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Old 20-08-2018, 20:46   #1
Marine Service Provider

Join Date: Aug 2018
Posts: 12
Arrow Solar Panels: What I can tell you about

Hi everybody!
I'll take some time of my holidays in order to write this post on some subjects that customers frequently ask me hoping that could help someone here. I think it will be useful to discuss them in a public post so that everyone can benefit from it. Some of you already know me because they have already bought some flexible solar panels from my company, however with this post I'd only like to share my knowledge with you. I feel it as a duty since I always follow this forum in order to learn new technical .. about sailing a subject in which I don't know that much (I don't think I am a great sailor lol).

Anyway, I don't want to talk about my company, this is only an informative post.
It is difficult to summarize highly technical and nuanced issues in few words but I'll try to give you some basics about this theme.

Chapter1
SOLAR PANELS PRODUCTION DIFFERENCES

TRADITIONAL SOLAR PANELS (RIGID ONES)
Traditional solar panels are produced following the scheme below:



SEMI-FLEXIBLE SOLAR PANELS
Semi-flexible solar panels are produced following the scheme below, they can have two or more encapsulating layers (EVA) and different surfaces (PET, PTP, ETFE).




RELEVANT DIFFERENCES:
Semi-flexible solar panels have a different weight (usually 80% less than traditional ones) and they can take a more or less bowed shape, according to the kind of cell and the production process.
NB: Rigid panels are LESS expensive because they are produced in automatic production lines, moreover, since this panels don't have to flex, the materials used are completely different.
However, 90% of rigid panels are not covered by warranty if installed in the marine environment. Only a few producers build them following the standards of "salt mist" test. This means not only that panels will suffer frame and encampsulation damages since traditional panels have a rigid frame, they only have two layers of encapsulating coating while semi-flexible panels usually have four layers but also that they are not covered by any warranty.

Corrosion test allows verifying the resistance of components and materials used in high salt mist density areas. Indeed, salt can reduce the resistance both of metal and non-metal parts.level 1 of corrosion test, according to regulation IEC60068-2-52, is used to test products used in marine environments or near the sea and exposed to this conditions for the majority of their working life (e.g. Naval items). Level 1 is usually used as a general corrosion test in the warranty procedures for the components quality.
This test usually lasts 28 days and is made of 4 cycles. Modules are put in a specific room for 7 days. A salt mist solution is nebulized in the room at 33C and 85% of humidity. This procedure is repeated for times in each test cycle. The accelerated lab test simulates the effects of an environment characterized by high salt concentration, during the entire life of the panel.

Chapter 2
POLYCRYSTALLINE MONOCRYSTALLINE - SUNPOWER
first of all, I'd like to highlight that SUNPOWER CELLS ARE MONOCRYSTALLINE CELLS. They have the same structure of monocrystalline cells, the only difference is that they have contacts at the back of the cell, allowing it to have a uniform production surface. Since BUSBARs are not present on the cell, it produces more nominal power output at the same amount of surface. For this reason, I will talk about Sunpower as about any other monocrystalline cell.

The main difference between mono and polycrystalline is that the former can usually reach a higher percentage of efficiency (w/m2). However, this gap has been reduced in the last years and is now about 1.5% (between the best mono and the best polycrystalline).
On the other hand, polycrystalline panels are less expensive (the production process is simpler) and usually more flexible.

Which is the best one?
The only answer is that it depends on the situation...
Monocrystalline panels usually produce more instant Ampere when the sun is perpendicular to cells (orientation of crystals), on the contrary, polycrystalline ones will have lower peaks of production when the sun is perpendicular to cells and higher peaks when not perfectly exposed to the sun. Let us omit the description of the reasons (orientation of crystals).

So, can you direct the panel? You'll need a monocrystalline.
Is the panel flat maybe because placed on bimini? Do you have enough space? A polycrystalline will be the right choice.

You don't have much room, you should choose high-efficiency panels as Sunpower ones.


I'll show a simple video, made by our customer, in order to show you what I have explained. The panels are laid out as if they were on Bimini. Results: Sunpower panel: 4.5A; poly panel: 5A. If directed, the result will be the opposite.


https://youtu.be/EYxvz4bLsQk



Chapter3
Differences among semi-flexible solar panels

I'll try to explain the differences among the panels and how this influences the price.

