Earth Notes: Saving Electricity and Gas

How we cut carbon emissions at home from 6 tonnes of CO2 per year to zero, for all 4 of us!
fuel use 2007 to 2017 bare

If you cut waste and use energy more effectively, you'll save money on your bills, be more comfortable, and save the planet to boot! Whether or not it's fashionable to be frugal this week, energy thrift is always good.

The basics are simple:

Look at the 'See also' links for other great ideas to save your wallet.

Every unit (kWh, kilowatt-hour) of electricity saved avoids emission of CO2 (up to 2015 assuming a little over 400g CO2 emissions per kWh used has been a reasonable estimate).

Every kWh of gas (burnt on-site for heat) saved avoids production of ~0.19kg of CO2.

If you want to see the gory details (and data) of how we kept our comfort but reduced our energy consumption by about a factor of three and went carbon negative doing so, please read on.

We started our trek back in the mists (well, June) of 2007...

June 2007

PM 230 plug-in power meter

To that end I bought a PM230 kWh meter meter to accurately measure what energy/power a device is consuming, even when apparently off (eg the dreaded "standby" or "vampire" consumption).

I measured the power used by some gadgets around the house and in my study, to see what is worth turning off or even replacing, given that some is old.

Having done this survey (June 2007), we're going to make more effort to turn things such as the PC and cable TV box and stereo off completely, but the biggest potential saving is to replace my aging servers with one low-power laptop (still providing essentially the same services) for less than 5% of the electricity. At some point the laptop might even be moved 'off-grid' to solar power, but that's a separate consideration. The laptop should pay for itself in one year in reduced electricity bills. Thanks very much to Adam of [defunct: ""] XePhi for suggesting and devising configurations and power-saving tweaks, measuring power draw of his stock kit, etc!

I'm also replacing the last few old-style incandescent (filament) bulbs with modern CFLs for about one 5th the power consumption. In particular, the main living-room dimmer switch (which no one liked anyway) has been replaced and the 3x60W bulbs are being swapped out for CFLs. Only the bathroom light and one exterior bulb won't be replaced with CFLs since I'm concerned about condensation getting into the electronics and damaging them or even risking a fire. (Update Aug 2007: testing CFL in bathroom and watching carefully for problems; no problems observed as of Jun 2011.) (Update Jun 2008: our gas supplier, Altantic Electric and Gas, sent us two more CFLs unbidden, which creates an interesting problem since we already have CFLs virtually everywhere possible. Maybe I'll see if I can give them away creatively to neighbours without.)

Without giving up any creature comforts we should be able to reduce electricity use at home near 5x, to maybe ~3kWh/day base load with maybe another 3kWh/day for one wash and one dry with the washing machine and one dishwasher load and other sundries each day, ie ~200kWh/month (£20/month); probably somewhat higher in the winter when more time is spent indoors, etc. I confirmed with our power company that our current load (as of June 2007) is ~30kWh/day. (Update Jun 2011: we're down to ~4kWh/day.)

July 2007

As of late July 2007 the old server farm has been turned off and replaced with a much lower-power solution saving ~640W+ every hour of every day.

graph of electricity usage to August 2007graph of electricity usage to October 2007

(Update Oct 2009: the servers had by now been migrated to an 'embedded' Linux system consuming ~4W (excluding the ADSL modem/router/WiFi), completely silent, very small including its no-moving-parts bulk storage, and running entirely from off-grid solar power.)

August 2007

In late August 2007 our quarterly electricity bill arrived with a huge 30% drop even though most of the power savings had only been in place for about 1 month before the meter reading! So almost all our electricity had been for powering these servers, and I'm now getting almost all the features that I was before for a tiny fraction of the energy and a lot less noise and heat in my office. On 1st September, at home all day (though on my own as it happens), less than 4kWh of mains electricity was used over a 24-hour period, compared to ~33kWh/day average for the previous quarter last year, thus nearly a 90% reduction in usage if this day proves anything like typical. Also, 4kWh/day is just about do-able by solar PV in the UK in our local area (there's a practical limit of about 4kWp of RE that the local electricity distribution network (EDF) will allow to be attached to one phase in a small domestic installation), and 4kWp should be able to generate 4kWh/day even on almost the darkest London winter days, so we could, with a grid-tie, be a net exporter overall, and on almost every single day too.

Now that I've stopped using expensive computing equipment as space heating, it will be interesting to see if our gas usage/bill goes up any in winter to compensate. (As of 2008/07 it would seem that we're up from ~9.1MWh/y to ~9.8MWh/y.) Even if it does, it's still better in money and CO2 terms to use mains gas (methane) to generate heat on site than to use electricity. If the house is too cold after this change then it will be worthwhile improving our insulation, not so before, which will be another good thing! (For the record, the August 2007 gas bill was ~£30 for 28 units (875kWh) for the quarter, ie ~10kWh/day, which is for heating and cooking, and is about 1/3rd the cost of electricity for those purposes.) On average a London 4kWp solar PV system might generate an average of ~10kWh/day (across the whole year) so we'd still be net overall consumers of energy between gas and electricity, especially in winter.

