Solar Panel Efficiency Question

[Adelie]

Originally Posted by Letterkenny

Well my original question was posted in theory but here are the two panels that I am referring to. The Ecoflow is 10 watts more but otherwise the two are very close in specification with the exception of the Renogy being under 15% efficient per the specs and the Ecoflow being 21%. Curious what that means in the real word and if I should get rid of the Renogy panels in favor of something more similar to the Ecoflow.

https://ecoflow.com/products/110w-solar-panel
https://www.renogy.com/100-watt-12-v...e-solar-panel/

Despite having the lower efficiency the Renogy has a smaller foot print, similar width but 15” shorter.

[Jim Cate]

I suspect that the apparent conflict in claimed efficiency vs. Gord's watts/sq ft is that the efficiency quoted by the manufacturers is likely based on the area of the individual cells, not the total frame footprint. Some panels have much more "wasted" area around t he cells than other designs.

But the efficiency rating doesn't really matter in terms of usage. If you run the panels in parallel into a single regulator they will work ok.

Jim

[donradcliffe]

Forget efficiency. Measure the output of each panel when they are side by side in the sun. I always measure new panels open circuit voltage and short circuit current.

[zstine]

If both panels have the same output, but have different efficiency, then the lower efficiency panel has more surface area and the higher eff is smaller. That's it... Period


Efficiency is power output for a given surface area.

[contrail]

Originally Posted by zstine

If both panels have the same output, but have different efficiency, then the lower efficiency panel has more surface area and the higher eff is smaller. That's it... Period


Efficiency is power output for a given surface area.

That is the correct answer....and if one delves into the Renogy website, they specifically mention that their panels have different efficiencies leading to larger or smaller sizes. As it happens, I was looking at that site, earlier today!

[valhalla360]

Originally Posted by zstine

If both panels have the same output, but have different efficiency, then the lower efficiency panel has more surface area and the higher eff is smaller. That's it... Period


Efficiency is power output for a given surface area.

This is the correct answer...though there is a lot of flim-flam marketing among so called "eco/green" products, so it's often difficult to cut through the BS and it's not unusual for them to make up their own version of a standard to make their product look better.

If you are just adding a single 100w panel, efficiency is all but irrelevant.

It's when you are trying to cram as many panels as possible onto a boat that it becomes important. Assuming you can fit 100sft of panels onto a the boat, higher efficiency will mean more watts are available.

General rule of thumb, you can expect around 4-5 times the rated wattage in watt hours (ie: a 100w panel will generate around 400-500watt-hours per day)...of course, if the panel is shaded or it's overcast that goes out the window.

[sailorboy1]

Originally Posted by Letterkenny

Curious what that means in the real word and if I should get rid of the Renogy panels in favor of something more similar to the Ecoflow.

I feel it means basically nothing.

I have 640W of solar that is only 3 years old. I don't think I have ever seen more that 500W out of them. Used to have only 290W and rarely saw 200W out of it. So while the "spec" efficiency and watts may mean something in a lab, actural conditions mean more.

Instead of worrying about replacing panel, unless you are doing to just get more wattage, spend your money on a good MPPT controller and larger wiring.

[SOLAR SUPPORT]

Originally Posted by Letterkenny

After some failed Googling, thought I would throw this one here. If I have two different solar panels at both 100w at 18.5v but one is 15% efficient and the other being 21% efficient, what does that mean? Is it that the more efficient panel will produce more electricity on average or that by being more efficient, the panel would be smaller?

Solar efficiency is found by the ratio of the electrical power obtained from the unit area of ​​the solar panel to the maximum solar energy falling perpendicular to this area and at a cell temperature of 25 °C. The ratio between the surface areas of solar panels with two different surfaces with the same power should be equal to the ratio between the efficiency coefficients of these two panels.

[Adelie]

It’s the ratio of cell areas not panel areas.

A panel with lower efficiency cells packed tight may be smaller than a panel with higher efficiency cells with big gaps between.

That appears to be the case with the panels the OP listed in the first post.

[HeywoodJ]

Originally Posted by zstine

If both panels have the same output, but have different efficiency, then the lower efficiency panel has more surface area and the higher eff is smaller. That's it... Period

Efficiency is power output for a given surface area.

+1. The panel with higher efficiency will be smaller, but both will put out 100W under nominal conditions.

Just to confuse things, and as shown with Gord's math, there are two efficiency numbers used in the solar industry; cell efficiency and module efficiency. When solar companies crow about their "highest efficiency on the market" it is usually cell efficiency. Same with research papers touting their efficiency increase by doing xyz. Module efficiency accounts for the dead space between cells and also the frame of the module, it is calculated (per industry standard) as the total area of the module using maximum exterior dimensions against output of the module. When comparing efficiency numbers you have to be very careful to make sure you are not comparing cell vs. module efficiency.

In the OP's case Renogy's datasheet is very clear "Module Efficiency 14.9%."

EcoFlow's is not clear "Efficiency 21%–22%". If you take exterior dimensions of 1.58 * 0.514 = 0.812m2, at 110W/module you get 110/0.812 = 135 W/m2 → 13.5% module efficiency (power rating is at 1000 W/m2 STC, so 135/1000 * 100 = 13.5%). Clearly, the value published by EcoFlow is cell efficiency, so you are comparing apples with caterpillars.

The Renogy panel actually wins in terms of module efficiency, presumably because of the folding space in the EcoFlow. From a low-light performance perspective you actually want to know cell efficiency, the more efficient cells are generally higher-end and generally have better performance in non-optimal conditions. Not every vendor publishes cell efficiency, and it is not easy to calculate because you need to know the area of the cells in the module, and that number, too, is not generally published.

[Martkimwat]

If you are not worried about the extra space the lower efficiency panel will take up, I would go ahead and install them but ideally you should use two separate regulator controllers rather than put them both through one controller.

[Martkimwat]

If you are not worried about the extra space the lower efficiency panel will take up, I would go ahead and install them but ideally you should use two separate regulator controllers rather than put them both through one controller.

[Redline452]

Originally Posted by Adelie

Sounds like Norm.

huh? Someone called me?


-- Norm

[Adelie]

Originally Posted by Redline452

huh? Someone called me?


-- Norm

I've known Cal40John for 36yr in real life. Norm is a mutual acquaintance of Cal40John & myself.

[seandepagnier]

Originally Posted by smac999

100w is 100w. The more efficient one will be smaller. More efficient per size.

My "120w" panels have never output more than 80w. In fact, typically 30-50w (I don't tilt them). I also have chinese electronics rated for 3 amps but they output 2 amps. You would say "3 amps is 3 amps", but apparently if this thing outputs 3 amps in china and you bring it here, it will only output 2 amps.