Will solar work in a power outage?

Why sunshine is not enough

A grid-connected system normally operates alongside the utility supply. During an outage, that connection has to be handled safely; a standard installation cannot simply keep energizing utility lines.

A backup-capable design isolates the home’s backed-up loads from the grid and supplies them through suitable power electronics and controls. The Department of Energy describes the role of solar, storage and islanded operation in its solar resilience overview.

There are product-specific designs that can supply limited daytime power without a battery, subject to sunlight and load constraints. Do not assume this feature exists in a standard installation. Ask the supplier to demonstrate the proposed configuration’s documented outage behavior.

Battery storage and backup are separate specifications

A battery may be installed to shift energy use between hours. That does not necessarily mean the system includes the equipment or wiring needed to support loads during an outage. The proposal should state the backup function explicitly.

Ask whether solar can recharge the battery while the grid is down, whether the system can restart after the battery is depleted, and what happens when demand exceeds the available output. Those answers depend on the equipment and configuration.

Functional overview, not a wiring diagram. Equipment compatibility and installation requirements must be verified for the project.

Choose the loads before choosing the battery

Make a list of what you need during an outage: refrigeration, internet equipment, selected lighting, a well pump or other essential loads. Record large or motor-driven loads separately. Starting demand may differ from running demand.

Decide which loads you can leave off or run at different times. A system intended to keep selected circuits available can be very different from one intended to support the whole home without changing normal habits.

If someone depends on electrically powered medical equipment, use the equipment provider’s continuity guidance and an appropriate emergency plan. A household solar estimate is not evidence that a particular medical device has reliable backup.

Read both kW and kWh

Kilowatts (kW) describe power: how much equipment can operate at once. Kilowatt-hours (kWh) describe energy: how much can be delivered over time. You need both numbers to evaluate backup.

As a simplified illustration, 10 kWh of usable energy serving a steady 1 kW load corresponds to 10 hours before additional losses, reserve settings or other operating limits are considered. A 2 kW average load would halve that arithmetic result. This is not a prediction for a particular product.

Actual runtime depends on the usable starting charge, load cycling, conversion losses, controls, temperature and any solar recharge. Ask for scenarios that show assumptions rather than a single claim that a battery “lasts all night.”

Plan for your California outage scenario

A short evening interruption and a longer outage during poor solar conditions require different planning. Ask the designer to examine the events you want to prepare for, the loads you selected and the operating reserve you intend to maintain.

There can also be a tradeoff between using stored energy for bill savings and retaining energy for a possible outage. Request an explanation of the proposed operating mode and how you can change the reserve without compromising the loads you depend on.

California’s Self-Generation Incentive Program supports eligible storage projects. Funding, program category and eligibility need a current check; do not treat a rebate as secured until its status is confirmed. Begin with the CPUC’s SGIP page.

Questions for a backup proposal

Use the answers to compare actual backup capability. Battery capacity by itself is an incomplete purchasing specification.