Essential Guidelines on Mobile Solar Power for RVs, Caravans, Campers or Boats

Yes, a solar power system on your RV or boat brings freedom, independence, and pleasure at weekends.

Also, it makes you look both ‘green’ and ‘cool.’ Indeed, if you have a motorhome, what’s wrong with adding solar panels on the roof and enjoy the free electricity?

Well, nothing’s wrong, but the devil is yet in the details.
Although not costing a fortune, installing a solar panel system on your RV is not cheap and takes time both to do the planning and install the hardware.

What size of solar panel system you need or whether you even need any, depends on your camping style.

This article presents the milestones of mobile solar power systems. Also, it’s not an attempt to talk you out of installing a PV system you might need. Instead, we are going to help you carefully weigh the pros and cons so that your mobile solar project turns into a successful investment.

Do You Need a Solar PV System?

Above all, you should never forget that in a mobile solar power system, the solar array is just an option to recharge your leisure battery.

Apart from the solar array, you can also have an external generator, a shore power source (‘hook-up’), or a vehicle alternator.

Here is a comparison of the various ways to recharge your leisure battery, rated by their powerfulness:

• Assumptions:
  • The output current of the solar panel forming a solar array is the optimum operating current Imp at 12V system voltage, which corresponds to about 18V optimum operating voltage Vmp of the solar panel
  • Since the maximum power of a standalone solar panel for 12V system voltage is in the vicinity of 150W, the cited above solar arrays consist of several 12V solar panels connected in parallel.

The conclusion is that a solar array on the roof of your RV or boat is the least powerful option to charge your leisure battery.

Here ‘the least powerful’ means the most time-consuming approach, which might turn into a problem in case of few PSH (Peak Sun Hours) available for charging the battery through the PV system.

As even in summer, PSH is limited, to prevent any nasty surprises from occurring, your system should be adequately designed.

As you know, the Peak Sun Hours (PSH) should not be mistaken with the available sun hours at a given location.

Depending on solar irradiance, the available peak sun hours at any location are usually less than available sun hours there.

You can learn more about peak sun hour and how to determine their value at your location in our article devoted to estimating the real energy you can get from your solar panels.

Indeed, there are some cases where you can do without a mobile solar power system just because, based on your camping habits, you don’t need it:

• You spend most of your time at RV parks with shore power nearby. Instead of using solar-generated electricity, you can power the devices in your RV by any electrical hook-up you have access to.
• You spend most of your time on the road rather than on campgrounds. As shown above, solar power is just one of the ways to recharge your leisure battery, and it is far from the most advantageous one. If you do much more driving than camping, then it would be smarter to recharge your RV battery either by your RV’s alternator or by installing a second alternator.

However, solar panels can exactly match your specific case. It can happen, for example, if you go camping at locations without access to electric hook-ups, and you stay there at least a few days. In such a case, a second alternator obviously won’t do much use, while a diesel generator would be a noisy and somewhat unclean solution.

Often it turns out that solar on RV does not make much sense unless you are an avid boondocker who likes camping far from any hook-ups.

If you usually camp at campsites, where hook-ups are common and affordable ($40 average hook-up fee per night), RV solar is a costly pleasure that is going to pay off soon.

Yes, solar panels on your RV’s roof give you freedom.

Yes, solar power is clean and quiet, does not need any fuel, and requires almost no maintenance.

But the issue is: will it help you save money or not? It is not cost-effective if you report such cost savings only after years of use!

Also, you should not forget that all the above mentioned various power sources for charging your leisure battery are not ‘ON’ or ‘OFF’ at the same time.

When driving, you are connected neither to shore power nor to the generator.

Thus, you have to use either the second alternator or the PV panels or both at the same time.

When you’re not driving in the daytime, you cannot use the second alternator.

However, you have all the other three options for charging available – an external generator, a shore power source (‘hook-up’), or solar panels.

At night, during quiet hours, you have the shore power only.

However, it does not matter – above all is your battery.

To power your appliances, you need your battery fully charged, no matter how.

Therefore, before starting with the design of the solar power system and components selection, you should make it clear to yourself how large solar power system you need.

