Earth Notes: Saving Electricity (2025)
Updated 2025-05-05.
2025
See the daily PV generation logs for 2025 as .csv and .png chart.
The gas meter has gone: we are electricity only at 16WW for . See the heat-pump activity fade out (heating off on the ) and diversion take over for DHW by the end of the month. With the additional grid battery and the energy stored in the DHW cylinder and Thermino heat battery, self-consumption was good and grid dependence low (~4%). Weekday 15-minute 2025-02: Trendline
hph4 heat pump electricity consumption (kWh) vs heating degree days (HDD12) with a linear fit. (Source CSV data, and as ODS spreadsheet.)
hph4 heat pump electricity consumption (kWh) vs heating degree days (HDD12) with a degree-2 polynomial fit. Electricity demand is expected to rise faster than linearly with HDD because higher HDD implies higher heat demand and lower CoP from the higher 'lift' required. (Source CSV data, and as ODS spreadsheet.)2025-03: Heat-pump Fadeout
2025-04: Self-consumption
con consumption and net imports for generated with sh script/storesim/load_profile.sh 202504. 
| 2025 | Electricity | |||
|---|---|---|---|---|
| Month | Consumed kWh (/d) | Generated -kWh (/d) | Period | Notes |
| 2025-01 | 425 (13.7/d) | -52 (-1.7/d) | 20251231T18:02Z to 20250131T18:00Z (31d) | Meter readings: electricity generation 51.7kWh, export 0.5kWh, import 374.0kWh (thus net consumption (I+G-E) 425.2kWh, self consumption ((N-I)/N) 12%). The Ecotricity bill for this month was lower than last January's even though this month was colder. The new bill was ~£130 for just electricity (about 100kWh more than last January) now that gas has gone. The previous January's bill was ~£160 of which ~£50 was gas. In effect ~100kWh of electricity more than substituted for ~500kWh of gas: an effective CoP of ~5, maybe, though ~100kWh of Thermino CoP 1 storage was being avoided too this month. Allowing for that suggests the equivalent of a ~200kWh rise in electricity against a ~600kWh fall in gas, ie an overall CoP of ~3. (Note that the months' billing days were slightly different, and the electricity unit rate fell but the standing rate rose.) For the month reported hph4 was 204kWh at ~89% coverage, thus likely ~230kWh. Linear regression of hph4 against HDD12 yields n=28, slope=0.96kWh/HDD12, intercept=0.07kWh, R^2=0.87. Due to an Eddi firmware fault between ~23rd and 28th, the underlying reported consumption data is partly wrong in that interval or entirely absent. Avoiding partial dubious data for those days yields n=25, slope=0.87kWh/HDD12, intercept=1.07kWh, R^2=0.88. The Enphase emailed monthly report for January (triggered ) says: produced (generated) 58.5kWh (max 4.8kWh on the 30th), consumed 425.9kWh (max 18.0kWh on the 4th), grid energy imported 378.7kWh and exported 0.1kWh, grid dependence 90% (min 68% on the 30th). HDD12=235 vs 199 last January. |
| 2025-02 | 353 (12.6/d) | -110 (-3.9/d) | 20250131T18:00Z to 20250228T18:20 (28d) | Meter readings: electricity generation 110.3kWh, export 6.0kWh, import 248.2kWh (thus net consumption (I+G-E) 352.5kWh, self consumption ((N-I)/N) 30%). The Ecotricity bill for this month was ~£20 lower than last February's even though this month was colder. For the month hph4 was 182kWh. Linear regression of hph4 against HDD12 yields n=28, slope=0.58kWh/HDD12, intercept=2.76kWh, R^2=0.64. The Enphase emailed monthly report for February (triggered ) says: produced (generated) 111.2kWh (max 10.1kWh on the 28th), consumed 333.7kWh (max 22.2kWh on the 16th), grid energy imported 244.8kWh and exported 4.8kWh, grid dependence 73% (min 32% on the 18th). HDD12=180 vs 91 last February. |
| 2025-03 | 356 (11.5/d) | -351 (-11.3/d) | 20250228T18:20 to 20250331T17:08 (31d) | Meter readings: electricity generation 351.4kWh, export 60.3kWh, import 64.7kWh (thus net consumption (I+G-E) 355.8kWh, self consumption ((N-I)/N) 82%). The heat battery (indeed all storage including off-grid) filled up for the first time this year on the 31st. Sunny month, but colder than last March. The Ecotricity bill for this month was ~£50 lower (more than halved) compared to last March, even though this month was colder. For the month hph4 was 98kWh. Linear regression of hph4 against HDD12 for the first 18 days of the month until we turned off space heating (though cold nights means that pipe-freeze protection runs compressor and pump) yields n=18, slope=0.50kWh/HDD12, intercept=1.61kWh, R^2=0.69. The Enphase emailed monthly report for March (triggered ) says: produced (generated) 353.0kWh (max 18.7kWh on the 30th), consumed 330.3kWh (max 15.2kWh on the 30th), grid energy imported 62.6kWh and exported 57.5kWh, grid dependence 19% (min 2% on the 29th). HDD12=124 vs 100 last March. |
| 2025-04 | 360 (12.0/d) | -533 (-17.8/d) | 20250331T17:08 to 20250430T17:23 (30d) | Meter readings: electricity generation 532.8kWh, export 188.6kWh, import 15.3kWh (thus net consumption (I+G-E) 359.5kWh, self consumption ((N-I)/N) 96%). This month we passed 42MWh exports and 47MWh generation on the first array (just under 62MWh generation total). The Ecotricity bill for this month was ~£20 lower (about halved) compared to last April. This month was marginally warmer. For the month hph4 was 17kWh. The Enphase emailed monthly report for April (triggered ) says: produced (generated) 534.0kWh (max 25.3kWh on the 29th), consumed 340.5kWh (max 17.5kWh on the 25th), grid energy imported 12.8kWh and exported 185.0kWh, grid dependence 4% (min 2% on the 29th). HDD12=50 vs 67 last April. |