Earth Notes: Saving Electricity and Gas

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

(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.)

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. That compares well 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.) That 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.

I have now 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.

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.)

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.

Cost

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.)

On the heating (gas) side we have 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 consumption 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).

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

We had our single-glazed front door replaced with a double-glazed unit. 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.

For 2009 daily electricity consumption is down to a little over 5kWh (5 units). On average the solar PV generates much more than we use. We export 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. The increased output from the expanded system matched 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. 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.

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

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. The residual grid load is ~80W according to the Loop energy monitor. ~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. Candidate always-on items are the oven standby and clock, hob standby, MHRV fans, smart lighting controls, cordless phone, trailing mains socket/adapter 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 the 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:

• 40W: fridge/freezer
• 8W: oven+hob
• 2W: kitchen MHRV

See which electrical appliances use what at home.

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

The installation of the first chunk of grid-coupled storage improved our self-consumption. This reduced flows to and from the grid.

This system was subsequently expanded four-fold.

The Sunamp Thermino heat battery was installed. The Thermino allows us to avoid gas for most DHW (hot water). This is by diversion from solar PV in summer, and from low-carbon grid electricity mainly in winter.

A heat pump was installed. The gas supply was capped. That is the ultimate gas saving...