eSolar cell output degrades and the cell heats up.  A solar panel power rating is established at standard test condition (STC) of 77 degrees Fahrenheit and at 1,000 W/sq meter of light.  At 135 degrees Fahrenheit, a typical solar panel will degrade in performance by at least 10%.  It is not uncommon for a solar panel to reach 170 degrees in full sun on a warm day.  So, it is beneficial to solar panel performance to cool the panel as much as possible.  One way to accomplish this is to place 4 or 6 mm twinwall polycarbonate under the panel.  This enables some airflow under the panel thus cooling the panel.  Twinwall polycarbonate is often available at Home Depot or Lowe's or online.  Twinwall polycarbonate can also be used under a flexible pane on bimini canvas installation where the panel is going over a support tube.  This takes the pressure off the solar cells caused by bending at the support tube.  The panel and twinwall polycarbonate can be attached to the supporting surface using the CMP bolt on system or for semi-rigid panels the J extrusion system.

Bonus water heating idea:.  8 mm twinwall polycarbonate will accept 1/4" irrigation tubing.  The tubing can be run through the twinwall polycarbonate and attached to a small pump and the boat water heater.  Circulating water through the tubing under the panel will both cool the solar panel and heat the water in the hot water tank.  Free warm water!  See our water heating section on the website for further ideas on how to install such a system. 

Most of us have shading on our boats from rigging, equipment poles or other boat structures.  Reduction in performance due to shading is a significant issue for solar panels.  We at Custom Marine Products have developed a new panel design that significantly reduces the impact of shading and clouds on solar panel performance.

First, a bit of background on how typical solar panels are designed.  Solar cells are wired in series to get the panel voltage up to a level that is appropriate for its application.  These series strings usually go down and up the length of the panel.  A solar panel may have one to 5 series strings. Higher quality solar panels have the cell strings isolated with diodes so a shaded string does not reduce the performance of unshaded strings. If there is shading across the panel, each shaded series string is significantly reduced in power output.

Our new CMPower shade tolerant solar panel is designed with multiple shorter strings of half-cut solar cells.  These flexible panels have four strings (four quadrants) all isolated with diodes.  The result is a panel that will perform well with boom shading across the panel.  In fact, our testing indicates that these panels have double the output of a standard panel in shaded conditions.  These panels are currently available in 115 watt and 145 watt sizes.  The junction box and wires are in the center of the panel rather than at an outside edge.  This may be problematic for some installations.
​See diagrams below for clarification.

We are often asked if there is a way to keep a lead acid start battery and install LiFePO4 batteries for the house and charge them from the same alternator. The answer is generally yes. Lead acid or AGM batteries should never be combined with LiFePO4 batteries.  These are totally different battery technologies and they are not compatible.  Thus, a battery combiner is not an option.  Here are two alternatives for charging both battery banks from a single alternator.

A DC-DC charger enables two battery banks to be charged from a single alternator while being isolated from each other.  The Victron Orion DC-DC charger is an excellent option.  It enables the start battery to be charged directly from the alternator and at the same time charge the LiFePO4 house battery bank with a different charging profile.  The advantages of this approach include:
– Multiple batteries of different types can be charged independently.
– Multiple battery charging profiles.
– Easy to install and monitor
– Protects the alternator
– Multiple Orion units can be wired in parallel for higher power charging.

The Orion is available in two types; isolated and non-isolated.  The isolated unit is designed for unit in boats or vehicles with battery banks that do not have a common ground.  The non-isolated unit is designed for boats or vehicles that have a common ground.  Most boats are wired with a common negative ground throughout so a non-isolated Orion unit is appropriate for most marine applications.

Below is a wiring diagram for a single Orion DC-DC charger with two battery banks:​

A battery isolator enables the charging of multiple battery banks while keeping them isolated from each other.  The Victron ARGO FET Battery Isolator enables the charging of three battery banks.  The disadvantage of this approach is that there is a single charging profile applied to all three battery banks.  Thus, if the start battery has a significantly different charging profile from the LiFePO4 battery bank, this may not be a good option.
​
Advantage – multiple batteries can be charged independently.
Disadvantage – only one battery charging profile.

.A solar system will typically be putting out 10-30 amps to the battery bank.  An alternator will typically be putting out 45 - 200 amps to the battery bank. So you want everything you can get from the alternator when the engine is running.  Sometimes, on some boats, the alternator will sense the net voltage of the battery bank plus the voltage from the solar controller and see a higher voltage than the actual voltage of the battery bank.  This may cause the alternator to prematurely go into the float charge phase which is low amps.  Thus, the batteries are not getting the full charge from the alternator.  When this happens, you use the switch between the solar array and the controller to turn off the solar so you get full power from the alternator. 

