2022-09-01

Battery, part 2

Tesla Gateway 2
This is just about the install. I have yet to get in to the details of APIs, and apps and so on. So just the install for now.

It is all pretty simple to be honest. Battery on the wall outside, and "gateway" box inside.

The gateway is put in line from the incoming power, so the tails in to the consumer unit had to be fished out and fed in to the gateway and then new tails to the consumer unit. The battery is then connected to the gateway. There is comms to the battery, and a current clamp for the solar incoming. The unit has ethernet, but also has wifi and cellular.

I say it is simple, but fishing the tails meant eventually making holes the other side of the internal wall. The holes through the wall to the battery outside involved big drills, and eventually an endoscope I happen to have! Both tasks probably involved about an hour of "no progress". But the job was done in the day, and nicely done by Green Park Power.

It is worth explaining, this "gateway" allows me to work off-grid as well, running just from the battery. Ideally, to do this, I need to put some circuits on a separate "no-backup" circuit. I'll get a small additional consumer unit installed for that. It will have the tumble drier, hot tub, heated kitchen floor, EV charger, on it. For now, we have the whole house on battery, which will not cope if we go over 5kW during a power cut.

Right now my solar and demand have, as normal, gone up and down, but the battery has balanced it all so zero grid usage, either charging or discharging the battery. That alone is quite amazing.

Tesla app

There are a lot of settings, and I have not even started to look at them. I need to read up on this, and work out the best way to keep my power usage sensible. I also need to mess with a couple more current clamps as I no longer see the final import/export on my own monitoring, or the solar edge.

Longer term I need to work out if there is a good tariff to be on, and separately if I can use an agile tariff in a clever way. What we do have is wiring for a second battery - but that may take 6 months to get.

First gripe: Cannot work out if any way to turn of WiFi AP SSID from it!

13 comments:

  1. I wonder if you could use the gateway API to control mechanisms that trigger when the battery is full? Perhaps to drive turning excess energy into heat and further squirrelling it away in a heat battery for your hot water or to heat hottub etc? I imagine the vehicle charger is already intelligent enough to interface like this.

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    1. Quite, I can perhaps incorporate using immersion heater, and hot tub controls in the algorithm as well.

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    2. Oh, and I don't have an EV - my son nicks some sunshine when he visits.

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  2. we use a myenergi 'eddi' to divert spare solar to the immersion heater when the 'zappi' hasn't got to the 1.2kw minimum the car wants (or the car is out)

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  3. Lithium batteries can be badly damaged by charging at low temperatures. I wouldhave thought that the battery should be fitted indoors. Is there anything in the Tesla manual warning about this? Perhaps it has a heater?

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    1. My understanding is Tesla are good at this stuff, and I think it may have a heater, but they do know when it is safe to charge, etc. They do cars as well you know :-) Outside is for safety as well.

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    2. If it's OK to charge below 0 C, I reckon it must have a heater and I expect that there's a way of detecting a failed heater. As you say, this stuff has been thrashed out in electric cars but the basic physics of lithium batteries can't be changed.

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    3. Page 8 describes the Powerwall deliberately raising it's own internal temperature during pre-conditioning: https://www.tesla.com/sites/default/files/pdfs/powerwall/Powerwall_2_AC_GW2_UK-EN_Installation_Manual.pdf
      I assume this thermal control system is what you're describing anon?

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    4. Yes, the paragraph at the bottom of that page spells it out. Don't expect great performance in long, cold spells.
      Don't know why my comments now come out as anonymous - it used to be as BillP.

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    5. The Powerwall is entirely designed to live outside, so nothing to worry about - it's not like someone chanced it outside - it is a supported/expected scenario.

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  4. TEP from Octopus looks good.. you become part of a virtual power network, and in return get rates of 24p/kwh for both import and export (used to be 12p but.. energy crisis..)

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  5. The always on WiFi AP is annoying. As is the bug where the Gateway's WiFi interface randomly fails to reply to ARP requests directed towards it for a period of time. No issues if you connect it via Ethernet, but having it randomly unreachable over WiFi is a pain. Fixed locally with a static ARP in the router.

    If you have an EV, the Octopus Go package is good. Put the Gateway in Time-Based Control and it'll charge overnight at the off-peak rate if the "AI" determines next day's solar will be insufficient. The "AI" was rubbish up until around March '22, but has been pretty decent since then.

    Your meter will still register some grid usage. The Powerwall takes a few mS to respond to changes in demand, especially if switching from charging to discharging. So you'll import briefly from the grid until the Powerwall picks up the slack.

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    Replies
    1. That is interesting. One issue is the battery cannot run the whole day so likely paying higher rate using power later in the day. Once I have a second battery I expect we can. I don't have data for winter yet to see how that goes either.

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