solar panel efficiency and comparing panels?

[Sgt Raven]

Solar panel efficiency. Is there a formula to compare output of panels against other panels of different wattage? If a lower wattage panel is 20% efficient and a higher wattage panel is 15%, how do you compare them at the amount of power to the SCC? Could a lower watt panel actually out perform the larger watt panel for total output? There must be a formula for this, but I'm not using the right question is a Google search.

I tried a forum search but didn't find an answer.

 

[nosys70]

we already discussed that.
there is no "efficiency" for a solar panel of particular wattage. any 200w panel is a 200W panel.
The only efficiency you could compare is how much surface is needed for same power.
This could be useful for mounting on a RV where space is very limited.
differences you could also find is the Vmax of panel. some 24v panels are close to 24V and others are closer to 35V for example.
this could be important if you plan to mount them serial, in order not to reach the input limit of the SCC.

 

[Dzl]

If you are space constrained this is an important factor, if you are not space constrained, don't worry about efficiency.

Watts are watts, a 300w panel that is 15% efficient and a 300w panel that is 20% efficient will both produce 300w (in ideal test conditions). But the 15% efficient panel will need more square footage to produce the same amount of power.

 

[Sgt Raven]

we already discussed that.
there is no "efficiency" for a solar panel of particular wattage. any 200w panel is a 200W panel.
The only efficiency you could compare is how much surface is needed for same power.
This could be useful for mounting on a RV where space is very limited.
differences you could also find is the Vmax of panel. some 24v panels are close to 24V and others are closer to 35V for example.
this could be important if you plan to mount them serial, in order not to reach the input limit of the SCC.

Could you point me toward that? I wouldn't be surprised it has been gone over. Like I said, I wasn't using the right search question/s.
And yes I'm thinking of it inline with mounting panels on my camper shell.

 

[Sgt Raven]

If you are space constrained this is an important factor, if you are not space constrained, don't worry about efficiency.

Watts are watts, a 300w panel that is 15% efficient and a 300w panel that is 20% efficient will both produce 300w (in ideal test conditions). But the 15% efficient panel will need more square footage to produce the same amount of power.

OK, now I got it. It's just size related.

 

[Dzl]

And yes I'm thinking of it inline with mounting panels on my camper shell.

In that case, efficiency is worth considering, though I've found that how the specific dimensions of specific panels fit your specific roof space is still a more important factor. But if space is limited, efficiency is worth considering.

 

[nosys70]

then it is not a choice for brand or model, but a choice for technology.
panels with "cells"(usually mono or polycristalline ) lost a lost of space in the arrangement.
Poly and thin film are better in using surface.
unfortunately , the one that has the better use of surface (thin film ), is the less efficient, so monocristalline is probably the one
that offers the best. unfortunately again, mono is very sensitive to shading, so even a slight shading will put you under what
a poly can deliver.
So the best is to take mono or poly and avoid thin film

 

[maxx123]

to me it is easy what is the best deal at the time when you factor in the quality of the product.

polycrystalline-based solar panels is typically 14-16%

Monocrystalline silicon solar panels are space-efficient. Since these solar panels yield the highest power outputs up to 22% more the high end
space, quality to last 25 years or more

 

[svetz]

You might be interested in the thread Comparing Solar Panels.

 

[maxx123]

I bought Sunpower 327 for the quality, and for the minimum depreciation of loss over 25 years so to get 80% that would be over 40 years a pretty good investment for used panels

 

[JoeHam]

And here is efficiency on what is available:

Solar Panel Efficiency Explained: Most Efficient Solar Panels 2024

Most solar panels in 2024 are between 19% and 21% efficient, but top brands like SunPower have almost reached the 23% mark.

www.solarreviews.com

 

[Dzl]

then it is not a choice for brand or model, but a choice for technology.
panels with "cells"(usually mono or polycristalline ) lost a lost of space in the arrangement.
Poly and thin film are better in using surface.
unfortunately , the one that has the better use of surface (thin film ), is the less efficient, so monocristalline is probably the one
that offers the best. unfortunately again, mono is very sensitive to shading, so even a slight shading will put you under what
a poly can deliver.
So the best is to take mono or poly and avoid thin film

What is it about Poly that does better in shade? I know how tech like bypass diodes, using half-cells, or rear contacts can improve partial shade performance. But I've never understood how the cells themselves do better or worse in shade.

Also, is thin film the stuff that is generally used on the flexible solar panels?

 

[hankcurt]

It is also important to consider the power output at NOPT (Normal Operating Temperature) vs. STC (Standard Test Conditions). I was looking at some Panasonic HIT panels that appeared to be twice as expensive as the cheapest ones, but they only lost .3% per degree Celsius temperature rise, as opposed to others with .5% loss per degree. At rooftop temperatures, this can make a big difference in the output you actually receive. Then if there is a difference in degradation rate, there can be a significant output difference over the next 20 years. Once I factored these things in, the Panasonic HIT panels were only 10 to 20% more expensive. (this is all based on new purchase prices) I was about to buy them when I saw a deal in Will's affiliate links that were too good to pass up for Solar World panels with nearly the same specs and form factor as the Panasonic panels, and got them instead.

