DIY Powerwall Calculator and Battery Planner

It depends on your daily energy use and how many days of backup you want. A typical US home uses about 30 kWh per day. For one day of backup at 80% depth of discharge with 93% inverter efficiency, you need roughly 40 kWh of nameplate capacity. With 280Ah prismatic cells in a 16S configuration, that is a 16S5P build: 80 cells. The calculator above sizes this automatically from your inputs.

48V for most builds. A 16S LiFePO4 configuration gives you 51.2V nominal (44.8V to 58.4V range). Higher voltage means lower current for the same power output, which lets you use thinner cables and reduces heat. 24V (8S) works for smaller systems under about 5 kWh, but the higher current at lower voltage makes wiring more expensive and less efficient.

Match the BMS to your series count and your peak discharge current. A 16S powerwall needs a BMS rated for 16S (or a range that covers 16S, like 8-24S). For current, calculate the maximum wattage you plan to draw and divide by your minimum pack voltage. A 5,000 watt load on a 48V pack draws about 109 amps. You would want at least a 200A-rated BMS for that setup. The planner recommends a specific BMS from Battery Hookup based on your numbers.

The battery portion (cells plus BMS) typically costs $500 to $2,000 depending on cell prices and how much capacity you build. Add $100 to $300 for bus bars, compression hardware, fuse, and cable. A complete 14 kWh system (16S1P with 280Ah cells) often comes in under $1,500 total. Compare that to $12,000 to $16,500 installed for a Tesla Powerwall 3 with 13.5 kWh usable. You still need an inverter separately, which runs $500 to $3,000 depending on the model.

Depth of discharge (DoD) is how much of the battery's rated capacity you actually use. LiFePO4 cells can safely discharge to 80 to 90 percent of their rated capacity on each cycle. Using 80% DoD gives you longer cycle life. Using 90% gives you more usable energy per cycle but wears the cells slightly faster. At 80% DoD, a 280Ah cell provides 224Ah of usable capacity. The planner defaults to 80% and lets you adjust.

Yes. You need a solar charge controller (MPPT type) rated for your panel voltage and your battery bank voltage. The charge controller sits between the panels and the battery, converting solar input into the correct charging voltage and current. This planner does not size a solar array, but it does ask for your approximate solar wattage so it can check whether your panels can recharge the bank in a day.

LiFePO4 cells are rated for 3,000 to 6,000 cycles to 80% of original capacity at 80% DoD. At one cycle per day, that is 8 to 16 years of service. Calendar aging also plays a role, but LiFePO4 ages more gracefully than other lithium chemistries. Storing at moderate temperatures and avoiding full discharges extends life further.

Prismatic cells (like the EVE 280Ah or CALB 314Ah) are large flat rectangles, typically 280 to 340Ah each. You bolt them together with bus bars. No spot welding. A 16S1P powerwall is just 16 cells in a row. Cylindrical cells (18650, 21700) are small tubes at 2.5 to 5Ah each. You need hundreds of them spot-welded together for the same capacity. Prismatic cells are simpler to assemble for large stationary storage. Cylindrical cells make more sense for portable builds where shape and weight matter.

Prismatic cells connect in series using copper bus bars bolted to the cell terminals. Positive to negative, cell to cell, for the full series string. The BMS balance leads connect at every cell junction plus the two end terminals. A fuse goes on the main positive lead. If you have multiple parallel strings, each string is wired as a complete series chain, then the strings connect at their end terminals (positive to positive, negative to negative). The wiring diagram above shows the layout for your specific configuration.

Yes, if you want to power standard household appliances. The battery bank outputs DC power. An inverter converts that to 120V or 240V AC. Size the inverter to your peak simultaneous load including motor startup surges. A 5,000 watt inverter handles most essential loads. Whole-home backup with AC and a well pump might need 8,000 to 10,000 watts. The planner does not recommend specific inverters, but your inverter choice affects cable sizing and BMS current requirements.