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

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. Plug in your appliances, adjust a few settings, and it tells you exactly what size battery bank, solar array, and inverter you’re likely to need. No electrical engineering degree required.

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 four key numbers: your total daily energy usage, recommended battery bank size, solar panel wattage, 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 wattage (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.

💡 Pro Tip: Refrigerator Hours

For appliances that stay plugged in around the clock like a refrigerator, don’t enter 24 hours. A mini fridge motor cycles on and off throughout the day and actually runs for roughly 8 hours out of every 24. Check your appliance’s documentation if you’re unsure, or use 8 hours as a reasonable estimate for a small fridge.

💡 Pro Tip: Standby Power (Vampire Power)

Some appliances draw power even when they appear to be off. A TV in standby mode, for example, stays powered enough to receive a remote signal — typically drawing 1–5 watts continuously. For a more accurate calculation, consider adding your TV as two separate entries: one for active viewing hours at full wattage, and one for standby hours at around 2 watts.

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 — This is the average number of hours per day your location receives strong direct sunlight. A quick Google search for “peak sun hours in [your state]” will give you a reliable number.

System efficiency — Leave this at the default if you’re unsure. It accounts for natural energy loss in the system.

Depth of discharge — This is how much of your battery capacity you’re willing to use before recharging. 80% is typical for lithium batteries, 50% for lead acid.

Inverter safety margin — A buffer to make sure your inverter isn’t running at its absolute limit. The default is fine for most people.

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.

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.

Battery bank size — This is the minimum capacity you’ll want in your battery storage system. When shopping for batteries, look for ones that meet or exceed this number.

Recommended solar panel wattage — This is your total solar array size, not the size of one individual panel. For example, if the calculator suggests 400 watts, that could be two 200-watt panels or four 100-watt panels.

Inverter size — Size your inverter at or above this number. Going slightly larger gives you headroom for unexpected loads.

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.