Green Energy on Board - Solar Power for your Boat

Green Energy on Board - Solar Power for your Boat

Find out everything about solar panels and how to install them correctly on your boat in this guide. Discover where to put them and how to choose the right solar panels for sailing and motor boats in our online guide to photovoltaic systems on board. It contains all the important information about charge regulators and other components, plus information on relevant cables and connection. We hope you will find it useful so that you too can harness the power of the sun!

What are the components of a solar energy system ?

To produce electricity from the sun, one or more solar cells are needed. A solar panel is comprised of several individual solar cells that are connected together to generate power.

The way a solar system works is, in fact, very simple. As soon as light hits the panel and activates it, the cells produce electrical current. The voltage and amount of current produced depends on the amount of light captured.

In addition to solar panels, a PV system also includes a solar charge controller or charge regulator. Its job is to regulate the current flowing from the solar panel into the on-board network in such a way that the batteries can be safely charged by the solar system on board.

Components of a solar system

How much electricity does a solar system produce?

Before installing a solar system, you must first know about the factors that can determine the amount of electricity that is produced. This depends on several things: First and foremost is the sun. Without sunlight, the solar cells on board your vessel cannot produce any energy. At midday, when the sun is at its highest, the most amount of energy possible is produced.

Electricity from a solar system

However, the angle of the sun's rays can also influence how much energy a solar system can produce. In the Northern Hemisphere, the sun will be in the south at midday, in the Southern Hemisphere, it will be in the north, and on the equator, it is exactly above the boat at midday. So , when sailing in the Northern Hemisphere remember the following:

If you tilt your solar panels so that they are facing slightly to the south, your solar system will produce more electricity than if it is oriented to the north. Of course, on a moving boat it won't always be possible to perfectly align your panels, especially if it is either swinging at anchor or when sailing against the wind. Therefore, a common compromise is to mount solar panels horizontally, so that at least some light is captured from all directions. A more effective way is to use active tracking to orient panels towards the sun. The increased energy that is generated by active tracking means fewer panels are needed, which takes up less surface area space and reduces costs.

The second important factor that can influence the amount of energy produced is the size and quality of the solar system itself. The amount of energy that can be generated is dependent on this. The maximum peak power of a photovoltaic installation under ideal conditions is expressed in watt peak (Wp) (see FAQ below).

As we have seen, the energy produced not only depends on the amount of light the panels can absorb, it also depends on the quality of the panels used. However, choosing the right type of wire is also crucial to its operation and efficiency. Using the wrong type and size of wire might result in power losses. Similarly, the type, size and age of battery and charge controller also determine energy yield.

When does a PV system produce (the most amount of) energy?

Solar modules generate energy most effectively when the sun is exactly 90 degrees to them. On the equator, when the midday sun is directly above the boat, the amount of radiation on the earth's surface is also significantly higher than, for example, at midday in the Arctic Circle. There, the sun only peaks at 45 degrees a few days a year.

Using movable solar panels can compensate for this to a certain extent. Even if these usually have to be manually adjusted to the position of the sun, it is worth it! Installing small movable panels can be much more effective than a larger, stationary panel on deck, and is especially useful when there is little space available. Even better is to mount solar panels along the rail on the pushpit or on an equipment carrier for solar cells above the cockpit:

This is because panels that are mounted flat on the deck will always be subjected to some slight shading from the mast, sails and rigging. The loss of power through even partial shading is bad for PV systems. Slight shading can reduce the voltage in a solar panel to such an extent that it can reduce the output to almost zero. Although manufacturers usually provide some reserve to compensate for partial shading of a few cells, the shadows of two or three halyards running across a panel can be enough to compromise the output of the whole panel. In this case, no more electricity will be generated at all. It is therefore particularly important to pay attention to the correct mounting location of the solar panels.

Shading of a solar system

Tip for globetrotters: The classic 'Barefoot' route usually runs from east to west, slightly north of the equator. The sun there usually peaks in the south. Foldable solar panels on the port side rails therefore facing south during the long legs of the journey heading west will get more sunlight there than on the opposite side of the cockpit. When going south of the equator, however, the opposite is true.

