Methodology

What we do

Enough Watts reads published specifications and does the arithmetic below. We do not test power stations or measure appliances. Every number on the site is a figure from the data or the result of a formula on this page.

Sources

Power station figures start on an official page: the maker's product page, manual or specification sheet. Appliance figures come from appliance makers, government lists of certified models and generator makers' wattage charts. Each record lists its pages and the date we checked them. Retail sites help us find products. We take a fact from a retailer in one case only: a list price for a product the maker sells through retailers alone, marked as a retailer price.

Each appliance on your list

You set how many (1 to 20) and the hours of use per day (0 to 24). Each appliance type starts with a default number of hours. For each line the calculator works out four numbers.

• Running watts: the watts you enter from the label when you use Use the watts on your label, otherwise the typical running watts of the appliance type.
• Starting watts: for your own appliance, the starting watts you enter. For an appliance type, its typical starting watts where a source publishes them. Otherwise the running watts, which means no start surge. A starting figure at or below the running watts counts as no surge.
• Peak running watts: running watts × quantity.
• Watt hours per day, by the first rule that applies: with label watts, running watts × hours × duty cycle × quantity. For an appliance type with published energy per day, daily kWh × 1,000 × (hours ÷ 24) × quantity. Otherwise, running watts × duty cycle × hours × quantity. Your own appliance counts running watts × hours × quantity.

The duty cycle is the published share of the time an appliance draws power while it is switched on, and 100% where none is published. Of the 79 appliance types in the data, 6 publish energy per day (refrigerators and freezers) and none publishes a duty cycle, so the others count their full running watts for every hour you enter.

A motor or compressor type with neither a duty cycle nor energy per day counts its running watts for every hour entered. For those, the hours field reads "Hours the motor actually runs per day" and the line carries this note: "Assumes the motor runs the whole time; real use is often less." A refrigerator or freezer with label watts is counted the same way and gets the same note, because the label watts replace its daily energy.

A motor or compressor type with no published starting watts carries this note: "Starting watts not published; motors often need 2 to 3 times their running watts to start." Its start is checked at running watts, so a station is never rejected on a guess. 9 appliance types rest on weaker sources; their watts carry the label "estimate" wherever they appear.

Your list in total

• Running watts = the sum of peak running watts. Everything on the list runs at the same moment, the cautious case.
• Starting watts needed = running watts - the running watts of one appliance + its starting watts, taken for the appliance where this is largest, among those that start above their running watts. One unit of one appliance starts while everything else runs. With no such appliance it equals the running watts.
• Watt hours per day = the sum of the watt hours per day of each line.
• Average draw = watt hours per day ÷ 24.

Two lines appear under the totals. Always: "Watts vary by model and age. Check the label on your own appliance and enter it for an exact answer." When the list holds medical equipment: "For medical equipment, confirm the power needs with the device maker and keep a backup plan. This page is not medical advice."

Each power station

• Usable watt hours = rated capacity × efficiency. Efficiency is the share of the rated capacity that reaches the outlets: 85% by default, adjustable from 75% to 95% under Assumptions and solar.
• Output check: the continuous AC output must be at least the running watts.
• Surge check: the surge rating must be at least the starting watts needed. Where a maker publishes no surge rating, the check uses the continuous output and the result says: "Surge rating not published, so the check uses the continuous rating."
• 240 V check, only when an appliance on the list needs 240 V: it passes on a station that supplies 240 V on its own and fails on one that cannot supply it. A station that needs a second unit linked fails, with the note "240 V needs two units linked." A station whose maker does not state it passes, with the note "240 V support not published."
• Runtime = usable watt hours ÷ watt hours per day × 24. This is calendar time while you follow the daily routine you entered, and the number compared with your goal. A list that uses no energy has no limit.
• Nonstop runtime = usable watt hours ÷ running watts, the time with everything running at once. Shown as the second readout, never compared with the goal.

The 85% default

85% is the site's own assumption, not a measured figure. It covers the losses in the inverter and in the conversion from battery to outlet. The real share varies with the station, the load, the temperature and the age of the battery. Why you get less than the rated capacity explains when to change it.

The verdict

The goal is how long the list must run without recharging: 4, 8, 24, 48 or 72 hours, 24 by default.

• Boost mode. When the output check fails and the maker's reduced voltage mode covers the running watts, the verdict stays Cannot power it and a note names the mode, for example: "Its boost mode can run this at up to 2,400 W by lowering the voltage. That suits heaters and kettles, not motors or electronics."
• Expansion. When a station runs the list but not for long enough, and the largest capacity its maker lists with expansion batteries × efficiency ÷ watt hours per day × 24 reaches the goal, the result adds: "Enough with expansion batteries." More batteries never fix a failed power check, so the note never appears under Cannot power it.

The order of results

• Enough: the smallest capacity first, because it is the closest fit, then the lower price, then the lighter unit.
• Runs it, but not long enough: the longest runtime first, the station closest to the goal.
• Cannot power it: the same order as Enough.
• Other orders: price, weight, runtime (longest first) and price per watt hour. They apply to the first two groups, and ties fall back to the closest fit. A missing price or weight sorts last.

Every list ranks the 54 stations in the Enough Watts data set and nothing else. Whether a link can earn us money never changes the order, the groups or the wording. See how we make money.

One appliance on its own

The tables on station and appliance pages check one unit of one appliance at its default hours, with the same output, surge and 240 V checks and the default efficiency.

• Running time = usable watt hours ÷ average draw.
• Average draw = daily kWh × 1,000 ÷ 24 for an appliance type with published energy per day, otherwise running watts × duty cycle. Watts you enter replace both.
• Minutes of use = running time × 60, shown for appliance types used less than an hour a day.

Solar recharge

• Solar input = the smaller of your panel watts and the station's solar input limit. A station whose maker publishes no limit gets no solar figure.
• Daily harvest = solar input × peak sun hours × 0.75. Peak sun hours default to 4. The station keeps up when the daily harvest is at least the watt hours per day of your list.
• Hours of sun to refill = rated capacity ÷ (solar input × 0.75), from empty.

The 0.75 is our planning figure for the losses between the panel rating and the battery: heat, panel angle, dirt and the charge controller. The refill time assumes full sun for the hours entered and ignores the slower charging some stations use near full.

Prices

Each station carries one US price with the month we saw it: the list price on the maker's US store, or the only price the store shows, or a retailer price where the maker sells only through retailers. Sale prices are not stored. Price per watt hour is that price ÷ rated capacity.

What the numbers assume

• Everything on the list runs at the same moment, and one appliance starts at a time.
• Daily use is spread through the day. With a goal shorter than 24 hours, the runtime counts the share of the day the goal covers. If all of a day's use falls inside the goal, such as a television on for 4 hours of a 4 hour outing, set the goal to 24 hours to count the full day.
• Watts vary by model and age. The typical figures cover a range of models; the label on your own appliance is the better number.
• The usable share changes with temperature, battery age and load. The default does not model any of them.
• Surge ratings are taken as published, with no account of how long a station can hold them.
• Nothing was tested. The results come from published figures and the formulas on this page.

Corrections

To report a wrong number, send the maker's page that shows the right one to hello@enoughwatts.com. We check every report against that page.