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A dark house during an outage makes the question urgent, and how much solar panels to power a house depends on what your home runs. A fridge, lights and phones need far fewer panels than a home with air conditioning, an electric water heater and a well pump, and the gap comes from power use, roof space and sun, not from the panel brand alone. The steps below show how to work it out, so you can judge any quote on its own figures.
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The quick answer
Start with your home’s power use, then turn it into panel watts. A home that runs lights, a fridge and phones needs far fewer panels than a home that also runs air conditioning, an electric water heater and a well pump. Roof space, sun and shading set how much each panel can make, and a battery sets how much of that power you can use after dark. Work through the steps below with your own meter readings and roof measurements, and the panel count follows from them. See how much solar panels cost for the price side of the same question.
Start with your home’s power use
The most reliable figure is your electricity bill, which shows how much power your home used over the month, and the meter, which shows what it uses right now. List the loads that must run during an outage: fridge, lights, phones and medical devices, then the big loads: air conditioning, electric water heating, well pump and electric cooking. A plug-in watt meter between an appliance and the outlet measures real use over a day, which is the best reading if you can get it. Add the loads that run at the same time, allow for the fridge compressor starting, and size the array for the worst season, not the best day.
| Home | Loads that run | What to check |
|---|---|---|
| Small home | Lights, fridge, phones | Panel watts and battery size |
| Home with air conditioning | Cooling, fridge, lights | Surge watts and inverter output |
| Home with electric heating | Heating, water heating, cooking | Array size and roof space |
| Home with a well pump | Pump, fridge, lights | Surge watts and battery size |
Turn power use into panel watts
Panel watts follow power use. A panel’s wattage is its peak output in full sun, and real output is lower on cloudy days, in the morning and evening, and in heat. Shade from trees, chimneys and nearby buildings cuts output further, so a roof that looks clear at noon may still lose power in the morning. A solar panel makes power from daylight, not just direct sun, so a cloudy day still gives some power and a sunny day gives far more. A home in a sunny region needs fewer panels than the same home in a cloudy region, and a home with long winter nights needs more storage than a home with short summer nights.
Check the roof and the sun
Roof space sets the panel count. A south-facing roof with no shade gives the most power, while east and west roofs give less and a shaded roof gives far less. Roof angle, age and material decide whether panels can mount at all, and a roof that needs replacing soon should be fixed before panels go on. Local sun, season and weather set how much each panel makes over the year, so check the roof from the ground at several times of day and in several seasons before you commit. A roof survey shows how many panels fit, where they face and what shade falls on them.
Plan the battery and the inverter
Panels make power in the day; a battery stores it for the night. Without a battery, the panels stop when the sun sets, and the home goes dark again. With a battery, the home runs after dark until the battery runs out, and the battery size sets how long that lasts. The inverter turns panel and battery power into household AC, and its output must cover the loads that run at the same time. A hybrid inverter charges the battery from the panels and feeds the home from both, while a separate charge controller and inverter do the same job in separate boxes. Check the inverter’s output against your loads before you buy, and see the best portable power stations for home backup for smaller backup options.
Ways to use less power
Efficient appliances push the panel count down: a modern fridge uses less power than an older fridge, and LED lights use less than old bulbs. Insulation, shading and habits push the count down too: a well-insulated home needs less cooling, and running heavy loads in the middle of the day uses solar power directly instead of storing it. A home that runs heating and water heating on gas needs fewer panels than a home that runs them on resistance heat. Turn off the loads you do not need during an outage, and the array you need shrinks with them.
How much solar panels to power a house: the short version
Work out your home’s power use from the bill and the meter, turn it into panel watts, check the roof and the sun, and plan the battery and the inverter. A small home with light loads needs a small array, a large home with air conditioning and electric heating needs a large array, and the panel count follows from your own figures. For the wider picture, see the benefits of solar panels and how to connect to solar panels.
FAQ: power away from the grid
Can solar panels power a whole house?
Yes, if the array, battery and inverter all cover the loads. A small array with a small battery runs lights, a fridge and phones, while a large array with a large battery runs air conditioning and electric heating too. The panel count follows from your home’s power use, roof space and sun.
Do solar panels work on cloudy days?
Yes, but with less output. Panels make power from daylight, not just direct sun, so a cloudy day still gives some power and a sunny day gives far more. A home in a cloudy region needs a larger array than the same home in a sunny region.
Do I need a battery with solar panels?
Not for daytime use, but a battery is what keeps the lights on after dark. Without a battery, the panels stop when the sun sets. With a battery, the home runs on stored power until the battery runs out, and the battery size sets how long that lasts.
How much roof space do solar panels need?
It depends on the panel count and the panel size. A small array fits on a small roof, a large array needs a large roof, and shade, roof angle and roof age all cut the usable space. A roof survey shows how many panels fit and where they face.
