How much solar power do I need for my RV? This is a question we get asked all the time. So often, in fact, we developed this article from a compilation of emails and educational resources we’ve put together over the years.
Another common question we get asked is, can I run an air conditioner on solar power? The short answer is: of course! If money is not an issue, you can do almost anything with solar. But the real question is, what is the minimum amount of solar power needed to power everything in your RV without wasting money? If you’ve been trying to figure this out, keep reading!
As mentioned above, solar power is almost unlimited. It just takes more space (for more panels) to make more energy. The ultimate limitation of solar power for RVs is the amount of available space on the RV’s roof as this is where solar panels are most often installed.
Over years of increasing our RV’s solar capacity, we have maxed out the number of flexible solar panels we could install on our 33-foot roof. The system we designed in our ultimate off-grid solar build maxes out around 2000 watts of produced power in peak sun. This is similar to running a small generator under full load. Of course, this is a lot of power and runs most everything in our RV. Yet, we still have some limitations with high load appliances. It will run the AC for a few hours each day, but not all the time.
This is all great, but having invested so much in this system, most of the power would go to waste if we didn’t have our electric car to dump power into. Therein lies the crutch. Too much solar will go to waste (unless you have a big load), and too little may not meet your needs. This is why it’s great to try and find the right size before you begin installing.
Three main limitations need to be considered when building any solar power system for your RV.
For most of us, the cost of the solar system is one of the biggest limitations, and staying within a budget is always important. But sometimes you need to price out a system to even have any idea of how much it will cost.
Weight is so very important to any vehicle because anything we add takes away from our GVWR and cargo capacities. Some RVs have a lot more capacity than others. Always figure out how much weight you can add to the vehicle before beginning. Don’t make the mistake we did with our first RV and end up overweight!
Along with weight, RVs have obvious space limitations. You’ll not only need roof space for the panels but also storage space for electronics and batteries. Deciding where solar components will go and maximizing space is very important when starting to think about your solar design.
Once you know how the limitations above will affect your decisions, you can then start thinking about what it is you want to accomplish with solar. Usually, people want solar to run their appliances and meet their RV’s power needs while limiting their dependence on generators or external power.
Unless your limitations are minimal, systems are usually designed to provide power for 50% to 90% of energy needs. Of course, this is with the understanding that certain scenarios will still require an external power source. It’s all a balancing act to try and determine how much solar generation you need to meet the demands of your use (a.k.a. load).
Before you try and figure out how much solar to install on our RV, you need to determine what your energy needs are. This is done with an RV power system audit. In the audit, you will be trying to determine how much energy you use so you can offset it with solar. There are two primary methods for completing an energy audit:
If you already have an RV that you are adding solar to, figuring out how much power you need is as simple as using your RV. If you don’t have an RV yet, I would recommend waiting. This way you can use Method 1 as it will be the most accurate by far. Otherwise, if you still want to determine your solar needs without owning an RV yet, skip to Method 2.
To get the best results, I recommend adding your first solar component to your electrical system (even though you don’t have solar yet). The component I am talking about is the battery monitor. This is one of the most critical pieces of a solar system.
Knowing your battery’s capacity is essential, but a battery monitor can also be used to figure out how much energy you use. I highly recommend the Victron BMV 712 Battery Monitor Unit.
This unit includes a shunt that installs on the negative line between the battery and RV. It also has a computer that calculates all of the energy into and out of the batteries. This device monitors the current into and out of the system to give you a very accurate state of charge of the batteries. This is critical to a solar system as the batteries are the heart of the system.
Once you have your battery monitor installed, get the batteries fully charged. Then turn off the charger and use the RV. Usually, you can turn off the charger circuit from the RV’s breaker panel. Watch your battery power level with the meter and plan to recharge them when they reach 50% of their capacity with lead-acid or 80% with lithium (only 20% Left). Note how long you ran for before hitting the 50% (20% for lithium) mark and read out the Amp hours used from the battery meter.
Now take the Amp hours consumed and multiply that number by the system’s nominal voltage (usually 12.6V for lead-acid or 13V for lithium). This will give you the Watt hours.