October 2007

From 1st October 2007 we have switched to the Ecotricity "New Energy Plus" tariff, so every single unit (kWh) we pull from the grid has been directly (or offset) generated by some mixture of wind/solar/hydro/wave "deep green" (mainly wind) for a 5% premium above our old rate from our current provider (EDF). Since we have cut our power usage by 80%--90% then we can easily afford to pay the extra 5% on the reduced bill! Interestingly, Ecotricity claims that 99% of their customers don't choose the 'Plus' tariff, so are presumably still very price sensitive, possibly overly so since trimming waste by 5% is likely to be easy for most of them. (As of 2007/09 we're using about 7.1kWh/day, and as of 2007/10 very slightly under 7kWh/day, which is somewhat higher than my target of 5kWh/day. On a sample January 2008 day with only me at home but typical consumption from running one load for the dishwasher and one for the washing machine, I observed between 5kWh and 6kWh use for the day. The BWEA figures suggest that ~13kWh/day (~390kWh/month) per household is typical for the UK (though government figures suggest ~9kWh/day), so we're pretty efficient already IMHO.)

March 2008

As of 2008/03/03 when we replaced our old fridge/freezer with an A+ rated one, I expect our gross consumption to fall to ~6kWh/day, and with the solar PV installed the previous week I expect our year-round net consumption to be ~5kWh/day, ie my original target for the whole house. On 2008/03/13 with the rest of my family away and almost no discretionary usage other than my laptop and a few cups of tea, I achieved a (nearly) 0kWh day, ie the import meter was reading the same kWh units at the end of the 24h as at the start. In reality I used about 0.8kWh more than was PV-generated.

For a tiny bit of perspective, one (now defunct) investment bank said that if all the computer monitors in its London head office were switched off every evening as of October 2007 then the bank would save as much as 500,000kWh per year worth £35,000 and reduce its carbon footprint by 21,000 kg of CO2. Total electricity use in the UK in 2006 was 382.5TWh, ie 382,500GWh, of which ~37% was coal, 36% gas, 18% nuclear and 4% renewables (see chapter 5 of the UK's 2007 Energy White Paper (EWP)). The Indian government target is to make available 1kWh/day to each household.


As of 2008/02/08, given the latest hike in rates and the fact that our usage is low enough that we are always in the first charging band (900kWh/quarter) which basically incorporates the standing charge for connection to the Grid, our electricity is now costing us about 16p/kWh, so ~£34/month. (~19p/kWh as of 2008/08.) So our dishwasher costs maybe 20p to run, the washing machine 10p each time, and the fridge over 30p/day; all extra incentives to trim a little further. (Ecotricity's "New Energy Plus" tariff charges a small premium over our regional supplier's (EDF's) standard rate to give us '100% green' power.)

November 2008

On the heating (gas) side we've added a total of maybe 26cm+ of loft insulation, put in thermostatic radiator valves (TRVs) where possible (and we're turning down or off each radiator when not in the room), put cardboard and/or foil behind radiators on exterior walls, put up a letter-box draught excluder and a door curtain for the front door, replaced some cracked/old/leaky (double-glazed) windows, put in an internal door curtain for our living room, and generally tried to trim heat demand. It seems from last month's figures that we may have nearly halved consumtion for a given number of heating-degree days, though it's difficult to tell yet.

Against that we have a newborn in the house this month which means more heat, washing and drying (and no chance to dry outside on the line).

December 2008

In 2008 we consumed just over 2MWh of electricity (<6kWh/d) and exported/generated 0.9MWh (solar PV, resulting in net consumption ~3kWh/d), and total mains natural gas consumption was well under 9MWh.

July 2009

We had our single-glazed front door replaced with a double-glazed unit, and we had an internal door fitted to our living-room, absent since move-in. We hope that both will reduce heating demand and improve comfort.

December 2009

For 2009 daily electricity consumption is down to a little over 5kWh (5 units), but on average the solar PV generates much more than we use, exporting a net excess of about 1MWh (1000 units) per year to the grid.

A new washing machine that allows cold and 30°C washes is probably saving us about 0.5kWh/day compared to last year, as is the latest energy-sipping incarnation of my Internet server.

In March--August 2009 (inclusive) the solar PV generated just over 2MWh with the increased output from the expanded system matching our expected consumption for the whole year.

Gas consumption for cooking, hot water and radiators has been a little over 6MWh for the year, down from ~9MWh/year previously.

As a result our net carbon footprint for the house is a little over 0.7tCO2/y, or maybe one eighth of that from before we started energy conservation, and possibly less than one-sixth of an average UK house's (based on 3.3MWh/y typical electricity use at 0.43tCO2/MWh thus 1.4t, and 18MWh/y gas at 0.19tCO2/MWh thus 3.4t, so 4.8tCO2/year total).


