Hi there parked in paradise visitors! We have a cool solar panel calculator on our site and i’m going to walk you through how to use it because there are a lot of steps involved and sometimes just seeing someone go through it helps quite a bit.
So this is in our solar and electricity guide. And it’s our camper van solar system calculator. This is for all you do-it-yourself (DIY) solar system sizing folks out there.
I’m going to talk a little bit about what it’s good for and what it’s not. And some of the things that are covered in it. Now each of these different subjects in this we cover more extensively in a post on our site so if you’re not able to follow along or have some more questions about some details – those you’ll be able to find elsewhere in the electrical guides on our site.
This is kind of just a guide for how to use the calculator itself and what some of the different numbers and that kind of thing mean.
Now if you’re not familiar with working with electricity at all, you should probably have a professional or a mentor of some kind helping you through this. There’s a lot of little details. 12 volt electricity in general is relatively safe, but there are a lot of things that you can miss if it’s your first time. So it gets a little overwhelming, but it’s not too bad. It’s mostly plug and play and it’s pretty fun doing it on your own not only because you save some money and you can have a system sized exactly to what you need it, but it also helps you diagnose issues later down the road if you know what’s going on.
This calculator kind of walks you through the order that you need to figure things out in when you’re sizing this. So even if you’re not using this calculator itself, this is kind of the direction that you need to go.
The first thing that you need to figure out is all of the components that you’re using in your RV or camper van.
In this case we have a list set up and you can add and delete component lines. What you’re going to want to do is everything that uses electricity, you’re going to write down. What we’re trying to figure out is our daily electrical usage, or our max average.
Because each day is like its own reset in terms of the electricity that you’re going to use. Now there are some cases where for off-grid and storage and stuff things change a little bit, but for an RV or a camper van this is a good starting point.
So in this case we’ll just kind of run through an example camper set up. We have a fridge, and I know this fridge draws 3.9 amps. In solar electrical calculations you can set everything up to figure out your amp hours or your watt hours.
We like to use watt hours because it’s a more accurate estimate of actual power usage, because amps are determined by your voltage. Also some of the newer lithium batteries on the market (if you’re getting a custom Tesla battery or something), those are measured in watt hours.
It’s a more accurate measurement of how much actual electricity you have.
Now a lot of systems use amps just because that’s how 12 volt systems have always been measured in the past, and in vehicles it’s a good transition.
That aside, we know that I have 3.9 amps and this is a 12 volt fridge. So this calculator at the top, if you put your amps and your volts, it does a simple calculation and gives you your watts.
So we’re going to say 47 watts for my fridge.
And I chose kind of a complicated component to start out with. Your fridge is going to be on and plugged in 24 hours per day in a camper van. There is a lot of different components that have variations on this. That fridge when it’s drawing power, it’s powering a compressor and that compressor is only kicking on to cool the fridge down to a certain temp and then that compressor turns off.
This is how the high efficiency fridges and the fridge in your house work. So when that compressor is off, it’s not using electricity even though the fridge is plugged in.
In hotter weather that compressor is going to be on a lot more because that internal temperature is going to raise up a lot. And in cooler weather it might only be on for a few hours a day.
Our fridge on average is running about 8 hours a day. Different fridges run a little different. If you’re in the hot weather all the time you might want to boost that even double it up to 16 hours. But for the most part, ours is running hours per day. We’ve done tests on it, we can see the average.
At night when the temperature drops, the compressor won’t be clicking on and off as much. Our fridge clicks on and off every 10 minutes or so, and then it will run for a few minutes and then it will click off.
And this fridge is running straight off of our batteries. It is a DC powered fridge, so that means it’s plugging right into the DC electrical system. Direct current.
AC components are running off of your inverter.
An inverter is less efficient. So you have to account for that efficiency when we’re counting how much energy we’re using. As you can see, if you run everything DC powered your efficiency is going to be higher in terms of how much power you’re getting out of that. If you run an AC powered object like my laptop, then that efficiency is going to be reduced so you’re going to have to use more energy to charge the laptop than you would if it were DC powered.
