How To Choose The Right Battery
Maximize your battery life, avoid common mistakes and reduce costs by learning how to select the right battery for your system every time.
Did you know that batteries, even with nearly identical specifications, may have unequal life and performance? It’s true. Choosing the right model for your system can mean the difference between long project life, low maintenance and high performance — or frustrating downtime and early failure.
All batteries are made differently. Some manufacturers use heavier grids and more lead, robotic assembly and automated quality control, and exhaustive performance testing. Other manufacturers make batteries using manual assembly and outdated materials that can compromise performance. Low-price batteries seem like a bargain, but they often require more maintenance, fail earlier and cost more in the long run.
By asking the right questions, you’ll be able to identify differences in design, materials, manufacturing and quality control to choose the best battery for you.
Understand Different Battery Types
The first step is to select the right type. Lead-acid batteries are made for specific applications, and some aren’t a good fit for renewable energy (RE) systems. Automotive and commercial starter batteries deliver short bursts of power and stay at full charge most of the time, making them unsuited for such applications. Uninterruptable power supply (UPS) batteries are designed to provide backup electricity during power outages but will not tolerate continuous discharge and charge cycles.
Deep-cycle batteries deliver electricity for a long time, even multiple days, because they’re designed for constant discharge and charge cycles. The difference between deep-cycle and RE-specific batteries is that RE batteries’ basic design accounts for the specific requirements of renewable energy applications.
Flooded batteries are the most commonly used batteries in RE and grid-backup systems, because they’re affordable, easy to maintain, long-lasting and reliable. Valve-regulated lead–acid (VRLA) batteries, such as absorbent glass mat (AGM) and gel, are maintenance-free but typically more expensive. Whatever type of battery you choose, know which materials, construction methods and quality control systems translate into affordable, reliable power for your system.
Materials And Manufacturing Matter
A battery produces electrical current through a reaction that converts its stored chemical energy into electrical energy. This process starts in the lead itself. Most manufacturers in the North American battery industry use recycled lead, so the performance and lifespan differences between lead in the batteries come from the amount of lead, additive formulation, lead-oxide production methods and quality controls employed by producers.
Metal grids that hold lead paste make energy storage possible. Thicker, heavier plates withstand corrosion longer and hold more lead for chemical reactions, so they increase battery life. But raw lead prices have skyrocketed since 2006, and since lead comprises 60 to 80% of a battery’s cost, there’s pressure to cut corners to offset raw material price hikes.
Manufacturers that understand the importance of quality still produce a superior product. They do not try to cut costs through cutting back on key materials like lead, but by improving manufacturing efficiency and using of active lead materials. Ultimately, more lead and advanced manufacturing save customers money because they don’t have to replace their batteries as often.
Even grid production methods affect life. Some manufacturers use expanded metal and stamped grid production because they’re quicker, but these methods embed impurities and porosity into grid wires. In contrast, grids produced by gravity casting contain no impurities and near-zero porosity. Gravity-cast plates extend life and improve reliability.
Active lead material is applied to plates in a process called pasting, and dozens of variables in paste mixing significantly affect battery performance. In conventional systems, these variables are adjusted by hand and paste is only as good as its operator. Computerized paste mixing alleviates these problems by instantly adjusting variables.
Once grids are pasted, they’re cured (dried in specialized “curing ovens” at a particular temperature and humidity) to bond active lead materials to the grid for better performance and longer life. Look for batteries built with plates prepared in curing ovens, which optimize important variables such as temperature and humidity at every stage of the curing cycle to ensure all plates deliver optimal capacity and service life.
After curing, battery plates are stacked in groups and connected by fusing the plates together with a lead strap that creates a parallel circuit between the plates. Many companies still use strap-assembly processes that originated in the first half of the 20th century because they’re economical. Workers manually attach lead lugs to a strap and burn them together one-by-one using a torch and lead stick or by manually pouring molten lead around a jig. Manually welded straps have weaker connection points.
Other companies use cast-on-strap (COS) assembly systems that fuse battery plates together simultaneously at the optimal temperature. Because COS allows for 4,000 adjustments versus only 40 for hand welding, it ensures consistent, low electrical-resistance welds that strengthen connections, resist cracking and improve battery life. Robotic COS assembly also prevent failure modes that are common with manually-assembled batteries, such as “lead run-down” between plates, and allow for features that reduce corrosion, increase current and reduce maintenance costs.
Properly integrating the COS process can be expensive and time-consuming. Make sure your battery manufacturer has had time to refine its COS system. If a company advertises using COS, make sure to ask if it produces 100% of its offerings using COS manufacturing.
Following assembly, batteries are charged for the first time in a process called formation that converts lead sulfate and ensures maximum capacity. Some companies “speed up” formation using higher currents, which cut production time at the expense of active (usable) material and lifespan. In contrast, lower current over a longer time always results in longer life.
Quality control should be built into all stages of production to improve product quality and consistency. In more advanced plants, this includes machine testing for short circuits, along with computerized welding and heat sealing. Some battery companies even use vision systems (image capturing and advanced software that automatically inspect parts) to spot defects humans can miss.
When you know what to look for — and what to avoid — in a renewable energy battery, it’s much easier to find the best model for your needs. To compare manufacturing techniques and materials and get a better idea of which batteries will perform better and last longer, visit your RE battery manufacturer’s website or call the manufacturer or your distributor.
Battery Characteristics – Factors to consider
The choice of batteries possibly the biggest decision to be made if planning a solar power system of any size.
Unless you are looking at a very small system, possibly using a truck battery, upgrading your battery capacity is likely to be difficult and expensive. If you are using a 24 volt battery and decide you need more storage,you will either need to replace the battery for a larger one or connect a second battery of the same size in parallel with the first.
