Why are charging slots selected like this?

[ridax67]

What happened

The charging layout is good, but why isn't it perfect? Instead of charging 14.45, it could charge cheaper 15.15 and 16.00. I am not saying it is completely wrong it is nice to have some cheap slots left if harvesting wasn't as good as expected, but does the algorithm have this kind of thinking really, orcwhat is the mathematical reason behind it?

Debug bundle

Please drag-and-drop bess-debug-2026-07-13-080839.md from your Downloads folder into the editor below before submitting.
The file contains your version, settings, recent logs, and the raw HA discovery dump that the maintainers need to reproduce the issue.

[ridax67]

bess-debug-2026-07-13-080950.md

[ridax67]

[johanzander]

Thanks for the detailed report and debug bundle — the schedule here is actually working as intended, and the reasoning is worth spelling out.

Why it charges at 14:45 instead of "waiting" for the cheaper 15:15/16:00 slots: at 14:45 your solar panels are producing more power than the house is using, and the battery is simply absorbing that extra solar (shown as SOLAR_STORAGE in the schedule) — no electricity is being bought from the grid in that slot, so the buy price shown next to it isn't actually being paid; it's an informational column, not the cost of that energy. Solar available at 14:45 can only be stored or exported right then — it can't be saved up and "charged in" at 15:15 or 16:00 instead, because solar production drops off through the afternoon (only about a third as much by 16:00 as at 14:45). If the battery hadn't taken it at 14:45, that energy would just have been exported at the (lower) feed-in price instead — worse for you, not better.

A more subtle related point, digging into the numbers around 14:15–14:30: in this window the optimizer briefly switches to exporting solar directly to the grid instead of storing it (visible as BATTERY_EXPORT), because the marginal value of holding that energy in the battery for later use versus selling it right away comes out almost exactly balanced. In your version (9.8.1), that near-tie got resolved in favor of exporting a touch earlier (14:15/14:30) than at 14:45, even though 14:45 has a very slightly higher sell price — traced to a known precision limitation in how that version represents battery charge levels internally (the same category of issue already fixed for a related report, #275/#279). Re-running your exact day's data through the current development version, it exports through 14:15, 14:30, and 14:45, with the reward increasing in step with the rising sell price across those quarters — the more intuitive behavior. So this specific edge case is already improved, just not yet in the version you're running.

If you'd like to try the improved version early: add the beta repository, https://github.com/johanzander/bess-manager-beta, as a Home Assistant add-on repository (Settings → Add-ons → Add-on Store → ⋮ → Repositories → paste the URL), then install "BESS Manager (Beta)" from there. Install it alongside your current stable add-on, but only run one at a time (stop the stable one first, since they'd otherwise fight over the same inverter). No changes needed beyond installing and enabling it.