How much RV Solar do I need?
Calculating your RV Solar Needs
Today we’re talking how much RV solar you need! If you’re not super familiar with RV Solar, why you would want solar for your RV, how it works, or if we think it’s worth it – click here to see our previous post. If you’re here, we’re assuming you already realize how amazing RV solar can be in providing you with freedom to park wherever you want with the creature comforts you want and expect with an RV.
Figuring out that you want solar is only the first step. Now you have to determine what size inverter and charge controller you need in addition to how many batteries and solar panels will do the job for off grid camping on your rig.
Calculating your Solar System needs with watts
Start by writing down every appliance on or in your RV that you want to use with your solar set up. Write down the output wattage. It can either be on a label of the appliance, or if the label is gone or unfound, you can use a Kill A Watt EZ for to find the output wattage.
RV Example 2: Our MacBook computer charger did not have the watts on the label, it only had an output voltage of 24 Volts, and 4.25 amps. So I had to use the formula, Watts = Volts x Amps (24V x 4.25a = 102 watts). Another way to test the wattage if you don’t want to do math or the label is gone, is by using the Kilowatt EZ. When I plugged my charger into the Kilowatt EZ and operated the laptop while charging, it read 100 watts. When I had my computer closed (not using it) and charged it, it read 85 watts.
RV Example 3: Our CO2 sensor only said “108 milliamps, and 12V, so I had to find the amps in order to calculate the wattage. I used the formula, milliamps / 1000 = amps, to then calculate the wattage using the formula watts = amps x volts. (108 milliamps / 1000 = .108 amps, then I calculated .108 amps x 12 volts = 1.296 watts, or rounded up to 1.3 watts.
Important Note: Most battery banks are 12-Volt or 24-Volts, meaning they “push” D/C power at a weaker rate than per say a generator, which is typically 110 Volts A/C Power. Most electrical outlets are 120 Volt and operate off A/C power, so if you use the Kilowatt EZ to read you wattage, do not use this to measure amps, as the amperage will be from 120 Volts A/C power, not 12 Volts D/C power like your battery output will be.
Toothbrush charger 0.5
Coffee Maker 960
Fridge on propane 300
Fridge on electric 600
Convection Microwave 1,450
Weboost Cell Booster 8
Vent Fan 138
CO2 Sensor 1.3
Next, you need to calculate your actual usage on a given day. Essentially, how many watts you use on an average day. To determine this, you will need to write down the number of hours or minutes you operate that appliance on an average day and multiply that by the number of minutes you operate or hours a day it runs. Take a look at our examples below.
RV example 1: Our coffee maker uses 960 watts. If we use the coffee maker for 10 minutes each morning, we would multiple 960 x .17 which equals 163 watts.
RV example 2: Our WeBoost cell Booster runs 24 hours a day, so I multiply the 8 watts x 24 that gives me a total of 32 watts.
Example calculation for our Amp-Hour Needs for an average day. If my actual calculation is less than 1 amp hour, that means I rounded up for good measure.
Update: If you don’t want to do calculate this by hand, you can use AltE Store’s load calculator.
Appliance watts Time used total watts
Jetpack 8 24 hours 192
Liz Laptop 90 4 hours 360
Dennis Laptop 70 4 hours 280
Toothbrush charger 0.5 1 hour 0.5
Blowdryer 1,120 15 minutes 280
TV 68 3 hours 204
Coffee Maker 960 10 minutes 163
Blender 1,200 3 minutes 60
Fridge on propane 33 24 hours 792
Microwave 1,000 10 minutes 170
Convection Microwave 1,450 10 minutes 246
Weboost Cell Booster 8 24 hours 192
Vent Fan x 2 54 4 hours 216
CO2 Sensor 1.3 24 hours 32
LED lights x 4 1 4 hours 4
Total Estimated watts Used Per Day: 3,181 watts
But that is if we use EVERYTHING every day, which we don’t. Realistically, we need about 2,000-2,500 watts each day.
determining your RV battery bank needs
One thing we wish we knew before full time RVing was how to take care of batteries properly. It’s really important to never let your batteries drop below 50%. If that happens (which it did for us…several times before we knew better), expect to dramatically decrease the effectiveness of the batteries (their ability to hold charge), and the overall life of the battery. All in all, you’ll have to replace them a lot sooner than you would have to if you monitored them and always kept them above 50%.
If we are getting partial to great solar we can go a full week or more without ever having to on our generator and using our appliances comfortably throughout the day and night. If we are getting partial sun or limited sun (because it’s rainy or overcast), we do have to supplement with our generator every other day. For us it’s a trade off. We did what we could afford and had space for at this time, and while it’s not the perfect set up, it gives us a huge amount of freedom to camp where we want without our generator running constantly. Ultimately we’d love to increase our battery bank using lithium (to save on weight and space overall) while still have higher amp-hours, but we’re big believers in do what you can now and upgrade when the moment is right. Get our 1st battery bank here or check out our updated battery bank here.
