What Size Lithium Battery Do You Need For Solar? [Everything You Need To Know Before Buying]

While a personal solar energy system is a noble investment, unless you’re Elon-rich, it’s not something you can rush into willy-nilly. It takes research, forethought, and lots of preparation.

There are a number of questions you have to ask yourself just to ascertain what sort of equipment you’re going to need, and one of the most vital components in your solar network will be the battery — A lithium battery if possible.

But deciding what size lithium battery to pick up is tricky. Not to worry though, friend; I’m going to fill you in on all you need to know before you hand over your hard-earned cash!

Lithium Solar Battery Size: A Moving Target

I’d love to be able to give you a quick answer to your question right here, but as is the case with most things in this life, it’s not quite as simple as that.

There is no optimal battery size for solar circuit integration. As long as a battery is designed for use in a solar harvesting system, it doesn’t matter what size it is.

All that matters is that it fits seamlessly into the system you have in mind and is therefore capable of facilitating your solar mission statement.

Coming Up With A Solar Mission Statement

What’s a solar mission statement, you ask? Well, it’s essentially just a plan. It sets out what you want your solar panel system to be capable of and gives you a target to base your purchases around.

Without this target, you may end up spending a small fortune on components that are either overkill or no kill at all, if you will.

Grab a pen and paper, and take a few minutes to note down what you want to accomplish with solar power.

Do you want to power everything in your house or just your lights? Is this battery only going to power a few appliances when camping, or will it power your RV when you hit the road?

Be as specific as you can, as this will help guide you directly to the type of equipment you’ll need, including a battery of suitable size.

The Language Of Batteries

If you’ve never dealt with complex electrical equipment before, when you start looking for solar panels and batteries, it feels like you’ve been inundated with a multitude of  impenetrable jargon.

Volts, watts, watt-hours, amps, amp-hours, kilowatt-hours… What does it all mean?

Well, each of these units could be considered relevant to the “size” of a lithium solar battery, so let’s break them down one by one.

Voltage (V) 

Many don’t realize it, but electrical current doesn’t just flow in one direction by accident; it’s actually a very deliberately designed part of the circuit.

The pressure that keeps everything moving in the right direction is known as voltage.

You can think of voltage like water pressure in a hose pipe — remember this, as I’m going to be dragging this hosepipe analogy out for a while.

The higher the pressure, the more current is forced through the circuit from one point to another, but what happens if the intended destination of the current has a higher voltage than the starting point? Very little, actually.

What This Has To Do With Solar?

In this context, our starting point is our solar panel and the destination is our battery.

If our battery has a higher voltage than our panels, the pressure is working against the flow of the current, which will inhibit charge significantly.

What this means in terms of battery “size” is that the combined voltage of your panels should be at least 20 to 30% higher than that of your battery.

So, if you’re planning a 56 V panel array, you’ll need a battery that’s no bigger than 48 V, such as this Ampere Time unit.

Amps (A)

Amps are a measurement of current, or, returning to our hose pipe analogy, the amount of water flowing through the pipe. 

What This Has To Do With Solar?

To streamline your solar network and optimize your energy yield, you need a battery with an amperage close to the maximum amperage of your panel array, but never above it.

The amps of a rechargeable battery are basically an input unit. They state that the battery needs this much current to charge sufficiently.

Watts (W)

Watts are similar to amps, which confuses many a mind, but thankfully, our hose pipe analogy is here to save the day. 

So, we’ve established that volts are the water pressure within the hose, and amps are the water traveling through the hose.

Watts are the water coming out of the nozzle of the hose.

What This Has To Do With Solar?

Watts are a measurement of the usable energy output of a battery, but it’s not ideal for figuring out battery size for solar.

Watt-hours are far more helpful.

Watt-Hours (Wh)

Being that there’s a time-based aspect to capacity, we need a slightly different unit to measure it: Watt-hours.

This unit is a measure of power output over time (an hour). In our hose pipe analogy, watt-hours would be the time it takes for the source of the water to run dry.

The hose thing is getting a little unwieldy at this point, though, so let’s take a look at a simple practical example…

Let’s say that you’re trying to power a 100-watt light bulb, and you’re using a battery rated for 400 watt-hours; theoretically, you should be able to run that light for 4 hours.

You can figure out the watt-hours of a battery by multiplying the voltage by the amps.

What This Has To Do With Solar?

Watt-hours are important because they let us know how long we can run our electronics with a solar battery, but if you’re dealing with a large number of powerful appliances and oodles of watts, it’s best to use a more macroscopic unit — enter the kilowatt-hour!

Kilowatt-Hours (kWh)

There are 1000 watts in every kWh, and they can be calculated by multiplying the volts by the amps of the battery and then dividing the answer by 1000.

What This Has To Do With Solar?

As a measurement, that simplifies the numbers involved with extensive wattage calculations, they’re a lot easier to work with when figuring out whole house loads.

Amp-Hours (Ah)

Amp-hours are to amps what the watt-hour is to watts — a measure of amps with an additional temporal aspect.

Whereas amps refer to the current as a fixed notion, amp-hours refer to it as a moving notion.

What This Has To Do With Solar?

This is another measure of capacity, but we can also use amp hours to ascertain how long it will take our solar panels to charge up our solar battery.

Say for example we have an empty 100 Ah battery connected to 100 amp solar panels; on paper, it should take one hour to fully recharge.

Figuring Out Combined Load

Now that you speak fluent battery, it’s time to use what you’ve learned to figure out what sort of battery your solar energy system needs.

You’ll need to establish how much power each of your appliances use, then use the sum of these various outgoings to find a battery (or batteries) that has a matching or higher kWh rating.

Choosing something with a bit of headroom is particularly important if you live in an area with a gloomy climate, as you’ll need enough power stored to hold you over until the sun shows its face.

That said, as your panels will be uber-productive in sunny climates, even if you don’t need all their energy, it might be worth harnessing it and selling it back to the grid.

Final Thoughts

There you have it! — Although there is no one-shoe-fits-all lithium solar battery, you now have all the lingo on lock, and you can shop around for solar batteries with confidence.