It’s not only your appliances that matter but also how many of the other battery charging options you have available and for how long.

To charge your batteries by shore power, you need an inverter/charger rather than a pure off-grid inverter.

Such an inverter/charger might be capable of providing 100 amps of charge.

External diesel generators are an excellent option to charge your batteries. As these generators produce AC electricity, you need an inverter/charger or converter to supply AC power to the battery.

Smaller generators have a power output of between 2,000 and 2,500 watts (between 167 and 208 amps of charge).

They are ideal for powering large loads, such as air-conditioners and cooking appliances.

Still, you should mind that in case of high instant energy consumption, the remaining power for battery charging might turn out to be insufficient.

Using a fuel generator, however, is noisy and polluting. Unlike solar power, fuel is not free, so you always have to pay at least $1 per hour for fuel.

Furthermore, a fuel generator is always related to higher repair and maintenance costs than a solar power system.

Finally, there are places where running a fuel generator is restricted, especially during the evening hours.

Mobile Solar Components

In your RV, you have two kinds of devices – operating on AC power or DC power.

For example, your microwave oven, roof conditioner, hairdryer, and satellite modem operate on 120V AC power, while lights, various chargers, radio, and water pumps operate on 12V DC power.

If you don’t have any other option to power your AC devices, you need an AC power hook-up available at campgrounds.

Alternatively, if you have a DC power source, you can connect it to an inverter to convert the DC power into AC power.

As to 12 V DC, you can get it from your leisure battery, which should be regularly recharged.

Of course, you can also use your car battery, but it is not advisable unless you have to power a tiny device for a short time.

Car batteries are not designed for regular deep discharges and recharges.

Typically, a mobile solar power system comprises the following components:

• Solar panels – they act as a solar power generator.
• A solar battery – it’s your leisure battery, which is designed for deep cycle operation. It is different from your automotive battery.
• A charge controller – the battery manager.
• An inverter – to power your AC devices. Note that your RV might already have an inverter.

Solar Panels

Solar panels are one of the main components of a solar power system. According to their type of production, they are crystalline (monocrystalline or polycrystalline) or thin-film.

If your roof space is limited, crystalline panels are the preferred option. According to mobility, they can be fixed-mounted or portable.

According to rigidness, they can be standard or flexible.

While for residential photovoltaic systems standard (rigid) solar panels are used, in a mobile solar power system, they can be either standard or flexible.

Standard PV panels are more efficient (they produce more power per unit of area) and more durable.

Typically, they are more expensive than flexible solar panels and come with a warranty.

Flexible solar panels do not have these advantages (they are thin-film ones, unlike rigid panels that are crystalline ones), but they are thinner and can bend over curvatures, which is a benefit if you don’t have enough flat space on the roof.

The advantage of thin-film solar panels is their lower cost compared to crystalline panels and the flexibility ability to bend over shapes, which are typical for most RVs.

Another advantage is their better performance at higher temperatures.

Also, unlike mono- and polycrystalline panels, thin-film panels are not fragile and can withstand higher mechanical loads.

Due to their low efficiency, however, they are much more rarely used than crystalline PV panels except in cases where available space is not an issue, which is uncommon in mobile solar power systems.

For mounting the solar panels, flat mounts (also known as ‘flush mounts’) are recommended for most RV or boat solar power systems.

Also, tilting mounts are reported to gain an increase of 10-15% in the solar-generated power.

Climbing on the roof and manually setting tilts, however, is quite a hassle.

What is more, tilting panels is pointless if you spend most of your time on the road.

On the other hand, if you have managed to park your RV in full sunlight, with no nearby obstacles and the roof facing South (or North, for Australia, New Zealand, or South Africa), you might turn out not to need this 10-15%.

Anyway, regardless of whether you intend to provide an optimal tilt to the solar array, a tilt of at least 5 degrees is okay just to prevent water from standing on the panels after it has washed any dirt and dust away.

Also, you should mind the additional costs of such a tilting mount and that the wind loading of the roof increases.

When camping, you can fortify your installed solar power by using additional external portable solar panels.

