skip to Main Content
school bus build school bus interior school bus build school bus interior school bus build school bus interior school bus build school bus interior

Solar Panel And Charge Controller Basics

When it comes to powering your van, there is a lot more involved than just going to the store and buying solar. Solar power sounds complex, and this is because there are so many different options to choose from. Before going into how many watts of solar you need to buy, let’s take a look at the different types of solar panels available.

Determining which type of panel is right for your lifestyle will help give you a better idea of how efficient you need the panels to be. This is usually determined in tandem with calculating how many watts of solar to buy.

Solar Panel Types: Rigid vs Flexible

When looking at solar options, you will see that there are two general panel types:

  • Rigid: Rigid panels are mounted on a metal frame –usually aluminum- and are protected with a sheet of glass. Glass is quite durable when it is fixed in the frame, and resistant to scratches. Rigid panels are cheaper per watt and generally come with a good warranty. These are by far the most common outside of the vanlife, although the difficulties of mounting them on a vehicle mean flexible panels have their perks.
  • Flexible: Flexible panels use the same underlying solar technology as rigid panels but instead of glass they are encased in a softer material. This allows them to bend up to 30 degrees. Because the material has to be softer to flex, these panels are more prone to getting scratches on the surface, reducing efficiency. This same feature however, does make them less likely to crack. These panels also benefit from being very lightweight. Flexible panels usually come with a significantly shorter warranty period, which gives a hint to their long-term reliability.

Solar Panel Placement

The two ways to gather solar on the road:

  • Fixed Solar: these panels are permanently attached to the van, usually the roof
  • Portable Solar: These panels are stored away when driving and then placed in the sun when parked.

Fixed solar panels

Fixed solar panels are usually attached to the roof of the vehicle and collect energy any time there is sunlight. This is one of the most common solutions for vandwellers, and once they are installed they won’t need much ongoing maintenance. The size and shape of your vehicle’s roof is going to be a big determining factor in how many solar panels you can attach. Oddly shaped roofs may require several smaller solar panels vs a few larger ones.

When planning your solar placement, know that solar panels perform best when cool. For this reason, it is ideal to have a gap between the panel and the roof for air movement. Mounting or gluing panels directly to the roof should be avoided if it is not a critical part of the build design. Most mounting systems that you buy place the panel .5”-1” above the roof for this reason. We have seen quite a few van owners switch from flexible to rigid panels because flexible panels mounted directly to the roof didn’t perform as well as they were planning.

Fixed panels are going to be labor intensive up-front. You can mount the panels directly to the roof by drilling holes for bolts that hold the solar mounts. You can also mount the panels to a roof rack on your van, and finally you can tape or glue them directly to the roof. If your roof is round, this option only works for flexible panels.

Some notes on drilling: It is understandably intimidating to punch a bunch of holes in your new vehicle. Many people have a tendency to want to be able to “undo” everything in their build because that’s how we treat most of our vehicles. While you do want to be cautious, it is cathartic to fully commit and “own” your build. With some silicone and washers we are confident that everyone can mount their solar, have it be water tight and benefit from a cleaner setup. We go more into specifics of mounting here (COMING SOON).

You will also need to attach these solar panels to batteries within the vehicle, so a little wiring work and drilling will be required through the ceiling.

Fixed solar panels are not always very stealth. Most people are going to be able to tell you’re living in a van, or powering something if they see these on the roof. However, this can be reduced with things like creative rack placement so that it doesn’t look out of place in a parking lot. Alternatively, mounting flexible panels directly to the roof will have a very low profile.

With fixed panels, you won’t have to worry too much about people trying to steal them. That is going to take a lot more effort than with a portable solar panel.

Portable Solar Panels

Portable solar panels

Solar panels do not have to go on the roof! Portable solar panels are simply panels that you keep inside the vehicle and then pull out to get sunlight once the van is stopped.

Portable solar panels have a lot of advantages over the fixed kind. Overall, they are often cheaper because of the lack of a mounting materials required. With portable solar panels, you are not limited by surface area of the van in how many you can buy.

