There are usually small differences in sizes and also layouts for the cell rows. Eg 6 x6 or 4 x9 cells. But what is important is the number of cells on the panel for battery charging. You need 36 cells for 12V batteries and a PWM regulator. Each cell gives 1/2 volt which adds up to 18V in full sun, but less in dull sun. If it only has 30 cells you only get 15V which is not enough to charge a 12V battery on a caravan roof, and nothing if dull sun.
So look at the specs and see they are the same. The power is not the only important figure. The V MP must be around 18V not lower than 17 V to be able to work well on a hot roof. Post the specs of the ones you are interested in so we can advise.
The last dimension 30 or 35 is the depth of the aluminium side support rails.
I would recommend that you do not use big panels like that. You are usually better off with more smaller panels, 80W or 60W are good. Slightly more work but more performance in shaded conditions etc and less risk of damage. Read some of the other threads in Solar for ideas.
Jaahn
-- Edited by Jaahn on Saturday 5th of May 2018 08:32:59 AM
There are usually small differences in sizes and also layouts for the cell rows. Eg 6 x6 or 4 x9 cells. But what is important is the number of cells on the panel for battery charging. You need 36 cells for 12V batteries and a PWM regulator. Each cell gives 1/2 volt which adds up to 18V in full sun, but less in dull sun. If it only has 30 cells you only get 15V which is not enough to charge a 12V battery on a caravan roof, and nothing if dull sun.
So look at the specs and see they are the same. The power is not the only important figure. The V MP must be around 18V not lower than 17 V to be able to work well on a hot roof. Post the specs of the ones you are interested in so we can advise.
The last dimension 30 or 35 is the depth of the aluminium side support rails.
I would recommend that you do not use big panels like that. You are usually better off with more smaller panels, 80W or 60W are good. Slightly more work but more performance in shaded conditions etc and less risk of damage. Read some of the other threads in Solar for ideas.
Jaahn
-- Edited by Jaahn on Saturday 5th of May 2018 08:32:59 AM
Hi Jaahn, interesting. I have noticed that many of the flexible portable panels only have 4 x 8 cells. Does the above apply to these supposedly high output flexible panels?
There are usually small differences in sizes and also layouts for the cell rows. Eg 6 x6 or 4 x9 cells. But what is important is the number of cells on the panel for battery charging. You need 36 cells for 12V batteries and a PWM regulator. Each cell gives 1/2 volt which adds up to 18V in full sun, but less in dull sun. If it only has 30 cells you only get 15V which is not enough to charge a 12V battery on a caravan roof, and nothing if dull sun.
So look at the specs and see they are the same. The power is not the only important figure. The V MP must be around 18V not lower than 17 V to be able to work well on a hot roof. Post the specs of the ones you are interested in so we can advise.
Jaahn
Hi Jaahn, interesting. I have noticed that many of the flexible portable panels only have 4 x 8 cells. Does the above apply to these supposedly high output flexible panels?
Joe
Hi Joe
I have never owned a flexible panel so have no direct experience. But a basic cell only puts out about 1/2volt so does not matter what else is true 32 cells only puts out about 16V. What does "high output" actually mean ??? Just BS usually ! But it might mean slightly more current.
Look at the specs is always the answer. By having only 30 or 32 cells the current looks bigger for the same wattage panel, but there is no margin for charging under lower sun or poor angle to the sun or hotter panels etc. So the result may be no current delivered often.
I have had some 32 cell panels I used as portable ones. They worked OK as portable because I could set them up square to the sun and move them during the day to get full output. But they were a mistake and cheap, and I do not think they are a good idea. Have not bought them again
Jaahn
-- Edited by Jaahn on Saturday 5th of May 2018 02:22:23 PM
Some panels are more efficient than others. They may have different spacings between the cells. Some manufacturers fudge their figures by using different test specifications such as their rated output is guaranteed over a shorter life time.
The first two are about the same area. The last one has a lighter mounting frame and perhaps not as robust as the other two.
As for your flexible panels. They all would need 36 cells to match the others. I think you are counting blocks of cells and not individual cells. Even in the fixed panels I have found it hard to count the cells occasionally.
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PeterD Nissan Navara D23 diesel auto, Spaceland pop-top Retired radio and electronics technician. NSW Central Coast.
By having only 30 or 32 cells the current looks bigger for the same wattage panel, but there is no margin for charging under lower sun or poor angle to the sun or hotter panels etc. So the result may be no current delivered often.
