How to choose the best battery for solar energy storage ?

How to choose the best battery for solar energy storage ?

The subject has been written by many people in the past such as Energysage

There are 3 basic parameters to determine the best battery for solar energy storage

1/ Power

It is so easy to mix up power and capacity of a battery system. Power is in KW (Kilo-watt) while Capacity is in KWh (Kilo-watt hour).

Equipments and home appliances all have a power rating in KW.

The Power rating of the energy storage system should be designed to handle the sum of all power rating of equipment and appliances of a premise or facility.

2/ Capacity and Effective Capacity


Capacity, with a factor of time, determines how long the energy storage system will last to support all power requirement of the premise or facility.

For example, a premise of equipments with total 10KW can be supported by a energy storage system with 10KWh capacity for one hour.

Effective Capacity

Effective capacity or the actual capacity may vary with the power requirement or discharge current (P=V x I)

Lead-acid battery’s capacity is typically rated at 20 hours discharge time or 0.05C discharge current.

0.05C discharge current means that battery will discharge completely in 20 hours, 1C means 1 hour, and 3C means 1/3 hour.

However, Lead-acid battery’s effective capacity at 1C drops to 60% of the rated capacity, a 1 KWh rated Lead-acid battery will only have effectively 0.6 KWh capacity. At 3C, the effective capacity can drop below 40% of the rated capacity. (use AGM as an example)

On the other hand, Lithium-ion battery will have a very steady effective capacity even at very high discharge current from 1C to 3C.

The price for a Lead acid battery is typically 25% of the price of a Lithium ion battery. But if effective capacity is taken into account, the price advantage of Lead acid battery will only have 50%

3/ Battery life

The cycle life of Lead-acid batteries only has 400 cycles at 80% D.O.D. (use AGM as an example). Most of the Lithium-ion batteries have cycle life over 2000 cycles at 80% D.O.D.

The price for a Lead acid battery is typically 25% of the price of a Lithium ion battery. If cycle life is taken into account, Lead-acid battery is 20% more expensive than Lithium ion battery.


The selling price of a battery system can be deceiving. We need to take into consideration of all factors such as effective capacity and battery life to determine the effective cost of the battery system.

It is so obvious that Lithium-ion battery system is the best choice over Lead-acid battery.

In addition, long service life will save labor cost to replace the battery system.

The author has over 30 years of experience in the Lithium-ion battery industry from the laptop application, electric vehicle, to large energy storage.

To purchase Lithium-ion batteries for solar storage system, please visit

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