Solar upgrade

[gordonsick]

Originally Posted by DogFather

Thanks, Gordon, that's very good info.

I don't think my panels have the diodes, but I'd like to add them as you discussed.

Do you have a diode spec or link to other info on this?

John,
I just bought a bunch of diodes from an electrical supply store with various current capacities. My 100W solar panel is rated for a maximum of 5.62 amps with a maximum of 18volts per panel, so I need a diode that will handle at least 5.62 amps and 18 volts. So, if I had 3 amp diodes, I'd use two in series for one panel, for example. And, both panels need the diodes.

For example, Fry's sells a bunch of diodes and here is a Zener diode that handles 43V and 2.8 amps. You'd need two (or 3 for safety) for each panel:
https://www.frys.com/product/1002223...romSearch=true

Note that I haven't done the installation yet, but I'm confident that this is the right setup. If we have an electronics guru who knows more about Zener diodes, I'd be happy for confirmation or correction.

–Gordon

[gordonsick]

In a private message, I was directed to a web page by AM Solar that seems to claim that using diodes is problematic. The web page is at https://amsolar.com/solar-panels-for...nt-do?rq=diode

I believe that web page is very misleading. Here is part of my response to the sender, who was using his panels in parallel, rather than series, so my first remark is about parallel rather than series connections, which is not the primary content of the AM Solar page.

1. If you are using a high performance controller, it will be an MPPT controller (maximum power point tracking), but these controllers require high voltage, typically 35-50 volts. If they only have 18v of input, their performance degrades to that of the cheaper, low-performance, PWM controllers (pulse-width modulation). So, I assume you are running a PWM controller, since you are running the panels in parallel and thus only getting a maximum of 18 volts. In that case, AM Solar is right and there is no advantage to running external shunt diodes.

2. AM Solar describes an unlikely situation where you could burn out the diodes by connecting them in reverse. It is true that you could hook up the diodes in reverse and burn them up. But, if the diodes are installed by the panel manufacturer, it is unlikely that they would install them in reverse. And, the MC-4 connectors are polarized, so it is unlikely that a clumsy installer would get them backwards. BTW, as I read the documentation on Zener diodes, it appears that they do not burn out when connected in reverse. They just stop the current. Other types of diodes can burn out if facing a large reverse voltage.

3. An ideal solar panel would have a diode shunting across each cell. This would have to be done in the manufacturing process. While I can't be sure if the good manufacturers are doing this or only installing two diodes across series banks of 18 cells as in the the AM Solar diagram. But, if every cell has a diode shunt, a shaded cell would only drop the voltage by 1 volt, and the rest of the panel would be providing enough voltage for an MPPT or PWM controller to work well.

4. Finally, I believe that the 2nd and 4th diagrams in the AM Solar page are erroneous. The diagrams suggest that one or two shaded cells would cause the diode across 18 cells to shunt. As I understand things, that shouldn't happen: the shaded cells would drop the voltage, but they wouldn't drop the voltage to zero, which is where the diode would kick in.

It seems likely to me that AM Solar is not selling panels with the diodes and is trying to confuse users into thinking they are a leading supplier.

–Gordon

[TitanMike]

Originally Posted by gordonsick

John,
I just bought a bunch of diodes from an electrical supply store with various current capacities. My 100W solar panel is rated for a maximum of 5.62 amps with a maximum of 18volts per panel, so I need a diode that will handle at least 5.62 amps and 18 volts. So, if I had 3 amp diodes, I'd use two in series for one panel, for example. And, both panels need the diodes.

For example, Fry's sells a bunch of diodes and here is a Zener diode that handles 43V and 2.8 amps. You'd need two (or 3 for safety) for each panel:
https://www.frys.com/product/1002223...romSearch=true

Note that I haven't done the installation yet, but I'm confident that this is the right setup. If we have an electronics guru who knows more about Zener diodes, I'd be happy for confirmation or correction.

–Gordon

Zener diodes are voltage regulating diodes. They block current flow until their design voltage is reached and then allow it to flow freely. Used in voltage regulating circuits where a set voltage is required.

The type of diode used in solar panels are Schottky diodes. Fast switching action and low forward voltage drop.

There's more to adding diodes to panels than just soldering in some random diodes.

How many buses connecting individual cells do your panels have? The diodes connect the buses to the output leads.

Also, it's best to select Schottky diodes on the basis of lowest forward voltage drop rather thsn price.

[TitanMike]

Originally Posted by TitanMike

Zener diodes are voltage regulating diodes. They block current flow until their design voltage is reached and then allow it to flow freely. Used in voltage regulating circuits where a set voltage is required.

The type of diode used in solar panels are Schottky diodes. Fast switching action and low forward voltage drop.

There's more to adding diodes to panels than just soldering in some random diodes.