How do you know if the alternator is going into float mode prematurely?  You see it on the amp meter or the battery monitor if the boat has one.  Otherwise it is difficult to tell.  This is the only reason to shut off solar with the switch.  The switch is between the solar panel and the controller because the controller is powered by the battery, not the solar panels and you want to keep power to the controller rather than reboot it all the time. 

There is no harm in having solar, generator, shore power or alternator connected at the same time.  Another consideration: If the batteries are low, it is unlikely the net of the battery voltage and the solar is enough to move the alternator to float mode.  This only happens when the batteries are nearing full charge and it is midday and the solar is putting out a full charge.  It happens on our boat only under these conditions.  Then there is the difference in charging voltage of lead acid and LiFePO4 batteries.  It would seem more likely to happen with LiFePO4 batteries since the charge curves are at a higher voltage.

One of our customers was getting less than 20% of the rated power from his solar panels and he called us for help.  He had 400 watts of solar, was using a Victron MPPT controller and two CMPower 120 Ah LiFePO4 batteries.  He should have been getting 25+ Amps of charging power from the controller to the batteries but was only getting 4 Amps.  We spent several hours troubleshooting; charging and discharging the batteries, testing the solar panels reprogramming the MPPT controller all to no avail.  He texted me a picture of his installation and happened to mention he was temporarily using a 25 foot long 12 gauge wire between the controller and the batteries.  I suggested he try a short 10 or 8 gauge wire and see what happens.  Magically, the system began to work perfectly.  I reproduced the same situation in our shop and achieved the same results.  The bottomline:  The wires between the controller and the battery bank MUST be adequate to handle the load otherwise the performance of the solar system will be severely restricted.  Don't skimp on the wire.  The same applies for the wire from the solar panels to the controller.

Custom Marine Products now sells and supports inverters and inverter.chargers made by Victron and EP Solar.  The following explains the difference between inverters and inverter/chargers.  For more information on this topic check out our web page on inverters under our Products section.

Inverters - The purpose of an inverter is to supply power to AC appliances (such as a coffee maker or microwave) by inverting DC battery power to AC power.  An inverter draws power from the battery bank and supplies it to AC appliances.  Inverters are available in various sizes measured in watts of output.  The most common inverter capacities range from 1,500 watts to 3,000 watts.  Most inverters are about 80-90% efficient which means 80-90% of the power drawn from the battery bank is converted to AC power.
​
Inverter/Chargers - The purpose of an inverter/charger is to both supply power to AC appliances from the battery bank and to charge the battery bank from grid power or a generator.  In summary, invert DC to AC current for powering appliances and invert AC to DC current for charging the battery bank.  Most inverter/chargers are equipped with an automatic transfer switch (ATS).  When grid or generator power is applied to the inverter/charger, the ATS bypasses the inverter and passes the AC current through to the AC appliances and also connects to the built in battery charger to charge the battery bank.  When grid or generator power is turned off or removed from the inverter/charger, the ATS automatically disconnects the battery charger and connects the inverter so the AC appliances are powered by the battery bank.   

First some background -  solar controller
​I look at the solar controller as a negotiator of sorts.  It uses MPPT (Maximum Power Point Tracking) to determine the best combination of voltage and amperage to pull the maximum power (Watts) from the solar panels.  The MPP will continually vary depending on the panel design, sun angle and shading.  The solar controller also senses what is the best voltage and amperage combination (Watts) for the battery bank. V x I = Watts.  Watts into the controller from the solar panels about equals watts out to the batteries minus conversion efficiencies.  So the solar controller negotiates the best power from the panels and best power to the batteries.  While the solar controller senses the voltage of the batteries to determine how much power to supply to them (charge), it has no way of sensing what has been or is being taken out of them (discharge).

Some more background -  LiFePO4 batteries
​The discharge curve for LiFEPO4 batteries is very flat.  They supply a steady voltage of between 13  and 13.4 volts up until 95% of full discharge.  This is unlike lead acid batteries that reduce in voltage from 13 to 11 or less volts as they discharge.  Thus, voltage only is not an accurate way to determine the state of charge (SoC) of LiFePO4 batteries. 

