The Proper Way to Connect a Solar Panel to a 12 Volt Battery

While many of the products we review here are readily available to purchase and operate without a license, we always recommend hiring a qualified electrician to install and demonstrate their use.

In some cases, improper use and installation may result in a breach of insurance. Even worse, you could be putting yourself or your family at risk as an incorrectly installed electrical device could start a fire. So, don’t risk it - seek the services of a fully licensed electrician instead.

Solar panels are an environmentally friendly method of creating power, and if you’re reading this then you probably already know that. But the reason why people are buying solar panels to create energy at home is not just because it’s a green way of living.

Solar panels can bring down your energy bill, saving you money in the long run as you produce your own energy. Another way to save money is to connect the solar panel to the battery by yourself!

The Proper Way of How to Connect a Solar Panel to a 12 Volt Battery

The problem is, you don’t know how to connect a solar panel to a battery! If done incorrectly, you could burn up your solar panel, overload your fuse box, and waste a ton of money in the process. So is there any point in getting a solar panel if the risk is this high?

Of course, there is! If you are a professional electrician then this will be child’s play for you. But to everyone else, this article will walk you through the process. You just need to know the proper way to connect a solar panel to a 12 volt battery.

What will you need?

Before we start the process of connecting your solar panel to a 12 volt battery, we first need to gather the right equipment for the job. On the way, we will explain what the tools are and what they are used for, so you know that you’re on the right track.

1. Wires

The first thing you need to get is the right wires. The type of wire you need depends on the current, voltage, and length of the wire that is being connected from the solar panel to the battery. 

If your solar panel says which wires it is using, or gives you wires in the packaging, then make sure to use the ones it mentions. Otherwise, a standard commercial solar panel can handle up to 30 amps per solar panel, so you should buy a 10 gauge wire. 

Amps is the term for measuring the electrical flow, and the gauge of wire is the measurement of diameter.  

2. PV Junction Box

A junction box is the part of the wiring which stops your solar panel from short circuiting which would otherwise lead to fires. Your solar panel might already come with a junction box. If not, you’ll need to get a PV junction box and glue it to the back of your solar panel with a silicon adhesive. 

3. Solar Inverter

A solar inverter is what you need to convert the direct current of electricity into an alternating current of electricity. This basically means converting solar energy into the grid’s energy. If you don’t have a solar inverter, then you won’t be able to sell the energy back to the grid or use any high tech digital appliance which relies on the grid’s alternating current. 

4. Charge Controller

Also known as a charge regulator, the controller regulates the current or voltage in the batteries and stops it from overcharging. You need this piece of tech in between the solar panel and battery to keep them both in check.

There are two types of charge controllers, MPPT and PWM. We recommend you have the MPPT, which stands for Maximum PowerPoint Tracking, this is because the PWM can cause power losses.

Wiring your solar panel to a 12 volt battery

Before you start connecting your solar panel to the 12 volt battery, it should be made clear that they shouldn’t be connected directly. Instead, you will need a charge controller, which should be connected between the panels and batteries. So it goes Solar Panel, Charge Controller, Battery. 

Step 1 - Mounting the Solar Panels

Most solar panels should be installed onto a roof. This is because it is the most likely place which isn’t being actively used, and it is probably going to get the most exposure to sunlight. 

Once you have secured the panels to the roof using a platform, you will be ready to wire the panels in parallels or series.

Step 2 - Wiring the panels in Series or Parallels

First figure out the positive terminal and negative terminals on your solar panel. It should come with a diagram, if not there should be a (-) sign and a (+) near the ends. Once you found them, you should place the panels next to each other, so you can place a positive (+), next to a negative (-).

Wire these opposite terminals together. You should end up with either a positive or negative terminal at the beginning of the series, and the opposite terminal at the end. These are the two end pieces that we can connect to the charge controller. 

Step 3 - Wiring the Solar Panels to the Charge Controller

The “amps” of a Charge Controller that you need for this next part depends on the solar panel’s watts. The watts or wattage is the amount of power being used or transferred. Most residential solar panels have a wattage of about  250 and 400 per hour.

The equation we need to use is wattage per hour ÷ voltage = amps.

Assuming the wattage is 300 and our voltage is 12v then our amps will be 25. 

300W per day ÷ 12V = 25 Amps.  So our Charge Controller should be 25 Amps. 

