Harnessing the power of the sun is what all the cool kids are doing these days and adding solar to your van doesn’t need to be that hard or expensive. This post will explain all the elements of a vanlife solar system so you can build the best system for your needs. Use the list below to jump to specific topics. You can find links to all the components we used in our build in the van build shop. Remember, it’s perfectly okay to outsource the wiring of your van to a professional or have a professional inspect your work. We are not professional electricians so take our advice with healthy skepticism. This post contains affiliate links, we earn from qualifying purchases at no cost to you.
Basic Solar Setup
Above is a very basic solar system so you can familiarize yourself with each of the components and how they work together.
Solar Panel Types
Mono panels are the OG of solar. They’ve been around the longest and are the most efficient type of panel at about 20%. Because of their high output, they tend to be smaller then polycrystalline panels, are less sensitive to high temperatures, and have the longest lifespan. The downside, they are the most expensive. You will need a roof rack or brackets to mount these rigid panels. You can identify them by their classic black color.
Poly panels are a newer type of panel and are slightly less efficient then mono at about 15%. Because they’re less efficient their footprint tends to be a bit larger as well. They are more sensitive to high temperatures then mono panels and have a slightly shorter lifespan but are also cheaper. Just like mono panels, these are also rigid so a roof rack or mounting bracket is necessary. These panels tend to be blue in color.
Thin Film (flexible)
Flexible panels are the new kid on the block. They have the lowest efficiency rating at about 10% but are also extremely lightweight and inexpensive. Because they’re flexible, you can mount them in a number of configurations including just gluing or taping them straight to the roof of your van without any roof rack. They generally aren’t as durable as rigid panels however and don’t have as long of lifespan.
Solar Panel Specifications
Maximum Power (Pmax)
The amount of watts the panel will produce in one hour in perfect conditions.
Maximum Power Voltage (Vmp)
The Vmp is the voltage when the power output is the greatest. This is the actual voltage you’ll see when it is connected to a charge controller (in optimal conditions)
Maximum Power Current (Imp)
The Imp is the current (amps) when the power output is the greatest. It is the actual amperage you’ll see when it is connected to a charge controller.
Remember Watts = Volts x Amps so it makes sense that a 100W panel producing 18.6 volts (The Vmp of a 12V panel) would produce 5.38 Amps (the Imp of a 12V panel)Confused? See nominal voltage below
Open Circuit Voltage (Voc)
Open circuit voltage is how many volts the solar panel outputs with no load. This is a very important number, as it is the maximum voltage that the solar panel can produce under standard test conditions, so this is the number to use when determining how many volts your array can theoretically produce and by multiplying this number by 1.25 (125%) you can choose the correct size for your solar controller.
Short Circuit Current (lsc)
Short circuit current is how many amps the solar panels are producing when not connected to a load. This is the highest current the solar panels will produce under standard test conditions. When determining how many amps a connected device can handle, like a solar charge controller the Isc is used, generally multiplied by 1.25 (125%)
Nominal voltage is really just a category, not an actual voltage you measure. For example, a nominal 12V monocrystinllne solar panel has a Voc of about 22.8V and a Vmp of about 18.6V. The nominal voltage is just used to make sure you’re buying the correct panels for your battery system. If you have 12V batteries (which aren’t really 12V) then you should be buying 12V solar panels (which aren’t really 12V). It’s like they are trying to make it as confusing as possible!
Simply how efficient the panel is at converting sunlight into electricity. 10% is a relatively low rating 20% is a relatively high rating.
Solar Panel Configurations
You can wire solar panels in parallel or series configurations and each has its pros and cons but for small vanlife solar applications series is the way to go. The main thing to know is that when wired in series, the voltage of the panels is added together but when wired in parallel the amperage of the panels is added together. Remember that higher amps = bigger cables = most cost.
Although parallel arrays have the advantage of maintaining efficiency while partly shaded, that’s really where the advantages stop when talking about small vanlife solar setups. The higher voltage offered by a series array gives your charge controller a wider operating range which will ultimately means more power coming into your batteries longer. The downside of a series array is that if one panel is partially shaded, it affects the whole array. Lucky for you, your home is on wheels so you can just move into full sun.
How Many Watts Do I Need?
This will be determined by four things. (1)Your budget and goals, (2) your battery chemistry and charge controller type, (3) your daily power consumption and (4) available space.
Your Budget and Goals
If your goal is to spend as much time off grid boondocking as possible then of course you’re going to prioritize solar over someone who wants to spend most of the time in campgrounds hooked up to shore power. Likewise if you’re on a budget (who isn’t) then you may consider sizing down your vanlife solar system. But in my opinion, solar components are already pretty inexpensive, so you might as well maximize the efficiency of you system within your budget. It would suck to spend $500 on a setup and be unsatisfied when you could have spent $650 to make it a lot better.
Battery Chemistry & Charge Controller Type
The charge efficiency of your batteries will also affect how much power from the sun you can soak up. Lithium Ion batteries can capture 99% of the energy your solar panels provide whereas lead acid will only soak up 80% which means you’ll need more solar wattage of the roof to get the same amount of energy. Learn more about batteries here.
Your charge controller will also determine how many amps you’re actually harvesting from your panels. We talk all about charge controllers in the next section but generally MPPT controllers will be more efficient then PWM controllers.
