“Why do cables matter, they are all just the same, just copper in a plastic tube” this used to be my attitude when prototyping small electronic devices running at 5V on my bench and for 99% of the time I was right, it was not until I got involved in low power DC systems i.e. Power Over Ethernet and fibre that 48V being used as a power distribution system for networking and domestic DC power then voltage drop become an issue.
For your Solar Panel wiring, we need stranded wire so it is flexible, it needs to be tin coated so that it does not corrode, especially useful on a boat, then the jacket needs to be UV safe as it is going to be left out in the sun, while also being tough and durable as it will be bent and flexed multiple times.
Typical Solar PV Cable
Solar or PV cabling being tin coated means we are not looking at strands of copper that are directly touching each other, each wire in this case has a thin coating of the less conductive Tin, Tin is only 15% as conductive as copper. This has a very slight effect on the resistance of the wire, also being stranded we have a minimal air gap between the strands so 4mm2 of stranded copper wire is not as conducive as 4mm2 of solid copper wire.
When I have calculated the resistance of copper wire in the past I have only used the resistance of pure copper in my calculations, but now things are getting a little more complex.
When planning your install you also have to remember there is a positive and a negative cable in the circuit, so a 20m distance between your solar panels and your MPPT or PWM solar controller is really 40m of cable, so double the resistance.
To enable me to see how much the resistance of the wire changed I originally built an excel spreadsheet that took into account the resistance of the solar stranded tinned copper wire at different diameters in mm2, lucky the manufacturers only make a limited range of diameters of cable for solar systems with 2.5, 4, 6 and 10mm2 being commonly available and they provide the resistance per Km for these.
For your use, I have converted the spreadsheet into some javascript code for this page, so you can input your requirements and see the effect of that cable resistance in terms of Voltage Drop as a value and as a % will have on your plans.
Typically for this kind of DC installation you want a voltage drop of less that 2% is best.
Have a play about and see what is the best cable size/cost is best for your installation
Prototype Voltage Drop Calculator
Prototype Voltage Drop Calculator
Select cable size in
mm2
Enter cost per meter of your cable
Enter the system nominal DC voltage in volts
Enter the current draw in amps
Enter the one-way circuit length in meters
NOTE: This Voltage drop calculator is designed for Solar PV Cable, with Class 5 stranded tinned copper wire, which has a slightly higher resistance than solid copper wire.
Lots of acronyms floating about in the solar industry, and as we are looking at Solar Panel controllers we have two more to look at PWM (Pulse Width Modulation) and MPPT (Maximum Power Point Tracking) these acronyms actually describe how each of these controller works.
Why do we need a solar panel controller, a 12V solar panel actually outputs between 18-20 volts so to stop your solar panels overcooking your battery we need to control the output to match the best charging voltage for your battery. Lets look at each type of controller see how they work and what the advantages and disadvantages of each have…
What is PWM – Pulse Width Modulation
Victron PWM Controller
PWM is an robust technology that is used in many devices around your home, I have used this to control motors, dim lights etc etc.
The idea behind PWM is that we take an incoming supply and switch it on and off quickly the difference between the on and the off parts can vary so for example a motor or light that gets a quickly pulsed (25+ timesaver second) at 50% on 50% off a motor will run at ½ speed or a lights output would be 50% dimmer, in these cases the speed of the modulation needs to fast so that the output looks smooth.
Example of PWM at 25, 50 and 75% pulse width.
PWM Controllers act like a switch, with the panels and battery connected the battery will pull the voltage down to its own level. As the battery charges that voltage increases until the batteries are fully charged. At this point the controller starts its float stage, switching on and off the supply from the solar to in effect trickle charge the batteries as required.
The inefficiency of the PWM controller comes from the way it the battery pulls down the supply voltage from the solar panels reducing the available power.
