Monday, 13 November 2017

My Observation of Tesla PowerWall2

My Tesla Powerwal 2 (PW2) summary, freshly installed just 3 days ago:
[UPDATED 7 May 2018: see point 6 below]
  1. PW2 can be installed in multiphase (mine is 3-phase). PW2 monitors each phase current using Current Transformer (installed by the installer of course).
  2. PW2 basically absorbs all your solar power instead of injecting them back to the grid. What is worth to be noted, although you have load on different phases, the PW2 will compensate this so that your electricity meter reads export as 'zero' (since Australian domestic electricity meters don't care on which phase you're consuming). So, in my example, I was using an induction stove top at 1000 Watts on the 'white' phase, and the PW2 injecting back to the grid at 1000 Watts at 'red' phase, resulting net zero export. To mention the obvious, PW2 inverter maxed out at 5kW power.
  3. Non-noticeable transfer time when the grid has failed. I've tested this 2 times: at first attempt, the solar panel inverter anti-islanding has to reset (causing the solar power to cut for about a minute). In the second attempt, the solar inverter didn't trip at all (as if nothing happen). I'm definitely impressed on this one. To mention the obvious, only 'red' phase of my home is backed up by PW2. Other phases are not. Now I can officially welcome mad max scenario!
  4. During daytime (when the solar panel is active), I've noticed PW2 constantly draws around 100 Watts from the grid, but not at night time. I can't find any info in the internet on the why, yet. My guess, PW2 requires power for its own functionality and ineffeciencies in converting AC to DC and somehow only compensates during daytime? 
  5. It is also worth to be noted, unlike the Tesla cars, users can't set the maximum charge level on PW2. My guess, Tesla is now extremely confident that this is no longer required. Maybe combination of newer chemistry and internal software to limit when required during hot days?
  6. My particular one consistently under report kWh used and exported to the grid by roughly 15 - 20% (compared to my grid provided meter). However, the solar energy kWh is spot on (compared to my soalr inverter kWh measurement). No idea the why. Anyone experiencing the same issue?

What it doesn't do and I wish Tesla will update this functionality sometimes in the future:

  • Change the timing on the 100-Watt constant draw from the grid. I wish this is user configurable. For example, to draw this at night time, or to use solar panel instead. For me who on Time of Use plan, this total of 1kWh on daytime is something I'm not willing to pay the grid for. Call me stingy.
  • Ability to charge PW2 from the grid during off-peak via the app. At the moment PW2 only absorbs power from solar panel. Since my solar panel is not enough for my usage, I'd love to have the ability to get cheaper electricity at night to be used by my household during peak time. Quicker ROI anyone?

Now, to how I use the Tesla app:

  • Once the installer enter account holder details via the installer page, your PW2 will be immediately visible on the Tesla app (you'll need wi-fi router for PW2 to connect to Internet). I haven't accessed the PW2 directly via the ethernet router (no reply). Will try again next time.
  • The visualisation of the app is indeed very useful. For a data hoarder like me, the visualisation has altered my energy usage. For example, now I know my inverter reverse cycle Air Conditioner doesn't have linear energy consumption (I thought it does). It has step changes, i.e. 2.4kW at full power, then 1.5kW, then 900 Watts at lowest power (in cooling mode). When the PW2 is low in charge, I deliberately turn off my air-con to minimise grid usage and happy with slightly higher room temperature (but still comfortable). My guess, sometime in the future, all home appliance will talk to each other (via ethernet router, just like the PW2 at the moment) and have AI (Artificial Intellegence) based on user preference on how and when to consume energy (whether to save energy, or maximum comfort).

So here is my data, just 1 day after it's being installed (grid data not shown for clarity):

Tesla PW2 App Visual

The data above is definitely not my average day. I had to travel 120-ish km on that day, so most consumption gone to EV (I'm guessing around 18kWh).

Now my debt has increased significantly again (thanks to PW2 as an expensive toy), so the family now have to be content living from boiled water and salt. At least we have a good-lookin' dead weight on the wall now (wheel added in MS Paint to make me feel less guilty by the dead weight):

[UPDATE 12 Oct 2020 for 2018 annual figure]:

No comments: