PREDBAT or not?

Hi,
I have had my AIO 13.5 + GW running for 6 months now, but only had my smart meters fitted late in September, so I only have 3 months experience with the Cosy Octopus tariff and the fixed 15p/kWh export tariff. I have 3-4 months worth of HA experience and installed predbat with GivTCP very early on.

My electricity import rates are 12.92p, 26.35p and 39.53p and the only electricity that I purchase at other than cosy rates is to power my cooker and the ASHP in my wife's garden studio. These two circuits are outside the AIO.
According to Octopus, I am importing just over 1,000kWh per month (yes, I know that is high) and I try to limit peak rate usage by turning off the ASHP etc. 90%+ of my overall usage is at Cosy rates

My AIO is configured with Power Priority="Load First", EPS=ON, ECO=ON and is behaving as I expect

I have experimented with predbat with a variety of scenarios but am currently running without predbat and charging my AIO to full capacity during the Cosy periods and using the stored energy at other times. My current thinking is that this is good enough for the summer because I can use solar power to keep the battery charged and simply export any excess at 15p/kWh. I might be able to shave a small amount off the overall bill by better balancing of the import vs solar charging of the battery, but once I take into account losses, is it worth it? Having my battery at a high SoC gives me comfort and my overall savings by having a battery still provide a decent ROI on the initial capital investment.

Therefore despite me loving both the concept and the implementation of predbat, I have decided that (to keep things simple), I have uninstalled predbat for the moment. I am open to being convinced that I have been mistaken and of course, as and when tariffs change, I ill be re-evaluating things.

As an aside, it would be nice to have larger capacity storage and take advantage of even lower import prices, I am not sure I can justify the expense given that I estimate I would be saving only around and extra £50/mo max.

Weasel Horses for courses.

Predbat can handle any different tariff but its going to give you more benefits with more dynamic tariffs. With Cosy, Flux or Go where the patterns are predictable you can just use the in build inverter charge/discharge slots. Especially with anything newer than the Gen 1 hybrids and AC coupled inverters that are very limited in the number of slots you can configure.

The other possible use case is smart charging overnight on cheaper rate to maximise your export potential but with Cosy in my region being 12.65p in the cheap rate, by the time losses are included you’re only talking about saving pennies against the 15p export rate even on a full battery.

So I understand your logic.

Extra battery storage is nice but the payback is absolutely rubbish I agree. Its usually only for the winter it would make a difference (although there is the potential to export more at peak rate in summer on Flux or IOF), and then you are only saving the difference between the day and overnight rate. 10-15p/kWh x battery capacity x half a year, the sums don’t add up

geoffreycoan
I ran the numbers and I reckon I would need to increase my battery capacity by at least 50% to break-even on a tariff such as Go, with a single, super cheap period each day.

I haven't (yet) done the analysis on any agile tariffs and am a bit unsure how I might make an accurate estimate. Therefore, I will stick with Cosy and sick up the extra costs knowing I am better protected against grid failure

Weasel at least with your AIO and or a multi-AIO setup you get a decent charge rate, for me with a hybrid inverter the charge rate becomes the first constraint you hit

If you look at the energy stats UK website you can get an idea of historical agile prices. I looked at overnight average, cheapest 8-slot average and average excluding peak.
At the moment Agile prices are not cheap, around 20p overnight, but this is a short term blip caused by cold weather, little wind, some nukes and interconnects offline, Trump and Ukraine/Russia uncertainties etc.
My average import rates for Nov-Mar 2023/4 were 18.5p, 14.9, 17.0, 12.7, 11.2p and Nov-Dec 24 18.5 and 15.4p

Cosy is easier

geoffreycoan
Cosy is definitely easier🙂
I checked out my usage on the Octopus Compare app and even with some more load shifting, Cosy Octopus has worked out the cheapest tariff for me