Payap scenario: Part/Draft model with roof, rooftop PV and PV parking canopies

New FreeCAD model docs/cnx_vinyl_parametric_payap_parts.FCStd: the Payap
scenario rebuilt from plain Part solids and Draft (arrays, labels,
dimensions) on the same Params sheet, no BIM objects, plus:

- monopitch roof 10 deg, low eave 7.0 m south, high side 11.4 m north
  (phase 1 RFQ geometry); gables and the fire wall follow the roof
- rooftop PV: 901 x 580 W placeholder modules, ~523 kWp, 17 rows in
  blocks of four with walkways, 1 m edge strip, 2.5 m clear over the
  fire wall (estimate)
- car canopy (10 bays, 72 modules) and scooter canopy (30 spaces,
  22 modules), ~54 kWp, RFQ footprints and heights
- module counts and kWp as sheet expressions; ~577 kWp in all

FreeCAD 26.3 RC1 does not propagate spreadsheet edits: CNX_apply_Params
macro touches the dependents and recomputes; parametric test (factory
length, pitch, car bays, walkway) matches the sheet counts.

site-candidates.md: roof/PV/canopy section with the export, battery and
BOI questions a 577 kWp array raises; mirrors in sustainability.md and
scale.md; README layout lines.

docs/site-candidates.md

@@ -281,4 +281,53 @@ and every equipment envelope is an estimate.
 
   All of it is an estimate to settle against the real plot.
 
+### Roof, PV and parking canopies (Part and Draft model, October 2026)
+
+A second model of the same scenario,
+[cnx_vinyl_parametric_payap_parts.FCStd](cnx_vinyl_parametric_payap_parts.FCStd)
+([isometric](cnx_vinyl_parametric_payap_parts.png),
+[top view](cnx_vinyl_parametric_payap_parts-top.png)), is built from plain
+Part solids and Draft (arrays, labels, dimensions) instead of BIM objects,
+on the same `Params` sheet, and adds the roof, the PV and the parking
+canopies. Module counts are expressions on the sheet (`pv_roof_n`,
+`pv_cp_n`, `pv_kwp`), so the drawing and the kWp change together when a
+parameter does.
+
+- **Roof**: monopitch at 10° with the low eave (7.0 m) on the south side
+  and the high side 11.4 m above the floor on the north, the geometry of
+  the [phase 1 RFQ](finance/phase1-construction-rfq.md) and the
+  [sustainability](sustainability.md) roof study. On this plot (road
+  assumed south) the whole field faces south; once Payap names a plot,
+  its bearing sets the azimuth and the yield derate. The fire wall rises
+  with the roof, 0.5 m above it.
+- **Rooftop PV**: 901 modules of the generic 580 W placeholder, ~523 kWp,
+  in 17 rows (blocks of four with a walkway, 1 m edge strip, as in the
+  sustainability study): 45 columns west of the fire wall and 8 east of
+  it, with 2.5 m of roof kept clear over the wall (estimate; check the
+  Thai code and the insurer).
+- **Parking canopies**, both in the car park clear of the footpath:
+  - car canopy, 10 bays, 27.7 × 7.0 m at 4.1 m: 72 modules;
+  - scooter canopy, 30 spaces, 13.7 × 5.5 m at 3.5 m: 22 modules.
+
+  Together ~54 kWp. Covering the canopies fully gives more than the
+  ~40 kWp the RFQ states. The RFQ heights are read as the high side; at
+  the 10° tilt used for self-cleaning (estimate for the canopies) the low
+  side clears 2.9 m (cars) and 2.5 m (scooters).
+- **Total ~577 kWp**: at 1,400 to 1,500 kWh/kWp/yr that is about 810 to
+  870 MWh a year before any azimuth derate, roughly 55 to 85 % of the
+  1,000 to 1,500 MWh mature two-shift use ([scale](scale.md)). Three
+  things follow before this size is fixed:
+  - at midday the array can exceed the plant's load (weekends, single
+    shift), so PEA's export terms decide whether the surplus is sold or
+    curtailed;
+  - the 271 kWh battery is sized for ride-through, not to absorb it;
+  - the BOI solar measure caps eligible spend per MW ([BOI](boi.md)).
+
+FreeCAD 26.3.0 RC1 does not pass a cell edit on to the parts that read
+the cell (a normal recompute updates only the sheet). After editing
+`Params`, run the macro [CNX_apply_Params.FCMacro](CNX_apply_Params.FCMacro)
+(copy it to the FreeCAD macro folder): it touches every object that reads
+the sheet and recomputes. Tested with factory length, roof pitch, car bays
+and walkway width; the drawn module count matches the sheet each time.
+
 The Mueang Chi model and everything sited on it stay as they are.