Layers number: semi-flexible panels are made of at least 5 layers. Chinese panels usually use 5 layers, in order to keep prices lower (the structure is similar to that of rigid panels). High-quality panels are usually made of 7 or 9 layers, according to the type of superior and inferior layers.
Cells quality: like all industrial products, also cells have a rating of their qualities. They are divided in:
1. GRADE A: perfect cell
2. GRADE A-: (valid only for mono) the cell is perfect form the technical point of view but as non-uniform color
3. GRADE B: not perfect cell
4. GRADE C: cell with flaws
- BUSBAR type and connections, silver or aluminum
- Production materials, excellent encapsulators, PET or ETFE (this is a long issue if someone is interested I can write a comment on it).


How can we recognize them? It is impossible if you don't have a flash test machine. Anyway, some Chinese panels with Sunpower cells are sold at a price that is equal to the price of purchase of the Grade A Sunpower cells. This can make you understand that the cells used are not of grade A..





PET coating :In our case, it is used as an external coating for flexible panels because it has good mechanical resistance, malleability, and flexibility.


Given the degree and duration of the protection offered by the usage of these materials, it is difficult to suggest indiscriminate use in areas with constant or persistent adverse weather conditions. It is well known that PET has a low thermal resistance in the short term and therefore usage in very hot environments is not recommended.



In addition, PET is unable to withstand chemical attacks caused by the various acid and alkaline compounds dissolved in the water which will, in the long run, cause yellowing and then delamination or breakage of the plastic layer.

The strengths of this type of product thus focus on the flexibility of the panel, its low weight and small dimensions (for both panel and the junction box) and above all in the economical saving due to the use of widely used and easy to fabric plastic polymers.


However, if we look at a field of application such as the nautical one, we realize that these properties, though surely beneficial, are not sufficient to guarantee a high durability of the product.
At sea, exposure to deteriorating agents is practically constant, and in some cases, physical stress caused by a very rough sea conditions can also cause damages to the photovoltaic cells if they do not have adequate protection. For this reason, the best performing panels are built using ETFE.



Etfe is a fluoropolymer, or a polymer (a macromolecule consisting of a chain of the same molecules) that contains fluorine atoms.
The basic molecule is Ethene, the simplest of alkenes, unsaturated hydrocarbons having a double covalent bond between two carbon atoms. Its chemical formula is C2H4. The main feature of fluorinated polymers, and in particular ETF, lies in the fact that most of the chemical bonds present are of C-F (Carbon-Fluoro), one of the higher energy covalent bonds.
It follows that the molecules are very stable, able to withstand high levels of thermal stress and chemical aggression, more than other polymers. This is one of the important reasons why we use it for our nautical products.
In addition, Etfe is totally permeable to UV rays, so the transparency of the Etfe is 95% for a radius of 400 to 600 Nm, ie the spectrum of visible light, with a percentage of diffused light of 12 % and direct light equal to 88%
Chapter 4
Installation: parallel or in series?
Classic question, simple answer. Parallel when the panel could be potentially covered by shadows. If the panels are compatible the best solution is to install them using Schottky diodes. I found this video (that allows me to avoid a long explanation) that explains briefly why parallel installation is to prefer.


https://youtu.be/1qD3mN8VotQ


Chapter5
PWM or MPPT

MPPT and PWM are the two main types of charge controllers used in the photovoltaic industry for the charging management of the batteries connected to the PV system and during the planning phase of a stand-alone (which means it's not connected to the grid) or on-grid PV system, the right choice of the method of charging and the corresponding controller, is a key component for a smart and conscious setup of your own photovoltaic system.
Our comparison, however, cannot start without the necessary description of the two distinct types of regulators.
Following a chronological order, it makes sense to introduce for first the PWM (acronym of the English term Pulse Width Modulation) technology, introduced on the market when the interest in photovoltaics was addressed solely to off-grid and stand-alone applications.
In this sector, in fact, the "classics" photovoltaic modules features a 36-cell structure with an open circuit voltage equal to about 18 / 20V, designed for charging of the typical 12V batteries even in case of panel overheating conditions as a result of which it can, in fact, occur a decrease in the voltage output by the module itself.
Precisely because the fact that the normal photovoltaic modules deliver current at a voltage which is normally higher than the one at which the storage system operates, the principle of operation of the PWM regulators can be imagined as a switch that operates a rapid series of connections and disconnections between panel and battery in order to protect and control the battery voltage since this is never connected for excessive periods of time to the panel.


Therefore on a practical level, during the charging phase (we assume that the battery is initially discharged) the panel voltage is reduced depending on the closing and opening time of the PWM controller switch so that the panel voltage is the same of the battery. As the battery keeps charging, the charging voltage continues to increase. Finally, when the battery voltage absorption threshold is reached, to protect it from overcharging problems, the regulator switch is constantly open and closed. It is precisely from this mechanism that takes name the PWM class regulators.


