Performance Comparison of a 130 Watt Mono-crystalline and a 140 Watt Poly-crystalline Solar Panel in a Cruising Application

In an earlier blog entry dated 8/10/2011 I documented the performance of our 130 watt mono-crystalline solar panel on a 22 day cruise in the upper Great Lakes.  This year I documented the performance of our 140 watt poly-crystalline solar panel on the same boat under similar conditions.  The only variables were the weather and the running of the engine when moving from anchorage to anchorage (wind was on our nose quite often this summer).  Also this panel performance was documented over a longer period of 34 days.  

Test conditions:

• The boat has two deep cycle wet cell battery banks; 315 amp hours and 105 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 3 amps.  All lights are LEDs.
• When motoring, the panel was usually connected to the controller.
• The dual bank controller shuts off power from the panel when the batteries are fully charged.  i.e. After 3 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 cruise.
• The tilt angle of the panel was rarely changed; usually about 45 degrees.  The panel was rotated for optimum sun angle on an average of 3 times per day.

Test Results:

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

Average amp hours per day produced under various conditions:

                                                  130 Watt, mono    140 Watt, poly

Overall average output per day         54 amp hours    53 amp hours

Sunny days                                    71                          69
Mostly sunny days                          51                          50
Mostly cloudy days                         46                          35
Cloudy days                                   24                          32  
                    
Output on days at anchor                62                          62
Output when engine was used         35                          43 (difference because 130W was disconnected often
                                                                                       when engine was used.  Not so this year for 140W)

 Min amp hrs for a day                    16                          27

Max amps output                           10.5 amps           10.5 amps

Interpreting the Results:

Both solar panels performed as expected.  Their average daily output was about equal.  The 130 Watt mono panel provided a slightly higher average output on sunny days and the 140 Watt poly panel provided a higher average output on cloudy days.  My sense was that the poly-crystalline panel was less sensitive to shading from the rigging but this is difficult to document.  On sunny days, both solar panels often performed above their sticker rating of 130 and 140 watts by as much as 50 watts (9.5 amps at 21 volts is 189 watts) .  I believe this is due to the high quality of silicone crystals used.

Observations:

Both the 130 watt solar panel and the 140 watt solar panel generally met our power needs for the duration of the cruises.  We occasionally ran a small deficit of amp hours during an extended anchorage when cloudy 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 solar panel.

Choosing the right type of solar panel:

Based on the performance data, both solar panels will perform adequately under most  conditions.  The 130 watt mono-crystalline solar panel is an excellent choice for boats in mostly sunny areas with little possibility of shading from the rigging.  The 140 watt poly-crystalline solar panel is an excellent choice for areas with more partly cloudy and cloudy days and on boats where there is some shading from the rigging.