Eeeep! My first bill in debit in 12 months!

If you have been following some of my previous blog posts you’ll note that I have been posting monthly (or so!) updates on the savings my family has had on our energy bills since adding solar and two Tesla Powerwall 2 batteries.

I’ve started to become more active on YouTube so have added some thoughts in the clip above but will drill down on some more of the analysis below. A special thanks to the user swainstm on Whirlpool who made some comments around my past analysis so I will take some of that into consideration below.

A caveat on some of the figures I comment on. I’m on an AGL TOU plan which actually makes it quite difficult to break down the figures per time period as the Tesla app isn’t very historical and our Enphase system counts all the battery charging as solar consumption. For the “pre-solar/battery” costs, I’ll use a standard all day figure of around $0.23 per kWh moving forward. The other item that makes it quite difficult is that Tesla calculates a month as the previous 31 days where that doesn’t always line up with AGL’s billing period so the figures could be slightly off.

June figures without Solar and Powerwall 2

  • Daily Supply Charge – $0.924 per day * 31 = $28.64
  • Power Usage (from grid) – $0.23 per kWh * 580 = $133.40
  • Total bill = $162.04

June figures with Solar and Powerwall 2

  • Daily Supply Charge – $0.924 per day * 31 = $28.64
  • Power Usage (from grid) – $0.23 per kWh * 22.7 = $5.22
  • Solar Credits (to grid) – $0.20 per kWh * 80.2 – ($16.04)
  • Total bill = $17.82

Powerwall 2 Efficiency and Utilisation

  • Efficiency: 83.4% – down by 2.5% since the last report. Could be due to the colder operating temperatures?
  • Utilization: 39.1% – up by 2.8% since the last report.

Savings specifically due to Powerwall

If we look at the raw data, our two Powerwall 2’s supplied 328kWh of energy to our house this month, that’s 57% of our total household use. Based on a modeled cost of $0.23 per kWh, that’s savings of $75.44 for the month


Author: Adam

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