What size inverter do I need for my RV?
Since you already wrote down the number of watts each appliance uses, you want to look at the highest wattage to determine your inverter size needs.
RV Example: out of all of our appliances we tested, we found our highest use appliance pulled 1,575 watts. So we knew a 1,500 watt inverter wouldn’t do the job. We went up to the next size of 2,000 watts, which gives us more than enough power even for our highest consuming appliances.
We use “light load” appliances whenever we need, but are careful with our usage of “heavy load items” like coffee maker, blow dryer, microwave, or convection oven. We just can’t blow-dry our hair and make coffee at the same time (we’re okay with that). We made sure the inverter we bought, a 2,000 watt inverter allowed us to use most items on our rig with the exception of our A/C, electric fire place, or washer/dryer combo. If 2,000 watt inverter doesn’t do the job for you, there are a range of sizes to chose from; 1,000 watt, 1,500 watt, 2,000 watt, 2,500 watt, or even 3,000 watt inverters. Obviously the higher the wattage, the higher the cost. If you’re trying to be budget friendly, really think about the size you need (not necessarily want). We’ve never felt we didn’t have enough power with our inverter even though it’s 2,000 watts.
How many solar panels do I need for my RV?
I wish there was any easy formula that said a panel (like a 100 watt panel) would produce x amp-hours of usable power per day, but I can’t. The actual amount of amps a panel produces is largely affected by the latitude your at, the angle of your panel to the sun, the amount of sun produced in the given day (such as cloudy day vs. full sun or the season you are in). We’ve found that our 100 watt panels produces anywhere from 4 to 8 amps per hour a piece (and that’s in partial to full sun). To be safe, you can estimate that a 100 watt panel will give you around 25 – 35 amp hours per day. So with 300 watts you would have 90 amp-hours being stored in your batteries. With 500 watts, you’d have 150 amp hours per day!
We have 420 watts of solar with our Renogy 300 watt solar roof kit and our 120 watt Go-Power Portable Solar Panels, which gives us around 110 – 130 amp-hours per day. Get 10% off your Renogy order using code “RenogSolar10”.
That is more than enough to keep our batteries topped off and well above the 50% mark even into the dark. If it’s cloudy for a few days in a row, we simply turn our generator on to top our batteries off until the sun comes back and works its magic.
A big misconception with RV solar is that you need 500, 600, or 900 watts of solar for it to be worth it. Reality is you only need as many panels as your batteries are able to store, and your usage warrants. It doesn’t matter how many panels you have if you don’t have the battery bank to store the energy your panels are pulling in! That’s why we went with the lower amount of panels since many times our batteries are reading as full when we have optimal sun. The system has to work together, and why spend money when you aren’t able to reap the benefits? We suggest investing in your batteries as they are the power house (literally) to the entire RV solar set up. You can always add more panels later if you find you would like more energy to be put into your battery bank.
Our 300 Watt Renogy Solar Kit came with a 40amp solar charge controller which more than fit our needs for 300 watts and potentially 400 watts if we really wanted another panel. A 30amp solar charger is more than enough if you have 100 – 300 watts of solar. If you want to go to a 40amp, 50amp or 60amp solar charger because you think you’ll eventually have 400 watts or more of panels then we suggest buying that size the first go around. It’s also important to note there are two different types of solar charge controllers, PWM (Pulse Width Modulation), or MPPT (Maximum Power Point Tracking). MPPT’s are more efficient than PWM, so for that reason we suggest buying an MPPT charge controller if you have the option. We love the Renogy kit’s because they come in a range of solar panel wattage and includes everything (well almost everything) you need for your solar install, including the solar charger. Take a look at some of Renogy’s other Solar Kits.
Liz & Dennis
We’re two travel-loving, real estate investing, foodies exploring North America as full-time RV’ers. This blog is where we share our lessons learned, tips and tricks, and favorite places to eat, see, and RV across North America! We hope it helps you find your wanderlust, plan and prepare for RV life, and get out on the road!
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Thanks for the informative comments here. I’m no engineer so it’s a challenge. I have a trailer with a 12 V refrigerator
that pulls 11 amps…no gas only juice…also a small outside one pulls 3 amps. So…I’m using 2 Tesla 24 Volt,264 amp hour, 6.4 kWH batteries, Victron 24/3000/70 inverter, Victron 100/50 MPPT, two Zamp portable panels totaling 370 watts/20.6 AH. I’m making a couple of cheap sun activated lazy Susans for the panels so they maximize solar input. So here goes…..
“RV example 2: Our WeBoost cell Booster runs 24 hours a day, so I multiply the 8 watts x 24 that gives me a total of 32 watts.”
Math Doesn’t add up… Just saying.
Hello, Your right about math. Your example using your coffee maker…..Where did you get the 1.7 from? I don’t know what I’m missing. Thanks
It looks like they accidentally multiplied 8 by 4 instead of 24 earlier, but fixed it in the grid. As to the 0.17, that came from converting 10 minutes into 0.17 hours (10/60).