PV longevity?

jumper

How long do PV panels last?
What percentage of initial output can one count on after say ten years?

hot_rod

Brand name panels come with 25 year warranty 
After 20 years they should be at 90%

JakeCK

I wonder how much more efficient PV panels will be in 25 years. Instead of having to replace all of my panels I wonder if I could get away with only replacing 1/2 or even 1/3 and end up producing more than I am now.

Jamie Hall

JakeCK said:

I wonder how much more efficient PV panels will be in 25 years. Instead of having to replace all of my panels I wonder if I could get away with only replacing 1/2 or even 1/3 and end up producing more than I am now.

Unless different materials are used, probably only slightly more efficient. The "efficiency" of the panels is really a misnomer -- what is actually happening is that the photoelectric effect on which they are dependent is, because of the inherent physics of the material, only capturing a relatively small portion of the solar spectrum. Just visible light, and not even all of that. They don't capture any infrared at all -- and that's over half the incoming power.

Hot_water_fan

Efficiency can be (and is!!) much higher for certain panels. But the price vs efficiency balance is more important. 

Larry Weingarten

Hi, My understanding is that panels are considered to be at the end of their life when they are down to 80% as efficient as they were new. That could be 25 or more years. I'd just leave a little room on the rack to add a few more panels in 25 years By the way, most of the panels on my house are now 23 years old and seem to be working fine.

Yours, Larry

SlamDunk

JakeCK said:

I wonder how much more efficient PV panels will be in 25 years. Instead of having to replace all of my panels I wonder if I could get away with only replacing 1/2 or even 1/3 and end up producing more than I am now.

The construction company that installed near 1400 panels of high efficiency pv panels on our warehouse said that they were ordered a year and a half ago and right out of the box, were already less efficient then what is available today.

Jamie Hall

There is room for increased output from a given area of panel (NOT to be confused with efficiency, strictly speaking. This comes in two areas: alteration in the semiconductors used to absorb the incoming light, and improvements in the optical characteristics of both the cells themselves and particularly the protective covering (especially for off-axis illumination). Of course, improvements in either direction tend to drive up costs...

The biggest thing the owner can do to help themselves is to keep the arrays clean... and unscratched.

jumper

Does climate matter much? I'd think that colder and less hours of sunshine wears out PV slower.

JakeCK

Jamie Hall said:

There is room for increased output from a given area of panel 

Which can be expressed as efficiency... X amount of solar radiation hits any given area of the surface of the planet. If you only capture 20% of it that can be expressed as only 20% efficient right? How is this different then when you dump x number of btu's worth of fuel into a boiler but only get say 80% of it as usable heat?

And if I'm not mistake the standard amount of solar radiation used to calculate efficiency is actually the amount that potentially reaches the equator, not what can potentially land on the ground in a state such as Ohio. 

Jamie Hall

jumper said:

Does climate matter much? I'd think that colder and less hours of sunshine wears out PV slower.

They don't wear out in the usual way we think of it. More like spot faiures in the PV cells, and degradation of the over.

JakeCK said:

Jamie Hall said:

There is room for increased output from a given area of panel 

Which can be expressed as efficiency... X amount of solar radiation hits any given area of the surface of the planet. If you only capture 20% of it that can be expressed as only 20% efficient right? How is this different then when you dump x number of btu's worth of fuel into a boiler but only get say 80% of it as usable heat?

And if I'm not mistake the standard amount of solar radiation used to calculate efficiency is actually the amount that potentially reaches the equator, not what can potentially land on the ground in a state such as Ohio. 

One can definitely think of it as efficiency. And there is an efficiency aspect to it -- the cover over the junction itself does restrict the amount of light coming in, and that is efficiency. However, the conversion from photons to free elections either happens or not, and depends entirely on the wavelength of the photon and the materials of which the junction is made.

