What Size Solar Battery Do I Need for My House in 2026?

Almost everyone asks this in kilowatt-hours, and that's the wrong place to start. What size solar battery you need depends on why you're buying one. Backup during outages and bill control under NEM 3.0 are two different jobs, and they point at two different sizes. Battery sizing comes down to two numbers. Capacity (kWh) is how long it runs. Power output (kW) is how much it can run at once. Most California homes buying storage for evening bill control land somewhere in the 10 to 20 kWh range, while whole-home backup for a day or more usually means stacking multiple units. Your real number depends on your usage, which circuits you want covered, and how long you want them covered for. First: are you buying it for outages or for your bill? These sound like the same purchase. They size very differently. Backup is about riding through a grid outage. The question is which circuits stay on and for how long. Fridge, internet, a few lights and outlets is a small load. Central AC and an electric range and an EV charger is a completely different machine. Bill control is about NEM 3.0. Since exported power now earns a fraction of what you pay to buy it back, a battery lets you hold your midday production and spend it during the expensive evening window instead of selling it cheap and rebuying at peak. That job only needs enough capacity to cover your 4pm to 9pm draw, which for a lot of homes is smaller than people expect. Plenty of people want both. That's fine, and it usually means a slightly bigger system than either goal alone. Just know which one is driving your number, because if you size for backup and never lose power, you paid for capacity you don't use. Capacity vs power output, and why the second one trips people up Capacity is kilowatt-hours. It's the size of the tank. A 13 kWh battery holds 13 kWh of energy, minus whatever reserve the system keeps. Power output is kilowatts. It's how fast you can pull from the tank. Home batteries commonly deliver somewhere in the 5 to 11.5 kW continuous range, and that ceiling is what decides whether your air conditioner can actually start. Here's where it bites. A homeowner buys a large battery, loses power in August, and finds out the AC won't run because the compressor's startup surge exceeds what the inverter can deliver. Capacity was never the problem. Some systems solve this with a soft starter on the AC unit, some by adding a second battery to raise the combined output, and some by simply leaving AC off the backup panel. If central air, a well pump, or an electric range is on your must-run list, ask about continuous and peak kW on every quote. It's a spec that quietly separates otherwise similar-looking proposals. What a typical California home actually needs Rough numbers, and they are rough. A California home without an EV or a pool tends to use somewhere around 20 to 30 kWh across a full day. Solar covers a big chunk of the daylight portion, so the load a battery is really asked to carry is the evening and overnight stretch. That's often in the 8 to 14 kWh neighborhood. Which is why a single battery in the 10 to 16 kWh usable range is the common starting point for evening bill control, and why homes wanting real whole-home backup for more than one night usually end up with two or more units. Add an EV that charges at home and the picture changes fast. A single charging session can pull more energy than the rest of the house uses all day. Most people solve that by charging off-peak from the grid rather than trying to size a battery around it. Pools, electric heat pumps for space or water heating, and home offices with heavy equipment all push the number up. Gas heating, gas water heating, and no EV push it down. How SGIP fits into the sizing decision California's Self-Generation Incentive Program pays a rebate on battery storage, and the amount is not the same for everyone. The tier you fall into depends on your utility, your equipment, and factors like whether your address sits in a high fire-risk district or whether the household meets certain program criteria. The gap between the general tier and the higher tiers is large enough that it can change which size makes sense. It's paid per kilowatt-hour of capacity, which means it interacts with sizing directly. Worth checking what tier applies to your address before you settle on a number, and worth asking a tax professional or the program administrator about your own eligibility rather than taking anyone's word that you qualify. Can you add battery capacity later? Usually yes, and it's a legitimate strategy. Most modern battery systems are modular, so you can start with one unit and add another later if your usage grows or you decide the backup window is too short. Two caveats. Adding later often means a second trip, a second permit, and a second round of labor, so the incremental cost per kWh is typically higher than buying it upfront. And equipment lines change. The exact unit you install today may not be the one available in three years, and mixing generations isn't always supported. If you're genuinely torn between one unit and two, ask each installer directly what expansion would cost later and whether their equipment supports it. The answers vary more than you'd think. Getting your actual number instead of a range Everything above gets you into the right neighborhood. The specific answer needs three things: your real annual usage, the list of circuits you want backed up, and how many hours you want them running. That's what a battery sizing tool does in a couple of minutes, without a rep walking your house first. From there you can put quotes from multiple installers next to each other and see how the capacity, the power output, the equipment tier, and the price actually differ. Different installers will propose different sizes for the same house, and seeing that spread side by side is usually more informative than any single recommendation. Size a battery for your home and compare quotes in minutes at solarconnect.com. No calls, no pressure, and you decide who you talk to.