Updated: Sep 23
Did you know that the amount of sunlight that strikes the earth's surface in an hour and a half is enough to handle the entire world's energy consumption for a full year! Solar power for van conversions is totally essential. In this guide you will learn how solar panels work, how to choose the right solar panels, how to size your solar panels and leisure batteries, how long it will take to charge your batteries, and I will show you how to install the solar panels from start to finish. This information-packed guide will have solar panels on your campervan in no time! I'm Shane, I've been teaching people to convert campervans for many years, I'm the author of The Van Conversion Newsletter, the van conversion instructor at Udemy, and the proud owner of a beautiful self-build campervan called Beans. So let's jump in and have a look at shore power for van conversions!
Note: Items linked in this guide are paid affiliate links. By using these links, you are helping me to continue writing free educational van conversion content! You can find the full list of van conversion supplies here.
Note: Before we hop in, you will definitely want to grab yourself a wiring diagram which you can get for free by signing up to The Van Conversion Newsletter (the wiring for solar power is included in the diagram 🙂 - wiring diagram gets sent out to you straight away).
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The anatomy of a solar power system for a van conversion
To install solar power in your van conversion, you need three components:
A solar charge controller
I am going to go into detail on each of these three components in this article; how to choose them, and how to wire them all up.
How do solar panels work?
Photovoltaic panels (PV), also known as solar panels convert energy from the sun (photons) into electricity which you can use to power your campervan.
When the sun shines onto a panel, the energy is absorbed by the PV cells. The photons knock electrons free from atoms, generating a flow of electricity.
The solar cells form an electrical circuit in the panel, thus allowing the flow of electrons through the circuit, creating electricity.
Monocrystalline vs. Polycrystalline vs. Thin Film solar panels
There are three types of solar panels you can use for your campervan: monocrystalline, polycrystalline, and thin film. Monocrystalline and polycrystalline are both rigid, while thin film is flexible.
Monocrystalline solar panels
Pros: Most efficient solar panel, long life, long warranty (20 years on average)
Cons: Heavier, bulkier, don't bend, less rugged
Polycrystalline solar panels
Pros: long life, long warranty (20 years on average), cheaper than monocrystalline
Cons: Heavier, bulkier, don't bend, less rugged, not as efficient as monocrystalline
Flexible solar panels
Pros: Very light, super-slim (stealthy), bendy, more rugged
Cons: Less efficient, shorter warranty (5 years on average)
What do I have in my van?
I used 4X 100w monocrystalline solar panels for my van conversion.
How to wire up solar panels
You can wire up solar panels either in series or in parallel. We will be discussing Volts, Amps, and Watts in this section, if you want a refresher on those concepts, you can check out this guide.
Wiring Solar Panels in Series
In order to wire solar panels in series, we daisy chain them together. The positive of one panels runs into the negative of the next panel. We then run the last remaining positive and negative cable down to our solar charge controller.
When we wire solar panels in series, the amperage (current) remains the same, but both the voltage and wattage increase. For example, Each solar panel in the diagram below is a Renogy 100W monocrystalline panel. Each panel has a max voltage of 18.6v, giving us a max of 5.38a per panel. When we wire the four solar panels in series, the voltage increases to 74.4v and the wattage increases to 400w.
In a nutshell, when we wire solar panels (or any device) in series, they act as a single unit - like one huge solar panel.
Advantages Of Wiring Solar Panels In Series
Can use smaller wire size due to lower current
Wiring is more simple, requiring less connectors and equipment.
Normally output higher power
Distance is less important to efficiency
Wiring Solar Panels in Parallel
In order to wire solar panels in series, we connect all the positives together and all the negatives together. The single positive and negative cable runs down to our solar charge controller.
When we wire solar panels in parallel, the voltage remains the same, but both the amperage and wattage increase. For example, Each solar panel in the diagram below is a Renogy 100W monocrystalline panel. Each panel has a max voltage of 18.6v, giving us a max of 5.38a per panel. When we wire the four solar panels in series, the voltage remains at 18.6v but amperage increases to 21.52a and the wattage increases to 400w.
