Solar panel wildly different prices. How to decide?

[neoflyer]

After originally planning installing four 210w panels from Continuous Resources fir $194 ea. I’m thinking instead of going with two and possibly later a third 370w solar panel in my motorhome. I’ve found two products to choose from with wildly different prices. A Seraphim 72 cell mono from Santan Solar for $158 ea. or a REC 60 panel one from Wind and Sun for $357.67 ea. How do I decide?

https://store.santansolar.com/product/seraphim-370w/?ref=errolprowse

https://www.solar-electric.com/rec-rec370aa-alpha-series-370-watt-module.html

Thanks

 

[snoobler]

Seraphim is a "standard" 72 cell panel.

Rec is a half-cut 60 cell panel. Half-cut cell panels are more expensive. Think of it as 2X 185W panels in parallel in one panel with one panel on the top and one on the the bottom divided by the horizontal line you see in the middle.

Under identical unshaded conditions, there will be negligible different between the two.

If you shaded the bottom half of the Seraphim, almost all power would stop. Actually, all you have to do is shade ANY single row of cells, and all power would stop:



If you shaded the entire bottom half of the REC, the top half would still perform without hinderance, so you'd get 50% of the panel power.

If you THINK you MIGHT get a third panel in the future, get it now. It's just easier to deal with it now. The exact model might not be available economically in the future. and you'll have to get a similar one that might adversely impact the performance of the rest of the array.

Given that RV rooftops are prone to shading, you'll want to keep your panels in parallel and not series. You may find that the half-cut cells with their ability to still deliver 50% of rated power with the top or bottom half completely shaded may be worth the extra price.

Also look at shipping. Shipping may be vastly different for the two options.

 

[HRTKD]

If at all possible, avoid mixing panels of (widely) different specifications. It creates a wiring/configuration/controller hassle. It can be done, but the results often are not optimal.

As stated above, get the panels you need now. The panels you see available today, may not be the panels that are available tomorrow. This can be especially true of Santan since they're selling whatever they can find. Brand new panels from an established manufacturer will have better longevity in the supply chain, but I still wouldn't depend on that.

 

[iamrich]

I would still go with four panels if you can fit them. If it were me (out of those two) I would go with the Seraphim x4 (same price as x2 REC). I figure panels all over the roof should produce more power and maybe you can face them different directions to extend the solar day? I know nothing about motorhomes, but I a sucker for more panels

 

[neoflyer]

Seraphim is a "standard" 72 cell panel.

Rec is a half-cut 60 cell panel. Half-cut cell panels are more expensive. Think of it as 2X 185W panels in parallel in one panel with one panel on the top and one on the the bottom divided by the horizontal line you see in the middle.

Under identical unshaded conditions, there will be negligible different between the two.

If you shaded the bottom half of the Seraphim, almost all power would stop. Actually, all you have to do is shade ANY single row of cells, and all power would stop:

View attachment 42172

If you shaded the entire bottom half of the REC, the top half would still perform without hinderance, so you'd get 50% of the panel power.

If you THINK you MIGHT get a third panel in the future, get it now. It's just easier to deal with it now. The exact model might not be available economically in the future. and you'll have to get a similar one that might adversely impact the performance of the rest of the array.

Given that RV rooftops are prone to shading, you'll want to keep your panels in parallel and not series. You may find that the half-cut cells with their ability to still deliver 50% of rated power with the top or bottom half completely shaded may be worth the extra price.

Also look at shipping. Shipping may be vastly different for the two options.

Great information. Exactly the things I need to know.

 

[neoflyer]

I would still go with four panels if you can fit them. If it were me (out of those two) I would go with the Seraphim x4 (same price as x2 REC). I figure panels all over the roof should produce more power and maybe you can face them different directions to extend the solar day? I know nothing about motorhomes, but I a sucker for more panels

Three of these panels are about my limit, spacewise. I can fit 6 of the 210a Continuous Reasorces ones though which would only be 13.5% more wattage than 3 of the 370w units.

 

[iamrich]

Seemed simple, but they are about the same price. The smaller panels might even be cheaper to ship. 13% is an appreciable amount I think when you are limited on real estate. I withdraw my suggestion and sulk away while no one is looking...

