Planning an Off-Grid Solar System
An off-grid solar system must cover daily energy use without support from the utility grid. The design starts with loads. Each light, fan, pump, charger, or refrigerator adds watt hours. A small mistake can reduce comfort during cloudy days. This calculator keeps the main parts together. It links energy demand, sun hours, losses, panel size, battery storage, and controller current.
Why Daily Energy Matters
Daily energy is the base number. It is measured in watt hours per day. A 100 watt load running for five hours uses 500 watt hours. Many appliances do not run all day. Motors, fridges, and pumps cycle on and off. Use realistic hours and add a margin. Extra margin helps when weather changes or users add devices later.
Battery Bank Planning
Batteries store energy for night use and bad weather. The calculator uses autonomy days and depth of discharge. Autonomy is the number of days you want backup energy. Depth of discharge is the safe usable share of the battery. Lower discharge improves battery life. Battery efficiency also matters. Some energy is lost when charging and discharging.
Solar Array Sizing
Solar panels must replace used energy during available sunlight. Peak sun hours are not the same as daylight hours. They describe useful full-power solar time. Losses come from wiring, dirt, heat, charge control, and mismatch. Panel derating adds a practical safety layer. Oversizing gives faster recovery after cloudy periods.
Inverter and Controller Choice
The inverter should handle continuous load and surge load. Pumps, compressors, and tools can start with high surge power. A weak inverter may trip even when daily energy seems low. The charge controller must handle array current safely. Current is based on array watts and battery bank voltage. A safety factor protects the controller on bright, cool days.
Using the Result
Use the result as a planning estimate. Check local codes before installation. Confirm product ratings with datasheets. Match batteries, controller, wiring, fuses, and panels carefully. Off-grid systems work best when loads are efficient. Start by reducing waste. Then size the system. This approach often saves money and improves reliability. Review the estimate again after seasonal load changes. Summer cooling and winter lighting can change the design.