Whole-home backup planner: from load list to solar

Step 1 of 4

Inventory your loads

Every later number is only as honest as this list. Walk the house and record, for each load you care about in an outage, two figures: its watts and the hours it actually runs in a day. The home-energy calculators price the awkward ones for you — the refrigerator's duty cycle, the water heater's recovery cycles, the well pump's head — so start there rather than with nameplates.

Mark each load critical or optional as you go. The split matters more than any single wattage: in the refrigerator guide's worked example, the critical set (fridge, chest freezer, temperature monitoring) uses 3.56 kWh a day, while the full appliance list it was drawn from uses 6.32 kWh. Sizing for the critical list first is what keeps the system affordable.

Next: Step 2 — Size the whole-home system

Step 2 of 4

Size the whole-home system

Now open the whole-home calculator and describe the house itself: floor area, AC tonnage and SEER rating, heating type, refrigerator count, and whether a well pump, sump pump, electric dryer, or backup heat strip is in play. It hangs its own wattages on those descriptors — motors with their starting surges included — totals the continuous and surge load, and returns a recommended system size: the inverter or generator class the rest of the plan hangs off. There is nowhere to type your step-1 watts, and there doesn't need to be — this step's job is the size class, not the energy audit.

Step 1 earns its keep here as the cross-check. The calculator also turns its load model into a battery capacity for your chosen runtime; if the daily energy behind that figure lands far from your step-1 totals, your house isn't the average house its built-in wattages assume. Trust your measured list for the energy figures — step 3 takes daily kWh directly — and this calculator's surge-aware total for the system size. And use the critical/optional split where you can: sizing to the full list buys capacity for loads you marked optional, while sizing to the critical list (and load-shedding the rest during an outage) is usually the difference between a battery wall and a battery room.

Next: Step 3 — Size the battery

Step 3 of 4

Size the battery

Storage turns the system size into hours of cover. The battery sizing calculator takes your daily energy need and how many days of autonomy you want, and returns the battery bank capacity that delivers it — the usable-kWh figure step 2's loads will draw against.

Decide the autonomy target from the outages you actually get, not the worst imaginable: each extra day multiplies the bank. If the battery number comes back larger than the project allows, the generator fork is the pressure valve — size a smaller battery for the first hours and let a generator carry the long tail, with the fuel calculator pricing that choice in gallons.

Next: Step 4 — Add solar — size the array, then check the run

Step 4 of 4

Add solar — size the array, then check the run

Solar turns a backup system from a countdown into a cycle: each day's production refills what the night drew. The sizing question comes first — how much array your daily kWh calls for — and the off-grid solar sizing calculator answers it from exactly the numbers you already hold: feed it step 3's daily energy need, your location's sun hours, shading, and days of autonomy, and it returns the array wattage the plan requires (with battery and inverter sizes alongside, which should land near steps 2 and 3 if the chain is consistent).

Only then does the run matter. Panel runs are long and carry real current, so voltage drop is a first-order loss, not a rounding error — the same I² × R physics the EV charging guide prices for car cables. With the array wattage now known, run the panel-to-battery distance and gauge through the solar panel cable calculator before fixing the array's position: moving panels closer, or stepping up a gauge, is cheapest on paper.