kWp vs Current Power / Actual Performance

[SunRunSux]

I'm sure this has been brought up before, but I have a 15-panel system which is rated at ~4.9 kWp, but I've never seen anything above 3.9 kW at any given point (so ~20% under peak). This seems like an obvious issue to me, but I'm wondering what others have experience with their home setups. I'm in a desert community, so there are plenty of optimal performance days. I've also spoke to SolarEdge several times and they informed me my inverter was only rated for 3.8 kW, so it seems like a limitation on my inverter? I'm surprised my solar installer would even build a system with obvious limitations, but I've also heard that a 3.8 kW inverter can be overbuilt and accept more than rated?! I've been going back and forth with technical support, but I'd like to get some more data from other home users to better inform myself. I do own my system as well.

SolarEdge Inverter - SE3800H-USMNBBL14
7x Jinko JKM320M-60HBL panels
8x JA Solar JAM60S17-325/MR as well

 

[BentleyJ]

PV panel ratings are done under Standard Test Conditions. These are the STC ratings that are usually used for advertising and are found in the panel model number. Most reputable manufacturers also include NMOT ratings which are more typical, realistic output numbers at Normal Module Operating Temps. Keep in mind output goes down when temperatures go up. This is why it is necessary to calculate temperature corrected open circuit voltages for an array in cold climates because Voltage goes up.
Refer to the datasheet for the solar panel brand and model number you have. The volt-temp coefficient will be something like -0.34% per deg C.

What you are describing is typical behavior especially in the desert where it is easy to mistake actual solar irradiance as being very high when its only because it "feels" HOT.

 

[SunRunSux]

PV panel ratings are done under Standard Test Conditions. These are the STC ratings that are usually used for advertising and are found in the panel model number. Most reputable manufacturers also include NMOT ratings which are more typical, realistic output numbers at Normal Module Operating Temps. Keep in mind output goes down when temperatures go up. This is why it is necessary to calculate temperature corrected open circuit voltages for an array in cold climates because Voltage goes up.
Refer to the datasheet for the solar panel brand and model number you have. The volt-temp coefficient will be something like -0.34% per deg C.

What you are describing is typical behavior especially in the desert where it is easy to mistake actual solar irradiance as being very high when its only because it "feels" HOT.

Thank you for the reply! Unfortunately no NMOT or realistic ratings were ever provided, so I'm just going off the information provided. My Solar energy system size / Peak power rating is the only thing listed across my installer and inverter sites. I definitely understand this is only onder peak perfect conditions, but it still seems odd to me that my system has never gone above ~80% of this hypothetical range. 5-10% I understand, but 20% seems excessive to me. Meaning, after looking back at the reports and data of Life Time power generation, it's never once gone above ~3.9 kW system power generation at any given moment. This would even account for those perfect sunny days with 70 degree temps and good air quality.

 

[BentleyJ]

It is possible that the 3.8kW inverter is clipping some of the available PV between 11 am and 1 pm so it doesn't overheat and damage itself. If your system can provide a graphical representation of solar output for the whole day it should look very much like a textbook bell curve. If on a clear day the chart is flat across the top more like a mesa than a smooth curve then you are probably experiencing some inverter related limitations.

 

[wattmatters]

I've also spoke to SolarEdge several times and they informed me my inverter was only rated for 3.8 kW, so it seems like a limitation on my inverter?

No matter the peak capacity rating of the PV array, the maximum power output from a grid-tied PV system is limited to no more than the output capacity rating of the inverter.

It is normal/common for the kWp of the array to be higher than the output rating of the inverter.

Indeed it's good practice.

Most (decent) GT inverters can accept about 30-50% more PV input than they can generate in AC power output. Some might have a lower limit, some might allow more.

Yes there will be occasions in very good solar conditions when the inverter is at its capacity limit and some of the potential generation capacity of the PV array is left on the table, but that is made up for when the sun is lower in the sky, during the Winter half of the year and on cloudy/rainy days. This is when the "oversized" PV array helps to generate more power.

Having the PV array kWp rating about 1/3rd higher than the inverter's max output capacity rating makes for a nice balance between not losing too much PV generation capacity in good conditions and getting good capacity utilisation of the inverter vs not spending more on a bigger capacity inverter just to capture a bit more energy when you least need it. The amount of "lost energy" really isn't a lot.

If you really want more than 3.8 kW output at any time, then you'll need an inverter rated to generate it.

 

[JRH]

The location of my panels ,altitude of land and being very remote in the mountains with clean air and cold / cool temps even in summer unfairly affect my output …If I were just 25 miles west or east or near a town or industry it would worse.

Simply put after a year of tracking outputs even my cheapo panels do very well.

