Best Practices for Sizing Solar Batteries with Generators?

Calculating System Requirements

When sizing solar batteries with generators, it’s essential to calculate the system’s daily energy requirements. Start by determining the total daily energy demand of your load, including appliances, lights, and other devices. For example, if your system needs 1 kWh of energy per day, you’ll want to add a 10% to 20% buffer for system losses and inefficiencies. This means you’ll need a minimum of 1.1 to 1.2 kWh of energy per day.

Generator Capacity and Auto-Start

A common practice is to size the generator to 30% to 50% of the system’s daily energy demand. This allows the generator to start automatically when the battery state of charge (SOC) reaches a certain level, usually around 20% to 30%. A rule of thumb is to choose a generator with a capacity of 100 to 200 watts for every 1 kWh of daily energy demand. For example, if your system needs 1.2 kWh per day, a 120 to 240 watt generator would be sufficient.

Battery Sizing and Configuration

When sizing solar batteries, consider the generator’s capacity, the solar array’s output, and the system’s daily energy needs. Typically, a 10 to 20 kWh battery bank is sufficient for a small to medium-sized off-grid system. For a system with a 1.2 kWh daily energy demand, a 12 to 24 kWh battery bank would be suitable. When configuring the battery bank, consider a 1C to 2C discharge rate, which means the battery can handle a maximum discharge rate of 1 to 2 times its capacity per hour.