Earth Notes: Saving Electricity and Gas (2017)Updated 2021-09-10.
2017 data (kWh: e used 1862, e gen -3794, g 3423).
Off-grid 99.2kWh captured by primary (MPPT) solar controller.
See gas kWh vs heating degree days (HDD) regression for 2017 as .png chart.
2017-05: Ecotricity sent our annual summaries for electricity and gas, stating that we had used just over 1.3MWh of electricity (~£270) and a ~4.2MWh of gas (~£262).
The gas figure is higher than usual, given that it was a cold winter. ~3.5MWh would be more typical (maybe ~£250).
Given that we don't yet have a heat-pump, but that resistance heating is beginning to approach the carbon intensity of gas on the GB grid (currently ~300gCO2/kWh vs ~190gCO2/kWh), what would be the effect of moving from gas to electricity for all heat including water (DHW)?
At ~17p/kWh for electricity that 3.5MWh would be ~£600. But getting rid of gas and its standing charge and an annual gas boiler inspection/service would leave us 'just' net ~£250 per year worse off. So we might expect a £900/year electricity bill, rather than a £550 dual-fuel total (+~£100 maintenance).
Moving all our DWH consumption to solar PV that we'd otherwise export (eg with the help of a resistance-driven Sunamp store) would be roughly cost neutral, since the gas per-kWh cost is similar to what we are paid for electricity exports.
Even in the depths of winter, we export in electricity ~10% of what we consume in gas. A heat-pump and store could double that to ~20%, still requiring us to import the remaining 80%. In the shoulder months with a suitable Sunamp-like store we could probably cover all space heating. Without a heat-pump the effect on utility bills of using our own power locally is roughly neutral, though kind to the grid in avoiding shipping that energy back and forth.
2017-09-22: I just had to fork out ~£250 for a boiler repair, most of which was the cost of a new diverter valve. (And it took several attempts to find someone available, which ate a lot of time.)
2018-01-01 18:23Z: total solar PV generation from the grid-tied PV to date, as reported via the inverters and the Sunny Beam, is 33,666.4kWh.
|Month||Consumed kWh (/d)||Generated -kWh (/d)||Consumed kWh (/d)||Period||Notes|
|2017-01||207 (6.7/d)||-71 (-2.3/d)||867 (28/d)||20161231T18:29Z to 20170131T18:44Z (31d)||Meter readings: electricity generation 70.6kWh, export 41.1kWh, import 177.7kWh (thus net consumption (I+G-E) 207.2kWh); gas ~77.2m^3 (so 867kWh @ 11.1kWh/m^3). |
HDD12=248 vs 173 last January.
|2017-02||163 (5.8/d)||-109 (-3.9/d)||497 (18/d)||20170131T18:44Z to 20170228T23:37Z (28d)||Meter readings: electricity generation 109.4kWh, export 78.8kWh, import 132.4kWh (thus net consumption (I+G-E) 163.0kWh); gas ~44.8m^3 (so 497kWh @ 11.1kWh/m^3). |
HDD12=139 vs 199 last February.
|2017-03||166 (5.4/d)||-300 (-9.7/d)||357 (12/d)||20170228T23:37Z to 20170331T16:29Z (31d)||Meter readings: electricity generation 300.2kWh, export 244.3kWh, import 110.0kWh (thus net consumption (I+G-E) 165.9kWh); gas ~32.1m^3 (so 357kWh @ 11.1kWh/m^3). |
HDD12=77 vs 162 last March.
|2017-04||143 (4.8/d)||-482 (-16/d)||117 (3.9/d)||20170331T16:29Z to 20170430T20:45Z (30d)||Meter readings: electricity generation 481.9kWh, export 407.5kWh, import 68.8kWh (thus net consumption (I+G-E) 143.2kWh); gas ~10.5m^3 (so 117kWh @ 11.1kWh/m^3). |
HDD12=65 vs 104 last April.
|2017-05||149 (4.8/d)||-528 (-17/d)||142 (4.6/d)||20170430T20:45Z to 20170521T19:54Z (31d)||Meter readings: electricity generation 527.7kWh, export 450.5kWh, import 71.5kWh (thus net consumption (I+G-E) 148.7kWh); gas ~12.8m^3 (so 142kWh @ 11.1kWh/m^3). |
HDD12=23 vs 23 last May.
|2017-06||139 (4.6/d)||-622 (-21/d)||109 (3.6/d)||20170521T19:54Z to 20170630T19:28Z (30d)||Meter readings: electricity generation 621.7kWh, export 545.4kWh, import 63.1kWh (2.1kWh/d) (thus net consumption (I+G-E) 139.4kWh, self consumption ((N-I)/N) 55%); gas ~9.8m^3 (so 109kWh @ 11.1kWh/m^3). |
HDD12=1 vs 2 last June.
