By Brett Duguay | BD Electrical & Solar | September 30, 2026
“How long will a battery run my house?” is a reasonable question. It needs another question before it has a useful answer: what do you want to keep running?
A refrigerator, a well pump, and a few lights create a different requirement from whole-home heating, cooking, and EV charging. The same distinction applies at a business, where keeping communications online is very different from operating an entire production line.
Two ratings tell two different stories
Battery power, measured in kilowatts, describes how much equipment the system can supply at once. Energy capacity, measured in kilowatt-hours, describes how much energy it can deliver over time. You need both numbers.
For a simple illustration, 12 kilowatt-hours of available energy divided by a steady 1-kilowatt load gives 12 hours. At 3 kilowatts, the same energy gives four hours. Real runtime also depends on conversion losses, reserve settings, temperature, battery condition, and changes in demand. This is arithmetic to explain the relationship, not a runtime promise for a particular product.
Starting a motor can also require more power than keeping it running. A system with enough stored energy for a pump may still need a closer review of its starting demand.
Why batteries matter beyond outages
Batteries play a growing role in grid operations. Storage can absorb energy at one time and deliver it at another, and suitably designed systems can respond quickly to changes in demand.
That timing has practical value at a property too. Solar energy produced while a homeowner is away may be stored for evening use. At a commercial building, a battery may help reduce a short demand peak. Whether either strategy saves money depends on the actual utility tariff, the load pattern, and system losses.
A battery installation is not automatically a backup system
A system designed to operate alongside the grid may not be configured to power a building when the grid fails. Backup requires compatible equipment and controls that separate the protected loads from the utility and establish a stable local supply.
Solar must also be able to operate with that backup system if daytime recharging during an outage is part of the goal. Simply having panels and a battery at the same address does not establish that capability.
Choose priorities before adding capacity
For a home, write down the essentials and the desired outage duration. Then distinguish equipment that must remain available from loads you are comfortable postponing. Smart controls can help manage those choices, but the owner should understand what may turn off and when.
For a business, start with interval demand data and the cost of interruption. Peak reduction and emergency backup can compete for the same stored energy. A battery discharged for an economic purpose has less energy available if an outage arrives immediately afterward.
Long outages need a realistic plan
A battery does not have an unlimited fuel supply. Solar recharging depends on weather, season, array output, and the amount of energy the building continues to use. For some properties, a properly integrated generator and battery can serve different parts of the resilience goal. The combination must be designed for compatibility.
BD evaluates battery energy storage as part of the complete electrical system. Start with the loads and the operating goal; then select the equipment and capacity needed to support them.