Off Grid Power

I was wondering what I could run off grid and wanted to start with an off-grid phone experiment, not really that radical, but more something for me to test the latest technology and to do the calculations around batteries, solar panels and power consumption – does it really add up?

2nd December 2017:

  • Samsung Phone and BERNET Solar PowerBank fully charged off mains, the experiment starts now.
  • How many days can I go before I have to resort to an alternative form of charging?


  • Battery Capacity:24000mAh
  • Output:5V/2.4A
  • Input:5V/2.1A
  • Solar Panel:5V/200mAh 1W

The solar panel is just meant to be a top-up, but lets have a go. 5 hours of input from the sun every day should be enough to top-up what I remove with my phone.


  • Samsung J5
  • 3000mAh battery
  • Estimated battery life from full charge is 52h 48m based on last 7 days of use
    • This means power demand from the phone on average is 3000/52.8=56.8mA
    • Nominal voltage of the battery is 3.6V
    • 6×0.0568=0.204W on average

The average numbers suggest that I’m going to be ok with running my phone on solar power acquired by the powerbank whilst I’m away from base.

10th December 2017:

  • I’ve charged the phone at least twice in the last week and still going strong.
  • Battery bank shows white light still and so either I’ve not used much or the solar is keeping up.

21st December 2017

  • Could only charge phone to 26% and stopped
  • So, this has worked for 19 days
  • 0.204 x 24 x 19 = 88Wh used over 19 days = 93.02Wh
  • Battery bachup + phone = 24Ah x 3.6V + 3Ah x 3.6V = 86.4Wh + 10.8Wh = 97.2Wh available in both devices
  • This implies:
    • energy used = energy in both batteries at the start
    • zero solar power…..


This is a fine power bank, but the solar panel is next to useless in the UK in December.

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