How To Determine Your RV Power Usage For Solar Design
Welcome to Part 2 in our 5 part series on how to design your own RV solar system. Let’s talk about RV Solar System goals and RV power usage!
In the last video and post we went over the basics. We talked about how RV electrical systems work and some terminology. Again, I’m breaking this up into chapters in the video and description and sections in the post below. I encourage you to check that out and skip ahead to whatever is most interesting or helpful for you. This topic is just SO broad, no two setups are going to be completely alike.
We have 15 solar panels on our roof, but we’ve boondocked in places where there was a couple in a teardrop trailer who went the full 14 days at this particular BLM location with just 2 solar panels on a stand and never ran a generator. So, in this video and post we’re going to talk about what is required for your RV to function the way YOU want it to when you aren’t in a campground.
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RV Power Usage Video Transcript:
RV Solar System Design Series Part 2
I think most of us get into RVing thinking we’re going to spend all this time in these amazing, open areas, out in nature. Then we end up packed into an RV park thinking this isn’t necessarily what I signed up for! Our first travel trailer was 23ft long came with a single deep cycle battery. It didn’t have an inverter and the fridge ran on propane, so there wasn’t much power draw. Of course the very first night we tried to stay at a Walmart, the battery died. And we actually had to use jumper cables from our tow vehicle to the trailer battery just to get the slide back in the next morning!
5 years later we hit the road full-time in a 41ft 5th wheel with two kids. This time we had a residential refrigerator that would run on a 1200W inverter powered by now TWO deep-cycle batteries that it came with. The result was still the same, we needed to run our generator all night to keep from killing the batteries. So let’s face it, RVs are only designed to go from campground to campground. Some of that is starting to change, but mostly it’s the same old story.
Generators ARE a great option. Many RVs come with one or it’s an option you can add when buying new. Of course that’s not ALWAYS the case, but portable generators are also a popular option. That’s actually what we went with!
Since I mentioned generators, let’s also just throw it out there that unless you are looking for a very small solar setup, a generator is probably going to be the most cost effective way to power yourself off-grid. Of course you have to buy fuel for it and maintain it, while solar is quiet and doesn’t produce any exhaust. One of the many factors that spurred us on to go ahead with our solar project was that running a generator all night isn’t the best boondocking etiquette. Especially for Harvest Hosts, or places like that.
Our Generator is a Honda EU2200i: https://amzn.to/34FUwpo
Honestly, as much as we love our little Honda generator, the prices have gone up substantially since we bought it. If we were buying today, we would probably go with a Predator from Harbor Freight.
RV Solar Power Consumption
Moving on, let’s talk about how out how much power you need. This is going to vary wildly for many of you. I strongly suggest you get a notepad or start an Excel file or whatever your favorite method is for getting organized. Some just try to figure out a really rough estimate off the top of their head. And I really think you’re going to be disappointed with the end result if you do that.
Refrigerator Power Consumption
The very first question to answer is what kind of refrigerator do you have and how much power does it use? Obviously this is an appliance you can’t just turn off if you need to save power, so it’s a good place to start. A refrigerator running on propane uses the least amount of power, but still a little bit to run the control board. A 12V refrigerator uses a bit more, but a full size residential refrigerator is by far the biggest power hog.
Estimating RV power usage can be a little bit tricky. Every electrical device comes with a sticker or information on the power supply about its electrical needs. It’s a good place to start, but it isn’t always completely accurate. For example, we have a big residential style fridge. The sticker just says its full load rating is 7.2A and it’s a 120V appliance. That’s 864W, but that’s really only what it uses right when it starts up. From doing some testing, I’ve found it very briefly starts up with a big power surge, which is why our RV came with a 1200W inverter to run it when we were in transit. But normally it runs at about 110W.
It gets even more complicated because of course it doesn’t run all the time. You can pay close attention to how often your fridge runs over the course of a couple of hours and make an estimate from there. I’ve found that just to get through a night, I would need a full 100AH Lithium battery to run just the fridge.
Use An Electricity Usage Monitor
Probably the best way to know for sure how much power any of your 120V devices use over the course of a day is to buy an Electricity Usage Monitor off of Amazon. Kill-a-watt (https://amzn.to/3sB2r14) has been a popular brand for years, but there are lots of other cheaper options as well. You plug it into your wall socket, then plug your device into the monitor. And it’ll record its power usage for you. I’ll include a couple of links in the description.
I’ll admit, I ended up doing a lot of math and estimating all of our RV power usage when designing our system. It works, but I’d only suggest it if you’re super confident that you can estimate it all correctly. However, directly testing everything will easily be the most accurate way. Test or estimate the power usage for everything that you want your system to be able to run, and document it. It will take a while, but doing the legwork up front will help you tremendously. Take your time with this step because you’ll be basing the design of your system off of it.
