Your batteries are what turn daytime sunshine into evening light, so understanding them is as important as choosing panels.
What the battery bank does
The battery bank stores energy collected during sunny hours so you can use it at night and through cloudy periods. The charge controller sits between the panels and the batteries and stops them being overcharged. For a modest home, the book suggests a starting bank of about 4 to 8 kWh alongside 1,000 to 2,000 watts of panels, as a planning starting point rather than a fixed rule.
The two main technologies in the book
Lead-acid
- Lower upfront cost, but heavier and needing more maintenance.
- Shorter life: about 3 to 7 years according to the book.
Lithium iron phosphate
- Higher upfront cost, but lasts about 10 to 15 years and needs no maintenance, per the book.
- Performs better in cold temperatures.
The book also notes that lithium batteries can be discharged more deeply without damage, and concludes that for a long-term off-grid setup they offer better value over time despite the higher purchase price. If money is tight now, lead-acid can be a reasonable stepping stone, as long as you budget for replacement.
Think in usable capacity
The number on the label is not the amount you can safely use. How far a battery can be drained depends on its chemistry and the manufacturer's guidance, so size the bank around usable capacity. Then decide how many days you want to run without strong sun and make sure those days fit comfortably inside the safe range. The solar power for beginners article walks through that sizing logic.
Practical checks
- Match the battery type to your climate, budget and how much maintenance you will realistically do.
- Keep the bank somewhere ventilated and protected from extreme temperatures, following the maker's instructions.
- Plan for the cost of eventual replacement as part of your project budget.
Batteries are one piece of the larger energy plan covered in the Off-Grid Energy Systems guide. If you want the whole system in one place, Off Grid Survival for Beginners works through energy alongside water, food and shelter.