How much do your panels produce when it is overcast and raining?

[Mattb4]

It was a dark and gloomy day... My 3100w worth of panels this morning (10am ST) are putting out about 130w. Although not much it about equals my loads. 130w is around 4% of rating. Not enough power coming in to charge back my batteries from the nighttime deficit. But it is something.

It does make me wonder though if there are panel types that would produce more wattage even with low light daytime conditions. My panels are all mostly Mono with the exception of 4-100w poly. I have no Bifacial, half cut or use any optimisers. So what are the percents of rated wattage others are seeing during the less than stellar weather conditions?

 

[seneysolar]

Lots of overcast days here in Michigan, generally I can count on 7-10% of rated output.

The ones I watch the most are my REC 365 N-peak panels. I have 6 on a pole mount for a 24V system. Midnite Classic 150. Overcast day normally gets me around 7 amps @ 26.xxV while in Bulk mode.

 

[Mattb4]

Lots of overcast days here in Michigan, generally I can count on 7-10% of rated output.

The ones I watch the most are my REC 365 N-peak panels. I have 6 on a pole mount for a 24V system. Midnite Classic 150. Overcast day normally gets me around 7 amps @ 26.xxV while in Bulk mode.

That is pretty good.

Makes me wonder if Panel manufacturers should establish a rating for rainy days instead of STC (Standard Test Conditions) but RDTC (Rainy Day Test conditions)or perhaps ISOTC* to designate how they perform. I know that I would be more interested in knowing how a panel stacks up when it is not bluebird weather outdoors.


*It Sucks Outdoors Test Conditions

 

[seneysolar]

That is pretty good.

Makes me wonder if Panel manufacturers should establish a rating for rainy days instead of STC (Standard Test Conditions) but RDTC (Rainy Day Test conditions)or perhaps ISOTC* to designate how they perform. I know that I would be more interested in knowing how a panel stacks up when it is not bluebird weather outdoors.


*It Sucks Outdoors Test Conditions

Yeah, there's lots of degrees of overcast.

I would like to have a meter to measure Irradiance at the time of measuring panel performance. Then it could be compared to the STC rating.
I use the NMOT rating on panels more often for planning purposes. Its more realistic for folks above the 45th parallel mainly due to the lower Irradiance testing value.

 

[David in nh]

lets see right now i am making 56 watts at noon on a rainy day out of 900w of panels

 

[Mattb4]

lets see right now i am making 56 watts at noon on a rainy day out of 900w of panels

That comes in ~6%. What kind of panels do you have?

 

[Ampster]

My 8kW system produces as much as 50kWhs on perfect cool and clear Spring days and as little as 1 kWh on cloudy days. High clouds can be surprisingly good because of the cloud edge effect.

 

[JRH]

It was a dark and gloomy day... My 3100w worth of panels this morning (10am ST) are putting out about 130w. Although not much it about equals my loads. 130w is around 4% of rating. Not enough power coming in to charge back my batteries from the nighttime deficit. But it is something.

It does make me wonder though if there are panel types that would produce more wattage even with low light daytime conditions. My panels are all mostly Mono with the exception of 4-100w poly. I have no Bifacial, half cut or use any optimisers. So what are the percents of rated wattage others are seeing during the less than stellar weather conditions?

Sometimes is easier to use a WORD than a Number to get across a point efficiently.

So instead of calculating 0 ,and a decimal point and more 0’s ….and a % value….
I will just say ..” GAGGY “ ………..” GAGGY PRODUCTION”.

There are other words that would apply ….

But GAGGY pretty well sums it up…

 

[millsan1]

between basically nothing and 15%

 

[Mattb4]

I did get up to 5% by noon with steady rain.

 

[SparkyJJO]

All I know is it sucks. 3+ inches of snow sucked worse though (not even 600Wh from 8400W of panels on a super clear sunny day)

 

[Mattb4]

Sadly it looks like test conditions can no longer be met since the rain has quit. PV production has jumped up to the 10% range with just overcast skies.

 

[JRH]

Sadly it looks like test conditions can no longer be met since the rain has quit. PV production has jumped up to the 10% range with just overcast skies.

I would say 10 to 15 % is about right , but the clouds can foo ya ( at least me) sometimes it can be 30% then 20 again…it’s hard to call.

 

[JRH]

Sadly it looks like test conditions can no longer be met since the rain has quit. PV production has jumped up to the 10% range with just overcast skies.

On your topic from yesterday…it’s foggy now …and heavy overcast with drizzle in the NC Mtns..
A peak of the day 1:00 pm real time reading of my PV power has been all morn , and IS now, about 4-5 %….

Like I said, that’s pretty gaggy.

J.

 

[Mark-]

Overcast and drizzle here (Deep East Texas) and there.
https://hmisys.com/SolarMain.jpg updates every 5 minutes are so.

 

[Mattb4]

Just overcast today with no rain so far so my PV percentage has run between 10 and 20%. It is ~500w at the moment which gives me some charge to my batteries over house loads (200w).

Any folks out there with Bifacials to report on their rainy day experience with them?

 

[wattmatters]

Crap days can be pretty crap.

Daily PV Production (kWh)
11 kW PV / 10 kW grid-tied inverter. 
Nthn NSW Australia.
 
Year     Avg      Min      Max
2018    55.58     0.85    70.47  (installed late-October)
2019    38.97     6.16    69.47
2020    34.42     2.75    67.96
2021    36.88     3.08    67.31
2022    34.58     1.49    66.24
2023    40.01     3.56    69.05
2024    42.58    11.13    65.94  (YTD 8 March)
Total   37.57     0.85    70.47

 

[rhino]

Makes me wonder if Panel manufacturers should establish a rating for rainy days instead of STC

There is already a Nominal Operating Cell Temperature that some panel specs list which uses only 800W/m^2 instead of 1000 for STC.

 

[Mattb4]

There is already a Nominal Operating Cell Temperature that some panel specs list which uses only 800W/m^2 instead of 1000 for STC.

Yeah but that is figuring for average good weather. Tells you nothing when the chips are down or when a Nor'easter is ripping through your neighborhood. Might need calibrated for your typical rain amount. Drizzle, Light rain, Steady rain, Raining cats and dogs, and Better build an ARK.

 

[rhino]

The only thing that really makes a difference in that scenario is the W/m^2. Different rain amounts or whatever is just going to adjust that value because it is darker or lighter out which is what the W/m^2 is indicating. So it may be helpful if they had something that is even lower like 400W/m^2 which may start differentiating panels that work better in lower light.