Tesla Powerwall – Early Differences In Grid Consumption

It’s been just over 5 months since we had our Tesla Powerwall installed and I thought I’d give an early update on the difference it’s made to our grid consumption so far. It is still early days and I will provide another update once I have a few more readings – probably late next year.

Our electricity billing periods are:

  • Jan 16th
  • April 16th
  • July 16th
  • October 16th

Our Tesla Powerwall was installed on June 1st 2018, which means the July bill should have showed some difference in kWh grid consumption (especially given the lovely summer we had this year!) even though it was a partial month of having the Powerwall, whereas the October bill was a complete month of having the Powerwall in operation.

I think the graph says it all! Even on the July bill, we saved 266* kWh or a 37.5% drop and on the October bill we saved a massive 560* kWh or 70.3% drop!

I just wish we’d had the battery installed 6 weeks earlier to benefit even more from the fantastic summer weather we had this year! 🙂

* based on the average of units consumed 2013 to 2017

For those interested in the figures:

July October
2013 663 814
2014 694 778
2015 783 847
2016 724 792
2017 681 754
2018 443 237

… but solar panels don’t work in the winter!

I’ve had my solar panels since October 2011 (details about my system can be found on this post) and I’m always telling people how good they are. When I tell people about my solar panels, I get one question – “how much do they generate” and the second is a statement that always makes me want to bang my head against a brick wall – “… but solar panels don’t work in the winter!” Don’t they??

When I first started telling people they should buy solar panels, all I could them was how much electricity they would generate and potentially cut from their bill, but since then I’ve added monitoring to the system which uploads the data to the internet. After the person I’m talking to has used the infamous statement about not producing electricity in the winter, I then proceed to show them the stats from my solar panels.

In the UK, winter solstice is a day between 20th and 23rd December and for more than a week each side of winter solstice, there are less than 8 hours of sunshine in a day. It’s quite literally the worst generation time of the year for solar panels in the UK – especially combined with the weather that you can get at that time of year… But when the sun does shine in the winter, you can get very good solar output days!

This December gone, I checked my system from work during lunch (as I do most days! sad, yes I know…) and noticed the solar panels had heated the hot water. To heat the hot water, there has to be enough energy generated by the solar panels to not only cover the house’ standby usage (350 ish W/h), any additional power being used by family members and also the 1kW/h immersion.

What’s more impressive is that the date was 16th December!
(the red block indicates the immersion is switched on)
16dec15

In fact we even had brief solar water heating on the 19th and 20th but they aren’t as visually impressive…
19dec1420dec14

But what all three of those charts show is that solar panels do work in the winter. They can even generate enough electricity to cause a surplus and power devices around the home!

It is true that the panels do not generate as much electricity during the winter, due to the angle of the sun in the sky and the length of the day, but we still generate in the order of 100kW/h of electricity each December.
last12monthsapr15

And on a perfect day, it’s possible to generate 9kW/h.
6dec14