Following the same positive and negative terminal connections, you established in step 2, connect the solar panels to the charger controller. The wires you have bought should come with wire terminal connectors. These are materials that allow you to connect the wires to another device. 

Step 4 - Wiring the Charge Controller to the 12 Volt Battery

When connecting the wiring, you should be following the positive and negative terminal pattern you created in step 2. And as said in Step 3, you should have connectors to link the wires and devices together. As you did in step 3, clip the wires from the charge controller to the 12 volt battery. 

Step 5 - Wiring the 12 Volt Battery to the Solar Inverter

With the same method of wiring that you’ve done in steps 2, 3, and 4, you need to connect the battery to the solar inverter.

The solar inverter should not be placed in sunlight. If you have a garage, this would be a great place to put the inverter. There should be 6 inches free on all sizes of the inverter once it has been installed. It should be in a room with no moisture and good ventilation. 

Step 6 - Connect the Solar Inverter to your Fuse Box or Circuit Breaker

Looking at the solar inverter, you should find that it has a couple of transformers and switches. These are for converting the direct current of electricity into an alternating current of electricity.

Using a screwdriver, you will need to connect the white wire in the inverter to the ground bar on the circuit breaker. There should be a black or red wire in the inverter too. You will need to connect this to the backside of the circuit breaker.

And you’re done!  You’ve connected the solar panel to your battery and your home!

Finding this difficult to understand?

Youtube has a lot of videos to show how these steps can be done. If you need more help with connecting your solar panel to a battery, we recommend scrolling through youtube as a visual representation can be super helpful.

Frequently Asked Questions

Where should I put my solar panel?

Your solar panel should be placed where it will get the most sunlight. Your roof is the most obvious answer, but it all depends on your property and location. 

If you live in the northern hemisphere, you should have your solar panel face south. If you live in the southern hemisphere, you should have your solar panel face north. This is because the different hemispheres receive sunlight differently. Placing your solar panels in the right direction will allow them to receive direct sunlight throughout the day.

How do solar panels collect energy?

Most solar panels are made out of photovoltaic cells. This is why equipment used to help collect and use this energy is often called PV or Solar PV. In between each level of photovoltaic cells are semiconducting materials; normally silicone. When the sunlight hits the panels, the photons become energized and create an electric field. 

Do I really need a Charge Controller?

Without a charge controller, your solar panel will still charge the battery. It will work fine for a while, but eventually, the sun will go down or the battery will overcharge.

When the solar panel is in darkness, the electricity can leak from the batter to the panel. This isn’t something to worry about and is more of a waste than anything else.

The problem comes with an overcharged battery. The acid in the battery will bleed out, corroding your wires and the solar panel as well if left unnoticed.

An easy way to stop this from happening is installing a charge controller to go between the battery and the solar panel. 

How do I connect two batteries to a solar panel?

To connect two batteries to a solar panel, you can use a jumper wire to connect to the batteries in a series. To do this you use the jumper wires to connect the negative terminal of your first battery to a positive terminal of the second battery. Continue on this pattern until you have connected all your batteries so that all the terminals are connected to the opposite charge. 

Another way to connect multiple batteries is in a parallel circuit. To do this you need to connect positive to positive and negative to negative. 

What's the difference between batteries joined in parallel and series?

Batteries joined in parallel, meaning they connect the positive terminal to another positive terminal, keep the same level of voltage but increase the amp rating as the number of batteries increases. Batteries joined in a series, meaning they connect positive terminals to negative terminals, keep the same amp rating but increase in voltage as the number of batteries increase. 

Depending on the outcome you are after, both connecting styles are viable solutions. 

How many solar panels are needed to power a house?

Every house uses a different amount of electricity per year, especially depending on the generation and location you are in. In the U.S the average home uses 10,400 kWh per year and this number grows every year as we become more technologically advanced. 

Using this number, you would need 28-34 solar panels to generate enough energy to power one American home. 

How many solar panels are needed to power the world?

Assuming all the solar panels are using the same wattage, and are the same size. It would take 51.4 billion solar panels to power the world, and they would need over 115,000 square miles to do this.

This might sound like an impossible amount, but let's break it down into numbers we can understand. 115,000 square miles is a little bigger than Arizona and a little smaller than New Mexico. These are the 5th and 6th biggest states in America. In comparison to the rest of the world, that’s not very big.

Now we don’t need to evacuate Arizona to make way for a state sized solar farm. Instead, if half the buildings in America alone had solar panels on their roofs, then we could fuel the whole world!