What Size Solar Panel To Charge 12V Battery

What Size Solar Panel To Charge 12V Battery?

If you are using solar energy to power your electronics, a battery system may be the next thing on your shopping list. If you are not connected to grid power, a solar panel battery is a must to ensure you can power your electronics day, night, rain, or shine.

Chances are, you don’t know where to start when selecting the right deep cycle batteries for your setup. But, much to your benefit, the process isn’t too difficult with the right resource or help guide.

This article walks you through everything you need to know regarding solar panel battery selection, usage, and charging. Importantly, we answer what size solar panel to charge 12V battery. Read on to get started.

Key Terms to Know Before Getting Started

Throughout this article, we use various technical terms that may be a bit confusing at first. However, here are the key terms we will use and what they mean:

  • Amp-hours: How many amps the battery offers in a one hour span.
  • Amp rating: Often another word for amp hours, but sometimes refers to amperage and wattage.
  • Charge controller: A device that controls when your solar battery is charging, almost like an on/off switch.
  • Inverter: Connects to your solar panel to convert unusable DC energy into usable AC energy for your home.
  • Solar system: All of the parts used to power your home by solar energy, including the PV panels, connectors, inverter, battery, etc.
  • Voltage (voltage rating): Tells you the potential output of your solar panel or battery.
  • Wattage: The operating power of solar panels or batteries.

Now that we have gotten the technical jargon out of the way let’s dive into solar panel batteries, why you need them, and how to select the right system for your needs.

Why Solar Panel Batteries Are a Must

Whenever people get solar panels for the first time, they aren’t quite sure why they need a battery, to begin with. Although this question is a natural one, the answer is rather easy to understand.

As you know, solar panels only provide electricity whenever the sun is out. Therefore, on a cloudy day or nighttime, the solar panels may not produce enough electricity to provide your setup with the power required to go about your regular activities.

That doesn’t mean you can’t use solar panels. On the contrary, you can continue to use solar panels, but you need a solar panel battery to keep the power coming even when the sun is down.

The purpose of a solar panel battery is to provide you with solar energy, regardless of the sun’s status. Your solar panels will harness the sun’s energy to power your setup during the day, but your battery will kick in during the night.

deep cycle battery 5

Are Batteries Always Required?

Technically, deep cycle batteries are not required for every setup. However, here is a short way to understand when batteries are required for your solar systems:

If your solar panel system is connected to the grid, batteries are not necessary, but they can still be a good addition as battery backup. Comparatively, battery systems are required if you are not connected to the grid.

For example, grid-connected solar-powered systems don’t need a battery. That’s because the grid connection provides the setup of traditional electricity during nighttime or cloudy days.

That being said, systems connected to the grid can still benefit from batteries. Even if you use solar panels, your electricity flow will be cut off if there is a power outage in your area to protect city workers.

To ensure that you still have electricity, you can use a solar battery as backup. In other words, you still get electricity even if the grid is down.

Solar batteries are required if you use solar panels to power an RV or other devices not attached to the grid. It’s up to you to determine if batteries are required for your setup. At least the process of making this decision is pretty easy.

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About Deep Cycle Batteries

You need to understand what we mean when we talk about solar panel batteries. The type of batteries we are talking about are not the kind that power toys or that you can fetch easily from your storage closet.

Instead, solar panel batteries refer to deep cycle batteries. By appearances, deep cycle batteries look like car batteries, but they are completely different.

Whereas car batteries provide energy in short bursts, deep cycle batteries are designed to discharge energy repeatedly.

There are different types of deep cycle batteries available. The primary options include:

  • Flooded lead-acid
  • Lithium iron phosphate
  • Sealed lead-acid batteries

deep cycle battery

Each of these deep cycle battery varieties come with their own benefits, drawbacks, and ideal usage.

What Is Deep Cycle Battery Best?

So, which deep cycle battery is best? Knowing the different types available means nothing if you don’t understand their differences.

Generally speaking, lithium iron phosphate batteries are considered more efficient and have a faster charge rate than both other varieties. These two facts make them the best deep cycle battery in terms of performance.

Because lithium iron phosphate batteries are so efficient that they can be expensive and outside of some people’s price range, there are drawbacks to using this top deep cycle battery.

Even though lithium iron phosphate batteries are considered the best, all three of the deep cycle batteries mentioned in this article are considered great options—many people like lead-acid batteries for their affordability.

You can decide which deep cycle battery you want by looking at the battery capacity, life cycle, and price. But, of course, don’t sacrifice quality for money since you can find very efficient batteries yet more affordable than other models.

deep cycle battery 1

What Is a Solar Charger Controller?