So my laptop brick is rated at 170 watts, it’s a big engineering thing, but my laptop itself is rarely ever pulling 170 [watts]. The most I’ve ever seen it pull is 150 [watts] and usually it’s closer to 120 [watts].
Laptops are another variable component in that they’re only pulling their max watts. The watts that you’ll see on that power brick when they’re charging the battery and when they’re running high processing things. So if I’m running a simulation, a 3D simulation then that thing is going to be pumping out 150 or 170 watts.
But if it’s just charging the battery and I’m surfing the internet – 120 [watts]. If it’s not even charging the battery, if it’s just plugged in and idol it’ll be down in the 50 watt range. It doesn’t take much just to run the laptop. What it’s doing is also charging your laptop battery.
Now because of this, my laptop is only plugged in and charging about 2 hours per day. And then the other 2-3 hours that I’m using my laptop it’s running off the battery power that it was charging at 120 watts earlier.
My wife’s laptop is a Macbook and she’s not running as much high processing powered things. So she’s only running about 85 watts and she’s also kind of using it in the same manner. She’ll charge that thing for 2 hours and then she’ll run it for another 3 or 4 because it’s battery is so much better. So it can make a lot better use of that battery.
Now, those of you who are trying to run desktop gaming stations or something in your camper van, you’ll pretty quickly realize that the processing and the CPU and that type of thing in your gaming tower takes a lot of power. Because they’re meant to be plugged into a wall. A gaming laptop is a lot more efficient than one of the towers just because the CPU is designed to be able to run off the battery. So they have to make it kind of reasonable so you can at least run the laptop off the battery for an hour or two of gaming.
We also have two phones, and our phones are I think 3 amps but at 5 volt USB so they’re each running about 15 watts and they’re plugged in 3 hours per day. There’s two of those so we’ll say 6 hours per day.
Vent fan. I think that thing was pulling 2.9 [amps]. These are example numbers, I don’t actually remember exactly what the vent fan is but the numbers are out there somewhere 35 [amp hours].
Cell booster. Oh that vent fan is on maybe 4 hours of the day, at night to cool the van off. And the cell booster, that thing is only running about 2 amps so like 24. And that thing is running about 5 hours per day.
So once you get all of your components listed out, this is all of your electrical things. If you have things like toasters, if you have things like blenders, you’re going to see how quickly those things add up your electricity.
Now one thing I forgot is the laptop and the Macbook are both running off of AC power. So if you notice this number jumps up. From DC it’s 170 watts, accounting for the inefficiency it’s 187 watt hours because it’s running off an inverter. So that’s the amount of power that it needs.
Then we get a total power calculation.
So in this case were using 1127 watt hours per day. Now that’s on our average, high usage day. Some days I might not be running my laptop, some days I might be running a little more. But what I want to do is kind of estimate so I’m not going to be tanking my battery bank every time I use my general lifestyle equipment.
So once you know your total watt hours, the next thing that you need to pick in your system is your battery size. Now your batteries need to be able to discharge this amount of watt hours throughout the day and then we will recharge those with solar.
Your battery can be either AGM and FLA (those are both lead acid battery types). So the AGM is the absorbent glass matt, or flooded lead acid. Both of those have similar profiles in that you don’t want to discharge them more than 50%. If you do that, you’ll start reducing their lifespan significantly.
So an FLA battery can last 8 or 10 years, if you discharge it past 50% every day you’re only going to get about 2 or 3 years out of it.
Batteries are the most expensive component in your electrical system, so you don’t want to wear those out too quickly. You kind of want to make sure that those are running efficiently.
Now if you want to get your batteries to last longer, you can discharge them to only say, 20%. The 20-50% range is where you want to be in. But with a 20% discharge you need a lot bigger battery if you’re only going to be discharging it the same amount.
Now in this battery section we have a total for watt hours as well because a lot of the lithium batteries now are listed in watt hours and like I said, it’s a little more accurate. So in this case, to discharge 1127 watt hours per day, we need a 470 amp hour battery if we only want to discharge it 20%. If we’re ok with discharging it up to 50% we can drop that down to a 185 amp hour battery.