Portable panels can be easily adjusted once outside so you can capture as much direct sunlight as possible. They will also allow you to park your van in the shade while still catching direct sunlight with a solar panel.

Portable solar panels cannot collect sunlight while you are driving or on the move. Because they need to be placed outside, they are not very stealth. Portable panels will not work well if you intend to van life in the city because they cannot be concealed. You may worry about them getting stolen if you are around a lot of people so it will be important to be aware of surroundings.

Portable solar panels will also require you to store them within the vehicle (taking up space), then hook them up each time you use them. This is a little bit more manual than a fixed solar panel, because with those you can just set it and forget it.

Portable solar panels are a good solution if you have a small budget, intend to spend a lot of time outside of the city, and are ok with a little bit of manual labor every day.

Companies such as Goal-zero sell portable solar “generators” that can be used to charge small electronics. These are usually a panel combined with a battery and inverter in one unit. Goal zero panels are compact and easy to buy as an all-in-one solution, but significantly more expensive than putting together a full solar kit on your own. Making your own solar kit also gives you more flexibility in upgrades and repairs.

Solar panel efficiency

Now that you have a general idea of the types of solar panels out there, let’s look into how to get the most efficiency out of your setup. Once again, before going into how many watts you should purchase we are going to delve into the things that make some solar panels more efficient than others. These include:

  • Age and quality of solar panels
  • Weather conditions
  • Angle of solar panels
  • Shade
  • Monocrystalline vs. polycrystalline vs amorphous technology

Age and quality of solar panels

Solar panels have become exponentially more efficient in just the past 10 years. This means that it might be worth the money to invest in a newer solar panel rather than buying panels that are a few years older.

No-name brands of solar panels are quickly becoming just as good as the name brands. Although some companies such as Renogy offer all-inclusive solar packages that are very well illustrated and come with all of the necessary components, be aware that you can get the same quality panels at a cheaper cost by sourcing all the parts on your own. Renogy kits are very well put together, though, so for many it’s worth it to pay a little premium for reassurance.

Take extra caution when purchasing highly discounted or cheap solar panels. Pay attention to the reviews and warranty offered. Many popular brands offer warranties of 20 years on their solar panels. If the brand you are looking at offers a significantly shorter warranty, that might be a red flag.

The more solar panels you can buy, the more power you are going to get. If you choose to purchase a cheaper, more inefficient solar panel – you are going to need more of them to get a reasonable amount of power. Generally, the larger the solar panel, the cheaper it is per watt of power. 

Weather conditions

Solar panels work by converting sunlight to electricity. The more sunlight in the sky, the more power you will be able to collect with solar panels. Once you have installed a solar panel, weather is going to be the biggest concern (and major headache) when it comes to collecting power.

Remember back to our post on calculating how much electricity you need to live in a van. In that post, we walked through step-by-step how to calculate how much energy was needed to charge lights, a cell signal booster, two laptops and a refrigerator. That estimate came out to roughly 98 amp hours per day.

When charging your van with RV hookups or a generator, power calculation is simple. If you need 98 amp hours per day of power, that’s all you need to collect. When it comes to solar power however, weather conditions are going to make a huge difference in how much power you need to collect.

To start, the amount of solar power you can collect at night is going to be negligible. Just like that, there goes 8-10 hours of power that you can’t count on from those panels. In addition, the sky is not going to be sunny and cloudless every single day. Unless you plan to spend your entire road trip in Phoenix, Arizona it will make sense to build in a buffer of energy collection for cloudy days. In addition, during the winter, there will be 1.5 hours less sun and it will be lower in the sky, significantly reducing your peak sun availability.

It is difficult to predict exactly how little sun coverage there will be in the sky on any given day. However, there are ways to calculating an approximate amount of energy to power your devices.