If you want to use a battery system with your solar panel setup, you need more than just the battery itself. As you probably expect, you will need wires and cables to connect the battery to the solar panel, but one part is equally as important: the solar charge controller.

The battery charger controller improves the charging quality of the battery and prevents it from overcharging. It may be helpful to think of the solar charge controller as an on/off switch that will turn off the battery charging function once it is fully charged.

solar charge controller

When You Should Use a Controller

If your solar panel system has over 5 watts, a solar charger controller is a great investment. Likewise, solar charger controllers are ideal if you use flooded lead-acid batteries, prone to overcharging.

Even though solar charger controllers make the cost of your battery system go up, it is something you should buy.

Not only will it improve the quality of your battery, but it protects it from breaking, forcing you to buy another battery prematurely. In other words, it can help you save money in the long run.

Not to mention, it can be tough to predict the overheat or overcharge state without knowing the battery configuration.

So, even if you don’t use a flooded lead-acid battery or have a 5-watt system, we still recommend a solar charge controller.

What About a Power Inverter?

In addition to the solar charger controller, you must get an inverter. So even if you do not opt for a battery-powered system, you still need an inverter.

“Why?” you might ask. Well, the answer is straightforward: even though the sun’s rays provide energy, the energy is not in a form usable for your home’s electricity needs.

The role of the inverter is to turn the sunlight energy into usable electricity for your home use. Without the inverter, your solar panels are essentially useless.

solar power inverter

A Closer Look at How Inverters Function

Whenever your solar panel traps the sunlight, the sort of energy produced is called DC energy. DC power is not a form of electricity used to power up your home and appliances – that form of energy is called AC power or energy.

DC energy is sent to the inverter, where it runs through a transformer. The inverter essentially “tricks” the transformer into acting as though it is running AC energy instead of DC.

From this trickery, the transformer essentially forces the DC power to act as AC energy. Of course, the inverter doesn’t actually trick the transformer, but the example suffices.

Once the energy goes through the inverter, it is now in a form usable for your home devices and appliances. Hence, it is sent to your home for use.

Don’t Forget About Cables.

The last thing you need to get to use a solar battery is cables or connectors. These devices simply connect the battery to the inverter and overall solar systems.

You shouldn’t have any difficulty picking out the right cables or connectors. So, we won’t waste a lot of time on them.

de bull deep cycle battery 1

How Does the Solar Panel Battery Charging Process Work?

Now that we’ve looked at the main function and parts of a solar panel battery system let’s learn about the battery charging process. Understanding how your battery works can help you select the best system for your needs.

How exactly your solar panel system works depends on whether it is connected to the grid or not. Let’s look at both off-grid, on-grid, and battery-free setups to understand the process fully.

Off-Grid Setups

Off-grid setups are the type of systems that need battery power the most. But, as we learned above, off-grid systems risk losing power if there’s not enough sunlight or nighttime.

The charging process begins with your solar panel. As you likely know, solar panels come with technology that can trap the sunlight’s energy.

Using an inverter, the sunlight’s energy is turned into usable energy. At this point, the inverter will send the usable energy to the battery bank if it is not charged.

If the battery bank is fully charged, the solar charger controller will essentially turn off the connection between the inverter and battery bank.

At the same time, the inverter sends the usable electricity to your home, RV, or wherever your solar panels are connected. You can use your electronic devices.

After the sun goes down, your solar panels don’t produce any more energy. However, you can still get usable energy due to the battery bank system.

The process repeats different battery charging stages, such as a “trickle charge” stage, to ensure the battery is always ready.

On-Grid Setups

On-grid setups work essentially the same way in terms of storing energy with the battery. The only difference is that the utility grid and utility meter are involved in the process.

Once the battery is completely charged, all usable electricity will be sent from the inverter to the home, just as before. The difference between off-grid and on-grid systems occurs after energy has been sent to the home.

All of your home’s energy production and usage is tracked using a utility meter. Net metering is what allows you to get paid for excess energy produced and put back into the grid, as well as create your electricity bill if you’ve used more grid energy than solar energy.

The utility meter will communicate with the utility grid. Because of this utility meter and utility grid, homes connected to solar power will be cut off from electricity in the case of a power outage.

The battery can be turned on as a backup option whenever you are cut off from grid power. For this reason, many people connected to the grid still opt for a deep cycle battery.

No Battery Setups

If you are unfamiliar, grid setups without batteries work the same way, except they don’t have the battery. In other words, the solar panel captures the sun and sends the DC energy to the inverter.

The usable AC energy is sent to your home to be used as usable electricity from the inverter. Like the on-grid battery setup, a utility meter tracks your usage and production and communicates it with the utility grid.

During this process, a battery is involved simply because it is not hooked up to the system. Whenever a power outage affects your utility grid, your power will go off, too, even if your solar panels are working.

