Friends, till now we have learnt few basic things about solar panels, solar charge controllers and their working along with the designing of the solar power system.
Now, for an effective and efficient solar power system, battery plays a very important role.
It is true that your system will not work when there is no sunlight and its performance can fall significantly, when the sunlight is less due to cloudy weather, dust, haze etc.
Here you need something which can support and back up your solar power system that can fulfill your electricity needs.
Obviously, in such conditions or circumstances the performance of your system will depend on the choice of your battery.
With the improvement in the technology, several options are available for the consumers but at the same time this has made it more difficult for them to choose the best one meeting their energy needs.
An undersized battery may not be able to meet your daily energy needs
an over-sized battery will not only cost your more but also the solar panels will not be able to charge it fully.
Hence it remains under-utilized.
The size of the battery depends on the array size, type of the system (On-grid or Off-grid), and your daily energy needs.
Are you confused?
I have researched the best solar batteries for you.
What are the best solar batteries in 2021?
How to select the right solar battery?
The important specifications that decide the effectiveness of the battery are:
Capacity & Power rating:
Capacity is the amount of energy stored in the battery.
it is expressed in Watt-hours (Wh)
The voltage of the battery is generally fixed due to its internal cell chemistry like whether it is lithium-ion or lead-acid battery.
So, we are left with Ampere-hour.
That is why, we don't find battery in W-hr specifications in the market.
You'll see batteries marked with AMPERE-HOUR.
To know the W-h of any battery, just multiply its ampere-hour rating with its nominal voltage that is printed on it.
For example, a 100 A-h battery with nominal voltage of 12 volts will provide you energy of 12 volts x 100 A-h = 1200 W-h.
The capacity of the battery tells you how big is a battery but it doesn't tell you how much electricity it can provide.
Therefore, knowing only the Ampere-Hour rating of the battery is not enough.
To get more clarity, we should either know the C-rating (lead-acid) or Power rating (lithium-ion) of the solar battery.
It is the charging and discharging rate (in hours) of the solar batteries.
The C-rating or the power rating tells that how quickly the battery can provide electricity in specified time.
The C-rating of C/20 means that the entire current from the battery would be discharged in 20 hours.
For a battery of 100 Ah @ C/20 rating, the discharge current would be 5 amperes per hour.
It is not that you can not withdraw more than 5 amperes. You can still withdraw 10 Amperes or 15 Amperes current but the battery capacity will reduce.
Similarly, a battery of 1200 kWh with power rating of 2 kW means that it will provide 2 kWh in 1 hour.
The battery with high capacity and low power rating means that it provide less current (enough to run your crucial appliances in power shutdown) but will last longer.
a battery with less capacity and more power rating will provide more electricity but for less time.
Depth of Discharge (DOD)
Most of the solar batteries need to retain certain amount of charge in them due to their cell chemistry.
If you use 100% of the charge, their performance will reduce significantly with time.
In short, their useful life will get shortened.
The depth of discharge indicates the amount of charge that can be taken out of the battery without impacting its useful life.
A high DOD means that you can extract more charge while the lower one indicates that less charge can be extracted.
For example, a 1200 Wh battery with 80% DOD that you can withdraw 80% of 1200 Wh = 960 Wh for the optimum performance of the battery.
A battery with high DOD is preferred over the one with lower DOD's.
Round Trip Efficiency
It is the ratio of energy put into the battery to the energy retrieved from it.
For example, solar panels provide 1200 Wh energy to the battery in a clear sunny day.
This energy gets stored in the battery as a chemical energy.
In the night, the same battery provides 1080 Wh of energy to run the electrical appliances.
In that case, the round trip efficiency of the battery is 90%
The 1200 Wh - 1080 Wh = 120 Wh of energy gets wasted as heat and other losses.
The solar batteries with higher round trip efficiencies are preferred.
Warranty and life cycles:
When you use solar battery for home it is likely that 1 cycle (1 charge and 1 discharge) will be utilized daily.
Just like any other electrical appliances, the batteries do lose their charge holding capacity with time.
Your solar battery might be warranted for 10 years and then ensuring 80% of the capacity retention after 10 years.
It means that after the end of the warranty period, the battery will lose 20% of its holding capacity.
Your solar battery might be warranted for certain number of useful cycles like 5000 cycles.
even if you utilize 1 cycle daily then also it is going to last more than 13 years.
(Working: 5000/365 = 13.7 years)
In that case, how long would my solar battery last depends on the consumption of the useful battery cycles.
Solar battery technologies
There are 2 main technologies that are used for energy storage:
The lead-acid batteries are great fit for large scale energy applications with lot of storage space and low energy requirements.
while on other hand,
if you want an effective solution in less space then Lithium-ion batteries are the best.
How to size the solar battery?
When sunlight is not available, it is the battery that provides energy to run the electrical appliances.
The under-sized battery may not be able to meet your energy needs
the capacity of the over-sized one will not be utilized fully and that would be costly also.
Therefore, it is important to size the battery of your solar power system.
The sizing mainly depends on 3 important parameters: