How we compare stations

Where figures come from

Each figure is read from the maker's manual first, then the maker's spec page, then a filing or datasheet. Where documents disagree, the station's own page says so. Where a maker prints nothing, we say "not published" and never estimate.

Usable capacity

Runtime uses 85% of the rated watt-hours, to allow for inverter and battery losses. Real results vary with the load and the temperature.

Runtime

Hours are usable watt-hours divided by the appliance's average draw. Average draw comes from published yearly energy use for appliances that cycle, such as refrigerators, and otherwise from running watts. Every appliance figure lists its source on its own page.

Startup power

Motors pull more power for a moment at startup. We compare the published startup figure with the station's printed surge or peak figure. Makers describe that figure in different ways, and a station can still shut off.

Solar panel fit

A panel's voltage rises in the cold. We take its open-circuit voltage, adjust it to 14 F using its printed temperature figure, or minus 0.3% per degree C when none is printed, multiply by the panels in series, and compare the result with the station's printed maximum. A pass needs 10% of headroom. A panel under the maximum with less headroom than that is marked as close to the limit. The panel's running voltage must also clear the station's minimum.

A pass means the printed numbers line up. It is not a maker's approval and it is not wiring advice. Some makers limit warranty on other brands' panels.

Solar recharge time

Hours assume panels reach 75% of their rating, capped by what the station accepts. State figures are yearly averages for one city in each state on a panel tilted 20 degrees, worked out with NREL's PVWatts, so flat panels and shade give less.

Overall score

The top five on the best-of page use a score from 0 to 100. It averages where a station stands among all stations on five printed figures: watt-hours per pound, rated cycles, hours to refill at full solar input, hours to refill from the wall, and warranty years. A station must print at least four of them, must still be sold by its maker and must be listed on Amazon to place. The figures carry equal weight and price plays no part.

Rankings

Every list states its rule. The order comes from the printed figures, not from commissions or opinion.