Daily Power Consumption
In a previous post we leaned how to calculate how many amp hours of battery you need in your van build. That will be the first step in determining how many watts of solar panels you need so if you haven’t done so already, check out that post.
If you’re in a VW bus, you wont have as much roof space as a extended sprinter so it’s time to climb up onto the roof of your rig and bust out the tape measure. Remember to think about vent fans and other things you might want to mount up there too. Limited roof space might force you to consider flexible panels or you might be able to squeeze a single moncrystalline panels up there but most likely polycrystalline panels are out for you.
Putting It All Together
Let’s run though an example together. Lets assume you calculated that you will use 75 amps per day to run all of your electronics. Solar panel output is rated under optimal conditions, meaning no clouds on a cool day with clean panels at the equator. Because conditions are never perfect it’s reasonable to expect that your panels wont perform at 100% of their rating most of the time. A typical 12V 100W monocrystalline solar panel will produce about 5.38 amps per hour. (100W divided by 18.6Vmp = 5.38A)
Now guess about how many hours per day your panels will be exposed to sun. Of course because the sun arcs across the sky, the morning and evening hours will not be a productive as mid day is and it might partly cloudy, and you could be in higher latitude so its never going to be perfect. Lets assume the panels will get 5 hours of sun a day.
If we have three 100W panels wired in series, we would produce 5.38 amps, @ 55.8V (In optimal conditions). A MPPT charge controller will handle this load differently then a PWM controller but moving forward lets assume you have a MPPT controller. The MPPT will drop the voltage to 14.4V (the voltage your battery wants to charge) and boost the amperage the same ratio so the actual amps coming from your charge controller would be ~ 27.8 amps. So over a 5 hour period you could expect to get ~139 amps into your batteries, way above the 75 amps you calculated you’d consume in a 24 hour period.
That’s all very confusing and the real world will never match the math so as a general rule of thumb you should at least match the amps hours of battery with watts of solar; so if you have 200 amp hours of batteries you should at least have 200 watts of solar.
A charge controller takes the energy from the solar panels and regulates it to charge your batteries. There are two different types of charge controllers, pulse width modulation (PWM) and maximum power point tracking (MPPT). PWM controllers take the voltage from your panels and switch it on and off really fast (pulse width modulation) to regulate the voltage to charge your batteries. A PWM controller will need the voltage coming from your solar array to be well above the voltage of your batteries to start charging, potentially missing out on early morning and late evening sun. This is why wiring your panels in series is best because it multiplies the voltage not the amperage. PWM controllers are less efficient then MPPT but they are cheaper.
MPPT controllers are more like a smart DC/DC charger in that they step down the voltage coming from your panels to whatever your battery needs and then boost the current by the same ratio the voltage is dropped. This leads to a much more efficient charging profile that can adapt to changing conditions. For small solar setups like on a van, an MPPT controller will allow you to get the most performance from your solar panels. We recommend Victron Energy’s MPPT Solar Charge Controller.
Charge Controller Size
Charge controllers will be rated for the maximum voltage and amperage they can handle/output. See the blue Victron controller above? 100/30 means the max voltage is 100 and max amps is 30.
You will need to get a controller that is rated at least 125% above the maximum power voltage (Vmp) AND short circuit current (lsc) your array is capable of producing. For example if you have two 12V 100W (Vmp of 18.6V) panels wired in series they would be capable of producing about 37.2V and 5.88A. Therefore you would need a charge controller that rated for at least 125% of 37.2 volts and 125% of 5.88 amps. Hope that made sense.
You will need to incorporate a circuit breaker into your system on the positive pole (+). This is important for safety of course but it will also give you a way to isolate your solar panels from your batteries. You never want to allow your charge controller to ‘see’ your solar panels without being connected to a battery. To say that another way, the charge controller always needs to be connected to the battery first, before connecting it to the solar panels. The controller can be damaged if it has nowhere to send the energy coming from the panels.
A breaker acts like a switch between your panels and solar controller and will allow you to isolate the two components when needed. The proper breaker size is 125% of the short circuit current (lsc) rating of your array rounded up to the nearest breaker size. For example if you have three 12V 100W panels in a series configuration, then the Isc is 5.88amps. If the same three panels were wired in parallel then the array would produce ~23.5amps.
A good source for quality solar equipment including breakers is MidNiteSolar.com
You’ll route your cables from the outside of your van to the inside using one of these. They have a rubber gasket that tightens around the cable for a watertight seal. Drill a hole in the roof of your van big enough to fit your solar panel wires though, then either glue or screw (why not both) the entry gland over the hole. Don’t forget to paint the bare metal edge of the hole you drilled and pick up any metal shavings!
Use one of these rubber grommets around the hole you drill in the roof of your van under the entry gland. They come in every size you can think of and are pretty cheap. You’ll feel super professional and your wires will be protected from chafing.
This is what you’ll use to join panels together. Most of the time they come preinstalled, but if you need to modify the wiring, these come in a number of configurations.
My Two Cents
If you’re going to make an investment in solar, you should get state of the art equipment. Monocrystalline panels wired in series and a MPPT charge controller for sure. If you can pair that with lithium batteries, you’re going to be a happy camper. Our setup consists of 300W of mono panels a Victron MPPT 100/20 and two hundred amp hours of lithium ion batteries from Renogy and it’s been awesome.
Hope this guide has given you some value and clarified the confusing world of solar. You can find links to all the the components we used in our van in our van build shop.