This is the most important number in off-grid planning. Get it wrong and you'll either run out of power in February, or you'll spend thousands on panels and batteries you don't need.
The Average American House
A typical US home uses about 11,000 kilowatt-hours per year. Divide by 365 and you get about 30 kWh per day. That's enough to run a fridge, lights, a TV, a laptop, and some other stuff.
A 6 kW solar system in Arizona makes about 10,000 kWh a year. So a sunny-state house can almost run itself on solar. The same panels in Scotland would make maybe 5,000 kWh. Half the power. That's why location matters so much.
Why Your House Is Different
Three things move the number up or down a lot.
How many people live there. Two people use about half the power of four.
How big the house is. More rooms means more lights, more heating, more cooling.
What you do with your power. An electric heater running all winter is a power monster. A gas furnace with the same heat output costs almost nothing in electricity.
Doing The Math
List every device, what it pulls in watts, and how many hours a day you run it.
A fridge runs 24 hours but only draws about 150 watts when the motor kicks in, so roughly 1.5 kWh per day. An LED light is 10 watts. Five bulbs for five hours: 0.25 kWh. A laptop is 50 watts. Four hours: 0.2 kWh.
Add up every device. Now you've got your real number. Most off-gridders are surprised. Some find they use way less than the national average. Some find one secret hog (an old fridge, a hot tub) is eating most of their power.
→ Use the energy needs calculator
Cut First, Then Buy
Cutting your usage costs nothing. Adding solar costs thousands. So cut first.
Swap any old bulb for LED. Unplug things that draw power when "off". Find the secret hog and fix it. Most people can shave 20 to 30% off their bill before adding a single panel.
Then The Solar Math
Once you know your daily use, you can size a system. A house using 10 kWh a day needs roughly 2 to 3 kW of panels in a sunny area, and 10 to 15 kWh of battery storage for normal days.
→ Full guide to calculating your solar needs in kWh
