My attempt to live without paying for electricity using a PowerBanx home battery worked well on Day 1 so I was optimistic going into Day 2. As we have seen, the day started with the battery still half full at midnight. The night-time loads were small so there was still 30% in the battery at 8am and, as we saw, no grid electricity had been used by that point.

However, the day turned out to be disappointing. It rained and rained through the morning up until noon. Some solar electricity was generated but only enough to match the electricity being used in the house so the PowerBanx couldn’t charge and sat at 30% through the morning.

At noon the sun finally came out and stayed out for the rest of the day, but was pretty weak. The PowerBanx home battery charged up to 50% by 2pm. I was feeling confident that the sunshine was going to continue to improve so, partly because I was planning to show off my electric car that evening (a BMW i3), as an experiment I put the car on to charge.

However, charging the car takes a lot of power and, as the sun disappeared behind clouds, the PowerBanx started to empty fast. I stopped charging just before 3pm but not before the battery had dropped to its minimum level of 20%, i.e. it had been emptied. At 5.30 I tried again as the battery was back to half full but the sun was feeble so I stopped the charging after 45 minutes with the PowerBanx below 30%. I reset the car’s timer to charge on Economy 7 overnight instead.


We can clearly see the poor generation in the morning in the day’s charts. We can also see the effect of charging the car, with the PowerBanx battery’s state of charge (SOC) diving just before 3pm/1500 and again just before 6pm/1800.

Not surprisingly the PowerBanx battery now struggled to power the house for the evening, and in fact was empty soon after 9pm and I was back paying for electricity. I checked the meters again at 8am the next morning.


The daytime meter has moved on 4 units and the night-time/Economy 7 meter 18 units. The latter is to be expected as it’s from charging the car (for about £1.30), and at this time of the year it’s rather optimistic to expect to be able to do that from solar. However, by attempting to charge the car during the day I had ended up having to pay for grid electricity for the house and that was a big disappointment.

So I learned something from this – don’t attempt to:

  • power the house
  • charge the PowerBanx battery
  • charge an electric car

all from solar when it’s raining half the day. The result was that I had paid for grid electricity to run the house (about 60p) when I needn’t have.

I determined to do better – and did so the next day, see my Days 3 and 4 blog post.


Electricity costs for the house so far:

  • Day 1: 0
  • Day 2: 60p

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