How sailing area can impact on type and size of a PV system

It is easy to understand how the angle of the sun's rays can affect the yield of your on-board solar cells by looking at the light emitted by a simple torch: Let's assume that the torch (the sun) emits the same amount of light constantly. If you shine it vertically onto a tabletop, you can clearly see the cone of light. Now, shine it at an angle of 45 degrees at the same distance and the light cone will become oval and its area larger. At the same time, the light cone also becomes somewhat darker. This is because the same amount of light is distributed over a larger area.

The same principle also applies to the sun on the earth. The more directly the sun's rays hit the solar cells, the more energy per square centimetre will reach the solar panels on the boat.

Therefore, the closer you sail to the equator, the greater the yield and subsequent energy output of the solar panels, and at higher latitudes, the sizing of the PV system should be adjusted. This is because at the equator, the sun is at its highest peak at noon. Nevertheless, it is also possible to get a good yield from panels in higher latitudes. As described, this can be achieved using trackable panels. The sun may not shine as intensively there, but it does shine for up to 20 hours a day in the summer. You should also consider seasonal climate factors. During the rainy season in tropical regions, the amount of energy absorbed is significantly lower than on a clear sunny day in Europe.

What are the ideal properties of a solar module for boats?

Solar panels installed on deck are subjected to particularly high amounts of stress. They are in permanent contact with salt water due to sea spray. All connections, screws, and the solar panels themselves must therefore be well protected against corrosion for use on board. There is also always a risk that they could be walked on accidentally. Solar panels on board should therefore ideally be walkable, and firmly supported underneath so that a falling shackle from the masthead will not damage them.

The weight of a solar panel is also important, especially if they are mounted on equipment racks on the stern or rails. Another important factor to consider, is that solar panels are more effective when they are cool. For this reason, make sure mounting brackets ensure good ventilation from below, especially if your sailing route will be in tropical areas.


  • ! Protect all connections and contacts from corrosion with heat shrink tubing and insulating tape.
  • ! Only install impact and shock-resistant modules on deck
  • ! Protect panels from storm and sea water by reinforcing supports and brackets.

What are so-called plug & play PV modules?

The simplest type of solar system on board is a complete set with 12V solar panels. These sets include an integrated solar regulator.

Buying one of these sets is the easiest way to start using the sun's energy to supply power to your boat. All you need to do is place them next to the device on deck or in the cockpit and power it directly.

There are also larger versions of these types of plug 'n' play PV modules that can be used to charge your boat battery itself. These plug-and-play systems are particularly popular on boats that do not have shore power at berth or that are attached to a mooring buoy. Here, a plug & play solar cell can maintain the charge of your on-board battery, even when no one is on board and is simple to install.

What can solar power be used for on my boat?

In general, the electricity created by a solar panel can be fed into the on-board network via the regulator and then used by any consumer. Solar energy must be used straight away, since the PV system itself does not store electricity. This is done by the batteries, and is the only way to be able to use this power later for lights or similar devices on board.

Usually, the standard consumer battery or a rechargeable on-board battery bank is used, and serves as backup for times when less energy is produced or many devices are activated. This way, the on-board network is supplied with a constant flow of power and makes solar energy available for use at night too.

All battery types on board can be charged with solar power. The crucial element is always the charge regulator. It must be adapted to the respective charging voltage of the existing battery. In addition to acid batteries, AGM, gel or even ultra-modern lithium batteries can also be charged on board with solar power without any issues. However, if different battery types are to be charged in separate battery banks, each of these battery banks needs its own separate charge controller.

How large does the PV system for my boat need to be?

  1. First of all, it is important to determine what you want your system to do. If you only want to keep charge at your berth, a single small plug-and-play module is usually sufficient. It can be mounted on cabin roofs, bimini tops or just lying flat in the cockpit. These mobile solar devices for boats are also suitable for charterers going from bay to bay.
  2. Expand your system one step further and increase your boat's operating range. With one or two flexible modules on deck, your battery life at anchor or on a cruise can be significantly extended by several days. It usually won't be enough to make your boat completely self-sufficient with solar power, however, if you have no large consumers on board and keep a few tricks in mind, you can manage without shore power for a few days.