This mechanism makes several aspects clear, such as PWM controllers are simple switches and NOT "DC to DC" converters since, to protect the storage system, they are forced to give up part of the additional power that the panel could generate because they can not convert it to amperes at the correct voltage. On the other hand, as the system is brought to the operating standard of the batteries, they undergo less thermal and electrical stress during the charging phase, thus extending life and allowing a virtually permanent state of float (ie maximum charge). It should also be kept in mind that being this the oldest technology, PWM controllers are generally cheaper and more reliable, especially when it comes to the complexity of internal electronics, compared to the MPPT counterparts.
Changing side, we come now to talk about the most recent of the two photovoltaic recharge technologies, introduced when the photovoltaic industry was also beginning to take up on photovoltaic systems connected to the national grid.


Here, however, the panel standard changes and from modules of 30/36 cells it passes to 60 or more cells, with (much) higher open voltages than 30V. In dealing with these panels but always using common 12V batteries, it immediately appears clear that using a PWM controller would waste at least half the power that the panel could deliver from its operating voltage.
It is, therefore, necessary to have a more complex energy collection mechanism that takes into account all the electrical characteristics of the system: from panel to battery.
These features and their correlations can easily be understood by using graphs describing the Ohm law P = V*I on a Cartesian plane Voltage (Vx)/Current (Ay), in which the power of the panel is expressed as the curve shape:



Then the same curve is matched with a second graph placed on a Cartesian plane Power (W)/Voltage (V) always observing the Ohm law P = V*I and deducted by the inverse derivation of the first (of which it represents the slope, that is the graphical representation of the derivative concept), which allows us to understand under what conditions we can obtain as much energy as possible from the panel at a given operating voltage, i.e. The MPP (Maximum Power Point).



The Determination of the Maximum Power Point within this graph occurs between two extremes: the case where the panel does not produce energy since it short circuit (0*I = 0) and the case where there is no load applied to the panel (V*0 = 0). Within this range, you can locate an area underneath the power curve, which reaches its maximum area just when the MPP meets the panel power curve:







Leaving aside further mathematical or geometric considerations on the identification of this point, we can state that the peculiarity of an MPPT regulator lies in its ability to detect the amperage and working voltage of the panel and convert them to the battery amperage and voltage, which makes these appliances real power converters.
In practice, an example of this kind can be helpful: assuming a 3A panel current, with a conventional PWM regulator this current (already calibrated by the controller for a 12V charging system) would be directly transferred to the battery.


An MPPT regulator analyzes the power generated by the panel (P = V x I, as mentioned before), and therefore considers the voltage as well: if we assume that this voltage is at that moment equal to 17V, the power delivered by the panel is 17V x 3A = 51W.


This means that if the battery charge voltage is 13V, considering the maximum power output of 51W, the charge current that will be transmitted to the battery is 51W/13V = 3.9A, which is about 30% more than what can bring the PWM controller.


Another remarkable feature of MPPT technology is its wide inter-compatibility: which means that it is possible to use panels designed to work at high voltages also to charge storage systems that work at significantly lower voltages. This, in turn, leads to another advantage: a lower power loss along the cables. In fact, by using high voltage panels, even considering long cable sizes from the panel to the controller, the loss of power at such high voltages (36V, 48V or more) is irrelevant to what would be on 12V systems.


Given their sophisticated technology, it must be noted that MPPT regulators generally have more advanced charging control functions: they often have systems that, by disconnecting panel and battery, prevent the inversion of the flow of current, a phenomenon that can occur at night when the panel does not produce electricity.


Given all these peculiarities, however, they can not miss some "disadvantages", which do not make the MPPT controller the only possible choice when looking for a charge controller for photovoltaic.
First of all, there is the purely economic factor: all the technology incorporated in the MPPT controllers often makes it double the prices, if not more, than the PWM counterparty with the same dispensable amperage, which is not an indifferent aspect for those who are planning a small-size system and therefore could decide to invest more on the panel than on the controller.

I hope you can be helpful, for any questions I am available
TD P { margin-bottom: 0cm; }P { margin-bottom: 0.21cm; }A:link { }
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Old 21-08-2018, 06:28   #2
Registered User

Join Date: Aug 2011
Location: Lake Macquarie NSW Australia
Boat: 2004 Lagoon 410S2
Posts: 378
Re: Solar Panels: What I can tell you about

Great Stuff. Your write up greatly assisted me in my final decision in purchasing 4 x 300 watt Monocrystalline panels and two MPPT controllers. I was having a look at the current wiring on m boat and was horrified to see that there are no isolation switches between the solar panels and the solar controller or any type of fuse from the controller to the battery.

