Understanding the needs of remote customers, manufacturers are enhancing efficiencies of solar batteries and making them more affordable, rugged and long lasting, even in extreme conditions
The prime function of solar batteries is to store the power generated from a power source (for example, solar panels) and discharge it when the power is required (through an inverter). These batteries are of three types—lead acid solar batteries, sealed maintenance free valve regulated lead acid (SMF VRLA) batteries and deep cycle solar batteries. These are well proven technologies that have been in use for a long time. Therefore, what players offer as new batteries are modified versions with added features, while the technology remains the same.
Solar batteries are the core component of solar applications, both off-grid and grid connected. Also called deep cycle batteries, solar batteries aren’t the regular type of batteries. Off grid photovoltaic (PV) solar power equipment requires a battery to store the energy accumulated during the sunny hours, for use at night. These solar batteries store power from the main source (sun) unlike the conventional batteries where the power source comes from the mains (electricity). In most applications, lead acid batteries are preferred as these are maintenance free and do not emit any harmful gases during the charging process.
Solar batteries are widely used in solar home lighting systems and solar streetlight systems. Apart from this, they are used for rural electrification through micro grids. Solar lanterns use small capacity batteries from 4.5 Ah to 7 Ah, mainly in emergency lighting in rural areas, and in off grid or hybrid solar systems at homes and remote offices or sites with no grid connectivity.
What’s new in the market
Keeping the needs of the customers in mind, manufacturers are bringing in batteries that are more rugged, affordable and long lasting even in extreme conditions. With not much technological advancements in these batteries, makers are continually introducing changes in these batteries as they have to cater to the varied needs and demands of customers. They try to enhance the efficiencies of the raw material used in different types of rechargeable batteries. This helps in reducing the internal resistance of the cell of the battery, which in turn, enables it to withstand high temperatures and humidity.
Manufacturers are also offering batteries with high cycle life as compared to SMF batteries. For example, Artheon Electronics offers the complete 12 V and 2 V range from 20 Ah to 3000 Ah, which can withstand high temperatures, as these are generally used in off-grid areas. “These batteries have a better life due to the tubular nature of the plates, and are of industrial grade with 6 to 8 mm thick gauntlets,” shares Sunil Bhatnagar, director, marketing, Artheon Electronics Ltd.
Greenvision Technologies has launched a new type of 12V SMF VRLA battery with tubular positive plates. “This battery is a good option for solar applications. It provides deep cycle capabilities and long life of tubular batteries with the no hassle, maintenance free characteristics of SMF VRLA batteries,” says Biju Bruno, managing director, Greenvision Technologies.
Incorporating the latest glass mat and PE envelope separator for double life, Okaya Power Ltd has launched c10 batteries of 40 Ah, 75 Ah and 100 Ah in April this year. It offers a high efficiency grid design for enhanced performance and it has a deep cycle design with 99.994 per cent purity lead, which enhances performance. “Its intelligent air tight construction for reliable performance is suitable for frequent power cuts and the worst power conditions. Its Dura-charge technology helps in maximum charge retention and fast recharging. Also, its compact and safe design requires less floor space,” adds Rajesh Gupta, director, Okaya Power Ltd.
Luminous has launched its solar flooded tubular monobloc batteries, which are deep cycle batteries suitable for rural areas as these require minimum maintenance. The batteries have a capacity to withstand partial state of charge (PSOC) operation and are available in 12 V from 20 Ah to 200 Ah at C10 at 27°C to 1.80 vpc. These batteries can be adapted to use auto fill systems and air agitation systems for faster charging, and to avoid acid stratification in standby cells.
Southern Batteries has unveiled its range of flooded tubular lead acid batteries with features like extremely low water loss during operation, which helps the battery to withstand deep cycling requirements. It also offers good charge acceptance with minimal stratification related problems.
With Torr tubular technology, Exide offers batteries that can deliver reliable and consistent performance. They are designed to operate in partial charge condition. The tubular plates are cast with low antimony content, which reduces the topping up frequency (once in 8-10 months), placing the battery in the low maintenance category. This also keeps the total charging current at a lower value, thus minimising the total energy requirement. Exide batteries are suitable for frequent cyclic duty with superior voltage and energy output.
