Location
Step 1: where is the home? Required before results show. No street address needed.
Your estimate
Loads
Each card is one appliance. Use running watts, not the biggest label number. Turn on "Runs together" for loads that could be on at the same moment; that sets your inverter size. Cards marked Typical estimate came from the quick questions; change a number and the card becomes Your number.
For a fridge, divide the EnergyGuide label's yearly kWh by 365 and enter that as watts over 24 hours. Count the electric parts of propane appliances. The surge factor is a rough multiple of running watts (1 = no startup surge); motors often draw 3 to 8 times their running current for a moment at startup.
System settings
Monthly peak sun hours
Filled in from your location: built-in NLR PVWatts values for your 3-digit ZIP area, south-facing panels tilted at latitude (long-term station data from the national lab formerly called NREL, now NLR). Replace them with your own site's monthly "solar radiation" values from PVWatts (pvwatts.nlr.gov); kWh/m²/day equals peak sun hours.
Where will the battery bank be installed?
Many off-grid planners use 1 to 3 days of autonomy when a generator is available, more without one. LFP batteries are commonly used to 80 to 100% depth of discharge; use your battery maker's number.
Results
Month by month
Winter vs summer
- Wire, fuse, breaker, and grounding sizes
- Panel string voltage in cold weather and charge-controller input limits
- Battery charge and discharge current limits
- Shading, snow cover, roof direction, and tilt at your site
- Local electrical code and inspection rules (see Before your inspection above)
- Whether specific products work together, warranties, and costs
Electric vs propane
Propane tank and refills
Generator
Sizing batteries and solar for the worst week of the year with no generator usually costs far more than owning a generator and some fuel. Choose a system that can charge the battery from the generator, and check how much solar your charger can actually accept: panels above that limit are mostly wasted. The 7 kW generator, 1.2 gal/hr, and 25% bad-weather figures are examples; use your generator's spec sheet.
I already have equipment
Enter what you own or were quoted. See how much of your load list it covers month by month, and how many sunless days the battery carries.
How it's calculated
Location privacy. Your location stays on this device. It's used only to look up sunlight and typical heating and cooling weather for your area. It isn't sent to us, isn't saved on any server, and isn't shared with anyone. Your plan, location included, is kept only in this browser and in this page's link so it's there when you come back; if you share that link or print your plan, the location goes with it. The map is drawn inside this page, so tapping it doesn't contact any map service. "Use my current location" asks your phone or browser for a position; the page only reads it on this device. The only things this page loads from the internet are its fonts and icons, and those requests carry no location.
Appliance types: typical watts and sources
| Default | Value | Source |
|---|---|---|
| Example load list | 12.8 kWh winter, 17.7 summer | Book companion spreadsheet v2 example house (generic example, not measured) |
| Peak sun hours | Jan–Dec 3.0, 3.8, 4.9, 5.8, 6.2, 6.4, 7.0, 6.9, 6.4, 5.1, 3.2, 2.7 (worst month Dec 2.7; Jun–Jul 6.7) | Long-term station data (NREL, now NLR), a built-in example used only until you set a location; check pvwatts.nlr.gov |
| Solar derate | 0.77 | PVWatts default 14% losses plus inverter |
| Days of autonomy | 2 | Planning target with a generator |
| Depth of discharge | 90% | LFP commonly 80–100% |
| Efficiency | 90% | Planning estimate |
| Inverter headroom | 25% | Generic planning margin |
| Motor start multiples | 1 to 4 | Generic examples; motors often 3–8× running current |
| Generator | 7 kW, 75% load, 90% charging, 1.2 gal/hr, 25% bad-weather sun | Examples |
Quick-estimate typical loads
Each quick answer adds the loads below. These are typical planning figures, not measurements or guarantees; your appliances' labels and spec sheets beat all of them.
| Answer | Typical load added | Band | Basis |
|---|
Sources: U.S. Department of Energy, Energy Saver appliance energy guidance (typical appliance wattage ranges) and ductless mini-split guidance, energy.gov/energysaver; ENERGY STAR product data for refrigerators, freezers, dishwashers, and washers, energystar.gov; EV efficiency from fueleconomy.gov; solar resource from PVWatts (NLR, formerly NREL). ZIP-area winter and summer weather (how far each month's days run below or above 65 °F): NOAA NCEI Global Summary of the Month, 2021–2025 average of HTDD and CLDD at the station nearest each 3-digit ZIP area's center that reports all 60 months (next-nearest if not), ncei.noaa.gov; a few areas without a complete recent station use NOAA 1991–2020 U.S. Climate Normals, ncei.noaa.gov. Built into this page; one station can differ from your exact site, especially in mountains. ZIP-area sun hours: NLR PVWatts v8 monthly solar radiation (solrad_monthly; south-facing, tilt = latitude, 14% losses) at one point per 3-digit ZIP prefix; each point is the average of that prefix's ZIP Code Tabulation Area internal points from the U.S. Census Bureau 2024 Gazetteer files, census.gov. Approximate for large or mountainous ZIP areas. Propane: 91,500 BTU per gallon; assumed efficiencies are furnace 92%, tankless water heater 82%, burner cooking about 40% vs electric 75%; an absorption (propane) fridge uses about 5 to 7 gal/month. Generator: 75% load, 90% charging, fuel from the spec sheet. Surge factors by load type: resistive and electronics ×1, inverter-driven (soft start) ×1, small motor ×2, motor ×3, compressor ×3, well motor ×4. Heating and cooling per square foot are planning rules of thumb, which is why their bands are wider.
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