Understanding your solar data

Unleash your inner geek!

Reading the graphs and logging the data may seem very geeky and boring, but by understanding what your solar panel system does, it can really help you get the best settings and, in many cases, save you a lot of money. At the very least, by checking from time to time, you can see if something has gone wrong.

This graph (from the Givenergy app) is based on a cold day in March. The temperature was -1º at night and rose to 6º during the day, which was mostly fairly sunny. The house is a 5-bedroom 1920s detached house with heat loss approaching 16kWh. All energy used in the house is electric, with the highest use being for the Air Source Heat Pump and Hyundai Kona EV.

Electricity is supplied by Octopus Energy on the Intelligent Go Tariff, which means cheap off-peak 7.5p per kWh from 23:30 – 05:30, then 30.6p during peak times. Off-peak times are shown on the graph by shaded background.

Given Energy 5kWh Inverter 2 x Given Energy 9.5kWh batteries. (Large storage due to high house electricity demand and to take advantage of 6 hours of off-peak charging).

The heat pump is weather-compensated so that it runs at high-temperature flow when it is cold outside and low temperature when it is warmer. At night when it is -1º, it can be running at about 52º using 6k – 7kWh, but during the day, it generally runs at 45º and uses between 2 – 4kWh.

The blue line shows the battery %. The grey shaded background shows off peak tariff.

  1. Battery on timed charge from 23:30 – 05:30 off peak. This is just long enough to get it to 100%
  2. Teal colour shows (very high) house load (not inc battery). Most of this is heat pump and car charging.
  3. Red area below the line shows grid import which is for the heat pump and car as above, but also plus battery charge. The heat pump is set to warm the house well during the off peak rate, and then set back at 05:30 so then there are two hours of minimal load on the grid as the house is still quite warm.
  4. After a small boost at 07:00 the heat pump settles down to working efficiently and running off the battery.
  5. Solar generation runs heat pump so that:
  6. Excess solar is recharging battery.
  7. Heat pump is taking a rest as the house retains its heat.
  8. Battery has recharged fully so excess solar is exported to grid (at 15p per kWh)
  9. Heatpump comes back on and starts to discharge battery. Gradually uses more electricity due to weather compensation settings as temperature drops outside.
  10. Battery is fully discharged. Grid import takes over.

Although this was still a cold day, no significant energy was imported from the grid at peak times.

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