Tip: You can save energy by placing frozen cooked food (for example a roast chicken or similar) inside your cooler, then setting the temperature to 8 degrees instead of 4 C. It will slowly defrost over the course of the day and saves the cool box from having to work so hard to achieve the desired cooling effect.

To extend battery life, complete solar sets are also suitable, and are simply mounted on board and connected to your on-board battery via the included charge controller. These are often offered, somewhat misleadingly, as 12V solar cells.

However, if you want to make your boat completely self-sufficient with solar power, detailed planning is important. This involves determining how much electricity you will need on a daily basis, by analysing all electrical consumers and their operating times. After this you can calculate the power of the required solar modules. This will also depend on the technology used in the solar cells, and should be considered.

What types of solar panels are available for boats?

Solar cells may look similar at first glance, but there are actually significant differences between them. Different efficiencies can be achieved depending on the type of solar cell installed.

Solar panel efficiency is the ratio of the panel area and its output. Only the part of the module that is covered by solar cells is used in the calculation, not the entire surface of the module. These values are determined under lab conditions and makes it possible to compare the quality of different modules. It is a way of indicating the quality and purity of the solar cells used, and not the maximum amount of electricity a solar panel can generate.

The structure of the individual solar cells determines the properties of the entire solar module: Classic solar cells are based on silicon semiconductor. The raw material is melted down and either pulled into rods or cast into blocks when it hardens. The blocks or rods produced in this way form the basis for monocrystalline or polycrystalline solar cells.

Pulling is a technique used to grow a continuous, uniform crystal. This creates a monocrystalline structure. The rods are cut into slices and then connected to form solar cells.

Monocrystallin e silicone is very conductive due to the diamond lattice structure in the crystal and the even edges with a uniform structure make it easy to produce large areas. This type of solar cell can achieve an efficiency of over 20 percent. In fact, in most monocrystalline solar panels, average efficiency is only just below 20 percent.

Another process involves pouring liquid silicon into a block and allowing it to harden there. The block is then also cut into slices and made into solar cells. But hardening in this way does not create a uniform structure. In the block, multiple crystals grow in different directions to form a polycrystalline structure.

Polycrystalline silicon is much easier to produce, which is reflected in the price and in turn makes them popular with customers looking to install solar panels on a budget. However, the efficiency of polycrystalline silicon is lower because they contain multiple silicon cells, which means the electrons cannot move as easily. Constructing larger surfaces is also more complicated because there is no uniform structure. Polycrystalline solar cells have about three percent lower efficiency than monocrystalline solar cells. One way to compensate for this disadvantage is to place the current contacts on the back of the cells, which results in more surface area on the front side to generate electricity.

Something that all silicon-based solar cells have in common is that they have a rigid crystal structure. However, newer technologies, such as amorphous cell types, are also booming. These solar modules, also called thin-film solar cells, are used particularly often on board:

Thin-film solar modules are based on artificial semiconductors, for example from the compounds copper-indium-selenium (CIS modules) or copper-indium-gallium-selenium (CIGIS modules). The major advantage of these modules is that, as they are flexible solar modules, they are not rigid and can thus also be mounted on uneven surfaces, for example fibre glass surfaces on the deck of a yacht. Depending on the model, these can also be walked on. On the flip side, amorphous modules usually have a significantly lower efficiency of 16% at most, often only around 14%, and are somewhat heavier than silicon-based cells with the same surface area.

Nevertheless, if space on board is not limited and more panels can be installed over a large area, this compromise can be advantageous.

The technical development here, however, is far from over. Research is currently being carried out on different types of cells for flexible solar modules, in which organic materials are used in amorphous cells in order to be able to utilise a wider spectrum of sunlight. In the future, it may even be possible to use whole entire sails to produce electricity on yachts. These cells and so-called hybrid cells, which contain crystalline and organic components, have already achieved efficiencies of over 40 per cent in laboratory tests, but they only have a short lifespan.

