How To Connect Solar Panel to Battery: Why a Solar Charge Controller is Needed

Georgette Kilgore headshot, wearing 8 Billion Trees shirt with forest in the background.Written by Georgette Kilgore

Solar Panels | March 15, 2024

Men holding a solar panel and a battery with wires wonder how to connect solar panel to battery, diagram, steps for using solar charge controller and how to connect solar panel to a 12v battery.

Have you ever wondered how to connect solar panel to battery systems? It’s actually easier than you might think.

In fact, you can connect a solar panel directly to a battery by using wires to connect the positive and negative terminals on both. But, there are drawbacks to this type of ‘direct’ connection.

Without a diode, the electrical charge can leech back into the solar panel. And, without a charge controller connected, the panel itself can ‘overcharge’ the battery.

That’s why you need a solar charge connector to ensure that your energy system works as efficiently as possible, and provides electricity exactly when you need it.

This complete guide explains how to connect solar panel to battery and why charge controllers can be crucial, along with inverters for workable solar energy.

How To Connect Solar Panel to Battery: Step-By-Step Process

Learning how to connect solar panel to your battery employs basic electrical knowledge.7

Some people find the process a little tricky because batteries and panels aren’t listed in the same measurement. Batteries are usually measured by voltage while solar panels by watts.

Graphics of solar panel connection showing solar panels, solar charge controller, DC loads, battery, 12V inverter, and AC loads are connected with the use of fuse and cables.

It’s important to note that you should never connect a battery directly to a solar panel because you risk damaging both pieces of equipment.1 There must always be a controller or regulator between the two.

The parts required to connect a solar panel to a battery include:

  • 15A fuse
  • Inline fuse holder
  • Connectors
  • 12-gauge wire
  • MPPT regulator or Solar charge controller
  • Battery
  • Solar Panel

When learning how to connect a solar panel to a battery, the installer needs the following tools:

  • Multimeter
  • Wire cutter or Scissors
  • Heat gun
  • Wire stripper
  • Screwdriver

Step 1: Use Fuses To Connect Terminals

A solar charge controller has two terminals. One for the panel and one for the battery.

Wire the positive terminal on the charge controller using a fuse. Also, wire the 2 negative terminals to the charge controller.

Then, using a fuse, wire the second positive charge controller terminal. Make sure to use weatherproof wiring practices including using heat shrink tubing to cover the bare wire.

While proponents of sustainable development argue that solar energy is a significant carbon offset, it’s always a good idea to check with your local building codes before installing solar panels yourself.

Step 2: Connect Charge Controller to Battery and Then to Solar Panel

First, attach the battery’s negative terminal to the controller’s negative terminal.

Then, using MC4 or another connector cable adapter, connect the panel’s negative terminal to the charge controller, filled by the fused positive terminal.

Step 3: Place the Array in the Sun

Set the panel in a bright sunny spot (or if you are using a full system), simply allow the sunlight to generate the charge and fill the battery.

Of course, in order to use the Direct Current (DC) you’ve just created, you’ll need to have an inverter for alternating current devices.

What Is a Solar Charge Controller or Solar Panel Controller, and What Is Its Use?

When learning how to connect solar panel to battery, you will come across a solar panel controller, commonly known as a solar charge controller.5

This equipment usually regulates the current moving from solar panels to the battery.

The purpose of a solar panel is to recharge the electrical capacity of your battery, while solar generators convert and store power in the battery. If you have PV solar arrays that feed a battery bank you need solar charge controllers to prevent electrical surges from damaging the battery and reducing its lifespan.

A solar charge controller, two deep cycle batteries, and an inverter on top of a plywood in a garden shed.

(Image: Cody Kabus, U.S. Department of Energy10)

Solar charge controllers moderate the voltage transmission from solar panels to batteries. Due to the differences in voltages, solar panels usually have a higher voltage than a battery. For example, a 12V battery will have solar panels rated for 17V.2

While this seems counterintuitive, it’s with good reason. Solar panels usually do not output their total power rating because of dirt on panels, clouds, and other environmental factors.

