Regimes and surplus

The regime and the surplus are read from the median PV case's projection, slot by slot.

How a slot's regime is read

In order, the first that holds:

1. PV spilling (exported or curtailed): export, or curtail where more is curtailed than exported.
2. At the grid's import limit: battery, since a kWh more cannot be imported and comes from the battery's charge or discharge; or import where load is unserved, as a floor.
3. The grid serving the house or charging the battery: import.
4. The battery serving a load, or PV charging it that a load could take: battery.
5. Otherwise import.

Why surplus is the projection's export

Surplus is what the projection exports or curtails, not PV minus load. The difference is the battery: on a morning when the battery is charging with room to spare, PV exceeds the load, yet nothing is spare, because every kWh is going into the battery that the house will draw on tonight. Taking it is a cost the price captures, not free power. Battery export is left out for the same reason: it is stored energy, priced, not spare PV.

Surplus is the projection's on the median day and on the 0.1-quantile day (surplus_kw, surplus_kw_p10); the p10 one is never above the median's.

Why both the price and the surplus

The price answers "what would it cost?"; the surplus answers "is there spare power to soak up, and how much?". A load that should only use spare PV reads surplus_kw. A load that will run anyway and wants the cheapest time reads marginal_cost. On a morning with the battery charging there is no surplus, yet the price can be low, because the battery will fill anyway.