About

How the Homestead Lab model works

The Lab is a teaching model. It steps forward one hour at a time, tracks a few budgets (electricity, water, heat, food, money), and settles water and food once a day. It is built to show trade-offs honestly, not to design a real system.

This page is generated from the model's own parameter object, so it always matches the code. Of 91 parameters, 63 are marked as teaching simplifications: rounded or assumed values that a reviewer should check before relying on them.

Each hour

1. Weather. Each day is drawn from the zone's monthly normals with a fixed random seed: temperature with a day-to-day drift, overcast or clear, and rain or snow on some overcast days. Hours follow a daily temperature curve and the sun's real position.
2. Solar. Sunlight is split into direct and diffuse and projected onto the tilted panels. Output = sunlight × panel rating × system derate × heat penalty, and much less after snow on low tilts.
3. Loads. Appliances follow daily profiles. Water pumping, hot water, heating and cooling add electricity when they are electric.
4. Heat. In four 15-minute steps: heat lost through walls, roof, floor, windows and air leaks, minus sun through windows and heat from people and appliances. The heater makes up the difference up to its size. A wood stove only burns when someone is home and awake, then banks overnight.
5. Battery and backup. Solar serves loads first, then charges the battery. When the battery reaches its reserve, the grid (if connected) or the generator (if fitted) takes over. Anything left unmet is an hour without power.

Each day

• Water: rain (minus first flush) fills the tank until it overflows; household, animal and garden use draw it down. Unprotected tanks freeze in cold spells. A dry tank means hauled water and a thirsty garden.
• Food: beds grow when the month is warm enough (season extension stretches that). Yield falls with heat and with missed watering. Surplus is preserved into the pantry, which loses a little each month. Hens lay with day length.

Scenarios are tested both ways

Each scenario has an automated test where the starting setup must fail and a sensible set of changes must win. If a model change breaks that, the build fails.

• A cloudy week in December: Keep the lights and fridge on for 7 overcast days without the batteries running flat.
• Drought summer: Get from June 1 through August without the rain tank running dry.
• First winter in a drafty cabin: Keep indoors at 59 °F (15 °C) or warmer for at least 95% of hours, December through February, on 2,500 kg (about 1.5 cords) of wood.
• Add a second person: Run a full year for two people with fewer than 24 hours without power and no days with a dry tank.
• Plant to plate: Grow at least 25% of the vegetables two people eat over a year.
• Grid-tied to off-grid: Drop the grid near Chicago (zone 5A) and run fewer than 5 generator hours in every month of the year.