The new system I am installing will consist of two by two panels wired in parralell with each going to two seperate 60 amp MPPT
solar controllers. I was going to take the output of each controller to a busbar so that I would have each of the two positive cables joined at a busbar then one larger current carrying capable cable going to the battery connection. Haivng gone through a lot of different forums and sources there seems to be some debate that you should not parralel solar controller outputs together, yet each output ultimately connects to the one battery bank effectively parraalling the system up. Can you assist with your thoughts.



Greg H
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Old 21-08-2018, 22:16   #3
Marine Service Provider

Join Date: Aug 2018
Posts: 12
Re: Solar Panels: What I can tell you about

Hey mate,

First of all, I'm glad that my post helped you a bit. Second, regards your request, well depends ...


Normally the MPPT solar chargers have an internal voltmeter and according to the battery setting, they decide the battery status ( Full, flat, etc). In certain case wiring 2 solar chargers at the same pole of the battery can cause a "mismatching" on the voltmeter that instead of detecting the real battery voltage, it detects the voltage emitted by the other regulator (which will always be higher than the battery voltage) and this can cause that one of the solar chargers goes into floating mode or blocks the charge.


You can avoid that problem in two ways, wire one MPPT to one battery, and the other to the opposite battery of the bank (even if are all wired in parallel together). This will prevent an incorrect evaluation of the battery status by the regulator. Or even better, you can put them in parallel following the factory directions if the solar charger allows the parallel setting. Some regulators in their manuals explain how to set the parallel (there are settings to be set on the controller) that allows you to have no problem.


About the protection, I always suggest one Schottky diode for each panel in parallel and one fuse with a breaker between batteries and solar charger.



Tip> On some MPPT you have to open the case for change the fuse and that makes you lost the warranty, so or you send it to the factory to change a fuse or you put a fuse on the wiring line so you change that not the internal one.
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Old 22-08-2018, 00:03   #4
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Re: Solar Panels: What I can tell you about

Thanks very much for making the effort with this post - great.
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Old 22-08-2018, 01:24   #5
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Join Date: Aug 2016
Location: Becalmed in the Med
Boat: Prout Snowgoose 35
Posts: 625
Re: Solar Panels: What I can tell you about

I have two 110w fly solar tech panels bought at the start of the year from Qookka. They are connected to a Victron 75/15. Happy with them so far, though was disappointed one arrived with a scratch on. As I was in Greece in wasn't worth the effort of trying to post it back.

Yield is as you'd expect so happy enough with that. The Fly Solartech decals faded in about 4 weeks.
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Old 22-08-2018, 01:38   #6
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Join Date: Aug 2018
Posts: 12
Re: Solar Panels: What I can tell you about

Quote:
Originally Posted by mikedefieslife View Post
I have two 110w fly solar tech panels bought at the start of the year from Qookka. They are connected to a Victron 75/15. Happy with them so far, though was disappointed one arrived with a scratch on. As I was in Greece in wasn't worth the effort of trying to post it back.

Yield is as you'd expect so happy enough with that. The Fly Solartech decals faded in about 4 weeks.

Good to know that, prob the scratch was made in the transport.. they are very easy to scratch (just the superficial layer). But fortunately, a scratch doesn't involve any loss of performance.


BTW, the logo is made of a special painting that changes color according to the temperature, if it has become whiter or completely transparent white it is normal. We use this painting bc in the case of panels comes back for warranty check with some problems we can analyze the temperature at which they worked
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Old 22-08-2018, 02:33   #7
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Re: Solar Panels: What I can tell you about

Quote:
Originally Posted by FLYsolartech View Post
Good to know that, prob the scratch was made in the transport.. they are very easy to scratch (just the superficial layer). But fortunately, a scratch doesn't involve any loss of performance.


BTW, the logo is made of a special painting that changes color according to the temperature, if it has become whiter or completely transparent white it is normal. We use this painting bc in the case of panels comes back for warranty check with some problems we can analyze the temperature at which they worked
Good to know. Thanks. Planning on another two this winter, just need to find somewhere to mount them.

