Earth Notes: Saving Electricity and Gas (2021)

Updated 2024-02-26.
Meter readings at home. #4kWhDHWClub
2021 PV Output
Meter readings and analysis of our electricity and gas carbon footprint at home in 2021.


2021 data (kWh: e used 2205, e gen -3501, g 3379).

See the daily PV generation logs for 2021 as .csv and .png chart.

2021-02: Beast From the East II

20210211 demand around evening peak in coldest part of February 20210219 demand around evening peak in coldest part of February

A view of demand from February 2021 when "Beast From the East II" arrived, with high gas consumption days (eg >40kWh/d, 13th) between the 6th and the 15th.

The heating is off from 4pm to 7pm, and the house coasts thermally then. The only heavy load that routinely happens in that slot (we avoid washing and dishwashing for example) is cooking with induction hob and fan oven.

2021-04: April Swerves

The central heating was off for the whole of April other than a couple of specific events...

20210413 16WWmultisensortempL
Reheating the home after a few days with most people away (7.7kWh to raise house temperature 3.5°C).
20210429 16WWmultisensortempL
Impulse heating test to characterise one room better (5s, 13.0kWh over 7.2h).

2021-06: Dull June

20210701 gridTiePowercm
June was a dull, overcast month, so poor solar PV generation!

2021-11: Chilly November

Heating went on 2021-11-06, and it's getting chilly with ~7°C outside 2021-11-22...

20211115 Pilio 16WW heating performance chart
Nominally very efficient heating at 1kWh/HDD12, but lack of significant figures makes it hard to tell.

Meanwhile UK energy suppliers going down like ninepins (Bulb, today, ~#22, 1.7M customers and ~6% of the market) caught between sky-high wholesale gas (and electricity) prices and the government-imposed consumer price cap.

