I promised @toodles that I would provide an update and offer my opinion on the Intelligent Octopus Flux (IOF) tariff, and now August is complete and I have a full month of data, here are my observations.

About us: We have solar and a battery (13.5kWh Tesla), and typically use ~12kWh per day in summer. We have an ASHP which uses considerably more in winter.

IOF is for battery (and solar) owners, and GivEnergy, Enphase, SolarEdge and Tesla brands are currently supported.

IOF is a net metering tariff, meaning the import rate and export rate are the same (understanding this is key). The day rate for my region is 22.36p and the peak rate (4-7pm) is 29.82p (for both import AND export) whilst the Ofgem capped SVR for my region is 26.32p (and SEG export rate is currently 15p)

Octopus take control of your battery and generally charge it from the grid (inc any solar available at the time) whenever the grid is cleanest/cheapest. For me, this has mostly been midday to early afternoon, but occasionally overnight. Typical operating pattern is to ensure the battery is fully charged ready for the peak rate period and then to discharge down to the preset 20% reserve during the peak rate slot (4-7pm), and to recharge either overnight or the following day ready for peak rate again the following day. The house does not run off battery at all, other than when it is exporting during the peak rate period.

Being a net metering tariff, if does not matter if you import electricity for the house or use from the battery, as it costs the same (it's actually slightly cheaper to import as there are no conversion losses). The battery's sole purpose is to support the grid during the peak rate period by exporting it's content. An additional benefit for the grid is that when charging occurs during midday to early afternoon, I am not exporting prodigious amounts of solar just at the point the grid needs it least (on other tariffs my battery was full by 10am so I was exporting large amounts of solar all day which is not particularly helpful to the local grid).

Lets look at some data for August. We used 358.6kWh in the month (11.57kWh per day). We generated 882.4kWh from solar, so our net export (882.4-358.6) was 523.8kWh. Or cost of export - cost of import gave us a profit of £152.11 for the month. £152.11/523.8kWh gives us an effective rate of 29p per kWh for the excess solar we have generated. Our usage was calculated as Import + Generation - Export (as we have no reliable measure of what we've used other than from the Tesla app which is always a little out)

The full data was import 341.6kWh at cost of £76.43 (average 22.37p). Exported 865.36kWh for £228.54 (average 26.4p).

Lets have a look at how that net profit of £152.11 would stack up against other tariffs. If we were on the SVR with 15p SEG for export, our usage would have been fully covered by solar so use can be subtracted from generation to give export of 523.8kWh at 15p = £78.56. Likewise, if we were on Octopus Cosy, our use would have been at the cheap rate import price of 12.91p costing £46.30 (ignoring conversion losses) and export of all 882.4kWh of solar at SEG rate of 15p = £132.36. Subtracting import from export gives £132.36-£46.30 = £86.06

We don't have an EV, but for comparison our usage at the cheap rate for Octopus Go (8.5p) would have cost £30.48 giving £132.36-£30.48 = £101.88 making IOF still 1.5 times more profitable, even if we were eligible.

Hopefully I have demonstrated that IOF is an incredibly profitable tariff for anyone with a compatible battery and who is a net exporter of electricity, as the rates are just so much higher than the SEG rates currently on offer. The more you export, the more profitable it will be. It is also a tariff that help supports the grid. It does this in two ways - firstly Octopus use the battery to support the grid during the peak evening demand period by exporting it's content. Secondly, Octopus can schedule recharging of the battery when energy is cleanest or abundant. Often this happened during peak solar periods which means I'm no longer contributing to the issue of local solar excess during charging periods. The final benefit of IOF is that because Octopus are in control of your battery, there are no automation or monitoring concerns, you can just sit back and leave Octopus to get on with it knowing it's going to be the most financially beneficial tariff over summer.

Clearly there are better options in winter, when one goes from being a net exporter to a net importer. For us, that will be in autumn when solar diminishes and the heating goes on (and our usage instantly doubles). September will be interesting as there is less solar during the lucrative 4-7pm peak window, but our projected generation is still more than our usage so long as the weather remains mild and the heating stays off. Entering September, I am closely watching the 10 day weather forecast for any substantial drops in temperature ready to switch back to Octopus Cosy for winter.

I'll finish with the only downside I can see, and that is the battery is being cycled harder than it would otherwise be. On IOF the battery is cycled 100%-20%-100% daily. When I was on Octopus Cosy, my battery charge levels typically only dropped down to 75-80% overnight (100%-75%-100%) before recharging from solar to 100% the next day, so was cycling far less heavily. Some may see this as a concern with respect to longevity of the battery and can make a judgement whether they think the extra revenue of IOF offsets any potential degradation.