Interesting information on the logo. I guess when I got the panels it wasn't hot yet. As soon as spring came it went more white/transparent as you say.
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Old 22-08-2018, 03:50   #8
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Join Date: Apr 2018
Posts: 7
Re: Solar Panels: What I can tell you about

Quote:
Originally Posted by FLYsolartech View Post
Hi everybody!
I'll take some time of my holidays in order to write this post on some subjects that customers frequently ask me hoping that could help someone here. I think it will be useful to discuss them in a public post so that everyone can benefit from it. Some of you already know me because they have already bought some flexible solar panels from my company, however with this post I'd only like to share my knowledge with you. I feel it as a duty since I always follow this forum in order to learn new technical .. about sailing a subject in which I don't know that much (I don't think I am a great sailor lol).

Anyway, I don't want to talk about my company, this is only an informative post.
It is difficult to summarize highly technical and nuanced issues in few words but I'll try to give you some basics about this theme.

Chapter1
SOLAR PANELS PRODUCTION DIFFERENCES

TRADITIONAL SOLAR PANELS (RIGID ONES)
Traditional solar panels are produced following the scheme below:



SEMI-FLEXIBLE SOLAR PANELS
Semi-flexible solar panels are produced following the scheme below, they can have two or more encapsulating layers (EVA) and different surfaces (PET, PTP, ETFE).




RELEVANT DIFFERENCES:
Semi-flexible solar panels have a different weight (usually 80% less than traditional ones) and they can take a more or less bowed shape, according to the kind of cell and the production process.
NB: Rigid panels are LESS expensive because they are produced in automatic production lines, moreover, since this panels don't have to flex, the materials used are completely different.
However, 90% of rigid panels are not covered by warranty if installed in the marine environment. Only a few producers build them following the standards of "salt mist" test. This means not only that panels will suffer frame and encampsulation damages since traditional panels have a rigid frame, they only have two layers of encapsulating coating while semi-flexible panels usually have four layers but also that they are not covered by any warranty.

Corrosion test allows verifying the resistance of components and materials used in high salt mist density areas. Indeed, salt can reduce the resistance both of metal and non-metal parts.level 1 of corrosion test, according to regulation IEC60068-2-52, is used to test products used in marine environments or near the sea and exposed to this conditions for the majority of their working life (e.g. Naval items). Level 1 is usually used as a general corrosion test in the warranty procedures for the components quality.
This test usually lasts 28 days and is made of 4 cycles. Modules are put in a specific room for 7 days. A salt mist solution is nebulized in the room at 33C and 85% of humidity. This procedure is repeated for times in each test cycle. The accelerated lab test simulates the effects of an environment characterized by high salt concentration, during the entire life of the panel.

Chapter 2
POLYCRYSTALLINE MONOCRYSTALLINE - SUNPOWER
first of all, I'd like to highlight that SUNPOWER CELLS ARE MONOCRYSTALLINE CELLS. They have the same structure of monocrystalline cells, the only difference is that they have contacts at the back of the cell, allowing it to have a uniform production surface. Since BUSBARs are not present on the cell, it produces more nominal power output at the same amount of surface. For this reason, I will talk about Sunpower as about any other monocrystalline cell.

The main difference between mono and polycrystalline is that the former can usually reach a higher percentage of efficiency (w/m2). However, this gap has been reduced in the last years and is now about 1.5% (between the best mono and the best polycrystalline).
On the other hand, polycrystalline panels are less expensive (the production process is simpler) and usually more flexible.

Which is the best one?
The only answer is that it depends on the situation...
Monocrystalline panels usually produce more instant Ampere when the sun is perpendicular to cells (orientation of crystals), on the contrary, polycrystalline ones will have lower peaks of production when the sun is perpendicular to cells and higher peaks when not perfectly exposed to the sun. Let us omit the description of the reasons (orientation of crystals).

So, can you direct the panel? You'll need a monocrystalline.
Is the panel flat maybe because placed on bimini? Do you have enough space? A polycrystalline will be the right choice.

You don't have much room, you should choose high-efficiency panels as Sunpower ones.


I'll show a simple video, made by our customer, in order to show you what I have explained. The panels are laid out as if they were on Bimini. Results: Sunpower panel: 4.5A; poly panel: 5A. If directed, the result will be the opposite.


https://youtu.be/EYxvz4bLsQk



Chapter3
Differences among semi-flexible solar panels

I'll try to explain the differences among the panels and how this influences the price.

