STALE — references the retired BedSun (90°) mode, the BMI160 IMU, and 0–90° tilt range. The current hardware maxes at 35° tilt (structurally capped per analysis/wind_load.py); the IMU is disabled; the 90° mode fails the wind calc and was retired in v3.1. Treat as design intent and update before printing. See firmware/README.md and README §”Status & roadmap” for the current truth.

A single-page, 8.5×11 take-home. Source for this is the markdown below; render to PDF for printing (Vistaprint, FedEx Kinko’s, or pandoc).

Wattplot

Give an old solar panel a second life. Shade + food + power, in one raised bed.

A planter up to 8 ft × 5 ft with a hinged, ballast-mounted solar canopy. Fits any panel up to 97” × 61”, new bifacial from the manufacturer, or old salvage from a decommissioned rooftop that would otherwise be landfilled. The smart controller tilts the panel to follow the sun, fold for wind, verticalize for rain, and shut off the motor before it stalls.

Full-size build: up to 8 ft × 5 ft, ~$1,400 in parts (new bifacial) or ~$800 in parts (with a salvage panel), ~10–15 hours over a weekend.

This table: 18” × 14” mini, ~$193 in parts, ~3–4 hours. Same firmware, same MPPT, same sensors, same decision stack.

Why upcycle?

~10M tons of solar panel waste globally by 2050 (IRENA). Most panels are removed because the racking or inverter failed, not the cells. A 12-year-old 250 W panel is still a 235 W panel. For shade + some power, that’s a free 235 W, and you delay recycling by 10-20 years.

The numbers (full-size, Phoenix, AZ)

What	Value
Power (35° tilt, 235W salvage)	~850 kWh/yr
Power (35° tilt, 620W new bifacial)	~2,240 kWh/yr
Tomato yield (4 plants)	~124 kg/yr, about 250 lb
Wind design	115 mph 3-sec gust (ASCE 7-22, Cat II 700-yr)
Tilt range	0° (storm, stowed flat) to 35° (structural max)
Panel	Any up to 97”×61”, 30+ year life
Battery	12 V 100 Ah LiFePO4, ~10 yr life
Microinverter	Enphase IQ7+ or APsystems DS3, 240 V
MPPT	Victron SmartSolar 100/30 (full-size) or Sunapex 10A (salvage)
Controller	ESP32 + custom PCB, ~$30 in parts

Fits any panel up to 97”×61”

Salvage panel	L × W (in)	New W	Derated W	Bed (in)
Residential 60-cell	65 × 39	250 W	235 W (12 yr)	65 × 39
Residential 72-cell	77 × 39	300 W	288 W (8 yr)	77 × 39
Commercial 96-cell	65 × 41	400 W	388 W (6 yr)	65 × 41
Large 1m65 (bifacial)	65 × 41	400 W	392 W (4 yr)	65 × 41
LONGi 620 W bifacial (new)	97 × 44.6	620 W	620 W	96 × 44.6

All five are validated presets in wattplot_params.py. Bring your own panel, measure the aluminum frame dimensions and call apply_panel_preset(name). The bed resizes automatically. The cut list is derived from the bed.

See docs/upcycling.md for the full guide.

How it works

Sun hits the panel.
MPPT charges the 12 V battery and feeds the microinverter.
Microinverter exports 240 V AC to the home or grid.
ESP32 controller decides panel angle from weather, soil, time of day.
Linear actuator tilts the frame 0–90°.
IMU measures actual tilt, closed loop on motor current.
Bed below gets morning and evening sun, midday shade.

   NWS weather ─┐
   Soil sensors ─┤
   Time of day ──┼──►  decision stack  ──►  θ_desired
   User override ─┤                          │
                 ─┘                          ▼
                                          ┌────────┐
   INA219 motor I ──►  PI loop ──► actuator  ──►  panel
   BMI160 actual θ ──┘

The smart controller, priority-ordered decision stack

#	Source	Action
1	User override	any
2	Hard current limit	θ = 0 (safety)
3	NWS rain + dry soil	θ = 0 (capture rain)
4	NWS wind > 50 mph	θ = 15 (preemptive)
5	Wind > 50% safe	pause tracking
6	Soil wet 72h+	θ = 90 (wring out)
7	Soil dry 48h+	θ = 35 (conserve)
8	Tracking mode	θ = 0-90 (azimuth)
9	Power mode	θ = 35
10	Bed-sun mode	θ = 90

Full spec: docs/control_law.md. Implementation: firmware/wattplot.yaml (ESPHome).

The build, what’s in the box

Bed walls, 2×12 PT Douglas Fir, sized to your panel
Frame rails, 2×6 PT DF, with 2×4 diagonal brace
Skids, 4×4 PT DF
Hinges, galvanized butt, ½” pin, continuous rod
Panel, your salvage (or new)
Hardware, all off the shelf, no welding, no miter cuts
All FSC, sustainable lumber where available

The full-size is ~$800-1,400 in parts (depending on panel source). The mini on the table is ~$193.

How to get started

Step	Time	Cost
1. Read `README.md` and `docs/upcycling.md`	30 min	free
2. Source a salvage panel (Craigslist, salvage yard, your own rooftop)	varies	$0-200
3. Measure the panel frame, call `apply_panel_preset(...)` or set dims	30 min	$0
4. Build the Mini first to validate (`docs/build_guide_mini.md`)	3-4 hr	~$193
5. Calibrate the IMU, flash ESPHome	1 hr	$0
6. Order the full-size lumber + MPPT (sized to your panel)	30 min	$300-600
7. Build the full-size	10-15 hr	$0
8. Plant tomatoes, run the dashboard	forever	tomato seeds

The single most important thing to do first: build the mini. It’s the same firmware, the same MPPT, the same sensors. If the mini works, the full-size works.

Open source

Wattplot is MIT-licensed, open-source, code-first.

Repo: github.com/mokahlo/wattplot
3D viewer: mokahlo.github.io/wattplot
Upcycling guide: docs/upcycling.md
License: MIT (use, modify, sell, attribution appreciated)

If you build one, send photos. If you sell one, attribution. If you find a bug, open an issue.

Contact

Project lead: mokah (GitHub)
Faire booth: Sept 25–27, 2026, Mare Island, Vallejo CA
Email: see repo Issues

Made in the open. Tested in the sun. Built from old panels.

Wattplot, One-Pager (booth handout)