Determining LIFePO4 battery SoC
There are two ways to determine the SoC of LiFePO4 batteries; an external battery monitor or information directly from the Battery Management System (BMS).  A battery monitor (Victron makes one) has a shunt on the negative wire between the batteries and the battery chargers and appliances using power.  The battery monitor measures the power crossing the shunt in both directions (charge and discharge) and computes the State of Charge of the battery bank. This technique can be reasonably accurate but most battery monitors are designed for lead acid and AGM batteries and have to be reprogrammed for LiFePO4 because LiFePO4 batteries charge so much more efficiently than lead acid.  The battery monitor has enough data to compute the SoC but can be inaccurate because battery charging efficiencies vary.  The diagram below may be helpful.

A well designed battery management system (BMS) can measure the charge and discharge rate and the battery voltage and accurately compute the SoC for each battery in the bank.  The BMS can also compute the time to full charge and the time to full discharge.  In addition, the BMS monitors and manages the SoC of each of the 4 cells within a LiFePO4 battery so it can provide diagnostic data to identify a potential balancing issue which could lead to a potential failure. 
​All this information can be made available through a well designed BMS Bluetooth App.

This year we again tested our CMP 175 Watt SunPower cell solar panel with our integrated water heating system on a 4 week cruise in the Canadian waters of Northern Lake Huron.  The area is known as the North Channel and is at a latitude of about 46 degrees. The 175 watt panel provided the power necessary to meet our 70 amp hour per day requirements.  Our CMP pole mounting system enabled me to 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.  When more power was needed to bring up the batteries, I would tilt the panel to capture the maximum possible sunlight.  We used an EP Xtra-N 20 amp MPPT Controller (same as last year) to manage the solar charging and to capture solar system performance data.  

Operating statistics:

Our power usage averaged approximately 70 amp hours or 850 watt hours in a 24 hour period. Our appliances at anchor included a laptop computer several hours a day, refrigerator/freezer running 24/7, cell phone chargers, our LED lights in the evening, and our radios and instruments during the day.  We have a 75 amp Balmar alternator with a smart regulator.  We are using two 100 amp hour CMP LiFePo4 batteries for our house bank and one for our starting battery.  This is the second year for the CMP LeFePO4 batteries and they again performed beyond our expectations.

Results and findings:

1. Even running the ice maker late in the day, our LiFePO4 battery bank was fully charged by 2 PM most sunny or mostly sunny days when at anchor; about the same as last year.
2. The EP Xtra-N MPPT controller with the remote display proved to be an excellent piece of equipment.  On occasion we disconnected the remote meter and plugged in the BLE Bluetooth dongle to monitor the solar system from our phones and tablets.  Both monitoring techniques worked well however the meter captured more cumulative data such as watt hours produced so I used it more.  It was interesting to watch the solar system pouring in as much power as available to recharge the LeFePO4 battery bank then pull back in the afternoon when the batteries reached full charge.  There is no need for a float charge phase with these batteries.
3.  Rotating the panel during the day to achieve optimum sun angle, especially in the morning, significantly increased the power generation of the panel.  When we would leave the boat for extended periods for exploring and kayaking I would tilt the panel to the near horizontal position.
5. The data gathered confirmed that this panel configuration supplied all the power we needed on sunny days and had sufficient capacity to catch up on battery charge after a string of cloudy days; although sometimes it took a day or two to fully catch up.
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%.  Panel performance degraded by over 70% on heavily cloudy days.
7. The heat exchanger on the back of the panel for our water heating system  worked well on sunny days so we had warm water for showers and dish washing.  Power consumption of this system was minimal.

Data:

This year - 2019

175 Watt Solar Panel                    At anchor   Motor         Sunny to         Cloudy to
                                                                                        Mostly Sunny  Mostly Cloudy

Average watt hrs per day                     766        495              930                 423
Average amp hours per day                     59          38                72                   32
​Maximum watt output in 24 hours    1,130        810           1,130                 810
Maximum amp hours in 24 hours             87          62                 87                   62

Last year - 2018
 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
​
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 1,280 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.  We did not use shore power to charge the battery bank for the entire cruise.

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.

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.  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.

Data:

 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
​
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 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.

Results:

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.

Custom Marine Products will be conducting three seminars at the Pacific Sail and & Power Boat Show in Richmond, CA April 20, 21 and 22.  These seminars will provide an introduction to the basics of PV marine solar panel technology and how to apply this technology to design a solar system for your cruising needs.  The seminars will also include a mini workshop in determining your electrical energy usage as a first step in designing a custom marine solar system.  I have presented many of these seminars at various boat shows and they have been well received.  No sign up is required.  Just attend and enjoy. 

The seminar material can be found on our website under SUPPORT, MANUALS & INFO, last item.
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