Sizing a Solar Lantern: Panel Watts and Battery Watt-Hours for 100 Lumens for Four Hours a Night, by Climate Class, with the Cloudy-Day Failure Line

Derives panel and battery size for 100 lm for 4 h/night: 3.899 Wh/night from battery, 2.0 Wp panel (arid tropical), 2.5 Wp (tropical humid), 4.5 Wp (temperate winter), 12.18 Wh for 2-day and 18.27 Wh for 3-day autonomy; a common 1 Wp / 3.7 Wh lantern supports only 0.55 of a night per day in the humid class. Failure line is about 4 consecutive cloudy days.