Solar Array Production
Comments
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Re: Solar Array ProductionThis is well known, you can find the NOCT (Normal Operating Cell Temperature) values for many panels. They tend to be 75-80% of panel rating.
Then there are PTC Ratings used for some california rebates/credits these I think use yet another set of values.
Yes, I was aware of the effect of temperature on panel output, but did not realize the extent of the effect, especially at very cold temp's. At times, I am getting in excess of 25% more than rated output, but typically is between 10 and 15 %. Thanks for that link photowit. My array has a PTC rating of 1272 watts. -
Re: Solar Array Production
I usually put in the what the acronims stand for and couldn't recall, PTC is PVUSA(Photovoltaics for Utility Scale Applications) Test Condition and the wattage listed on your panel is STC or Standard Test Conditions.Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites, Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
- Assorted other systems, pieces and to many panels in the closet to not do more projects. -
Re: Solar Array Productionnortherner wrote: »Yes, I was aware of the effect of temperature on panel output, but did not realize the extent of the effect, especially at very cold temp's. At times, I am getting in excess of 25% more than rated output, but typically is between 10 and 15 %. Thanks for that link photowit. My array has a PTC rating of 1272 watts.
Voltage variance due to temperature for most modules is about 0.3-0.4% of Voc per degree C. Current varies directly with insolation (strength of sunlight) which under certain conditions can exceed the 1000W/m^2 which is the standard by which the module is rated. Power is voltage times current, so on a cold clear day in very bright sunlight you can be getting a boost in both voltage and current, and the power boost you get is the product of the two. -
Re: Solar Array Productionnortherner wrote: »Yes, I was aware of the effect of temperature on panel output, but did not realize the extent of the effect, especially at very cold temp's. At times, I am getting in excess of 25% more than rated output, but typically is between 10 and 15 %. Thanks for that link photowit. My array has a PTC rating of 1272 watts.
Panels warm up quite a bit, and in these conditions they're definitely above freezing (because ice/snow melts away), and they even warm to touch. So, the temperature effect cannot be any higher than 107%, and that is before charger efficiency loss.
The high production that we see in the north is most likely because of the reflection of the solar radiation from the snow. It only happens in March. You won't see it in September with seemingly the same sun position. -
Re: Solar Array ProductionPanels warm up quite a bit, and in these conditions they're definitely above freezing (because ice/snow melts away), and they even warm to touch. So, the temperature effect cannot be any higher than 107%, and that is before charger efficiency loss.
The high production that we see in the north is most likely because of the reflection of the solar radiation from the snow. It only happens in March. You won't see it in September with seemingly the same sun position.
Just wondering where you got that 107% figure from, as I was researching the effect of panel output vs cold temperatures, and didn't find much. So you are saying that reflected light from snow has a greater effect on solar array output than extremely cold temps. I wasn't aware of that.
By the way, we do occasionally have snow on the ground in September, but doesn't stick around long.:p September temps here are usually more summer like, whereas March is closer in line to winter, so just comparing outputs for the 2 months wouldn't be a totally fair comparison, at least here in northern AB.
By the way, I'm on track for an estimated output of 200 kwh from my 1.4 kw array for the month of March. I can hardly believe it! -
Re: Solar Array Productionnortherner wrote: »Just wondering where you got that 107% figure from, as I was researching the effect of panel output vs cold temperatures, and didn't find much. So you are saying that reflected light from snow has a greater effect on solar array output than extremely cold temps. I wasn't aware of that!
They're not that cold. When there's -20C outside, they may be +5C. That's why the now melts on them. So, there's no huge temperature difference from +25C.
If you look at the spec sheet for your panels, there should be a temperature coefficinet. It's a little bit different for different brands, but it's usually around -0.3%. So, if panels are slightly above freezing, it's 7% gain. To reach 25% gain, you would need to keep them around -60C, so the ambient would have to be -80-90C. So, you cannot explain your higher production with temperature alone. -
Re: Solar Array Production
I don't see a temp coefficient listed in my spec sheet. I believe that with most panels, the change in output with temperature is not linear. As the panels get warmer, panel output decreases to a greater extent, but of course this would not apply here anyway. Just pointing that out.
