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 of them in turn 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
- How each battery works
- Lead-acid vs. lithium-ion performance
- Cost of each battery
- Maintenance of each battery
Before you choose your inverter battery, get the facts about your battery options so you can make a properly informed choice.
How To Calculate The Battery Size You Need
The wattage is an AC measurement, but the batteries run on DC, so you now need to convert the AC power to DC amp-hours to determine the size and quantity of batteries your inverter will require.
To calculate the battery requirements, here are four simple steps to determine battery size :
- Divide the total AC wattage by the DC current (we’ll use 12V) for this so = 1980W/12V = 165 amp-hours. This is how much current your battery will have to produce in a single hour to power these devices.
- Now, multiply the number above by the number of hours required = 165 X 4 = 660 Amp-hours.
- Factor in the loss – add 5% to the amp-hour figure to get a final DC amp-hour figure = 660 X 5%= 33Amp -hours + 165 amp-hours = 693 amp-hours total.
- If your battery is rated at 100 DC Am-hours, you need 7 of them to deliver the power requirements.
Your battery size will determine how long you can operate these devices, and to do that, we need to convert the AC wattage to DC amp-hours, giving use the battery size required.
First, convert the AC wattage to DC Amp-hours by dividing the total wattage by the DC, in this case, 12v.
1980W/12V= 165 Amp-hours.
Then multiply this by 2 hours to get the total DC power required = 330 DC Amps per hour.
As we did with the inverter, we added 5% to compensate for the efficiency loss as no system is 100% efficient to get a final figure = 16.5 amp hours + 330 amp hours = 346.50 DC amp-hours in total.
Now you can determine how many batteries you would need based on the battery power rating.
If the battery is rated 100 DC Amp-hours, you need four 12V batteries to run these devices for two hours.
Now that you have all the info on battery options and how to calculate the inverter and battery sizes, you are ready to go ahead and get your power back system done.
How The Kind Of Power Supply Issues Affect Your Battery Choice
When you have power failures or supply interruptions very occasionally, your backup power requirements will be far different than if you have regular supply failures that last for 4 hours or more.
When looking at which inverter battery is best, you need to consider the kind of usage it will provide and when you have long periods without power.
Your inverter choice and battery choice will be vastly different where you need to keep food cold or frozen and run other appliances for 8 hours against running your TV and WIFI for a few hours.
So take a few minutes now and consider what situation you find yourself in regarding power backup, and we’ll now look at the different types of batteries and the applications they are best suited for.
What Are The Types Of Inverter Batteries?
Backup batteries for inverters come in two basic options, lead-acid batteries or lithium-ion batteries—each work of a slightly different chemical composition that creates the electrical reaction inside it.
Let’s look at lead-acid batteries first and establish which backup situation would be a better choice than lithium-ion batteries.
What Are The Types Of Batteries Available And How They Work?
Lead-acid and lithium-ion are the two main types of batteries available for inverters. Still, the chemical structure and design of each are different, affecting their performance their 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 that are 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.
Types Of Lead Acid Batteries
Lead-acid batteries come in a few different 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 in general. They emit toxic fumes during charging and discharging.
These are similar to the kinds of batteries used in cars originally 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. There is no maintenance 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
- 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, the tubular batteries are more complex in design and more costly than standard batteries.
How Are Lithium-Ion Batteries Better Than Lead Acid?
Lithium-ion batteries are becoming the battery option of choice as they last longer, produce more power with fewer batteries, and cycle deeper than lead-acid batteries can.
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 more discharging them will decrease performance over time and reduce current output. Lithium-ion can discharge to around 85% of their 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 the lead-acid batteries, the long-term spend on kilowatt-hours will be far less than lead-acid systems.
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 ot every four lead-acid batteries.
When it comes to 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 levels of discharge at approximately 80%.
The lithium-ion battery bank would also weigh about 1/3 of the weight of the lead-acid banks and would require less space as well in terms of placement and storage. While the lead-acid systems would require maintenance,lithium-ion would be maintenance-free.
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 be dependent on the level of current required and how many times you would use them during a year.
Comparison Of Efficiency Between Lead-Acid And Lithium-Ion
Efficiency measures how much power is 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 1000W of power capacity after charging. With lead-acid, that availability would be around 800W-850W, while lithium-ion would deliver 950W off the same amount of 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 as it affects 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.
Which Battery Would Be Best Suited For An Inverter?
There is no single correct answer to this question as it does depend on the various factors you need to consider about your specific situation.
If this is just a backup system for sporadic and short-lived power cuts, investing in lithium-ion batteries would probably not be the best option. The cost would be high, and you would probably only need one battery.
In this situation, you would be better off with a Sealed Lead Acid Battery and probably the tubular plate battery. They are more efficient in delivering current and charging, plus no maintenance is required.
For scenarios where the power cuts are longer, and you’d need a bit more power for longer. To power more devices, the tubular lead-acid batteries would be a better option than the others, and perhaps lithium-ion would be an option, even though the upfront costs would be higher.
As the power and time requirements get longer, with more frequent and lengthier power outages, more lithium-ion batteries become a better option as you can power more devices for longer with fewer batteries.
Not only that, but in this case, the available charging time from the grid will be tenuous. So it would be considerably better if you had batteries that can charge faster and don’t need maintenance, will last for longer, and ones that can also discharge deeper and deliver more power for longer.
Another consideration here is should you decide to upscale your system should you need to power more devices; you’d only need to add another single lithium-ion battery instead of three or four.
This will save you storage space, as well as maintenance costs and this, is ideal if you are using your inverter in a remote place like a hunting cabin or similar environment, so before choosing your batteries, take some time to assess your real needs and then decide which battery would be best for your inverter.