Angle of solar panels

Any time a solar panel is not directly facing the sun there is going to be less energy gathered. A tilt mount will allow you to adjust the solar panels to face the sun directly during sunrise, sundown, and everything in-between. Tilt mounts can be an extra step to mounting solar panels on the roof of a van. If you have the budget and space, tilt mounts can increase your solar power capacity by as much as 25%. Portable solar panels are advantageous in that you can easily adjust their angle throughout the day.

Remembering back to rigid vs. flexible solar panels, you will recall that flexible solar panels cannot be easily attached to a tilt mount as you would have to build a frame to hold them (effectively turning them into a rigid panel anyway).

Not everyone decides to splurge on tilt mounts. Whether you are using them or not, always keep in mind the direction the solar panels are facing in relation to the sun. Yes, this means you may want to re-park your car multiple times throughout the day so the solar panels are facing the sun more directly.


Another big thing to know about panels is that most of the tech very sensitive to shade. All the little blocks on the panels that you see are wired in a way that if one of them is shaded, the whole row can’t produce energy. Because of this, you can reduce your energy produced by up to 90% if a certain 10% of the panel is covered.

This is important when placing the panels and critical when planning the roof layout of the van. If you have a roof rack, chimney or storage box covering your panels you are significantly reducing your energy.

Monocrystalline vs. Polycrystalline vs Amorphous solar panels

You will see these terms come up when looking at panels. This is tech talk about what the solar gathering part of the panel is actually made of. This is not a subject to waste too many brain waves on as it is relatively unimportant to the system as a whole. In general:

Monocrystalline panels are a little more expensive and a little more efficient. These panels will be take up a little less space for the amount of power they produce, so if you are fighting for every square inch you will benefit from them. These panels have that familiar white diamond shape in between all of the solar cells.

Polycrystalline panels are a bit cheaper and bigger per watt, but still share most of the same longevity and durability attributes as Monocrystalline panels. You really can’t go wrong with either option as long as you take measurements and make sure everything fits. Some people like the aesthetics of Poly- panels because they are sectioned off in squares and a bit more conspicuous than Mono- panels.

Amorphous panels are an entirely different tech that most people don’t find beneficial to van life. They are significantly less efficient- taking up more weight and space- and are more expensive per watt. These panels do tend to be the most durable and work in cloudy weather and in the shade much better. These panels are all one color with faint lines running one direction.

How much solar power do you need?

Once you have a general idea of whether you want fixed or portable panels, flexible or rigid solar panels, it’s time to figure out how much solar power you actually need. If you haven’t done so already, go back to our first post on how to calculate energy needs for you van.

In that post, we did a step-by-step calculation of how many Ah you would need per day to power a refrigerator, lights, two laptops and a cell signal booster. The numbers we came up with in this example of a high-use summer day are:

Norcold Refrigerator (running 24 hours per day) = 38.4Ah
16.4’ LED light strip (running 6 hours per day) = 12Ah
WeBoost Cell Signal booster (running 4 hours per day) = 10Ah
MacBook Pro (running 3 hours per day) = 9.9Ah
Lenovo Thinkpad (running 3 hours per day) = 28.05Ah
Total = ~98Ah per day

You’ll notice that solar panels are measured in Watts. And you’re probably asking why we would make you go to all that work to calculate amp-hours when these things are measured in watts! That bit is coming, but first a couple of notes:

When pairing solar with batteries you want to try to top the batteries off to 100% each day to keep them healthy. This means that if we’re using 98Ah of energy throughout the day on a worst-case scenario, we want to produce at least that much from our panels on most days. Because the sun is notoriously variable, we like to give a good safety margin.

If you only produce 90Ah and use 98Ah, after a day or two you’ll notice that in the morning when you wake up and try to plug your computer in the batteries won’t have any juice left over from being depleted with no sun. Not only is this a bit frustrating, it will significantly impact the long-term performance of your batteries.

