Critical Loads Only Backup

Critical loads only backup is a battery storage configuration that powers only selected essential circuits during a grid outage — such as the refrigerator, key lighting, internet, phone chargers, and medical equipment — rather than the entire home. It is the most common and cost-effective approach to solar battery backup.

With critical loads backup, a dedicated subpanel (the critical loads panel) is installed and wired to only the circuits you deem essential. During an outage, the battery powers only these circuits, conserving energy and extending backup duration significantly. A single 13.5 kWh battery powering 1–2 kW of critical loads can last 8–15 hours overnight, and if the sun shines the next day, the solar panels recharge the battery for continued operation — potentially providing indefinite backup during multi-day outages. The main limitation is that high-power loads like central air conditioning, electric water heaters, and electric dryers are typically excluded from the critical loads panel because they would drain the battery too quickly. This trade-off keeps the system affordable (one battery vs. three or four for whole-home) while providing meaningful backup for the loads that matter most during an emergency.