E.G. 100W Solar panel provides 20V at 5A
20V x 5A = 100W*
When pulled down to the battery voltage it is only now supplying 13V at 5A
13V X 5A = 65W*
A loss of potentially 35W or 35%
*These are simplified figures to make the calculation simpler to understand
One of the other major drawbacks of this method is that you are working at lower voltages on the solar panel side of the system as they must match the battery requirement. With lower voltages the cable losses start to add up very quickly, meaning you will need thicker less lossy cables to connect your panels to the controller (We will cover cabling in a later post).
PWM Advantages
• Low Cost 10-25% of MTTP • Simple reliable technology • Available in sizes up to ~60 amps
PWM Disadvantages
• Potentially higher cable losses • Less efficient ~75% conversion • Solar Panel voltage must match battery nominal voltage.
What is MTTP – Maximum Power Point Tracking
Victron MPPT controller
An MTTP controller is divided into two parts, input from the solar panels and output to the battery. The input can take a much higher voltage that what is required charge the batteries. The send part of the MTTP controller, the output will convert this to the correct voltage for your battery to charge correctly (it is a smart DC to DC converter)
So:-
200W Solar panel providing 40V at 5A
40V x 5A = 200W**
This is converted to 13V at 200W increasing the output to 15A
200W / 13V = 15A**
**These are simplified figures to make the calculation simpler to understand and exclude any losses in the dc-dc conversion
A correctly spec’d MPPT controller can accept much higher voltages from the solar panels, so we can use these higher Voltages on the solar side of the system to increase efficiency, and it will drop this voltage to the correct level for the battery current state of charge, it also monitors the panels Maximum Power Point (MPPT = Maximum Power Point Tracking) as it varies during the day to make best use of the power( Watts) available from the solar array.
While being much more efficient for larger systems (<200w) it also enables us to put the panels in series increasing the output voltage of the array therefore allowing us to use thinner cable while maintaining efficiency.
While PWM controllers are rated in Amps as they are fixed to the voltage of the solar panels, a MPPT controller is rated in Watts as they can accept higher input voltages.
Amps X Volts = Watts
50A X 12V Solar Array = 600 Watts
50A X 48V Solar Array = 2400Watts
50A X 100V Solar Array = 5000 Watts
A Watt is the measure of the amount of energy available, as we increase the voltage, we can get more Watts for the same number of Amps supplied.
MPPT Advantages
• Efficient ~95% conversion • Solar not limited to battery voltage • More efficient cabling options
MPPT Disadvantages
• Cost significantly more that PWM • Larger requires more space • More complex design (less reliable)
Conclusion – Which one will we use?
As you can already probably guessed, we are going for the most efficient 800W+ system we can get and in our case that means using an MPPT controller. We have limited space for panels, but almost no limit on battery size and the necessary equipment storage so the advantages of the MPPT outweigh those of the PWM Controller.
While researching this we did come across a video from Australia that is directly targeted at the Van-life market, but had excellent examples of PWM and MPPT with solar.
The MC4 connector has become the standard for connecting to solar panels, it is IP67 rated being both water and dustproof, they are relatively simple to install with the correct tools and luckily these tools and getting cheaper and cheaper.
Most solar panels already come with a male and female MC4 connector already fitted for ease of connection.
These connectors can be used on 2.5mm, 4mm and 6mm single core solar PV cable, it is highly recommended to use the correct cable as the outer sleeve is designed to provide protection from heat, UV, oils, and solvents, it is basically a tough robust cable that is designed for outdoor use.
Today I am going to show you how to crimp on your own MC4 connectors using a cheap crimping tool kit that is available from eBay and amazon.
10 Female metal ferrules and 10 Male metal ferrules
All you will probably need now is some wire cutters and strippers and you are ready to install your own connectors.
Each MC4 connector is made up from a male and female plastic parts and male and female metal ferrules, the male metal ferrule fits inside the female plastic body and vice versa.
We made a video to show you how simple this can be
How to release the male/female parts
The plastic parts normally come already clipped together, you can use your fingers to release the clips holding the male/female parts together, but it is much simpler and safer to use the two prongs on the end of the blue plastic MC4 spanners provided.
Crimping on the connector
First we need to stripped back the plastic coating to expose approximately an 1/2 inch / 12 mm of the copper wire.
