6 cents per KWH. You have a pretty big effeciency in cost to overcome. I believe if you run all the numbers, charging from the PV array directly is not the way to go.
     
  6. VolkerP

    VolkerP EU Model S P-37

    Joined:
    Jul 6, 2011
    Messages:
    2,455
    Location:
    Germany
    There seems to be no economic point in charging directly from PC. You can justify that investment only with other topics, e.g.
    - prove that anybody can do it (same like driving an EV)
    - get autonomous energy supply in case of grid outage (there were some roadster owners immobilized this year during Irene)
    - take overall energy efficiency to the possible maximum

    any other ideas?
     
  7. TEG

    TEG TMC Moderator

    Joined:
    Aug 20, 2006
    Messages:
    17,252
    Location:
    Silicon Valley
    I think you covered it. This question comes up from time to time as it just seems "elegant" to take DC directly from solar panels and charge the battery pack directly. Unfortunately the irregular voltage output, and irregular current output from Solar panels means that you still likely need a bunch of electronics in between to treat the batteries right and you are limited to charging during daylight hours only.
     
  8. W.Petefish

    W.Petefish Active Member

    Joined:
    Apr 29, 2011
    Messages:
    1,059
    Location:
    North Texas (DFW)
    The only economical way to do this is with a grid-tied system using micro inverters.

    But if you want to do something like an off-grid system, it'll cost at least $30k. (figuring $16k for the batteries alone) Not to mention that the size of the battery array that would be needed presents serious space issues. (think truck container just for the batteries) If you had an implausibly large array you could do it, BUT Tesla has repeatedly said that they are not going to sell the DC fast charger. (I tried to get one installed, and was even willing to pay for the install and they still turned me down.)
     
  9. widodh

    widodh Model S R231 EU

    Joined:
    Jan 23, 2011
    Messages:
    4,822
    Location:
    Middelburg, The Netherlands
    This thread is old but still relevant. Now that there is a CHAdeMO adapter for Model S, wouldn't it be possible to build a mini-CHAdeMO charger at home?

    As far as I know you can charge with as little as 1A using DC. So if your Solar array is generating 1kW you can put that directly into your Model S. Super slow, I know, but a lot more efficient then going from DC -> AC -> DC.

    The DC protocols are also much more advanced then the J1772 AC signaling.

    Would be kind of cool if you could charge a Model S (or any CHAdeMO vehicle) using DC directly from a solar array.
     
  10. FlasherZ

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

    Joined:
    Jun 21, 2012
    Messages:
    7,019
    I'm not familiar with the DC protocols, but am wondering if they would permit a rather sudden decrease in power availability (e.g., clouds) without generating an error on the car?
     
  11. widodh

    widodh Model S R231 EU

    Joined:
    Jan 23, 2011
    Messages:
    4,822
    Location:
    Middelburg, The Netherlands
    I don't know either, I would love to read the specs somewhere. But as the internal charger of the car is by-passed I think that the outside charger is in full control.
     
  12. AWDtsla

    AWDtsla Active Member

    Joined:
    Mar 3, 2013
    Messages:
    2,135
    Location:
    NE
    You would still need DC-DC conversion. Supercharger/onboard/chademo are not just AC-DC converters, they have control over the DC level. You can't just take solar panels and plug them directly into a battery. You could try, but that system would be extraordinary inefficient as it would throw away any energy produced above or below the required voltage. DC-AC-DC conversion isn't so bad, just multiply the two efficiency numbers together. There's not much to gain.
     
  13. Chris TX

    Chris TX Active Member

    Joined:
    Sep 30, 2013
    Messages:
    1,486
    Location:
    Dallas, TX
    Solar panels-powerwalls-CHAdeMO would do it. If there's a way to dial down the DC amps advertised to the car, it would allow for continuous charging. The PowerWall would just be to absorb any fluctuations.

    Electric Motor Werks, Inc. - QuickCharge-25000 HV - a 25kW PFC charger for HIGHER voltage batteries
     
  14. wk057

    wk057 Senior Tinkerer

    Joined:
    Feb 23, 2014
    Messages:
    4,722
    Location:
    Hickory, NC, USA
    I charge my two Model S with my off-grid solar system. When there is sufficient sun the cars do charge directly from the PV power without using battery storage. PV->Charge Controllers->Inverters->Model S AC to DC Charger->Battery. Long road. By my estimates I end up with about 77-82% of the incoming PV power at the panels as power in the Model S battery this way.

    I think a direct DC-DC converter cutting out the DC->AC inverters and onboard AC->DC chargers would be a little more efficient... but would be pretty complex and probably not worth the effort for maybe a ~10% efficiency gain. In my case I would need something like a 500 amp DC input from my main DC bus for my system to convert to 20kW worth of DC power for the Model S. Those components aren't going to be cheap either.

    Long story short, unless you designed the system with this in mind from the beginning, and were willing to just accept that it isn't cost effective, there really isn't going to be a good cost benefit to doing something like this. It would likely be cheaper in the long run to just add 10% more PV to account for the efficiency losses.

    Now I would like to get something like a 40-50kW DC charger for myself... but probably not worth the effort either. lol.
     
  15. Chris TX

    Chris TX Active Member

    Joined:
    Sep 30, 2013
    Messages:
    1,486
    Location:
    Dallas, TX
    Couldn't you just tap into the PV-Battery DC high voltage lines and connect it to a CHAdeMO charger? It would pull from both PV and battery.
     
  16. wk057

    wk057 Senior Tinkerer

    Joined:
    Feb 23, 2014
    Messages:
    4,722
    Location:
    Hickory, NC, USA
    Doesn't quite work like that, at least not for my setup or any other configuration I can think of. The mid-voltage PV (~170V for me) is connected to charge controllers which regulate the voltage that goes to the batteries (~38-50V, depending on SoC) at high efficiency (93+% usually). That isn't really bidirectional either. Nothing can feed from battery to PV.

    Edit: For my setup the best place to tap would be the main DC bus (~44V nominal) with a high efficiency DC-DC step-up converter of some sort to reach Tesla pack voltages.
     
  17. green1

    green1 Active Member

    Joined:
    Mar 25, 2014
    Messages:
    4,116
    Location:
    Calgary, Alberta, Canada
    That said, if the batteries were configured at a higher voltage, it should be trivial. (though few setups do that)
     
  18. Bangor Bob

    Bangor Bob Member

    Joined:
    Jan 5, 2015
    Messages:
    485
    Location:
    Bangor, ME
    You'd need to build a Chademo that accepts DC input, they're mostly expecting to receive three-phase AC, aren't they? At least, the one ABB unit I just checked the specs on does.

    [edit] And variable DC input, at that. Ick. You would need a very flexible (and efficient) DC/DC converter. [/edit]
     
  19. wk057

    wk057 Senior Tinkerer

    Joined:
    Feb 23, 2014
    Messages:
    4,722
    Location:
    Hickory, NC, USA
    Yeah, higher voltage pack would be ideal, but a lot more safety related mechanisms needed in that case vs low voltage. Tesla cheats with the PowerWall by using a built in DC-DC. The issue is the availability of off-grid inverters that can utilize a HVDC battery bank.

    You would still need to regulate the voltage getting into the car, though, regardless.
     

Share This Page