|2017 running total (Jan--Jun)||967 (5.3/d)||-2112 (-12/d)||2079 (11/d)||20161231T18:29Z to 20170630T19:28Z (181d)||Implies total footprint to date -46kgCO2: electricity (average 223W gross) -492kgCO2e @ 0.43kgCO2/kWh (netted), gas 395kgCO2e @ 0.19kgCO2/kWh.|
|2017-07||147 (4.8/d)||-561 (-18/d)||105 (3.4/d)||20170630T19:28Z to 20170731T18:56Z (31d)||Meter readings: electricity generation 560.5kWh, export 477.3kWh, import 64.2kWh (2.1kWh/d) (thus net consumption (I+G-E) 147.4kWh, self consumption ((N-I)/N) 57%); gas ~9.5m^3 (so 105kWh @ 11.1kWh/m^3). |
HDD12=0 vs 0 last July.
|2017-08||97 (2.9/d)||-519 (-16/d)||60 (1.8/d)||20170731T18:56Z to 20170902T17:26Z (33d)||Meter readings: electricity generation 519.0kWh, export 472.3kWh, import 50.1kWh (1.5kWh/d) (thus net consumption (I+G-E) 96.9kWh, self consumption ((N-I)/N) 48%); gas ~5.4m^3 (so 60kWh @ 11.1kWh/m^3). |
Two weeks' holiday reduced fuel demand as expected. Baseline gas demand is ~0 at this time of year (demand DHW only). Baseline electricity demand is ~1kWh/d, mainly for fridge (imports 0.8kWh/d while away). Compare daily consumption w/ July, given ~50% absence this month.
HDD12=1 vs 0 last August.
|2017-09||143 (5.1/d)||-287 (-10/d)||113 (4.0/d)||20170902T17:26Z to 20170930T19:26Z (28d)||Meter readings: electricity generation 287.3kWh, export 234.7kWh, import 90.8kWh (3.2kWh/d) (thus net consumption (I+G-E) 143.4kWh, self consumption ((N-I)/N) 37%); gas ~10.2m^3 (so 113kWh @ 11.1kWh/m^3). |
Reduced support from off-grid may account for higher electricity.
HDD12=10 vs 2 last September.
|2017-10||150 (4.8/d)||-180 (-5.8/d)||101 (3.3/d)||20170930T19:26Z to 20171031T18:34Z (31d)||Meter readings: electricity generation 179.7kWh, export 142.3kWh, import 112.1kWh (3.6kWh/d) (thus net consumption (I+G-E) 149.5kWh, self consumption ((N-I)/N) 25%); gas ~9.1m^3 (so 101kWh @ 11.1kWh/m^3). |
HDD12=18 vs 38 last October.
|2017-11||179 (6.0/d)||-91 (-3.0/d)||344 (11/d)||20171031T18:34Z to 20171130T22:12Z (30d)||Meter readings: electricity generation 90.6kWh, export 63.0kWh, import 151.5kWh (5.1kWh/d) (thus net consumption (I+G-E) 179.1kWh, self consumption ((N-I)/N) 15%); gas ~31.0m^3 (so 344kWh @ 11.1kWh/m^3). |
HDD12=128 vs 154 last November.
|2017-12||178 (5.7/d)||-46 (-1.5/d)||619 (20/d)||20171130T22:12Z to 20171231T18:45Z (31d)||Meter readings: electricity generation 45.8kWh, export 23.8kWh, import 156.1kWh (5.0kWh/d) (thus net consumption (I+G-E) 178.1kWh, self consumption ((N-I)/N) 12%); gas ~55.8m^3 (so 619kWh @ 11.1kWh/m^3). |
HDD12=187 vs 160 last December.
|2017 total (Jan--Dec)||1862 (5.10/d)||-3794 (-10.4/d)||3423 (9.38/d)||20161231T18:29Z to 20171231T18:45Z (365d)|| HDD (897 vs 990) and gas usage (3851kWh last year) both down. |
Electricity use and generation both up slightly.
Note that grid electricity carbon intensity dropped significantly again in 2017, which would reduce the benefit of our electricity exports, but previous (0.43kgCO2/kWh) figures will be used for comparison.
|kgCO2||801kg (2.2/d)||-1632kg (-4.5/d)||650kg (1.8/d)||~-0.18tCO2 (~-0.50kgCO2/d) gas/electricity emissions total for 4 people, based on 0.43kgCO2/kWh for electricity (netted) and 0.19kgCO2/kWh for gas, ie slightly carbon negative.|
Note that we haven't flown this year again, we still don't own a car and travel almost entirely by (usually-electrified) public transport.