Note * winter is awful because of trees ….. and snow and whatever.. im working on it….

I’m not considering overcast , cloudy or bad days in my % numbers, but a normal “nothing special” sunny day. Those will mostly always produce about 85 to 95 % if not cloudy .. sometimes a haze or smoke will knock that down a bit. Sometimes % will hover right around 100% for quite a bit during the midday……
… high temps in summer rarely are over 70- 75…..80 F sometimes … so ambient temps are usually at or lower than STC.

I see 100 + % quite often for a while midday and cool and actually had a 25 % boost one time last fall on a very cool and bright clear day … it was of short duration ,and I don’t know why …no clouds anywhere.?

I am using numbers from the Victron equipment I receive from blue tooth…

If I were not located in a good place I’m sure the numbers would not be what they are…if I didn’t have a tilting / rotating array it would not be as good either …

I’m enlarging the array now by 3X and hope this trend continues.

J.

 

[SunRunSux]

It is possible that the 3.8kW inverter is clipping some of the available PV between 11 am and 1 pm so it doesn't overheat and damage itself. If your system can provide a graphical representation of solar output for the whole day it should look very much like a textbook bell curve. If on a clear day the chart is flat across the top more like a mesa than a smooth curve then you are probably experiencing some inverter related limitations.

Thank you for the great explanation, this makes much more sense now. Looking over this past week, it does seem to be a nice bell curve, so perhaps this is just normal operations for my system. Since I'm on the enduser side, I just take everything at face value, so it's a bit confusing.

 

[SunRunSux]

No matter the peak capacity rating of the PV array, the maximum power output from a grid-tied PV system is limited to no more than the output capacity rating of the inverter.

It is normal/common for the kWp of the array to be higher than the output rating of the inverter.

Indeed it's good practice.

Most (decent) GT inverters can accept about 30-50% more PV input than they can generate in AC power output. Some might have a lower limit, some might allow more.

Yes there will be occasions in very good solar conditions when the inverter is at its capacity limit and some of the potential generation capacity of the PV array is left on the table, but that is made up for when the sun is lower in the sky, during the Winter half of the year and on cloudy/rainy days. This is when the "oversized" PV array helps to generate more power.

Having the PV array kWp rating about 1/3rd higher than the inverter's max output capacity rating makes for a nice balance between not losing too much PV generation capacity in good conditions and getting good capacity utilisation of the inverter vs not spending more on a bigger capacity inverter just to capture a bit more energy when you least need it. The amount of "lost energy" really isn't a lot.

If you really want more than 3.8 kW output at any time, then you'll need an inverter rated to generate it.

Thank you for the great explanation! This is all making a lot more sense to me and I'm starting to see why the solar companies hide a lot of information from their clients as well. I suppose this is normal practice and how the system should be operating. I'm just trying to get my EoY trueup down more and this seemed like some low hanging fruit at first. Thanks again for explaining this in detail.

 

[SunRunSux]

The location of my panels ,altitude of land and being very remote in the mountains with clean air and cold / cool temps even in summer unfairly affect my output …If I were just 25 miles west or east or near a town or industry it would worse.

Simply put after a year of tracking outputs even my cheapo panels do very well.

Note * winter is awful because of trees ….. and snow and whatever.. im working on it….

I’m not considering overcast , cloudy or bad days in my % numbers, but a normal “nothing special” sunny day. Those will mostly always produce about 85 to 95 % if not cloudy .. sometimes a haze or smoke will knock that down a bit. Sometimes % will hover right around 100% for quite a bit during the midday……
… high temps in summer rarely are over 70- 75…..80 F sometimes … so ambient temps are usually at or lower than STC.

I see 100 + % quite often for a while midday and cool and actually had a 25 % boost one time last fall on a very cool and bright clear day … it was of short duration ,and I don’t know why …no clouds anywhere.?

I am using numbers from the Victron equipment I receive from blue tooth…

If I were not located in a good place I’m sure the numbers would not be what they are…if I didn’t have a tilting / rotating array it would not be as good either …

I’m enlarging the array now by 3X and hope this trend continues.

J.

Nice, I'd be interested to know the specifics of your equipment after reading some of these other replies. Do you have an inverter that is rated perfectly for your panels or higher? It seems like my system was built with an inverter which is less-capable than the amount of panels can produce in theory, but it seems like this may be industry standard. I've been thinking about adding another system in the future since I still have to pay the power company a trueup yearly.

 

[JRH]

Nice, I'd be interested to know the specifics of your equipment after reading some of these other replies. Do you have an inverter that is rated perfectly for your panels or higher? It seems like my system was built with an inverter which is less-capable than the amount of panels can produce in theory, but it seems like this may be industry standard. I've been thinking about adding another system in the future since I still have to pay the power company a trueup yearly.