The current drive towards sustainable energy has significantly boosted development in the solar sector over the last ten years, and the effectiveness of conventional solar module types continues to be significantly improved.

Which solar module is the best?

Choosing the most suitable module depends mainly on where it is to be mounted. If installation must be on deck (the least favourable location), it’s worth considering semi-flexible thin-film solar modules. These can be adapted to fit the slight curvature of your cabin roof, for example, and are usually also walkable. This is particularly important on sailboats, e.g., when rigging the boom.

Installation of a solar system

However, if it is possible to mount the module flat, for example on an equipment rack, then rigid modules with aluminium frames and a monocrystalline structure are an obvious choice. The same applies to the roof of your navigation area. Solar cells generate heat as well as electricity, so the better ventilation they have from below, the more effectively they function.

Installation of a solar system

On-board consumption

The solar power system on your yacht should be based on the total energy requirements on board. Only then can the required output of the solar panels be calculated.

1. To do this, first create a simple table listing the consumption of all appliances over a 24-hour period. It is important to consider the respective operating times: A chart plotter with 0.8 amps consumes much more electricity in 24h than a pressurised water pump with 8 amps, which is only used for a total of two minutes a day. At the end of the table, add up the total consumption to find the minimum amount of electricity needed per day. Typical values for modern cruising yachts are often over 60A/day depending on the equipment

2. In a second table, list all the generators and think about how they are used: If, for example, the engine is started every morning at anchor to produce hot water for a shower, the alternator will also charge the battery bank during this time (30 min x 40 A already means 20 Ah). In the end, there will be a difference between consumption and production. This is the amount of electricity that the solar system will have to generate in order for the boat to become self-sufficient. In the example, this is 40A per day.

Consumer Number Individual power consumption Total power consumption Voltage Amperage Time in use / Day Time in use / Day Wh/Day Ah/Day
Navigation light, green 1 20 Watts 20 Watts 12 V 1,67 A 5 min 0,08 h 1,67 Wh 0,14 Ah
Navigation light, red 1 20 Watts 20 Watts 12 V 1,67 A 5 min 0,08 h 1,67 Wh 0,14 Ah
Stern light 1 20 Watts 20 Watts 12 V 1,67 A 5 min 0,08 h 1,67 Wh 0,14 Ah
Masthead light 1 20 Watts 20 Watts 12 V 1,67 A 5 min 0,08 h 1,67 Wh 0,14 Ah
Anchor light 1 10 Watts 10 Watts 12 V 0,83 A 480 min 8,00 h 80,00 Wh 6,67 Ah
Deck lights 2 20 Watts 40 Watts 12 V 3,33 A 120 min 2,00 h 80,00 Wh 6,67 Ah
Search light 1 100 Watts 100 Watts 12 V 8,33 A 10 min 0,17 h 16,67 Wh 1,39 Ah
Chart table lights 1 10 Watts 10 Watts 12 V 0,83 A 20 min 0,33 h 3,33 Wh 0,28 Ah
Saloon lighting 6 20 Watts 120 Watts 12 V 10,00 A 240 min 4,00 h 480,00 Wh 40,00 Ah
Galley 2 20 Watts 40 Watts 12 V 3,33 A 120 min 2,00 h 80,00 Wh 6,67 Ah
Cabin 2 20 Watts 40 Watts 12 V 3,33 A 120 min 2,00 h 80,00 Wh 6,67 Ah
Compulsory lighting 2 20 Watts 40 Watts 12 V 3,33 A 240 min 4,00 h 160,00 Wh 13,33 Ah
GPS 0 2 Watts 0 Watts 12 V 0,00 A 0 min 0,00 h 0,00 Wh 0,00 Ah
Plotter 1 8 Watts 8 Watts 12 V 0,67 A 0 min 0,00 h 0,00 Wh 0,00 Ah
Radar 1 50 Watts 50 Watts 12 V 4,17 A 0 min 0,00 h 0,00 Wh 0,00 Ah
Radio communication 1 5 Watts 5 Watts 12 V 0,42 A 120 min 2,00 h 10,00 Wh 0,83 Ah
Notebook 1 40 Watts 40 Watts 12 V 3,33 A 120 min 2,00 h 80,00 Wh 6,67 Ah
Windlass 1 500 Watts 500 Watts 12 V 41,67 A 0 min 0,00 h 0,00 Wh 0,00 Ah
Bow thruster 1 2.000 Watts 2.000 Watts 12 V 166,67 A 0 min 0,00 h 0,00 Wh 0,00 Ah
Water pump 1 40 Watts 40 Watts 12 V 3,33 A 10 min 0,17 h 6,67 Wh 0,56 Ah
Refrigerator 1 50 Watts 50 Watts 12 V 4,17 A 240 min 4,00 h 200,00 Wh 16,67 Ah
Bilge pump 1 25 Watts 25 Watts 12 V 2,08 A 0 min 0,00 h 0,00 Wh 0,00 Ah
Shower pump 1 25 Watts 25 Watts 12 V 2,08 A 20 min 0,33 h 8,33 Wh 0,69 Ah
WC 1 100 Watts 100 Watts 12 V 8,33 A 10 min 0,17 h 16,67 Wh 1,39 Ah
Radio 1 25 Watts 25 Watts 12 V 2,08 A 240 min 4,00 h 100,00 Wh 8,33 Ah
Other 1 20 Watts 20 Watts 12 V 1,67 A 0 min 0,00 h 0,00 Wh 0,00 Ah
Total = 3418 Watts = 284,83 A = 1608,33 Wh = 134,03 Ah