For those folks who like to get detailed, there are lots of specific solar energy calculators online:
Renogy Solar Calculator Calculator

For those who are intimidated or don’t want to deal with specifics use these general rules of thumb:

  • If you plan on dwelling in a sunny climate: Double your calculated daily amp hours to get the approximate Watts in solar you need.
  • If you plan on dwelling in a cloudy climate: Triple your calculated daily amp hours to get the approximate Watts in solar you need.

This is just a general guideline and there is a little wiggle room built in. These guidelines are taking into account energy a little bit of energy variability from sunlight, temperature and charge controllers. We estimated for energy loss when using inverters in the calculating energy post. Remember these factors as you plan for solar:

  • Flat mounted panels will be less efficient than tilt mounted panels
  • Flexible panels tend to not perform quite as well for their wattage rating
  • Hooking to an alternator can supplement the energy you get from solar

As an example, if you calculate that you need about 150 Watts of solar but are mounting it flat, you would consider getting 200W of solar.

Because the rule of thumb is generous, if you estimate that you need 130 Watts of solar but are getting optimum sunlight from a portable briefcase, you would be safe getting a 120W briefcase because they don’t sell 130 Watt sizes.

Based on our numbers with a healthy buffer built in:

98.35Ah x 3 = 295 Watts needed in a cloudy climate

Solar Charge Controller

Charge controllers: we’re not done quite yet!

When powering a vehicle with solar panels, it is necessary to use a charge controller. As you will learn in our next post on choosing a battery for your campervan, the majority of people will run a 12V battery system. However, most ’12 Volt’ solar panels produce around 16 – 20 volts of energy when in direct sunlight. Batteries are finicky, and if they get too high of voltage too many times, their lifespan shortens and eventually they die or become damaged.

A charge controller helps regulate how much energy is going from the solar panels into the battery. Charge controllers can also keep track of how much power is currently in the battery. A charge controller will feed power faster to a low battery (stopping short of overheating) and slow down the power going into the battery as it gets fuller.

If a battery becomes 100% full, and the solar panels are still bringing electricity to it, the battery will become overcharged, and that is bad! Hooking up a charge controller will prevent the battery from becoming overcharged.

Many charge controllers come with digital displays which are very useful to keep track of how much voltage the battery is at, and most even have a low voltage cutoff that make it so you don’t risk taking too much energy from the battery. As stated in the battery post, a healthy battery should not drop below 50% charge so this is important information to be able to regulate.

Parts of a solar power system

Standard Charge Controllers (PWM), vs MPPT Controller

This third piece of the puzzle is what gets the unwieldy energy that your solar panels are spitting out into tame and usable energy for your batteries.

There are two types of charge controllers, standard and MPPT. Standard charge controllers cost significantly less than MPPT charge controllers, but they are also less efficient. Why is this?

When a solar panel produces 18v of electricity, the charge controller has to convert that to a safe 14v or so that is healthy for the batteries. A standard controller will effectively throw the extra voltage away so you lose some of the energy produced.

An MPPT Controller uses electrical wizardry to lower the voltage but increase the amperage to get more power from the panels than a standard controller. Generally, a standard controller gets about 80% energy from the sun and an MPPT controller is about 92% efficient. Our rule of thumb for calculating how many watts of solar you need assumes an average of these two.

When buying a charge controller, you need to figure for up to 7 amp capability for every 100 watts of solar. For example: if you’re getting a 200W panel setup, you need at least a 14 amp charge controller (they come in 15 or 20 in this case). If you think you might upgrade your solar in a year or two, it’s a good idea to buy a larger controller in advance so that you don’t have to buy another one later.

In general, if you are getting 200W or less of power there isn’t as big of a need for a more expensive MPPT controller. You will benefit from it, but you’re not getting as much for the price.

If you are financially limited between 200W and a standard controller ($325 from Renogy) or 100W and an MPPT controller ($270 from Renogy) you will get significantly more power with the 200W standard controller option.

Still have questions? Comment below and let us know how to improve this article.

This Post Has 2 Comments

Leave a Reply

Your email address will not be published. Required fields are marked *

Back To Top