Flooded lead acid batteries may be the oldest type of rechargeable battery on the market, but they must be maintained and topped up with distilled water on a regular basis. Dimi Kyriakou compares this to alternative types of ‘sealed’ batteries that are popular in off-grid solar installations.

If you are working in the specialised field of off-grid solar installations, then trying to decide on the type of battery to use can become as confusing as sorting through the different brands of solar panels and inverters.

From an Australian perspective, D.C. Solutions is a distributor of high quality, eco-friendly technologies that include batteries for solar applications. According to national technical sales director David Petrie, the battery is an essential part of an off-grid solar installation.

“The battery is the equivalent to the lungs of the system – the overall system is really only as good as the batteries that are installed with it,” he says.

When we’re talking about ‘green’ energy, there are three main types of deep cycle batteries that usually come into play.

According to renewable energy solution provider Energy Matters, flooded lead acid batteries (also referred to as ‘wet cells’) are the oldest type of rechargeable battery still in use. They contain a liquid in an unsealed container, which means that the battery must be kept upright and in a well-ventilated area. While they do need to be regularly topped up with distilled water, flooded batteries have a high surge current and are relatively inexpensive.

On the other hand, gel batteries are a sealed valve regulated lead acid (VRLA) battery with a gel electrolyte. Unlike the flooded version, these batteries do not need to be kept upright. Gel cells virtually eliminate evaporation of the electrolyte, spillage and subsequent corrosion issues, and boast greater resistance to extreme temperatures, shock and vibration.

The third type of deep cycle battery is one that was originally developed for military aircraft in the 1980s, so it is quite robust. Absorbed Glass Mat (AGM) batteries are a class of lead acid battery in which the electrolyte is absorbed into a fiberglass mat. The internal resistance of AGM batteries is lower than traditional cells and they can self-discharge more slowly. These batteries also have a valve which will activate when the battery is recharged at high voltage, but this will allow some of the active material to escape and can decrease the overall capacity of the battery.

While different manufacturers will claim that each is well-suited to a particular purpose, you should choose carefully – after all, a deep cycle battery can be quite an investment so you’ll want one that will last the distance.

Energy Matters suggests that one way to determine this is by looking at the cycle rating – that is, the number of times the battery can be discharged and recharged. One of the best benchmarks to measure this against is the International Standard IEC 896-2 Stationary lead acid batteries of the VRLA type, which provides a good baseline to draw comparisons between different brands, or battery lines from the same manufacturer.

A popular battery in off-grid solar installations is D.C. Solutions’ PowEx line of tubular gel batteries. The PX-OPZV series has been designed and developed to meet the needs of the rapidly growing solar industry through a range of high performance VRLA maintenance-free gel batteries.

“Most solar installations in the past have used the conventional wet cell batteries, which work quite well and are relatively affordable. But if you ask any of the installers, they will tell you that they’re not easy to install,” David says.

“Gel batteries are certainly not new to the market, but they are much easier to install and have a similar cost to the wet cell batteries.”

The PowEx series consists of 2V products that range from 240Ah to 3500Ah of battery capacity. According to David, the most popular battery is the PX-OPZV-600-Solar which produces 600Ah. This is a unit of measurement that refers to the amount of energy a battery can store – it is obtained by multiplying a current flow in amperes by the number of hours it takes to discharge the battery.

“From a physical perspective this product is a good size – it weighs about 42kg so it’s not too heavy to carry – and electrically it’s a good fit with the majority of systems,” he says.

“Being a gel battery, the amount of maintenance required is very minimal because it is sealed. You don’t have to top it up with water regularly like the traditional wet cell battery.”

Another player in the solar battery market is GNB Industrial Power, which has the Sonnenschein Solar Block and A600 Solar series of gel batteries on offer to installers. Both versions consist of VRLA batteries that are suitable for use in smaller holiday and weekend houses, as well as rougher applications.

GNB sales and technical Australasia director Srinivas Bharadwaj says the Solar Block range is the ideal energy source for small to medium industrial solar systems, while the A600 Solar series was developed for medium to large solar-powered applications.

“Sonnenschein is a popular German-based design that has between 15-20 years of design life. Typically they are used in off-grid solar applications, and sometimes wind power applications,” Srinivas says.

“The Solar Block series can be either a 6V or 12V cell that is available in 60Ah to 330Ah, whereas the A600 Solar series consists of 2V cells that range from 290Ah to 3820Ah. The recyclability and long storage life makes this environmentally-friendly solar battery system suitable for various applications.”
GNB Industrial Power also has an AGM battery available to installers, which falls under the banner of Absolyte GP. This product is one of the world’s best selling VRLA battery brands that is also ideal for photovoltaic (PV) and alternative energy applications.

“The grid alloy provides an excellent life cycle for PV applications and it offers a wide band of temperature operation – it retains more capacity in cold temperatures than the traditional flooded batteries,” he says.

“The modular steel tray design provides excellent heat dissipation in high temperature applications. These batteries can also be used in a cyclic application, which means that they can be discharged and charged every day.”

Leaving the technical information aside for the moment, Srinivas also reminds installers of the safety aspects that need to be taken into consideration when it comes to working with solar batteries, whether they’re flooded, gel or AGM.

“All batteries are heavy and can often weigh anywhere between 20kg to over 300kg, so you need to be careful when lifting them. Also, because we’re talking about DC power, you will need to follow the usual safety precautions and wear rubber gloves, proper footwear and eye protection. In this case, Australian Standard 4086 Secondary batteries for use with stand-alone power systems will list the safety measures that are required,” he says.

Another key point to remember is to ensure that the size the battery is suited to the particular load of the application. Otherwise, there is a danger of over-discharging the batteries, which can possibly reduce its predicted life span.

“What happens occasionally is that installers, in their eagerness to win the job for a client, will aim for the cheapest quote and choose a smaller battery that has a shorter life span, rather than a more powerful battery that will suit the load of the installation.

“It is very important to educate the end user on what they’re getting for their money. Batteries are a key part of the overall solar installation, so it’s important to make the right choice from the start.”