No, it hasn't been -80 to -90C here, although, some days it feels like it.:p
Another factor that may play in is the performance rating of the panels and for mine are +10/-5 Percent of P max under STC's. Maybe mine are closer to +10% than -5%? -
Re: Solar Array Production
Voltage change due to temperature change is calculated as linear as either percent of Voc (or rarely, Vmp) per degree C or as millivolts per degree C. In the case of lower cell temperature than 25 degrees C and higher than 1000 W/m^2 insolation, the increase in power over the STC rating would be the STC voltage times the change in current, plus the STC current times the change in voltage, plus the change in voltage times the change in current (VdC + CdV + dCdV). Calculus 101.northerner wrote: »I don't see a temp coefficient listed in my spec sheet. I believe that with most panels, the change in output with temperature is not linear. As the panels get warmer, panel output decreases to a greater extent, but of course this would not apply here anyway. Just pointing that out.
Look at your spec sheet again. I haven't seen a spec sheet without a temperature coefficient for voltage in years. -
Re: Solar Array Productionnortherner wrote: »I don't see a temp coefficient listed in my spec sheet. I believe that with most panels, the change in output with temperature is not linear. As the panels get warmer, panel output decreases to a greater extent, but of course this would not apply here anyway. Just pointing that out.
It might be unlinear, but not much. It has to be a temperature coefficient of some sort, because it's needed for proper charge controller sizing. For example, for my panels, I got three separate coefficients:
TC ISC = 0.004%/K
TC VOC = -0.30%/K
TC PMPP = -0.45%/Knortherner wrote: »Another factor that may play in is the performance rating of the panels and for mine are +10/-5 Percent of P max under STC's. Maybe mine are closer to +10% than -5%?
It's interesing that Sharp, Kyocera and other "old" producers have much lower rating (e.g. 235) on the panels of similar size than modern ones (260 even 265 or 270 sometimes). May be they rate them more conservatively. -
Re: Solar Array ProductionIt might be unlinear, but not much. It has to be a temperature coefficient of some sort, because it's needed for proper charge controller sizing.
I was referring to higher temps that really begin to affect array output when the panels get very warm. Yes, it is very close to a linear coefficient for temps below 25C.It's interesing that Sharp, Kyocera and other "old" producers have much lower rating (e.g. 235) on the panels of similar size than modern ones (260 even 265 or 270 sometimes). May be they rate them more conservatively.
I know that the Sharp panels (at least the ones I bought) are not nearly as efficient as other panels available, perhaps reason for lower output for roughly the same size.Look at your spec sheet again. I haven't seen a spec sheet without a temperature coefficient for voltage in years.
There could be a spec sheet, but I did not receive one with the panels. I did get an installation and user manual, and electrical ratings are listed for various models, but they didn't include temp coefficients. Perhaps they just left them out. -
Re: Solar Array Production
What is the module make and model? Data sheets are usually pretty easy to find on line.northerner wrote: »There could be a spec sheet, but I did not receive one with the panels. I did get an installation and user manual, and electrical ratings are listed for various models, but they didn't include temp coefficients. Perhaps they just left them out.
What is it that makes you say that voltage variation due to temperature change is linear for temps lower than 25 degrees but nonlinear for higher temps? Do you have data from the manufacturer that says that? -
Re: Solar Array ProductionWhat is the module make and model? Data sheets are usually pretty easy to find on line.
What is it that makes you say that voltage variation due to temperature change is linear for temps lower than 25 degrees but nonlinear for higher temps? Do you have data from the manufacturer that says that?
Yes, I did find the data sheet online after a bit of searching, thanks. My panel has a temp coefficient for Pmax of -0.485%/C.
It was my understanding that panel output dropped considerably with temperatures above 25 C? If the temperature coefficient is relatively constant throughout the temperature range, then perhaps it's actually the temperature of the panels that is rising considerably for operators in warm climates, responsible for reduced outputs. A misinterpretation on my part if that's the case. -
Re: Solar Array Productionnortherner wrote: »Yes, I did find the data sheet online after a bit of searching, thanks. My panel has a temp coefficient for Pmax of -0.485%/C.
It was my understanding that panel output dropped considerably with temperatures above 25 C? If the temperature coefficient is relatively constant throughout the temperature range, then perhaps it's actually the temperature of the panels that is rising considerably for operators in warm climates, responsible for reduced outputs. A misinterpretation on my part if that's the case.