Since these panels are lightweight and designated for mounting on the ground, they can easily be tilted and pointed directly out to the sun.

By doing so, you can squeeze the maximum power from the sun.

  You can learn more details about solar panels for RVs

You can discover even more practical info in our bestselling ebook and paperback book Off-Grid Solar and RV Solar Power For Everyone .

Solar Charge Controllers

The solar charge controller is responsible for managing the voltage provided to the battery so that the latter would not be exposed to overcharging or over-discharging.

Since the output voltage of the solar array can vary, while the battery voltage is fixed (6V, 12V, or 24V DC), the solar-generated voltage should be made equal to the input battery voltage.

There are two main types of charge controllers – PWM (‘Pulse Width Modulation’) and MPPT (‘Maximum Power Point Tracking’) ones.

PWM controllers are less expensive, but their MPPT counterparts are more efficient.

MPPT charge controllers ensure that the solar panels operate at the maximum voltage, thus being capable of ‘squeezing’ up to 30% more solar-generated power.

MPPT controllers are usually preferred in larger solar panel systems and higher solar array voltages.

You can learn more about solar charge controllers in our Definitive Guide to Solar Charge Controllers

You can discover even more practical info in our bestselling ebook and paperback book Off-Grid Solar and RV Solar Power For Everyone .

Solar Batteries

The solar battery, which in your RV is the leisure battery, should be deep-cycled.

Automotive or car-engine batteries cannot be used as solar ones, as they are not intended for frequent and deep (down to 50%) discharging and recharging.

In RV solar panel systems, either lead-acid batteries (AGM or gel cell ones) or lithium batteries are used.

AGM batteries are often regarded as the optimal solution for RV solar power, due to the initial high cost of lithium batteries.

Such a high price, however, always pays off sooner in the long term.

Although designed for multiple discharges, solar lead-acid batteries should be left to discharge more than 50% since their lifespan is severely shortened.

Therefore, a typical Depth of Discharge of 50% (80% for lithium batteries) should always be set among the initial conditions when you determine what battery size you need and how much solar-generated power you need to recharge it.

Determining the battery size is one of the essential milestones when designing a solar power system for your RV.

It is not, however, what you should start with.

Above all, you need to estimate how much electricity you need per day while camping.

Your daily energy use is based on which devices you use every day and for how long. It is called ‘load analysis,’ and shows how ‘large’ photovoltaic system with how ‘big’ components you need to cover your daily electricity needs.

In general, batteries for RV solar (leisure batteries) are similar to batteries used in residential solar power systems – they are deep-cycled rather than engine-starting ones.

Yet, they are placed in a different environment, as in an RV or boat:

• Space is limited,
• Extra weight is an issue, and
• Shocks and vibrations are frequent,

While safety remains a must. For these reasons, standard flooded lead-acid batteries are not recommended.

Instead, AGM and lithium batteries are commonly used.

There are two types of batteries commonly used in RV and marine solar power systems – lead-acid and lithium-ion. Sealed lead-acid batteries can be AGM (Absorbed-Glass-Mat) or Gel.

AGM batteries are more recommended and more widely used than gel ones.

Below you can find the essential pros and cons of the most commonly used battery types in solar power systems.

(Traditional) Flooded lead-acid batteries:

• Are the cheapest option. However, they are not recommended for mobile solar power systems due to safety reasons – the ones mentioned above + vulnerability to shock and vibration.
• Are large and heavy and should not be discharged under 50%.
• Need regular maintenance.

AGM batteries

Advantages:

• Lower cost than lithium batteries.
• Can withstand shocks and vibration.
• More efficient than traditional lead-acid batteries, but twice as expensive.

Disadvantages:

• Larger and heavier than Li-batteries.
• Cannot be left uncharged for a long time.
• Lower performance at low temperatures.

Lithium batteries

Advantages:

• Lightweight (twice less than lead-acid)
• Maintenance-free
• Smaller
• More efficient
• Can be recharged much faster than lead-acid ones.
• Can be left discharged for a longer time.
• Safer – there is no gassing during charging, so a lithium battery can be put inside a living space without fear of spilling acid.
• Have a four times longer lifespan than lead-acid batteries.

