The best solar battery : lithium or lead acid?

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The best solar battery : lithium or lead acid?

Dec 17, 2020 | Brand Reviews | 0 comments

image comparing the best solar battery

Everyone wants to know the best solar battery because the batteries are the most expensive pieces in a solar system. Before we even mention about the brands of the best solar battery, we first need to understand that there are different types of batteries available for sale in Zimbabwe. However, in solar installations, the two main rivals are Lithium ion batteries and Lead Acid batteries.

In addition, lead acid batteries also come in different types. These are normally labelled, Valve Regulated Lead acid batteries [VRLA], AGM batteries, Flooded Non-Sealed Lead Acid batteries and, GEL batteries. All these are in the group of Lead-Acid solar batteries. But, in order to make life for all of us easier, we are putting all types of lead acid batteries in one group because they are all manufactured using the same battery technology. So, we are comparing these Lead Acid batteries with Lithium ion batteries which is also using the new Lithium ion technology.

Another interesting thing about this comparison is this: In Zimbabwe we are seeing solar systems getting bigger to power up heavier electrical appliances like pumps, fridges, office equipment and to some even cooking and ironing. The old day small solar system which was only used for lighting and playing the radio is slowly fading into the backdrop. Solar is becoming the backbone of powering our farming projects, homes, hospitals, businesses and our places of worship. I have also witnessed many solar systems also being used in business arears which use machinery such as compressors, grinders, drilling machines, electric motors and pumps.

This article will also help you to determine the best solar batteries for use in such different scenarios. Different solar batteries come with different characteristics and for them to last you long, they have to be used for the most appropriate application. Hence, we are going to analyze the different battery characteristics and then conclude the best solar battery on each section. In the end, this short discussion will help you determine the best solar battery for your next solar project.

Now let’s get into it!!


The best solar battery on Useable energy

image showing that lithium batteries have more useable energy

A solar battery stores energy that is generated from your solar panels. But, unfortunately, not all the energy that your solar battery stores is usable. To avoid damaging the battery, you are only limited to discharge it to a certain level.

The level to which we can safely discharge a solar battery is called the Depth of discharge (DOD), and it is given as a percentage. This means if you discharge your solar battery until it runs flat, you would have ran it down to a depth of discharge (DOD) of 100%.

It is generally accepted that the most economic and practical depth of discharge (DOD) for a lead-acid battery is 50%. For Lithium-ion batteries 80% DOD is used. Beyond that point, you risk shortening their lifespan. Based on this it is reasonable to say that a lead-acid battery will need to be twice the Ah rating of a Lithium one. Therefore, if your energy requirement needs, for example, a 100ah battery, you should put a 200ah or more if you are using a Lead-Acid battery, and if it is a lithium ion battery, a 120ah will do.

Therefore, for the same rated battery capacity, a lithium ion battery has more usable energy than a lead acid battery. Subsequently this makes the lithium ion a better solar battery of the two.

In practice, if you have a 100ah lead-acid battery, remember you can only use half the capacity of it, which means you have only 50ah of battery capacity. On the other hand, of the 100ah you have on a lithium, you can use a decent 80ah out of it.


The best solar battery on Price

What about price? For the same amount of useable energy, Lithium ion batteries are 3 times more expensive. Based on this you might immediately conclude that Lithium is not cost effective. It is very understandable if we consider the souring economic environment in which we are living in. For a proper lithium ion battery, you might need to part with over $1000USD and believe me you, it is still a fortune to many of us in Zimbabwe.

But however, there is long term cost and short-term cost. It is clear that the lead acid battery is the best solar battery if we are looking it in terms of short-term cost. How about long-term cost? Let us find out as we continue to discuss about each battery characteristic one by one.


The number of appliances you can power at a time

image showing discharging a solar battery

Most batteries’ Ah rating are quoted at a 20-hour rate. This means that a 200ah battery will only give you that storage capacity if it is discharged over 20hours. Now, to discharge a 200ah lead acid 12v battery over 20 hours you need to be running appliances consuming not more than 120 watts until the battery is totally flat. And that will be a DOD of 100%.