Panel temperature is not the same as air temperature. Panels in operation will be higher. The 25C rating is for panel temperature; when they do this test the panels are 'flashed', not left on to warm up to Normal Operating Condition Temperature - which is often twice that.
However higher (or lower) air temperature affects how well the panel can radiate heat, and they are not good heat radiators. As such slight increases in ambient temperature cause greater increases in panel temperature.
By the same token the reverse is true. This is why in the Great White North we have to deal with psychotic Voc, and get it under control before the panel can be connected to power anything - at which point the Voltage is pulled down and the panel begins to warm up and the problem goes away. We still get some pretty good increases in Voltage as a result of running them at -40C, because the panels will operate substantially below the rated 25C.
It's science until you get into the real world, then it becomes art.
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Re: Solar Array ProductionCariboocoot wrote: »By the same token the reverse is true. This is why in the Great White North we have to deal with psychotic Voc, and get it under control before the panel can be connected to power anything - at which point the Voltage is pulled down and the panel begins to warm up and the problem goes away. We still get some pretty good increases in Voltage as a result of running them at -40C, because the panels will operate substantially below the rated 25C.
If you set up your system properly and use an mppt charge controller, there shouldn't be a problem with an excessive Voc. I tried hooking up 4 of my Sharp panels in series, before installing them on the roof, and I found that at times the voltage would go above 150v, the limit for the Midnite Classic CC, and would not accept the input until it dropped below 150. Three panels is the limit for that CC.
As you mention, I could see certain charge controllers, particularly PWM types, that could have a problem with excess Voc's at very low temp's.
Not only will the air temperature affect the panel temp, but also the panel exposure to the air, and movement of that air (ie wind). -
Re: Solar Array Production
For most PWM type controllers Voc is not an issue at all.
For most MPPT controllers it is because the input can be hit with excessively high Voltage and do damage. Only MidNite Classics have the HyperVoc function.
In a land where cold Voc can be 1.3 times its STC rating anyone who is trying to get a maximum array Voltage (as in to overcome long wiring resistance) will run into this trouble. It is necessary to take it into account. -
Re: Solar Array ProductionCariboocoot wrote: »For most PWM type controllers Voc is not an issue at all.
For most MPPT controllers it is because the input can be hit with excessively high Voltage and do damage. Only MidNite Classics have the HyperVoc function.
In a land where cold Voc can be 1.3 times its STC rating anyone who is trying to get a maximum array Voltage (as in to overcome long wiring resistance) will run into this trouble. It is necessary to take it into account.
That would depend on your setup as well. MPPT controllers can take advantage of much greater range of voltage, but I could see them being susceptible to hyper Voc if operating near their upper limit. I would think that most users would operate closer to that limit, but 3 (24 volt) panels should give plenty of leeway, if your controller typically could handle 150 volts. There are many different controllers out there, and most I am not familiar with.
I thought that most PWM controllers could only take advantage of a narrower range of voltage for efficient operation. So are you saying that they could handle a much higher voltage without a problem, or that hyper Voc is not a factor within their limited range.
I could also see that those that are running much longer lines at higher voltages could have the potential for greater swings in voltage. -
Re: Solar Array Production
This is why the old rule of thumb about nominal array Voltage being no more than 2X nominal system Voltage works. Pretty much eliminates Voc problems if the array will be <100 Volts nominal. Reduces conversion inefficiency too.
But hey, there's a darn good reason why those clever people at MidNite came up with HyperVoc and put it on controllers that can take up to 250 Volts input. -
Re: Solar Array Production
Notherner, you were very lucky that you did your experiment with a midnite classic and not a different MPPT controller, because it's the only one on the market that will safely shut down if you exceed the 150V limit. If you had done that with any other it mostly likely would have been permanently damaged. -
Re: Solar Array ProductionNotherner, you were very lucky that you did your experiment with a midnite classic and not a different MPPT controller, because it's the only one on the market that will safely shut down if you exceed the 150V limit. If you had done that with any other it mostly likely would have been permanently damaged.