We are now going to crimp on the male metal ferrule.
Push the stripped wire into the ferrule so that the insulation is pressed up to the tabs we are going to crimp.
Then depending on the wire size select the smaller position on the crimp tool for 2.5mm, the middle for 4mm and the largest for 6mm wire, there are normally marked with the correct sizes.
The ferrules tabs should point towards the top of the crimp tool so that as they are crimped the tabs are folded over to tightly grip the exposed wire.
You can use the ratchet on the crimp tool to hold the ferrule while you insert the wire into the correct position before crimping.
Now push the male metal ferrule into the back end of the plastic female connector as until it clicks home.
If you are using the 6mm cable, you may have to unscrew the cap and removed the silicon seal with its crown clamp ring and push these onto the cable first before pushing the ferrule into the body of the connector.
Then push the silicon seal carefully in to the connector body and then lightly screw down the cap.
You should then use the MC4 spanners to tighten the cap firmly onto the body so that no screw thread is visible, at which point the connector will click, it should now fully tightened and sealed, best to give it a visual inspection to make sure you have not crossed the threads 🙁
We have now completed one end of the mc4 connector, we now repeat the process but using the male plastic connector and the female metal ferrule to make up the other side of the connecter.
Solar panel technology is a fast moving area, but as of today in 2023 there are two types of solid panels as well as flexible panels that are available for boats.
Solid Monocrystalline & Polycrystalline Panels
Monocrystalline are the current premium panels, they are made from silicon that is formed into bars and then cut into wafers. Monocrystalline can be identified as the surface looks dark and uniform, these are the most efficient of the main panel types.
Monocrystalline are around 20% efficient, in that they can convert about 20% of the energy that falls on them into power.
Polycrystalline are cheaper and less efficient, they are made by melting fragments of silicon to form wafers, they can be identified due to there blue speckled look.
Polycrystalline are around 14-16% efficient, in that they can convert about 15% of the energy that falls on them into power.
These silicon solar cells are placed between protective layers and bonded together in a similar way to the laminator you use in the office but on a much greater scale and higher heat, the quality of the encapsulation and material used in vital to the life of the panels. To finish the panels a frame is added and this is also carefully bonded to the now laminated panel with the wiring often via a flying lead with an MC4 connector already attached.
There are many other solar technologies that are yet to make it to the marine market either due to lower current efficiency or higher costs.
Flexible & Semi-Flexible Solar Panels
These are getting more common on boats and as it is a popular option on narrow and wide beam canal boats to have a curved roof. Made with a printed photovoltaic material or a fine Monocrystalline solar cells. Flexible panels are both lighter and robust once fitted and can be walked on, they do however have a shorter lifespan and are less efficient that they’re solid counterparts at between 10-15%. The cost in greater per Kw and also need to be glued to the roof, which can be a problem of you damage one or need to repaint, it also makes them impossible to tilt for optimal performance in poor light conditions.
Flexible panels would be a good option for us if our boat was newer with a more stable roof paint layer as we could cover much more of the roof with them without loosing any visability or access to the roof.
Our selection at the moment is still the Monocrystalline 415W Perlight Delta panels on the tilting mountings at the moment, but we will have a bit to investigate.
Over the past few years we have looked at a lot of solar panel mounting systems, the major problems on canal boats seems to be that the roofs are curved, they are then also covered in vents, ropes and storage for poles, and planks etc.
While we are moving the boat we want as lower profile as possible so we have a good clear view ahead without having to worry about low bridges etc . Our current mooring is near the fearsome M5 tunnel on the Droitwich Canal, which on a bad day, looks like it can scalp anything off the top of your boat.
All the systems we have seen are compromises dependent on the design of your boat, the design/size of your panels and layout of your roof.
Types of Solar Panel Mountings
Flat Mounting systems
Flat solar panel mounting systems are fitted directly to the roof of your boat they are probably suited to boats used in the summer months are the sun is more directly overhead.
