.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.
​

Our 120 watt rigid marine solar panel with premium SunPower cells has been so popular we have expanded our product offering to include 100 and 160 watt rigid marine solar panels with premium SunPower cells.  These high performers are well suited for top-of-pole mounting or frame mounting on a bimini or on dinghy davits.  This line of marine solar panels is made to our specification and offer the highest output per square inch in the industry.

I have installed our radiant water heating heat exchanger to the back of a 160 watt SunPower panel and will be testing and reporting on performance after our cruise in the North Channel of Lake Huron later this summer.  This promises to be our best top-of-pole system yet.  See my earlier blog reporting on the 120 watt SunPower cell panel from last year's cruise.

I recently ran across this article from the Department of Energy about solar panel performance.  It identifies the three key factors related to panel performance; heat, dirt and shading.
​Link to article:   Getting the Most Out of Solar Panels

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.

We have been testing our 150 and 160 watt solar panels for the past few years on extended cruises.  While at anchor, on a sunny day, our battery banks are usually topped off by about 1 PM.  We run our refrigerator/freezer 24/7. So why not use a smaller 100 or 120 watt  solar panel and plug in a flexible panel on the rare occasion we need more charging power?  This is what we will be testing while cruising this summer.  It's a simple arrangement.  We will carry a 100 watt flexible solar panel under a bunk cushion.  If we need extra charging power we will simply plug it in using a T-branch connector at our pole mounted 120 watt panel and secure the flexible panel to the bimini top.  That gives us 220 watts of power through our 20 amp MPPT controller.  Several of our customers have reported using this configuration and are very satisfied with it.  I'll report our results at the end of the season.  Now, gotta go sailing and start testing.