Batteries are now often the most expensive part of your solar system and choosing which battery technology suits you can be tricky.
Typically there are lead acid and lithium batteries on the market, both have pros and cons.
Lead Acid - Cheap, Better in cold weather, higher discharge capacity, simple to manage
Lithium - Lightweight, greater cycle life, easier to monitor, faster charging, voltage remains stable throughout
Lead Acid - Heavy, limited cycle life, monitoring capacity is tricky and requires extra equipment, slow to charge, voltage drops as discharges
Lithium - Expensive, Most do not work in close to or sub zero temps, low peak discharge rate, equipment needs to be compatible
Lead Acid Monoblocks (12V or 6V) - Typical 2 to 5 year lifespan
Lead Acid Traction (2V) - Typical 5 to 12 year lifespan
Lead Acid Sealed AGM/VRLA - Typical 2 to 5 year lifespan
Lithium LiFePO4 - Typical up to 10 year lifespan
Lithium LTO - Potentially up to 30 years+ *new technology, lifespan to be proven
Living with a battery
If you want your batteries in your living space they need to be sealed lead acid or lithium batteries. All sealed lead acid batteries need to be located in an enclosure with good air flow and an air vent to allow any gases to escape to outside. They do not gas as a rule, but they can gas in an emergency to prevent an explosion, and this gas needs to vent outside as it can be dangerous if left to build up.
We do not recommend wet (unsealed) lead acid batteries if the application is mobile such a road going vehicle or boat that experiences rough conditions it is strongly recommend not to use wet batteries as the electrolyte which contains dilute sulphuric acid can be expelled from the top of the batteries due to the movement of the vehicle or boat.
Size and Weight
Consider weight when selecting your battery and give some consideration to passive temperature control - keeping them cool in the summer and warm in the winter.
A rough rule of thumb is between 100AH and 200AH of batteries, in a 12 Volt system, per 300W of solar PV present, depending on usage all year vs summer.
The amount of Amp hours of battery capacity you choose needs to be able to be maintained by the size of your solar system.
Often folks buy a bigger battery bank to give them more usable power, forgetting that there is a relationship between the size of battery and power coming in. If your battery bank is not charged fully, regularly - the batteries will stop holding a charge and eventually fail completely. You can mitigate this by having regular mains charging as part of your regimen, which is also recommended as a matter of course if possible.
After this it's personal preference on how much you want to spend and how much redundancy you want to have.
Getting the most from your battery
All batteries types will last longer if kept full as often as possible. Creaming of the top of your battery bank will prolong their life more than regularly discharging to 50%. We would advise not designing any system that will deeply discharge your batteries daily beyond 50% depth of discharge. Most systems should be designed with a number of hours or days of autonomy to cover days when there is little to no sun.
Why do lead batteries have different ratings?
All lead acid batteries have C5, C10, C20, C100 ratings to stand for the amount of time the battery is discharged. C5 is capacity if discarded in five hours, C10 in ten hours etc. You get more from your battery if you discharge it slowly, that is the nature of lead acid chemistry.
Our comparison chart below
The chart is separated into battery type sections.
Click below to choose which section you wish to view:
We have added a Price per Kilowatt Hour and a price per Kilowatt Hour per Cycle to give a good comparison of the costs for each battery and lifetime costs. Click the title heading in blue to sort in this order.