While using our PowerBanx home battery got us through Day 1 without paying for any electricity to run the house, attempting to also charge the car on Day 2 had meant that we had ending up using some mains electricity to get through the evening (about 60p worth).

I should have learnt my lesson about not charging the car on a dull day – but I hadn’t entirely. Day 3 was quite a bit sunnier than Day 2 so I couldn’t resist having another free charge at about 1530.


I monitored the PowerBanx battery on my phone this time and once it had dropped to 2/3 full I stopped charging the car – thinking the remaining sunshine would be enough to fill it back up again. But it wasn’t, over the next couple of hours it barely matched the consumption in the house and the battery stayed at 2/3 full (see SOC – state of charge – in the chart).


That was better than Day 2 and was nearly enough: this time the battery powered the house until nearly 2am, but then we started to use a small amount of mains electricity before the solar started for the day at 6am.

Again I checked the meters at 8am:


I was disappointed to see that both the daytime and night-time meters had increased by 1 unit (from 63264 to 63265 and 24866 to 24867 respectively) which cost us about 23p for the 24 hours. Better than Day 2, but not free as I had hoped.

Naturally, on Day 4 having finally learnt my lesson, I completely resisted the temptation to charge the car at all. Even so, it wasn’t a particularly sunny day and the battery never quite got to 90% full.


However, with all of that stored electricity available just for the house the battery was still 60% full at midnight, and never dropped below 40% the next morning before the solar restarted and it began to refill.

I checked the meters again at 9am:


I was very pleased to see that the meter readings were still the same as the day before. A bonus I spotted for the first time was the red lights shining constantly on the meters, confirming that they couldn’t detect any electricity being used.

So in Day 4 we had achieved another day without paying for electricity even with the battery not receiving enough solar to get fully charged.

The weather forecast predicted a very sunny bank holiday weekend to come so I was really looking forward to Day 5.


Electricity costs for the house so far:

  • Day 1: 0
  • Day 2: 60p (caused by car charging)
  • Day 3: 23p (caused by car charging)
  • Day 4: 0
  • Average cost per day: 21p

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