When connecting batteries in parallel however, it is important that the batteries are similar. For this reason it may not be advisable to add to the battery after you have been using the system for a while, by which time there would have been some reduction in battery performance.
Measurement of Battery Capacity
The capacity of a battery or cell is measured in amphours. A 100 amphour battery in theory can supply a current of 1 amp for 100hrs before becoming fully discharged (although a battery should never be discharged below 20% of full capacity, and on a regular daily basis should not be allowed to go below 60% of full capacity)
As the efficiency of a battery, and therefore it’s amphour rating varies according to how quickly it is discharged, a standard discharge time is used when quoting a batteries capacity.
If a battery is quoted as having a capacity of 100 amphours (c10), that infers that the it will supply 100 amphours when discharged over a 10 period.
100 amphours (c100) would indicate that the battery will supply 100 amphours when discharged over a 100 hour period. For a particular battery, the c100 rating would be expected to be significantly higher than the c10 rating.
If two batteries are connected in series, the total amphour rating will be same as each individual battery (which should be the same size).
If two batteries are connected in parallel, the total amphour rating will be the sum of that of the two batteries.
Factors Influencing Size of Battery Required
Don’t underestimate the size of battery required. It can be frustrating to have a system where the battery size does not give you enough stored electricity to get you through a dull day and also finding that your battery rapidly becomes fully charged on a sunny day and further output from your panels cannot be used.
Factors to Consider:
What is your daily usage in Kw Hours. This is a little tedious to calculate but necessary.
How reliable is your sunshine – do you generally get clear sun most days or is it much less reliable.
How long do you expect your system to cope without sunshine.
Do you also have a wind turbine, and if so, how reliable is the wind.
How efficient and convenient is your backup system? If you have an efficient diesel generator that starts automatically when required, this will reduce your need for battery storage.
You will also need to consider when you might use any appliances that have a high power requirement. The highest power requirement in a solar powered home may be the washing machine, using something approaching 3 Kw when it is heating water. A battery that is not fully charged may be able to run low energy lighting for many hours but may not be capable of providing 3Kw without the battery voltage dropping to the point that the inverter cuts out for protection.
Drawing a high current causes the battery voltage to drop, possibly returning back to it’s original level as soon as the appliance is switched off.
With a larger battery, together with having more electrical power stored, the voltage drop resulting from drawing a particular current level will be less, possibly enabling more of the battery’s capacity to be used.
Another fact to consider is that, although we are talking about batteries that are designed for deep cycle use (they are expected to cope being regularly drained and then recharged), the greater depth to which they are discharged, the shorter their life is likely to be. Deep cycle batteries can generally cope with regular discharging down to approximately 60% of their capacity and occasional discharging down to 20%.
Therefore, all else being equal, a larger capacity battery should have a longer life.
Battery Bank Tutorial – Series and Parallel
What is a bank of batteries? No, it’s not some kind of financial battery establishment. A battery bank is the result of joining two or more batteries together for a single application. What does this accomplish? Well, by connecting batteries, you can increase the voltage or amperage, or both. When you need more power, instead of getting yourself a massive super tanker of a battery, you can construct a battery bank.
The first thing you need to know is that there are 2 ways to successfully connect two or more batteries. The first is Series and the second is Parallel, lets start with Series.
Series adds the voltage of the two batteries, but keeps the same amperage rating (also known as Amp Hours). For example, these two 6 Volt batteries joined in series now produce 12 Volts, but still have a total capacity of 10 Amps.
To connect batteries in a series, use a jumper wire to connect the negative terminal of the first battery to the positive terminal of the second battery. Use another set of cables to connect the open positive and negative terminals to your application.
Never cross the remaining open positive and open negative terminals with each other, as this will short circuit the batteries and cause damage or injury.
It is best to be sure the batteries you’re connecting have the same voltage and capacity rating. Otherwise, you may end up with charging problems, and shortened battery life.
The other type of connection is Parallel. Parallel connections will increase your current rating, but the voltage will stay the same. In the diagram above, we’re back to 6 Volts, but the Amps increase to 20. It’s important to note that because the amperage of the batteries increased, you may need a heavier duty cable to avoid the cables burning out.
To join batteries in parallel, use a set of cables to connect both the positive terminals and another set of cables to connect both the negative terminals of both batteries to each other. Negative to negative and positive to positive. You then connect your load to ONE of the batteries, but both drain equally.
It is also possible to connect batteries in what is called a Series/Parallel configuration This may sound confusing, but we will explain below. This is the way you can increase your voltage output and current rating. To do this successfully, you need at least 4 batteries.
If you have two sets of batteries already connected in parallel, you can join them together to form a series. In the diagram above, we have a bank that produces 12 Volts and has 20 Amp Hours.
Don’t get lost now. Remember, electricity flows through a parallel connection just the same as it does in a single battery. It can’t tell the difference. Therefore, you can connect two parallel connections in a series as you would two batteries. Only one cable is needed, a bridge between a positive terminal from one parallel bank to a negative terminal from the other parallel bank.
It’s alright if a terminal has more than one cable connected to it. It is necessary to successfully construct these kinds of battery banks.
In theory, you can connect as many batteries together as you want. But when you start to construct a tangled mess of batteries and cables, it can be very confusing, and confusion can be dangerous. Keep in mind the requirements for your application, and stick to them. Also, use batteries of the same capabilities. Avoid mixing and matching battery sizes wherever possible
Always remember to be safe, and keep track of your connections. If it helps, make a diagram of your battery banks before attempting to construct them. Good luck!