Layers number: semi-flexible panels are made of at least 5 layers. Chinese panels usually use 5 layers, in order to keep prices lower (the structure is similar to that of rigid panels). High-quality panels are usually made of 7 or 9 layers, according to the type of superior and inferior layers.
Cells quality: like all industrial products, also cells have a rating of their qualities. They are divided in:
1. GRADE A: perfect cell
2. GRADE A-: (valid only for mono) the cell is perfect form the technical point of view but as non-uniform color
3. GRADE B: not perfect cell
4. GRADE C: cell with flaws
- BUSBAR type and connections, silver or aluminum
- Production materials, excellent encapsulators, PET or ETFE (this is a long issue if someone is interested I can write a comment on it).


How can we recognize them? It is impossible if you don't have a flash test machine. Anyway, some Chinese panels with Sunpower cells are sold at a price that is equal to the price of purchase of the Grade A Sunpower cells. This can make you understand that the cells used are not of grade A..





PET coating :In our case, it is used as an external coating for flexible panels because it has good mechanical resistance, malleability, and flexibility.


Given the degree and duration of the protection offered by the usage of these materials, it is difficult to suggest indiscriminate use in areas with constant or persistent adverse weather conditions. It is well known that PET has a low thermal resistance in the short term and therefore usage in very hot environments is not recommended.



In addition, PET is unable to withstand chemical attacks caused by the various acid and alkaline compounds dissolved in the water which will, in the long run, cause yellowing and then delamination or breakage of the plastic layer.

The strengths of this type of product thus focus on the flexibility of the panel, its low weight and small dimensions (for both panel and the junction box) and above all in the economical saving due to the use of widely used and easy to fabric plastic polymers.


However, if we look at a field of application such as the nautical one, we realize that these properties, though surely beneficial, are not sufficient to guarantee a high durability of the product.
At sea, exposure to deteriorating agents is practically constant, and in some cases, physical stress caused by a very rough sea conditions can also cause damages to the photovoltaic cells if they do not have adequate protection. For this reason, the best performing panels are built using ETFE.



Etfe is a fluoropolymer, or a polymer (a macromolecule consisting of a chain of the same molecules) that contains fluorine atoms.
The basic molecule is Ethene, the simplest of alkenes, unsaturated hydrocarbons having a double covalent bond between two carbon atoms. Its chemical formula is C2H4. The main feature of fluorinated polymers, and in particular ETF, lies in the fact that most of the chemical bonds present are of C-F (Carbon-Fluoro), one of the higher energy covalent bonds.
It follows that the molecules are very stable, able to withstand high levels of thermal stress and chemical aggression, more than other polymers. This is one of the important reasons why we use it for our nautical products.
In addition, Etfe is totally permeable to UV rays, so the transparency of the Etfe is 95% for a radius of 400 to 600 Nm, ie the spectrum of visible light, with a percentage of diffused light of 12 % and direct light equal to 88%
Chapter 4
Installation: parallel or in series?
Classic question, simple answer. Parallel when the panel could be potentially covered by shadows. If the panels are compatible the best solution is to install them using Schottky diodes. I found this video (that allows me to avoid a long explanation) that explains briefly why parallel installation is to prefer.


https://youtu.be/1qD3mN8VotQ


Chapter5
PWM or MPPT

MPPT and PWM are the two main types of charge controllers used in the photovoltaic industry for the charging management of the batteries connected to the PV system and during the planning phase of a stand-alone (which means it's not connected to the grid) or on-grid PV system, the right choice of the method of charging and the corresponding controller, is a key component for a smart and conscious setup of your own photovoltaic system.
Our comparison, however, cannot start without the necessary description of the two distinct types of regulators.
Following a chronological order, it makes sense to introduce for first the PWM (acronym of the English term Pulse Width Modulation) technology, introduced on the market when the interest in photovoltaics was addressed solely to off-grid and stand-alone applications.
In this sector, in fact, the "classics" photovoltaic modules features a 36-cell structure with an open circuit voltage equal to about 18 / 20V, designed for charging of the typical 12V batteries even in case of panel overheating conditions as a result of which it can, in fact, occur a decrease in the voltage output by the module itself.
Precisely because the fact that the normal photovoltaic modules deliver current at a voltage which is normally higher than the one at which the storage system operates, the principle of operation of the PWM regulators can be imagined as a switch that operates a rapid series of connections and disconnections between panel and battery in order to protect and control the battery voltage since this is never connected for excessive periods of time to the panel.


Therefore on a practical level, during the charging phase (we assume that the battery is initially discharged) the panel voltage is reduced depending on the closing and opening time of the PWM controller switch so that the panel voltage is the same of the battery. As the battery keeps charging, the charging voltage continues to increase. Finally, when the battery voltage absorption threshold is reached, to protect it from overcharging problems, the regulator switch is constantly open and closed. It is precisely from this mechanism that takes name the PWM class regulators.