The BIG advantage to wiring in parallel is that the panels are not inter-reliant on each other; if one of the solar panels is dirty/in the shade/broken, the others are not affected. In contrast, when wiring in series, if you are parked partially under the shade, your solar panel efficiency will be greatly reduced.
This is a big advantage, as in my experience I have found it very common that I am parked partially in the shade. However the advantage comes at wiring that is a pain in the butt.
If you have multiple panels on your roof, you will need a device called an MC4 connector. this device routes many wires into one. If you have 2 panels, you will need a 2-to-1 MC4 connector, or if you have 4 panels like me, you will need a 4-to-1 MC4 connector!
Depending on your choice of solar panels, you may also need to get inline MC4 fuses.
Solar Charge Controllers
A solar charge controller is a device which keeps our leisure batteries from overcharging by regulating the voltage and current coming from the solar panel to the battery. It converts the powerful electricity from our solar panels into electricity our leisure batteries can use.
Let's have a refresher on the charging profiles of leisure batteries (which was discussed in this guide to leisure batteries).
Charging profiles of leisure batteries
Charging profiles of leisure batteries normally follow three stages: bulk, absorption and float. The charging limits differ between the different battery types.
Bulk: a fast, constant current charge up to ~80% State of Charge (SoC)
Absorption: much slower, constant voltage charge to reach 100% SoC
Float: a constant voltage charge which maintains 100% SoC by counteracting self-discharge
Note how different batteries charge best at different voltages. Lead-acid batteries (AGM, Gel, FLA) in particular require large voltages in the constant and current stages of the charge profile. Lithium batteries are the inverse - they require less power initially and gradually ramp up.
It is also worth pointing out that the current (amperage) works in the opposite way - at the beginning of the charge profile, the amperage starts high and gradually gets lower.
A solar charge controller ensures that the voltage and amperage matches the expecting charge stage of the battery. It is paramount that is does its job correctly. For example, if we had four solar panels wired in series (74.4v) wired directly to our leisure batteries, we could be in for a very, very dangerous time indeed. The sulphuric acid will begin to boil and the plastic casing will start to melt... 😲
What is the difference between a PWM and a MPPT solar charge controller?
There are two types of solar charge controllers: MPPTs (Maximum Power Point Tracking) and PWMs (Pulse Width Modulation). MPPTs are a little more expensive, but accelerate solar charging of the battery up to 30% per day. I have an Epever 40a MPPT Solar charge controller. You can also plug an MT50 remote display into your solar charge controller for extra solar and battery monitoring. I would highly recommend this - I have found it to be a very useful device. Alternatively, you can use a Renogy solar charge controller and bluetooth monitor.
A PWM is a relatively simple device that is essentially a smart switch. It pulsates on and off, recognising when it needs to send power to the batteries (per the charge profile). It is about half the price of an MPPT, but about 30% less efficient per day (big difference!)
PWMs draw current from the solar panels just above the voltage of your leisure batteries.
A MPPT is a solar charge controller which digitally tracks the charge profile of the leisure batteries in order to be as precise as possible with its energy delivery. They are a lot more efficient than PWMs
MPPTs draw current from the solar panels at the max voltage possible.
What size solar charge controller do you need?
Let's say we have four 100w Renogy solar panels wired in series. Given the 400w of solar power flowing to our 12v batteries (wired in parallel), we need to size our solar charge controller.
We must figure out how many amps at 12v our solar panel set will actually produce. We can see that our solar charge controller must be able to handle 400W/12V = 33.7a. So we should to buy a solar charge controller that is slightly bigger, for example a 40a solar charge controller.
How long will it take the solar panels to charge your batteries?
If you want a recap on some of the concepts touched on here (Wh, Ah, parallel vs. series, etc.), you can check out this guide.
Let's say that we have two 130Ah 12v sealed lead acid leisure batteries in our van. We wire them in parallel, giving us a total of 260Ah capacity. This equates to 3120Wh in total (12v X 260Ah). Calculating what battery size you need is discussed at length here.
