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 following is the result of testing the CMP130 watt monocrystalline solar panel with the top-of-pole mount and dual output controller cruising for 3 weeks in the North Channel of northern Lake Huron.  The panel mounting system is shown on our Gallery of Installations; the Ericson 38.  (Well, somebody has to do it. :-)   )

Test conditions:

  • The boat has two deep cycle wet cell battery banks; 240 amp hours and 120 amp hours.
  • The boat has holding plate refrigeration which draws 5 amps.  The weather was very warm so the frig compressor ran more than usual; 8+ hours a day.  The lap top computer was used for navigation and draws 5 amps.  Most lights are LEDs.
  • When motoring, the panel was usually disconnected from the controller so the smart regulator would get an accurate reading of the battery bank condition thus achieving max output from the alternator.
  • The dual bank controller shuts off power from the panel when the batteries are fully charged.  i.e. After 4 or more hours of motoring.
  • The Remote Display of the dual bank controller was used to collect all the data.
  • Our mode of cruising was to anchor for 2-4 days at a time and move on to another anchorage.  We did not dock and use shore power during the three week cruise.
  • The tilt angle of the panel was rarely changed; usually about 45 degrees.  The panel was rotated for optimum sun angle about 4 times per day.
Test results – raw data for solar panel output:

Date     Amp      Conditions of the day
            Hours

7-7        46     At dock, shore power on
7-8        39     Motored 4 hours, partly cloudy
7-9        17     Motored all day, cloudy tried solenoid
7-10     26     Cloudy, motored 1 hour, sun 5-6 hours
7-11     55     Mostly sunny, travel day – under sail
7-12     64     Mostly sunny, at anchor
7-13     79     Mostly sunny, at anchor, reset meter when rewired batteries
7-14     70     Mostly sunny, at anchor, panel not turned for part of the day
7-15     49     Cloudy morning, sunny afternoon, motored for 2 hours with solenoid on
7-16     51     Mostly sunny, motored 2 hours with solenoid on, topped off batteries
7-17     34     Mostly cloudy, at anchor all day
7-18     47     Mostly cloudy,  motored 2 hours
7-19     20     Hazy, cloudy, motored 2 hours
7-20     71     Sunny, at anchor
7-21     80     Sunny, at anchor
7-22     67     Mostly sunny, ran engine 1.5 hrs, topped off batteries
7-23     39     Mostly cloudy, at anchor
7-24     73     Mostly sunny, at anchor
7-25     68     Mostly sunny, at anchor
7-26     16     Hazy, cloudy, motored 4 hours, topped off batteries
7-27     26     Cloudy, hazy, motored 9 hours, batteries charged
7-28     42     Mostly sunny, motored 2 hours with panel connected, batteries charged

Analysis:

Definition: amp hour – amps produced or consumed in one hour

Average amp hours per day produced under various conditions:

Overall (22 days)                         54  amp hours
Sunny days at anchor                  71
Cloudy days at anchor                 37
All days at anchor                         62
Days engine was used                35

Max amp hrs for a day                 80
Min amp hrs for a day                  16

Max amps output                         10.5 amps

Conclusion:

The 130 watt panel generally met our power needs for the duration of the cruise.  We occasionally ran a small deficit of amp hours during an extended anchorage but never used the engine alternator to charge the battery banks except when motoring from place to place.   On days when the engine was used we often had an excess of power generation from the 75 amp alternator and the 130 watt solar panel.

The solar panel is very sensitive to cloudy days and to shadows.  The panel output on sunny days exceeded it rating.   This is the nature of mono-crystalline solar panels.

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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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