Off-Grid Solar Battery Bank Sizing: How to Size Your LiFePO4 System

Sizing an off-grid solar battery bank comes down to two numbers: how much energy you use per day, and how many days of backup you want without sun. Get those right and the rest — voltage, chemistry, inverter, and charge controller — falls into place. This guide walks through the calculation and the Epoch and Victron gear that builds a reliable off-grid system.

The short answer: how to size your bank

Start with your daily energy use in kilowatt-hours (kWh), multiply by the days of autonomy you want (typically 1–3 days of backup for cloudy stretches), and divide by the usable depth of your batteries. With LiFePO4 you can use nearly the full rated capacity, so a bank rated close to your target kWh works — unlike lead-acid, where you'd need to roughly double the nameplate. Example: 5 kWh/day of use × 2 days autonomy = a 10 kWh usable bank.

Step 1: Calculate your daily loads

Add up every device's wattage times the hours it runs per day. Lights, a fridge (which cycles, so estimate ~1–1.5 kWh/day), a well pump, electronics, and any HVAC are the big ones. Sum it to a daily kWh figure. Be honest and include a buffer — under-sizing is the most common off-grid mistake.

Step 2: Choose your days of autonomy

1 day is minimal — fine if you have a generator backup and reliable sun. 2–3 days is the sweet spot for most off-grid homes, covering typical cloudy stretches. More than 3 days gets expensive fast; a generator is usually the cheaper backstop beyond that.

Step 3: Pick your system voltage

For anything but the smallest systems, build at 48V. Higher voltage moves the same power at lower current, which means thinner cables, less heat, and less loss — and it's what larger Victron inverters and Epoch server-rack batteries are designed around. A stack of 48V LiFePO4 batteries is the modern off-grid standard.

Step 4: Battery chemistry and the bank itself

LiFePO4 is the right chemistry for off-grid: deep usable capacity, thousands of cycles, and safe, stable operation. Epoch's 48V server-rack and Elite batteries stack to build the kWh you need. Size the bank to your usable kWh target from the calculation above, and remember you can parallel batteries to grow capacity.

Off-grid system sizing example

Step 5: Pair the inverter and charge controller

Your inverter/charger turns the bank's DC into household AC and recharges from grid or generator — a Victron MultiPlus-II for most homes, or a Quattro when you need dual inputs. A Victron SmartSolar MPPT charge controller harvests power from your solar array into the bank. Size the MPPT to your array voltage and current. Our MultiPlus vs Quattro guide helps you pick the inverter.

Build your off-grid system

Start with the solar and battery power collection for inverters and controllers, choose your bank from the 48V lithium batteries and Epoch Batteries range, and add Victron Energy monitoring to tie it together. Every component is in stock and backed by manufacturer warranty.

Related reading: Victron Inverter/Charger Buying Guide · Victron MultiPlus vs Quattro · Marine Lithium Battery Buying Guide