You’re ready to invest in an RV solar system but are not sure what you need. How many panels? How much wattage? Should you buy two 100 watt panels or one 200 watt panel? Is 400 total watts enough? Are rigid or flexible panels better?
Related post: Top 5 Reasons to Not Buy RV Solar Panels
The simplest way to look at it is the amount of solar power you need is the amount necessary to keep your batteries charged as much as possible for as long as possible. You’ve already purchased a battery bank that provides the amount of DC power you need to keep you happy boondocking, right? If not, you need to figure that out first.
Calculate your daily usage, multiply that amount by how many days you want to stay charged up (best case scenario) and go from there.
Estimate how much RV power you are using
What AC appliances do you plan on using when not plugged into shore power? You know everything works when you are at a campround and have access to electricity, but how much power per day are you actually using? This is the number you want to get a grasp on. Then you can estimate the size of solar panels you need to keep your battery bank charged up.
Are you using up 2000 watts of power per day or 20,000 watts? Will it be hot and you’ll need to run your AC or freezing cold and you’ll want to keep your propane furnace on at night?
Amps X Volts = Watts
To convert amps to watts simply multiple by the voltage. Your 120 volt electric coffee maker has a label that says “8 amps.” So multiply that number by 120 (voltage) = 960 watts.
And don’t forget to account for time. How long will you use the appliance? Energy ratings are always in one hour increments. So that 960 watts above is for running the coffee maker for one hour. Adjust accordingly. You’ll probably have a hot pot ready in five minutes, so your actual usage per day will be 80 watts i.e. 960 divided by 12 (5 is 1/12 of an hour).
The biggest energy hogs in your RV will most likely be the AC unit, water heater, and fridge. Check the specifications to see how much power they consume.
Related post: How To Calculate How Much RV Battery Power You Need
A 100 watt solar panel generates approximately 400 watts per day
A 100 watt solar panel under optimal conditions provides 100 watts of DC current per hour. That’s in a laboratory setting. In the real world you may have 3-5 hours of full sunlight (peak sun hours) if lucky, and approximately 400 watts of energy produced by the panel during the day, more hours of sunshine can generate up to 900 watts. Cloudy days will be less, of course.
So now that you have a ballpark figure of how many watts of energy you consume daily you can figure out how many 100 watt panels (or 200 watt, or a combination of both) you may need. How? By simply dividing that number by 400. Are you using around 2000 watts of energy per day? Then you divide 2000 by 400 and get 5. So you would need five 100 watt solar panels, or one plus two 200 watt panels to produce 2000 watts of DC current flowing to your battery bank per day.
400 watts of solar DC current provides 33 amps to your battery
Five 100 watt solar panels may produce 2000 watts of DC current in one day, but how much power actually gets to your rig depends on the size of your battery bank and how quickly the batteries charge i.e. are they lithium or lead-acid, etc. Battery capacity is rated in amp hours (AH). So you want to convert your solar power estimate into amps using this calculation:
Watts ÷ 12 Volts = Battery Amp Hours (AH)
A 100 watt solar panel that provides 400 watts of DC current in a day is sending 33 amps to your battery i.e. 400 divided by 12 equals 33.
A 100 AH battery provides 1200 watts of power
You also need to know how many amps are in your battery or battery bank to determine how many solar panels you may need to power them up. What is the AH rating? Or if you have more than one battery… how many total amps are in your battery bank?
A 12V 100AH battery provides 1200 watts of power. We want to have around 2000 watts available per day right? So let’s say your battery bank consists of one 200AH lithium battery or two 100AH lithium batteries – good on you! That will make an estimated 2400 watts available to run stuff in your rig.
To charge up a 200AH battery we want to send 200 amps of solar power its way during the course of a day. If one 100 watt panel provides 33 amps, we would need six 100 watt solar panels to charge up a 200AH battery or battery bank.
Does that make sense? If you want to provide 1200 watts of power per day using a 100AH battery you would need how many 100 watt solar panels? Three! To get 100 amps passed to it via DC current flowing from your solar setup it would take three 100 watt solar panels (each one providing 33 amps in a day) to charge it back up.
Figure out estimated usage and power needs and don’t stress out!
There are a zillion possible variables when it comes to solar power, solar panels, RV batteries, etc. We played with numbers for an estimated total of 2000 watts of power needed per day and 400 watts as the average output of a 100 watt panel during the day. If there is a lot of sun, the amount of DC current produced by your solar panels could almost double—so should you buy fewer panels? Or if it is cloudy with less sun, it will take longer to charge up a battery. So should you buy more solar panels?
Everything depends on your wants/needs and how much cash you want to spend. Work out a solution that works best for you.
Cheers.