Before selecting or purchasing any equipment required for a hybrid or stand-alone power system, the installer should have a good understanding of the basics of sizing energy storage systems. The most important part of the process is developing the load profile or building a load table to estimate the amount of energy required to be generated and stored per day. If you cannot develop a load table then a professional solar installer or system designer should be consulted. The general steps are as follows:
- Estimate the loads – how much energy is required per day in kWh. For off-grid power systems, a load table should be developed for both summer and winter requirements. The surge loads, power factors, and maximum demand or peak demand also need to be considered when selecting the battery and inverter-charger.
- Determine the battery size required in Ah or Wh. To ensure accuracy, take into account the battery type and chemistry, maximum depth of discharge (DoD), round-trip efficiency, days of autonomy, and maximum charge rate.
- Determine what size solar array in kW is required to charge the battery and supply the loads taking into account local conditions such as – average solar irradiance throughout the year (peak sun hours), shading issues, panel orientation, cable losses, and temperature derating (loss factors).
- After steps 1 to 3 have been established, you can then select the appropriate size inverter-charger, solar inverter or MPPT Solar Charge Controller to suit the system.