Poly vs mono and SMA vs Enphase

[Noob]

This was never meant to be a science experiment. I have no political point to score. I have access to two systems in the area in the same area, with the same KW system with different inverters and I like to share some observations. One system has shade the other doesn't. The one without shades consistently outproduce the one with shades on sunny days. On overcast days, the reverse is true. The information are all AC watts from SolarCity's "envoy" like device and Enphase envoy so they should be the same. If weather patterns are truly random, then statistically, it should even out over time rather than favor one system over the other (which over three months should prove). There is no way to explain swings of 3 - 8 kwhr on shaded days otherwise. No different panel maker at the same KW size could have wild swings like that. I thought this information could be useful for Solar users out there.

Instead of taking it for what it is, MY observations, I feel like this information is not wanted. Inferring that I'm a "clown" by a moderator tells me that I'm overstayed my welcome. It's never good to be called a clown by the site moderator.

Chill out, he said "some clown", not "some other clown" (meaning I don't think he was calling you that) and besides, a lot of us find this little experiment/observation exercise interesting. Thanks for sharing it.

[russ]

Instead of taking it for what it is, MY observations, I feel like this information is not wanted. Inferring that I'm a "clown" by a moderator tells me that I'm overstayed my welcome. It's never good to be called a clown by the site moderator.

I never called you a clown - that was in reference to something from a couple of years back - PV Watts will never be "right on"so claiming to be with PV Watts is meaningless - I don't even know if the guy really had a solar system.

Your search for a difference over a short term does seem silly though. With no shade there is very little difference outside of sales pitches.

[bonaire]

I do like your data and it is meaningful however, clouds (not clowns...) differ on different days.
When it's cloudy out in PA here, my system is producing from 10% to 40% of the nameplate rating.
When it is sunny, I'm seeing nameplate+ during the peak sun hours of 11am-1pm. Cloudy days in PA seem to outnumber sunny days this year.

If a certain module types or inverters work better when the majority of days is cloudy, then they may benefit those in cloudy climates and customers can choose accordingly. Do you have poly modules on one and mono on the other? What exact modules do you have and that would make for interesting reading to see what the details are of each system.

[cyph]

Your search for a difference over a short term does seem silly though. With no shade there is very little difference outside of sales pitches.

I think you misunderstand me. I am not comparing the systems with no shades. The no shades is the baseline which shows the string inverter system beating the micro at 1-3 kwhr consistently. This makes sense because I've seen that the string is actually MORE efficient with no shade because the string inverter is running cooler (away from the roof and panels). I've seen it hit 4.3 kwh conversion on a 70 degree day whereas the micro will get around 4.1-4.2 due to the micro running at 30-40 F higher than ambient. Also, the string system has no shades which allow it to gather more in the morning and late afternoon. On the other hand, when it's colder outside (or after cloud formations have passed), the micro has hit 4.4-4.5 kw peak and my panels max out at 225-227w. It can't sustain this because with the rush of power, the micro heats up. For those in cold climates, I can see the micro maxing out at 225 consistently.

What I am trying to gain is whether on cloudy days where it's not optimal sun and lots of shades, how well the micro perform over the string. So far, I've seen that micro does in fact perform better. To exclude random cloud formation (even within 5 miles), I will have to average all the cloudy days. I think if I average out all cloudy days (basically any days where the string is producing less than 30 kwhr), I can come to some sort of conclusion. A 1 kwhr swing can be chalked up to random variations. However, if I see swings of 2 or more kwhr, it can be safely inferred that micros are superior when there are shade issues. Shade issues aren't always due to trees but clouds as well. For those living in non-sunny states, this could be a factor in their decisions.

[cyph]

I do like your data and it is meaningful however, clouds (not clowns...) differ on different days.
When it's cloudy out in PA here, my system is producing from 10% to 40% of the nameplate rating.
When it is sunny, I'm seeing nameplate+ during the peak sun hours of 11am-1pm. Cloudy days in PA seem to outnumber sunny days this year.

If a certain module types or inverters work better when the majority of days is cloudy, then they may benefit those in cloudy climates and customers can choose accordingly. Do you have poly modules on one and mono on the other? What exact modules do you have and that would make for interesting reading to see what the details are of each system.

