This year we tested our new 175 Watt SunPower cell solar panel with our integrated water heating system on a 6 week cruise in Northern Lake Huron at a latitude of about 46 degrees. We used an EP Xtra-N 20 amp MPPT Controller. The 175 watt panel provided plenty of power to meet our 70 amp hour per day requirements. The 175 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 estimate we got about 30% more performance over a fixed horizontally mounted panel.
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. We changed our battery system this year by installing two 100 amp hour CMP LiFePo4 batteries for our house bank and one for our starting battery. I will post more about these batteries and our exciting findings soon. We started the engine to move anchorages about every three days.
Results and findings:
1. Our battery bank was fully charged by 1 PM most sunny or mostly sunny days when at anchor. This is about the same charging time that we experienced last year with the 160 watt solar panel.
2. The EP Xtra-N 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 6 to 10 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. Because we have excess power in the afternoon on sunny days, we installed an inverter and purchased an ice maker. This turned out to be worthwhile purchase. Ice for drinks was a free luxury (power wise) that we really enjoyed.
4. Rotating the panel during the day, especially in the morning, significantly increased the power generation of the panel.
5. The data gathered confirmed that this panel configuration supplied all the power we needed and had excess capacity to catch up on battery charge after 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%.
7. We installed a new larger heat exchanger on the back of the panel for our water heating system This worked well on those sunny days so we had warm water for showers and dish washing. Power consumption of this system was minimal.
175 Watt Solar Panel At anchor Motor Sunny to Cloudy to
Mostly Sunny Mostly Cloudy
Average watt hrs per day 750 480 900 435
Average amp hours per day 58 37 69 33
Maximum watt output in 24 hours 1,280 750 1,280 570
Maximum amp hours in 24 hours 98 58 98 44
160 Watt Solar Panel At anchor Motor Sunny to Cloudy to
Mostly Sunny Mostly Cloudy
Average watt hrs per day 660 480 700 400
Average amp hours per day 51 37 54 31
Maximum watt output in 24 hours 1,210 770 1,210 770
Maximum amp hours in 24 hours 93 59 93 59
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 1,280 is not the maximum output capacity of the system in a 24 hour period because the batteries were charged by 1 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 an auxiliary flexible solar panel we store under a bunk. We did not use 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 120 watt panel last year.
On sunny days at anchor we had warm water for showers and dish washing. The water temperature in our 6 gallon hot water tank would warm from 60 degrees to about 105 degrees in 2-3 hours on a sunny calm day. 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.
Thomas Trimmer has been cruising with his Ericson 38 sailboat on the Great Lakes for over 20 years. He has pioneered the use of solar energy for wilderness cruising. He is continually designing and building equipment to simplify and enhance the cruising experience.