This mechanism makes several aspects clear, such as PWM controllers are simple switches and NOT "DC to DC" converters since, to protect the storage system, they are forced to give up part of the additional power that the panel could generate because they can not convert it to amperes at the correct voltage. On the other hand, as the system is brought to the operating standard of the batteries, they undergo less thermal and electrical stress during the charging phase, thus extending life and allowing a virtually permanent state of float (ie maximum charge). It should also be kept in mind that being this the oldest technology, PWM controllers are generally cheaper and more reliable, especially when it comes to the complexity of internal electronics, compared to the MPPT counterparts.
Changing side, we come now to talk about the most recent of the two photovoltaic recharge technologies, introduced when the photovoltaic industry was also beginning to take up on photovoltaic systems connected to the national grid.


Here, however, the panel standard changes and from modules of 30/36 cells it passes to 60 or more cells, with (much) higher open voltages than 30V. In dealing with these panels but always using common 12V batteries, it immediately appears clear that using a PWM controller would waste at least half the power that the panel could deliver from its operating voltage.
It is, therefore, necessary to have a more complex energy collection mechanism that takes into account all the electrical characteristics of the system: from panel to battery.
These features and their correlations can easily be understood by using graphs describing the Ohm law P = V*I on a Cartesian plane Voltage (Vx)/Current (Ay), in which the power of the panel is expressed as the curve shape:



Then the same curve is matched with a second graph placed on a Cartesian plane Power (W)/Voltage (V) always observing the Ohm law P = V*I and deducted by the inverse derivation of the first (of which it represents the slope, that is the graphical representation of the derivative concept), which allows us to understand under what conditions we can obtain as much energy as possible from the panel at a given operating voltage, i.e. The MPP (Maximum Power Point).



The Determination of the Maximum Power Point within this graph occurs between two extremes: the case where the panel does not produce energy since it short circuit (0*I = 0) and the case where there is no load applied to the panel (V*0 = 0). Within this range, you can locate an area underneath the power curve, which reaches its maximum area just when the MPP meets the panel power curve:







Leaving aside further mathematical or geometric considerations on the identification of this point, we can state that the peculiarity of an MPPT regulator lies in its ability to detect the amperage and working voltage of the panel and convert them to the battery amperage and voltage, which makes these appliances real power converters.
In practice, an example of this kind can be helpful: assuming a 3A panel current, with a conventional PWM regulator this current (already calibrated by the controller for a 12V charging system) would be directly transferred to the battery.


An MPPT regulator analyzes the power generated by the panel (P = V x I, as mentioned before), and therefore considers the voltage as well: if we assume that this voltage is at that moment equal to 17V, the power delivered by the panel is 17V x 3A = 51W.


This means that if the battery charge voltage is 13V, considering the maximum power output of 51W, the charge current that will be transmitted to the battery is 51W/13V = 3.9A, which is about 30% more than what can bring the PWM controller.


Another remarkable feature of MPPT technology is its wide inter-compatibility: which means that it is possible to use panels designed to work at high voltages also to charge storage systems that work at significantly lower voltages. This, in turn, leads to another advantage: a lower power loss along the cables. In fact, by using high voltage panels, even considering long cable sizes from the panel to the controller, the loss of power at such high voltages (36V, 48V or more) is irrelevant to what would be on 12V systems.


Given their sophisticated technology, it must be noted that MPPT regulators generally have more advanced charging control functions: they often have systems that, by disconnecting panel and battery, prevent the inversion of the flow of current, a phenomenon that can occur at night when the panel does not produce electricity.


Given all these peculiarities, however, they can not miss some "disadvantages", which do not make the MPPT controller the only possible choice when looking for a charge controller for photovoltaic.
First of all, there is the purely economic factor: all the technology incorporated in the MPPT controllers often makes it double the prices, if not more, than the PWM counterparty with the same dispensable amperage, which is not an indifferent aspect for those who are planning a small-size system and therefore could decide to invest more on the panel than on the controller.

