OPT-11 P4: solar forecast and day plan

A Home Assistant solar forecast (Forecast.Solar, Solcast or Open-Meteo
shapes) and the add-on's own hourly house use decide, before each cheap
run, whether the sun will fill each battery before the expensive hours.
Leftover solar then buys from the grid only the shortfall; Cheap hours only
skips the part the sun covers; Solar first never grid-charges. No, stale or
failed forecast: P3 option A exactly (12 digests pinned from 5a4cdc2).

Replay (16 recorded days, forecast errors from Elia's day-ahead BE solar):
year-earlier prices P4 19.15 vs P2 19.33 / option A 19.44 / old trade 18.14;
real 2026 prices P4 29.19 vs 32.26 / 32.01 / 31.40 EUR net.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

goodwe_controller/DOCS.md

@@ -184,6 +184,9 @@ The label and description each setting shows on the Configuration tab, in tab or
 | Hardware · Inverter list | Usable battery capacity (kWh) (optional) | `inverters.capacity_kwh` | This battery's usable capacity from its datasheet. Fill it in on every inverter or on none. The add-on then shares the work by the energy each battery has left. |
 | Hardware | RS485 emergency stop is fitted | `estop_fitted` | Switch this on if the emergency stop is installed. It only changes a warning on the status page. |
 | Hardware | Battery modes | `battery_modes_enabled` | Give each battery an on and off switch and a mode, set on the Batteries screen. |
+| Hardware | Solar forecast, today (kWh) | `pv_forecast_entity` | Optional. A forecast sensor with today's remaining solar energy, such as Forecast.Solar or Solcast. A battery then buys only what the sun will not give. |
+| Hardware | Solar forecast, tomorrow (kWh) | `pv_forecast_tomorrow_entity` | Optional. The same forecast for tomorrow. It helps plan a cheap hour before midnight. |
+| Hardware | Trust in the forecast (%) | `solar_trust_pct` | Forecasts are often too sunny. At 70 % the add-on plans with 7 of every 10 kWh forecast. |
 | Hardware | Solar production entity (W) | `pv_entity` | Optional. Your solar inverter's power sensor, positive while producing. The add-on records it and does not use it for control. |
 | Hardware | Solar production entities, per inverter (W) | `pv_entities` | Optional. Use one row per solar inverter instead of “Solar production entity” when you have several. If one stops reporting, no total is recorded. |
 | Hardware | Reversed-sign solar entities | `pv_invert_entities` | Optional. Add each solar entity above that reads negative while producing, spelled the same way. Its sign is flipped before adding up. |
@@ -522,7 +525,7 @@ Off by default. Turn it on, restart the add-on, and the Batteries screen (and Se
 - **On or off.** Off asks the battery for 0 W and starts no monthly cycle on it. A cycle that is running stops, and the add-on log says so. The peak limit may still use it, but only for what the other batteries cannot cover.
 - **Mode.**
   - *Solar first* charges from spare solar before the other batteries and covers the house at any hour. It never charges from the grid and never sells.
-  - *Leftover solar* charges from the solar the others cannot take, never from the grid (until the solar forecast arrives). It saves its power for the expensive hours and covers the house then.
+  - *Leftover solar* charges from the solar the others cannot take. With a solar forecast it may also charge from the grid, but only what the sun will not give (see below). It saves its power for the expensive hours and covers the house then.
   - *Cheap hours only* charges from the grid in the cheapest hours, saves its power for the expensive hours and covers the house then.
 - **Selling** is off until it can be judged on the price the grid pays (owner decision 2026-09-29, option A).
 
@@ -535,6 +538,16 @@ With battery modes on, these choices replace the *Charging and selling on price*
 - A carried (not yet published) price is never used. A run that has started runs to its end.
 - With no prices, or too small a gap, every battery follows the house.
 
+**Solar forecast** (`pv_forecast_entity`, optional). A Home Assistant sensor with the solar energy still to come today, in kWh. These work: Forecast.Solar (`sensor.energy_production_today_remaining`), Solcast PV Forecast (`sensor.solcast_pv_forecast_forecast_remaining_today`) and Open-Meteo Solar Forecast (`sensor.energy_production_today_remaining`). Set `pv_forecast_tomorrow_entity` to the matching *tomorrow* sensor to plan a cheap run before midnight.
+- Before each cheap run the add-on asks: will the sun fill the batteries before the expensive hours? It counts on `solar_trust_pct` of the forecast (70 %), less what the house uses. Solar first batteries get that sun first.
+- *Leftover solar* then charges from the grid only the shortfall: what the house will draw from it in the expensive hours, less its share of the sun. Not up to the top level.
+- *Cheap hours only* fills to the top level less its share of the sun.
+- *Solar first* never charges from the grid.
+- The house use is the add-on's own measurement (grid + battery power) per hour, over the last 7 days. It needs one day of it before the first plan.
+- The plan is checked every 15 minutes. A planned level moves only by 1 kWh or 10 %, so a wobbling forecast does not flip it.
+- No forecast, one older than 3 hours, or no house use yet: *Leftover solar* takes solar only and *Cheap hours only* fills to the top level. The Batteries screen says so.
+- A battery needs its capacity (`inverters.capacity_kwh`) for a plan.
+
 **What always comes first.**
 - The peak limit, the safety stops and the monthly cycle come before a battery's mode.
 - A grid charge is sized so the 15-minute period stays under the peak limit less its margin (`peak_margin_w`). It starts only at 500 W or more. Once the peak limit stops it, it stays off for the rest of that 15-minute period.