Wattcellar

Methods and sources

Every formula, every default, and where each number comes from. If a figure here is wrong or out of date, tell us.

Last updatedOct 18, 2026

Sources readOct 18, 2026

Runtime

Hours = rated capacity (Wh) × share you can use × inverter efficiency ÷ (sum of appliance average watts + station idle watts).

The default efficiency is 85%, from Jackery's published formula, "Working time = Explorer's Watt-Hours × 0.85 / operating power of your device" (Jackery FAQ; the same factor is in Jackery's watt-hour guide). BLUETTI publishes the same calculation with separate terms, "Runtime (hours) ≈ Battery capacity (Wh) × DoD × η ÷ (Load power + self-consumption)", and gives DoD 90%, η 85% and self-consumption about 15 W for the AC180 (BLUETTI EU; see also BLUETTI US). Those are used when you pick the AC180. For other stations the share you can use defaults to 100% (the station's own cutoff) and idle draw to 0 W, both labeled as examples, because their makers don't publish them.

Output and surge check

Running watts are everything on the list at once. Start-up watts are running watts plus the largest single gap between an appliance's start-up and running watts, assuming one motor starts at a time. Whirlpool: "Depending on the motor's efficiency, it may require two to three times the running amps to start. On refrigeration, for example, we recommend doubling the running wattage for motor start-up consideration" (Whirlpool). GE gives the same guidance: about 2× the running power, lasting a second or two (GE Appliances). We apply 2× to fridge and freezer compressors and the window AC compressor, and 3× to sump pumps by default. These are rules of thumb. A frost-free fridge's defrost heater runs while its compressor is off, so the output check also covers the list with one fridge in defrost: running watts minus that fridge's compressor plus its heater.

Sizing

Energy per day = Σ watts × count × hours a day. Capacity to look for = energy per day × days ÷ (share you can use × efficiency). A station "fits" when its capacity, AC output and surge (where listed) all cover the list.

Solar recharge

Watt-hours into the battery per day = min(panel watts, station solar limit) × (1 − system losses) × peak sun hours. Losses default to 14%, the PVWatts default. Peak sun hours are PVWatts v8 monthly solar radiation (kWh/m²/day) for a fixed, south-facing array tilted at the site latitude, requested on Oct 18, 2026 with system_capacity=1, module_type=0, losses=14, array_type=0, azimuth=180, for the largest city in each state (PVWatts v8 API; NREL is now named NLR). We plan on the worst month. Battery charging losses inside the station are not included, so real refills may be slower.

Charge time

Charging figures are from each maker's US product page, read Oct 18, 2026; they're listed on the charge-time page. Where a maker publishes a full-charge time for a mode, we use it and scale it by the share being filled. Where it publishes only input watts, hours = capacity × share to fill ÷ (input watts × factor). The wall factor, 0.74, is the median of what makers' own figures imply when they publish both watts and a time for the same mode: capacity ÷ hours ÷ watts. That covers six pairs on five stations (RIVER 3 Plus, DELTA 3 Plus, AC180 standard and Turbo, Elite 200 V2, C1000 Gen 2 UltraFast), ranging 0.62 to 0.82. The car factor, 0.89, is the median of the 12 V pairs (Jackery's two published car times at 12 V ⎓ 8 A, plus RIVER 3 Plus). Solar uses the same PVWatts sun hours, 14% losses and solar input cap as the solar page, then divides by the same 0.89 factor for losses inside the station. Charging usually slows over the last few percent, so a top-off to 100% can take longer than the straight-line estimate.

Daylight strip

Sunrise, sunset and civil twilight on the strips come from the sun's position, computed in your browser with standard low-precision almanac formulas (accurate to about a minute), for the city coordinates listed in the sun-hours table. Day is the sun's center above −0.833°, twilight down to −6°.

Appliance figures

"Average" is what the runtime and sizing math uses; "running" and "start-up" feed the output check. ENERGY STAR figures are medians of certified models in the dataset on Oct 18, 2026, converted from kWh a year to average watts by dividing by 8,760 hours. Certified models are efficient ones; older or uncertified appliances often use more.

