Surface calculator

Assumptions

• Indoor efficiency follows a smooth curve through 20% at 150 lux, 24% at 400 lux and 26% at 1,000 lux, easing back toward 20% under very bright light. Outdoor efficiency is 20% under 100 mW/cm² standard sun (AlphaGlass and AlphaVis).
• Room light is white LED at 300 lm/W, so 300 lux is 1 W/m² of optical power.
• Outdoor energy follows a daily profile, not peak × hours: irradiance rises and falls as a half-sine across the daylight hours, which delivers 2/π (about 64%) of the peak-hours figure.
• Indoor and outdoor hours together cannot exceed 24.
• The converter's efficiency rises smoothly with power, from about 50% at very low power to 91% above 50 mW. MPPT tracking accuracy is 96%.
• Rated voltage is the module's voltage at maximum power in full sun, as on the datasheets. The subcell count is set once from it at 0.9 V per subcell, rounded up, and stays fixed when the light changes.
• In other light, each subcell delivers about 0.8 V in Sunny Indoor and 0.7 V in Pure Indoor, so the module's working voltage is lower than its rating; voltage and current are shown for the selected light.
• Battery life follows the day: daylight hours, then indoor hours, then dark, with the battery starting full each morning. "Indefinite" means the battery also carries the load through every night.
• The calculator uses conservative design values, lower than the certified efficiencies quoted elsewhere on this site.
• Outdoor hours assume full sun, about 100,000 lux.
• Battery standby is added to the load: about 0.5 µA at the battery voltage for the charger, plus self-discharge of about 2% of the battery's capacity a month.
• Open-circuit voltage is about 1.1 V per subcell in full sun, 0.95 V in Sunny Indoor and 0.85 V in Pure Indoor, and rises about 0.1% per °C below 25 °C.
• AlphaVis output scales with opacity: a panel that is 40% transparent (60% opaque) gives 60% of AlphaGlass's output.
• AlphaGlass: rigid perovskite PV on glass. Module dimensions are limited to 450 × 300 mm.