I wrote a few months ago about making the most of my solar panel and battery system through a smart tariff designed for households with such a system called Octopus Flux.
It’s time to update as I’m no longer on that tariff. Why? Because I’ve gone cosy – Cosy Octopus, that is.
When I signed up to the Flux tariff, we only needed to think about the solar panels and battery. But then we had a heat pump and a hot water cylinder installed and the gas boiler removed. Our house is all electric now. I remember reading somewhere that a heat pump doubles the electricity consumption of a typical house, and while it is vastly more energy efficient than a gas boiler in terms of kWh, the unit price of electricity is vastly higher than that of gas.
Good news is that some energy suppliers offer tariffs for heat pump users, and Octopus is one of them. Called Cosy Octopus, their heat pump tariff has a 3-hour peak rate period between 4-7 pm (during which the grid is strained so you are encouraged to avoid drawing too much power from the grid) just like Flux, but also three cheap (half price) rate periods spread out through the day – early morning, early afternoon and late night – totalling eight hours. The idea (I think) is that you heat your hot water and crank up heating during these cheap periods then coast along with the heat without drawing too much power from the grid when the price is higher.
You can squeeze even more out of the cheap periods when you have a battery though, because if you charge the battery as well as heating water and space during the cheap periods, you can reduce the amount of grid power you use in winter even further. The afternoon cheap period is between 1-4 pm, and in summer the battery is reliably full of free electrons during this period, but in winter our solar panels generate hardly any electricity, and the battery would be empty and in reserve mode all day. With the Cosy tariff, you can fill up the battery in the afternoon before the peak rate kicks in and use the cheap electricity stored in the battery to boil the kettle, cook dinner, wash up and watch TV in a warm living room without importing from the grid.
Curiously, when you use the smart tariff selector on the Octopus website, it directs you to Flux if you have solar panels and a battery but not an EV, whether or not you tick heat pump. I find this counterintuitive. Maybe it’s different if you have a big enough battery to run a house with a heat pump for full 24 hours and/or can generate an adequate amount of power even in the middle of winter, but in our case (with a fairly small battery and east-west facing panels in Northeast Scotland), you can save far more with the Cosy tariff than Flux.
So I switched to Cosy Octopus, combined with the Outgoing Octopus export tariff (which will give us a lot of credit from spring to autumn). I charge the battery twice a day, during the cheap periods of 4-7 am and 1-4 pm. I suppose this may shorten battery life – I would love to hear how other Cosy users with battery storage use the cheap periods. I heat water and turn the heating up during the three cheap periods, and set back the heat pump during the early evening peak period and while we are in bed. Some people say that this is a less efficient approach and you should aim to maintain constant temperature instead. Maybe I should experiment a bit? If I do, I’ll report back.
Related read: Unlocking Home Efficiency: The Value of Multiple Technologies