How To Size A Home Solar Battery Bank — Complete Guide

Choosing the wrong battery size is the most expensive mistake in solar installation. Too small and you run out of power. Too large and you waste thousands of euros on unused capacity. ## Step 1 — Know Your Daily Energy Consumption Check your electricity bill for monthly kilowatt-hours used. Divide by 30 for daily average. Most German households use 8-12 kilowatt-hours per day. ## Step 2 — Decide How Many Backup Days You Need One day backup: multiply daily use by 1. Two day backup: multiply daily use by 2. Most homes choose one to two days backup capacity for practical and cost reasons. ## Step 3 — Account For Depth of Discharge LiFePO4 batteries can be safely discharged to 80-90% of capacity without damage. Divide your required capacity by 0.8 to get the actual battery size you need to purchase. ## Step 4 — Choose Your System Voltage 12V systems work well for small cabins and campervans. 24V systems suit medium off-grid homes. 48V systems are recommended for full home solar installations for maximum efficiency. ## Practical Sizing Example Daily energy use: 10 kilowatt-hours Backup days needed: 2 Raw capacity needed: 20 kilowatt-hours After depth of discharge calculation: 25 kilowatt-hours For this home we recommend five EG4 LL-S 48V 100Ah batteries providing 25.6 kilowatt-hours of total capacity. ## Common Mistakes To Avoid Do not undersize to save money upfront. Battery capacity cannot easily be added later with all systems. Always plan for 20% more capacity than your current calculation suggests to allow for future growth especially if you plan to add an electric vehicle. ## Final Advice Buy slightly more capacity than you calculate today. Energy needs grow over time particularly as electric vehicles and heat pumps become standard in German homes.