Efficiency of Solar Panels – Transition Line

Solar Panel Efficiency and the Factors that Affect it.

Cool the panels. When I water mine down they instantly feed ca. 200 watts more into the grid.

But only until they warm up again.

You can measure efficiency from many different perspectives.

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Here is one. ( Energy output/Energy of incident light ) x 100% =

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Here is another ( (Expected lifetime energy output) x (expected comparable cost of purchased energy) ) / ( (total lifetime cost including real estate, permits, solar panels, ancillary equipment like inverter, batteries, controllers, etc, installation and connection, etc) x (financing cost for level payment over expected life of purchased equipment))

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There are many other ways to judge efficiency.

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Likewise there are many other ways to improve efficiency.

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One thing that might improve efficiency in the first example but not in the second would be to run chilled water over the solar panels, since many solar panels have improved output if kept at a lower temps...yet the additional cost of building, running and upkeep probably does not provide a benefit as calculated in the second example.

I quiet agree, watering down was only a weekend task to get the dirt off. But I tested the improvement when they where dry and clean just to see what cooling gets you. I would not go as far to waste water to do it, because it does not pay by the little improvement it does.

Hi lyn, thank you very much for this link, it help me a lot, if you have more links about these issues so I will glad if you can post them in this thread.

I will glad to read also about transmission line from the sun to the solar panel.

Hi anonymous poster #2, these issues in this thread are very important for me, I will glad if you can stop to ruin this thread.

Hi trust is not a compromise, I very love to read your answer, I find a lot of smartness in this answer.

In the first equation you wrote is about energy efficient so to improve the efficiency I need more electrical current will go out from the solar panel if less light is touch the solar panel, am I right?

After I read it, I receive another question, my question is: the Earth is all the time moving so the direction of the light of the sun is also moving in the day, so in the morning is in one direction, in the noon is in other direction and in the afternoon is in another direction, so what need to be the best angle from that the light touch the solar panel, maybe it need to be Bruster angle, maybe other angle, and why it need to be this angle, how to calculate the best angle that the light touch the solar panel.

The second equation you wrote is about cost efficient, I am interesting to know more about the parameters that influence on cost efficient.

Do you have any link about the influences of different temperatures to the energy efficient of solar panel? I am interesting to know more about that.

Hi forum members, I will glad to receive more replays that are related to these issues.

AP#1

Thank you for the feed back to our replies. Many people who post questions, don't give any feed back at all. It is nice when someone like yourself does.

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There is a language barrier here, so sometimes things can be misunderstood. I think that might be the case with your understanding of what AP#2 wrote; I don't think he was trying to ruin the post, he was relating the same thing I mentioned later in the post; that cooling the panels down with water can increase output.

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'...to improve the efficiency I need more electrical current will go out from the solar panel if less light is touch the solar panel, am I right?...'

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I think you have the right idea, but just to be clear let me put it this way....

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Greater efficiency can mean:

For the same light hitting the panel, more electrical energy is produced

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To produce the same amount of electrical energy, less light is required.

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'...so what need to be the best angle from that the light touch the solar panel,...

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... I am interesting to know more about the parameters that influence on cost efficient....'

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These two questions may seem very different, but one leads nicely into the other:

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The best angle for a solar panel (to produce the most electricity) is..... Always facing the direction it will produce the more electrical energy.... which is usually the direction the most light will strike it.... which for a large part of the day is usually with the surface normal to incident sunlight.

So basically that means it is moving all day long.

Because this means a structure that pivots and turns, and is powered somehow....that can add a lot of expense.

This is another case where the most efficient per amount of incoming sunlight is not necessarily the most efficient in terms of return on investment.

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Many people are tricked into evaluating efficiency mainly in terms of the amount of electricity produced for a certain amount of sunlight.

In most situations that is not the most important consideration.

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How much was your sunlight bill last month? What's that? You didn't get charged for your sunlight?

