What Home Battery Storage Actually Does
A home battery stores electricity. When your solar panels produce more than you're currently using, the excess charges the battery instead of going to the grid. When the panels aren't producing (at night, during cloudy weather, or during a grid outage), the battery supplies that stored electricity.
That's the core function. Whether it makes sense for your home depends on which benefits you need and whether the economics justify the cost.
The Two Main Use Cases
Use Case 1: Backup Power During Outages
A grid-tied solar system without a battery goes dark during a grid outage — by design. The system shuts down as a safety measure to prevent it from sending power to lines where utility workers may be present.
With a battery, your home can island from the grid during an outage. Your essential loads — refrigerator, lights, phone chargers, medical equipment — stay powered. If the outage extends overnight, the battery depletes. When the sun rises, solar recharges the battery and the cycle continues.
How long the battery lasts depends on its capacity (measured in kilowatt-hours) and what loads you're powering. A single battery (10–13 kWh) powering essential loads typically lasts 10–24 hours, depending on the combination of loads.
Use Case 2: Bill Optimization
For homeowners on time-of-use (TOU) electricity rates, batteries allow you to store solar energy produced during low-value midday hours and use it during high-value evening peak hours — shifting consumption away from expensive rate periods.
The value of this use case depends heavily on your utility's rate structure. If you're on a standard flat rate with full net metering, the economics of bill optimization through battery storage are generally less compelling — the grid essentially acts as a free battery through net metering. If your utility has TOU rates or limited net metering, battery economics improve.
Verify your utility's current rate options and net metering policies before assuming battery economics for bill optimization.
Critical Loads vs. Whole-Home Backup
Most home batteries are sized for critical loads — the equipment you most need to keep running during an outage — rather than whole-home backup.
Critical loads typically include: refrigerator, freezer, select lighting circuits, device charging, internet router, and any medical equipment. These draw relatively modest power compared to heavy loads like electric dryers, electric ovens, or electric vehicle chargers.
Whole-home backup — powering everything in the house as normal during an outage — requires significantly more battery capacity and often multiple battery units. It's available but substantially more expensive. SPM will conduct a load analysis to help you determine what level of backup coverage makes sense for your priorities and budget.
Battery Sizing Basics
Battery capacity is measured in kilowatt-hours (kWh). SPM installs Enphase IQ Battery and Tesla Powerwall systems:
- Enphase IQ Battery 5P: approximately 5 kWh usable per unit, can be stacked
- Tesla Powerwall 3: approximately 13.5 kWh usable
The right configuration depends on your critical loads, desired backup duration, solar system size, and budget. One battery is typically sufficient for critical loads backup on a solar system. Multiple batteries are needed for extended backup or whole-home coverage.
Incentives for Battery Storage
ComEd has offered rebates on battery storage for residential customers through the ComEd Energy Efficiency Program. The program's availability and rebate amounts change over time — verify current offerings directly with ComEd.
Battery storage paired with solar also has a history of qualifying for federal tax incentives. Tax incentive details should be verified with a qualified tax professional, as they depend on current law and your specific tax situation.
When Battery Storage Makes Sense
- You have frequent or extended power outages in your area
- You have medical equipment or other critical systems that need continuous power
- You have solar and want to maintain power security during outages without a generator
- Your utility has TOU rates where battery arbitrage adds economic value
- You want to maximize your solar self-consumption and minimize what you send to the grid
When Battery May Not Pencil Out
- Your area has very reliable grid power with infrequent, short outages
- You have no medical or other critical loads requiring continuous backup
- Your utility has full retail net metering, which already credits your excess solar at full value
- Your budget is constrained and the solar system itself has a faster, more certain payback
SPM will give you an honest assessment. Battery storage isn't the right addition for every solar home — and we won't recommend it unless it makes sense for your specific situation.
Frequently Asked Questions
Can I add a battery to my existing solar system?
In most cases, yes — with caveats. Battery compatibility depends on your existing inverter and system design. Enphase systems integrate readily with Enphase batteries; Tesla Powerwall can be added to many existing systems. SPM will assess your existing system during the consultation to determine what's compatible and what's involved in adding storage.
Do I need solar to install a battery?
No. A battery can be installed as a standalone backup system without solar. It would be charged from the grid (during off-peak hours if you have TOU rates) and discharged during an outage or peak periods. The economics of a standalone battery without solar are typically less favorable than battery paired with solar, but the backup value may still be worth it for some homeowners.
How long does a battery installation take?
Battery installation is typically a one-day project for most configurations. Like solar, it requires a permit and utility inspection before activation.
Interested in battery storage? Learn about SPM's battery storage options or start with a free assessment that covers your full energy picture including backup power options.