Now, what if we increase the number of appliances we are using? For Lead acid batteries, there will be a shrinkage in the rating. As the rate of discharge increases, the battery’s available storage capacity decreases. This sadly means you can no longer get the rated energy out of the battery. That is when your batteries seem to last a bit less than normal.

This effective shrinkage in the rating is known as Peukert’s effect. With lead acid the higher the load, the more you need to increase the Ah capacity of your battery to help alleviate this.

 With Lithium however this Peukert’s effect is not an issue at all.  This is what makes Lithium particularly suitable for high loads. If you are going to be running loads like pumps, consider installing lithium batteries. Lead acid batteries tend to turn against you when loads get higher and heavier.


The best solar battery on Efficiency

efficiency of a solar battery is important

Now let us consider battery efficiency. When we are talking of efficiency of a solar battery, we mean that you should be able to use the amount of energy you have stored in your solar batteries. Here we mean that if 100 units of energy are pumped into your batteries, you should also use the stored 100 units to power your gadgets. This value is measured as a percentage. Now let us take a look at how the lithium and lead-acid batteries perform on this regard.

Lithium batteries are more efficient. This means that more of your solar power is stored and used. As an example, lead acid batteries are only 80-85% efficient depending on the model and condition. In layman’s terms that means if you have 100 units of electrical energy from your solar coming into the batteries, you can only enjoy only 80-85 units to power your appliances.

In comparison, Lithium batteries are more than 95% efficient. In the same example, you’d have over 95 units to use of the 100units of energy you would have stored. Higher efficiency means your batteries charge faster. Depending on the setup of your solar system, it could also mean you buying fewer solar panels, less battery capacity and a smaller backup generator. If you will be using Zesa to charge your batteries, this also means you will not lose much of your Zesa units when charging Lithium batteries as compared to when you are charging Lead-Acid batteries.

Therefore, on this aspect again, the lithium ion technology wins.


Which of the two battery types charge faster?

image showing that the best solar battery charges faster

Another reason why people in Zimbabwe install many solar panels is to ensure that they charge their batteries to full capacity in the shortest period of time. In this regard, they reason that when their batteries run through-out the night, they need to be recharged fast when the sun comes up so that they work the next night. But sadly, this is not always a good experience with some Lead acid batteries.

Lead-acid batteries are limited in how much charge current they can handle, mainly because they will overheat if you charge them too quickly. In addition, the charge rate gets significantly slower as you approach full capacity.

Lead acid batteries can tolerate high charging currents during the ‘bulk phase ‘(up to 85% capacity). After that, the battery charger automatically slows down to top off the batteries. This means lead acid batteries take longer to charge, in some cases more than 2x as long as a Lithium alternative.

On the other hand, with higher efficiency also comes a faster rate of charge for lithium batteries. They can handle a higher amperage from the charger, which means they can be refilled much faster than lead-acid.

Sometimes you really need your batteries to charge very fast, especially in winter and during cloudy days and these days give you a short window period to charge your battery. Consequently, if you see yourself in such situations, the lithium ion technology is worth your consideration.


The best solar battery on Cycle life

image showing lifespan of different solar batteries

When you discharge a battery (use it to power your appliances), then charge it back up with your panels, that is referred to as one charge cycle. We measure the lifespan of batteries not in terms of years, but rather how many cycles they can handle before they expire.

Think of it like putting mileage on a car. When you evaluate the condition of a used car, mileage matters a lot more than the year it was produced.

Same goes for batteries and the number of times they’ve been cycled. A sealed lead-acid battery at a vacation home may go through 100 cycles in 4 years, whereas the same battery might go through 300+ cycles in one year at a full-time residence. The one that has gone through 100 cycles is in much better shape.

Cycle life is also a function of depth of discharge (how much capacity you use before recharging a battery). Deeper discharges put more stress on the battery, which shortens its cycle life.