How many buses connecting individual cells do your panels have? The diodes connect the buses to the output leads.

Also, it's best to select Schottky diodes on the basis of lowest forward voltage drop rather thsn price.

Btw, open the junction box on the back of your solar panel where main wires come out. Chances are you will find diodes already installed.

[gordonsick]

TitanMike,
That is some useful information. Thanks.

The Zener diode that I linked to from Frys switches at 1 or 2 volts. That would work well for a whole 18v panel, but not good enough for shunting an individual cell.

As you say, the Schottky diode seems to the be preferred shunt diode in this solar panel setting. That is mentioned at https://en.wikipedia.org/wiki/Schottky_diode

At Fry's this particular Schottky diode might work well: https://www.frys.com/product/1003123...romSearch=true
It will carry 10 amps and opens the shunt at .57V - .84V, if I understand things correctly, so it would work well if we have two panels in series.

I could open the strip where the wires come out of my panel, but I'd risk the weatherproofing.

The reason I haven't done anything on my panel yet is that I had originally planned to test whether I was getting a voltage drop from shaded cells. I haven't gotten around to that project yet. There is too much shade in my back yard to do a proper test. But, I do have good sun on my panel at the storage yard. I'll do that in the late spring or summer when the sun is good. I've just been do busy to give that project a higher priority...

–Gordon

[TitanMike]

You're going down the wrong road with zener diodes. They will flow current both ways. That voltage rating is when two-way current occurs.

There is a reason Schottky diodes are the preferred item. Because it's the right one.

Originally Posted by gordonsick

TitanMike,
That is some useful information. Thanks.

The Zener diode that I linked to from Frys switches at 1 or 2 volts. That would work well for a whole 18v panel, but not good enough for shunting an individual cell.

As you say, the Schottky diode seems to the be preferred shunt diode in this solar panel setting. That is mentioned at https://en.wikipedia.org/wiki/Schottky_diode

At Fry's this particular Schottky diode might work well: https://www.frys.com/product/1003123...romSearch=true
It will carry 10 amps and opens the shunt at .57V - .84V, if I understand things correctly, so it would work well if we have two panels in series.

I could open the strip where the wires come out of my panel, but I'd risk the weatherproofing.

The reason I haven't done anything on my panel yet is that I had originally planned to test whether I was getting a voltage drop from shaded cells. I haven't gotten around to that project yet. There is too much shade in my back yard to do a proper test. But, I do have good sun on my panel at the storage yard. I'll do that in the late spring or summer when the sun is good. I've just been do busy to give that project a higher priority...

–Gordon

[gordonsick]

The Dokio panel on Amazon https://www.amazon.com/DOKIO-Semi-Fl...rnFromLogin=1& says that it has the ETFE laminate, which is claimed by others to be the best coating. And, it shows a picture that says "Built-in Diode" and seems to point to a single cell (at the back). It could also be pointing to a descriptive label for the whole panel.

Thus, it might be indicating that each cell has a shunt diode, which I believe is best, but also expensive, or that the panel as a whole has a shunt diode. The fact that it says "diode" rather than "diodes" may suggest a single diode, but it could also be written by someone who can't distinguish singular from plural.

The price is low, so I'm tempted to buy a couple of their panels in the spring so that I can check them out in the sun.

–Gordon

[tomkatb]

Owners report 25 amps of charging generally from flat 100 watt installed panels per day.

In the Midwest we have many trees and lots of clouds that reduces solar output.

Batteries are still the weak link. Probably until 2030 or later.

How much solar you add depends on your usage. In the Midwest air conditioning is a must. Solar is a drop in the bucket.

[TitanMike]

Originally Posted by gordonsick

The Dokio panel on Amazon https://www.amazon.com/DOKIO-Semi-Fl...rnFromLogin=1& says that it has the ETFE laminate, which is claimed by others to be the best coating. And, it shows a picture that says "Built-in Diode" and seems to point to a single cell (at the back). It could also be pointing to a descriptive label for the whole panel.

Thus, it might be indicating that each cell has a shunt diode, which I believe is best, but also expensive, or that the panel as a whole has a shunt diode. The fact that it says "diode" rather than "diodes" may suggest a single diode, but it could also be written by someone who can't distinguish singular from plural.

The price is low, so I'm tempted to buy a couple of their panels in the spring so that I can check them out in the sun.

–Gordon

Reading their literature "diode" may well be singular. In the context used it's to prevent reverse current from battery through pv cells.

A blocking diode, not bypass diode.

As for modifyint these flex panels, best of luck.