Appliance watts used by the tools (16 items)
ApplianceAverage, WRunning, WStart-up, WSource and basis
Refrigerator, top freezer41.4160320ENERGY STAR certified-product data (data.energystar.gov): Median 363 kWh/yr across 750 ENERGY STAR top-freezer models (middle 80%: 297 to 450 kWh/yr), averaged over 8,760 hours.Compressor running: 160 W. Embraco's 115 V household compressors draw about 90 to 162 W at the catalog's rating point (−23.3 °C evaporating, 54.4 °C condensing, harsher than a kitchen); we use the top of that range. NEEA's metering study logged about 120 W while the compressor ran on a 2006 20 cu ft fridge. Start-up: 320 W, twice running. GE and Whirlpool both say to allow about double the running watts for a refrigerator compressor to start, for a second or two. Defrost heater: 425 W, a brief separate load. NEEA measured defrost spikes of 425 W (2006 fridge) and 800 W (1995 fridge) in 5-minute data; the compressor is off while the heater runs, and GE says it runs about twice a day.
Refrigerator, bottom freezer64.6160320ENERGY STAR certified-product data (data.energystar.gov): Median 566 kWh/yr across 1,524 ENERGY STAR bottom-freezer models, averaged over 8,760 hours.Compressor running: 160 W. Embraco's 115 V household compressors draw about 90 to 162 W at the catalog's rating point (−23.3 °C evaporating, 54.4 °C condensing, harsher than a kitchen); we use the top of that range. NEEA's metering study logged about 120 W while the compressor ran on a 2006 20 cu ft fridge. Start-up: 320 W, twice running. GE and Whirlpool both say to allow about double the running watts for a refrigerator compressor to start, for a second or two. Defrost heater: 425 W, a brief separate load. NEEA measured defrost spikes of 425 W (2006 fridge) and 800 W (1995 fridge) in 5-minute data; the compressor is off while the heater runs, and GE says it runs about twice a day.
Refrigerator, side by side73.1160320ENERGY STAR certified-product data (data.energystar.gov): Median 640 kWh/yr across 123 ENERGY STAR side-by-side models, averaged over 8,760 hours.Compressor running: 160 W. Embraco's 115 V household compressors draw about 90 to 162 W at the catalog's rating point (−23.3 °C evaporating, 54.4 °C condensing, harsher than a kitchen); we use the top of that range. NEEA's metering study logged about 120 W while the compressor ran on a 2006 20 cu ft fridge. Start-up: 320 W, twice running. GE and Whirlpool both say to allow about double the running watts for a refrigerator compressor to start, for a second or two. Defrost heater: 425 W, a brief separate load. NEEA measured defrost spikes of 425 W (2006 fridge) and 800 W (1995 fridge) in 5-minute data; the compressor is off while the heater runs, and GE says it runs about twice a day.
Upright freezer50160320ENERGY STAR certified-product data (data.energystar.gov): Median 438 kWh/yr across 474 ENERGY STAR upright freezers, averaged over 8,760 hours.Compressor running: 160 W. Embraco's 115 V household compressors draw about 90 to 162 W at the catalog's rating point (−23.3 °C evaporating, 54.4 °C condensing, harsher than a kitchen); we use the top of that range. NEEA's metering study logged about 120 W while the compressor ran on a 2006 20 cu ft fridge. Start-up: 320 W, twice running. GE and Whirlpool both say to allow about double the running watts for a refrigerator compressor to start, for a second or two. Defrost heater: 425 W, a brief separate load. NEEA measured defrost spikes of 425 W (2006 fridge) and 800 W (1995 fridge) in 5-minute data; the compressor is off while the heater runs, and GE says it runs about twice a day.
Chest freezer24.9160320ENERGY STAR certified-product data (data.energystar.gov): Median 218 kWh/yr across 9 ENERGY STAR chest freezers in the dataset (small sample), averaged over 8,760 hours.Compressor running: 160 W. Embraco's 115 V household compressors draw about 90 to 162 W at the catalog's rating point (−23.3 °C evaporating, 54.4 °C condensing, harsher than a kitchen); we use the top of that range. NEEA's metering study logged about 120 W while the compressor ran on a 2006 20 cu ft fridge. Start-up: 320 W, twice running. GE and Whirlpool both say to allow about double the running watts for a refrigerator compressor to start, for a second or two. Chest freezers are usually manual-defrost, so no defrost heater is added.
Microwave oven1,1001,1001,100Whirlpool, Generator Usage with Appliances: Upper end of Whirlpool's 800 to 1,100 W running range.Same figure. No start-up surge is applied.
CPAP (ResMed AirSense 11) medical56.173.273.2ResMed AirSense 11 user guide, technical specifications: Typical power consumption 56.1 W (111.5 VA).Peak power consumption 73.2 W (137.6 VA); 65 W power supply unit
Oxygen concentrator (Philips EverFlo) medical350350350Philips Respironics EverFlo brochure: Average power consumption 350 W at 120 VAC, 60 Hz.Same figure. Philips does not publish a start-up surge in this brochure, so none is applied.
Sump pump, 3/10 HP (Zoeller M53)1,1161,1163,347Zoeller Model M53 spec page: 9.7 A at 115 V = 1,116 W, an upper bound from the amp rating, not measured watts.Start-up surge 3 times running watts: Whirlpool says motors may need two to three times running amps to start. A rule of thumb.
Window AC, 8,000 BTU5335331,066ENERGY STAR certified-product data (data.energystar.gov): 8,000 BTU/h divided by median CEER 15.0 across 91 ENERGY STAR 8,000 BTU models (range 500 to 606 W).Surge 2 times running, applying Whirlpool's refrigeration-motor rule of thumb to the compressor.
Space heater (Lasko 754200)1,5001,5001,500Lasko 754200 product page: 1,500 W on high (900 W on low).Same figure. Resistive heat has no motor surge to speak of.
Ceiling fan, 50 to 54 in, high28.628.628.6ENERGY STAR certified-product data (data.energystar.gov): Median high-speed power 28.6 W across 687 ENERGY STAR fans 50 to 54 in.Same figure.
TV, 55 in96.596.596.5ENERGY STAR certified-product data (data.energystar.gov): Median on-mode power 96.5 W across 21 ENERGY STAR 55 in TVs (90th percentile 111.5 W).Same figure.
Internet gateway (Xfinity XB8)171717CableLabs Energy Reporting, Comcast small network equipment: 17.00 W reported for Comcast CGM4981COM (XB8).Same figure.
LED bulb, 60 W equivalent (Feit OM60DM)8.88.88.8Feit Electric OM60DM/927CA product page: 8.8 W rated.Same figure.
Phone charger (Apple 20W USB-C)202020Apple 20W USB-C Power Adapter: 20 W adapter rating, an upper bound; a phone draws less as it fills.Same figure.

