Selecting the right lead carbon high-cycle or Lithium battery solution for your solar inverter system can be a difficult process, with many choices. To do so requires a detailed analysis of the following:
- Initial cost versus number of cycles.
- Number of cycles at your selected DOD. How much capacity you remove each time you discharge a battery is called the depth of discharge (DOD), so, for example, a 30% DOD means that after a discharge of your specified time frame which is usually 4 hours with current load shedding levels, the battery will still have 70% of its rated capacity available. The deeper the DOD, the fewer cycles you will get out of a battery.
- Available recharge time until the next discharge being sufficient for the battery to get to 100% capacity again.
- Available recharge current and voltage from your solar inverter’s battery charger.
- Availability of the battery to accept recharge.
- Replacement cost for the battery after it is used up, i.e., after it has performed so many cycles that it can no longer deliver the required power.
- Battery warranty and the fine print behind it.
- Depending where the battery is to be installed, take into consideration that Lithium products are known to self combust and catch fire. Consider how to minimize the risk of the building burning down and will your insurance cover such an incident?
- Remember, you need a COC for the installation to be legal!
Battery Capacity and How it is Calculated
A battery’s capacity, or available power, is determined by the amount of current measured in amps, that it can deliver within X amount of hours to a stated minimum voltage. Usually in emergency backup and UPS applications, a battery will be rated at the 10 hour rate in ampere hours (AH). So, for example, a 100 AH can deliver 10 amps for 10 hours to 1,8 volts per cell.
Some high rate UPS batteries are rated in watts for 10 minutes or 15 minutes to a certain minimum voltage. So the same battery could be a 390 watts per cell for 15 minutes to 1,65 volts per cell and that same product could also be labelled a 450 watts per cell but for 10 minutes to create the impression that it is a much bigger capacity cell when in actual fact it is the same as the 100 AH.
This is also referred to as C rate such that C10 would be the ampere hour rate for 10 hours, C1 the ampere hour rate for 1 hour, etc.
In the photovoltaic world, the age old way of talking about batteries has changed and batteries are rated in watt hours. Simply put, the AH (Ampere Hours) of a battery multiplied by its nominal voltage will give you the watt hour rating of the battery. So, for example, a 100 AH with a nominal voltage of 12 volts will be a 1200 watt hour battery and a 100 |AH with a nominal voltage of 49 Volts DC will be a 4800 watt hour battery.
Battery Technology: Selection and Cost
For high cycle applications, there are only 2 options available commonly in the market:
- Lead carbon
- Lithium, with the battery product being Lithium Iron Phosphate or LiFePhO4.
Lead carbon is more suited to the pocket, being about half the cost of lithium while still being capable of the same amount of cycles. Its recharge time is slightly slower than lithium, with charging being limited preferably to about C3 and a recharge time to 100% capacity within 8 to 12 hours. It is heavy compared with lithium, but unlike lithium batteries, which cannot be recycled in South Africa, lead carbon is 100% recyclable locally. This is because it is essentially a lead acid battery product, exactly the same in its basic structure and design as high-rate VRLA, high-rate general purpose, or telecoms Gel batteries. However, it is designed to operate at higher temperatures than standard VRLA with high cyclability for off-grid or rolling blackout applications, with a strong resistance to partial state-of-charge discharges, or PSOC discharges as they are known, unlike its high-rate lead-acid cousin, which easily sulphates under such conditions, resulting in reduced capacity.
What Does Battery Warranty Mean?
In short – nothing. Why? Lithium technology batteries are as readily available as lead-acid, with many more manufacturers making them in China, BUT unlike lead-acid batteries, which have been in the field for many decades, Lithium technology is still very new.
So, the sales promises made on paper when you buy lithium products are, to a large extent, still laboratory-tested statistics and thus unproven in the field, with the detail being in the fine print, which no one reads. Unproven promises of “Lifetime guarantees” and “10-year or 20-year guarantees” are what is currently driving product sales.
With so many “expert companies” having sprung up in the last 2 to 3 years during the solar expansion we have been experiencing, as everyone desperately scuttles to find a solution to load shedding, which of these companies and importers will even still be operational in 3 or 5 years’ time if you want to claim a warranty? Do they have the financial capabilities and technical capabilities to support their products over the next 20 years? The answer for 99% of these companies is NO and NO.
In short, when it comes to any battery, the “warranty” or “guarantee” is full of loopholes in the fine print and after 12 months, you will struggle to get a response, if any at all.
Conclusion
Although it may be useful to refer to social media platforms, YouTube videos, and public ratings of various battery products, many of these opinions are based on an individual’s personal experiences in the now. Very few batteries have issues upon installation. It is only after they are subjected to 100s of discharges, in the case of cycling battery products, that the problems show themselves. They generally start with reduced capacity, meaning less backup time at the same load as when installed. This reduced capacity would be as a result of the battery being “used up”, but it could also be a sign of many other problems.
Remember any battery is a consumable item and will require replacement every few years depending on cycling and DOD, so rely on a UPS and battery expert company that is technically competent to understand and put together in-depth and reliable solutions for your solar inverter or UPS needs. For more information on choosing the right batteries for your UPS system, read our blog on the subject.
To speak to one of our battery experts, visit Standby Systems’ website or contact us at 011 794 2541 or 011 794 3406 or WhatsApp 082 450 2361.
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