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Solar electric power for boats
Interactive guide to help you find the optimal solar solution
for your boat and needs!

(click on one)
What size of installation do I need?
Where should I install the panels?
What type of panel should I choose?

This interactive guide is protected under U.S., EU and other international copyright laws and may not be reproduced or used outside our web site without the explicit permission of Aurinco. The answers provided are only for guidance, we cannot guarantee the performance of an individual installation.

What type of panel should I use ?
Panel will be mounted where it will not be stepped on or hit by objects. It does not need to adapt to a curved surface.

You could choose a conventional framed glass solar panel. The advantage is a lower cost and availability of large sizes. There are also some more expensive glass panels with an extra photon-collecting layer for enhancing efficiency. But make sure you get a panel that has been tested for marine salt-water use. Some panels have had problems with salt creeping in between the frame and the glass laminate. So you may want to consider panels embedded in a synthetic resin, see the column at right. Or to continue with framed modules go to:

Types of photovoltaic cells

Panel will be placed where it might be stepped on or hit by objects.

OK, you don't want to mount a panel where you walk all the time because with time the surface will become dull with small scratches, just like a hatch window. And no panel will resist hard hits, like dropping an anchor on it. What we are talking about is a place where you might step occasionally or which could be hit by a falling pulley, a winch handle or by an oar. Panels that can be stepped on are usually built on a metal, fiberglass or plastic plate or sheet, where the photovoltaic cell(s) are laminated and embedded in a transparent synthetic resin.
Continue to:

Mount the panels flat or curved?

Mount the panels flat or curved?
Mount flat or on a slightly curved surface

Panels with crystalline solar cells embedded on a semi-rigid metal, fiberglass or plastic plate can be mounted flat but they usually also adapt to a slightly curved surface. Crystalline silicon is brittle so don't try to bend a panel by force. There has been a lot of problems with broken cells on crystalline panels built on thin stainless steel plates where the panels were claimed to be "flexible". If the panel does not quite fit along the curvature of the surface, you can place mouldings of marine grade rubber or plastic -or thin bars of stainless steel, aluminum or marine wood - to fill in gaps on the sides.

What about the material of the plate? Semi-rigid stainless steel is OK, but make sure it is marine grade. Some people complain that panels have left rust spots that are impossible to remove. Also, steel is heavy which may be a negative factor if you are racing. Marine grade anodized aluminum resists corrosion - there are aluminum boats that have been in salt water for 50 years. Glass fiber is another marine material, although eventually it needs to be resurfaced if it is exposed to UV. Many plastics are also quite UV-resistant, including the plastics used for embedding the solar cells. Like a hatch window they may dull or yellow a bit over a very long time but the loss of transparency is very gradual. Continue to:

Types of photovoltaic cells

Mount with a moderate curve

Your only choice today is a panel where the solar cell(s) are made using an amorphous semiconductor (usually silicon) which has been applied as a thin film on a flexible sheet of metal, fiberglass or plastic. But don't expect to be able to bend them at any angle, they will just tolerate a moderate amount of curvature. See column at left for sheet material considerations. To compare amorphous solar cells with crystalline cells, continue to:

Types of photovoltaic cells

Types of photovoltaic cells
Monocristalline silicon

These cells are made from very thin slices ("wafers") of a single silicon crystal. It is the most efficient photovoltaic material in commercial use, converting about 15% of the incoming sunlight into electric energy. For the same amount of space a monocristalline panel produces more electric power that other types of panels. Crystals can be solid blue or black, black crystals will cover a larger part of the light spectrum as it varies during the day. A disadvantage is that crystalline silicon wafers are brittle, they don't tolerate much bending.

Continue to What about shading and low light conditions?

Polycristalline silicon.

These cells are made from very thin slices ("wafers") of a "loaf" of smaller silicon crystals that have been fused together. They are usually bluish with a glitter from the individual crystal faces. Because of internal electric resistance and spectral and reflectance characteristics they are somewhat less efficient than monocrystalline cells. However, they are typically less expensive. As with monocrystalline panels there is the disadvantage that crystalline silicon wafers are brittle, they don't tolerate much bending.

Continue to What about shading and low light conditions?

