Power consumption & battery sizing

Add the things you want to keep running. Each row has typical running watts, start-up surge, standby ("idle") draw and hours per day – edit any of them to match your labels. Idle draw is counted for the hours a device is plugged in but not running; it is what quietly empties a battery overnight.

Power consumption & battery sizing

Add devices, adjust hours, read the totals. Your list is saved in this browser.

Add a device

Device	Qty	Running W	Surge W	Idle W	Hours/day	of which after dark	Wh/day

No devices yet. Pick one above, or (fridge, freezer, furnace blower, router, lights, phones, CPAP).

Pin down what runs after dark (optional)

Hours per day says how long a thing runs, not when it runs. Filling in how much of that runtime lands after dark does not shrink the array, because over a full day the panels still have to produce every watt-hour either way. What it changes is the battery. A bank that only has to reach sunrise is a lot smaller than one sized to carry the whole load through days with no sun at all, so this is where you find out what you can get away with. Anything that runs longer than the day is light is put on the night for you.

Hours of darknesshRoughly 10 h in midsummer to 15 h in midwinter across the lower 48. Size on the winter figure.

Size the bank for

Days with no sunJust the night

This choice is what the rest of the flow carries: the module count, the refill target in step 2 and the parts list at the end all follow it.

Assumptions

Days of autonomyDays without sun or grid

Usable depth of discharge

Inverter efficiency

Build the bank fromModules are sized from the manufacturer's published kWh.

Show Ah at

12 V24 V48 V

Wh per day (incl. idle)

Wh/day of that is idle draw

W likely running at once

W if every last thing ran together

W surge on top of the likely load

W worst-case surge on the full sum

kWh battery bank

Ah at 48 V

W inverter (likely load + 25%)

W inverter to cover the full sum

How much solar replaces this? →See your build so far

Typical figures, not measurements – check the label on your own appliances. Motors (well pumps, compressors, AC) surge for a second or two at start; make sure the inverter's surge rating covers the worst-case line, not just the running total.

Planning figures, not a design. These calculators give you ballpark numbers to shop and plan with. They are not an electrical design, they cannot see your site, your loads or your local code, and they may be wrong. Inverter and battery sizes here come from typical appliance figures, so confirm the surge rating against the nameplate on anything with a motor. Wire sizing, over-current protection, grounding, rapid shutdown and interconnection must follow NEC 690 and your local code. Have any design checked by a licensed electrician before you buy or energize anything. You use these tools at your own risk.More on safety.