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 needs
Watts are a measure of power. That means how much power your appliance draws to use it. It is important to calculate the power (watts) an appliance draws from the inverter. Knowing your total average consumption in terms of wattage is they key to determining your battery bank size, inverter size, and the number of solar panels you will want or need.
Volts or voltage is a unit of electrical potential. In layman’s terms, volts is a measure of “push.” 12 volts is much “weaker” than 110 volts. To be able to convert the different voltage levels from a generator or batteries, you have your converter.
1. Calculate your wattage
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). Remember to use the label for that with the formula W = V x A. And if needed, milliamps / 1000 = amps.
RV Example 1: Our microwave’s label said it has an output wattage of 1,000. That means it draws 1,000 watts of power to operate.
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.
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.
2. Calculate voltage
Volts or voltage is a unit of electrical potential. In layman’s terms, volts is a measure of “push.” 12 volts is much “weaker” than 110 volts. To be able to convert the different voltage levels from a generator or batteries, you have a converter. Your RV should come with a converter standard. But if you upgrade to an inverter-charger it will have a built in converter for this.
|Fridge (on propane)||300|
|Fridge (on electric)||600|
2. Calculate your daily usage
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.
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|
|Laptop 1||102||4 hours||408|
|Laptop 2||70||4 hours||280|
|Toothbrush charger||1||4 hours||4|
|Coffee Maker||960||15 minutes||240|
|Fridge (on propane)||33||24 hours||792|
|Convection oven||1,450||10 minutes||246|
|Cell booster||8||24 hours||192|
|Vent fans (x 2)||54||4 hours||216|
|CO2 sensor||1.3||24 hours||32|
|LED lights||1||4 hours||4|
But that is if we use EVERYTHING every day, which we don’t. Realistically, we need about 2,000-2,500 watts each day.
Batteries typically have an amp-hour rating on them and that will vary by the type of battery you get.
Amps refers to the amount of electrical current a device draws. In other words how much electrical current an appliance draws from the batteries to run.
The Amp-hours tells you how many hours you can run your appliances from your batteries. For example, if your drawing 15 amps per hour from your batteries and your batteries are rated for 225 amp-hours then you would be able to go 15 hours without recharging in one form or another (either with solar, shore power, or generator).
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 expect to dramatically decrease the effectiveness of the batteries and the overall life of the battery.
To determine the battery bank size we needed for our usage, we used the online calculator from AtlE store. 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.
The 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 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 setup, it gives us a huge amount of freedom to camp where we want without our generator running constantly.
On our second RV, we upgraded to lithium batteries. This saved on weight and gave us more usable amp hours. Lithium batteries can be drained 100% without damaging the cells. With a 300 amp hour battery bank, we have 300 usable amp hours of power. Get our first battery bank here. Or check out our updated battery bank here. We rarely needed to use our generator with our 300 amp hours of battery in our second RV. But we also didn’t have as “power hungry” of an RV.
The inverter’s job is to invert the D/C power that is stored in the batteries into usable A/C power. In order to do that, you need to make sure your inverter can handle the wattage or “load” you are putting on it from each appliance.
You don’t want to overwork your inverter. So it’s important to have enough wattage to cover more than your needs. There are two types of inverters, modified sine wave and pure sine wave inverters. To keep it simple in this post, we suggest buying and using only pure sine wave inverters.
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 the 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 them. But we are careful with our usage of “heavy load items” like a coffee maker, blow dryer, microwave, or convection oven. We can still use all of those items we just can’t use them simultaneously.
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 AltE calculator will also tell you the ideal amount of panels in terms of watts. In addition to 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 you’re at, the angle of your panel to the sun, and the amount of sun produced in the given day. For example, a cloudy day gives very different solar exposure than a full sun day. The same can be said for the time of year you are in.
We’ve found that our 100-watt panels produce anywhere from 4 to 8 amps per hour a piece 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.
This was enough to keep our batteries topped off and well above the 50% mark even in 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.
On our new RV, we have 400 watts of solar power with Renogy’s rigid panels. Plus a battery bank of 420 usable amp-hours (lead acid batteries). We can go weeks in full sun without needing to plug in or turn the generator on. We haven’t seen many “non-sunny” days yet. So we’ll see how it does in less-than-ideal conditions.
A big misconception with RV solar is that you need 500, 600, or 900 watts of solar for it to be worth it.
The 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. Why spend money when you aren’t able to reap the benefits? We suggest investing in your batteries as they are the powerhouse of the entire RV solar setup. You can always add more panels later if you find you would like more energy to be put into your battery bank.
Solar charge controllers
Our 300 Watt Renogy Solar Kit came with a 40-amp solar charge controller which more than fit our needs for 300 watts and potentially 400 watts if we really wanted another panel. A 30-amp solar charger is more than enough if you have 100 – 300 watts of solar. If you want to go to a 40-amp, 50-amp or 60-amp 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), and MPPT (Maximum Power Point Tracking). MPPTs 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 kits because they come in a range of solar panel wattage and include everything you need for your solar installation, including the solar charger. Take a look at some of Renogy’s other Solar Kits.
We hope this post helped better explain how to calculate your RV solar needs for your rig and your setup. Everyone’s needs are different and there is no perfect solar setup, although we’ve seen some that are aiming for that title. We’d love to hear if you found this post helpful, what setup you have for your RV solar, or if you have any questions in the comments section below.