In northern Europe, you can expect effective solar radiation for about eight hours a day in summer. The PV system must therefore generate 40 amps of electricity in 8 hours (40A / 8h = 5A/h). In a 12V electrical system, 5 ampere hours correspond to 60 watt hours (12V x 5A/h = 60Wh).

A common mistake is to assume that a 60 Wp solar panel can produce the required amount of electricity in just one hour of midday sun. However, this 60 Wp peak output can only be reached under ideal conditions (see FAQ), which would most likely be the case in a refrigerator in Morocco! In reality, even on a sunny day in northern Europe, a photovoltaic system often delivers less than half of that. It therefore makes a lot of sense to plan with at least 50% more power in mind. Also, the amount of energy produced rises slowly in the morning and falls slowly in the evening. Therefore, one should not assume the same yield over the entire 8 hours.

Storing the electricity created by a PV system

The charge controller

It isn't possible to connect a PV system directly to a battery, as the voltage they produce is usually much higher than the one used in the on-board network. This is where a charge controller (or solar regulator) comes into play. It is used to adapt the current to that of the vessel's electrical system - a pretty important function!

The cheapest types are PWM (pulse width modulation) charge controllers. Here, only the voltage (pulse width) of the charge is adapted to the battery voltage in order to prevent it from overheating. Taking the example of our 60 watt solar panel from earlier, let's assume that it can generate 30 volts of power and a maximum of 2 amps of charging current: 60W / 30V = 2A

A PWM regulator now limits the voltage to 14.8 volts charging voltage for an ordinary car battery. However, the 2 amps of charging current remain and are fed into the battery. Thus, a maximum of 14.8V x 2A = 29.6W of power reaches the battery. - Half of the generated energy would therefore be lost to the charge controller under ideal laboratory conditions. In reality, more like 10-15 watts remain, i.e. just under 1 ampere of charging current. The desired 40A cannot even reach the batteries in this way in a whole day.

However, in most other cases, it's better to use an MPPT charge controller (Maximum Power Point Tracking). These types of regulators use the full power of your solar panels to charge your batteries, by first transforming the entire amount of energy to that of the on-board network and then feeding it into the battery bank. In the example above, this also means 14.8 volts but a full 4A of current under laboratory conditions (60W / 14.8V = 4.05A). In reality, a few percent are lost again for the transformation and the capacity achieved by the panel is lower than in lab conditions. Nevertheless, under the same conditions, 2-3 amps at midday are realistic here. This means that with an MPPT controller it should just about be possible to get to 40 Ah on a very sunny summer's day, provided that tracking is used and the sun is shining for a long time. Given the example, it's clear to see how MPPT controllers are superior to PWM regulators. It is important to note that charging a battery always requires a higher voltage than the battery voltage itself. With MPPT controllers, this is usually around 5 volts more so that the transformation can take place. So in our example, the solar system must first reach 20V before anything is charged at all.

