Download Q: How much solar power do I need for my boat? Q: Will a panel that

Q: How much solar power do I need for my boat?
Simple answer: To trickle charge, one small panel. For power, as much as space and budget allow.
This all depends on what you need solar power for. If it is just to keep a battery topped up while you are absent from your boat, with nothing
running except the occasional bilge pump operation, then you can get by with a single low-output marine solar panel. But if you want to be as
energy independent as possible, and need to be powering significant loads like lighting, refrigeration, instruments, etc., then you will need to install
as much solar power as your budget and available space will allow. Use the solar panel manufacturers’ estimated daily yield figures as a guide as to
what to expect, and match that against your estimated daily watt/hour requirements.
Q: Will a panel that is rated 50 watts actually deliver 50 watts?
Simple answer: Yes, but only under a rarely occurring combination of ideal conditions.
Most, but not all, solar panels are tested and rated at Standard Test Conditions (STC). These conditions are; 1,000 watts/sq meter solar energy, 25
deg C (77 deg F) temperature, and AM1.5 air quality level. It is very doubtful if any panel will see this combination of conditions consistently in the
real world, but because it is theoretically possible, then cabling and other components must be sized accordingly to be able to safely handle the
maximum possible power output. A more realistic figure to use for planning purposes is the manufacturer’s estimated daily yield in watt/hours,
which is typically 4 to 4.5 times the panel’s rated wattage.
Q: What is a watt?
Simple answer: Watts = Volts x Amps
A watt is a measurement of power that is commonly derived from volts multiplied by amps, where, in a solar application;
•
The voltage of a solar panel is the sum of the voltage of each cell (typically 0.5 to 0.7 volts) multiplied by the number of cells.
•
The current (amperage) of the panel is dependent on the size, type, and quality of the individual cells.
Example: A panel of 32 cells will produce the same current as a panel which has 42 cells of identical size and quality. But the smaller panel with
only 32 cells will have a lower voltage, and so the resultant power will be less than the larger panel. Example: 32 cells x 0.6v = 19.2v, whereas 42
cells x 0.6v = 25.2v
Q: If watts = volts x amps, then presumably a 50 watt, 12v solar panel should
produce over 4 amps at 12v. But the specs show less than 2.5 amps. Why?
Simple answer: Because solar panels produce voltages of 17v and above.
Although most marine solar panels have a nominal voltage of 12v, they actually produce a higher voltage, typically at least 17v and often
considerably higher. That is why a controller is necessary to reduce the voltage to a safe level that will not damage batteries and equipment. Solar
panel manufacturers’ designations are based on the voltage and current that has been measured at maximum or peak power at STC. So the “50
Watt” panel is indeed capable of producing 50 watts of peak power, but at 18 volts, not 12v.
Q: How will low light or shading affect the output of my solar panel?
Simple answer: Low-light or partially shaded conditions will lower the amperage output of a solar panel.
A typical marine solar panel comprises of a number of crystalline cells, usually 32 or more, connected electrically in a series string. Dim or diffuse
light will obviously reduce power output, but if just one of those cells becomes shaded, then the amperage output of that cell will be reduced in
proportion to the amount of shading on that cell. And as the amperage of the whole panel is dependent on the amperage of the poorest
performing cell, i.e. the weakest link, then the output of the whole panel will suffer from just one cell being shaded. This is true of ALL solar panels
that contain silicone cells, no matter what salesmen or advertising jargon may tell you. The only “shade tolerant” solar panels available are those
with an amorphous composition, but these have very low efficiency and output. A good MPPT controller will dramatically reduce shading effects.
Q: How will high temperatures affect the output of my solar panel?
Simple answer: The higher the cell temperature, the lower the voltage output.
Solar panels which are rated at STC conditions are rated at 25 degrees centigrade (77F). In practice, most panels operate at much higher
temperatures, especially those in southern latitudes, and the higher the panel temperature, the lower the voltage output. A silicone solar cell
produces 0.6 – 0.7 volts at 25 deg C, regardless of the cell size. The more cells there are in a panel, the higher the output voltage, and so the more
useable power there will be when the voltage is reduced in high-heat conditions. However, the smaller the cells, the more likely it is that the total
panel output power will be compromised by even the slightest amount of shading, as a small amount of shadow that completely shades a small cell
will shade only one quarter of a cell that has four times the surface area.
Over:
Q: What is the difference between mono-crystalline and poly-crystalline cells?