So you’ll notice your battery bank size changes significantly based on your depth of discharge.
We go into this a little more in our battery post, there’s a couple of things you need to keep track of. Your batteries do need to be able to be charged all the way as well so you can’t get too big of a battery bank or else you’ll start losing some of the charging efficiencies and your solar won’t be able to charge up those last few steps.
Now you can also select a lithium battery, and those can be significantly smaller because you can discharge those up to 90-95% without it harming any of the battery. And those don’t even need to be charged up all the way at the end of each day. So they’re a little more flexible in their use. They are also quite a bit more expensive, but they last longer. There’s a lot of benefits to lithium batteries. You kind of get a size difference there so you can either go with a 185 amp hour lead acid style or a 115 amp hour lithium battery.
This is our general recommendation. There’s a little wiggle room, so in this case if you were a little generous with some of your numbers up here, 115 amp hour battery you’re going to find a lot of lithium batteries that are 100 amp hours, you’re probably going to be ok with that. Because your alternative is to jump up to a 200 amp hour lithium battery and spend another grand on that.
So this is just something to keep you aware. Maybe you’ll say hey, maybe I want to trade in my laptop or before I buy a laptop I’ll get one that’s more efficient. Maybe I’ll get one that runs on a 90 watt power brick, and now all of a sudden my lithium battery isn’t quite as taxed by running that laptop.
So once you have your battery, your power storage, you know your power storage can discharge a full day’s use, you can always boost that if you want.
So if you say hey, I’m going to be in Washington I don’t think I’m going to see much sun, I need my battery bank to last a couple of days, or you run critical equipment. If you have sleep apnea and you have a breather that you need on you, you can boost your battery size to make sure that you have juice to run a few days without recharging.
The problem with that is then you also need to make sure you have enough panels to run that once is does drop for two days worth of use.
So after your battery, the next piece of equipment that you choose is your solar panels. You want your solar panels to handle all of the charge throughout the day of your usage. Now your solar panels, they only have a window of opportunity to gather your electricity.
So they can’t supply all of that charge throughout the day like your batteries are going to be able to discharge.
Your solar panels will have a selection down here for how many sun hours you think you’re going to use during the day. We use this a 4 generally for camper vans because if you’re flat mounting your solar panels on top of your van, in most cases they’re only going to see about 4 direct hours of sun.
If you have an angled system, so you can tilt mount your panels towards the sun, you can boost that up to 5 hours. If you’re in the desert southwest and an angled system you’ll have 6-7 hours of available sun.
Say you’re going to travel around sunny climates somehow, maybe you’ll see 7 or 8 hours. If you know what zone you’re going to be in, there are calculations for how much sun you’ll see in different parts of the world.
For the most part, people in RVs are traveling around so that’s too variable to really set how many sun hours you’ll have for sure. This is another generous thing, give yourself some wiggle room here.
So 4 sun hours, gives us 220 watts of solar. That will charge our 1061 watt hours of usage per day. Now, you can always go more solar. There’s no problems with going more solar. This is kind of our general advised minimum. You shouldn’t go below this necessarily.
If you have, let’s say you’re going to be in the desert southwest most of the time and you know you’re going to have tilt mount panels maybe you’ll see 6 hours of sun. You’ll notice that changes your solar panel size calculation.
Go bigger if you can with this, unless you don’t have enough roof space or if you’re on a significant budget. Now the other selection you have to do here is whether or not you’re using a PWM or MPPT controller. Again, we go through all of this on our charge controller post if you want to know details. We do have this in there.
MPPT controllers are more efficient so you need a little less solar panels to get to your watt hour usage. Now, the PWM controllers are significantly cheaper. So sometimes smaller systems, say in this case, let’s say you find a couple of 150 watt hour panels 160 watt panels – if you go 300 watts of solar and a PWM controller, you’re going to be paying less for more power than if you were to go with an MPPT controller. So that’s why we have this choice in here.
Most people are going to be going MPPT unless you’re on a heavy budget or really running the numbers to get the most efficient system possible for your dollar. Than you might be looking at PWM controllers for anything under about 400 watts.
