Tiny House Solar Calculator: How Much Power Do You Really Need?

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Figuring out how much solar power you need for a tiny house can feel overwhelming fast. You start researching and suddenly you’re drowning in watts, amp hours, depth of discharge, and peak sun hours — and you still don’t have a clear answer. I built this calculator to cut through all of that. Enter your appliances and daily usage, adjust the system assumptions, and get preliminary estimates for battery capacity, solar panel wattage, and inverter output. No electrical engineering degree required.

Solar is just one line in your build budget. Planning the whole thing? See how much a tiny house costs in 2026, with real example budgets and a full breakdown table.

Try the Solar Calculator

Go ahead and try it out. Add your appliances, adjust the settings to match your situation, and scroll down for your results.

Open the calculator full-screen

What the Calculator Does

This calculator is designed for anyone planning an off-grid or solar-powered tiny house who wants a realistic starting point before talking to an installer or buying any equipment. You enter the appliances you plan to run, how many hours a day you’ll use them, and a few system variables like peak sun hours and battery depth of discharge. In return it gives you five planning estimates: your total daily energy usage, DIY battery bank size, solar panel wattage, estimated peak load, and inverter size. Think of it as a planning tool — it won’t replace a professional assessment, but it gives you a solid ballpark so you’re not going in blind.

How to Use the Calculator

Using the calculator is straightforward. Here’s a quick rundown of each section: Appliances — Add each device you plan to run in your tiny house. Enter the appliance name, its AC wattage at the outlet (usually found on the device label or in the manual), how many hours per day you’ll use it, and how many of that item you have. The calculator models AC loads only, not 12V or USB DC devices.

💡 Pro Tip: Refrigerator Hours

A refrigerator cycles on and off, so compressor running hours are different from hours plugged in. The preset is only an example. Use measured energy or manufacturer data for your appliance, and make sure the wattage and hours describe the same operating condition. Confirm startup demand separately.

💡 Pro Tip: Standby Power (Vampire Power)

Some appliances draw power in standby. If you model active and standby use separately, use measured or manufacturer values and the hours spent in each mode. Avoid counting the same hours twice. Appliance standby consumption is separate from the inverter’s own idle draw.

Battery backup days — How many cloudy or low-sun days do you want your system to cover without recharging? Two to three days is a common starting point.

Peak sun hours — Use location-specific data from NREL’s PVWatts Calculator. Enter your address and use the “Solar Radiation (kWh/m²/day)” result; each kWh/m²/day equals one peak sun hour. Four hours is only an example starting value. For winter planning, use the lowest winter month rather than the annual average.

Solar delivery factor — The default 80% is an editable planning assumption for the combined path from rated panel output to appliance AC energy, including heat, wiring, charging/storage and inverter conversion. It is not a measured efficiency for your equipment. Inverter idle draw and recovery of an already depleted backup bank are not included.

DIY inverter efficiency — The default 85% is an editable planning assumption used for DIY battery sizing. Changing it does not change the solar delivery factor; review that combined factor separately. If you enter inverter idle draw separately, use conversion efficiency that excludes idle draw.

Inverter on-hours and idle draw — Enter how long AC output stays switched on each day, including time when appliances are not running. Use your inverter’s documented no-load consumption for idle draw, or leave it blank to exclude it. A blank field is an omitted allowance, not proof of zero consumption.

DIY battery depth of discharge — This is the usable share of the DIY battery before recharge. The calculator starts at 80% for lithium and 50% for lead-acid as editable planning assumptions; follow your battery manufacturer’s limits. These DIY settings are not applied to complete power stations.

Inverter safety margin — This adds an editable buffer above estimated peak load. Confirm your appliances’ starting demand and the inverter’s rated output and surge capability before choosing equipment.

Get the Free Tiny House Solar Sizing Cheat Sheet

Want a printable version of the formulas and appliance wattage estimates? Grab the free cheat sheet below.

What to Do With Your Results

Once the calculator gives you your numbers, here’s how to think about them: Total daily energy usage — This is your baseline. Everything else is built around this number. If it feels higher than expected, go back and look at which appliances are driving it.

DIY battery bank size — This is an estimated nominal capacity under your chosen backup days, depth of discharge, inverter efficiency and any entered idle draw. It is a planning starting point, not a guaranteed runtime or final equipment specification. Complete power stations are assessed separately using their own stated planning rules.

For a more complete battery-specific method—including losses, backup days, usable capacity, and peak-load checks—read the step-by-step tiny-house battery sizing guide. Recommended solar panel wattage — This is an estimated total array size for your appliance energy, not the size of one individual panel. It does not include inverter idle draw, and it does not check panel voltage, current or connector compatibility. For example, if the calculator suggests 400 watts, that could be two 200-watt panels or four 100-watt panels.

Inverter size — This is an estimated AC output requirement with your selected safety margin. Confirm running loads, starting demand and the inverter’s output and surge specifications before buying.

Remember, these are planning numbers — a good starting point before you talk to a solar installer or start pricing out equipment. Real world factors like your roof angle, shading, and local weather will affect your final system design.

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