Solar batteries for off-grid systems

In an off-grid solar system the battery stores what the panels produce during the day so you can use it at night and on cloudy days. It charges and discharges every day, so it needs a true deep cycle design.

Here you will find flooded, AGM, GEL and LiFePO4 solar batteries for country houses, cabins, water pumping and small stand-alone systems.

Sizing the battery bank

Start from your daily consumption in Wh and multiply it by the number of days you want to cover without sun. Divide the result by the system voltage and by the depth of discharge you are willing to accept. For example, 2,000 Wh a day with two days of autonomy, at 24 V and 50 % discharge on lead-acid, comes to about 333 Ah. Solar batteries are often rated at C100, which reads higher than C20, so always compare at the same rate.

System voltage and wiring

Small systems run at 12 V; above a certain power it pays to move to 24 or 48 V to cut current and cable size. Build the voltage with 6 V blocks or 2 V cells in series and avoid many parallel strings, which drift out of balance over time. Location matters too: lead-acid gives less in the cold and ages faster in the heat, so keep the bank somewhere cool, dry and sheltered.

Which technology to choose

• Flooded lead-acid: plenty of cycles for the money; needs water checks, periodic equalising and a ventilated room.
• AGM and GEL: sealed and maintenance-free, suited to closed or hard-to-reach spaces.
• LiFePO4: higher charge efficiency, deep discharge and long life, with a compatible inverter and controller.

TROJAN offers dedicated solar lines in both flooded and AGM. For grid-tied or self-consumption storage, see renewable energy storage batteries; every other option is under deep cycle.

FAQ

How should I set the charge controller?

Set absorption, float and, on flooded batteries only, equalisation according to the maker's datasheet. A temperature sensor on the battery fine-tunes charging in summer and winter.

Why does my bank never reach full charge?

Usually the panel array is too small for the load, especially in winter. Leaving lead-acid at partial charge for weeks causes sulphation; add generation or cut consumption.