Off-Grid Tiny House Systems: Power, Water, and Waste

Going off grid in a tiny house is more achievable than in a conventional home, because the loads are small. It is also easier to get wrong, because the margins are thin. A system sized for a sunny week in June will fail you in a cloudy week in December.

The right approach is to calculate your actual needs first and buy hardware second. Most off-grid disappointment traces back to doing it the other way around.

Step one: an honest energy audit

Before pricing a single panel, list every device you’ll use, its wattage, and the hours per day you’ll run it. Multiply and add. That gives you daily watt-hours, which is the number everything else sizes from.

A typical modest tiny house lands somewhere between 1,500 and 4,000 watt-hours per day with efficient appliances and propane or wood heat. It climbs fast if you add electric heat, air conditioning, an electric water heater, or an instant pot habit.

The devices that dominate the calculation:

• Anything that makes heat electrically. Space heaters, electric water heaters, hair dryers, toasters, coffee makers with hot plates, and electric cooktops. Each one can consume more in twenty minutes than your lights use all day.
• Air conditioning. A mini-split running in a hot climate can double or triple your daily demand.
• Refrigeration. Modest but constant. A 12-volt DC compressor fridge uses roughly a third of what a cheap residential fridge does.
• Well pumps. Brief but high-draw, which affects inverter sizing more than daily totals.

The cheapest kilowatt-hour is the one you don’t use. Propane for cooking, water heating, and a backup heater removes most of the heavy loads from your electrical system and dramatically shrinks the array and battery bank you need.

Solar sizing, in plain terms

Panels. A rough planning figure is that a 100-watt panel produces something like 300 to 500 watt-hours on a good day, less in winter, much less under cloud, and much less at northern latitudes in December. Take your daily watt-hour need, divide by your worst realistic production figure, and size accordingly. Design for the worst month you intend to live there, not the average.

Batteries. Lithium iron phosphate (LiFePO4) has become the default for good reasons: it tolerates deep discharge, lasts thousands of cycles, weighs far less than lead-acid, and needs no maintenance. It costs more up front and is meaningfully cheaper per usable kilowatt-hour over its life. Size for two to three days of autonomy so a cloudy stretch doesn’t leave you dark.

Charge controller. MPPT rather than PWM. The efficiency gain is real, especially in cold weather and low light.

Inverter. Pure sine wave, sized to handle your largest simultaneous load plus the surge draw of any motor, like a well pump or a compressor. Undersized inverters are a common and frustrating mistake.

Backup. A small generator or a grid connection you rarely use covers the edge cases. Many people who describe themselves as off grid have a generator that runs a handful of times a winter, and that’s a sensible design rather than a failure.

Winter reality. Panel output in a northern climate in December can be a fraction of July output. Snow cover stops production entirely until cleared. Mounting panels at a steep angle helps them shed snow and improves low-sun-angle capture.

Water supply

Well. The most self-sufficient option and the most expensive up front. Requires a pump, which requires power, and a pressure tank. Depth and geology drive the cost enormously.

Rainwater catchment. A roof plus gutters plus storage. A useful planning figure is that one inch of rain on 100 square feet of roof yields roughly 60 gallons, before losses. Filtration and treatment are mandatory for potable use, typically sediment filtration, carbon, and UV. Some jurisdictions regulate rainwater collection, so check locally.

Hauled water. Fill tanks and transport them. Low cost, high hassle. Some people do this for years and consider it a fair trade.

Storage. Fresh water tanks need to be kept from freezing, which means inside the insulated envelope or in a heated compartment in any climate with a real winter.

Conservation. Low-flow fixtures, a shower with a shutoff valve, and doing dishes in a basin rather than under running water can cut usage by half or more. In an off-grid system, water conservation is also power conservation, since pumping and heating both cost energy.

Waste

Composting toilets. The most common choice. They separate liquid and solid waste, use no water, and need no septic connection. The liquid container requires emptying every few days for two people, which is the part nobody mentions in the brochures. Solids compost over months. Some jurisdictions have rules about the final disposal of the compost, so confirm before you assume.

Incinerating toilets. Burn waste to ash using electricity or propane. No emptying beyond periodic ash removal. High energy draw per use and a significant purchase price.

Conventional flush with a septic or holding tank. Familiar and requires no behavior change. Needs either a septic system, a sewer connection, or a black tank you pump out periodically.

Greywater. Water from sinks and showers. Many rural jurisdictions permit greywater irrigation with restrictions on how it’s applied. Use biodegradable, plant-safe soaps if you’re irrigating with it. Never let greywater pool, and check local rules before designing the system, since this is regulated more often than people expect.

Heat and cooking

Off-grid heat is almost always propane, wood, or diesel rather than electric, because electric resistance heat is the fastest way to drain a battery bank.

• Propane heaters designed for small spaces are efficient and controllable. Direct-vent models are strongly preferred, since they draw combustion air from outside and vent to outside.
• Small wood stoves are wonderful and require clearances that are hard to achieve in a tiny space. Follow the manufacturer’s clearance specifications exactly, use proper heat shielding, and have the installation inspected.
• Diesel heaters are increasingly popular, efficient, and draw very little electricity.

Whatever you choose, install a carbon monoxide detector and a propane leak detector. In a space this small, a combustion problem becomes dangerous in minutes rather than hours. This is not an area to improvise.

A sensible order of operations

1. Calculate daily energy use from a real device list.
2. Move heat-producing loads to propane or wood wherever practical.
3. Size the battery bank for your worst month with two to three days of autonomy.
4. Size the array to refill that bank on a mediocre day, not a perfect one.
5. Choose water and waste systems that match your actual site and local rules.
6. Add a modest backup you hope not to need.

Systems built in that order tend to work. Systems built by buying a solar kit first and hoping tend to be replaced within two years.