These are the simplest to install, the most basic are ABS plastic corner mounts, that are fixed to the panel and directly to the roof. If you have a curved roof you will need mounts that lift the panel at each side high enough to clear the curve of the roof. They are probably best suited to narrow panels along the centre line of the roof.
Solid ABS-plastic Solar Panel Mounts
For long panels additional side mounts are recommended to keep the panels rigidly fixed, the example about is very common, this example comes from Sunworks UK.
Raised Solar Panel Mounting
There are may other flat style mounting, some are made of aluminium extrusion, but if you have a curved roof you will need to make sure they hold you panel high enough to clear mushroom vents and that dreaded rood curve.
Flat mountsare probably adequate in the summer with the sun overhead, but we planing on staying on our boat all year around so I have been investigating being able to tilt my panels.
I found this solar mounting on a boat in our marina, it is home designed by the boat owner, the adjustable feet have a ball joint and are bolted into the roof with a waterproof tape in-between, then an aluminium extrusion runs the length of the panel increasing the mounting hight and also adding signification strength to the panel, that can tend to flex under their own weight.
As you can see a lock nut holds the panel up and another clamps down on the aluminium this enables the hight to be adjusted. The owner also recommended a slight tilt from to back on the panels so that rain water did not collect on the panels.
The panels are then bolted to the aluminium extrusion , there are 6 of these mounting on each panel, making them very secure.
A lot of the advertised tilted panel systems come from the camper van market where they are often placed on the ground and turned to the best position, most of the ones I have seen and not designed for roof mounting and have a fixed tilt or only tilt to one side, not ideal for mounting on a boat roof.
One of the easiest and most common boat tillable mounting systems are these aluminium triangles, that allow some angle to be set and can adjusted to each side of the roof , while use with thin panels means they can be angled well it is not ideal for wider panel as the width of the panel makes it harder to get the correct and most efficient angles in the autumn , winter and spring (see chart below).
The ever popular triangle solar panel mounts
One of my favourite YouTube channels Minimal List modified some mounting to enable them to be used on the curved roof of there boat while also allowing them to be tilted to either site, I initially like this method, but further research and I think I have found and even better solution.
Minimal List Curved roof solution.
Probably for me so far the ultimate tilting panel mount comes from Midsummer Energy
May be the ultimate solar panel mount from Midsummer Energy
As you can see these mounts are not worried by the roof curve and have can be set at a very high tilt angle, ideal for all year round use, I have even seen these tilted front to back to a limited amount.
Have a look at a YouTube video from Never Enough Cruising to see them in action
Never Enough Cruising Solar Panel Setup
Why tilt your panels
Solar Panels work best when light from the sun hits them at a 90 degree angle, else as the angle gets near to 0 degrees the suns rays are reflected and bounce off the panel and are lost. Effective tilting of the panels can increase efficiency by upto 50%.
Over the year the Sun will be higher in the summer and lower in the sky during winter, using the example of Birmingham, as our boat is moored near there, I created a table of the optimum angles to tilt your solar panels during the day for the best power output.
Note:This could be still improved if you change the angle during the day as the sun is much lower in the sky in the early morning and late afternoon.
January
60°
February
57°
March
51°
April
43°
May
33°
June
27°
July
27°
August
33°
September
43°
October
51°
November
57°
December
60°
This table is based on the assumption that the solar panels are facing south and are not affected by shading or other obstructions. The optimal tilt angle is based on the latitude of Birmingham, which is around 52 degrees north. As you can see, the angle changes throughout the year to capture the most sunlight based on the sun’s position in the sky.
Note: Mounting your solar panels and galvanic corrosion
Galvanic corrosion is an electrochemical process where one metal corrodes in preference to another metal when it is in contact with through an electrolyte. The electrolyte is our case is dirty water. The metals are the steel roof and the aluminium solar mountings or the bolts that connect them.
You can minimise this corrosion using a painted finish, or by using non-metalic/rubber washers and or even a layer of sealant, like Sikaflex 291i Marine Adhesive & Sealant works well I am told and will be what I am using to seal/stick down my mounts
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