There are two kinds of batteries when it comes to powering inverters: lead-calcium batteries and lithium-ion batteries. Each battery has its pros and cons; let’s look at each and see which is best for an inverter.
Lithium-ion batteries are far superior to their lead-acid counterparts in overall performance, longevity, and maintenance. However, there have been improvements in lead-acid technology in recent years to make them more competitive with lithium-ion batteries.
To get a proper overview, we will look at the following characteristics of each.
- Lead batteries and what they are used for
- Lithium-ion batteries and their benefits
- Lithium batteries Vs. Lead Batteries
Before you choose your solar inverter battery, get the facts about your battery options so you can make a properly informed choice.
Lithium-Ion Battery Vs. Lead-Acid For Solar
Lead-acid and lithium-ion are the two main types of batteries available for solar inverters. Still, each chemical structure and design differ, affecting their performance and cycling capacities.
How Lead Acid Batteries Work To Create Current
Lead-acid batteries are the oldest batteries available and were the first kind of batteries to be offered to the market when inverters and solar PV systems were first introduced.
Lead-acid batteries consist of two electrodes dipped in the sulphuric acid electrolyte solution. One electrode is lead, and the other is lead dioxide. In the resolution, a chemical reaction occurs that creates the electric current.
What Are Lead-Acid Batteries And How Do They Work?
If you have a car, the chances are you already have a lead-acid battery or lead-calcium battery. Lead-acid batteries were the first rechargeable batteries produced, and they are freely available and cheap to buy.
These are called Flooded Lead-Acid (FLA) batteries because the plates are submerged in water. And you also have Sealed Lead-Acid Batteries (SLA), which are spill-proof and don’t need much maintenance.
The batteries’ electrodes are lead, and lead dioxide is dipped in sulfuric acid as the electrolyte that allows them to produce an electric current.
Lead-acid batteries have a few variations, too, from gel batteries which add silica to the electrolyte, which adds to the battery’s efficiency, and sealed lead-acid batteries(like the ones found in your car) require little maintenance, unlike the standard versions.
There is also a newer concept in lead-acid batteries called a tubular plate. The traditional flat plates are replaced with pencil-style tubular plates, which provide more power and reliability and can be used in various applications.
Types Of Lead Acid Batteries
Lead-acid batteries come in a few options: the flat plate, sealed/maintenance-free, and the tubular plate design. Each option has some advantages concerning cost, maintenance, and performance.
Let’s look briefly at each one and examine their respective benefits and disadvantages.
Flat plate lead-acid batteries :
- They are cheap and freely available
- They are lightweight and rechargeable
- Produce a large volume of current
On the downside, these batteries also require regular maintenance in topping up water, checking electrolytes, and keeping. They emit toxic fumes during charging and discharging.
These are similar to car batteries and were replaced by sealed, maintenance-free batteries as the technology evolved.
Sealed Lead Acid Batteries
The electrolyte is wholly enclosed and absorbed by the separator with sealed batteries, so there is no need for the unit to be topped up with water. No maintenance is needed, and as long as the battery is charged correctly and kept clean, it will give many years of service.
Advantages Of Maintenance Free Batteries
- Safer than lead-acid batteries
- No maintenance required
- It has faster charging than standard lead-acid batteries
- No topping up of water needed
- No toxic emissions
- It can be utilized and placed in any orientation
As with their standard counterparts, they have a relatively short life span and can be costly upfront, but they will be cheaper than lithium-ion batteries.
Tubular Plate Lead Acid Batteries
The flat plate is the older design, and the tubular plate is the newer and it is proving to be more efficient and durable than flat plate technology, and it uses armored pencil-type tubes that can deliver current for longer.
These are fast becoming more popular and the preferred choice for inverters as they provide current when power cuts are in effect for extended periods.
Tubular batteries have a tower-type abrasion-proof casing that is safer to use and requires little maintenance, and they are safe for the home with no toxic emissions during either charging or discharging.
