There has been a long discussion around 12volt 120Watt portable solar panels sold on ebay by Outbax camping and others on another forum.
Not being too technical I am reluctant to enter the discussion on the other forum because I may be completely on the wrong track.
The discussion centres around a few points :-
- The Voltage that maximum power occurs Vmp - 14volts on these ebay panels.
-The size of the conductors in the 9 metre cables 1mm squared
- The best placement of the regulator - at the panel or at the van.
Now I understand that the cable is much to thin and should be replaced with something like 6B&S cable. What I do not understand is that I would have thought that with a PWM controller placed at the panel end, the 14 Vmp is better than other panels that have an 18 Vmp. My limited understanding of a PWM regulator (MPPT is another story altogether) is that it throws away any excess voltage so a 18 Vmp panel has effectively 4 volts being thrown away (output around 14 volt). Therefore the 14V panels are more efficient for 12 volt charging providing the controller is kept at the panel and has very short leads between the controller and panel.
The experts though in the referenced discussion claim a Vmp of >17 volts is required for a 12volt solar panel.
Maybe there is someone on this forum that clear my confusion or point me to a web site that explains.
Hi PG1, In short they are right about the voltage.
When the sun is shining bright and the panel faces the sun then 14 volts is just enough to charge a 12 volt battery, but only just. However if the sun is a bit dull or the panel is not pointing square, or any other problem then the voltage will drop to not enough to fully charge. So in average conditions they may hardly charge much. That is why the normal panels have the higher voltage. Do not forget that if the panel does not get up to a voltage above the battery there is NO CHARGING at all. So you can only drop say 1.5-2volts with that panel to get nothing much. The regulator can also loose half a volt or more to work.
While the lower voltage panel may more 'efficient' when charging fully, its efficiency drops off to 0% when the sun power drops off by 20-30%. These panels have only 30 cells in series. So you are better off having a normal panel with 36 cells in series, as is the standard, and using a good MPPT regulator to get the extra voltage converted to extra current when it is available. The lower cell count panels are designed for roof top use in large systems for grid connect use not battery charging. They are just cheaper than the others if that is the 'efficiency' you want.
The controller is always better at the battery than the panel, no matter what. The losses are less this way no matter if the wiring is good or bad. That is the standard way it has been done since panels were sold. I have been using panels on my house and for camping etc since the last century and have some experience. Jaahn
-- Edited by Jaahn on Thursday 5th of February 2015 08:19:05 PM
Thankyou for a concise answer that is understandable to someone who is not a tech expert.
The interesting thing is that the ebay seller Outbax Camping is selling heaps of these panels. Thanks to your advice I will go with a 36 cell panel from another seller not the 24 cell panel they sell. Any recommendations?
I hardly believe a 24 cell panel would be any good except for running a fridge directly while the sun shines. No regulator would be required probably as they cannot get up any dangerous voltage If they are actually selling heaps of these, it would explain why some people are convinced solar is no good
I have 4x 80watt panels for my MH to put out. I use that size as they are easy to handle and stow away. Bigger panels are too hard to handle and too hard to find a place to put away. In good weather I may only need two, in poorer weather 4. Good size cables are important as the lead can be longer to make it easier to find the sun.
I bought these panels from a Queensland seller on fleabay with free freight for about $100+ each. They fitted nicely where I wanted to carry them.
I hardly believe a 24 cell panel would be any good except for running a fridge directly while the sun shines. No regulator would be required probably as they cannot get up any dangerous voltage
[1] If they are actually selling heaps of these, it would explain why some people are convinced solar is no good
I have 4x 80watt panels for my MH to put out. I use that size as they are easy to handle and stow away. Bigger panels are too hard to handle and too hard to find a place to put away. In good weather I may only need two, in poorer weather 4. Good size cables are important as the lead can be longer to make it easier to find the sun.
I bought these panels from a Queensland seller on fleabay with free freight for about $100+ each. They fitted nicely where I wanted to carry them.
If you want more information you could PM me.
Jaahn
!!!
HI Jaahn
Two good posts that explains it well
[1]It would also indicate that like many Ebay sellers ,THEY DO NOT HAVE A CLUE about the actual products they sell
They supply them with a regulator @ the panel
Like you, I have had solar panels since the last century,well from sometime in the 70s, from memory
-- Edited by oldtrack123 on Thursday 5th of February 2015 09:22:19 PM
Panels with a maximum power point voltage that is not around 17 V are useless when charging batteries when using PWM controllers. They are manufactured for the grid connect systems (ie those you see on houses) with MPPT regulators. Not only do you have the losses through cables, you have less voltage developed at light levels less than standard sunlight. There is good reasons that panels are manufactured with a VMPP of 17 V.
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PeterD Nissan Navara D23 diesel auto, Spaceland pop-top Retired radio and electronics technician. NSW Central Coast.
If they are actually selling heaps of these, it would explain why some people are convinced solar is no good 
,well from sometime in the 70s, from memory