Price trends
Prices of batteries are dependent on lead prices and have been stable for quite a long time now. The rates change frequently in the summer when the demand for inverter batteries increases and creates a supply shortage in the market. Apart from lead prices, the cost of solar panels and the technology used are other factors governing prices. Since the solar panel prices have been slashed down by almost 50 per cent, there has been a slight change in the prices of solar batteries. The price points of these batteries are similar to the regular tubular batteries and in most cases the design and formula is also the same. Depending upon various advanced features, the prices of solar batteries differ. Okaya batteries start from around Rs 8000. Artheon’s price range varies from Rs 500-Rs13,000. Other majors like Exide and Amara Raja cater to the high-end segments and offer multiple products, hence, they offer batteries at higher prices.
Buying tips
When you choose a solar battery, a few points need to be kept in mind.
Any battery you choose for storage must be capable of sustaining a charge that is at least 5 times the amount of your daily usage. Hence, before buying a battery, review which appliances you will be using. If you intend to use quite a lot of the solar energy collected through the day, you will almost certainly need to consider a high performance battery. So the ability of the battery to operate properly in partial state of charge, its deep cycle capability, long cyclic life and the reputation of the brand for its good service network are some of the factors to be kept in mind while purchasing a solar battery. For example, if you are using a 24 V battery and need more storage, you will either need to replace the battery with a larger one or connect a second battery of the same size in parallel with the first. Also, while connecting batteries in parallel, it is important to know that the batteries are similar.
The measurements of the battery is another important factor to be kept in mind. A 100 amphour battery in theory can supply a current of 1 amp for 100 hours before becoming fully discharged. Thus, if a battery is quoted as having a capacity of 100 amphours (c10), this infers that it will supply 100 amphours when discharged over a 10 hour period.
The size of a battery is another factor to be looked at. It is necessary to have a system where the battery size gives you enough stored electricity; hence, you will have to look at your daily usage in Kw hours, how convenient your backup system is, the time your system is expected to cope without sunshine, etc.
Suggests Biju Bruno, “Before buying a solar battery, customers must check the size of the battery bank with the help of technical experts, keeping in mind the likely load on a daily basis and the charging capability. The maximum problems are encountered due to undercharging of the battery, which also reduces its lifecycle.”
For Indian ambient conditions, certain types of lead acid batteries are not suited for the solar photovoltaic (SPV) operations and may end up with premature failures. After sales service is an important factor due to the remote locations these batteries are usually used in. Says Sunil Bhatnagar, “Test reports from the Ministry of New and Renewable Energy (MNRE), the Central Power Research Institute (CPRI), etc, which show the capacity and other parameters of the battery, are very important. Batteries should be tested for Bureau of Indian Standards (BIS) standards at these labs.”
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Different types of solar batteries
Lead acid solar batteries are available in wet cell (high maintenance) and sealed (no maintenance) versions. They allow users to add water and to recharge the electrolyte balance in the battery, leading to better performance.
Lead acid batteries use two technologies—absorbed glass mat (AGM) and tubular gel. The latter are designed to cater for deep cycle applications operated at higher temperatures; hence, they last a lot longer. Informs Raghavan Srinivasan, managing director, Southern Batteries, “For Indian working conditions and the tropical climate, flooded tubular lead acid batteries (the low maintenance type) that are specially designed for SPV applications are the most suited. In regions where temperatures are moderate, tubular gel VRLA batteries can be deployed for their maintenance free characteristics and because they are quite different from their flooded variants in terms of construction, material and working concepts.”
The disadvantage of lead acid solar batteries is that they have vents. This means that they cannot be used safely in enclosed areas. Subsequently, they have to be stored outdoors, which limits the ability of the user to regulate the temperature around the battery.
Sealed maintenance-free valve-regulated lead acid (SMF VRLA) solar batteries are commonly called sealed batteries. These are excellent as they do not need any maintenance. However, they are more expensive than other solar battery types. Also, the charging control has to be more accurate and, as a result, they have a shorter life span.
Deep cycle solar batteries resemble a car battery but their plate construction is different. Their storage capacity ranges from 60 Ah to 120 Ah at 12 V. Deep cycle batteries have a longer life and can cope well with constant charge and discharge. The solar deep cycle battery uses a different chemistry for the plates’ active paste material. This chemistry allows for a much longer life in deep cycle applications with only a slight reduction in maximum power output.
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By Richa Chakravarty