2021-12: Only Somewhat Chilly December

20211210 Pilio 16WW heating performance chart
Be careful of what you wish for! Apparently fab 1kWh/HDD turns out actually to be rather less shiny 1.94kWh/HDD once Pilio added more significant figures at my request...
2021 Fuel Consumption Data
MonthConsumed kWh (/d)Generated -kWh (/d)Consumed kWh (/d) PeriodNotes
2021-01 243 (7.8/d) -53 (-1.7/d) 592 (19/d) 20201231T18:13Z to 20210131T18:17Z (31d) Meter readings: electricity generation 52.7kWh, export 5.8kWh, import 196.4kWh (thus net consumption (I+G-E) 243.3kWh, self consumption ((N-I)/N) 19%); gas ~53.3m^3 (so 592kWh @ 11.1kWh/m^3).
Record high electricity consumption possibly in part from extra use of dehumidifier in kids' bedrooms (which could really do with their own MHRV), and national lockdown so more of everything including dehumidifier. Undoing lockdown gross consumption lift of ~20% would get us back to 6.5kWh/d, a far more reasonable winter figure!
Allowing ~4kWh/d for DHW, space heat is ~1.9kWh/HDD12 vs 2.6 last January. Warm bodies at home and the dehumidifier will have reduced space-heat demand, along with having most Radbots on 2 (17°C) rather than 3 (19°C).
HDD12=241 vs 142 last January.
2021-02 226 (8.1/d) -127 (-4.5/d) 464 (17/d) 20210131T18:17Z to 20210228T18:18Z (28d) Meter readings: electricity generation 126.7kWh, export 48.2kWh, import 147.3kWh (thus net consumption (I+G-E) 225.8kWh, self consumption ((N-I)/N) 35%); gas ~41.8m^3 (so 464kWh @ 11.1kWh/m^3).
Record high electricity consumption again, unfortunately. Both kids still doing school from home full time because of lockdown. There were some very high electricity consumption days (eg >10kWh/d, 7th) especially at the start of the month. Also high gas consumption days (eg >40kWh/d, 13th) between the 6th and the 15th (Beast from the East II). My son also has a new gaming PC...
From the 4th there is starting to be the tail end of PV generation at 4pm, taking the edge off peak-time consumption, alongside the battery. Mean daily PV generation was much the same as last February, but a bit lower than recent Februaries. Possibly pigeons taking to sitting on the panels, and a bit of snow, did not help.
HDD12=171 vs 128 last February.
2021-03 165 (5.3/d) -273 (-8.8/d) 450 (15/d) 20210228T18:18Z to 20210331T17:17Z (31d) Meter readings: electricity generation 272.8kWh, export 206.7kWh, import 99.3kWh (thus net consumption (I+G-E) 165.4kWh, self consumption ((N-I)/N) 40%); gas ~40.6m^3 (so 450kWh @ 11.1kWh/m^3).
Both children have been back at school since early (~8th) in the month, and so electricity gross consumption is back to a more normal 5.3kWh/d. The central heating was turned off at noon on the 29th, though we have a few cold days coming that may test us! (See next month's notes.)
Electricity imports were just under half of exports, ie 16WW switched to being net exporter this month. Also, by the end of the month (from the morning of the 29th onwards), some Enphase battery charge was lasting past midnight. In the (morning of) the 31st there was only ~1h fully discharged.
HDD12=138 vs 142 last March.
2021-04 168 (5.6/d) -512 (-17/d) 167 (5.6/d) 20210331T17:17Z to 20210430T17:16Z (30d) Meter readings: electricity generation 511.5kWh, export 380.4kWh, import 36.8kWh (thus net consumption (I+G-E) 167.9kWh, self consumption ((N-I)/N) 78%); gas ~15.1m^3 (so 167kWh @ 11.1kWh/m^3).
Note the dramatic increase in generation and self-consumption since March. Generation last April 536.0kWh from our 5.2kWp system, this April 511.5kWh, typical would be ~450kWh.
HDD was higher than March (and last April) but gas consumption down by ~10kWh/d, ie two-thirds lower. That saving of ~50kg of CO2 emissions is the force of of turning the central heating off entirely for a marginal month, and living with things slightly chilly.
I did turn the heating on for about 90 minutes just before the family returned from a few days away at the cost of 7.7kWh.
I also did an impulse heating test of one room (13.0kWh) to get a better handle on its thermal behaviour.
HDD12=141 vs 61 last April.
2021-05 166 (5.3/d) -490 (-16/d) 141 (4.6/d) 20210430T17:16Z to 20210531T17:13Z (31d) Meter readings: electricity generation 489.8kWh, export 360.6kWh, import 36.4kWh (thus net consumption (I+G-E) 165.6kWh, self consumption ((N-I)/N) 78%); gas ~12.7m^3 (so 141kWh @ 11.1kWh/m^3).
Generation by the last quarter of the PV passed 11MWh (vs 36MWh for the rest).
HDD was higher than last year and PV generation was lower: a dull and wet month.
HDD12=54 vs 31 last May.
2021-06 152 (5.1/d) -510 (-17/d) 127 (4.2/d) 20210531T17:13Z to 20210630T17:16Z (30d) Meter readings: electricity generation 509.7kWh, export 391.4kWh, import 33.5kWh (thus net consumption (I+G-E) 151.8kWh, self consumption ((N-I)/N) 78%); gas ~11.5m^3 (so 127kWh @ 11.1kWh/m^3).
Another dull (end to the) month.
HDD12=1 vs 4 last June.
2021-07 136 (4.4/d) -531 (-17/d) 116 (3.7/d) 20210630T17:16Z to 20210731T17:16Z (31d) Meter readings: electricity generation 530.8kWh, export 414.4kWh, import 19.1kWh (thus net consumption (I+G-E) 135.3kWh, self consumption ((N-I)/N) 86%); gas ~10.4m^3 (so 116kWh @ 11.1kWh/m^3).
We were away for a week, thus lower consumption figures.
PV generation has been reduced by overcast and rainy weather conspiring with pigeons choosing to stand on the solar panels...
The Enphase emailed monthly report for July (received 2021-08-13) says: produced (generated) 533.3kWh (max 28.3kWh on the 16th), consumed 132.4kWh (max 7.0kWh on the 10th), grid energy imported 12.0kWh and exported 406.8kWh, energy independence 90% (max 99% on the 26th).
HDD12=0 vs 2 last July.
2021-08 138 (4.5/d) -404 (-13/d) 109 (3.5/d) 20210731T17:16Z to 20210831T17:11Z (31d) Meter readings: electricity generation 400.4kWh, export 294.4kWh, import 32.4kWh (thus net consumption (I+G-E) 138.4kWh, self consumption ((N-I)/N) 77%); gas ~9.8m^3 (so 109kWh @ 11.1kWh/m^3).
