Solar Power Q & A

Choosing the Best Battery for OFF-GRID Solar Power Systems


Choosing the best “Battery” will be the key factor of getting the best and stable electricity out of your off-grid solar power system in sri lanka. This Choice of Battery will give you the benefit of stable power during day time in cloudy situations and at Night when used as “backup-power”. There are 3 Main Battery Types that are used on an “OFF-GRID Solar power system”.

  • Lead-Acid (normal vehicle batteries)
  • “DEEP-CYCLE-GEL Batteries”
  • Lithium ion Phosphate Batteries

If we compare the Above Battery Types, Lead Acid is the Oldest and cheapest variant and the LiFePo4 or “Lipo” Batteries are the Newest and most expensive type. “Deep cycle-Gel” batteries are intermediate and is an improved version of the Lead Acid concept.

Battery Type“Cycle-Life”Energy DensityMaintenanceDepth of DischargeEfficiencyCost
“Lead-Acid”300-700 cyclesLowHigh50%80-85%Low
“Deep-Cycle-Gel”500-700 cyclesMediumLow50-80%85-90%Medium
“LiFePO4”2,000-7,000 cyclesHighLow80-100%95-98%High
  • Cycle Life: The number of times a battery can be charged and discharged before its capacity significantly decreases.
  • Energy Density: The amount of energy that can be stored per unit of battery weight or volume.
  • Maintenance: The amount of maintenance required to keep the battery functioning properly.
  • Depth of Discharge: The percentage of the battery’s capacity that can be used before recharging is required.
  • Efficiency: The amount of energy that can be used from the battery relative to the amount of energy that is put into the battery.
  • Cost: The approximate cost of the battery per unit of energy storage.

Based on the comparison above, it is clear that LiFePO4 batteries have the highest cycle life, energy density, depth of discharge, and efficiency. They require less maintenance compared to the other two types of batteries. However, they are also the most expensive type of battery.

Deep cycle gel batteries are a good middle ground, with a moderate cycle life, energy density, and efficiency, and a slightly higher depth of discharge compared to lead-acid batteries. They are also less expensive than LiFePO4 batteries.

Lead-acid batteries are the least expensive option but also have the shortest cycle life, lower energy density, and lower depth of discharge compared to the other two types of batteries. They require more maintenance and have a lower efficiency compared to deep cycle gel and LiFePO4 batteries.

In summary, while each type of battery has its advantages and disadvantages, LiFePO4 batteries are the best option for those looking for high performance, long life, and low maintenance. Deep cycle gel batteries are a good option for those who want a balance between performance and cost. Finally, lead-acid batteries may be suitable for those who have a limited budget and are willing to trade off performance and longevity for affordability.

Difference Between LiFePo4 and Lead Acid Batteries

There are many differences between Lead-acid and LiFePo4, The Major difference is the Power density. Lead Acid Batteries can only discharge a small amount of their total capacity while the LiFePo4 Batteries can discharge up to 95% of their capacity.

“Lead Acid battery” Voltage will Drop Rapidly with the Discharge. LiFePo4 Battery Voltage will not go down during the full Discharge, until it reaches 90% of it’s rated capacity

Why LiFePo4 Batteries are a Long Term Investment for you

Battery Prices sky rocketed with the current economic crisis and the depreciation of the Rupee in Sri Lanka. Many people going for “off-grid solar power systems” purchasing “Lead-Acid” batteries in bulk also is a major factor for normal “Lead-Acid” battery prices to go up.

Lead-Acid Batteries with their limited discharge capacity will need replacements every 2 years or so depending on your usage habits. If your batteries fully discharge (which is not good for Lead Acid Batteries) they will need to be replaced soon.

LiFePo4 Batteries are rated for at least 3000 Cycles, (3000/365 = 8.2 years) this means if you discharge them every day (If you Encounter bad weather everyday of the year) you will still have more than 5 years of use. This adds to the value to your investment in the long run.

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