The battery / power bank

The amount of information about the type and size of battery bank is enough to fill a separate guide. What's important however, is that when operating a PV system, the boat batteries used must have high cycle stability (this refers to how often a battery can be charged and discharged), as they will be constantly loaded during the course of the day.

Your charge controller will also determine the type of battery. That said, better charge regulators can be adapted to the different characteristics and charge voltages of various battery types.

Installing a solar power system

What do I need if I want to install a photovoltaic system on board?

Installing a 12V solar system is relatively simple: mount the panels and charge controller according to the instructions and connect everything with the appropriate cables. You can build the brackets for the solar panels on board yourself, or you can use the manufacturer's mounting kits. Bear in mind that brackets should be designed so that modules do not break off, especially in the case of heavy waves and strong winds on equipment racks. In addition to technical know-how, there are also a few points to consider when setting up a solar system:

Solar power systems feature powerful voltages. Voltages between the solar charge controller and the solar panel are even higher than in the rest of the on-board electrical system.

Even if you know a great deal about on-board electricity, you should be particularly careful when calculating cable cross-sections. Voltage and amperage also vary depending on the manufacturer and type. Therefore, you should always install the same models, or understand the difference between series connections (voltage is the sum, current is the same and corresponds to the weakest panel) and parallel connections (voltage corresponds to the panel with the lowest voltage, but total current is the sum) and which type makes sense or could be dangerous. If you aren't sure, leave mixed installations in which different solar modules are connected to a professional.

You should also avoid lengthy cable runs. In general, it is better to install the charge controller close to the battery and the longer cables in the part with the higher voltage, i.e. between the panel and the charge controller. This also helps to reduce the required cable cross-sections for deck feed throughs. It is best to connect the solar regulator (charge controller) itself directly to the battery with its own fuse. Going through the battery will also ensure that not too much current is drawn when consumers with higher consumption in the on-board grid are switched on.

It is best to connect the solar regulator (charge controller) itself directly to the battery with its own fuse. Going through the battery will also ensure that not too much current is drawn when consumers with higher consumption in the on-board grid are switched on.

Parallel connection

In any case, the panels used determine the necessary specifications of the charge controller. The power specifications of the regulator usually do not refer to the vessel's electrical system. So, if a regulator is marked with a maximum of 100V/6A, this does not mean the maximum current that can be supplied to the on-board network! The specifications can be understood as follows: The current from the solar panels must not exceed 6 amps and the voltage of the solar modules must not exceed 100 volts. These values must be observed above all when several solar panels are connected. Because connected in series, their voltage is added up; connected in parallel, the amps to the charge controller are increased.

Can I install several solar panels on board?

If space is available, it's worth installing several panels. When connected correctly, this will also reduce the likelihood of breaks in power if, for example, one panel is shaded by the mainsail.

The charge controller will usually only need a few volts more power from the solar panel than in the on-board network in order to start charging. With MPPT charge controllers this is about 5 volts, with PWM solar controllers 1-2 volts more are already sufficient. Since solar panels are rarely orientated perfectly, especially on board, it is worthwhile connecting several panels in series in order to add up the voltage of the individual solar modules. For example: three modules with a maximum voltage of 20 volts are installed, and even under cloudy conditions they generate a few volts of power. Each individual solar module might only supply 6 volts. However, connecting them in series raises the voltage to the charge controller to 18 volts and it can feed the power generated into the battery. With four panels, the charging process already begins when each individual solar panel delivers 4.5V. - Even if this is only a few ampere hours in total, it is better than nothing. As long as cable cross-sections and power of the charge controller are adjusted, an infinite number of panels can be connected in series. The only limit is space on board.