What you really want to avoid is really underestimating your power needs and buying a bunch of equipment only to find out that you can’t actually do what you had envisioned. There’s absolutely nothing wrong with starting small, but plan for it. It’s no fun to realize you don’t have enough solar panels to charge your batteries back up, but you already maxed out your solar controller so you need to buy a different one. Maybe you didn’t have huge power goals but you WOULD like to be able to run your microwave briefly only to discover that those AGM batteries you bought have too much voltage drop under a big load like that and it makes your 2000 watt inverter shut off when it’s time to reheat lunch. By the way, we’ll go over batteries and inverters in the next video!
Use A Battery Monitor
In the mean time, let’s document what you want to run off of your 12V system. I strongly suggest buying and installing a battery monitor for this. Again, you can estimate your RV power usage, but I found that was kind of difficult for things like lights. Because being one of 4 people living in this thing, I wasn’t totally sure how many hours a day everything was being used. You WILL, without a doubt, want a good battery monitor to go with your finished system in the end anyway. So you might as well get a jump on it so you can use it to better estimate your power needs! I’m kind of partial to Victron equipment because that’s what I used. But there are lots of other good options out there as well.
I think most people prefer battery monitors that have Bluetooth built in so they can just check it with an app from their phone. Mine actually doesn’t have that because I have a central control panel for our equipment. Otherwise I would definitely bought a battery monitor with Bluetooth.
Victron Battery Monitor w/Bluetooth: https://amzn.to/3HMIGZ6
Parasitic Power Draws
You’ll also find that you might have a handful of devices that are off, but still plugged in and drawing power. Having a battery monitor and testing your 120V devices will help you to track down these parasitic draws on your system. They might not look like much, but over the course of 24hrs they can really add up! Especially on smaller systems, the amount of wattage your inverter uses when it isn’t even doing anything can be a little surprising too.
Power Hungry Appliances
I also want to mention that another surprisingly power hungry 12V appliance can be your furnace. If you aren’t going the super minimalist route, don’t forget to plan in the power needs of that furnace blower! (When you’re doing your audit you should be aware of the other seasons you might want to account for. I.e. don’t forget your furnace if you’re doing your audit in the summertime, A.C. if it’s the wintertime, etc., if these are appliances you plan to run off your system.)
In fact, we’ll be putting together a free, downloadable list on our website if you are interested. We will have the link in this article when complete. It’s a checklist of all the normal items that draw power over the course of a day that you might want to account for. There will be room in there to record the RV power usage that you tested or estimated as well.
Solar Power Consumption Calculators
The next step is to use one of the MANY online calculators to get an idea as to how big of a solar, battery, and inverter system you need to meet those power goals. If you just Google RV Solar Calculator you will get a TON of results. And honestly, most of them will get the job done. They all ask you to plug in your estimates. A lot of them say things like Microwave, Coffee Maker, 15W Lights, etc., and you put in how many hours a day you use everything to get an estimate. Those are okay for a rough estimate, and it might even be helpful to use one of those to see if the estimate is anywhere near what you came up with from your own power audit.
I like the calculator from Renogy. (Follow the link and click “Solar Sizing Calculator.”) If you’ve already documented your RV power usage you can just plug it right in. If they ask for the efficiency of your charge controller, you can play with what it looks like with various types. I think the Renogy calculator has suggestions for PWM vs MPPT. I think you’ll find the difference isn’t drastic. We’ll go over the specifics of that in a later video.
This should give you a pretty decent idea as to the kind of solar setup that would meet your power consumption goals. I’d actually say I think the general estimates for your solar panel wattage is a little low. I’ve gone over the amount of wattage we see with our setup in varying conditions in our Lessons Learned video as well as our 1 Year Solar Update video. Since our panels don’t tilt and we can’t always aim the back of the trailer toward the south because campsites face all sorts of different directions, our actual peak power is more like 80-85% of our total rated wattage.
At this point you might start thinking about what would physically fit for you. Or, if your power needs are really minimal, you might think about a portable setup! But first, we actually need to talk about something way more important than solar panels. Your batteries and inverter or inverters truly are the heart of the system. And that’s what we’ll go over next in Part 3 of this series!
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If you’d like to read about our RV and other RV adventures, then check out some of our other posts :
- RV Electrical Basics & Solar Design How To Intro
- Soft Starters For Your RV Air Conditioner, Why?
- RV Tank Sensors Not Working? We Use An RV Water Flow Meter Instead!
- Portable RV Waste Tank, Freshwater Tank and Pumps
- RV Solar System Installation Series // 7.2kWh Batteries & 6kW Inverter Upgrade
- RV Solar System Installation Series // 2625W of Solar
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