What Size Solar Panel to Charge 12V Battery – What You Need to Know

Finally, we have reached the real point of our guide: what size solar panel to charge a 12V battery?

If you want your solar system to be powered with batteries during downtime, you must match your battery to your solar system. If not, the two parts may not work together, rendering them useless.

Although it may sound intimidating to pick out the right solar panels based on a 12 Volt battery, this process is pretty simple. Let’s figure out what you need to do to pick out the right solar system for your battery.

You need to consider only a few factors when picking out solar panels, but the process can still be confusing. Here are the factors that go into picking out your solar system when using a 12V battery or any other battery:

  • Voltage
  • Wattage
  • Amps
  • Outside conditions

Let’s take a look at these factors one by one.

Factor 1: Voltage

The voltage tells you your battery’s potential. The higher the voltage, the more current can flow through the circuits. If you have a 12V battery, it means the battery’s voltage is at 12.

Most 12V batteries need 13.6 volts or more to charge completely. Therefore, it’s important to know the voltage of both the solar panels and battery to ensure they are the right match for each other.

You must know the voltage to determine how many solar panels you need for your 12 Volt battery and how long it will take for your panels to charge the battery.

Luckily, you don’t have to do any math to find the voltage. Instead, it should be listed on the solar panel and battery’s box, user manual, or manufacturer’s website.

Factor 2: Wattage

Next, you need to figure out the wattage. You only need this number to calculate the amp hours, which we will look at next.

Much like the voltage, you should be able to find the wattage of your solar panels easily. But, again, the information should be listed on your solar panel package or user manual concerning them.

For most people, solar panels with a wattage between 100 and 120 watts are enough to charge a 12V battery.

Factor 3: Amp Hours

Understanding amp-hours Ah) is crucial.

The main reason for looking at the wattage is to discover the amp hours. Amp-hours are crucial for picking out the right solar system to go with your 12V battery.

Simply put, amp hour is a rating that tells you how many amps the battery can offer in a one hour period. You should easily find the amp power rating by looking at the Ah number of your battery.

Manufacturers should give a specific amp hour rating. If you cannot find it in any of these locations, look online or contact the manufacturer.

The amp hours should look like this: 100Ah. Based on this example, the battery can work for 20 hours at 5 amps or five hours at 20 amps.

Factor 4: Outside Conditions

We would be amiss if we did not talk about outside conditions and their impact on your solar panel battery system. Since solar panels only produce energy whenever the sun is out, the conditions outside impact how quickly you can charge up the battery.

You should expect your solar panel battery to charge up much quicker on a sunny day than on a rainy day. But, of course, the same goes for a sunny day versus a cloudy day.

Even though cloudy and rainy days still produce sunlight, the sunlight is lessened due to the obstruction of the clouds.

When you calculate how many solar panels you need or how long it will take for your solar panels to charge your battery, you have to estimate how much direct sunlight exposure the panels will have.

You can use a sunrise and sunset calculator based on your location to better estimate the exposure. Keep in mind that this will just be an estimate since the weather is not completely predictable.

How Many Amps Do I Need to Charge a 12 Volt Battery?

Generally speaking, the amps aren’t as important as the amp hours. Amp powers tell you how much energy the battery can produce per hour.

You can find out how many amps your panel produces by dividing the watts by the voltage. Let’s give an example, so you better understand what we mean.

Let’s say that you have a 12V solar panel that has a wattage of 100. If all conditions are correct, the voltage will be right around 18 volts.

So, you divide 100 watts by 18 volts. The result is about 5.5 amps for one hour.

How Many Solar Panels Do I Need For a 12V Battery?

To find out how many panels you need to charge a 12 Volt battery, you need to do some math. This math will be based on the factors described above.

Step 1:

Begin by finding the amp hours and voltage to find the watt-hours needed. Simply multiply the amp hours by the voltage. Here’s an example:

12Vx210Ah=2520 watt-hours

Step 2:

Next, divide the watt-hours, which you found in step 1, by your estimated amount of sunlight in hours. Here’s another example when 6 hours of sunlight is available:

2520/6= 420 watts

This number tells you that you need to get the right solar panels to produce over 420 watts. Then, get however many solar panels are needed to exceed this amount.

Solar panel size will likely affect how many you need to keep your solar batteries juiced up. For example, a large size solar panel will be better than a small panel.


Keep in mind you want the solar panels to exceed 420 slightly. Most of the time, your solar panels won’t produce energy at their optimal levels.

For example, power can vary depending on sunlight and the number of charging cycles you’ve already done through.

As a result, getting exactly enough panels for 420 watts means that the wattage will be below what is needed for your battery.