Therefore, solar panels rated at 12V put out less power which a 12V battery cannot accept. At rest, a 12V battery is approximately 12.7V, and while charging, it’s around 13.7 to 14.5V, and this should be the minimum electrical output that a solar panel must generate.

In this case, the solar charge controller downregulates electricity from a 16 to 20V panel to the voltage the battery needs. This amount ranges from 10.6V to 14.6V depending on the temperature, battery’s current charge, and controller’s charging mode.

Power surges, inconsistencies in electrical output, and other factors can damage and overcharge a solar battery which is why a charge controller is absolutely necessary.

Types of Solar Charge Controllers

Charge controllers come in three types which sometimes overlap. None is necessarily better than the others, as they all have advantages depending on system components, array sizes, and climate.

They include:

Simple 1 or 2-Stage Controller

These controllers rely on relays or shunt transistors to regulate voltage in either one or two steps. They disconnect or short the solar panel at a specific voltage.

For all practical purposes, these are old-school controllers and are hard to find in the market these days. They are usually found on old systems, and anyone can get them cheaply on the Internet.

Their main selling point is their reliability, as they have so few components that there’s not much to break.

MPPT Solar Charge Controller

The Maximum Power Point Tracking (MPPT) controller is the most expensive of the three controllers and is significantly the most efficient in many circumstances. An MPPT controller draws out a current rate based on the maximum voltage of the panel.

You can use high-voltage arrays with low-voltage batteries. This charge controller is recommended for lower-cost, mass-produced PV models commonly found in residential homes.

An MPPT controller accepts and modulates varying voltages.3 It harnesses excess power that a PWM and stage controller would have otherwise wasted.

PWM Solar Charge Controller

Pulse Width Modulation (PMW) controllers are less expensive and much smaller than MPPT controllers. PWM controllers are best used with small solar systems such as small cabins and RV setups.

A PWM solar charge controller on white background.

(Image: Senlin Yang11)

A PWM controller should be used when the voltage from the array matches the battery voltage. The installer will require off-grid solar panels (rated 17-18V) when using PWM controllers, and these panels, more often than not, cost more than grid-tied panels (rated at 37V).

These controllers function best and ideal weather conditions- warm sunny days. The batteries operate less efficiently when the weather gets colder.

If you are interested in a PWM controller, you must know they have one dark mark on them; they cannot adjust voltages. Instead, they shut on and off as solar array voltage inevitably varies, and this auto shut-off leads to some power loss.

How To Connect Solar Panel to Battery: Why Do You Need a Solar Charge Controller?

Off-grid solar systems need solar charge controllers to regulate the movement of currents to and from batteries.6 However, you do not have to use a controller for renewable energy systems that are grid-connected because utility companies gather the excess energy and use the electricity.

Graphic image showing solar panel connections to a charge controller and battery using fuses for positive terminal connections.

Why do you need a solar charge controller? Here are a few reasons why:

To Block Reverse Current

A solar panel pumps current through the battery in one direction. At night, the panel may pump a small amount of current in reverse, which may lead to a slight battery discharge.

Though the potential loss is negligible, it’s preventable. Other renewable energy sources, such as hydro and wind generators, can also draw reverse currents once they stop, so this situation does not only occur in solar arrays.

Controllers in the market have a semiconductor, the transistor, that allows charging current to pass through and acts as a valve for controlling the current. This transistor is called a semiconductor because it allows current to move in one direction, preventing reverse current without extra cost or effort.

A few older controllers have electromagnetic coils that open and close mechanical switches called relays. These relays switch off at night, preventing reverse current.

These controllers are often called call shunt controllers.

To Prevent Overcharge

At full charge, batteries cannot store incoming energy any longer. Then when your panel continues to pump at full rate, the voltage from the battery goes up and up until it gets too much.

The battery degrades faster than you know it, and there is a chance of overheating. Not to mention, this excess voltage stresses the load (appliances, lights, etc.) and causes the inverter to shut off.