But remember: In the middle of the day, the voltage in this series connection can climb as high as 60 volts. Consequently, the charge controller must also be designed for a voltage of 60 volts. Such an installation therefore makes sense mainly when combined with an MPPT solar controller, which can also make use of the high voltages.

If panels are connected in parallel, however, the entire voltage goes through the module with the lowest voltage. So if the voltage drops below the battery voltage due to shading on an individual module, but not enough for a bypass diode (see FAQ) to trigger a cut-off, the entire charge will be immediately interrupted. In the above example, however, there is only 6 volts at all three modules anyway: On such a rainy day, the batteries would receive no current at all when connected in parallel.

Since current is accumulated when connected in parallel, the charge controller must also be sized appropriately to handle peak power in sunny weather. For three modules of 20 volts with 2 amps each, the charge controller must be designed for 20 volts with 6 amps.

Solar on bord

Where should I install a solar system on board?

Solar panels must be placed in such a way so that they are not shaded by the rig or other equipment. Good locations are on a pushpit or on the side of the cockpit by the rail. It's worth using movable brackets so that you can adjust the solar panel to the position of the sun. On the side of the cockpit, a hinged mount on a railing stanchion or pushpit is also a good option. This means that the solar panel can be adjusted during the day at berth or at anchor.

If you don't have enough space, a bimini is usually a good compromise, especially as the solar panels themselves can then be used as a source of shade. Of course, this is only possible if the boom is short enough and does not itself shade the solar panels.

The worst possible, but unfortunately also the most common, place to mount panels is on the cabin roof. It's tempting to mount them there because it's a nice, open space that is easy to work on, and it feels like a lot of sunlight can be captured. The reality is that part of the PV system there will almost always be shaded by the mast, sails or boom awning.

Such shading should always be considered when connecting your system. If you've installed several panels, you should use an MPPT controller. This is especially true if halyards running over panels can cast stripy shadows over the cells. If that is the case, your solar panel might as well just be there for aesthetic purposes only. It won't be much use to you and just result in high installation costs and low energy production, but at least it will look nice.

How and where can I fit the connection cables for solar modules and how do I get the cables below deck?

There are various types of accessories for on-board solar power systems, especially when it comes to feeding cables through to below deck. It is best to combine the supply lines of individual panels in a distribution box so that only one common cable leads to the charge controller below deck. Various splash-proof cable bushings and waterproof boxes are available for the wiring on deck, depending on the installation location.

Individual connection cables should also be routed on deck through electrical conduits or fixed cable ducts. This will prevent any boat hooks from accidentally getting caught on them and damaging the expensive equipment.

Sometimes a little creativity is needed when going below deck: for example, if two panels are mounted at the stern and two panels on the cabin roof: The solar panels at the stern are then best connected together above and routed as a common line through a locker to the charge controller near the battery. From the cabin roof, it is worth choosing a route along handrails under the sprayhood or towards the mast. There may already be cable ducts below deck that can be used.


What are bypass diodes and what is hotspot protection?

If solar panels are partially shaded, dirty or even defective, the solar system won't be able to function properly. Manufacturers of solar modules have come up with a solution to this problem in the form of so-called bypass diodes. They bridge parts of the panel if one solar cell in it delivers less current than the others. Without this bridge, the voltage in the entire panel would drop. This way, however, the rest of the panel can continue to produce (reduced) electricity. Depending on the manufacturer and size, 2-4 areas in a solar module are usually separated from each other.

However, as electrical components, these diodes are quite sensitive to strong overvoltage. This can be caused, for example, by thunderstorms with lightning strikes nearby, but is also possible due to a faulty shore power supply or an incorrectly connected wind generator. If, for example, the shore power is connected incorrectly and the protective conductor (earth) of the shore power connection is connected to the negative pole of the battery via the hull (steel yacht) or keel bolt (GRP boats), fault current flows not only via the keel bolt/hull into the water, but also via the battery to its negative pole. Then, 220 volts suddenly hit the wrong side of the diode and, in the best case, there will " only" be a short-circuit.