Disadvantages:

• Cost 5 times more a lead-acid battery, although a good investment in the long term.
• Need a Battery Management System.
• Need a charge controller supporting a ‘lithium battery mode’ during battery charging/discharging. Most of the charge controllers don’t have such a mode, and if you want to switch from a lead-acid battery to a lithium one, you have to consider the possible replacement of your existing charger controller.

You can discover even more practical info about solar batteries and their usage in our bestselling ebook and paperback book Off-Grid Solar and RV Solar Power For Everyone

Solar Inverters

You need a solar inverter if you are to power AC devices and appliances in your RV or boat.

An inverter converts the battery DC voltage into 120V or 240 V AC voltage.

The inverter can be either standalone or integrated into the solar panel system.

A standalone inverter will do if you need to power some small devices, such as a phone charger or a laptop.

Otherwise, you should use an inverter that is a part of the PV system and should be sized and selected along with the other system components.

Particular attention should be put on inverter/chargers. An inverter/charger is used not only to power all the AC devices in an RV, but also to charge the battery from a power source other than the solar panels.

Such a power source can be a fuel generator or shore power.

In such a case, the inverter/charger acts as a power converter or a battery charger rather than as a solar inverter.

When you go to a place with no power hook-ups, and you don’t have an AC generator, the inverter/charger will act as an inverter.

It will convert the solar-generated electricity stored in the battery into AC electricity. Since the output power of the inverter/charger is limited, some planning is also needed.

During the ‘load analysis’ (discussed below), you should consider the power-hungry AC devices you use, such as microwave ovens, driers, and, above all, air-conditioners, which need a large amount of energy over a relatively long period.

Please, have in mind that the right selection of the power of inverter/charger is crucial to your user experience.

For example, an underperforming inverter/charger may cause the power to drop out for a second or two, while the unit switches between different power modes, i.e., inverter, generator, or shore power, in the presence of high-power load. If you have electronic equipment that requires an interrupted power supply (UPS) or an internet connection, the constant switching might cause big trouble.

Another option to benefit from shore power is to use a converter that converts AC to DC electricity and is much less powerful than an inverter/charger, in terms of being able to deliver just half of the inverter/charger’s charging current.

You can discover even more practical info about solar inverters and their usage and proper selection in our bestselling ebook and paperback book Off-Grid Solar and RV Solar Power For Everyone

The Devices You Use in Your RV, Motorhome, Camper or a Solar Powered Boat

The load analysis is a vital stage. Otherwise, you might end up with either a system unable to cover your regular power needs or an unnecessary big and costly system you don’t need.

Both of these can ruin your pleasure of a couple of days or weeks spent somewhere in the open.

After summing the power (in Watts) and the time of the devices you use daily, you get the total electricity you need per day (in Watt-hours).

Such daily energy use will determine the size of the battery (in Amp-hours).

Here you should decide what battery type to buy based on how much space and money you have available.

Most devices used in RVs or boats operate on 12V DC:

Many devices, however, operate on AC power, and what is more, some of them are known as ‘power-hungry’ ones:

If you don’t feel like doing some maths for load analysis, there is another way to do that, based on practice.

First, you should get your leisure battery fully charged. Then you should go camping just for a day or two, to find out how long your battery can support your devices you use while camping, provided that you use them as usual – neither overuse them nor limit yourself.

Once you have calculated the battery size, you can estimate the size of the solar array to get your battery fully charged every day. And here comes the solar system size.

How Big Mobile Solar Power System Do You Need?

When talking about solar panels of the roof of an RV or boat, space is always an issue.

A smart way to start your mobile solar project would be to install as many solar panels on the roof as possible.

Then you can base all the following milestones on these panels and the solar-generated power you will eventually get – battery type and size, charge regulator, and daily electricity usage.

However, this is not the only approach – another way is to start from your leisure battery and then estimate how many panels you need to charge the battery.

The third scenario is to start from your daily power use, then calculate what battery size you need.