Now our charge controller, this is determined by our solar panel size. So for the charge controller this is a very generous size. Generally, you will be able to go down a size from this. So as you’re picking one out it’s ok to look at the specifications on this.
Say this number comes out to 25 amps, but you know your MPPT specs say that it can go to 240 watts and you only have 220 watts of solar, that charge controller can be a 20 amp charge controller.
This is just a general, you know that the size here is going to work. We can guarantee it for pretty much every situation. Sometimes if you size down it won’t quite work for a few specific panels and that kind of thing.
Ok, next up is the inverter. Now, this inverter number is only going to pop up if you have AC numbers selected. So if you notice when I deselect these DC numbers I’m not running anything off of household power (AC power). That inverter is going to come out blank.
That basically is just saying hey, you can save a lot of money and efficiency by not running an inverter. If you have to run these, this inverter number is our general recommended max size based on your batteries.
So the reason you don’t want to go bigger on your inverter for this is because a bigger power draw is hard on your batteries, it’s going to make them not last as long.
Batteries can handle quick discharges so if you’re running a blender or something for maybe 30 seconds you’ll be fine, but if you’re running a toaster oven or something where you need like a 120W inverter, in this case, you’re not going to be able to run a 120 watt inverter because your battery size isn’t big enough. It will significantly reduce the lifespan of your battery if you’re doing a constant high power draw from it, especially the lead acid battery types.
So if you find that this inverter number, it’s kind of a recommendation, you can go larger. Especially like I said if you’re running short bursts of power. But in general, if you’re going to go significantly larger, you’re going to want to double check your battery bank size.
We see this common mistake pretty often. The other thing to note is you can always go smaller. So in this case, I have two 90 watt DC powered components in my system. Those are the only things I plan on running off the inverter. So I don’t need anything more than a 200 watt inverter.
I might pick up a 400 watt inverter just because they’re easier to find, especially ones that plug into the batteries. But smaller inverters are more efficient. So the smaller you can go comfortably the better with this. You don’t want to grab a massive inverter just in case you want to run a power tool or something off of it.
There’s no reason to do that. If you’re ever going to run a power tool just get a battery powered one or run off of shore power.
You’re not going to want to run a coffee maker and you’re not going to want to run a toaster oven like I said. That’s a lot of the cooking elements that people try to run off inverters. Those things are not great to be battery powered. It’s hard on the batteries. It uses a lot of your juice, your electrical power available.
So this is where that [inverter] number is coming from. It’s based on your battery size.
Alright, so when you’re done with all of that. We don’t save any of your information. So if you’ve done all your calculations and you’ve written down your things. If you want to save all this, down at the bottom of the calculator we have a “print your numbers” button.
That will just print to PDF right there. Save it to your computer.
So we have this calculator here. This is nice to print off to show people. Maybe you’re having an electrician help you install this or maybe you want to share it online with someone. Say hey, here’s all my numbers, this is my daily power usage. These are the component sizes I’m going to go with. It’s a really good quick reference for your camper van.
So once you have that all figured out, how do you put it all together?
We have some solar panel wiring diagrams just for reference here. So, in this case we’ve got 220 watts. You can go down here and, these are all for reference. These are just to see which size components and how you want to plug everything together.
Everyone is going to be different so maybe you’ll find one 240 watt solar instead of two 100 watt panels. A lot of this stuff is variable and that’s why the solar diagrams you see online get kind of wonky and complicated because they’re for very specific set ups.
But this will at least give you an idea of how the components will be acquired together.
We have our solar panels running to our charge controller, our charge controller running to our battery. A lot of people will run off the load terminals to the fuse box. I find that to be a little redundant. Not really necessary in the larger set ups because your battery is better at handling that load anyway.
Either way works, it doesn’t really matter.
And then we have recommended components for those specific sizes. So say we have this fuse box here, you’ll be able to jump in this list of all of the components.
Now the one thing we don’t really list is the wiring because everyone’s wiring is going to be a little different. So this component is our general go-to if we were to build a camper van with our own money this is how we would use it. Sometimes in some cases there are much more expensive but only slightly better components that we don’t find necessary.
I think that should get you going!