To prevent overcharge, the energy flow to the battery must be reduced after it reaches a specific voltage, which is where a controller proves helpful.4 Moreover, if the voltage drops due to increased electrical usage or low sun intensity, the controller lets in the maximum possible charge again.

This process is known as ‘voltage regulating.’

Charging a 12V Battery With Solar Panels: Step By Step

Why do you need to know how to charge a 12V battery with solar panels?

Because, 12V batteries in the market today are as common as sand. If there is ever a need to know how to connect solar panel to battery, it’s here.

Dual-battery-solar-panel system set-up equipment showing a small portable freezer, foldable solar panels, deep cycle battery, cables, plugs, and connectors on a wooden floor.

(Image: Stephan Ridgway12)

To find the right solar panels you should consult a wiring diagram solar panels 12V.

Then, take the following steps:

Steps Instructions
Step 1: Start by mounting the solar panel. After purchasing a solar panel, your first step is to mount it properly and correctly to prevent it from getting damaged and falling off. Ideally, it would be best if you placed the panel in an area with enough sunlight free from shade.
Step 2: Place the 12V Battery and Charge Controller in their required position. This is a very straightforward and important process. Both pieces of equipment come with a manual that lets you know where each item should be placed and how to connect them.
Step 3: Verify that the solar charge controller runs properly. After you attach the solar charge controller to the battery, please turn it on to ensure it functions well. If you have more advanced MPPT controllers they come with LED signal lights or display screens that show status information and verify the functioning of the charge controller.

If you have a more basic PWM controller it comes with simple indicators that show they are on and running. Once you know the solar charge is running as it should, turn it off and move to the next step.

Step 4: Connect the charge controller to the mounted solar panel. It would be best if you connected the solar charge controller to the solar panel to the battery by keenly following the manufacturer’s instructions. Your solar panels have their own cables that can be connected to the controller. You can buy longer wires if need be.

This part of the process may need a solar power inverter. Solar panel to battery connection is not complete without an inverter, especially if you plan to run electronics that need Alternating Current (AC) power from the electricity stored in the 12V battery.

A solar power inverter converts Direct Current (DC) into AC power. These inverters also track the voltage of the solar array to find out the maximum power at which the panels can operate.

Step 5: Complete the installation. Now, if you are sure everything is in its place, switch on the system.

Solar Energy Facts: Pros and Cons of Solar Energy

One of the interesting solar energy facts is that the amount of sun energy produced in an hour is enough to power the whole world for one year. Therefore, solar energy is a powerful, renewable, inexhaustible source of energy. Here are the pros and cons of solar energy.

Pros Cons
Diverse application Causes a lot of pollution
Reduced electricity bill Needs lots of space
Renewable energy source Expensive storage needed for the energy
Little maintenance cost Weather dependent
Great technological development High installation cost

How To Connect a Solar Panel to a 12 Volt Battery: Finding the Right Solar Panels

One step you must consider when learning how to connect a solar panel to a 12 V battery is how to find the right solar panels.

Top shot of REPPS (Rucksack Enhanced Portable Power System) showing the anti-glint solar panels and battery connectors.

(Image: U.S. Army Combat Capabilities Development Command C5ISR Center9)

A 17V solar panel and a 12V battery go hand in hand and they are the best choice for you if you are starting out in the solar industry. Even so, you have lots to choose from with solar arrays.

So, 100 Watt 17 Volt monocrystalline Solar panel is the best and most affordable option for a 12V battery.8

You’ll need to use a solar charge controller between a battery and solar panel connection to prevent reverse current.

Knowing how to connect solar panel to battery systems can make installing your solar panels easier, and using solar energy more consistent.

Frequently Asked Questions About How To Connect Solar Panel to Battery

How To Connect Solar Panel to Dual Battery?

Dual batteries in solar arrays are attached in either parallel or series connections.

How To Connect Solar Panel to Deep Cycle Battery?

