Michigan homeowners ask about backup power for a specific reason: the outages here are long. In the summer of 2026 alone, single storm events left more than 490,000 DTE customers and more than 260,000 Consumers Energy customers without power.
There is a statistic worth understanding before any of the rest of this. Michigan’s utilities report reliability figures that exclude major event days — and on that basis DTE averaged about 141 minutes of outage per customer in 2024 and Consumers about 180, against a national average near 119. Both are already above average. But major event days are precisely the summer storms and winter ice events that cause multi-day outages, and they are excluded from those numbers. The outages that actually make you want a battery are the ones the reliability statistics leave out.
So: how long will a battery run your house? Here is how to work it out properly.
Start with what you are backing up, not what you own
The single biggest determinant of runtime is a decision made during design: whole-home backup or critical loads?
Whole-home backup keeps everything energised. It is simpler to live with and considerably more expensive, because it needs enough power capacity to handle whatever happens to switch on at once, and enough energy capacity to feed the entire house.
Critical-loads backup energises a selected subpanel. In Michigan that usually means four things:
- The furnace blower. The furnace itself may run on gas, but the blower is electric, and without it a gas furnace does not heat your house. Draw varies enormously by type — an older PSC blower can pull several hundred watts continuously with a surge on startup two to three times that, while a modern variable-speed ECM motor draws far less. This is the load worth having measured rather than estimated.
- The sump pump. A third-horsepower pump draws in the region of 750 watts running, with roughly double that on startup. In a spring thaw or heavy rain, this is the load that prevents a flooded basement, and it cycles.
- The well pump, if you are on a well. A half-horsepower pump runs near 1,000 watts and surges to roughly 2,100. No pump means no water, which changes an outage from an inconvenience into a reason to leave the house.
- The refrigerator and freezer. Around 700 watts running, with a compressor start surge over 2,000.
A Powerwall 3 delivers 11.5 kW continuously and is rated to handle motor starting up to 185 locked-rotor amps, so starting surges are generally not the constraint on a critical-loads panel. The constraint is energy — how many kilowatt-hours you have, and how fast you spend them.
The arithmetic
A Powerwall 3 holds 13.5 kWh of usable energy. Work out roughly what your backed-up loads consume in a day and divide.
A critical-loads panel carrying a furnace blower cycling through a cold night, a refrigerator, a sump pump running intermittently and some lighting might average somewhere in the region of 400 to 700 watts across a full day — call it 10 to 17 kWh over 24 hours. That puts a single Powerwall in the range of roughly one day of autonomy with no solar contribution at all.
Add a well pump, or back up more of the house, and that shrinks. Back up the whole house including electric range, dryer and air conditioning and a single unit may not last the evening.
If you need more, the Powerwall 3 Expansion adds another 13.5 kWh as a battery-only pack sharing the original unit’s inverter. Up to three can sit behind one Powerwall, taking a single system to 54 kWh.
Then add the sun — and be honest about the month
This is where a solar-plus-battery system separates itself from a battery alone. If the array is producing during the outage, it recharges the battery each day and your runtime stops being a fixed number and becomes indefinite.
That works beautifully in July. It works much less well in January.
Michigan production in December runs somewhere around a quarter to a third of what the same array produces in July. Shorter days, a low sun angle, heavier cloud cover, and — the part that does not show up in irradiance data — snow sitting on the panels.
The practical consequence for outage planning:
- A summer outage with a properly sized array is close to indefinite. The battery carries the night, solar refills it and runs the house by day. This covers the July storm events that hit Michigan hardest.
- A winter outage is a different calculation. A December ice storm may deliver a fraction of normal production, and if the array is snow-covered it may deliver nothing until it clears. Size for the battery carrying the load largely on its own, and treat any solar contribution as a bonus.
That asymmetry is worth designing around explicitly, because winter storms are exactly when losing the furnace blower and the sump pump matters most.
Sizing for a multi-day event, not a flicker
Most quotes are sized against a brief interruption. Michigan’s problem is the multi-day one. A more useful design conversation looks like this:
- How many days do you actually want to cover? Two days of genuine autonomy is a different system from four hours.
- Which loads are non-negotiable in February? Furnace blower and sump pump almost always. Everything else is a preference.
- Can loads be shed during an outage? Deferring the dryer and the dishwasher until power returns stretches a battery considerably, and modern systems can be configured to do it automatically.
- What is the realistic worst case? For most Michigan households that is a winter ice storm — coldest, longest, and least solar contribution.
You can model expected monthly production for your own address and array tilt with PVWatts, which gives a far better basis for this than a rule of thumb.
The part that pays for itself between outages
A battery bought purely as insurance sits idle most of the year. In Michigan it does not have to.
Under the Distributed Generation programme administered by the Michigan Public Service Commission, power you draw from the grid is billed at the full retail rate, while power you export is credited only at the power-supply component of that rate. The two are not equal — which means a kilowatt-hour you store and use yourself is worth meaningfully more than one you send to the grid.
A battery captures that difference every day. It also shifts your consumption away from the more expensive parts of DTE and Consumers Energy time-of-day pricing, and both utilities received approved rate increases in 2026 — DTE in March, Consumers in May — with further cases already filed. Every increase widens the gap the battery is arbitraging.
So the honest framing is not “a battery for outages.” It is a system that lowers your bill every single day and happens to keep the furnace running when the grid goes down.
Get the number calculated for your house
There is no universal answer to how long a battery lasts, because it depends on which circuits you back up, what those circuits draw, and what month the storm arrives in. All three are knowable. A proper design measures your actual loads, models winter and summer production separately, and tells you a realistic number of hours for each — rather than quoting a capacity figure and leaving you to guess.
Ready to take control of your energy costs and protect your home from Michigan’s frequent outages? Request a free, no-obligation quote from Stellar Solar Michigan — serving Michigan homeowners with solar and battery storage since 1998, A+ rated with the BBB — or call 858-395-6905.