This year we tested our new 120 Watt SunPower cell solar panel with our integrated water heating system on a 5 week cruise in Northern Lake Huron at a latitude of about 46 degrees.  We used an EP 20 amp MPPT Controller.  A 10 amp controller would have been sufficient but we wanted extra capacity so we could plug in an auxiliary 100 watt semi-flexible panel as a backup if we needed additional power because of a series of cloudy days. Plugging in an extra panel is simple using the MC4 connectors and an MC4 T-branch connector. We had mostly sunny days so we didn't need additional power beyond what the 120 watt panel provided.  The weather was awesome!  The 120 watt panel was mounted using our CMP pole mounting system so I could tilt and rotate the panel to achieve optimum sun angle.  I set the sun angle once and rotated the panel three times a day (morning, midday, evening) and figure I got about 30% more performance over a fixed horizontally mounted panel.

Operating statistics:

Our power usage averaged approximately 70 amp hours or 850 watt hours in a 24 hour period.  Our current draw was from a refrigerator/freezer running 24/7, our LED lights in the evening, cell phone chargers, laptop computer several hours a day and our radios and instruments during the day.  Our windlass is only run when the engine is running so we don't include it in our power consumption calculation as the alternator quickly makes up for its power usage.  We have a 75 amp Balmar alternator with a smart regulator.  Our house bank consists of 3 flooded cell batteries giving us a total capacity of 330 amp hours.  We started the engine to move anchorages about every three days.

Results and findings:

1. Our battery bank was fully charged by 2 PM most sunny or mostly sunny days when at anchor.  This is in contrast to 12-1 PM in past years using our 150 or 160 watt panels on poles.
2. The EP Tracer BN MPPT controller with the remote display proved to be an outstanding piece of equipment.  It was simple to program, easy to read, collected the appropriate data and was very efficient.  It was exciting (I get excited about these things) to see 8+ amps being poured into the battery bank in the morning.  It would be frustrating to see it only outputting and amp or two in the afternoon in full sun but then you realize it is doing its job.  It fully charged the batteries in the morning and was in float mode topping off the battery bank in the afternoon.
3. Rotating the panel during the day, especially in the morning, significantly increased the power generation of the panel.
4. Our weather was so sunny and the panel performed so well we had no reason to plug in the auxiliary 100 watt flexible panel using an MC4 T-branch for extra charging power.  I plugged it in one morning just to confirm the configuration would work and was easy to do.  It worked well and brought the charging amps to well over 12 amps.
5. The data gathered confirmed that this panel configuration supplied all the power we needed and has excess capacity to catch up on battery charge from a string of cloudy days.
6. The panel was affected by shading as would be expected.  Occasionally the panel was shaded by the back stay or the mast.  While the shading was minimal, it degraded the performance by up to 40%.

Data:
                                                  At anchor   Motor         Sunny to         Cloudy to
                                                                                 Mostly Sunny  Mostly Cloudy

Average watt hrs per day                  740        540             650                 290
Average amp hours per day                 57          45               50                   22
​Maximum watt output in 24 hours    960        630             960                 540
Minimum watt output in 24 hours        200         200             420                 170

Observations:
1. The minimum watt hour output doesn't mean much because it is dependent on both the cloud cover and the state of charge of the bank as a result of alternator charging,
2. The maximum watt hours per day of 960 is not the maximum output capacity of the system in a 24 hour period because the batteries were charged by 2 PM so the controller shut down the charge from the panel.  A higher drain on the house battery bank would have resulted in this number being higher.
3. Average amp hours per day is computed by dividing the watt hours by 13 volts.  This is a ballpark calculation.
4. This configuration proved to have plenty of capacity for our cruising needs even without using the auxiliary solar panel.  We have not used shore power to charge our battery bank for the entire summer.

Solar Water Heater:

We installed our new solar water heating system.  It consists of a heat collector or heat exchanger mounted on the back of the solar panel, and a circulating pump.  See our earlier blog for design considerations.  The pump circulates water from the water heater through the heat exchanger on the panel.  We used the same configuration on our 150 watt panel last year.

Results:

On sunny days at anchor we had warm water for showers and dish washing.  The water temperature in our 8 gallon hot water tank would warm from 60 degrees to about 105 degrees in 2-3 hours on a sunny calm day.  This was slower than the system we tested last year on our larger panel but it was perfectly adequate to meet our needs.  As expected, we confirmed that strong winds tend to cool the panel and reduce the heating efficiency as do clouds.  Overall, the water heating system cools the surface of the panel by at least 20 degrees.  This increases the efficiency of the panel since solar panel performance degrades as they are heated by the sun. Insulating the tubing running between the heat exchanger and the water heater significantly increased the efficiency of the system.  In conclusion, the radiant energy water heating system works well on sunny days with both our larger and our standard sized panels. See our product section or read our earlier blog for details.

When our supplier told me they had a new high output marine solar panel that was flexible I was skeptical.  The specifications seemed just to good to be true.  So I ordered some to test.  Well, I was pleasantly surprised.

These panels are very well constructed and they have a power generation comparable to our hard panels.  These panels can be flexed to 30 degrees so can conform to most boat curved surfaces.  The 100+ watt panels have an electrical box on the front (not shown in the picture) which contains two blocking diodes.  The 50 watt panel has one blocking diode.  The base material is very sturdy and strong.  Each panel has grommets for attaching the panel.  

I have tested the output of these panels under various weather conditions and their susceptibility to shading.  Below is a quick comparison of output of our three mid-range panels laying flat at mid day on a mostly sunny day measured with a meter:

                                                      Flexible 100 watt         Rigid 105 watt          Rigid 100 watt
                                                      Monocrystalline           Monocrystalline        Polycrystalline

Short Circuit Current (Isc)                      5.48 amps                   5.50 amps                5.26 amps
Open Circuit Voltage (Voc)                    19.2 volts                    19.7 volts                  20.5 volts
Computed Power (not rated power)         105 watts                    108 watts                 108 watts

Additional information is available on our solar panel page.

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.