At other places on this blog and on our web site we talk about how to determine the size of solar panel (how many watts) you will need to meet you power consumption requirements.  Once you know your panel size requirement there are some things to consider in selecting a solar panel.

Panel Type - There are many articles written on the two types of solar panels; monocrystalline and polycrystalline.  Monocrystalline panels are made up of single crystal silicon wafers.  Polycrystalline panels are made up of silicon that has a multiple crystalline structure.  There are pros and cons to each type of panel.  Monocrystalline panels have a higher output per square inch in direct sun but are very sensitive to shading and output will degrade faster on cloudy days.  Monocrystalline  panels are not as sensitive to being shaded and output will not degrade as much on cloudy days.  At CMP we offer both a polycrystalline and a monocrystalline panel.
Panel Crystal Quality - Because we have a confined space on our boats, we need to have the maximum output per square inch from our solar panels.  The quality of the silicon crystals used to make the panel is a key factor in determining the panel output.  Crystals are passed under a fixed light and graded as to their output (1-10).  Grades are grouped into classes.  Class A crystals are grades 8-10, Class B crystals are grades 4-7 and so on.  Crystal quality follows a bell curve; there are many more Class B crystals than Class A.  We at CMP specify only the best Class A crystals for use in our panels.  Less expensive Class B and C panels are often used on land based solar farms where space is not an issue.
Panel Shape - The largest market for solar panels is commercial applications where many many panels are mounted on a roof or in a field.  These panels are usually rectangular in shape often twice as long as wide.   This shape is often not ideal for marine application.  Often a more square shape is preferable, especially for pole mounting.

Choosing the right panel for your needs will require study and/or discussion with panel experts.
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The weather for our cruise in the North Channel of Lake Huron this year was excellent.  It was warmer and sunnier than last year.  Our Kyocera 85 watt solar panel performed very well.  The following are some statistics:

Days cruising:                                       22 days
Max power generation:                        40 amp-hours
Min power generation:                         13 amp-hours
Average power produced per day:  35 amp-hours

Average power consumed per day:      51 amp-hours

Our primary use of power was for the refrigerator/freezer.  We ran a power deficit each day of about 16 amp-hours at anchor but with our 360 amp-hour battery bank, this not a problem.  Moving on every 4 days or so gave the 75 amp alternator plenty of time to bring the batteries back up to charge.
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We spent the month of July in the North Channel in Northern Lake Huron north of the 45th parallel.  We logged the output of our top-of-pole mounted 85 watt Kyocera solar panel and our daily power consumption.  It was an unusually cloudy July.  Here are some statistics.

Weather
Mostly cloudy      7 days
Partly cloudy       8 days
Partly sunny        8 days
Mostly sunny       7 days

Power Generation
Maximum power produced in a day was 38 amp-hours
Minimum power produced in a day was 12 amp-hours
Average power produced per day for the 30 day period was 25 amp-hours

Power Consumption
Average power consumed for the 30 day period was 46 amp-hours

Our travel pattern was to stay at anchor for 2-3 days and then motor/sail to another anchorage.  We connected to shore power one night.  While we ran a power deficit of 21 amp-hours per day while at anchor, our high output 75 watt alternator quickly replenished our batteries on our travel days.

We ran our refrigeration/freezer every day as well as our computer (chart plotting) and autopilot when underway.  We found the combination of our 85 watt panel and our 75 watt alternator provided us with ample power for the trip.
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Solar panels provide an excellent solution for obtaining the electrical power needed  to support on-board electrical systems.  They are quiet, require little maintenance and are reliable.

While cruising, we take a very conservative approach to using electricity on board our 38 foot sailboat.  Even so, when considering the solar option, I concluded that  using solar panels to supply all our electrical needs would be expensive and would require considerable panel surface area.  With this in mind,  I set out to use solar power to augment the generation of power with the goal that we could be at anchor for three days without running the diesel to charge the batteries.

The 85 watt Kyocera KC85T is rated at 5 amps (17 volts) and measures about 26" by 40".  We can generate about 35 amp-hours on a sunny day on the Great Lakes by adjusting the angle 3-4 times a day for optimum efficiency.  Our energy usage is roughly 55amp-hrs a day at anchor.  Thus we run a deficite of about 20 amp-hours per day.

Here is how we calculated our energy usage per day at anchor.
Equipment            Amps            Amp-hours/day
Refrigeration          5                        20
Instruments            1                         4
Computer               4                         6
Lighting                  2 (avg)                10
Pumps                    5                         5
Other                     1                       10
 (propane monitor, etc.)
                                                ________
Total amp-hours                                55

When under sail we have an additional current draw of 20 amp-hours from our auto-pilot and instruments.

We have a 75 watt alternator on board and a 360 amp-hour battery bank.  Because we typically run the engine several hours on the days we are moving, the battery bank gets charged on those days.  This system works out well for us.

Each cruising boat has different patterns of energy usage and different requirements.  Calculate your usage, consider your sources of power generation and select the size of the solar array you will need.  Based on this, you can determine whether a single panel or multiple panels will be required to meet your needs.

Contact us if you would like assistance in determining the size of panel that will be required to meet your needs.



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Top-of-Pole Mount

The top-of-pole mount offers excellent functionality for getting the maximum performance out of your solar panel.  The closer the surface of the panel is to being perpendicular to the rays of the sun the higher the performance (amps output).  Thus, the panel needs to be both tilted and rotated.  I have found that adjusting an 85 watt panel 3-4 times a day will achieve power generation of up to 40 amp-hours on a clear day on the Great Lakes.

A panel mount should be adjustable easily without the use of tools.  Our panel mount provides 13 tilt positions by simply pulling a pin, tilting the panel and replacing the pin.  The panel, which is atop our crane pole can be rotated 360 degrees.  We provide a pole locking mechanism to keep the pole from rotating on a windy day and have found that using the mechanism as a brake to limit free rotation of the pole works well.

As shown in the picture, our pole is mounted to the stern rail away from the boom so there is nothing to cast a shadow on the panel.  Shadows can significantly reduce the efficiency of a solar panel.  The pole is mounted high enough to clear the bimini yet easy enough to reach to adjust the angle to the sun.

My sense is that the 120 watt solar panel is about the maximum size
(31" X 48") to mount on the top of a pole such as ours.  The limiting factor is the strength of the stern rails that stabilize the pole.  A larger panel would require bracing struts from the pole to the deck.  Clearly this is possible but I would recommend mounting larger panels to a frame above the bimini, on dinghy davits or directly to the stern rail.

Pro and Cons:

Top of pole mount
Pros: Easily adjusted for best sun angle, clear of shadows, out of the way.
Cons: Limited size of panel that can be pole mounted.

Bimini frame panel mount
Pros: Can mount large panels, out of the way.
Cons: Cannot easily adjust for best sun angle, often have shadows cast by the boom, back stay or topping lift.

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