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How Many Batteries for a 400-Watt Solar System

Sustainably powering your home with the sun’s energy is no longer an impossible task, but something that most of the world’s population has taken full advantage of. 

We have slowly started to migrate away from using non-renewable energy sources and turn to using the sun's full energy potential to power our homes.

Every person on Earth always has access to solar energy, so why wouldn’t we want to harness its full potential and power our homes with the energy it gives off? We will not only curb the effects of global warming, but we can also reduce our carbon footprints.

Fortunately for you, we will cover everything you need to know about these small 400-watt systems and their energy potential in this article.

By the end of the article, you will be a master of these small 400-watt systems and know the battery components associated with these systems.

Number of Batteries Needed

Modern solar panel systems come in a wide variety of sizes, from 10 kW systems, 5 kW systems, and the popular 400-watt solar systems, which have become the go-to systems for RVs and off-grid setups.

how many batteries do i need for a 400 watt solar system

Starting with a 400-watt system is an ideal start when it comes to solar panel systems. It’s powerful enough to provide your home and RV with sufficient electricity, and you won’t have to dish out a ton of cash for this specific system.

A common concern that new solar owners have around these 400-watt systems is how many batteries are needed for this type of system to run efficiently.

Adding batteries to a grid-tied solar system comes with a lot of advantages from energy storage for later use and cutting back on electricity bills. However, before we can determine the number of batteries needed, we first need to calculate how many watts our 400-watt solar panel produces in a day.

Once we have the amount, we can then move on to calculating the number of batteries we need.

The general equation used to work out wattage per day is your solar panel output multiplied by the number of sun hours your area receives in a day.


Let’s put it into perspective.

Let’s say you stay in an area that receives 6 hours of sunlight and there are no obstructions between your panel and the sun.

To work out the wattage per day, all you need to do is take your 6 hours and multiply it by the wattage of your panel, which in our case is 400 watts.

Therefore, 6 hours multiplied by 400 watts gives us a total of 2,400 watts a day. Remember this number can fluctuate depending on your location and cloud cover.

Perhaps you stay in an area that only receives 3 hours of direct sunlight and your output is only 350 watts. This means that you will get around 1,050 watts per day.

Now that we know the number of average watts you get daily, we can figure out the size of battery needed for your system.

Battery Size

Typically, you only need one battery for your 400-watt system. Lithium 100Ah (amp hours) batteries are highly recommended for these smaller solar panel systems. Let’s show you how to calculate the battery capacity for your solar system.

how many batteries do i need for a 400watt solar system

400-watt solar systems are generally 12 volts, which means you will need a 12-volt battery to ensure uniformity across your circuit. Having a small battery can cause an energy overload, which can lead to damage to your battery and potentially connected devices.

To determine the size of your battery you are going to need the daily watts of your solar panel, 2,400 in our case, and the voltage of your battery, which is generally 12 volts.

Take your wattage and divide it by the voltage of your battery to give you the amp hours. In this case, it's 2,400 watts divided by 12 volts, which equates to 200ah.

Remember this is for when conditions are perfect with no hindrance in the sunshine. In reality, amp hours are usually between 100 and 150ah.

This means that the minimum size battery you would need would be a 150ah battery. This is enough to store the energy produced by your 400-watt system.

However, your panel can produce more than the 150Ah we calculated and might even push it up to 200Ah. It’s always good practice to purchase a 200Ah lithium battery to account for the extra energy that might be produced.

how many batteries do i need for the 400 watt solar system

The 200ah batteries are the best because it doesn’t involve a complicated setup and you save a lot more money in the long run. You do have the option of buying four 12-volt 50Ah solar batteries, but this means connecting them to the circuit, which costs more.

Having a single battery also doesn’t take up as much space as having multiple batteries.

What Can You Run with Your 400-Watt Solar System

Getting the most power out of your 400-watt solar system depends on a couple of important factors such as weather, location, and season. Each one plays a significant role in increasing or decreasing the amount of energy produced by your specific solar system.

Weather and season are two of the most important factors that impact solar panel efficiency and output. You will need about 3-6 hours of direct sunlight to ensure that your solar panel is producing the highest amount of energy possible.

Any obstructions in the way of your solar panels, such as trees or high-rise buildings, can significantly reduce your solar system's energy potential and efficiency. Locations with prolonged sunny days will increase your annual electricity production by a whopping 30%.

It’s a good idea to do some visual scouting before deciding on the placement and orientation of your panels.

However, if you do stay in a location that is prone to overcast weather, then this is where the beauty of solar batteries comes into play.

On average, your 400-watt system produces between 160-200 ampere hours per day. This amount of electricity can power your fridge, TV, and other small electrical appliances.

To put in practice, with 2,400 watt-hours, you can run a 40-watt laptop for 6 hours, a 40-watt television for 4 hours, and a 90-watt fridge for 5 hours. The good news, you will still have energy left over after running these appliances.

How Long Does It Take to Charge?

how many batteries do you need for a 400watt solar system

Generally, it takes 4-6 hours to fully charge a 200Ah battery considering that conditions are perfect, i.e. minimal cloud cover and available hours of sunlight.

Typically, your solar panel won’t be completely drained, but if it is then your battery could take a little longer to fully charge.

For example, a 200Ah 12-volt solar battery typically has a discharge rate of 50%. This means that you have to charge your battery when it reaches 100Ah.

100Ah equates to roughly 1,200 watts, which means that your solar panel system needs to produce 1,200 volts to fully charge.

If your solar system produces 300 watts an hour, your battery will be fully charged in 4 hours. 

Thankfully, lithium batteries can charge faster than their lead-acid counterparts. Lithium batteries are the best batteries for RV solar systems and off-grid systems, and they require close to no maintenance.

If you are on a tight budget, then you could also opt for AGM batteries, which are an excellent alternative to a lithium battery.

how many batteries for a 400watt solar system


Solar panel battery systems technology has come a long way since its arrival with much more powerful and efficient systems emerging.

400-watt solar panel systems are becoming the go-to for many new solar panel owners because of their versatility and ability to power your home and appliances for several hours.

These types of systems are perfect for RVs and people who want solar panels for the off-grid cabin. There are many advantages to going solar from reducing your utility bills to allowing you to live a cleaner and greener lifestyle.

Solar battery storage systems costs are incredibly affordable and are an essential part of the overall solar panel system. If you  

or all your solar panel needs and queries, visit Shop Solar Kits. We have a wide range of solar batteries for every type of system. We can also assist you in finding the best possible system for your electrical needs.

We have quality products that are incredibly affordable and tailored specifically for your home. We also offer a solar panels affiliate program where you can earn cash back and discounts on future purchases.

Now that you know how many batteries are needed for your 400-watt system, it’s time to get out there and get everything that you need.

The time to go solar is now.

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