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Understanding Solar Battery Specifications

This article explains some useful battery specification terms you must know before making a purchase.
Sizing the Battery Bank

After you have decided on the solar battery types available to you to choose from, the next thing is to check if your choice meets the requirements of your PV design. In this article, I will explain some useful battery specification terms you must know before making a purchase.

Battery specification provides clear information on the general performance of the battery. Therefore, a battery specification (also referred to as “battery ratings”) is a document with a set of detailed information about the battery. The provided details tell you if the battery meets your project design requirements and also enables you to make an informed buying decision. 

Some of the common detail you will find in the specification datasheet include Capacity, Voltage, Battery Type, Charge/Discharge Rate, Physical Size, Weight, Storage Requirements, Environmental Condition, Warranty, Safety, Cost, etc.

Solar Battery Capacity/Ratings)

The power rating (Battery Capacity) is the capability of the battery to supply energy.  The measurement for battery storage capacity is in Ampere-Hours (Ah). Ampere-hour is the discharge current a battery can deliver over time.

Solar Battery Rating
Solar Battery Rating/Capacity

The image above shows a 12-volt battery rated at 200Ah. This rating means that the battery has capacity to store 2400Wh of energy. (12V X 200 Wh = 2400Wh)

However, the battery actual capacity is always less than the rated capacity because of the following :

Batteries have internal resistance
Batteries lose some energy during charging and discharging
Batteries cannot fully discharge all the energy it has stored

Different battery-types have varying Depth of Discharge (DoD).

DoD is the percentage of battery capacity it can discharge. The depth of discharge for a typical Lead-Acid battery is 50% while Lithium-ion battery is 80%. This means that if you fully charge your Lead Acid batter 100%, it will only supply you 50% of its energy, retaining 50%. That’s not so good, you’ll say!

In case of lithium-ion, it will supply you 80% while retaining 20%. That’s fair! And that’s why they are very expensive.

Solar Battery Voltage

Batteries are marked with nominal voltage. In the battery specification in the above image, the battery has nominal voltage of 12V. However, the open circuit voltage (OCV) on a fully charged battery is 5–7 percent higher. Chemistry and the number of cells connected in series provide the OCV. The closed-circuit voltage (CCV) is the operating voltage.

The requirements of battery installations limit the voltage of Lead Acid batteries to no more than 48 volts. If the batteries connected together produce more than 48 volts, then the batteries should be separated or connected in a way to only allow a maximum of 48 volts.

Always check for the correct nominal voltage before connecting a battery.

Charge/Discharge

The charge or discharge rate is expressed as a ratio of the battery capacity (C) to the charge or discharge time period in hours.

The 200-ampere-hour battery, shown in the above image, discharges at 20 ampere for 10 hours is rated C/10 or a 10-hour discharge rate.

Self-Discharge Rate – Batteries loses energy every time even without connected any load. Self-discharge rate measures the rate at which the battery loses energy sitting idle. Some Lead Acid can lose as much as 20% of its stored energy per month without any connected load.

Flooded Vs VRLA or AGM Vs GEL

Specification of batteries indicates the type or chemistry of a battery. In the image above, it indicates that the battery is a VRLA (Valve Regulated Lead Acid, also known as Sealed battery) as against Flooded Lead Acid battery.

After that, it indicated that the battery is GEL as against AGM.

Storage Procedure

Battery specification informs you how to store the battery for future use. Generally, you need to charge all batteries fully before keeping it in store.
Bear in mind that some batteries can self-discharge as much as 20% in a month. So, it makes sense to recharge the batteries you keep in the store for a long period.

Also, you need to Keep the batteries clean and always store in a cool, dry area. Where acid is stored or handled, good ventilation is necessary. Keep the bungs on the containers at all times.

Battery Life Expectancy

Another important information in the battery specification datasheet is how long the battery will last. Keep in mind that as the days go on, your battery will have less ability to hold a charge.

Each battery in the market is rated using the number of cycles it can perform before it begins to lose its ability to sustain a charge. The number of cycles, I mean here, is the number of times the battery can be fully charged and discharged before its ultimate death.

Therefore, if a battery is rated 2,000 cycles, it means that the battery can be charged and discharged for 2,000 times before its expiration.

The longevity of a battery depends much on the battery-type and the brand name (whether it’s a well-respected brand).

Trust me, the longer you want your battery to last, the more money you have to pay.

Manufacturer’s Warranty

A manufacturer’s warranty is a piece of information you’ll find in the battery specification datasheet. This warranty is usually written in the battery packaging, promising buyers to repair or replace the battery, if necessary, within a specified period.

Generally, a lithium-ion battery has a more favourable warranty period than a lead-acid battery.

A reputable Chinese brand of a lead-acid battery comes with at least a five-year warranty. These brands will readily replace the battery in case it malfunctions within the warranty period, provided that you meet the terms and conditions of the warranty.

In fact, the more you spend on your battery, and the more reputable the brand name is, the better this warranty will be favourable to you.

Operating Temperature

The temperature at which your battery choice will work optimally is stated in the specification datasheet. Too much high or low temperatures generally reduce the performance of most batteries.

For us that live in the north with high temperature, it makes sense to install air conditioners or fans in a large battery bank to maintain the stated optimal operating temperature.

More so, it’s not a bad idea to install a temperature monitoring device inside the battery bank (large battery bank). In most case, battery bank should not exceed an operating temperature of 50ºC.

Therefore, the operating temperature of your battery is an important consideration you have to make before buying a particular battery.

Safety/Environmental Concerns

Cries, loud cries have been raised by environmentalists against continuous use of lead in the production of the lead-acid battery. They argue that lead is toxic and hazardous to the environment. They strongly advocate for more environmentally friendly Lithium-ion and Nickel chemistry. Those chemistries are very expensive, especially lithium-ion.

However, Lead-acid battery has a 97% or more recycling rate and so poses a little environmental hazard and will likely continue to be around us for so many years to come.

Battery manufacturers will always warn in their specification: To keep batteries out of reach of children and never dispose of batteries in household waste.

More so, they usually encourage users to take their batteries to a certified recycling depot at the end of their life cycle.

Cost/Budget

Price of the battery is one of the most important purchasing decisions you will be making.

The price of your battery-choice must be commensurate with its performance. It follows that the more expensive the solar battery, the better it will perform and the longer it will last.

One thing I will want to say here in pigeon English is an adage: “better soup, na money make am”

However, ensure that the battery you chose will not increase the overall cost of the PV system abnormally.


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