Charging RV Batteries Using a Solar Panel

Camping in your RV can be a great way to relax and get away from life’s daily stresses. Camping is all about freedom and being able to spend time completely untethered from the world.

Your RV Battery can be charged through the alternator when driving, shore power, a generator, or via a battery charger at home.  The Alternator is not a good option if you won’t be driving for a long period of time and only offers a trickle charge to the RV batteries. Shore power will require hook-ups on campsites and a battery charger requires a power source. A generator will be too noisy even though it has some use cases.

Solar RV systems are an effective way to create self-power and to live off-grid. A proper solar panel setup can power your RV and allow you to travel without the need for public or commercial power sources. Even though you’re mobile, you can still enjoy the benefits of your electricity being produced by the sun.

Have you been considering installing a solar system on your travel trailer or camper, but don’t know where to start? If so, keep reading, this article will cover the basics of getting started with solar and what to consider. We’ll also give you tips on how to choose the right size.

How much Power to Run an RV

Running an RV is much like running a home. However, even with hookups, it is almost impossible to run all the appliances at once. To run all your RV appliances could require as much as 3000 watts. But you are rarely running all your appliances at the same time. 

 

Appliance

Wattage

Daily Watt-Hour Requirements

Refrigerator

400

3200

Lights

40

160

Mini Fan

40

400

Electric Water Heater

1200

300

Laptop

60

300

TV

30

150

Water Pump

60

300

 

For some devices like electric heaters or coffee makers, you will only be using them for a couple of minutes a day. So you will use a fraction of an hour for example using the electric heater for a total of 15 mins in a day will give you a quarter of an hour which equates to 300 Watt-Hours. 

The total wattage requirements for our example above is 2330 watts and the total watt-hour requirement is 4810 Watt-hours.  To calculate watt-hours you simply multiply the wattage by the number of hours you are running the device.

What Size Solar Panel for an RV

Using our example you will need up to 2330 watts to run the essential appliances in an RV. Running your whole RV system will need up to 3600 watts. 

So do we match our solar panels to our requirements and simply say a 3000-watt solar panel will run my RV. Not quite. Solar panels do not work alone and won’t directly power your appliances. The battery is still where you’ll get your power from either through an Inverter to get AC power or even 12v power directly from the battery. 

Your battery bank will determine the size of solar panel you can use on your RV, not your power requirements. 

What Size Battery Bank for an RV

From our example earlier we estimated that you will need around 4810 Watt-hours to run the essential appliances in your Rig. To get the Ah requirement for our battery we simply divide the watt-hours by the voltage of our system.

If it’s a 12v system then you will need up to 400 Ah or 200 Ah for a 24v system. This will be true for lithium batteries but will have to double up for lead-acid batteries as they can only be discharged up to 50%. So in this case you will need a 400 ah 24 AGM battery bank or 200 ah lithium battery.

What Size Solar Panel for Charging My RV Battery 

The size of a solar panel for your camper’s battery bank will be dictated by the ‘C’ Rating. A battery’s charge and discharge rates are controlled by battery C rates. The battery C Rating is a measurement of the current at which a battery is charged and discharged.

Usually, AGM or Lead-acid batteries are charged at 10% of their capacity meaning that a 100 Ah battery should be charged with 10 amps. So if you are running a 400 ah AGM battery in your camper you will need a charger that can provide 40 amps. 

The voltage of the solar panel is usually rated at 12V but is usually higher and can go up to 20V in order to provide the potential difference for the flow of charge between the solar panel and your battery.  To get 40 amps from a Solar panel you will need up to 720 Watts at an 18V Voltage. 

Wattage = Amps x Voltage

You can also wire two 360-watt solar panels in parallel and get 40 amps. This will combine the amps of the two panels while keeping the voltage the same.

This will take around 10 hours of sunlight to fully charge your battery. But because you only discharge your AGM battery up to 50%, 5 hours of sunlight will be enough to refill your usable capacity. 

You can choose to either mount the solar panels on your roof or place them on the ground. There are also various selections including solar panels that fold into a briefcase or non-portable rigid ones.

 

Charging Lithium Batteries 

Lithium-ion batteries are a newer and better technology and actually be charged at 100% of their capacity.  This means that you can flash a 100 ah lithium-ion battery with 100 amps and it can take it. However, it is recommended that you only do 50% of its capacity. So with a 200 ah lithium-ion battery, you charge it in 2 hours with 100 amps or five hours with 40 amps. 

You can still wire the two 360-watt solar panels in parallel to fully charge the battery in five hours.  

Can you Power Devices Directly from the Solar Panel?

A solar panel also provides DC current and most of the appliances in an RV run on 12v DC Current. This means after charging your RV batteries you can hook up the panels to some of your appliances directly including your laptop and phone.  You may also use an inverter in the setup and draw an AC current from the batteries while charging with DC power from the sun.

