Energy: PEA tariff, electric vs biomass steam, PV vs solar thermal

PEA tariff schedule (May 2023 onward, still current) filed under
docs/finance/pea/; Ft 0.1623 THB/kWh for Sep-Dec 2026 from the PEA Ft page.
The plant falls under Schedule 3.2.2 (Medium General Service, TOU, 22 kV).

New section in sustainability.md: blended ~3.81 THB/kWh for two-shift
production plus 132.93 THB/kW demand charge; electric steam ~4.7M-5.5M
THB/yr at maturity against ~0.35M-0.8M of biomass fuel; self-consumed PV
worth ~3.7 THB/kWh (~4.5-7 yr payback); solar thermal not recommended;
the battery earns little from TOU arbitrage or peak shaving. biomass.md,
scale.md, the utilities CSV note and the README follow.

docs/scale.md

@@ -169,6 +169,16 @@ conversion, which forestry land generally does not.
 Grid connection: a medium-voltage connection with a transformer in the
 **500 to 1,000 kVA** class from PEA, sized by the boiler decision.
 
+Tariff: PEA Schedule 3.2.2, Medium General Service on time of use at
+22 kV (the flat rate is closed to new customers): 132.93 THB/kW demand
+charge on the peak-hour maximum, 4.1839 THB/kWh peak (09:00 to 22:00 on
+weekdays) and 2.6037 THB/kWh off-peak, plus Ft (0.1623 THB/kWh for
+September to December 2026) and VAT. Two-shift production lands at a
+blended ~3.81 THB/kWh before the demand charge, roughly 4.3M to 6.4M THB a
+year without electric steam (estimate); the deposit for the connection is
+400 THB per kVA. Detail and what it decides for steam, PV and the battery
+in [sustainability](sustainability.md#grid-tariff-pea-and-what-it-decides).
+
 Galvanics (Phase 5) is not in the table yet. By the Pheenix Alpha and
 Sibert datasheets, one electroforming line plus the stamper prep machines
 is ~30 kVA connected, two three-phase plating units and the rest
@@ -188,8 +198,10 @@ small against the connection, but its own feeder and meter.
   (estimate), so 300 kWp covers roughly **28 to 45%** of consumption
   without electric steam, falling to **~17%** with it; a bigger array
   shifts that up
-- Battery: **271 kWh** Gobel stack (peak shaving and ride-through, roughly
-  two to three hours of the chiller's electrical draw)
+- Battery: **271 kWh** Gobel stack (ride-through, roughly
+  two to three hours of the chiller's electrical draw; peak shaving earns
+  little under PEA's time-of-use tariff, see
+  [sustainability](sustainability.md#grid-tariff-pea-and-what-it-decides))
 
 ## Steam and fuel