Refrigerators and freezers

Average watts come from ENERGY STAR certified-product medians (top freezer 363 kWh a year, bottom freezer 566, side by side 640, upright freezer 438, chest freezer 218), divided by 8,760 hours. They include compressor cycling and defrost.

Running watts are the compressor-on draw: 160 W for every type. Embraco's Americas compressor catalog (Embraco catalog, read Oct 18, 2026) lists cooling capacity and efficiency for each model at the ASHRAE check point (−23.3 °C evaporating, 54.4 °C condensing). Capacity ÷ efficiency gives power in for its 115–127 V, 60 Hz household models: EMU40CLP 117 W ÷ 1.30 = 90 W; EMU60CLP 164 ÷ 1.41 = 116 W; EMYE70CLP 205 ÷ 1.46 = 140 W; EGAS80CLP 245 ÷ 1.51 = 162 W (all R600a); EM2U3111U 167 ÷ 1.66 = 101 W and EM2U3115U 242 ÷ 1.65 = 147 W (R290). The check point is harsher than a kitchen, and we round to 160 W, the top of that range, so it errs high for small fridges and chest freezers. As a measured cross-check, NEEA's Residential Building Stock Assessment metering of 104 Northwest homes (5-minute data, 0.1 W resolution) shows about 120 W while the compressor ran on a 2006 20 cu ft fridge and about 200 W on a 1995 one (ACEEE 2014 paper, Figure 4).