So I would say that if space is at a premium, it is important to consider the total power output over time at actual operating conditions, not just the advertised wattage or efficiency, when comparing panels.

 

[mattsharon]

Yes, Solar panel efficiency is measured as a percentage (ranging between 15% to 22%) that determines how much energy a solar panel is able to produce over the course of a year. This is also referred to as solar panel performance.

Certain factors affect solar panel efficiency.

• Higher for monocrystalline solar panels
• Lower for polycrystalline and thin film solar panels
• Measured in watts per meter

Solar panel efficiency ratings are currently between 15% to a maximum of 22%. The higher the efficiency rating, the more energy your panels are going to be able to produce.

Here are some of the factors that affect solar panel efficiency.

• The location of your solar panels
• The tilt angle of your solar panels
• The weather conditions in your area
• How well you maintain your solar panels
• The build quality of your solar panels
• The number of peak daylight hours in your area

It is vital to go for the most efficient panels possible when you decide to go solar.

 

[Bvillebob]

Sorry, that's completely wrong. Efficiency has zero impact on how much power your panels are going to produce. As has been said over and over here, a 300 watt panel is a 300 watt panel, whether it's 1 per cent efficient or 100 per cent efficient. The only difference is the size of the panel, a higher efficiency panel CAN be smaller than a lower efficiency panel, depending on other factors. I just bought some current generation REC 370 watt panels that are only slightly larger than my 10 year old 250 watt panels, that's due to increased eifficiency and more modern technology, but it has no impact on the total power they put out, they're stll 370 watt or 250 watt as they are rated.

 

[GXMnow]

I have tried to explain this a few times myself. The panel rating is the power rating in standard conditions. Higher efficiency is just more power per square meter.

The main reason I am posting here, is I also saw a few comments about thin film panels. Battery Hookup just got a shipment of thin film solar panels that are "new old stock" and the cost per watt looks pretty good for panels that have never been used. But the math does not look good.

They panels are rated at just 120 watts each. I figured they would be smaller and I could arrange them to get a lot of power on my garage roof. But here is the problem. Each panel is 1.1 x 1.3 meters. They works out to a rather poor 9% efficient, or just 90 watts per square meter. OUCH!! Is there anything about these thin film panels that might make them worth while? They are selling them by the pallet, $1,080 for 24 panels. 24 x 120 = 2,880 watts total = $0.375 per watt. The problem is I just don't have enough room. I might be able to squeeze 9 or 12 panels on my garage. That is only 1,440 watt if I fit 12 of them. My original plan was just 6 x 400 watt panels, which takes up less space and makes 2,400 watts.

Then my other issue is the thin film panels are 140 volt VOC. OUCH!! That is way over the 80 volt limit even at per panel shut off. The maximum power point is 110 volts at 1.1 amps per panel.

I am curious what others think about these, but at this point I think I am going to pass. I really want over 2,000 watts on my available garage roof space.

 

[Hedges]

Look for something like the SunPower 327W or similar size. Over twice the efficiency and maybe about the same price, slightly used. I think some people found them for even less, but likely more demand this year.
Single crystal vs. thin film, probably much more life left in them.

 

[Hedges]

Several models of SunPower at SanTan right now. $0.39 to $0.44/W

One I would have less confidence in is the P17 series. Clever layout of smaller slices, optimized for a particular shading situation of commercial arrays. Unusual shingled assembly technique. Polycrystaline, it says.

At least the single-crystal ones are of a silicon doping that might be better off positive ground rather than negative ground for PID reasons, although SunPower says very low PID. I used to have mine paralleled with other brands and ungrounded (transformerless, half biased above ground and half below.) I now have the SunPower positive grounded and the other brands negative grounded.

 

[GXMnow]

I took another look at San Tan and they do have a few good choices now. But I am still trying to figure in their shipping costs. I should have ordered from Real Goods when they were offering free shipping. That would have made new Trinna panels about the same price per watt as used ones at San Tan. But shipping costs have now gone crazy.

I measured... even 60 cell solar panels won't fit in my C-Max. I actually drove near to San Tan in Phoenix when I was out that way for work. I really wanted to pile in 8 panels to bring home.

 

[GXMnow]

Looking at San Tan Solar again, and they do offer a fairly cheap truck freight option, if you can wait 2 weeks, I sure can. So the shipping is just $210 to get 8 panels to my driveway. About the cost of 1.5 panels at their current pricing. Have to see how much it adds if I get a few more panels. Since it is truck freight, it is usually a flat fee for the pallet. I'll have to see if any of my friends are ready for some more panels and we can pool an order.

Right now they have 2 options that look real good for my install.
used Sun Power e20 327 watt panels at $110 each, + $11.83 per panel in CA sales tax.
used SilFab SIL-330-HL panels at #115.50 each, + $11.95 CA tax per panel

The Sil Fab are a tiny bit large at 19.4% efficient to 20% for the Sun Power, but the SilFab ones are not as old. And my current 300 watt panels are matching all black SilFab as well, so they will match nicely, even though these are a newer and better panel. My current panels are likely more degraded than these. But they only have these in GA, so the shipping is also a bit more at $317

Tough call, they are both quality panels, but the Sun Power ones are at least 5 years old, and were in use that whole time. The SilFab actually has a better power warranty.