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 and becoming a Supporting Member. For more info: Support TMC

Charge PW2 with no surplus solar?

Discussion in 'Tesla Energy' started by copilot&Dj, Jan 7, 2020.

  1. copilot&Dj

    copilot&Dj Member

    Joined:
    Oct 16, 2019
    Messages:
    7
    Location:
    Sonoma
    New system. 24 solar panels (size unknown at this point), and one Powerwall 2.

    I was not told during the planning stages that the PW only gets charged via excess solar panel energy. Before the panels were connected, we kept the PW charged up via the grid. Now having mistakenly flipped the to Time Based control, the PW is down to 18%, and we can’t charge it til the winter sun comes up tomorrow?

    I think it will be a problem, as this morning the panels were only pulling in 1.9 - 2.0 kW, but it will be going to the house and the PW at the same time?

    If I select ‘Backup Only’ mode, will all solar go strictly to storage? I hope so.

    I’ve also seen comments that ‘Backup Only’ mode won’t charge as fast as ‘Self Power’ mode. True? Is there a limit? (I don’t have enough sun I don’t think to do SP mode)

    Any pointers? Thanks
     
  2. power.saver

    power.saver Supporting Member

    Joined:
    Mar 4, 2018
    Messages:
    471
    Location:
    Arcadia, CA
    Backup mode will use 100% of solar to charge. Leave it in that mode for a few days and you'll be charged up again.

    In the winter, when solar production in low, you have to decide how to manage energy so as to keep your PW at a reasonable charge level for outages. You can also set a higher reserve and operate in Self Consumption mode, but you may not get much above your reserve if solar production is low.
     
  3. copilot&Dj

    copilot&Dj Member

    Joined:
    Oct 16, 2019
    Messages:
    7
    Location:
    Sonoma
    thank you. It’s starting to make sense a bit more. PW @ 18% now.
    We’ll see how many days of the 2.0kW for 1.5 hours daily worth of direct sun it will take to fill up. Lol.
     
  4. miimura

    miimura Well-Known Member

    Joined:
    Aug 21, 2013
    Messages:
    5,875
    Location:
    Los Altos, CA
    I have my Reserve set to 75% because my Winter generation produces about 5kWh per day at best. It just bounces off the Reserve every day and discharges what it can during Peak with Time Based Control. That Advanced mode will show up after the system has been commissioned for a few days.
     
  5. bob_p

    bob_p Active Member

    Joined:
    Apr 5, 2012
    Messages:
    3,548
    We have 44 350W panels with 4 PowerWalls, setting the backup reserve to 20% on our system that became operational two weeks ago.

    During sunny days, we've been pleasantly surprised to see the PowerWalls get close to a 70% charge by the time the sun goes down - and have been operating off grid using solar/PowerWall power from around 8AM to after 10PM.

    Since we don't have a buyback plan right now, we want to keep the PowerWalls below 100% and avoid wasting excess solar power.

    At least based on our experience so far, I'll likely increase our reserve percentage to 30 or 40% and then continue to monitor as the days get longer, and adjust downward.

    Tesla could help owners manage the backup reserve settings by adding a "dynamic" reserve option - that would automatically adjust the backup reserve based on the actual charge levels observed in the PowerWalls. If the PowerWalls stay below 90% for several days, then the reserve % could be increased. If the PowerWalls go above 95%, the reserve % could be lowered.
     
  6. miimura

    miimura Well-Known Member

    Joined:
    Aug 21, 2013
    Messages:
    5,875
    Location:
    Los Altos, CA
    Maximum daily solar generation varies slowly by season, so that's a better variable to use for adjusting the Reserve percentage during the low generating seasons. As the days get longer, I adjust the Reserve lower to allow headroom for the available solar generation. Eventually, in the early spring, my generation exceeds my Peak period usage, so usage is the gating item for how much the Powerwalls are discharged, not the amount of available generation.
     

Share This Page

  • About Us

    Formed in 2006, Tesla Motors Club (TMC) was the first independent online Tesla community. Today it remains the largest and most dynamic community of Tesla enthusiasts. Learn more.
  • Do you value your experience at TMC? Consider becoming a Supporting Member of Tesla Motors Club. As a thank you for your contribution, you'll get nearly no ads in the Community and Groups sections. Additional perks are available depending on the level of contribution. Please visit the Account Upgrades page for more details.


    SUPPORT TMC