 

How to Set Up a Solar Panel System RV Batteries

First of all, you should never connect solar panels to your batteries directly. You need a charge controller to protect your batteries from overcharging.

  1. In order to start to determine the location to install the charge controller. This should be as close to the RV’s battery as possible. Make sure that this area is water-tight and allows for as much airflow as possible.
  2. Ensure you choose the right wire gauge for your cables. At the end of the cables use alligator clips or ring terminals that are to be hooked up on the batteries terminals. The clips should be labeled positive or negative depending on where the cable is hooked up on the panel.
  3. Access the battery and identify the negative and positive terminals. This is easy as the negative terminal which is the ground cable will have a negative (-) and the power or positive cable will have plus (+) sign.
  4. When using a Charge Controller the battery should be the first thing you connect to the Controller. You should NEVER connect a Solar Panel to the Controller without a Battery. The charge controller should be clearly labeled for ‘BATTERY + and -‘to make SURE the polarity is correct.
  5. Once you have connected the battery now connect the charge controller to the solar panels. The charge controller should also be labeled for a ‘PV INPUT + and -‘. This is where you hook up the panels. Make sure not to mix up the positive and negative Positive (+) is usually red, while a negative (-) is usually black. If you are not sure you can check polarity using a multimeter.
  6. Make sure to select the correct profile for your battery on the charge controller whether Lithium, Gel or AGM batteries. More on this next.

3-Stage Charging Using a Charge Controller

A charge controller will allow you to set how you want your battery to be charged. You can pick from the 3-stages depending on the level of charge of your battery or your battery type.

The three stages are; bulk, absorption, and float and are applicable to Wet, Gel, and AGM Lead Acid batteries.

Bulk Charging

Bulk charging is the normal battery charging that provides a fast charge. To provide a fast charge sufficient sunlight must be available and the battery must have been deeply discharged.

Absorption Charging

The Absorption stage is where the battery slows down the amps going in the battery once a certain voltage is reached.  It is conditioning mode to step down the charging but allow the panel to complete charging.

Float Charging

At the float stage, the battery is full and is only being topped off with a small charge to compensate for the idle discharge.

Equalization

Some MPPT Chargers will routinely (once a month) apply an equalizing charge. This is the intentionally overcharging of Lead Acid batteries to remove sulfate crystals that build upon the plates over time commonly referred to as sulfation.

Setting your Charge Controller for Lithium Batteries

Lithium Batteries use different settings as they are charged differently.  Lithium batteries just use bulk mode until a target voltage is achieved. You may set for absorption mode for a couple of minutes before going to float. But it is possible to go straight from Bulk to float.

The basic is to ensure the bulk voltage is set at around 14.4V, 14.6 for the absorption stage, and 13.5 or 13.6 for float.

But each battery should come with specifications from the manufacturer. Ensure you check the specified settings for your batteries by your manufacturer.

An Example for the Renogy LFP Batteries:

Standard Charge shall consist of charging at 0.2C constant current rate until the battery reaches 14.6V.
The battery shall then be charged at a constant voltage of 14.6V while tapering the charge current.
Charging will terminate when the charging current has tapered to a 0.02CA. Charge Time is approximately 7 hours. Safe Charging consists of temperatures between 32 ºF and 113 ºF. Battery Standard Discharge is a constant current of 0.2C to 10V.

Also, make sure to turn off Temperature compensation and Equalization features as these settings are not required for lithium batteries.

Sizing a Charge Controller

Charge Controllers have a power rating measured Amps. This rating is the maximum amount of electrical current the controller can handle without failing. Solar panel current or battery current should not exceed the maximum power rating of the charge controller.

It is recommended to oversize the controller by around 20% as this design will run smoother and cooler. Always ensure that the controller enjoys enough air circulation not to overheat.

Using a Solar Generator

You can also consider a portable solar generator or a portable power station which is a large battery pack with both DC and AC outlets.  You can use it to charge your camper’s batteries or run your AC appliances or power your DC lights.

It acts like a large power bank with an inbuilt inverter and controller and can be recharged via solar panels once fully charged you can use the solar panels to directly charge your devices such as phones and laptops and save up the power station for later.

Solar Trickle Charger

A solar trickle charger is a small 5 -10 watt solar panel that can be used as a maintainer to keep your batteries from dying. It charges the battery at the same rate it is discharging.

Whichever option you take make sure it is the right one and properly sized. You can combine two or more options to make sure your system is running seamlessly and powering all your devices. RVing is all about freedom and solar ensures you have the freedom to enjoy the outdoors fully untethered from the grid. It also acts as an emergency backup and having it as a secondary option to your main source of power will provide you with peace of mind.