Many people assume that solar panels automatically keep the lights on during a blackout. With a standard grid-tie system, they do not. This guide explains why, and how to decide whether you need a battery.
Short answer
You do not need a battery for a grid-tie system to work. A grid-tie solar system sends power to your home and exports extra to the grid. But without a battery or a special backup setup, it shuts off when the grid goes down.
Why grid-tie shuts off in an outage
Grid-tie inverters are designed to follow the grid's signal. During an outage, they stop on purpose, a safety feature called anti-islanding. It protects utility workers from power flowing back into lines they believe are dead. So even on a sunny day, a standard grid-tie system will not power your home in a blackout.
Your options
| Setup | Battery? | Works in outage? | Cost |
|---|---|---|---|
| Grid-tie (string inverter or microinverters) | No | No | Lowest |
| Grid-tie with battery backup (hybrid or AC-coupled) | Yes | Yes, for chosen loads | Highest |
| Off-grid | Yes | Always, since no grid is used | High, plus larger battery and often a generator |
When a battery is worth considering
- Frequent or long outages where losing power is costly or unsafe, such as medical equipment, a home business or a well pump.
- Low payment for exported power. If your utility pays little for the energy you send to the grid, storing it for evening use can save more.
- Time-of-use rates. A battery can charge from solar and supply the home when grid prices are highest.
- A wish for more independence from the grid.
When you can probably skip it
- Your grid is reliable and outages are short and rare.
- Your utility offers good net metering or export payments.
- You want the lowest upfront cost and the fastest payback.
Other things to check
- Utility rules and approval: connecting to the grid usually requires a permit and utility approval, and rules about export payments vary a lot by location.
- Incentives: tax credits, rebates and programs change often, so check current local information.
- Backup loads: a battery usually backs up only a chosen set of "critical loads" such as the fridge, lights, internet and a few outlets, instead of the whole house.
- Future-proofing: some hybrid inverters let you start without a battery and add one later.
How to size it
If you decide on a battery, list the appliances you want to keep running, total their daily watt-hours, and decide how many hours or days of backup you want. Our guide to sizing a solar battery bank walks through the math, and the calculator supports grid-tie, microinverter and hybrid setups.
Disclaimer: This article is for general information and education only. Numbers are estimates and examples, not professional advice or a certified design. Have your final design reviewed by a qualified electrician or installer and follow your local codes and utility rules.
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