The standard amount of radiation from the sun is the same everywhere -- conveniently, around 1 kilowatt per square meter with a clear atmosphere. However, that area -- the square meter -- is measured in the plane perpendicular to the direction towards the sun. So if the direction to the sun is not perpendicular to the ground or roof or wall or whatever, you have to engage in a little geometry to determine the energy per square meter of your angled surface. There is another factor as well: if the sun is shining on a potentially reflective surface, such as glass or the covering of a photocell array, then one needs to take into account the amount which is reflected and not transmitted to where you want it, and that increases sharply with off perpendicular incidence.

jumper

Some years ago vendors offered PV with output of about half of high efficiency. At about half price for panels but of course installation still costs same. No promises of better longevity. Still I suspected that degradation would be less severe. 20% of 10% sounds better than 20% of 20%. I'm still pondering.

JakeCK

Jamie Hall said:

One can definitely think of it as efficiency. And there is an efficiency aspect to it -- the cover over the junction itself does restrict the amount of light coming in, and that is efficiency. However, the conversion from photons to free elections either happens or not, and depends entirely on the wavelength of the photon and the materials of which the junction is made. The standard amount of radiation from the sun is the same everywhere -- conveniently, around 1 kilowatt per square meter with a clear atmosphere. However, that area -- the square meter -- is measured in the plane perpendicular to the direction towards the sun. So if the direction to the sun is not perpendicular to the ground or roof or wall or whatever, you have to engage in a little geometry to determine the energy per square meter of your angled surface. There is another factor as well: if the sun is shining on a potentially reflective surface, such as glass or the covering of a photocell array, then one needs to take into account the amount which is reflected and not transmitted to where you want it, and that increases sharply with off perpendicular incidence.

Doesn't the angle of incidence when the suns rays hit the atmosphere limit the amount of solar radiation available once you move away from the equator regardless of how clear the sky might be?

Of course it limits it even when it comes in at a 90 degree angle as it passes through but I would imagine the atmosphere reflects even more at a sharp angle. 

Jamie Hall

The atmosphere is a remarkably poor reflector -- though clouds, particularly high altitude ones, do reflect. On the other hand, there is the path length through the atmosphere which definitely has an effect, particularly if there is any significant amount of water vapour or dust. Thus at high latitude, where the path length is quite a bit longer as you note, there is more loss. Conveniently, most of the time the atmosphere is notably dust free and low on water vapour at those latitudes. Probably a wash, particularly when contemplating installations pretty much anywhere except the high desert.

ChrisJ

Wait


Solar panels don't use IR?

Larry Weingarten

Hi, photovoltaics work better if they are cooled by attaching solar thermal to the back side of the collector, but, no PVs don't do anything with IR but heat up, lowering efficiency.

Yours, Larry

ChrisJ

Larry Weingarten said:

Hi, photovoltaics work better if they are cooled by attaching solar thermal to the back side of the collector, but, no PVs don't do anything with IR but heat up, lowering efficiency. Yours, Larry

The entire reason I was interested in them was to keep the heat from going into my attic.

Apparently I had the wrong idea......

JakeCK

ChrisJ said:

Larry Weingarten said:

Hi, photovoltaics work better if they are cooled by attaching solar thermal to the back side of the collector, but, no PVs don't do anything with IR but heat up, lowering efficiency. Yours, Larry

The entire reason I was interested in them was to keep the heat from going into my attic.

Apparently I had the wrong idea......

Oh they will still reduce the heat into the attic. Laws of conservation dictate that. PV just doesn't use IR to make electrons move. Instead the panels absorb that energy and emit it back out. Maybe I'm completely wrong but how I see it you can look at it like this; take for example 100 btu's worth are absorbed from the sun and then emitted back out evenly in proportion to the surface area of each side, ignoring the edges for simplicity, since they're basically nothing, You'll now have 50 btu's out from the front facing side and 50 that are emitted towards the roof surface. The roof will absorb that 50 btu and emit it back out as well. 25 BTU out of the top and 25btu into the structure of the house. You'll cut that heat gain in half just by shading the roof with the panels. It's the physical separation that is critical. 

But like I said I could be completely off the wall with my math there. 