Example: 150Ah used x 12.6V = 1890 Watt hours
Note how long it took before you needed to recharge the batteries. If it was 12 hours, then you will want to double the number of Watt hours to meet your 24-hour power needs.
Keep in mind there are other power draws that you might not have accounted for. If it was not hot or cold outside, you may not have been using fans or a furnace. In this case, you’ll need to add the following energy numbers to your equation:
Ceiling Vent Fan-Tastic Fan running 12 hours: 720 Watt hours
Furnace 50% duty cycle running overnight: 1200 Watt hours
Example: The battery meter said 80 Amp hours used in a 12 hour period, so…
80Ah x 12.6V = 1008Wh
If you weren’t using the fan, for example, when you noted the Amp hours consumed, you’ll still want to account for that energy usage when calculating your overall needs. So, add the 720Wh to your total…
720Wh + 1008 Wh = 1728 Watt hours battery energy needed
Again, this was calculated for 12 hours of use, so you can multiply the total Watt hours by 2 to get a 24-hour estimate.
Now you need to determine if you will be using an inverter to power AC appliances. The inverter takes the battery power and converts it to an AC household current. You can use this to power computers, microwaves, and pretty much anything else that you plug in. If you use AC appliances, you need to figure out how much power you use on the AC side.
Like with the battery meter, one of the easiest ways to determine your RV’s energy consumption is with a meter. You’ll want one that reads all the power used by the RV, like the Watchdog EPO Surge Protector.
This unit has Bluetooth connectivity that gives you exact power use. Plus, the Watchdog is available in both 30A and 50A models. If you use a unit like this and will be installing an inverter, you do not need to use the battery meter and can leave the battery charger on. The reading you will get will be all power consumed by the RV.
Make sure the RV has been plugged in for at least 24 hours so the batteries are fully charged. Then reset the energy counter on the watchdog (or whatever power meter you’re using), and use the RV as if you are off-grid for 24 hours. Keep in mind that you will not be able to run your air conditioning. In fact, you should be conservative with all power use if you want to minimize solar needs.
At the end of 24 hours, check the reading on the meter. It will give you a reading in Kilowatt Hours (kWh). We will use this number later.
If you are interested in getting one of these awesome surge protectors and power meters we have a special discount for our readers. Use coupon code “Mortons” at checkout for 10% off your order.
I do not recommend this method compared to an actual energy reading, like Method 1. But if you are trying to get a ballpark number, this might help. What you need to do is figure out what each appliance uses for power and multiply it by the amount of time it will be operating. Write everything down in a spreadsheet to keep track of it and add up the result.
This tends to be a less accurate way to get an estimate but could get you a quick and dirty estimate of power use.
This method might be important if you need to run something like a CPAP overnight or other critical pieces of equipment. For these, add the number to the overall estimate or even the real world data you collected above if it was not included in the test.
To figure watt hours, multiply the appliance’s watts by the time (in hours) it will run. Then add them all together to get your estimate.
Now that you have the Watt hour or Kilowatt hour (Watt hour divided by 1000) energy required, you can figure out how much solar you need to meet your needs.
This can be a very tricky calculation to get completely accurate. Why? Because how much power solar panels actually make varies, depending on factors like location, season, weather, etc. What we will try to do, instead, is get a ballpark figure for the time of year and location you will be in.
To start, we can assume that a 100-Watt solar panel will generate on average 350 Watt hours of power per day. So if you need 1500 Watt hours, then a rough estimate would be…
1500Wh / 350Wh = 4.28W or 428 Watts of solar
The above calculation is a very rough estimate. We can get much more accurate numbers with a tool called PVWatts.
NREL has an amazing tool that can help us figure out how much energy we can get from our solar panels at any point in the country at any time over the year.
Start out here: https://pvwatts.nrel.gov/pvwatts.php
This tool is not designed specifically for RVs, so using it might seem a little strange. But it works well nonetheless! PVWatts takes weather and sun data from all over the country into its calculations and will give you a great estimate based on where you are. I have compared it to my solar output as we travel and have found it very accurate.
