Agile Outbound

TLDR

• Agile Outbound Prices are High at present
• With the right setup, you can make more money than fixed output, I believe around 30% at present for my "standardish" home solar setup (3.95kWh/9.5kWh)
• Active management is required, predbat can help that
• It's probably better suited to someone who thinks this sort of stuff is "fun", the actual money made isn't huge

UK Outbound Rates - General

Octopus Energy significantly increased the export rate to 15p/kWh flat for home solar in late 2022, as a result of high wholesale prices caused by the Ukraine War. Recently this was reduced to 12p/kWh, which reflected the underlying wholesales prices having reduced in interceding period.

Certain world leaders no doubt saw this and said "Hold my beer", and we're back with high wholesale prices again. So far this hasn't been reflected in the price of fixed rate outgoing, however the Octopus Agile tracks the wholesale market on a day-ahead half-hourly basis. There is also some weighting for the 16:00-19:00 peak period, where it benefits octopus to have exports.

Inbound and outbound tariffs aren't bound together in most cases, so I can continue to use Intelligent Octopus Go for inbound (5.2p overnight and when charging, 30p during the day).

@energystatsuk@mastodonapp.uk provides daily pricing graphs, these are also provided by the Octopus API. You can see the prices for tomorrow; the line at 12p is what I can get for fixed, and the bar graph shows the price at a particular time. You can see that the prices are a little lower than the fixed rate in the day, but that they're substantially higher in the evening period when there is the most demand on the grid.

On a particularly windy day when there is plenty of energy on the grid, the rates for agile might be substantially lower. In general, I'd say that Agile is better for the grid and overall carbon production than a flat rate, and I'm glad that the agile rates allow me to be a better grid citizen

Export Strategy

Agile requires much more active management than fixed rate; with fixed I simply needed to charge overnight and export as much solar as I could during the day. The strategy needs to change based on how much solar is available and the outbound rates.

Typical Day

Typically, I can import at 5.2p overnight, which is substantially above the export rate for most of the day. I want to fill overnight, try and export what I can first thing in the morning, before recharging my battery around lunchtime when the rates are lowest. I'll then want to export whatever I've been able to store during the highest paying slots in the evening.

Windy Day

On a windy day with good solar expected, I might actually want to avoid charging the battery overnight and leave some capacity to store solar rather than sell it to the grid cheaply. I might also want to try and get some clothes washing done if I'm home, and if I had further places to dump energy, so much the better (Immersion, EV charger). I'm compensated for what I lose on this sort of day by the decent export on typical days, the evening rates are good and at the end of the day I'm getting super cheap energy.

Predbat

Predbat will take the variables involved, and will do a good job of deciding which strategy I need for a particular day.

Predbat will take variables such as

• Expected Solar (Obviously a bit of a dark art)
• Expected Load (Based on historical use)
• Energy Prices
• Energy Events (Axle VPP, DFS, etc)

It will then build a plan for a particular day. The above strategies are illustrative, it will work out the many shades of grey between them. The system is imperfect, there will be situations where

• I have more load than expected; lots of cooking, for example
• Solar is worse than expected

Configuration

There is some fiddling to get Predbat to do what I want it to do, I do this with configuration profiles, which I have Home Assistant change at specific times.

Night

Overnight I want to think about how the Solar is looking tomorrow via Solcast, but solar predictions aren't perfect, and I can load my battery at 5.2p (+ Losses). I've configured

• A reserve of 30% to give me a very reasonable buffer
• PV10 Weight to 70%; Solcast provides confidence values for its predictions, and has a 10% probability lower bound. I've told Predbat to assume about 20-25% of the worst case. IE "Consider if it's pretty certain that I'll leave loads of solar tomorrow"
• Carbon Aware - so the battery charging is planned for when the grid is greenest

Daytime

I've configured a 14% reserve, this is primarily for the evening session. While I definitely want Predbat to export during the peak period, I want to leave a bit of buffer for unexpected load

Evening

I've reset back to 4%

Results so far

I think I'm doing about 30% better than the fixed 12p rate, especially in the shoulder season (March/April) when I don't have huge amounts of export, and this can be stored for the optimal export times. It doesn't hurt that my array is South-West facing, so will naturally export some solar in the late afternoon which fits into the higher export rates.