💾 Archived View for tilde.pink › ~ssb22 › e7.gmi captured on 2024-02-05 at 10:27:57. Gemini links have been rewritten to link to archived content

-=-=-=-=-=-=-

How to use Economy 7 effectively

This page is applicable only to dwellings whose Economy 7 meters are controlled by an *offline* timer. If your installation has a Teleswitch or Smart Meter, it can be remotely controlled by your supplier and you have *no way of knowing* the exact times it’ll switch in and out of Economy 7—they have the right to vary it from night to night to even-out the grid, and they can even give you one or more peak-rate “gaps” during the off-peak period—which means most of the optimisations on this page won’t apply and all you can do is let the supplier look after your storage heaters. But if your meter’s timer is *not* remotely controlled, read on.

Many people have Economy 7 but do not use it effectively. If you do it right, you might be able to put over 70% of your annual use into the cheap period (in which case watch out for meter readers swapping the figures!)

1. Know what your personal cheap period is. Not all meters are set for 12:00-7:00 GMT. Some are set for 12:30-7:30 or even odd times like 12:38-7:38; it can vary even in the same region with the same supplier—after all they wouldn’t want the grid to have to cope with everyone’s storage heaters beginning their charges at *exactly* the same time—and the supplier’s call centre is unlikely to be equipped to tell you exactly when *your* cheap period is, although they might give you a general idea. Also, check the meter’s clock and note how far *out* it is (again, power companies generally don’t mind some inaccuracy)—the cheap period *for you* starts and ends when *that* clock shows *that* meter’s preset times. Either work out how this translates to ‘real’ clock time, or find it emperically by listening for the “click” of the relay in the meter cabinet (not so easy when two or more flats share a cabinet), or by monitoring which rate the meter is displaying and/or whether a storage heater draws power when turned on at maximum input—if you can’t watch it closely enough to log the exact time of change, you might at least be able to sample it frequently enough to know it within narrow error bars.

The meter’s clock might need *further* checks every few months in case its drift has changed (it normally falls further behind, but running ahead *is* possible).

2. Try to adjust your sleep habits so you have an hour (or two) of cheap time while awake. This might simply be a matter of getting up a little earlier to catch the end of the period. (I do not recommend staying up all night for it.)

3. Schedule most of your high-energy activities for that time. Start the washing machine (if you have a full load). Vacuum. You might as well charge all batteries and run the printer too. (But don’t do anything not needed.) This strategy can make Economy 7 worthwhile even outside the heating season, especially if you are not a heavy user of electric cooking.

It might be considerate to wait until *just* before the end of the period before doing anything noisy. That’s why it’s useful to know the exact time it will end.
I previously included “heat the water tank (if it’s needed that day, and use a timer if you only need warm not hot)” in the above list, but be careful—storing water above 20C but below 50–60C can breed Legionella bacteria (this is particularly a concern if the water can get into air droplets via a shower or aerator). It’s better to heat only as much water as will be used, and use it soon.

4. Take more control of storage heaters. (This point assumes you have old-style analogue “input” and “output” controls; it shouldn’t be needed if you’re well-placed enough to have 2018 “Lot 20”-compliant digital storage heaters.) If you are awake an hour before the cheap period ends, then you have the option of changing the heater controls *at that time*. Rather than being limited to the full 7-hour charge, you could have a 1-hour charge or a 6-hour charge, or even change the level for the last hour. Since heat inevitably leaks out at night, it’s more efficient to refrain from generating at least most of it until that time, as long as you can still get enough (this depends on the weather, and also on the condition of the heater—it’s probably not applicable to a half-broken one that charges very slowly because only a fraction of its charging elements still work, although if you suspect you have one of those because a wireless “energy monitor” is telling you it’s taking only a couple of hundred watts, it’s more likely you’ve mis-connected the transmitter in a way that neglects cable 5).