To use PVWatts, the first thing you need to do is give it an address of where you think you will be camping. You will need to decide where in the country you want the system to perform and at what time of year. You can run as many calculations in as many locations as you want, but pick one to start.
For example, we want to be able to use our solar in the Upper Peninsula of Michigan in the summer. So we would find an address somewhere in that general area to use for PVWatts. We do this by going to Google Maps and just picking a random address. It doesn’t matter which one as long as it’s in the general region we’ll be staying in.
Take this location, plug it into the PVWatts calculator and hit “Go.”
The next page will give you a map of the location so you can confirm if it’s correct. If correct, click on the “Go to system info” arrow.
Now, on this next page is where we will input information about the system. PVWatts can take a solar array (multiple solar panels connected together) and give you an estimate of how much it will produce. This will be a little bit of trial and error.
Start with the estimated amount of power required from above (in our case 428 Watts, we will round it up to 450). In the tool, 100 Watts would be .1 because their system is in Kilowatts. Then select the panel type, using “standard” for regular glass panels or “premium” if using high-efficiency panels. “Thin film” panels are less common, but if you are using them, select this type.
PVWatts calculates system losses at 14.08%. Leave that number as is because 14% is a good estimate to account for inefficiency in the system. This is especially true if you are using an inverter. However, this number can be dropped to 8% if no inverter is installed.
In the tilt section put in 0 if the panels will not be tilted. Later you can play with this to see how tilting will affect performance and decide if you want to make your panels tiltable or not. No other parameters need to be modified, so click the “Go to PVWatts results” arrow.
The next page will display the results of how much solar power your system will provide to your RV per month at that location. Since we plan to be in Michigan in June, July and August, we will take the lowest monthly number during that period (57kWh) and divide it by 30 days, so…
57kWh / 30 = 1.9kWh
We had estimated that we would need 1500Wh (or 1.5kWh) per day, so a 450 Watt solar array should be enough for camping in the summer. You can take a look at the numbers through the rest of the year, however, and see we would need a lot more solar in the winter to meet this need.
From here, you can hit the back arrow, change the system size, location or tilting and keep running calculations.
Solar power is not the only thing you need to consider for off-grid energy. You also need battery power. Solar power only works when the sun is out so having extra batteries in your RV to store that energy overnight is important. How much battery you have is up to you. However, I usually recommend 24 hours’ worth of stored energy at a minimum.
I recommend you read through my blog about battery capacities, where I compare lithium batteries to lead-acid batteries, to learn more. Here is the general calculation, however:
Usable Amp hours x Nominal Voltage = Usable Watt hours
So, if we need 1500 Watt hours per day, it’s good to have at minimum 1500 Watt hours of energy storage. This would equate to about 2 100-Amp hour lithium batteries or 4 100-Amp hour lead-acid batteries.
I do not recommend lead-acid batteries for solar systems as their charging requirements do not jive well with the inconsistencies of sunlight. Meaning, they frequently do not get fully charged. While expensive upfront, lithium is the cheapest over its lifespan and will perform much better for your solar system.
Lithium batteries will also eliminate something called “battery anxiety.” This is where you worry extensively about your batteries’ health because you can easily damage lead-acid.
Solar power is wonderful! It can really make camping in your RV so much more pleasant (because you don’t have to listen to or mess with a generator). Unfortunately, though, there will be instances when the sun does not shine and you still need power. Make sure you have a good generator or alternator charging system to provide backup power when needed. It’s tempting, sometimes, after 6 months of not using our generator, to get rid of it. But then come those 10 cloudy days in a row and we need to break it out.
Even if you have figured out how much solar power you need, you don’t have to install it all at once. Another option to make sure you don’t waste money is to install less solar than you think you need. You simply design the system with the ability to add more.
This might be by adding more panels in series or having extra wires pulled to the roof to connect them into. I always recommend pulling an extra set of wires or oversizing the wires anytime you install solar panels with the intention of adding more later.
It may seem daunting to calculate how much solar you need, but we hope this article has helped make the job a little easier. If you go through the steps listed here, figuring it out will give you peace of mind and lessen headaches down the road.
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