One of the most common reasons people add a battery to a solar system is backup power. Understanding what a battery can realistically do sets expectations before any design decision.
What happens during an outage
In a grid outage, a plain grid-tied solar system shuts down its export — a safety requirement so the grid is not energized while line workers repair it. A system with battery storage and the right equipment can instead switch to running selected loads from the battery, recharging from the panels when the sun is out. The result is not necessarily a fully powered house; it is a house whose essential loads keep running.
What loads a battery can serve
Batteries are sized in energy and limited in how much power they can deliver at once. Essential loads — lighting, refrigeration, communications equipment, medical devices, fans — are typical candidates. Large, power-hungry appliances such as air conditioners, electric water heaters, and electric ranges can drain a typical household battery quickly and are often left off the backup list, or run only briefly. The backup plan is a design decision: which circuits, for how long, under what assumptions.
Backup versus self-consumption
Two goals often get mixed together:
- Backup keeps essential loads running during outages. It values the battery's stored energy as a reserve.
- Self-consumption uses the battery daily — charging from midday surplus and discharging in the evening — to reduce how much energy is drawn from the grid.
A battery can serve both goals, but the design choices differ: a reserve kept for emergencies reduces what is available for daily use, and vice versa. Being clear about which goal matters more is the first step in sizing.
Work with a designer
Load lists, run-time expectations, and chemistry choices are engineering questions best worked through with a qualified local professional who can model your actual consumption. Insolatio explains the concepts; your designer sizes the system.