How Much Wood a Solar Cooker Actually Saves: The Displacement Bound Set by Meal Timing, Weather and Use

This paper computes an upper bound on the fraction of a household annual fuelwood that a solar cooker can displace, from three stated factors: the share of cooking energy in meals whose timing a solar cooker can serve, the fraction of days on which the cooker is usable, and the fraction of usable days on which a household actually uses it. The work is simulated, not measured, and the calculation is an arithmetic bound, not a field measurement. With a stated meal pattern in which breakfast takes 0.20 of cooking energy, the midday meal 0.30 and the evening meal 0.50, and with the evening meal cooked after sunset, only the midday share of 0.30 is addressable without changing meal timing. With a usable-day fraction of 0.60 and a usage rate of 0.50, the displaced fraction is 0.09, which is 180.0 kg per year for a household using 2000 kg per year. Even with perfect weather and perfect use, the ceiling with unchanged meal timing is 0.30, so the claim that such a cooker halves fuel use does not survive the arithmetic for this meal pattern, and the claim that it replaces firewood does not survive in any household scenario examined. Large displacement becomes reachable only when meal timing itself changes, or in institutional midday cooking, where the computed displacement is 0.648 under stated favourable assumptions.