You use the same process of connecting a regular battery, first from the battery to the charge controller, then to the panel.

How To Connect Solar Panel to Battery and Inverter?

Match the negatives and positives when connecting the solar panel to battery and inverter.

How To Connect Solar Panel to Battery, MPPT vs PWM Solar Charge Controllers?

A MPPT vs PWM will tell that a PWM controller draws out current from the panel just above the battery voltage while an MPPT controller draws out the panel’s maximum power voltage.

Is Charging Tesla With Solar Panels Possible?

Though you will need additional solar panels to charge the vehicle entirely, charging Tesla with solar panels is possible.

What Are the Ways on How To Wire Solar Panels?

There are two ways on how to wire solar panels. You can do the wiring in parallel or in series, depending on the specifications you need.

What Size Solar Panel To Charge 12V?

A single 100-watt 17v solar panel.

Why Are Solar Panels So Expensive?

To answer the question, “Why are solar panels so expensive?” Constructing solar panels is a very advanced process and requires expensive raw materials.

Read More About How To Connect Solar Panel To Battery


References

1Joseph, A. (2022, August 23). How to Connect Solar Panels to Battery. Solar Energy Hub. Retrieved on March 31, 2023, from <https://solarenergyhub.com/how-to-connect-solar-panels-to-battery/>

2EcoFlow, Inc. (2022, December 13). What Is a Solar Charge Controller, and Do You Need It? Ecoflow. Retrieved on March 31, 2023, from <https://blog.ecoflow.com/us/solar-charge-controller/>

3Liter of Light USA . (2023, January 27). How to Connect a Solar Panel to A 12 V Battery? Liter of Light USA. Retrieved on March 31, 2023, from <https://www.literoflightusa.org/how-to-connect-a-solar-panel-to-a-12-volt-battery/>

4Beale, A. (2021, June 30). How to Connect a Solar Panel to a Battery: 5 Steps (w/Videos). Footprint Hero. Retrieved on March 31, 2023, from <https://footprinthero.com/how-to-connect-a-solar-panel-to-a-battery>

5Almazrouei, A. (2019, April 26). Solar Charge Controller. University of Evansville. Retrieved April 19, 2023, from <https://www.evansville.edu/majors/electricalengineering/downloads/projects-2019/solar-charge-controller-report.pdf>

6U.S. Department of Energy. (2023). Off-Grid or Stand-Alone Renewable Energy Systems. Energy.gov. Retrieved April 19, 2023, from <https://www.energy.gov/energysaver/grid-or-stand-alone-renewable-energy-systems>

7U.S. Department of Energy. (2023). Planning a Home Solar Electric System. Energy.gov. Retrieved April 19, 2023, from <https://www.energy.gov/energysaver/planning-home-solar-electric-system>

8Wikipedia. (2023, April 14). Solar panel. Wikipedia. Retrieved April 19, 2023, from <https://en.wikipedia.org/wiki/Solar_panel>

9REPPS Photo by U.S. Army Combat Capabilities Development Command C5ISR Center / Attribution 2.0 Generic (CC BY 2.0). Resized and Changed Format. From Flickr <https://www.flickr.com/photos/cerdec/8119544000/sizes/c/>

10Deep cycle batteries Photo by Cody Kabus, U.S. Department of Energy / United States Government Work. Resized and Changed Format. From Flickr <https://www.flickr.com/photos/departmentofenergy/36775931686/sizes/c/>

112KW wind & solar hybrid controller with inverter Photo by Senlin Yang / Attribution-ShareAlike 3.0 International (CC BY-SA 3.0) . Resized and Changed Format. From Wikimedia Commons <https://commons.wikimedia.org/wiki/File:2KW_wind%26solar_hybrid_controller_with_inverter.jpg>

12Eco-Camper 125W Flexible Solar Panel Photo by Stephan Ridgway / Attribution 2.0 Generic (CC BY 2.0). Resized and Changed Format. From Flickr <https://www.flickr.com/photos/stephanridgway/5388987683/sizes/c/>