If the diode is destroyed as a result, the current from the working cells will partially flow into the defective cell and heat it up. This literally creates hotspots in the solar module. Not only is the current converted into heat and energy is lost, but the heat development can even destroy the cell or lead to a fire in the module material. Therefore, in addition to a bypass diode, another diode is often built into the line that determines the direction of the current and prevents it from flowing back into the cell. This combination is called hotspot protection.

Solar on board

If several solar modules are connected in series, appropriate diodes should also be connected between the individual panel connections. This prevents an entire panel from becoming a hotspot if it is shaded while the others are fully exposed.

The breakdown voltage of the diodes (maximum voltage) should be slightly higher than the open circuit voltage of the fused solar module. Diodes simply break down at a certain voltage. Contrary to what one would expect, this then has the effect of allowing any current to pass in any direction afterwards. That is why 100V panels with 4A must best be fused with a diode that can withstand over 100V and 4A.

However, you can also connect 2 diodes @ 100V and 2A in parallel and then have "one" 100V 4A diode.

Unfortunately, diodes with a higher breakdown voltage and the required amps are relatively expensive and large. It is therefore common to install several smaller bypass diodes in parallel in the terminal box if you want to build the circuit yourself.

How can I tell if my on-board solar system is working?

As soon as the sun hits a solar system, you can use a multi-meter to see if voltage is increasing on the panel. Most charge controllers also have light-emitting diodes; they signal whether charging current is being generated.

As far as solar accessories are concerned, there are measuring devices with displays that can be permanently installed on board. A battery display helps to keep an eye on consumption, making it very easy to observe energy yield. Some charge controllers, from Victron for example, also transmit this data via Bluetooth to smartphones or tablets so that it can be analysed over a long period of time. This way, it is possible to compile statistics that quickly show errors caused by corroded connections, for example, as a drop in performance shown on a graph.

How long does a PV system last on board?

Some solar modules will last for decades. However, the efficiency of solar cells decreases over time. In practice, however, modules usually fail due to mechanical damage and not due to their age.

But it is worth keeping an eye on technical advances and note the differences in older installations. Modern solar cells generate more electricity on a fraction of the surface compared to old installations. This development is continuing rapidly, driven by changes in our approach to renewable energy, and it also affects the technology of the charge controllers. Today's solar charge controllers are becoming increasingly efficient.

Can I install a solar system on any boat if there was no system before?

Yes, provided there is space or an equipment rack can be installed, solar systems can be installed on any boat.

What manufacturers are there on the market for solar systems in yachting?

While there are only a handful of specialised manufacturers of solar cells, there are quite a few companies on the market that use these cells to build solar panels and systems. Large brand names with years of experience in solar module construction are, for example, Sunware or Solara. Other manufacturers, such as Sunbeam or Phaesun, are newer to the market but often offer lower prices.

In terms of charge controllers, manufacturers of on-board electronic components tend to be ahead of the game. This is especially true for specialists in batteries and charging technology. Victron is probably the top dog in this area. As an extra bonus, some Victron solar controllers even allow you to log the power yield on your smartphone via Bluetooth. However, most manufacturers of solar systems also offer their own controllers in their product range.

What does the watt-peak (Wp) specification on solar panels mean?

Watt peak is a comparative value for measuring solar systems. The maximum possible output is determined under specified ideal conditions. However, these ideal conditions hardly ever are a true reflection of reality. In detail: 1000 watts per square metre of solar radiation, 25 degrees Celsius module temperature and an air mass index of 1.5.

The 1000 W/sqm yield can only be achieved in northern Europe on an exceptionally sunny summer's day. Then, however, the module temperature will already be significantly higher, which lowers the output in reality. The air mass number is important to describe the loss of solar energy in the atmosphere. An air mass number of 1 corresponds to the amount of atmosphere that is vertically above a point on the earth. However, if the sun is at an angle of 45 degrees above the horizon, the path through the atmosphere is much longer. At this angle, the air mass number will be 1.5.

Author Hinnerk Weiler

Author Hinnerk Weiler

Hinnerk Weiler is a sailing journalist, long-distance sailor and real "old salt". He shares his knowledge on the topic of solar energy on board. An experienced sailor and expert in boat technology, he knows what he's talking about.

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