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. This probably isn’t a shocker, but we feel it should be said; we are not professional electricians, RV solar experts, or licensed to sell, install, or advice you on solar installations. We are simply sharing our research and knowledge on the topic (which to be honest is from watching a ton of youtube videos, reading other blogs, and from our own experience of trial and error). Please verify all information with a licensed professional before installing yourself! So let’s get straight to it and figure out how much RV solar you need!
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. Plug the Kill A Watt EZ into the outlet, plug your appliance in, operate your appliance then push up or down until you see the reading fo Watts. We feel the Kill A Watt EZ is the easiest way to find the output wattage without a lot of math. However, there are some appliances that you cannot test with the Kill A Watt EZ (like your CO2 sensor or lights), so remember to use the label for that, and the formula W = V x A if needed or milliamps / 1000 = amps.
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 .10 which equals 96 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.
Appliance watts Time used total watts
Jetpack 8 24 hours 32
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 168
TV 68 3 hours 204
Coffee Maker 960 10 minutes 96
Blender 1,200 3 minutes 36
Fridge on propane 33 24 hours 792
Microwave 1,000 10 minutes 100
Convection Microwave 1,450 10 minutes 145
Weboost Cell Booster 8 24 hours 32
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: 2,498 watts
But that is if we use EVERYTHING every day, which we don’t. Realistically, we need about 2,000 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%.
To determine the battery bank size we needed for our usage, we used the online calculator from AtlE store (https://www.altestore.com/store/calculators/off_grid_calculator/). Input the data you gathered about your average daily wattage use, how many days you’d like to run without needing to recharge, your location, controller type (either MPPT or PWM), and it will tell you the number of amp-hours your ideal battery bank would be.
Our calculator said we needed nearly 1,000 amp-hours of batteries to supply our needs for 2 days without recharging. While that’s the perfect setup, we just didn’t have the space or budget for that. So instead, we have four 6-volt batteries that are combined to make two, 12 volt batteries with 225 amp-hours each. That means our total battery bank has 450 amp-hours. However, since we cannot let our battery bank drop below 50%, we really only have 225 amp-hours of usable power at any one time.
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 exact battery bank here!
Lead Acid is the most cost effective, but typically don’t last as long as some of the other battery types. You also have to maintain these pretty regularly (top them off with water for example). The next tier up in terms of cost, is sealed batteries. They are similar to lead acid in terms of capacity and performance, but they don’t have maintenance. AGM is the next price bracket up, and with the higher cost you’ll start to see more benefits. AGM has the ability to deep cycle, and charge up to five times faster than a standard lead acid battery and weighs more or less the same (they are very heavy). The most expensive option for building your battery bank is lithium. Lithium is pretty superior in the world of batteries for a number of reasons. They are lighter, charge faster, holds charge for longer, have a longer life (meaning # of charge cycles), and you can actually use up to 80% of the battery capacity instead of the 50% like with other batteries.
We like to account for only the usable energy in our battery bank. Since we do not let our batteries go below 50% of total charge (at least we try not to), we consider the 50% mark, “empty” which is around 12.0 volts. We consider fully charged, 13.0 volts. Technically, you can drain your batteries lower than 12.0 volts, but doing so will be detrimental to the health of the battery. We made this helpful visual chart so you can better understand the usable energy in your battery bank in terms of volts and % of usable charge remaining. Please note, this is a generic chart, and may not accurately reflect your exact set up, batteries, or rig. If you are concerned with the numbers, a BMK might be a good solution for you!
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. (get our exact inverter here)
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.
The calculator you used earlier will also tell you the ideal amount of panels in terms of watts as well as the right sized solar charge controller.
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. 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 it’s 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.
We are Dennis and Liz! We’re two travel loving, real estate investing, foodies exploring North America full time in a Grand Design fifth wheel toy hauler. We share our lessons learned as full time RV’ers, travel tips and tricks, and the best places to eat and see in the US with you!
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