How much of your space if already used for things that require light to work... growing plants, hot water heater, light into living spaces....? If it isn't already all used, then you don't have to acquire the use of new square footage to install some solar panels, right?

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My point is that in most cases, the competitiveness of solar power has far more to do with lifetime cost per installed watt, than it does with watts of incident sunlight required to provide a watt of electricity.

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'...Do you have any link about the influences of different temperatures to the energy efficient of solar panel?...'

Here is a link to download a good paper on the subject.

I give this a GA and thanks for coming to my aid.

I was by no means trying to ruin the thread. Cooling is just one good option to increase efficiency (OP Please also see post #9.)

Not sure why that went down the wrong throat.

I like your post. Thanks

Hi - I don't think the temperature effects were addressed in the recent posts.

All PV semiconducting materials have a negative temp coefficient, which means that as the temperature goes up, the output goes down (lower the better). The values are measured at 25C or standard test conditions and indicate that for every degree above 25C there will be a corresponding drop in output. @45C the poly panel would drop by 10% (.5x20C).

Poly Crystalline ~ .5%

Mono Crystalline ~ .45%

Special Mono ~.4%

CdTel~.3%

You might want to describe what you are trying to accomplish because PV system designs have a few areas that can trip you up. For example, given a large space (not a fixed area) it is almost always less expensive to add a few more panels than to add the expense of tracking, mounting hardware, extra wire, control systems etc.

A 200W panel costs about $400US. If you had a 2KW system with 10 panels, the cost to add tracking will be > $2k, yielding a ~25% improvement in your system. You could instead add 2 panels @ $800 and get nearly the same improvement without ever worrying about a break down. In the second case, you might need a new inverter and so it all depends on where you are at in the process.

One last note, depending on where you live, the roof, and local codes, you be required to get structural improvements to the roof supports, all of which adds a bunch of additional costs.

Good luck!

Efficiency boils down to standards. One of the standards used is the Solar Spectrum AM 1.5 Global. See: Am 1.5 Global Spectrum

Temperature is usually specified at 25 deg C.

Getting that spectrum is quite difficult, but that's what solar simulators are all about.

As with any measurements, one requires standards. When I worked in the industry we used to have a few cells measured by NREL and then we cross-calibrated about 10 of ours. We calibrated with one and then checked with another and continuously rotating in the set of 10. The cells we calibrated with were crystaline Silicon without an anti-reflection coating.

For one of the materials we were working on, we had to use a filtered reference, I think because of the spectral content of our lamp.

If the cells were to be used in space, another solar spectrum would be chosen. I believe this would be AM 0.

Once you know the Short circuit current of your calibrated cell with the proper spectrum, you can calculate efficiency at maximum power. Max power is actually curve fitted.

Furthermore in our testing, we looked at the stability by seeping in both directions.

Our Solar simulator used a Xenon light source. As that light sourced aged, it would loose light in the blue. The lamps were replaced around 700 hours of use.

During use the lamp power would increase over time to get the same irradience and we would see changes in the calibrations of the filtered vs non filtered references. Our goal was within 1% of our "calibrated" values.

For another measurement of what we would call quantum efficiency (QE)would be just how much of much of a small band of light is converted. The x axis would be wavelenght and the y-axis QE (Max of 1). You can integrate the QE curve with the AM 1.5 Global curve and estimate the overall efficiency. It's an interesting instrument to create.

I would respectably disagree with the statement that efficiency has much to do with standards. The standards allow comparisons to be made. The artificial simulators are indeed tricky and can even be gamed if one so chooses to do so. However the Wp rating of a panel is typically executed at a certified agency that often tests many manufacturers panels. They too are challenged with aging, accuracy, calibration etc, but at least it is single set up with certified calibration cells that allow relative precision to be had. There are also several organizations that do real-world tests (outside) over several years and compare values to mature and stable products (at least well characterized). At the end of the day (no pun intended) it is all about how many watts can be produced at a particular location, thru a particular time period etc. A flash tester as described is only used to get a Watt peak value and not much else.