[rk06382]

I made sure my Renogy panels had bypass diodes before purchasing. I am using ten Renogy 100W Mono Compact RNG-100D-SS panels in parallel. I was still working when my installer mounted my first six panels. It was cheaper to get him to install in parallel than in series parallel. The Open Circuit Voltage of the RNG-100D-SS is 21.7v. High enough for me to get 700 watt from my ten panels.

quote below is from a Renogy "INSTALLATION GUIDE FOR PHOTOVOLTAIC (PV) MODULES" downloaded in 2018. (No longer on Renogy)
Renogy RNG_Installation_Manual_UL.pdf

5.3 Bypass Diodes
The junction boxes used with the Renogy modules contain bypass diodes that are wired in parallel with the PV string cells. In the event the modules experience partial shading, the diodes are activated to bypass the current generated by the non-shaded cells, therefore limiting module heating and performance losses. However, they do not protect the panel from over-current. Over-current protections devices must be used when connecting more than 2 modules in series.

 All modules rated greater than 55 Watt have bypass diode already integrated in the junction box.
 In the unlikely event of diode failure Renogy recommends a qualified service technician be employed to determine if diodes have failed and to make replacement.

[TitanMike]

Originally Posted by rk06382

I made sure my Renogy panels had bypass diodes before purchasing. I am using ten Renogy 100W Mono Compact RNG-100D-SS panels in parallel. I was still working when my installer mounted my first six panels. It was cheaper to get him to install in parallel than in series parallel. The Open Circuit Voltage of the RNG-100D-SS is 21.7v. High enough for me to get 700 watt from my ten panels.

quote below is from a Renogy "INSTALLATION GUIDE FOR PHOTOVOLTAIC (PV) MODULES" downloaded in 2018. (No longer on Renogy)
Attachment 245971

5.3 Bypass Diodes
The junction boxes used with the Renogy modules contain bypass diodes that are wired in parallel with the PV string cells. In the event the modules experience partial shading, the diodes are activated to bypass the current generated by the non-shaded cells, therefore limiting module heating and performance losses. However, they do not protect the panel from over-current. Over-current protections devices must be used when connecting more than 2 modules in series.

 All modules rated greater than 55 Watt have bypass diode already integrated in the junction box.
 In the unlikely event of diode failure Renogy recommends a qualified service technician be employed to determine if diodes have failed and to make replacement.

As a side note, for those that like to "tweak" their electrical systems, the diodes used for bypass can vary widely in the amount of forward voltage drop.

There have been numerous internet posts on how Schottky diodes can be tested and those with the lowest forward voltage drop used to replace the OEM diodes if they have high voltage drop.

Open the cover (which is usually sealed with an O-Ring so will still be weatherproof when closed back up) and carefully unsolder one end of each diode. Check forward voltage drop using an Ohmmeter. In one direction the diode will show almost infinite resistance and in the other it will show very little. The lower the number the better. Record this reading for each and then shop for the same current rating diodes that claim the lowest forward voltage drop. Also check the internet as many have tested different brands and have done the work already.

They're inexpensive so order more than you need and carefully select the lowest voltage drop diodes from the ones purchased. When I say inexpensive, one can purchase 25 of them for ~$8 on Amazon.

The more panels and likelihood of shading, the lower you want this forward voltage drop to be as it all adds up.

Here's what the inside of these junction boxes glued to the back of a solar panel look like if you haven't been inside one yet:

[gordonsick]

Originally Posted by rk06382

I made sure my Renogy panels had bypass diodes before purchasing. I am using ten Renogy 100W Mono Compact RNG-100D-SS panels in parallel. I was still working when my installer mounted my first six panels. It was cheaper to get him to install in parallel than in series parallel. The Open Circuit Voltage of the RNG-100D-SS is 21.7v. High enough for me to get 700 watt from my ten panels.

quote below is from a Renogy "INSTALLATION GUIDE FOR PHOTOVOLTAIC (PV) MODULES" downloaded in 2018. (No longer on Renogy)
Attachment 245971

5.3 Bypass Diodes
The junction boxes used with the Renogy modules contain bypass diodes that are wired in parallel with the PV string cells. In the event the modules experience partial shading, the diodes are activated to bypass the current generated by the non-shaded cells, therefore limiting module heating and performance losses. However, they do not protect the panel from over-current. Over-current protections devices must be used when connecting more than 2 modules in series.

 All modules rated greater than 55 Watt have bypass diode already integrated in the junction box.
 In the unlikely event of diode failure Renogy recommends a qualified service technician be employed to determine if diodes have failed and to make replacement.

Thanks. That's useful to know. It isn't explicit about how many bypass diodes they use in each panel, but it does look very encouraging.

–Gordon

[gordonsick]

Originally Posted by TitanMike

As a side note, for those that like to "tweak" their electrical systems, the diodes used for bypass can vary widely in the amount of forward voltage drop.

There have been numerous internet posts on how Schottky diodes can be tested and those with the lowest forward voltage drop used to replace the OEM diodes if they have high voltage drop.