- Greater efficiency and reliability
- Superior performance to standard lead-acid batteries
- Lower maintenance and longer lifespan
- Operate well under heavy-duty requirements
But, tubular batteries are more complex in design and more costly than standard batteries.
The Pros And Cons Of Using Lead Acid Batteries
Let’s start with the best one of all: the price. Lead-acid batteries are the cheapest of all the battery options, and they can cycle thousands of times if used properly.
Cycling means that they can charge and discharge without losing power or capacity. They have an 80%-85% efficiency rate, meaning they can use 80%-85% of the total power available in the battery.
Now, here is where they fall against their lithium-ion competition.
Because of how lead-acid batteries are designed, they need to be maintained. The water levels in the standard batteries need to be topped up periodically to ensure continued performance.
The standard batteries also emit toxic fumes when charging and discharging, so storing them indoors is not an option.
Another consideration is that they will deteriorate rapidly if discharged beyond 50%, so running them for long periods is not advisable. They are also big and heavy, and they take up space.
They also have a shorter lifespan, and although the more modern version of the lead-acid battery has better performance and longevity, for the most part, these batteries are better suited to occasional use over short periods.
Use lead-acid batteries when there is a very occasional power outage. You need to keep a few small devices running as fine as you won’t have to worry about the cost, maintenance, and lifespan of discharging them beyond 50%.
Another issue with lead-acid batteries is that they are particularly susceptible to damage from extreme temperatures, rapid charge, and discharge than lithium-ion. This is because lithium as a material is more resilient than lead.
Where Would Lead-Acid Batteries Be Used?
FLA and SLA batteries would be best suited when short but frequent power cuts, while tubular batteries would be suited to less frequent power disruptions that last longer.
Tubular plate batteries have a higher cycle life and are well suited for sensitive equipment or even supporting larger appliances where FLA/ SLA batteries would struggle.
The tubular-plate lead-acid battery would be best for your inverter if you are in a power situation like those above.
Lead-acid batteries are best suited where budget is considered and for occasional power interruptions.
What Are Lithium-Ion Batteries And Why Are They Better?
Lithium-ion or Lithium-Iron Phosphate, to be precise, is probably the best option for any inverter, regardless of the size and application.
Lithium-ion batteries like those made by Pylontech are some of the best available, and even though they cost considerably more, they are worth the investment.
Lithium-ion batteries are preferred by most solar PV installers worldwide because they are robust, require zero maintenance, are more compact, have better efficiency, cycle deeper and longer, and provide more power for extended periods than lead-acid hope to achieve.
How Efficient Are Lithium-Ion Batteries?
Let’s start with efficiency. Lithium-ion batteries have a 95% efficiency meaning that if there were 1000W available, they would be able to deliver 950W compared to the 800W/850W of lead-acid batteries.
Lithium-ion can cycle up to 80% discharge vs. 50% of lead-acid without damage, which means they can supply power for much longer than lead-acid batteries.
They also charge faster, so where you have an intermittent power supply, you need an inverter battery that can charge quicker and make optimum use of the power supply when available.
Lithium-ion batteries are much lighter, thinner, and more compact and don’t take up the amount of space lead-acid batteries do. Space would be a premium when using an inverter, so a thinner, more compact battery is optimal.
- One of the most significant advantages of lithium-ion batteries is their power capacity. Using an example of a 5 kW solar PV system, only 2 X 6.6kWH lithium-ion batteries were needed against the eight lead-acid batteries needed to deliver the equivalent.
A Working Example Of Lithium-Ion Efficiency
As an example, we will use a five kW system over the life of ten years and compare the cost and cycling. Where you would require eight lead-acid batteries to deliver 23kWh per day, you would only need two lithium-ion batteries to produce the same power level.
Remember that this is a complete solar PV System, but the comparison would be equally valid in terms of inverter performance even if only one battery were used. In this configuration, you would need one lithium-ion battery for every four lead-acid batteries.