We were away for another few days this month, thus lower consumption figures.
The Enphase emailed monthly report for August (received 2021-09-15) says: produced (generated) 401.6kWh (max 22.3kWh on the 10th), consumed 133.5kWh (max 7.6kWh on the 29th), grid energy imported 26.6kWh and exported 288.3kWh, energy independence 80% (max 99% on the 14th).
HDD12=0 vs 1 last August.
2021-09 168 (5.6/d) -308 (-10/d) 119 (4.0/d) 20210831T17:11Z to 20210930T17:15Z (30d) Meter readings: electricity generation 308.0kWh, export 188.8kWh, import 48.3kWh (thus net consumption (I+G-E) 167.5kWh, self consumption ((N-I)/N) 71%); gas ~10.7m^3 (so 119kWh @ 11.1kWh/m^3).
The off-grid and grid-coupled storage were respectively replaced and expanded this month. (Self consumption was 56% last September.)
With all the excitement in the energy markets (fast rising wholesale gas prices) Ecotricity is bumping up prices from November. Including VAT (at 5%) the kWh cost and standing charge per fuel is 35.1645p (up from 24.8745p) and 30.3765p for electricity, and 7.791p (up from 6.405p) and 30.093p for gas. That pushes up Ecotricity's prediction of our yearly bill for electricity a little over £400, and gas £300.
The Enphase emailed monthly report for September (received 2021-10-14) says: produced (generated) 308.7kWh (max 18.0kWh on the 6th), consumed 158.1kWh (max 9.0kWh on the 19th), grid energy imported 42.0kWh and exported 182.3kWh, energy independence 73% (max 95% on the 25th).
HDD12=3.5 vs 12 last September.
2021-10 174 (5.6/d) -179 (-5.7/d) 138 (4.5/d) 20210930T17:15Z to 20211031T18:15Z (31d) Meter readings: electricity generation 178.6kWh, export 65.8kWh, import 61.5kWh (thus net consumption (I+G-E) 174.3kWh, self consumption ((N-I)/N) 65%); gas ~12.5m^3 (so 138kWh @ 11.1kWh/m^3).
A further doubling of grid-coupled storage (to ~5kWh/1kW) happened at the end of this month (active 2021-11-01). (Self consumption was 42% last October.)
The Enphase emailed monthly report for October (received 2021-11-12) says: produced (generated) 178.8kWh (max 11.8kWh on the 5th), consumed 163.1kWh (max 7.7kWh on the 30th), grid energy imported 58.2kWh and exported 62.3kWh, energy independence 64% (max 97% on the 24th).
HDD12=23 vs 42 last October.
2021-11 210 (7.0/d) -80 (-2.7/d) 446 (15/d) 20211031T18:15Z to 20211120T18:17Z (30d) Meter readings: electricity generation 80.1kWh, export 2.1kWh, import 131.8kWh (thus net consumption (I+G-E) 209.8kWh, self consumption ((N-I)/N) 37%); gas ~40.1m^3 (so 446kWh @ 11.1kWh/m^3).
The expansion of grid-coupled storage (to ~5kWh/1kW) went live part way through the 1st of this month. Of the 2.1kWh exported this month, 0.8kWh was in that first day before go-live! (Self consumption was 28% last November.)
Gas consumption was much higher than last November where the heating was still off. Also, our bathroom MHRV is not working so we are trickle ventilating instead. Electricity consumption is likely high from a combination of some 1g use of the dehumidifier and us still being home more than pre-pandemic. Also the Enphase batteries now self-consume ~0.4kWh/d. As of 2021-11-06 noon-ish the central heating was on, set for times 06:30--10:59, 13:00--15:59, 19:00--21:44. This should help concentrate electrical demand to run the system away from 4pm--7pm peak grid times.
The Enphase emailed monthly report for November (received 2021-12-16) says: produced (generated) 80.9kWh (max 6.0kWh on the 7th), consumed 194.9kWh (max 8.9kWh on the 28th), grid energy imported 131.2kWh and exported 1.6kWh, energy independence 32% (max 71% on the 3rd).
HDD12=121 vs 87 last November.
2021-12 199 (6.4/d) -40 (-1.2/d) 576 (19/d) 20211120T18:17Z to 20211231T18:16Z (31d) Meter readings: electricity generation 39.7kWh, export 0.2kWh, import 159.8kWh (thus net consumption (I+G-E) 199.3kWh, self consumption ((N-I)/N) 20%); gas ~51.9m^3 (so 576kWh @ 11.1kWh/m^3).
The tiny (0.2kWh) export is because of poor PV generation, and the now-oversize Enphase battery fleet soaking up anything that might spill!
Our bathroom MHRV is still not working so we remain trickle ventilating. (I have what I think is the required replacement part, but have not fitted it.) Gas consumption is higher than last December even though this one is milder.
The Enphase emailed monthly report for December (received 2022-01-12) says: produced (generated) 39.6kWh (max 3.1kWh on the 2nd), consumed 185.4kWh (max 8.5kWh on the 19th), grid energy imported 159.0kWh and exported 0.1kWh, energy independence 14% (max 38% on the 2nd).
HDD12=134 vs 186 last December.
2021 total (Jan--Dec) 2205 (6.04/d) -3501 (-9.59/d) 3379 (9.35/d) 20201231T18:13Z to 20211231T18:16Z (365d) HDD of 1029 (vs 838 last year) slightly high, against 2008 to 2020 mean of 984.
Coronavirus disturbances to normal life again, for the whole year. Poor PV generation (3501kWh). Imports are only just over 1000kWh again. Self-consumption calculated as (N-Imp)/N was 54%.
kgCO2 948kg (2.6/d) -1505kg (-4.1/d) 642kg (1.8/d) ~+0.085tCO2 [though see below] (~+0.23kgCO2/d) gas/electricity emissions total for 4 people, based on fixed 0.43kgCO2/kWh for electricity (netted) and 0.19kgCO2/kWh for gas, ie slightly carbon positive.
We did not fly this year and still do not own a car.
With data from the Enphase metering and the FUELINST log I compute a potentially more accurate CO2 electricity balance, noting the relatively low carbon grid intensity when exporting summer PV and high intensity when importing in winter. (There is still the argument that any balancing at the moment is likely done by a gas turbine in practice.) See below for the computations — the estimated figure is now a slightly positive 0.313tCO2 (-0.329(e) + 0.642(g)) overall for gas and electricity.

