Free sizing tool
Off-Grid Solar Calculator
Tap the things you run, pick your state, and this tool sizes your whole off-grid system: how much solar, how much battery, what size inverter, and which charge controller. It is built for beginners, so you do not need to know the formulas. We show our math and hand you real numbers, with no email wall.
Step 1 of 3
What do you run in a day?
Start from a setup
Tap to add, tap again to remove. Need more than one? Set the quantity in your list below.
Fridges & freezers
Lights & electronics
Comfort & climate
Kitchen & cooking
Water, tools & laundry
Often forgotten
No appliance matches that. Add it as your own below.
Example load We filled in a common starter list so you can see how it works. Edit it, or
Edit any number. For a fridge or freezer the watts are the average across a whole day, so 24 hours is correct. Untick a row to leave it out.
Your list is empty. Tap an appliance above, pick a preset, or add your own.
Add your own appliance
Already added up your own appliances? Type the daily watt-hour total and the tool sizes around it. Switch back to Choose appliances to use the list instead.
Step 2 of 3
Where will it run?
How many low-sun days the battery should carry you.
Lithium safely uses more of its capacity than lead-acid.
Sun-hour averages compiled from published summaries of NREL data (fixed, south-facing panels). For an exact figure at your address, check NREL PVWatts.
Advanced assumptions
We pick this from your system size unless you set it.
How much of the battery you safely use. 0.8 suits LiFePO4.
Off-grid losses through the battery. 0.78 is conservative.
The single-panel wattage you plan to buy.
Days of good sun to refill the battery after a cloudy stretch. Lower means more panel.
Step 3 of 3
Your off-grid system
Your inputs changed. Size again to update the system below.
Your system plan
Prices change constantly, so we never show them here. Tap a button for the current price on Amazon. As an Amazon Associate we may earn from qualifying purchases.
Prefer our tested picks?
Hand-picked favorites at each size, instead of a search.
Frequently Asked Questions
How do I figure out my daily power use?
Tap the appliances you run from the list above and the calculator adds up their average watt-hours for you. The wattage on each is a typical average, so your exact model may pull a little more or less. For a fridge or freezer it shows the average draw across a full day (the compressor only runs part of the time), which is why it looks lower than the sticker on the back. If you already metered your own gear, edit any row, or switch to the manual total and type your own daily watt-hour figure.
Are these peak sun hours accurate for my state?
The annual figure is compiled from published state-level summaries of NREL solar data (fixed south-facing panels); we have not re-run PVWatts for every state ourselves. It is also an average: a sunny ridge does better than a shaded valley a few miles away, and winter runs much lower than the yearly number. For an exact figure at your address, look it up free on NREL PVWatts, and turn on the winter toggle if you run off-grid year-round.
What size charge controller do I need?
Divide your total panel wattage by your battery voltage to get the amps, then add about 25 percent for cold, sunny days when panels can briefly spike above their rating. A 600 watt array on a 12 volt battery is about 50 amps before margin, or roughly 62 amps once you add the 25 percent, so you would pick an 80 amp MPPT controller. Always round up to the next standard size, never down. Amperage is not the whole story: also confirm your panel string fits the controller's voltage window and maximum PV input.
How many batteries do I need to go off-grid?
Multiply your daily watt-hours by how many cloudy days you want to ride out, then divide by your usable depth of discharge, which is about 80 percent for LiFePO4 and 50 percent for lead-acid. The calculator also adds about 10 percent for inverter and round-trip losses, since AC appliances draw through the inverter, then turns the result into watt-hours and amp-hours at your system voltage. More days of autonomy means a bigger, pricier bank, so most off-grid setups land at two or three days.
What system voltage should I use, 12V, 24V, or 48V?
The calculator picks this for you from the size of your system, so you do not have to. As a rule, small van and weekend setups run 12 volts, larger rigs run 24 volts, and cabins or homes run 48 volts. Higher voltage moves the same power with less current, which means thinner, cheaper, safer wiring once a system gets large. You can override the pick under Advanced if you already know what you want.
Is MPPT or PWM better for off-grid solar?
MPPT controllers pull 15 to 30 percent more energy from the same panels, especially in cold weather and when the panel voltage runs higher than the battery voltage. PWM is cheaper but wastes that extra harvest, so it only makes sense on small, matched 12 volt systems. For anything you rely on, an MPPT controller pays for itself.