Regarding the cycling of the batteries, lead-acid batteries would have a cycling life of around 1000-1200 cycles and discharge to about 50%, while lithium-ion has virtually infinite cycling at much higher discharge levels at approximately 80%.
The lithium-ion battery bank would also weigh about 1/3 of the lead-acid banks’ weight and require less space in terms of placement and storage. While the lead-acid systems would require maintenance,lithium-ion would be maintenance-free.
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LITHIUM-ION VS. LEAD-ACID
How Are Lithium-Ion Batteries Better Than Lead Acid?
Lithium-ion batteries are becoming the option of choice as they last longer, produce more power with fewer batteries, and cycle deeper than lead-acid batteries. Their electrolyte is lithium-iron-phosphate, making them far more efficient than lead-acid units.
Most lead-acid batteries can cycle effectively to 50% of capacity to maintain a relatively consistent lifespan, but discharging them will decrease performance over time and reduce current output. Lithium-ion can discharge to around 85% of its ability without risk to performance.
Another big plus with lithium-ion is that they are much smaller than lead-acid batteries, and you can stack them inside the inverter to deliver equal or more power than lead-acid batteries could ever do.
By direct comparison, you would need fewer lithium-ion batteries to deliver the same amount of current. Still, while they cost much more than lead-acid batteries, the long-term spend on kilowatt-hours will be far less than lead-acid systems.
What Is The Difference In Costs Between Lead-Acid Vs. Lithium-Ion?
In this example, the batteries used are eight crown FLA and eight crown SLA batteries against 2 Discover AES 6.6kw Lithium-ion batteries.
The lithium-ion batteries cost around $13 000 for the two, while the lead-acid FLA is $2800 and the SLA is $ 3950, but you would need to replace lead-acid three times over ten years while not replacing the lithium-ion at all.
If you add up the maintenance costs, top-ups and replacements, and operational performance, you can see why lithium-ion batteries are preferred, and in the life of a PV system, they make more sense.
But, we are specifically looking at which battery is better for inverters, and again this will depend on the current level required and how many times you would use them during a year.
Comparison Of Efficiency Between Lead-Acid And Lithium-Ion
Efficiency measures the power available from the batter after charge and discharge. Lead-acid batteries typically offer around 80%-85% efficiency, while lithium-ion can provide as much as 95%.
In practical terms, let’s assume that the battery bank has a 1000W power capacity after charging. With lead-acid, that availability would be around 800W-850W, while lithium-ion would deliver 950W off the same maximum available power.
Which Battery Is More Susceptible To Temperature?
As a rule, the temperature in the environment where lead-acid batteries are stored can adversely affect their performance if it is too high or low, affecting the efficiency of the electrolyte. At the same time, lithium-ion is mainly impervious to this element.
Which Batter Charges Faster?
It’s better to have batteries for your inverter that can charge quickly, especially if you know you will have regular power cuts. In this category, lithium-ion is again superior as they charge about twice as fast as lead acid.
This is because lead acid can only handle a limited level of incoming current for charging. As such, they need to charge slower or risk overheating as the charging rate slows down as they approach total capacity.
Lead-Acid Vs. Lithium-Ion Costs
The only real drawback of lithium-ion batteries is the cost. They are considerably more expensive than their lead-acid counterparts, and many people looking to save money often choose lead acid.
They are usually about four times the price of the lead-acid batteries upfront, BUT this is offset over time as they have zero maintenance costs, plus their cost of energy storage is much cheaper.
Essentially you need fewer lithium-ion batteries to store electricity for redistribution than lead acid. Lithium-ion batteries are the best option for inverters if you can get past the initial costs and look at the performance, size, weight, efficiency, and charging features.
Now that we’ve had a look at the types of batteries available and their features as well as their pros, cons and which are best suited for the various types of backup power requirements, we need to consider what size inverter you would need and also how to calculate the battery capacity you would require.