Battery Storage Calculator

Enter your average daily electricity consumption in kWh (use our Energy Consumption Calculator if unsure). Select whether you have solar panels—this affects whether you're storing excess solar or just using the grid. Choose your backup priority: full home backup (all circuits), partial backup (essential loads only), or solar self-consumption (no backup focus). The calculator recommends battery capacity in kWh, shows compatible battery models, estimated total cost after incentives, and payback period based on your electricity rate and time-of-use savings potential.

### Battery Storage Buyer's Guide: Capacity, Coupling, and Value Optimization Battery capacity is the first number to focus on, but it's important to understand the difference between total capacity and usable capacity. A 13.5 kWh Tesla Powerwall 3 has a 90% depth of discharge (DoD), meaning you can actually use 12.15 kWh of that capacity before the battery stops discharging to protect its lifespan. Modern lithium iron phosphate (LFP) batteries typically have 85-95% DoD, while older lead-acid batteries only have 50% DoD. When sizing a battery for backup power, always calculate based on usable capacity: if you need 10 kWh per day to run critical loads, you'll need ~11 kWh of total LFP battery capacity, not 10. For full home backup for 24 hours, the average US home uses 30 kWh per day, so you'll need ~33 kWh of usable capacity, which translates to two Powerwall 3 units (27 kWh usable) or one 16 kWh LG RESU 16H plus one Powerwall.

The next critical decision is whether to choose an AC-coupled or DC-coupled system. DC-coupled systems connect the battery directly to your solar panels, converting DC power to AC only once when it's used in your home. This is 5-10% more efficient than AC-coupled systems, which convert DC solar power to AC first, then back to DC to store in the battery, then back to AC again when used. DC-coupled systems are better if you're installing solar and batteries at the same time, as they're more efficient and have lower installation costs. AC-coupled systems are better if you already have solar panels installed and want to add batteries later, as they don't require replacing your existing solar inverter. AC-coupled systems also work with any solar panel brand or age, while DC-coupled systems require matching inverter technology.

Your primary use case will determine the best configuration for your needs. If backup power is your main goal, prioritize a system with a built-in transfer switch that can isolate your home from the grid during outages automatically, and size the battery to cover your critical loads for at least 3 days if you live in an area with frequent long outages. If you're prioritizing load-shifting (storing cheap off-peak grid power or excess solar to use during expensive peak hours), a smaller 10-15 kWh battery is usually sufficient, and you don't need a transfer switch unless you also want backup capability. The value of your battery changes dramatically depending on your utility's net metering policy: if you have full retail net metering (you get paid the same rate for excess solar you export to the grid as you pay for power you import), batteries are rarely financially viable unless you need backup power, as you're better off exporting excess solar for credit instead of storing it. If you have partial net metering (you get paid 30-50% less for exports than you pay for imports), or no net metering at all, batteries can save you 20-40% on your electricity bill by allowing you to use all the solar you produce instead of exporting it for a low rate. When comparing quotes, make sure the installer clearly states whether the system is AC or DC coupled, the usable capacity of the battery, and the warranty terms (look for at least 10 years of warranty covering 80% of original capacity).