South Africans looking to purchase a backup power solution should be careful when considering suitable batteries.
The prevalence of load-shedding has led many to resort to battery-inverter systems that are able to charge when the power is on and then provide stored electricity for use during power cuts.
These battery systems are also used to store energy generated from renewable energy solutions like solar power.
Understanding the specifications of these batteries can be difficult for those unfamiliar with electrical systems, however.
Batteries that aren’t rated to perform as advertised are in the market, and even those who buy from respected sellers should be wary of misleading performance ratings.
Blue Nova Energy, which recently launched its MegaBoy intelligent Energy Storage Solution (iESS), told MyBroadband what to look out for – detailed below.
The problem with battery specifications
Certain vendors used load-shedding to exploit a lack of knowledge among consumers to sell battery products that aren’t necessarily intended for backup power.
While many vendors don’t explicitly lie about a battery’s specifications, subtle manipulations in how the performance factors are calculated can misconstrue its true capability.
“A lower-quality product can be made to look better on paper by obscuring or neglecting to mention certain product specifics, and therefore seem to be more affordable,” Blue Nova explained.
The company said that consumers tend to compare product prices, rather than taking long-term product running costs into consideration.
“The data available on the data sheets of these products is, for the most part, accurate. The difficulty is determining what the published data is based on exactly,” said Blue Nova.
“For instance, minimum cycle life depends mainly on chemistry, maximum daily depth of discharge (DoD) percentage, ambient temperature, and capacity retention at end-of-life.”
“The latter is sometimes mentioned in small-print in warranty documents,” the company added.
Despite certain chemistries being more suitable for specific applications, a battery’s chemistry is not always displayed clearly.
For example, most car batteries are made with lead-acid. Since these types of batteries are primarily used to start the engine, they are ideally suited for discharge cycles of no more than 5 minutes.
Since load-shedding typically lasts for two hours or more, this type of battery is not recommended for use as backup power storage, Blue Nova said.
However, several vendors are selling these batteries as viable backup solutions.
You could expect far fewer charging cycles and therefore a much shorter battery life if these units are used for hours at a time.
The company said that although there are variants of lead-acid batteries that offer deep-cycling capabilities, lithium-based batteries generally offer a greater number of cycles for applications where currents have to be supplied over longer periods.
This is why many backup power builds consist of lithium-ion phosphate (LiFePO4) batteries, which offer a higher cycle life and less capacity loss.
Another factor is the stated Ampere-hour capacity, which is frequently based on very long discharge rates.
Blue Nova said that certain sellers base this figure on a discharge rate of 100 hours (C100), despite the fact that for use-cases like load-shedding, the discharge rate will be much lower.
“A drastic reduction in usable capacity can be expected from a battery’s capacity specified at C100, if it is discharged in 10 hours or less,” Blue Nova noted.
The company specifies its products based on 10 hours (C10), which it said is more relevant to standard applications such as daily cycling.
Capacity Retention at End-of-Life (EoL)
Blue Nova said that the battery’s Capacity Retention at End-of-Life (EoL) is frequently not published, obscured, or only stated in small print.
This figure is directly related to a battery’s minimum cycle life, which is measured at a particular depth of discharge (DoD) – the extent to which the battery is drained on each occasion of use.
The minimum life cycle of the same battery could be higher if it is based on lower-capacity retention at EoL.
For example, if the battery’s cycle life is calculated on the basis of a 60% capacity retention at EoL, it would appear to have more minimum cycles than the same battery measured at 80% retention at EoL.
“BlueNova guarantees 80% capacity retention at EoL and specifies cycle life based on this. Many other LiFePO4 suppliers apply 60% to cycle life specifications,” the company said.
Battery charge or discharge efficiency
Different battery types have different charging and discharging efficiencies.
This refers to how effectively a battery can charge and discharge energy. The higher the efficiency, the less electricity will be needed to charge the battery, and the more will be available for use during discharge.
“The average charge efficiency of a lead-acid battery (regardless of specific type) is about 67%,” BlueNova explained.
As a consequence, roughly a third of the energy supplied during the charging of a lead-acid battery goes to waste. Effectively, this means that lead-acid batteries will use more electricity to be charged than LiFeYPO4 batteries.
“Shortening the recharge period will also lead to a decrease in the battery’s charge efficiency,” the company said.
“In comparison, BlueNova’s LiFeYPO4 batteries are 96% efficient if charged (or discharged) in as little as two hours, and 98% efficient if charged (or discharged) over 10 hours.”
Battery performance fades over time due to the natural process of cathode degradation. The fade rate of a battery increases with an increased DoD.
LiFeYPO4 batteries use Yttrium to protect the cathode against accelerated degradation.
This ensures that the fade over the battery’s minimum service life period of 3,600 cycles at 100% DoD does not exceed 20%.
“This is the main reason why we can guarantee at least 80% capacity retention at EoL,” Blue Nova said.
The ambient temperature issue
Blue Nova said another factor to look out for is the ambient temperature at which batteries are able to provide the number of cycles noted in their specifications.
As many of these batteries are manufactured in China, the indicated charging cycles are often based on typical ambient temperatures in much cooler environments than what can be found in Africa.
Although this does increase the usable battery energy, increased temperatures lead to a lower cycle life.
“The cycle life of most lead-acid batteries is effectively halved for every 8 degrees celsius above 25 degrees celsius ambient,” the company said.
“Usable capacity increases for LiFePO4 batteries at higher temperatures as well, but at a fraction of what can be expected from lead-acid batteries,” it added.
Other factors that matter
In addition to establishing the real performance characteristics of a battery as noted above, Blue Nova said consumers should also consider the following:
- Warranties and other supporting documentation
- Reputable installers and quality of installations
- System monitoring functionality
- Availability of support
Trusted vendors and distributors
Blue Nova said that large distributors it recommends are Current Automation and Rubicon, who operate both in South Africa and overseas.
“As a wholesale company, we supply to registered electrical installers and distributors only, throughout South Africa and neighbouring countries.”
The company said since its establishment in 2015, it has been monitoring a fair share of its systems remotely.
“As far as we can tell, all systems installed to date are still operating according to expectations, or better.”
“The LiFeYPO4 cells that we use are also used by other international companies, some of which have installations that are over 13 years old and still running beautifully,” Blue Nova said.