Open the cover (which is usually sealed with an O-Ring so will still be weatherproof when closed back up) and carefully unsolder one end of each diode. Check forward voltage drop using an Ohmmeter. In one direction the diode will show almost infinite resistance and in the other it will show very little. The lower the number the better. Record this reading for each and then shop for the same current rating diodes that claim the lowest forward voltage drop. Also check the internet as many have tested different brands and have done the work already.

They're inexpensive so order more than you need and carefully select the lowest voltage drop diodes from the ones purchased. When I say inexpensive, one can purchase 25 of them for ~$8 on Amazon.

The more panels and likelihood of shading, the lower you want this forward voltage drop to be as it all adds up.

Here's what the inside of these junction boxes glued to the back of a solar panel look like if you haven't been inside one yet:

TitanMike,
This is very useful. Presumably you are recommending to get Schottky diodes. You also have to make sure they will carry the maximum current (5 or 6 amps) of the panel.

It seems like you have a junction box for a hard panel, and it can be opened easily. All the flexible panels like Dokio and Renogy have a slim junction box that doesn't look like it is intended to be opened.

Also, it looks like you've got two diodes in your box, so they have split the panel into two sections of 18 volts. Presumably they are both hooked in parallel.

–Gordon

[gordonsick]

Hmm, looking more closely at the photo, it looks like the two sections are in series, so they are 9 volts each. That more closely resembles the philosophy of having a shunt diode on each cell.

Also, I noticed that the Renogy manual cited in the other post seems to be for hard-side panels and it does describe opening the junction box to replace diodes.

–Gordon

[TitanMike]

Originally Posted by gordonsick

TitanMike,
This is very useful. Presumably you are recommending to get Schottky diodes. You also have to make sure they will carry the maximum current (5 or 6 amps) of the panel.

It seems like you have a junction box for a hard panel, and it can be opened easily. All the flexible panels like Dokio and Renogy have a slim junction box that doesn't look like it is intended to be opened.

Also, it looks like you've got two diodes in your box, so they have split the panel into two sections of 18 volts. Presumably they are both hooked in parallel.

–Gordon

Actually, unless your panel is much larger and has a spec'd Imp over 6 amps, the Diodes only have to carry 1/3 the rated current (cells in panel connected in 3 separate arrays joined by diodes. A 3 amp Shottky will often be sufficient but most sold are at least 5 amp.

Going too large just runs the risk of creating a larger forward voltage drop.

As for Shottky's being preferred, the actual 'preferred' device is becoming the "Active Diode" which is an integration of diode and FET device and has a forward voltage drop of around 90 mv. vs up to .5 volts on regular Schottky's.

Based on current supply of these devices it appears that Solar manufacturers are gobbling all they can get up. Unit price if you want to buy 5,000 from China is ~$5-$6 ea but good luck buying any as a consumer right now.

[zb39]

When not on a trip I keep one battery tender on the chassis and one on the house batteries.

About $100 total. When on a trip I have all the power I need from the alternator or the 10K

genset.

[ricksmithgolfer]

I would suggest you go on the amsolar website and you will be amazed on all the info on their website. They are probably one of the premier rv specific installers in the states. I purchased all my solar needs from them and did the install myself. One cool thing they make are the solar panel mounts that allow you to tilt your panels. Great for being able to clean the roof under the panels. They also can mount their panels on a fiberglass roof using I believe VHS tape - no screws into your roof. They say after decades in the business they have never lost a panel on their installs. Another thing to consider if you want to expand your system is the importance of the gauge of wire that goes from the roof down to the controller in the bay. You need to verify this, but I was told by another member the Berkshires run only 10 gauge wire. Again, go on amsolar website and they have tons of info to help the do it yourselfer. This company is so popular I believe they are booked out for installs many months in advance. Hope this helps you out. I installed my 400 watt solar system on my Southwind and it works awesome. Hope sometime in the near future to purchase a Berkshire 39A. Good luck with your system.

[Jeff Walker]

Originally Posted by Trappfarmer

It seems like the rend is toward adding solar panels for charging batteries and maintaining batteries when not on a trip.
We have a 100w system that came with the unit from FR. Thinking of adding 1 or 2 or even 3 more.
Would like to here some comments from those that have done this.

I live in sunny Southern California. I added 3 panels, 6 lithium batteries controlled with a 2000 watt inverter. I’ve yet to plug in or run the batteries lower than 35%. Love it.

[Marv n Mabel]

We boondock 100% in Montana and went with 510 watts of panels. Absolutely love it! 3 inverted outlets, we want for nothing more

[Ripter]

Wow, this has gone deep into the weeds. I just installed two Lion lithium batteries, a single 315w Canadian Solar module and a victron smart MPPT charge controller. I couldn't be happier. Just buy good quality modules and you'll be fine. They'll have diodes but it's usually per row of cells or every other row. Not every cell.