Solar Panel Calculator
Add what you want to run from a searchable library of household loads, set the sun hours where you live, and see how many panel watts it takes to keep up with a day of use and how long your panels need to refill a battery.
The short version
- Search 140 household loads with typical watts, add your list, set peak sun hours, and see the panel watts you need and how long your panels take to recharge a battery.
- Typical estimates, not measurements.
A panel label is what it makes in perfect lab sun. On your porch, in October, at an angle, it makes less. This calculator starts from your daily watt hours, divides by the hours of strong sun you actually get, and adds a cushion for real world losses. Then it flips the math around and tells you how long the panels you already have need to fill your battery.
How to use
- 1Find your appliances. Type in the search box, like fridge, modem or well pump, or tap a category such as Kitchen or Medical. Tap any result to add it to your list as a card. Every item comes with typical watts filled in, so you do not have to look them up.
- 2Check the watts. Running watts is what the appliance pulls while it is working. Our numbers are typical estimates. If the label or manual on your own appliance shows a wattage, type that in instead.
- 3Set the duty. Duty is the share of the whole day the appliance is actually drawing power. A fridge compressor cycles, so about 33 percent. A router is on all the time, so 100 percent. A microwave used for 15 minutes a day is about 1 percent. Drag the slider or type a number.
- 4Set your sun. Drag the peak sun hours slider to match your area and season. Around 3 is a short winter day in the north, around 5 or 6 is a summer day in the south. Keep real world output at 75 percent unless you have measured your own setup.
- 5Read the results. The dark panel shows your daily use, the panel watts that would cover it, and how many sun hours your panels need to refill the battery size you enter. The two bars compare what you use in a day with what your panels make.
The calculator
3Your results
About these numbers.
Peak sun hours are the equivalent hours of full sun your panels see in a day. Across most of the United States they land somewhere around 3 to 6, lower in winter and higher in summer; NREL’s solar resource maps show your area. Real world output starts at 75 percent of the panel label to cover heat, angle, dust, wiring and charge controller losses. Portable panels propped on the ground often do worse. Recharge time assumes the battery is empty and the panels feed only the battery.
Panel watts vs battery size
Panels and batteries do different jobs. The battery carries you through the night and the gray days. The panels refill it. If your panels make less than you use, the battery still drains, only slower. If they make more, you finish each sunny day full. Most people backing up a fridge and the internet land somewhere between a few hundred and about a thousand watts of panels. The calculator shows where your list lands.
Why the 75 percent
Heat lowers panel output, so does a flat angle, a bit of shade, dust, long cables and the charge controller inside your station. Seventy five percent is a reasonable planning cushion for a well placed setup. If you have watched your own station’s input readout on a clear day, type in what you actually see. More on picking panels: the portable solar panel buying guide and folding vs briefcase panels.
Nobody here metered your appliances or your roof. These are typical estimates plus arithmetic. Method: how we work · corrections: contact.