Start-up is 2 × running, 320 W, following GE and Whirlpool. For a fraction of a second, inrush can approach the compressor's locked-rotor current, 7.33 to 18 A on the Embraco models above. NoOutage.com measured a 13 A peak lasting about half a second on a 1986 fridge whose plate said 5 A (NoOutage). We note this on the refrigerator page rather than size for it.

Defrost heater: 425 W for frost-free fridges and upright freezers, 0 for chest freezers, which are usually manual-defrost. NEEA's data shows defrost spikes of 425 W (2006 fridge) and 800 W (1995 fridge). Those are 5-minute averages, and the 2006 figure is used. GE says the heater runs about twice a day; the compressor is off while it does. Its energy is already inside the ENERGY STAR kWh, so it changes only the output check, not the hours.

Rating plate, shown as a cautious upper bound and never the default: amps × 120 V, or the maker's listed watts. GE says its rated wattage usually includes the defrost heater. The figures we show are: Frigidaire FFTR1814W top freezer, 3 A, 360 W (version 08/22); GE GDE21EGKWW bottom freezer, 248 W, 572 kWh a year (GE spec page); Frigidaire FFSS2314Q side by side, 8.5 A, 1,020 W (09/15); FFUH17F2N upright freezer, 5 A (07/13); FFFC07M4N chest freezer, 5 A (08/13); plus FGHT2055V, 2 A (10/23), and FRBG1224A, 1.1 A (04/26).

Change log. On Oct 18, 2026 we first replaced Whirlpool's rough 1,000 W guide figure with rating-plate watts. Later the same day we moved those plate figures to an upper bound, because a 2013 Canadian bottom-freezer sheet (11.6 A, 1,392 W, heaters included) overstated what a modern fridge draws. Food-safety times are from the FDA (content current as of Mar 5, 2024).

CPAP

AirSense 10 draw by pressure and humidifier setting is from the Air10 series DC-to-DC converter table in ResMed's battery guide (198103/7, 2018-08), amps at 12 V DC × 12. AirSense 11: 56.1 W typical and 73.2 W peak from the AirSense 11 user guide. Philips DreamStation 2: its instructions for use say an 80 W power supply is required for humidification and list AC input of 100 to 240 V, 1.0 to 2.0 A; we use 80 W as an upper bound. Nights assume 8 hours of sleep, the basis of ResMed's tables.

Sump pumps

Running watts are rated amps × rated volts: Zoeller M53 9.7 A at 115 V; Zoeller M98 9.4 A at 115 V (Model 98 technical data sheet); Superior Pump 92341 4.1 A at 120 V; Wayne CDU790 9.5 A and CDU980E 9.8 A at 120 V (Wayne manual). Start-up defaults to 3 × running, the top of Whirlpool's two-to-three-times range for motors. Cycles per hour and seconds per cycle are examples to replace with your own timing.

Oxygen concentrators

As each maker states it: Philips EverFlo 350 W average at 120 V; Invacare Platinum 5 400 W average (user manual); DeVilbiss 525DS 310 W average and 275 W at 2.5 L/min and below (DeVilbiss brochure); CAIRE Companion 5 285 W at 2 L/min, 350 W maximum; Inogen At Home 275 W power supply and 100 W on flow setting 2. None publishes a start-up surge, so the tools check running output only.

Station specs

From each maker's U.S. store product page on Oct 18, 2026. See the station specs table for the figures, gaps and price notes.

What we don't know