I hope you can be helpful, for any questions I am available
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Excellent post. Thank you.
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Old 22-08-2018, 05:32   #9
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Re: Solar Panels: What I can tell you about

This is great information and timely, since it was a topic I was researching for our next boat. Thanks for taking the time to put it all together. More please. (full disclosure: I wouldn't even know what questions to ask next)
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Old 22-08-2018, 10:59   #10
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Re: Solar Panels: What I can tell you about

Do rigid panels lose efficiency over time? For what reason? We have 4-80watt panels mounted horizontally on our radar arch. They are paralleled, with a Shottkey diode each, to a common bus bar, then to my Victron MPPT Controller, and to my 675amphr batt bank. We first installed them in Phuket, Thailand in 2012, and have noticed a growing decrease in their output over the years since. Now, in the Caribb at high noon, the BEST output we see is about 11 amps; it quickly decreases (as it should) as the sun sets. Thr outer covers on all 4 appear to be clear and in one piece, but a few of the cells are discolored. Or...are they just in need of replacement?
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Old 22-08-2018, 19:28   #11
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Re: Solar Panels: What I can tell you about

Sure there is decrease due to loss of efficiency. I am not a solar guy yet, but I would do the following first:
  1. Clean the surface of all panels with the appropriate solutions.
  2. Remove all terminals and joints, careully clean them and add a dielectric solution all the way to the controllers.
  3. Turn off or disconnect the battery and clean all controller and busbar connections to the battery.
  4. Then you are not finished. Clean and retighten all connections associated with your battery moniter. Also check to see where these sensors are located to make sure they are on or at most one connection away.
  5. Your enemy is time, oxidation and voltage drop.
You will hear a lot of other good suggestions from others.
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Old 23-08-2018, 02:33   #12
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Re: Solar Panels: What I can tell you about

Quote:
Originally Posted by sailcrazy View Post
Do rigid panels lose efficiency over time? For what reason? We have 4-80watt panels mounted horizontally on our radar arch. They are paralleled, with a Shottkey diode each, to a common bus bar, then to my Victron MPPT Controller, and to my 675amphr batt bank. We first installed them in Phuket, Thailand in 2012, and have noticed a growing decrease in their output over the years since. Now, in the Caribb at high noon, the BEST output we see is about 11 amps; it quickly decreases (as it should) as the sun sets. Thr outer covers on all 4 appear to be clear and in one piece, but a few of the cells are discolored. Or...are they just in need of replacement?

Yes they do it! Each photovoltaic panel has a gradual loss of performance. It is more pronounced if the product is less expensive because they used cheap products to produce it.

To explain it in few words, if one gram of silver costs 40 cents and one gram of aluminum costs 8 cents, if I had to build a cheap solar panel I would use an aluminum as conductor rather than silver, which does not have the same characteristics of conductivity, immutability, etc. .

The same applies to the EVA encapsulants that could be used to create the panel. Different EVAs could have a huge difference in transmission, resistance to detachment, etc.

The more economical the products are, the more this affects the drop in the performance of the panels.

This applies to both traditional solar panels and semi-flexible solar panels.Unfortunately, there is nothing you can do to revamp those panels.
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Old 23-08-2018, 02:43   #13
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Re: Solar Panels: What I can tell you about

Quote:
Originally Posted by rgleason View Post
Sure there is decrease due to loss of efficiency. I am not a solar guy yet, but I would do the following first:
  1. Clean the surface of all panels with the appropriate solutions.
  2. Remove all terminals and joints, careully clean them and add a dielectric solution all the way to the controllers.
  3. Turn off or disconnect the battery and clean all controller and busbar connections to the battery.
  4. Then you are not finished. Clean and retighten all connections associated with your battery moniter. Also check to see where these sensors are located to make sure they are on or at most one connection away.
  5. Your enemy is time, oxidation and voltage drop.
You will hear a lot of other good suggestions from others.

All exact! But if the cells are changing color that means that the EVA is not doing the protections work anymore and the cells are oxidizing (not the cells to be precise but the busbars).


Tip> If you are lucky that your panels are covered by a warranty even if they are installed in a Marine environment (as I said just less the 10% of the standard solar panels are), check what cleaning products you can use to clean them on the manual, many producers allow only water or they specify the type of detergents because of the characteristics of the glass.
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Old 23-08-2018, 03:48   #14
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Re: Solar Panels: What I can tell you about

Many thanks for the information. made my decision a bit easier and will take the output of the controllers to seperate batteries.



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Old 23-08-2018, 05:42   #15
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Re: Solar Panels: What I can tell you about

Great compilation. It took me nearly a year to figure most of this out on my own.

We learned from several lightning hits to be able to isolate electronics. I have two pole breakers, one per panel to isolate each totally from the vessel. Likewise, the ins and outs and battery sense for the MPPT controller are also two pole breakers. When a storm approaches, everything gets shut down. This wiring also makes any maintenance easier.
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