Steam Sterilization of Instruments with a Household Pressure Cooker, Priced from Physics — and an Honest Verdict on Solar Sterilization Claims

A validated steam cycle (121 C, 103 kPa gauge, 30 min wrapped hold) for 2.0 kg of instruments in a 10 litre pressure cooker requires 1.547 MJ of useful heat (1,331.3 kJ heat-up, 216.0 kJ hold losses), costing $0.091 on electricity (0.506 kWh), $0.061 on LPG (0.061 kg), or $0.083 on wood (0.413 kg), with 5 cycles per 8-hour clinic day on any source. Tested against the same budget, a glazed flat-plate solar collector has efficiency 0.21 at 121 C at 800 W/m2 and zero at 500 W/m2, where it cannot hold 121 C at any area; evacuated-tube and parabolic collectors can complete one cycle in about 0.94-1.47 sun-hours with 1-2 m2 on a clear day but cannot guarantee the hold. Solar sterilization is therefore energetically possible only with high-temperature collectors and backup heat, and is not reliable as a flat-plate sole-source method. SIMULATED, NOT MEASURED.