I knew the Classic 150 has a 150 volt limit for input and also knew that it has hyper Voc protection, so I wouldn't really call it lucky. Also, the voltage only went beyond 150 volts on a few occasions on cold mornings, and by only a few tenths of a volt. While that could cause damage to another CC, I would tend to think that if they had a similar rating, that they would have more tolerance than that? On the other hand, voltages in really extreme cases could go even higher, and yes then it could potentially cause damage to another unit. -
Re: Solar Array ProductionCariboocoot wrote: »This is why the old rule of thumb about nominal array Voltage being no more than 2X nominal system Voltage works. Pretty much eliminates Voc problems if the array will be <100 Volts nominal. Reduces conversion inefficiency too.
But hey, there's a darn good reason why those clever people at MidNite came up with HyperVoc and put it on controllers that can take up to 250 Volts input.
In the case where you do have long runs from array to the equipment, and others are using these higher voltage charge controllers, then that must speak that wiring losses would exceed losses from conversion inefficiencies for a greater than 2x system voltage array setup. But yes, you could be more susceptible to Voc problems. -
Re: Solar Array Production
I am thinking about eventually setting up to monitor, panel temperatures and compare to various levels of air temp and solar insolation, and record the power output at these levels. I think it would also be interesting to note the temperature of a panel that is not producing power as well. Just wondering if anyone has done this, especially in a northern environment, where cold temps and reflected light from snow, can significantly influence panel efficiency? -
Re: Solar Array Productionnortherner wrote: »... and reflected light from snow, can significantly influence panel efficiency?
As soon as all this snow gets on the ground and we get some sun, I'll measure to see if I get more than 1000W/m2. -
Re: Solar Array Productionnortherner wrote: »In the case where you do have long runs from array to the equipment, and others are using these higher voltage charge controllers, then that must speak that wiring losses would exceed losses from conversion inefficiencies for a greater than 2x system voltage array setup. But yes, you could be more susceptible to Voc problems.
This is exactly the problem: the V-drop is in effect on Vmp * Imp (full power output), but not on Voc (where current is essentially zero). It can be a real bear. -
Re: Solar Array ProductionAs soon as all this snow gets on the ground and we get some sun, I'll measure to see if I get more than 1000W/m2.
I look forward to your results! -
Re: Solar Array Productionnortherner wrote: »I look forward to your results!
Today at astronomical noon. Sun at 35 degrees from the horizon:
- At the panels inclination (25 degrees off horizontal) - 1130 W/m2.
- Looking at the sun - 1070 W/m2.
- Looking horizontally - 1080 W/m2.
- Maximum (about 15 degrees off horizontal) - 1150 W/m2.
So, reflection off the snow does add to your production. Combined with temperature effect, can be quite a bit. -
Re: Solar Array ProductionToday at astronomical noon. Sun at 35 degrees from the horizon:
- At the panels inclination (25 degrees off horizontal) - 1130 W/m2.
- Looking at the sun - 1070 W/m2.
- Looking horizontally - 1080 W/m2.
- Maximum (about 15 degrees off horizontal) - 1150 W/m2.
So, reflection off the snow does add to your production. Combined with temperature effect, can be quite a bit.
I take it the angles you mention are the direction the panels are facing (ie perpendicular to the plane they are on) and not the actual plane they are on.
If snow reflection is fairly significant as your results indicate, then it would make sense to hold off tilting the panels back (in a system where panels can be tilted seasonally) until the snow melts. Thanks for posting the results! -
Re: Solar Array Productionnortherner wrote: »I take it the angles you mention are the direction the panels are facing (ie perpendicular to the plane they are on) and not the actual plane they are on.
Yes, that's the angle between the line along witch the sensor is looking and the ground. Panel would be perpendicular to that line. -
Re: Solar Array Production
It's been such a nice summy weather here lately, so I made lots of measurements. 1200 W/m2 is not uncommon with snow reflection. -
Re: Solar Array ProductionIt's been such a nice summy weather here lately, so I made lots of measurements. 1200 W/m2 is not uncommon with snow reflection.
We've been getting plenty of sun too. Sounds like snow reflection is quite significant as well!
I had a good month of solar production in March with 214 kwh produced from my 1.4 kw array. It sounds like northern locations are matching production from more southerly locations, although after the spring equinox, we receive more day light hours. Countering that of course is the fact that the sun is not as high in the sky. But cooler temps and snow reflection add significantly to production.
My usage was 158 kwh yielding an overall efficiency of nearly 74%. I was making use of the excess power during the day by running an electric heater often in the afternoon, and reason for the high yield.
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