Thanks… I don’t think my equipment is the total reason of what I’m experiencing… yes that’s part of it…
I would also like to think I did a decent job hooking it up and selecting components ..that plays into performance too.

But……The location and weather I think is boosting what would be somewhat average performance if I were in a suburb or warmer place…

Jus my opinion….

When I used the word “ unfair” that’s what I was referring to…the gear will produce more if I have sun than it would for most people in a different location…..
that’s not a system or design specific…I didn’t wind up here by design , that’s just LUCK.

I have never heard of the term “ rated perfectly “ concerning an inverter and panels …nothing in my life is perfectly anything…I just Wing Things with what I got …

I know I’m underpaneled ….at this point , and I’m hookin up more PV to fix that..

I want to be about 30% over paneled for my 3000/ 24 multiplus , and I have separate SCC’s for each array.

I use only “ blue gear” …notice I didn’t use the “ V “ word….

.and blue seas accessories mostly….

My batts I can’t name here without stirring up a rowdy ruckus in the comment section.
Let’s just say their good ones…

I do use oversized wire and connections for most everything ..it runs cooler and looks cooler too.

Oh … and I like things with blinking or blue lights… thats always a plus…

That’s about it…

Good luck with your venture…

J.

 

[wattmatters]

There is an article on overpaneling on this site:

Overview of Over-paneling an MPPT controller

To get to the paper, click on the orange button at the top of the screen. There is a misconception that putting more panels on an MPPT controller than the controller is able to use will damage the controller. However, in almost all cases it is...

diysolarforum.com

Note the diagram on page 4:

 

[SunRunSux]

Thanks… I don’t think my equipment is the total reason of what I’m experiencing… yes that’s part of it…
I would also like to think I did a decent job hooking it up and selecting components ..that plays into performance too.

But……The location and weather I think is boosting what would be somewhat average performance if I were in a suburb or warmer place…

Jus my opinion….

When I used the word “ unfair” that’s what I was referring to…the gear will produce more if I have sun than it would for most people in a different location…..
that’s not a system or design specific…I didn’t wind up here by design , that’s just LUCK.

I have never heard of the term “ rated perfectly “ concerning an inverter and panels …nothing in my life is perfectly anything…I just Wing Things with what I got …

I know I’m underpaneled ….at this point , and I’m hookin up more PV to fix that..

I want to be about 30% over paneled for my 3000/ 24 multiplus , and I have separate SCC’s for each array.

I use only “ blue gear” …notice I didn’t use the “ V “ word….

.and blue seas accessories mostly….

My batts I can’t name here without stirring up a rowdy ruckus in the comment section.
Let’s just say their good ones…

I do use oversized wire and connections for most everything ..it runs cooler and looks cooler too.

Oh … and I like things with blinking or blue lights… thats always a plus…

That’s about it…

Good luck with your venture…

J.

Thank you and good luck to you as well! I, unfortunately, am extremely limited to what I can do personally here in California. I had no choice in my system as well, since it was part of a template for new constructions. As with anything cookie cutter....it's usually done on the Cheap! I do know these SolarEdge inverters are lemons (at least my model). I've seen coutnless videos on youtube of installers saying they have to replace 40%+ of them and I actually just had to replace mine after only a few years of service. I think I will try to stay away from SolarEdge in the future or at least heavily research the specific models.

Thanks again!

 

[SunRunSux]

There is an article on overpaneling on this site:

Overview of Over-paneling an MPPT controller

To get to the paper, click on the orange button at the top of the screen. There is a misconception that putting more panels on an MPPT controller than the controller is able to use will damage the controller. However, in almost all cases it is...

diysolarforum.com

Note the diagram on page 4:

View attachment 200491

Super interesting! I downloaded the report, but will need to read it over a few times to digest. So perhaps the one panel I'm seeing, which is producing 1/2 of all other panels, is also by design? Perhaps they had to tone one of the panels down to not over-input my controller? I'm glad I decided to engage you all here, this has been quite the learning experience for me.

 

[wattmatters]

Perhaps they had to tone one of the panels down to not over-input my controller?

That would mostly likely be due to some shading affecting that panel in particular. Could be a vent pipe, antenna, design of roof, tree. Doesn't need much. Solaredge uses optimisers on each panel to help with such things.

 

[SunRunSux]

That would mostly likely be due to some shading affecting that panel in particular. Could be a vent pipe, antenna, design of roof, tree. Doesn't need much. Solaredge uses optimisers on each panel to help with such things.

OK, Thank you, so I may have an issue then. There are no obstructions on these panels at all.