Now looking at the types of solar systems that many Zimbabweans are installing nowadays, batteries cycle a lot during rainy seasons and during winter. Typical Lead acid batteries give you 200-1000 cycles in their entire life depending on depth of discharge and operating temperature.  And some good ones like the Arco SSG250 250AH, are claimed to last you approximately 2000 cycles at a DOD of 50%. If you maintain a DOD of 50% the Arco will give you around 5 years and if you cycle them at a DOD of 80% the figure gives you at least 1000cycles which is about 3 years.[ Please note that this is true provided that you do not use them for high discharge applications like pumps and hot elements.]

In contrast, lithium will give you at least 3000 to 10000 cycles, depending on depth of discharge as well. For example, the BlueNova lithium claims to last you 5000 cycles if operated at 80% DOD. This means that if you cycle it everyday it gives you 13 mind blowing years! This figure can be higher if you discharge less. So, if your batteries are going to be for domestic use, where there is a likelihood of discharging them several times in a week, we recommend you to go for Lithium ion batteries. However, if they are for a vacation home, or for a few hours of backup in a week, you can consider getting the Lead Acid ones. They will do good for you.


Which one is the best solar battery if you plan to add more in the future?

Because of limited budgets, many people in Zimbabwe build their solar systems in stages. This includes maybe buying fewer solar batteries initially and increase them as one gets the money. However, this seems to be a good idea until you realize that adding on more batteries to older Lead-Acid battery will cause you problems.

Generally, you cannot mix lead-acid batteries of different cycles or ages. Battery manufacturers do not recommend it, and if some manufacturers find out, they will void any standing warranties. On the other hand, that is not an issue with lithium ion batteries. So, if you are thinking of an upgradable solar system, it is safe to start using lithium ion batteries, as they are very flexible. They can be added at any stage and thereby increasing the size of your battery bank.


The best solar battery on Weight

image showing that the best solar battery weighs less but has more useable energy

Most Ah ratings of batteries regardless of type are specified at the 20-hour rate. This was fine in the days of small solar systems, but as size of solar systems has increased over time, we also need to look at high short-term consumption appliances, medium- and longer-term ones for differing types of equipment. Now for our lead acid batteries, this can mean a large battery pack. At the extremes we might have air conditioning running for hours using 10 kW, compared to an LED light using 100 Watts in the old times.

 Balancing these differing requirements and all the loads in between becomes key. With a large lead acid battery pack to achieve this, it becomes clear just how heavy they can be compared to Lithium. This is called energy density. For the same energy requirements, it was seen that a Lead acid battery bank will be 4 times heavier than a lithium ion battery bank. This means that the energy density of lithium batteries is much higher than lead-acid, meaning they fit more storage capacity into less space.

For example, it takes two lithium batteries to power a 5kVA system, but you’d need at least 4 lead-acid batteries to do the same job. When you take the size of the entire battery bank into account, lithium weighs less than half as much.

This can be a real benefit if you need to get creative with how you mount your battery bank. If you are hanging an enclosure on the wall or hiding it in a closet, the improved energy density helps your lithium battery bank fit into tighter spaces.


What have we learnt?

No matter what battery choice you make there is also both a capital cost and technological risk at the outset. If you are in a position of having the capital for the higher upfront costs of Lithium, you might find that life is easier and that choice is a cost effective one over time. Much of this depends on the knowledge of the operator and how they treat a battery system. There is an old saying that batteries don’t die, they are killed. Good management practices are your insurance against early failure, regardless of the technology used.

Lithium-ion vs Lead Acid? The choice is yours. Personally, I think the time is right to consider Lithium in Zimbabwe as a cost effective, reliable, high performance solution.

At Taqon Electrico we sell both types of batteries. Moreover, we have the best brands and we also give a very generous warranty because we trust the brands we work with. Therefore, contact us so that we give you the best deal.


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Taqon Electrico

Taqon ElectriCo is a Solar and Electrical Systems Installer based in Harare Zimbabwe. Our aim is to give the best Electrical and Solar services, therefore, making our customers happy.

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