Why a Solar Backup System Fails — And How you Can You Fix It! A solar backup system is designed to give you peace of mind during outages, but sometimes it fails to perform as expected. Here are the most common reasons this happens: 1. Wrong Battery Size or Battery Health Issues If the battery capacity is too small for the load, or the battery is old and degraded, it will not store enough energy to sustain your appliances. 2. Faulty or Misconfigured Inverter Incorrect settings, outdated firmware,