2011 was likely slightly carbon-negative.

March 2012

SuperHomes logo

In March we were assessed to be a 'SuperHome' (number 119), with nominal carbon savings (ignoring our PV) of 62%.

May 2016

2016/05/14: with some adjustments to the off-grid battery logic and parameters all the Internet connection equipment (~12W) including the box for our FTTC (Fibre To The Cabinet) Internet connection (and the Loop energy monitor) are running off-grid all night leaving residual grid load ~80W according to the Loop energy monitor, of which ~40W is probably the fridge freezer. What portion of remainder is real (and used by which devices) and what is measurement error (ie bogus) is not clear. An 80W baseload does represent roughly one third of our annual electricity bill. Canidate always-on items are oven standby and clock, hob standby, MHRV fans, smart lighting controls, cordless phone, trailing mains socket/adaptor indicator lights, fridge-freezer (~40W), TV system standby on LIME controller ~0.5W, mains-powered 'smart home' monitoring/control devices (eg OpenTRV boiler control, though it should ~100mW and measures as zero), and night consumption by PV inverters. Occasional small extra loads of a few watts are expected from dishwasher and washing machine on delay waiting to start (and afterwards when done). Turning off all but the fridge and phone got reported overnight load to ~70W. So, out of ~80W night load breakdown of known parts is something like:

See which electrical appliances use what at home.

See also Saving Electricity and Gas: Side Story for a little more of the history.

Metered Mains Energy Use/Generation

Before Starting Energy Conservation

Before and after starting conservation, at the end of 2007, more than halving bills from 10,000 units per year of electricity and 9,000 units per year of gas...

We moved into our current house 2004/06/14. From 2004/06/14 to 2007/08/21 we used 30705 units of mains electricity (~31MWh) over 38 months, ie ~27kWh/day, or ~10MWh/year electricity ie ~4.3tCO2/year. From 2004/06/14 to 2007/08/21 we used 869 units of mains gas (28 units since 2007/05/17, and 865 units (~27MWh) over the 36-month period 2004/10/21 to 2007/10/17, with an annual HDD12* of ~1160) ie ~25kWh/day, or ~9MWh/year gas ie ~1.7tCO2/year.

Thus our total primary domestic energy consumption (gas and electricity) was responsible for ~6t CO2 per year for two adults (and then lately two children), or ~3t CO2 per year per adult.

After Starting Energy Conservation

Monthly Gas Consumption Since 2007Monthly Electricity Consumption Since 2007 (gross)Yearly Electricity Consumption Since 2005 (gross)Yearly Gas Consumption Since 2005Yearly E+G Carbon Footprint

From 2007/08/21 to 2007/12/31 (132 days) we used 936 units (kWh) of electricity ie ~7.1kWh/day, and 126 units (mains methane/natural) gas ie 3963kWh or 30kWh/day. That included:

  • Sep electricity 282 units (7.1kWh/day) + 10.2kWh/day gas over 40 days including end of Aug (*HDD12=13)
  • Oct electricity 206 units (6.6kWh/day) + 20.3kWh/day gas over 31 days (HDD12=53)
  • Nov electricity 205 units (7.3kWh/day) + 42.8kWh/day gas over first 28 days (HDD12=134)
  • Dec electricity 243 units (7.3kWh/day) + 52.5kWh/day gas over 33 days (HDD12=192; >60kWh/day coming up to Christmas)

(In 2007 up to 2007/05/09 used approx 4040kWh electricity (estimated), 2007/05/09 to 2007/08/21 used 1992kWh (from bill), 2007/08/21 to 2007/12/21 used 936kWh (from above), to a total of 6968kWh for 2007.)

(Assuming 1 unit (the meter says 100cuft) of gas as shown on our meter = 31.5kWh, with conversion figures taken from 2004/07 bill and verified with 2007/10 bill and 11.1kWh/m^3 after our meter change 2009/06/04. *HDD12 is 'heating degree days' for EGLL (Heathrow Airport, aka LHR, nearby) for a base temperature of 12°C, lower than the usual 15.5°C to better reflect our usage, c/o

Note that figures for kWh generated come from our Ofgem-approved meters, whereas the per-day log files are the slightly-less-generous outputs from the grid-tie inverters, thus there are small differences (~5% as of end-2009).

By Year

Jump to analysis and meter readings for year:

YearSummary (kWh)Solar PV
e used ~10000, g ~9000
e used 2036, e gen -901, g 88832008 PV Output
e used 1942, e gen -2958, g 62012009 PV Output
e used 1554, e gen -3547, g 57842010 PV Output
e used 1578, e gen -3998, g 39362011 PV Output
e used 1542, e gen -3778, g 37072012 PV Output
e used 1658, e gen -3740, g 38592015 PV Output
e used 1678, e gen -3944, g 29972014 PV Output
e used 1786, e gen -3229, g 28622015 PV Output
e used 1831, e gen -3739, g 38512016 PV Output
In progress...2017 PV Output