By exceeding the wattage slightly and still getting enough power to charge your battery.

How Long Does It Take To Charge a 12V Battery With A Solar Panel?

How long your battery charge takes to fill up will depend on many factors. For example, the efficiency of your solar system, quality of the battery, and sunlight exposure all affect charging time.

In the case that your battery has the same amp-hour rating as the amps produced by your solar system, it will typically take between five to eight hours to charge a totally drained battery to full capacity. Of course, this is assuming the weather out is an average sunny day.

If it is a sunny day out, the charging time will be on the lower end of this estimate, but rainy days result in a longer charging period. Old or inefficient items take longer to charge as well.

How to Set Up Your Solar Energy Station

Setting up your solar panel battery charging station isn’t too difficult. Just connect the battery to the solar panel and set up the solar panel as usual.

Connect the Battery to the Panel

To begin, you need to connect your solar panel to a regulator. After that, connect the regulator to the battery.

Most of the time, there should be instructions about how to do this. However, if you are hesitant, you can contact professionals in your area who can hook up the system for you or give you pointers.

solar energy station

Solar Panel Placement

You must place the solar panel in a way to maximize sunlight exposure. For example, the panel should be placed at a 45-degree angle directly up at the sunlight on a flat surface in an ideal world.

Your roof will be the best option simply because it comes with fewer obstructions. However, if your roof is not strong enough to hold the solar panels, you can place solar panels on the ground, assuming that trees and other items don’t cast shade over them.

If you do not have an area suitable for 45-degree angling, that is OK. Your solar panels will still produce energy, but they won’t be as efficient.

Continue to hook the solar panels up as normal.

Is There an Alternative to Solar Power Battery?

If you find it difficult to do the math and best predict what solar panels to get with your 12 Volt battery, you might want an alternative instead.

Solar power generators are great alternatives because they are easy to use and convenient, especially for beginners.

Instead of buying all parts separately, the solar power generator comes with the battery, inverter, and solar controller. As a result, you don’t have to buy all the parts separately, ensuring they go together perfectly.

lead acid batteries

You don’t have to buy special solar panels when using a solar panel generator, either. The same panels that power your battery will power the generator.

There are some downsides to using a solar generator. First, the price is much higher since it is more convenient and you can’t shop around for individual parts.

The high price and lack of customization are why many expert solar panel users opt for their own battery system. However, the convenience of generators may be ideal for beginners who are still trying to figure out the solar world.



How long will a 100-watt solar panel take to charge a 12V battery?

How long a solar panel takes to charge a battery will depend on many factors. Just knowing the wattage alone is not enough information to give an accurate prediction.

You can read above to learn about the factors to consider when predicting charge time.

In short, you need to know the amp hours and sunlight exposure on the day to predict charging duration.

Will a 5-watt solar panel charge a 12-volt battery?

Yes. A 5 Watt solar panel can charge a 12 Volt battery and maybe enough for some users. A higher wattage will likely be more efficient, though.

Do I need a solar generator?

If you get a solar system with a battery, a generator is not necessary. However, many beginners find using a solar generator easier and more convenient than the battery system.

A solar power generator acts as a complete solar power source. When you use a solar generator, you don’t need a battery since a battery is already included in the generator.

So, if you get a battery system, you don’t need a generator. Vice versa, if you get a generator, you don’t need a separate battery.

When is the best time to charge a solar battery?

The best time to charge your solar battery is when the sun is out, and the temperature is between 72 and 77 degrees Fahrenheit.

Although the sunlight rule may make sense, our temperature guidance may be a bit more confusing with what you have learned so far.

Simply put, most batteries have an optimal temperature, which is the temperature we described above.

If the temperature goes above 80 degrees, most batteries lose their capacity by 10% every additional 20 degrees.

At the same time, the capacity drops if the temperature goes below about 70 degrees Fahrenheit.

So, aim for the above factors to optimize your panel’s charging speed. If you have to charge your battery on another day, expect the battery not to be as efficient.

How long will my battery last?

How long your battery lasts will depend on the cycle life. The cycle life tells you how many power-ups and charge cycles your battery can last.

Final Thoughts

At the end of the day, solar power batteries are a must, whether you pick lead-acid batteries or lithium batteries. That being said, most people prefer lead-acid batteries.

Although they are necessary for those off the grid, even systems connected to the grid can benefit from battery backup.

Of course, getting the right system to accommodate your battery can be a bit difficult. You have to think about all the abovementioned factors and do the math to calculate your power needs and energy usage.

If you don’t want to put in all the work and effort it takes to set up your battery system; you can opt for a solar generator instead. Although it is slightly more expensive, it gives you all of the benefits of a battery in a much more convenient way.

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