 

[neoflyer]

Seemed simple, but they are about the same price. The smaller panels might even be cheaper to ship. 13% is an appreciable amount I think when you are limited on real estate. I withdraw my suggestion and sulk away while no one is looking...

3 Santan $644.66 pickup at dock. W&S $1355.42. 4 210w CR $776.00 w/free shipping(I think). During most of day should be no shading issues from items on roof. I like the tech of the W&S but over twice the price of Santans?

 

[neoflyer]

3 Santan $644.66 pickup at dock. W&S $1355.42. 4 210w CR $776.00 w/free shipping(I think). During most of day should be no shading issues from items on roof. I like the tech of the W&S but over twice the price of Santans?

With the 4 210w panels it looked like a no brainer to go series/parallel. 3 WS panels, all series, I think. Santans? Not sure.

 

[snoobler]

With the 4 210w panels it looked like a no brainer to go series/parallel. 3 WS panels, all series, I think. Santans? Not sure.

For the two panels you listed, I would only put them in parallel (assuming 12 or 24V system, if 48V, series Vmp-72Vmp min and Voc 130V max). If you insist on series, you're limited to 2S on most charge charge controllers.

 

[Cal]

The Santan panel will have excellent shade performance when using bypass diodes.

 

[svetz]

This might help too: Comparing Solar Panels

 

[snoobler]

The Santan panel will have excellent shade performance when using bypass diodes.

Please elaborate.

 

[Cal]

Don't know anything about Santan panels, but bypass diodes are inserted at the panel for current to bypass the shaded cells.

Let's say the panel has 4 bypass diodes and one section is shaded. The panel will output 3/4 of Vmp at rated current.

 

[snoobler]

Don't know anything about Santan panels, but bypass diodes are inserted at the panel for current to bypass the shaded cells.

Let's say the panel has 4 bypass diodes and one section is shaded. The panel will output 3/4 of Vmp at rated current.

Nope. # of series cells = voltage. Intensity of solar on cells = amps. Panel will output full voltage at reduced current causing all panels in series to reduce their current.

Please refer to the image I included above. Shading any single row of cells will drop panel output to 0. In fact shading only 3 of the 6 cells, every other (1, 3, 5 or 2, 4, 6) will drop panel output to 0. Shading even one full cell in a row will cut power by 1/3.

Bypass diodes are far less effective than most people think.

 

[Cal]

Nope. # of series cells = voltage. Intensity of solar on cells = amps. Panel will output full voltage at reduced current causing all panels in series to reduce their current.

Please refer to the image I included above. Shading any single row of cells will drop panel output to 0. In fact shading only 3 of the 6 cells, every other (1, 3, 5 or 2, 4, 6) will drop panel output to 0. Shading even one full cell in a row will cut power by 1/3.

Bypass diodes are far less effective than most people think.

I have no intention to argue with you. We'll have to disagree.

 

[snoobler]

I have no intention to argue with you. We'll have to disagree.

Shading losses in PV systems, and techniques to mitigate them

Shading can affect solar PV systems in a number of ways. Learn about solar shading losses, and how to mitigate them.

www.aurorasolar.com

Shading a solar cell is similar to introducing a clog in a pipe of water. The clog in the pipe restricts the flow of water through the entire pipe. Similarly, when a solar cell is shaded, the current through the entire string is reduced.

This is significant because every cell in the cell string has to operate at the current set by the shaded cell. This prevents the unshaded cells from operating at maximum power.

Essentially, every cell is like a chain in a link. The shaded cell is the “weakest link”, reducing all the remaining cell’s power availability. So yes, only a small amount of shading can have a dramatic effect on the power output of a solar panel.

Similar principles apply to PV modules connected together. The current flowing through an entire string of modules can be heavily reduced if even just a single module is shaded, leading to a potentially significant loss of power output.

 

[iamrich]

Shading a solar cell is similar to introducing a clog in a pipe of water. The clog in the pipe restricts the flow of water through the entire pipe. Similarly, when a solar cell is shaded, the current through the entire string is reduced.

This is a good analogy! But you can't create alternate paths for the flow because that would reduce the voltage? Just surprised they haven't solved this issue (or maybe they have).

 

[snoobler]

This is a good analogy! But you can't create alternate paths for the flow because that would reduce the voltage? Just surprised they haven't solved this issue (or maybe they have).

The solution is a bypass diode on every cell, but no one will pay that much for panels.