Solar and battery backup for sump pumps

A standard grid-tied solar system shuts itself off the instant the grid goes down. That is a safety requirement so line crews aren’t working on energized wires, and it means panels on the roof do nothing for your sump pump during an outage unless there is a battery and a transfer switch in the system.

If you already have solar and assumed it covered you, it doesn’t — and this is one of the most common misunderstandings we hear. Adding a battery to an existing array is a routine job, and it changes the answer completely.

Most residential sump pumps are 1/3 to 1/2 hp and draw roughly 400–800 W while running, with a startup surge of about twice that. They cycle rather than run continuously: a pit that fills every few minutes during a storm might have the pump on 15–30% of the time. In a wet stretch that works out to something like 2–6 kWh a day, more if the water table is truly high.

The surge is what trips up small inverters and cheap power stations. A home battery designed for backup loads handles it easily; a Powerwall 3 or a SigenStor with its backup panel starts a 1/2 hp pump without noticing. The daily energy is the part to plan around, because it decides how many days you can ride out.

A battery backup sump system is a second, DC pump sitting in the same pit with its own 12-volt deep-cycle battery and charger. Market prices run very roughly $400–$1,500 installed, prices vary, and a good one gives you several hours of continuous pumping or a day or two of intermittent cycling. It does one job and does it well. Its battery ages, needs checking, and covers nothing else in the house.

A home battery does the sump pump as one load among many. A single Powerwall 3 (13.5 kWh) can run a cycling sump pump plus a refrigerator, a furnace blower and lights for a day or more, and it recharges from the roof when the sun comes back. First-unit pricing runs roughly $15,500–$19,000 depending on brand, so it is a different order of purchase — one that also covers wildfire shutoffs and Xcel’s 5–9 pm on-peak pricing every weekday.

For a house with a sump pump and nothing else on the line, a dedicated backup pump is the sensible buy and we’ll say so. For a house with a finished basement, a freezer, someone working from home, or a well, a home battery earns its place, and a cheap backup pump can still sit in the pit as a second layer.

Most of Colorado is dry enough that basements never see water, but the exceptions are consistent: low ground along the South Platte through the metro area, older neighborhoods near Boulder Creek, and the Fountain Creek corridor south of Colorado Springs, plus any lot built into a hillside where snowmelt runs toward the foundation. Spring runoff from May into June raises water tables; July and August monsoon storms drop inches in an hour.

If your pump runs regularly in a normal year, you are in the group that needs to think about backup. If it runs only in a hundred-year storm, the risk is still real but the cheaper answer may be enough. Either way, the storms that cause the water are the same ones that drop the power, which is the whole problem.

With a backup-loads panel, we move the sump circuit — and typically the refrigerator, furnace, well pump and a few lights — onto the circuits the battery carries. With a whole-home setup the battery takes over everything, and the sump pump just keeps working the way it always has. Either way the switch-over is automatic and fast enough that the pump doesn’t stop.

As of September 2026, Colorado exempts residential batteries from state sales tax through 2032 and offers a 10% state income-tax credit on the battery purchase for tax years through 2026, which means the credit window is closing. The federal 30% residential credit ended for systems placed in service after 2025. Confirm your situation with a tax advisor.