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Battery guide

A variety of battery types can be used with offgrid solar systems. The two most common types are lead acid batteries and lithium ion batteries. 

Which battery should you choose Lithium ion or AGM/Gel?

Lithium ion, LiFePO4 batteries:

Lasts longer (10 year design life, dependent on usage)
Higher energy density (Smaller and lighter than the same capacity Lead acid batteries)
Higher upfront cost than AGM/Gel
Higher chance of fire/explosion (Dependent on the chemistry type)
Notes:
  • Battery management system (BMS) is usually included. DO NOT buy a Lithium ion battery without a battery management system.
  • LiFePO4 batteries should not be discharged completely. A depth of discharge (DOD) lower than 80% is recommended. Simply put, the battery should not be discharged more than 80% of the battery's rated capacity.
AGM/Gel VRLA
Lower upfront cost
Does not last as long as the Li-ion batteries (3 years, dependent on usage)
- Lead acid batteries last much longer if they are fully charged. 
Notes:
Battery balancers that balances the load between the different cells are recommended to be installed for large battery banks.
AGM/Gel VRLA batteries do not want to be discharged completely.

 

Tips for buying batteries

  • The weight of a lead acid battery is a good indicator of the battery quality. A heavier battery usually indicates a better quality battery.
  • Beware for manufacturers who overestimate their battery cycle life. Batteries with thousands of cycles have likely not been tested. The cycle rating is usually an estimate. Tests to determine the battery life can take years to complete.

Determining battery storage capacity:

To determine the storage capacity of a battery, the power that the battery can supply must be multiplied by the time that the battery can deliver the power:

Energy (Wh) = Power (W) x Time (h)

We don't have a power rating for the battery, but we can approximate it by multiplying the nominal voltage of the cell with the Ah rating.

Energy (Wh) = Nominal voltage (V) x Battery capacity rating (Ah)

For example: A 12 V, 200 Ah battery will be able to supply 12 V x 200 Ah = 2 400 Wh or 2.4 kWh
That means that one 200Ah battery contains enough energy to power a 2.4 kW element for an hour. If it is a Gel/AGM VRLA deep cycle battery it is recommended that you do not discharge the battery less than 50% of its capacity to ensure long capacity life, so it is recommended that only 1.2 kWh is used.
Please note that the Ah ratings are determined for different discharge times. Deep cycle battery ratings are usually determined at 20h-rate. That means the battery is rated to supply the energy over the given time period under standard temperature conditions.

 

For use with offgrid inverters:

Offgrid/hybrid type inverters can be set to:

  • limit battery charge rate, 
  • limit battery discharge amount and
  • switch to use the grid as a backup (depending on the inverter).

We do sell inverters that do not require batteries to function.