Efficiency is a function of converted photons into Watts. But then there is panel efficiency, low light efficiency, scattered light efficiency, thermal efficiency, $ in vs $ efficiency and much more. I think this is what the OP is likely asking about and that quickly gets convoluted. But as noted before, costs escalate quickly with any additional bits and bobs and adding a repair or two along the way makes it hard to justify tracking complexity. Especially true if space exists to just add a few additional panels.

The sad truth is that $B's have been spent over the last 30 years and overall panel efficiencies have only inched up over that time. The average cell efficiency in the 80's (ARCO Field in Correzzo Planes CA) for single junction was about 15%, and today it is about 20%. So instead of a 200W panel you now get a 210W panel. There are folks doing better for example Sunpower at 24% but that is a more complex cell that cost much more to produce. The real story is that Si has gotten cheaper and as a result the thin film and multi-crystalline technologies ran out of steam because they were half the efficiency but not half the panel cost. It was not the Chinese who blew the market.
Cheers,

I need to add this reference on the solar spectrum: Wikipedia - Air Mass Solar Energy

My engineers and I have designed two solar panel manufacturing facilities. In that time we have become quite familiar with all aspects of the process. The efficiency of the panel is tested with a certified sunlight tester. Think of it as a $ 100,000.00 light box. Most panels run between 12 and 15%. Samsung claims to have a low number of units at about 22%. It is the corruption and stupidity of the environmental movement that will forever keep the solar panel industry non-self sustaining!!!!!!!!!!!!!!!!

One thing that's come up a while ago and this thread is no exception. Efficiency isn't the only figure of merit.

If a Solar Cell were used in a space application, the merit of Watts per kg might be more appropriate.

Location, location, location! This is important as well. Will it involve tracking? Moving the array to track the sun. Are we talking concentrator cells?

We might tend to look at the payback period as well.

I recently went to a presentation on Solar instals for utility companies. One of the interesting things that a Solar Install can do is localized power factor correction primarily because of the inverter technology. This technology is easily turned off.

With Wind, for instance, you have to use it when it's there. Without a load, the blades spin out of control. Hydro and nuclear is very hard to turn off.

So, you can't look at efficiency alone. Each application has it's own requirements.

'...Hydro and nuclear is very hard to turn off.....'

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Not normally.....Only if something is severely damaged.

Hi truth is not a compromise, this is what I mean, but thank you for this clarification.

I will glad if you can write one link that talk about how to use maximum the space that we have to receive more green energy.

Hi tommyb2, I am interesting to know what the others different (not only the temperature) in the PV semiconducting materials are influences to PV.

I think you right sometimes is better to add more solar panels but sometimes there is not enough place to put more solar panels.

Thank you for your comment about standards.

I think that if a solar panel give in the 80's 15% efficiency 200 watt and not in is 20% efficiency so in need to be approximate 300 watt, am I right?

Can you explain more why thin film and multi-crystalline technologies ran out of steam?

Hi KeepItSimpleStupid, I will glad to read more information about these standards.

What are the measures and tests that NREL do?

What is the seeping for the both direction from the solar cell that you look for? Why you look for this?

How to do this filter to the solar cell?

Thank you for the air mass (solar energy) link I will glad if you can write in this thread more links that talk about what you wrote for examples links for: NREL, anti-reflection coating, filter for lamp, the spectrum for these processes and the Short circuit current and AM 1.5 Global curve.

What are the others things, except efficiency, that are important in the solar panel?

I will glad if you can write some links about the inverter technology for invert light to electricity.

Hi to all, I have one question in vocabulary - What is the different in the mining of solar cell and solar panel?

Assuming you plan on installing the solar panels without the expense of tracking, this website has an application that is very useful for determining optimum orientation.

Of course you also want to put the panels in a place with minimum obstructions/shading.

A solar cell is an individual unit that captures solar energy and creates eletrcial energy, while a lot of cells will make up a solar panel.

Glad to be of help!