Simple answer: Mono cells are from a single crystal of silicone. Poly cells are made up from lots of bits.
Mono cells are thin wafers of a single, round, crystal of silicone, whereas poly cells are slices of ingots that are formed from melting down off-cuts
of silicone from the semiconductor, solar, and other industries. Mono cells can be distinguished by having a black appearance, and one, two, or all
four corners of the cell being rounded off. Poly cells tend to be perfectly square and typically have a blue-ish tint and a mottled, flaky appearance.
Although both types perform similarly at ideal conditions, mono cells are the more efficient in low-light and partially shaded conditions.
Q: What is the difference between the Solara Professional and Premium 42-Cell?
Simple answer: Premium 42 Cell Series for hot climates; Professional Series for general applications.
The Premium 42-Cell series was specifically designed for installations on thick substrates like a deck or cabin top, where there will be little or no
cooling effect under the panel, and/or when plans include travel to high-heat locations, i.e. Florida, The Bahamas, The Caribbean, Mexico. The extra
cells, compared to the Professional series, will better compensate for the drop in output voltage associated with high cell temperatures. The
Professional series contain 35 or 36 cells and so work at a slightly lower panel voltage, but are of different dimensions to the Premium 42-Cell
series. It may be that the choice of which panel from which series comes down to a matter of which will make a better fit in the available space.
Q: What type of controller should I use?
Simple answer: Voltage-controlling models are inexpensive but give poor results in low-light/ partially
shaded conditions. MPPT controllers are at least 30% more efficient in low-light/shaded conditions.
There are two types of controller: simple voltage-controlling models, typically with PWM (Pulse Width Modulation), and those using Maximum
Power Point Tracking (MPPT) technology. The voltage-controlling models are inexpensive but result in lower power output than MPPT models,
especially under partially shaded or low-light conditions. MPPT technology looks for the best mix of voltage and current to give the highest possible
power output, and then tracks and changes this mix as heat, shading, cloud cover, etc. affect the cells. A good MPPT controller can increase output
by at least 30%.
Q: If I install more than one solar panel, how would they be configured?
Simple answer: A marine installation is very different from residential. Use one controller per panel.
Installing multiple solar panels on a boat is a very different prospect than on a house. In a residential application, no consideration is required for
undesirable shading effects, as the panels are installed in shade-free locations. In these residential situations it makes sense for multiple panels to
share one, high-capacity controller. But on a boat, some shading is almost always inevitable and unavoidable, and so ideally each panel should have
its own controller, preferably MPPT, so that if one panel gets compromised by shading it will not affect others. Most MPPT controllers on the
market are designed for land-based systems, and are too high capacity and price to consider using one per panel. But Genasun offers high-speed,
high efficiency MPPT controllers that are small, inexpensive, and specifically designed for use on individual panels in marine applications.
Q: I hear talk of diodes. What are these and do I need them?
Simple answer: By-Pass diodes prevent “Hot-Spots”. Blocking diodes prevent back-feeding.
Silicone solar cells will actually consume power if they are hard-shaded, and if that power comes from either the other cells in the panel, or from
other panels in an array, it can lead to localized heating, or “Hot Spots”. To prevent this, By-Pass diodes are required which will “turn on” and shunt
the potentially dangerous current past the affected cell(s) or panel. Most panel manufacturers include By-Pass diodes, either integral to the panel
or externally, on panels or groups of cells that exceed 50 watts. Blocking diodes are required to prevent back-feeding when two or more panels are
connected in parallel to share one controller and one panel becomes shaded. Their inclusion will reduce the panel output voltage by approximately
0.7 volts.
Q: Why are marine solar panels so expensive compared to residential models?
Simple answer: Marine solar panels are designed for the marine environment. Residential ones are not.
Marine solar panels are highly specialized items designed especially for the harsh marine environment. They are produced in relatively small
quantities specifically to withstand dousing with salt water and to withstand flexing, vibration, be walked-on, kicked, knocked, and suffer other
such abuses in everyday use. By contrast, residential type solar panels are intended for a far less strenuous life, typically in an array on a roof or on
solid ground, and so are much less expensive to manufacture. Mounting residential type solar panels on a boat presents a particularly difficult
challenge, and usually necessitates a heavy, unsightly, and expensive support structure, so these negative points have to be considered when
contemplating installing non-marine panels. Also, warranties for non-marine solar panels typically do not cover marine use.
Coastal Climate Control, Inc.
www.coastalcoolaids.com [email protected]
301-352-5738 - Annapolis MD USA