However, because these are lead acid batteries, we can (should) only discharge them by 50%, meaning we can only use 1560Wh of power from our batteries.
How long will it take the solar panels to charge our leisure batteries?
Given the above information, we know we have to fill up 1560Wh of battery using 400W of solar power. So: 1560wH / 400 watts = 3.9 hours
Hang on there Obama! Solar panels typically only output 70% of the rated wattage. This is primarily due to the angle of the sun. So: 1560wH / (400W * 0.7) = 5.5 hours
That's still pretty good!
How to Install Solar Panels on your Campervan (Step-by-step)
In this step by step guide, I will be showing you how to install solar panels on the roof of your campervan. First we will look at how to install flexible (thin film) solar panels, then we will look at how to install rigid mono/polycrystalline solar panels.
Note: Before we hop in, go grab yourself a wiring diagram which you can get for free by signing up to The Van Conversion Newsletter (the wiring for solar power is included in the diagram 🙂 - wiring diagram gets sent out to you straight away).
Step 1: Clean the roof
Not much to say here... Get up on your van roof with some warm soapy water and get to work!
Step 2: Remove rust from the top of the campervan
Whether or not you're installing solar panels on your campervan, removing rust is always a good thing! You can remove rust using a wire brush and metal paint. Check out this useful guide on how to remove from for your van conversion.
Step 3: Stick strips of 3M VHB (Very High Bondage) tape on the van
Place strips of the double-sided 3M VHB tape on the roof of your van. This stuff alone will stick the solar panels down for life.
Step 4: Stick the flexible solar panels onto the roof of the campervan
Carefully place the solar panels on top of the 3M VHB strips and gently press them down.
Two important things to keep in mind when installing flexible solar panels for your van conversion:
Cooler solar panels are more efficient. Flexible solar panels can get quite hot if there is no air gap underneath them. Luckily on the Ford Transit, there are ridges that run down the length of the van, providing an air gap of about an inch, through which air can flow. If your van does not have ridges, you can still install flexible panels, though they might not be as efficient. Alternatively, you could raise the panels up using metal risers.
Some people use high bondage glue (like sikaflex) instead of VHB tape. This is fine too. However, if you are using glue, make sure you pour it in strips, just like the VHB tape. DO NOT make an airtight seal with the glue - water can get trapped in there, expand, and do damage to the panels. It will also reduce the efficiency of the panels due to higher heat.
Some people choose to secure the panels to their van even more by using well nuts in each of the four corners of each solar panel. A well nut is like a rivet nut, and is used to fasten a piece and to seal the bolt hole. As it is a bolt is is screwed in, the well nut expands.
I can tell you that after three years of living in my van full-time, using only VHB tape, I have never had a single problem with my solar panels coming loose. In my opinion well nuts are not needed - however I will tell you how to use them in case you are tempted!
How to secure solar panels with well nuts
Drill a hole through the van to match the corner of the solar panel. The hole size should match the size of the well nut (M8 - M10 preferable for a solar panel)
Place the well nut through the panel and into the hole
Screw an appropriate bolt into the well nut and the well nut will gradually expand and seal the hole.
For extra waterproofing, I would highly recommend using some sealant on top of the well nut to be super-duper sure you won't get a leak.
Step 5: Stick down loose wiring on the roof using adhesive cable clips
Final step is to get the wiring out of the way and make it look nice! Use cable ties to bunch everything together and stick it to the roof with adhesive cable clips. I would advise using the 3M VHB tape to stick the cables down, rather than whatever sticky tape came with the adhesive cable clips.
How to mount rigid monocrystalline or polycrystalline solar panels on your campervan
First go grab yourself a solar panel kit, like this awesome 400w kit from Renogy.
First attach metal brackets to the solar panels. The Renogy kit comes with a Z-bracket mounting system, which allows an Inch of room underneath for airflow to increase the efficiency of the panels.
Bring the bracket-mounted solar panels up onto the roof of your van and mark with a pen where you need to drill into the van.