I agree it's random. Which is why an averaging should even out the random variations. The modules are all poly. I have Trina 240w on one and CS 250w on the other. They are 5.04kw and 5kw. The micro per panel produces between 197-225w depending on the temperature. On sunny days, they have consistently produce the same amount of power (string consistently better by 1-3 kwhr depending on ambient temperature). Therefore, I do not believe they are the cause of any discrepancies.

Heat is a huge factor with micros where I see it losing up to 10% output if the ambient temperature reaches 90 degrees or more.

[russ]

The panel output goes down with temperature - the inverters should not be affected.

[cyph]

The panel output goes down with temperature - the inverters should not be affected.

I'm not sure if this is totally true. The microinverters efficiency does go down as temperature go up. At any one time, each of my panels differ in AC production from 0-10 kw (higher differences on hotter days). It's not rare to see two of my inside panels produce 197 kw while the ones on the outside edge produce 210 kw. Checking the temperature, the outside micro inverters are always 10-15 degrees lower. It also consistently outproduces the inside panels. The ones with the lowest production at any snapshot in time also has the highest internal micro temperature as well. I believe temperature affects both panel and inverters efficiencies.

[inetdog]

I'm not sure if this is totally true. The microinverters efficiency does go down as temperature go up. At any one time, each of my panels differ in AC production from 0-10 kw (higher differences on hotter days). It's not rare to see two of my inside panels produce 197 kw while the ones on the outside edge produce 210 kw. Checking the temperature, the outside micro inverters are always 10-15 degrees lower. It also consistently outproduces the inside panels. The ones with the lowest production at any snapshot in time also has the highest internal micro temperature as well. I believe temperature affects both panel and inverters efficiencies.

When the input to the inverter goes down, the output must go down too!
I think that can explain the entire output difference you are seeing. Remember that the outside panels will be cooler than the inside panels, just as the outside inverters are cooler than the inside inverters.

The most likely effect of temperature on the microinverter with a constant input (like a temperature controlled panel) would be that as the inverter gets too hot its protective circuitry reduces its output. The efficiency may not change noticeably because it will just take less input power from the panel. But it would not be doing as good a job of getting all possible power from the panel.

[russ]

I'm not sure if this is totally true. The microinverters efficiency does go down as temperature go up. Where did you learn this point?

I believe temperature affects both panel and inverters efficiencies.

Again, can you provide any references about the loss of efficiency for the inverters with temp?

Panels - yes and the panel spec includes the information

[cyph]

Again, can you provide any references about the loss of efficiency for the inverters with temp?

Panels - yes and the panel spec includes the information

In order to keep the heat low, the inverter will stop generating power or reduce the amount of power it generates by “derating” as it passes programmed temperature milestones. Figure 1, below, from SMA, shows how an SMA inverter handles temperature derating. At about 45 degrees C. it starts to ramp down power.

The ambient temperature of the inverter. The hotter your inverter gets the lower its efficiency will fall. Which is why it should always be installed in a shaded, well ventilated location.

As a general rule, colder is better for efficiency. Most materials and components become more resistive as they get hotter. However, there may be a practical limit for how cold the system can reasonably function. Most electrical components are rated either to 0C or -40C as a minimum ambient operating temp.

[inetdog]

This is what I mentioned about how the output may be limited, even though the efficiency does not change. It may not be a factor for inverters designed for outside roof mounting like micro inverters:
In order to keep the heat low, the inverter will stop generating power or reduce the amount of power it generates by “derating” as it passes programmed temperature milestones. Figure 1, below, from SMA, shows how an SMA inverter handles temperature derating. At about 45 degrees C. it starts to ramp down power.

Context: "The two minor factors are:"
The ambient temperature of the inverter. The hotter your inverter gets the lower its efficiency will fall. Which is why it should always be installed in a shaded, well ventilated location.

Also minor and very generalized:
As a general rule, colder is better for efficiency. Most materials and components become more resistive as they get hotter. However, there may be a practical limit for how cold the system can reasonably function. Most electrical components are rated either to 0C or -40C as a minimum ambient operating temp.

...............

[russ]

Has anyone ever measured the temp on the back side of the panels where the microinverters are mounted?

I have done so with solar thermal panels but not PV panels.