The key to our twin ambitions is smart meters. Not because they are smart, as they're not, but because the increased frequency of metering enables energy suppliers to offer a much wider range of pricing options. Energy suppliers can offer varying pricing levels during the day, as a mechanism to shift energy usage to times of the day when the electricity on the grid is predominantly coming from clean sources. Something not possible with monthly readings.
Last year our energy provider had contacted us about upgrading our electricity and gas meters to new SMETS2 meters, so we took them up on the offer. Now we have a Landis & Gyr E470 electricity meter and Toshiba SKU1 cellular modem in the outside cabinet. Once or twice a day this automatically sends half-hourly meter readings back to the Data Communications Company (DCC), whom then send our readings onto our energy supplier. Unfortunately our gas meter couldn't be upgraded, so we still have to manually take readings and send these off ourselves. The electricity meter also came with an In Home Display (IHD), which is connected to the meter via ZigBee, so that we can see near real-time usage on a screen in the kitchen.
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| IHD, with red LED to indicate excessive power usage |
Our energy supplier only offered a fixed rate tariff, so we looked for alternatives and found Octopus Energy. As well as dual rate tariffs, like an Economy 7 tariff, that are aimed at charging electric vehicles overnight, Octopus offer a time-of-use tariff called Agile, where the price of electricity changes every half an hour. And every day.
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| Agile Octopus tariff for a 24 hour period |
If you can change your electricity usage so that you avoid the 4pm to 7pm period, then the cost comes down from the 20p/kWh flat rate we were paying our old energy supplier, to around 7p/kWh. Or less if we're paying attention.
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| Usage over a 24 hour period |
The graph above shows a car charging over night, then being topped up again in the middle of the day after a short trip. During the rest of the day there's about 600W of power being used constantly. Having visibility of this information is the first step to identifying where we can reduce our usage.
A side benefit of chasing the cheap periods in the day is that they correlate well with the times when the electricity on the grid is also the cleanest. Power from wind and solar are the cheapest being fed into the grid, with gas and nuclear being the most expensive. So if the power on the grid is cheap, it is likely to be predominantly from wind and solar.