Amorphous semiconductors

These cells are mady by spraying or otherwise applying a thin film of amorphous semiconductor particles on a surface. The semiconductor is usually silicon but other materials like indium-gallium have also been introduced. You will distinguish these cells by an even matte black or blue surface with no crystal pattern visible. The advantage of thin film amorphous panels is a low cost for flat rigid panels. Panels can also be made more flexible, although here the cost is quite high. But amorphous panels have the disadvantage of being much less efficient. For the same amount of watt power you will need almost twice the space when compared to a monocrystalline panel.

Continue to What about shading and low light conditions?

What about shading and low light conditions?
There are some facts and there are some myths - some of the latter is pure commercial hype. Let's examine them one by one:

"Some panels are more affected by partial shadow than others" True. Mono- and polycristalline panels consist of many individual solar cells connected in series to give enough voltage to charge a battery. A thin shadow may not affect output too much but if the shadow covers an entire cell it can block the current so that the output is greatly reduced. Amorphous panels are also affected by partial shadow but less dramatically so because they function more like one single cell. So if the panel is subject to partial shadow most of the time the amorphous panel will produce more. But then you could also consider two (or several) separate crystalline panels If one is in the shadow the other will still produce as much if not more than an amorphous panel in partial shadow . In most situations the total output from a crystalline panel will outperform an amorphous panel.

"This panel has a bypass diode, therefore it will not be affected by a partial shadow" Not true. It would be true if there would be a bypass diode for every solar cell in the circuit but there are no such panels on the market, simply because each diode steals some energy and the resulting expensive panel would have an efficiency on par with a less expensive amorphous panel. There are panels that have a bypass diode, but this is because they use cheaper cells that are damaged in partial shadow. There are also panels, which incorporate another type of diode (a back-diode) that will block current running back out from the battery at night. High quality monocrystalline panels have a very small nighttime back current and do not need any diode, it would just be a waste of energy.

"This panel produces power even during cloudy days and low light conditions" Hype. All panels generate a voltage and some current during cloudy days and as long as there is light. Some crystalline and amorphous panels may cover a wider light spectrum than others . But don't expect to generate much current under a leaden sky with any panel. Most of the solar energy is absorbed in the clouds or by the rain, only a very small portion reaches the ground as you can sense yourself with your eyes and against your skin. You cannot produce something out of nothing.

"This panel has 40 cells instead of 36 to charge better on cloudy days" Also hype. Sure, the voltage will be higher. But what matters is not the voltage, it is the amount of current reaching the battery. For a 12V system a 14V battery current is sufficient for charging. If light conditions are so poor that the panel voltage drops below this level, there is no current to speak of anyway, it does not help to pump up the voltage a few notches.

Continue to Temperature and different types of panels

Temperature and different types of panels
Solar panels produce more electric energy when they are cold. The hotter they get, the less the voltage output. And they will get hot in the sun. The dark surface of a photovoltaic cell will absorb almost all the incoming solar energy. But only a small fraction of the incoming energy is converted into electricity, the rest becomes heat. What are the factors to consider when choosing a panel?

Conventional framed glass solar panels may need to be vented if installed on a flat surface because the air trapped inside the frame is a poor heat conductor. This also applies to panels built on fiberglass, vinyl or other synthetic materials which conduct heat poorly.

Semi-rigid panels built on a metal plate will dissipate some of the heat because the plate acts as a heat sink. Avoid designs where the photovoltaic cells are mounted on a dark color surface, they may look nice but why absorb more heat than necessary?

Panels with 39 or 40 cell circuits do not run cooler than panels with 36 cells. Most use polycrystalline silicon with an electrical efficiency of 12% so the remaining 88% of solar energy becomes waste heat. To say that the higher voltage causes less resistance heat inside the panel is nonsense since resistance heat is negligible compared to waste heat. For battery charging at 14V a 39 or 40 cell circuit will only produce more charging current if the panel has a temperature above 80°C (176°F). You do not want such a hotplate on your boat! If very high temperatures are expected ventilation is advisable. Panels with higher voltage circuits also require step-down charge controllers in order not to damage the batteries. There is a case for a higher voltage if it is used to minimize resistance losses in cables, especially when the panels are far from the battery. But then you might as well consider using panels connected in series for even greater efficiency.

Please feel free to contact us for further advice or explanations.

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Last update 31OCT2014

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