Yash
Solar batteries act as a backup energy source.
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 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 to meet their energy needs.
An undersized battery may not be able to meet your daily energy needs
whereas,
an oversized 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?
Don’t worry
I have researched the best solar batteries for you.
Best solar batteries in 2022
- Tesla Powerwall
- LG Chem RESU
- Sonnen ECO
- Enphase Encharge
- Electriq powerpod
- Generac PWR cell
- Panasonic Evervolt
How to select right solar batteries?
The important specifications that decide the effectiveness of the battery are:
- Capacity and Power rating
- Depth of Discharge (DOD)
- Battery cycles
- Warranty
- Round trip efficiency
- Solar batteries technology
Let us understand each one of these:
1. Capacity and power rating
Capacity is the amount of energy stored in the battery.
And
it is expressed in Watt-hours (Wh)
Watt-hour = Volts (Voltage) x Ampere (Current) x Hour (Time)
Watt Hour is the voltage of the battery multiplied by the amount of current it can provide in 1 hour.
The voltage of the battery is generally fixed due to its internal cell chemistry like whether it is a lithium-ion or lead-acid battery.
So, we are left with Ampere-hour.
That is why we don’t find batteries in W-hr specifications in the market.
You’ll see batteries marked with AMPERE-HOUR.
i) W-hr rating of solar batteries
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 a nominal voltage of 12 volts will provide you the 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.
ii) C-rating of solar batteries
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 how quickly the battery can provide electricity in a 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 a 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 provides less current (enough to run your crucial appliances in power shutdown) but will last longer.
whereas
a battery with less capacity and more power rating will provide more electricity but for less time.
2. Depth of discharge of solar batteries
Most solar batteries need to retain a 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.
3. 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 of energy to the battery on a clear sunny day.
This energy gets stored in the battery as chemical energy.
At 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.
Solar batteries with higher round trip efficiencies are preferred.
4. Warranty and life cycles
When you use a solar battery for home it is likely that 1 cycle (1 charge and 1 discharge) will be utilized daily.
Just like any other electrical appliance, the batteries do lose their charge holding capacity with time.
Your solar battery might be warranted for 10 years and then ensure 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 a certain number of useful cycles like 5000 cycles.
And
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 depending on the consumption of the useful battery cycles?
5. Solar battery technology
There are 2 main technologies that are used for energy storage:
- Lead-acid batteries
- Lithium-ion batteries
Lead acid batteries
- Lead-acid is an old technology but is time-tested that has been used as energy storage for decades
- The lead-acid batteries are cost-effective
- Their maintenance is relatively high
- They are heavy and occupy more space
- Lower DOD and shorter useful life
Lithium-ion battries
- It is a relatively new, superior, and fastest-growing technology in the market
- Lithium-ion batteries are expensive
- They require less maintenance
- They are light and compact
- Higher DOD and longer useful lives
The lead-acid batteries are a great fit for large-scale energy applications with a 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 solar batteries?
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
whereas,
the capacity of the oversized 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:
a) Your budget
If your budget is low then there is no point in buying an expensive high capacity battery. A low capacity and economical battery may be sufficient.
b) Array size
Another criterion is the size of the solar panels. If the solar panels installed on the rooftop are of low power rating then it is difficult to generate excess electricity to charge the batteries in addition to running your electrical appliances in the daytime.
c) Energy needs
The 3rd important factor is energy needs. If your energy needs are less than a low capacity battery even with low DOD can work fine and these are economical too. But for high energy needs, a high capacity battery with higher DOD is preferred.