Edit: Or instead of being governed by the laws of conservation, maybe the laws of probability? Or are they one in the same? Lol 

Think like a bt... Think like a single quanta of energy.

Jamie Hall

If the PV array panels are separated from the roof itself by a few inches, so there is air circulation behind them, they will provide some shade to the roof -- not a bad thing in the summer! -- and they themselves will be cooler and much happier.

Or as @Larry Weingarten suggested, attach them solidly to an active solar thermal collector and cool them that way. Just be sure they can cool. Like any semi-conductor, excess temperature -- such as a stagnant solar thermal array -- will kill them.

JakeCK

Took these last year. The first two are of the underside of my garage roof, the third is of the house. Do you see the outline? 

JakeCK

Jamie Hall said:

Or as @Larry Weingarten suggested, attach them solidly to an active solar thermal collector and cool them that way. Just be sure they can cool. Like any semi-conductor, excess temperature -- such as a stagnant solar thermal array -- will kill them.

There is actually a company in Europe that integrate both thermal solar and PV into a single panel. If only I would have known about them 3 years ago. 

And I wonder if they can be used as a snow melt system too when the panels get covered. 🤔

Larry Weingarten

Hi, Combining phoyovoltaics and solar thermal is not a new idea. Many have tried to do it over the years, but it's challenging. My understanding is that there are some viable systems available now. Here's some writing on it. https://www.sciencedirect.com/topics/engineering/photovoltaic-thermal-hybrid-solar-collector
I like @JakeCK 's idea of running the thermal side to melt off snow. Many thermal things can be reversed.

Yours, Larry

ChrisJ

I like the idea of water cooling my roof.

A lot.

JakeCK

ChrisJ said:

I like the idea of water cooling my roof.

A lot.

You should see what misting the roof does. And it has to be a misting. If it's drenched where water runs off it doesn't work well. Something like 8000 btu's for every gallon that evaporates off the roof if I remember the numbers right. On a hot sunny day that's a lot of cooling. 

Solid_Fuel_Man

JakeCK said:

ChrisJ said:

I like the idea of water cooling my roof.

A lot.

You should see what misting the roof does. And it has to be a misting. If it's drenched where water runs off it doesn't work well. Something like 8000 btu's for every gallon that evaporates off the roof if I remember the numbers right. On a hot sunny day that's a lot of cooling. 

Phase change! 

Solid_Fuel_Man

A buddy of mine is buying a bunch of "old" panels which were removed to upgrade. 

He paid like 25% of new and supposedly the panels are 20 years old. I'll let you know how that works out. I'm interested in the same program too. 

Hot_water_fan

Not much to be gained from the panels themselves at the residential scale. 

JakeCK

Solid_Fuel_Man said:

A buddy of mine is buying a bunch of "old" panels which were removed to upgrade. 

He paid like 25% of new and supposedly the panels are 20 years old. I'll let you know how that works out. I'm interested in the same program too. 

Even if they're 80% of their rated capacity new if it's say a 300 watt panel that's still 240watts. If installed on a rack that tracks or is at least optimally positioned one might get better production numbers than new. 

And if it keeps it out of the landfill... 

jumper

That graphic indicates that electric parts of installation gets less expensive. Perhaps on account that inferior components are being used?

Hot_water_fan

I think it’s more likely that installations in the MWs get better prices and more optimal equipment than installations in the kWs. 

hot_rod

JakeCK said:

Solid_Fuel_Man said:

A buddy of mine is buying a bunch of "old" panels which were removed to upgrade. 

He paid like 25% of new and supposedly the panels are 20 years old. I'll let you know how that works out. I'm interested in the same program too. 

Even if they're 80% of their rated capacity new if it's say a 300 watt panel that's still 240watts. If installed on a rack that tracks or is at least optimally positioned one might get better production numbers than new. 

And if it keeps it out of the landfill... 

there are recyclers now 

JakeCK

hot_rod said:

JakeCK said:

Solid_Fuel_Man said:

A buddy of mine is buying a bunch of "old" panels which were removed to upgrade. 