Next, you should estimate how much solar installed power you need and, finally, you should search for solar panels that will fit this target.

In all cases, however, you should perform the system sizing to see whether:

• you have enough space on and in your RV,
• the system will be capable of covering your daily needs, and
• your budget will be enough to implement the PV system.

How many solar panels and what battery size you need depends above all on how much energy you need daily.

However, to do the maths correctly, you also need to know:

• Peak Sun Hours (PSH) value at your camping location and how efficient your solar power system is, in terms of component losses and inefficiencies.
• Your leisure battery type (lead-acid or lithium), how long it can be left without a charge (also known as ‘Days of Authonomy’ or DoA), and how deeply it can be discharged (also known as ‘Depth of Discharge’ or DoA).

For the below calculations, we assume PSH=4.5 and System Efficiency=0.7.

Also, we assume a commonly used AGM lithium acid battery (DoD=0.5), and we choose DoA=2.

Let’s start with an ultra-slim mobile solar configuration. For example, let’s assume you use just a couple of small devices, such as:

In such a case, you need 10-15 Wp installed solar power and a 10Ah battery for 12V system voltage, or, you can even do without a battery.

If you decide to take a laptop and a camera, you have:

In this case, you need 50-100 Wp installed solar power (one or more solar panels), a 50-100 Ah battery for 12V system voltage, and a 10 A PWM or MPPT charge controller.

Okay, let’s add some more appliances. Here is an example of a somewhat ‘moderate’ energy usage while camping:

Here you need panels of 200-300 Wp, a 150-250Ah battery for 12V system voltage, a 30A MPPT charge controller.

For the satellite modem or any other AC appliances you are going to use, you also need an inverter of 1,500-2,000W output power.

What you need here is 400-500Wp solar power, a battery of 300-400Ah for 12V system voltage, a 40A MPPT charge controller, and an inverter of 2,000-3,000W output power.

Some photovoltaic panels are said to be ‘shade-tolerant.’

Above all, however, you should remember that the power output of any solar panel is either reduced or cut off when that panel gets shaded.

A ‘shade-tolerant’ panel does not mean that you can afford to install such a solar panel somewhere in the shade and expect a well-performing solar system.

Instead, ‘shade-tolerant’ means that when the panel is partially shaded, it will still produce some solar-generated power, since each solar cell is provided with diodes bypassing (‘shunting’) that cell when it gets shaded.

A shaded cell, however, means reduced voltage per that cell, and if a couple of cells are eliminated in such a way, the total voltage fall below 13.5 volts (instead of the rated 17-18V), which are not enough to charge the battery.

Often RV or boats come with solar panels of low wattage. Such solar panels can be capable of recharging your leisure battery, but the recharge will take much longer than by a dedicated RV solar power system – days or even weeks.

The purpose of such ‘built-in’ solar panels is to prevent a full battery discharge rather than to provide a regular daily recharge.

Also, you should not forget that the wires coming with these panels are not designed to stand higher much power and current that a typical RV solar system would provide – the gauge is much smaller than needed!

If it is hard to find, for example, a single 12V-battery of 200Ah, it’s practically the same if you connect two 6V-batteries in series to obtain a battery voltage of 12V. Or, if you connect two 12V batteries of 100Ah each in parallel to get a total capacity of 200Ah.

The most important is to use a true deep-cycle battery as a leisure one and to have enough room to connect two (identical) batteries in series or parallel.

You can discover even more practical info about the sizing of RV solar power in our bestselling ebook and paperback book Off-Grid Solar and RV Solar Power For Everyone !

The book is written for the audience with no prior electrical experience in mind.

Get the book Now !

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Lacho Pop, Master of Science in Engineering

Lacho Pop, MSE, holds a Master's Degree in Electronics and Automatics. He has more than 15 years of experience in the design and implementation of various sophisticated electronic, solar power, and telecommunication systems.  He authored and co-authored several practical solar books in the field of solar power and solar photovoltaics. All the books were well-received by the public. You can discover more about his bestselling solar books on Amazon on his profile page here: Lacho Pop, MSE Profile

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