Off-Grid Solar Sizing API

Off-grid solar system-sizing maths as an API, computed locally and deterministically — the battery-bank, solar-array and charge-controller numbers an RV, cabin, boat or off-grid homeowner sizes a system with. The battery-bank endpoint gives the storage you need = (daily load × days of autonomy) ÷ (depth of discharge × round-trip efficiency), then ÷ the system voltage for amp-hours: the autonomy carries you through cloudy days and the depth-of-discharge limit protects the cells (lead-acid ~50 %, lithium 80–100 %, which is why lithium banks run smaller), so a 2 kWh/day load at 12 V with 2 days autonomy, 50 % DoD and 85 % efficiency needs about 785 Ah. The array endpoint gives the panels = daily energy ÷ (peak sun hours × system efficiency), where peak sun hours is the day's irradiance as equivalent full-sun hours (~3–6 by place and season) and the efficiency rolls up controller, wiring, heat and dust losses — about 670 W for that load at 4 sun hours and 75 %. The charge-controller endpoint sizes the controller = array watts ÷ battery voltage × a 1.25 safety factor, so a 700 W array on a 12 V bank wants roughly an 80 A controller. Everything is computed locally and deterministically, so it is instant and private. Ideal for solar-installer and DIY tools, RV/marine/cabin power planners, and renewable-energy calculators. Pure local computation — no key, no third-party service, instant. Size for the worst month. 3 compute endpoints. For solar irradiance and sun hours use a solar API; for battery runtime under load a battery API.