5. Check if you really need to store any heat at all. If the only heat you need is first thing in the morning, then a lower-wattage non-storage heater during the last part of the cheap period might be enough. (Watch the meter if you’re not sure of the wattage.) You may wish to measure the typical consumption of a night’s charge on “low”, calculate how many hours of *on-peak* heating you can do for the same cost, and don’t store on days you don’t need that many hours (the exact thresholds will vary but at least you have a starting point); if some of that non-storage heating will take place in the cheap period anyway then so much the better.

If all else fails, you *can* switch to a non-Economy 7 tariff without needing a meter change (they’ll just add the two readings together), but you might be surprised how low the annual percentage of night usage can go before this is worthwhile (do the equation, or use my energy deals coherence checker).

Use of time-switches

If you wish high-energy appliances to operate during the cheap period and are not able to get up to start them, you might consider automatic time-switches, but these do have limitations.

Typical plug-in timeswitches (or computer-controlled sockets like the Energenie PiMote add-on for the Raspberry Pi) are limited to devices that

1. connect via a plug (thus excluding many permanent installations of heating and hot water equipment),

2. draw no more than the timeswitch’s maximum current (this can exclude some washing machines), and

3. begin operation as soon as they receive power (thus excluding equipment that also needs a “start” button to be pressed on a control panel).

For this reason, if shopping for a device like a washing machine it is advisable to choose a model that has its own delayed-start function (you can check the cycle length and schedule it to finish when you’re ready to unload, to reduce creasing etc)—although you should also beware of noise levels if you wish to sleep during the cycle.
But that can still leave the highest energy devices—electric immersion heaters etc—on “manual control only” if a more complex system cannot be installed (e.g. in rented accommodation). To automate *these* it is necessary to obtain mechanical switch-pushing equipment.

Many immersion-heater switches are identical to light switches, but unfortunately the typical shape of domestic light switches varies from country to country, which means a mechanical switch-presser made for America might not work in the UK. (I did try an American “Switchmate” from eBay, but its Bluetooth transponder was ‘dead on arrival’, so I was unable to *test* if a working version could operate a typical UK surface-mount 1-gang plate switch, but judging by appearances it seemed unlikely.)

I *have* had some success with a Naran Inc. “MicroBot Push” on a UK immersion-heater switch:

setup was a bit awkward: a stack of three plastic mounting plates needed to be separated with some force before one of them could be stuck to the bottom-left of the switchplate (in correct position for the “pusher” to be hovering over the bottom of the switch’s rocker so it can press the switch ‘down’, which is “on” in the UK);
the Push can be set to switch in only one direction (on *or* off, not both) so manual attention is still required for the opposite action, unless two separate units can be crammed onto the switchplate;
you are required to run a proprietary “app” on an Android or iOS phone to program the unit over Bluetooth, although once programmed it *can* maintain a schedule without the phone (but its clock can drift by over a minute a month if not reconnected);
deleting a time on the app (swipe *fast* from right to left) does not always delete it on the device; to be sure, you also have to switch the device off for an extended period, but:
after the device is switched off for an extended period, launching the app does not always re-load the previously-set timers; to be sure, you must also delete all times from the app and re-add them;
occasionally the app will fail to communicate with the device until the device is reset with a bent paper-clip (and then in the app you might need to delete all times by swiping left fast, restart the app, and re-enter the times);
and we don’t yet know how long the mechanical part typically lasts, although the payoff period versus peak-rate water heating is unlikely to exceed 6 months even at only 20mins/day (which you’ll need to exceed at least *sometimes* to protect against Legionella). You may be able to increase the lifetime of the unit by reducing the maximum extension (via the app); we found a setting of “80%” sufficient to turn on our hot water switch consistently.

Legal

The above ideas are provided in the hope that they are useful, but they do not constitute medical or financial advice. Always consider the individual circumstances before implementing any energy saving plan. All material © Silas S. Brown unless otherwise stated. Android is a trademark of Google LLC. Bluetooth is a registered trademark held by the Bluetooth Special Interest Group. eBay is a trademark of eBay Inc. Energenie is a trademark of Sandal Plc. Any other trademarks I mentioned without realising are trademarks of their respective holders.