In this article, I will explain how to connect a solar panel to a battery step-by-step.
I will also share a few tips you need to know along the way.
Here is a diagram connecting a single 100W solar panel to a 12V 100Ah lithium battery and a 500W inverter:
Step 1: Connect the battery to charge controller
In the first step, you will wire the battery to a charge controller. It is essential to wire this component before you wire the solar panels. If you wire the solar panels to your charge controller first, the fuse of the charge controller might blow.
If your charge controller has no replaceable fuse, you can’t use it anymore.
Always connect your battery to the charge controller first.
The thickness of the wire will depend on the type of charge controller you get. If you get a 20 amp charge controller, you need to use a wire thickness that can carry 20 amps without overheating (AWG14 / 2.5mm² or bigger). Flexible wires with a nylon coating are preferred (THWN-2 cable). Learn how to select wires and thicknesses in my book.
The manual of the charge controller will also suggest a wire size and a fuse size.
You need to keep these wires as short as possible because they will be expensive.
Step 2: Wiring the Loads
The following step is to wire the loads. These can be an inverter, 12 volts dc box or both. You have two options here:
- Attach the loads to the charge controller output terminal
- Attach the loads to the battery terminal
Only use this option if you have a small DC load. These terminals cannot deliver high currents but will protect your battery from over-discharging.
For example, the renogy rover 20/40Amp series, can only supply 20 Amps at its load terminals both for the 20 amp and 40 amp version. You can only attach 240 Watts (20 amps x 12 Volts) to the load terminals. You see that this is very limited. It’s not enough to connect an inverter to it.
If you have a device that can draw a lot of current, like an inverter or battery charger, you must attach the wires directly to the battery terminals. From here, you can wire it directly to the inverter or to a busbar. See the following diagram for reference:
Using this setup, you have to monitor the battery levels. Use a volt meter in case of lead-acid and a shunt for lithium batteries.
Before the next step, ensure you have programmed your battery type in the charge controller. This will be explained in the manual of your chosen charge controller.
Step 3: Connect solar panels to charge controller
The final step is connecting the solar panels to the charge controller.
If you have more than one panel and are unsure if you need to connect it in series or parallel, check out my article here, or if you have two solar panels and one battery, check out the wiring diagrams here.
Are you confused about the specifications of the solar panel you got? Check out my article, where I explain all the parameters of a solar panel here.
Use the cables that come with the solar panel, which are UV-resistant. Other cables will crack and break over time when exposed to UV radiation. This is the part when you need to oversize the diameter of the wire to account for voltage drop. Try to keep the voltage drop under 3%. Click here to calculate the voltage drop.
What is voltage drop?
Voltage drop occurs when a long cable delivers energy from point A to point B. The cable’s length increases the cable’s resistance, reducing the voltage at point B.
For example, your solar panel delivers 18 Volts DC and 5.8 amps to the charge controller, and the wire length is 40 feet.
As you can see in the calculation, the voltage drop is 4.09%, reducing the overall power delivered to the charge controller.
Let’s calculate the amount you will lose:
0.74 volts x 5.8 amps = 4.3 Watts
This is not much, but it can add up quickly with multiple panels. In your country, it could be that the voltage drop may not be above 3% by law. To reduce the voltage drop, you use thicker wire.
The final version will look like this:
You need to have fuses in between your devices. The main objective of having fuses is to protect the wires from overheating or catching fire, not to protect the device. This is because you will size the wires to the amount of current that can flow from one device to the other.
You need fuses in the following places:
- From battery to the charge controller
- From battery to inverter
- From battery to DC fuse box
You have come to the end of this article. Hopefully, you know how to connect a solar panel to a battery.
If you have questions, please write them in the comment section below.
Can I connect a solar panel directly to a battery?
No, there is no way for the solar panel to stop charging the battery, resulting in overcharging the battery.