Drill into the spots you have marked on the roof with a drill bit appropriate to the size of your bolt
Bolt the solar panels into the roof (place the bolt into the hole from above, and screw the nut on from inside the van)
Note: To get a waterproof seal, I would advise applying a good amount of sealant around the hole you have drilled before tightening down the bolt. Alternatively, you could add a small piece of mastic / butyl tape over the hole to get a really nice seal. Some people also choose to use Loctite Marine Adhesive. All three of these options will work.
Here is a great video on how to install rigid solar panels on a campervan.
Step 6: Wire up the solar panels and bring the cables inside the van
Wire up the solar panels either in series or parallel, as discussed above. Most people use 8AWG cable for this job (they normally come with the solar panel kit).
Then bring the positive and negative wires inside the van. The wires enter into the van through a solar cable entry gland. I discussed how to install a solar cable entry for your van conversion in this guide.
Step 7: Add a fuse to the solar wiring before the solar charge controller
Add an appropriately sized circuit breaker to the positive wire running to your solar charge controller. I used a 40a inline breaker (because I can expect 33.3a maximum to be delivered under normal circumstances... calculation was done earlier in this guide). We want to place the breaker as close to the panels as we can get it (to protect as much of the wire as we can.
A close up look at the Epever 40a MPPT
The Epever MPPT has three separate ports:
(Left) Input power from solar panels
(Center) Output power to leisure batteries (after solar charge controller converts solar electricity to clean power, it is routed to the leisure batteries)
(Right): Run cable out to our 12v appliances. This is optional as I mentioned above, but I would highly recommend it :)
VERY IMPORTANT NOTE:
DO NOT HOOK UP THE SOLAR CHARGE CONTROLLER TO THE SOLAR PANELS UNTIL THE LEISURE BATTERIES ARE CONNECTED. It can fry your solar charge controller! Beware.
Step 8: Connect the solar charge controller to your bus bars
Next, wire the Solar charge controller to your positive and negative bus bars. The bus bars run down to your batteries. We add a 50a inline breaker to the positive line running to the bus bars. I used two 300a heavy duty bus bars and 8 AWG cable for my van conversion.
The wire from the solar charge controller is connected to the bus bar using a large lug.
Step 9: Connect the positive and negative bus bars to your leisure batteries
The last step of the solar system is running the busbars to our batteries. We run a single positive and negative cable from each busbar to the leisure batteries. I used 0AWG cable for this (Very beefy 🐮). Learn all about leisure batteries here.
On the way to the batteries, we are going to chuck an isolator switch on the positive line (a giant switch that will cut-off all electrics if switched). We will also add a 250a fuse (or similar) onto the cable as a last ditch effort to protect the batteries in case of electrical overload.
Some people will opt for a single leisure battery, while others will opt for multiple batteries, thus increasing storage capacity. If you are using multiple batteries, make sure you wire them in parallel to keep the voltage at 12v; if you wire in series the voltage increases as a factor of the number of batteries attached. I used two 130aH leisure batteries.
Don't forget to ground your batteries!
It's very important that you ground your leisure batteries! It's very simple, you can learn how to do it here.
Step 10: Connect your 12v fuse box to your solar charge controller
Last step! Connect your 12v fuse box to your solar charge controller. This will send power to all your 12v appliances (like fan, heater, lights, etc.). I used 8AWG cable in my van build and added a 40a breaker onto the positive wire (as close as possible to the solar charge controller).
Connecting your fuse box to your solar charge controller is technically optional; some people will connect the fuse box directly to the bus bars. However I have found the battery monitoring capabilities of the Epever 40a MPPT Solar charge controller and MT50 remote display top class!
Most people will also wire up a 12v switchboard after the fuse box before running out cables to the individual appliances so that they can turn individual appliances on and off.
And there we have it! What an adventure that was... I truly hope you found this article on how to install solar panels in your campervan useful! Don't forget to subscribe to The Van Conversion Newsletter for everything you need to get started with your own van conversion (I'll send you a free wiring diagram when you sign up).
If you're converting a van but unsure of how to do it, you could also check out the Van Conversion Course on Udemy. In the course, you'll learn directly from me how to convert a van into your dream home - no prior experience needed!
Until next time,