2021: ToD Carbon Calculation

(See calculation with workings from 2020.)

Calculating carbon emissions by time-of-day (ToD) involves the FUELINST data from Elexon / National Grid, and the locally sampled 16WW grid import/export flows using the Enphase system.

I have put together an extra script to do the whole calculation this year.

% sh script/analytic/ 2021
Created/updated out/yearly/Enphase-1h-2021.csv.gz
Created/updated out/yearly/FUELINST-1h-2021.csv.gz
Unique hours in data:     8760
Created/updated out/yearly/Enphase-join-FUELINST-1h-2021.csv.gz
Unique hours in joined data:     8681
Scale factor to allow for missing data: 1.0091
Raw 16WW electricity CO2 kg for 2021: -325.707
Adjusted 16WW electricity CO2 kg for 2021: -328.671

A sort of the FUELINST data reveals the range of grid intensities over 2021:

% gzip -d < out/yearly/FUELINST-1h-2021.csv.gz | sort -t, -n -k2 | head
% gzip -d < out/yearly/FUELINST-1h-2021.csv.gz | sort -t, -n -k2 | tail

I ran this new script for last year's data to check for agreement, and all is good:

% sh script/analytic/ 2020
Created/updated out/yearly/Enphase-1h-2020.csv.gz
Created/updated out/yearly/FUELINST-1h-2020.csv.gz
Unique hours in data:     8781
Assuming this is a leap year...
Created/updated out/yearly/Enphase-join-FUELINST-1h-2020.csv.gz
Unique hours in joined data:     8732
Scale factor to allow for missing data: 1.00596
Raw 16WW electricity CO2 kg for 2020: -374.478
Adjusted 16WW electricity CO2 kg for 2020: -376.71
16WW Energy Consumption Trends
YearC=I+G-EEImpEExpEGEN1EGEN2Gas (m^3)

All the columns from EImp rightwards are based on annual manual reads of the supply meters, which should be accurate and definitive.

In particular the EImp (electricity imports) value is flat or trending slightly downwards and is around 1MWh per year. This is good.

The Gas value has no clear trend but remains roughly 3MWh per year. Also reasonably good. I hope to reduce this by 1MWh/y (almost all DHW) using a heat battery, reducing carbon footprint significantly while doing so.

What is less comfortable is the gross electricity consumption figure (C=I+G-E, ie Consumption = Imports + Generation - Exports) that reflects what we actually use in the house as if we had no PV. From a low point of about 1.5MWh/y this is now well over 2MWh/y, and contributes to a slightly positive energy carbon footprint for 2021.

Some of that rise for the last two years will be covid leading to increased occupancy of the house. Plus use of gadgets such as laptops by the kids for school at home during lockdowns. Some is just that they are now teenagers and have and use more gadgets.

The Enphase grid-coupled storage has improved self-consumption, so exports (EExp) have taken the hit, down by very roughly 1MWh/y.

Ofgem's 2020 TDCVs [PDF] (Typical Domestic Consumption Values) have 'low' gas at 8MWh/y, medium at 12MWh/y (unchanged from previously). Electricity (class 1) is at 1.8MWh/y low, 2.9MWh/y medium. So we're already very low on gas and the Eddi/Sunamp diversion should take us lower. Our gross electricity consumption with diversion would get us towards the 'medium' category, but as none of the diversion (~50% or more) will cause imports, those should still be very low at maybe 1.5MWh/y.

Note: if we shifted all our 3MWh/y gas to electric resistance heating for DHW and space heating we'd be 'high' (4.3MWh/y) for class 1 electricity imports, and 'medium' (4.2MWh/y) for class 2 (90% of users are on Economy 7). So still quite respectable.

2022-01-02: Bill

Today's bill for the month just gone shows the effect of the big rise in energy prices that have been allowed to reach the consumer: about £130 for the month. (Unit/kWh prices are currently 33.49p for electricity "Green Electricity", and 7.42p for gas "Green Gas", both excluding VAT.) This is about twice December 2020.

Ecotricity's estimates for our annual consumption are about 1.1MWh/y for electricity and 3.2MWh/y for gas, so close to actuals.)