He paid like 25% of new and supposedly the panels are 20 years old. I'll let you know how that works out. I'm interested in the same program too. 

Even if they're 80% of their rated capacity new if it's say a 300 watt panel that's still 240watts. If installed on a rack that tracks or is at least optimally positioned one might get better production numbers than new. 

And if it keeps it out of the landfill... 

there are recyclers now 

Good. But can they scale up to meet demand and will it be economical. 

And still at the end of the day which is less energy intensive? An old panel that is still functioning that can be reused as is or expending more energy to break down and recycle then manufacture a new panel with what resources could be recycled plus the new material input?

CLamb

Solid_Fuel_Man said:

JakeCK said:

ChrisJ said:

I like the idea of water cooling my roof.

A lot.

You should see what misting the roof does. And it has to be a misting. If it's drenched where water runs off it doesn't work well. Something like 8000 btu's for every gallon that evaporates off the roof if I remember the numbers right. On a hot sunny day that's a lot of cooling. 

Phase change! 

I don't think it's a phase change. For a phase change the roof would have to be about 212°F. It's the water evaporating into the air.

ratio

CLamb said:

I don't think it's a phase change. For a phase change the roof would have to be about 212°F. It's the water evaporating into the air.

Ummm...

JakeCK

ratio said:

I don't think it's a phase change. For a phase change the roof would have to be about 212°F. It's the water evaporating into the air.

Ummm...

Lol

😂

Jamie Hall

Your local friendly pedant here. The water evaporating is a phase change -- liquid to water vapour -- just at a lower temperature.

The French are working on ways to recycle PV panels at a commercial scale. They aren't there yet. The problems so far seem to involve getting the glass at a purity which is usable as glass (rather than aggregate) and more difficult -- much more difficult -- recovering the silver and copper. Both are a a relatively small fraction by weight, and are distributed in the panels, but are also where the resource intensity is and the cost.

Solid_Fuel_Man

CLamb said:

JakeCK said:

ChrisJ said:

I like the idea of water cooling my roof.

A lot.

You should see what misting the roof does. And it has to be a misting. If it's drenched where water runs off it doesn't work well. Something like 8000 btu's for every gallon that evaporates off the roof if I remember the numbers right. On a hot sunny day that's a lot of cooling. 

Phase change! 

I don't think it's a phase change. For a phase change the roof would have to be about 212°F. It's the water evaporating into the air.

I thought liquid turning into vapor (evaporating) was phase change.....

Jamie Hall

Solid_Fuel_Man said:

CLamb said:

Solid_Fuel_Man said:

JakeCK said:

ChrisJ said:

I like the idea of water cooling my roof.

A lot.

You should see what misting the roof does. And it has to be a misting. If it's drenched where water runs off it doesn't work well. Something like 8000 btu's for every gallon that evaporates off the roof if I remember the numbers right. On a hot sunny day that's a lot of cooling. 

Phase change! 

I don't think it's a phase change. For a phase change the roof would have to be about 212°F. It's the water evaporating into the air.


I thought liquid turning into vapor (evaporating) was phase change.....

It is a phase change -- from liquid to gas. In the case of water, the water to vapour -- or solid to vapour, which will be familiar (though usually not noticed) to those in the north country -- can occur at any temperature, depending on pressure. And it does require energy to go from solid to liquid, or liquid to gas -- thus cooling the whatever is adjacent -- or, conversely, releases energy going the other way, thus warming whatever is adjacent.

WMno57

" There are two types of vaporization: evaporation and boiling. Evaporation is a surface phenomenon, whereas boiling is a bulk phenomenon.
Evaporation is a phase transition from the liquid phase to vapor (a state of substance below critical temperature) that occurs at temperatures below the boiling temperature at a given pressure. Evaporation occurs on the surface. Evaporation only occurs when the partial pressure of vapor of a substance is less than the equilibrium vapor pressure."
https://en.wikipedia.org/wiki/Vaporization