Source for predicting cloud cover?

[rhino]

Is there a source that I can use that will tell me what the expected cloud cover will be?

The national weather service in the USA is terrible for this even for basics. Today for instance was going to be cloudy when it actually turned out to be sunniest day we had in a long time and was able to fully charge my battery. Even when it is "cloudy" there are obviously different levels of cloudiness that may allow a significant percent of charge. Surely the big PV farms have this type of info, where are they getting it from?

 

[jonas]

Did you try https://vlab.noaa.gov/web/mdl/ndfd

 

[sunshine_eggo]

Is there a source that I can use that will tell me what the expected cloud cover will be?

The national weather service in the USA is terrible for this even for basics. Today for instance was going to be cloudy when it actually turned out to be sunniest day we had in a long time and was able to fully charge my battery. Even when it is "cloudy" there are obviously different levels of cloudiness that may allow a significant percent of charge. Surely the big PV farms have this type of info, where are they getting it from?

I'm from OK. Grew up hearing: "If you don't like OK weather, wait a minute... it'll change." To this day OK residents laugh at the idea of a 10 day forecast.

Pretty sure NWS is about as good as it gets. I use weather underground, and for our spot in northern AZ, it's accurate enough. It said snow today, and it snowed. It says partly cloudy tomorrow, and no snow. It will probably be right. It draws from both NWS forecasts and my personal weather station on site.

Did you try https://vlab.noaa.gov/web/mdl/ndfd

Per that page, it draws from NWS field offices. It's all under the NOAA. Click on the maps, and it takes you to NWS.

Do you have more insight into usage?

 

[green mountain boys]

Doesn't the PVWatts calculator factor in cloud cover based on the location and historical averages for that location?

https://pvwatts.nrel.gov/

The could cover next year should be fairly comparable to the historical average for the last 20 years, right?

 

[jonas]

I'm from OK. Grew up hearing: "If you don't like OK weather, wait a minute... it'll change." To this day OK residents laugh at the idea of a 10 day forecast.

Pretty sure NWS is about as good as it gets. I use weather underground, and for our spot in northern AZ, it's accurate enough. It said snow today, and it snowed. It says partly cloudy tomorrow, and no snow. It will probably be right. It draws from both NWS forecasts and my personal weather station on site.



Per that page, it draws from NWS field offices. It's all under the NOAA. Click on the maps, and it takes you to NWS.

Do you have more insight into usage?

I don’t but there seems to be a rest api to access the data but not sure how to use it.

 

[MisterSandals]

Astronomers plan observing conditions with : https://www.cleardarksky.com/csk/

I think there is a way to get data thru an API.

 

[sunshine_eggo]

Doesn't the PVWatts calculator factor in cloud cover based on the location and historical averages for that location?

https://pvwatts.nrel.gov/

The could cover next year should be fairly comparable to the historical average for the last 20 years, right?

PVWatts looks at the last 30 years of weather on each day, calculates the average day over those 30 years and then it PICKS the day that most closely matches the average, and that's your performance for that day. It doesn't know anything about the weather, all it knows is the irradiance, W/m^2 on an hourly basis. It does this for all 365 days of the year - the most average day of the last 30 years is picked for that day.

It is completely useless for predicting weather's effect on PV on any given day. It is reasonably reliable for predicting weather's effect on PV for individual months and more so for the whole year.

 

[sunshine_eggo]

Astronomers plan observing conditions with : https://www.cleardarksky.com/csk/

I think there is a way to get data thru an API.

I hate to be that guy... but we're concerned about clouds during daytime... not night.

 

[MisterSandals]

I hate to be that guy...

The hours 0 thru 23 pretty much cover day and night.

 

[green mountain boys]

I think we are trying to say about the same thing... you probably said it better than I. There is no need to predict cloud cover on a given day but the average irradiance over a period of time like a month or a year is what is important and it is also the best we can do.

@sunshine_eggo

 

[rhino]

I think we are trying to say about the same thing... you probably said it better than I. There is no need to predict cloud cover on a given day but the average irradiance over a period of time like a month or a year is what is important and it is also the best we can do.

I am actually wanting cloud cover for given day.. like tomorrow since that may decide whether or not I can use more power the night before.

 

[green mountain boys]

I am actually wanting cloud cover for given day.. like tomorrow since that may decide whether or not I can use more power the night before.

I misunderstood, I thought you were trying to plan/size an array. You are trying to predict the weather tomorrow? Good luck!

 

[MisterSandals]

You are trying to predict the weather tomorrow? Good luck!

I'd bet it will be pretty cloudy in this part of Minnesota tomorrow.

 

[BentleyJ]

Austin, TX Hourly Weather Forecast | Weather Underground

Austin Weather Forecasts. Weather Underground provides local & long-range weather forecasts, weatherreports, maps & tropical weather conditions for the Austin area.

www.wunderground.com

Here is a link to weather underground for Austin, TX tomorrow. It gives hourly cloud cover percentages. I my experience its not 100% accurate, but pretty good. Over the last weekend it predicted within 30 min when the afternoon rain would end so we could plan when to take the dogs out for a walk in the park.

 

[rhino]

Astronomers plan observing conditions with : https://www.cleardarksky.com/csk/

I think there is a way to get data thru an API.

This actually looks somewhat useful... I'll see how well it does.

Here is a link to weather underground for Austin, TX tomorrow.

I checked the "history" for my location and did not indicate it was sunny today

I just assumed these PV plants would have fairly accurate predication for the next day to know what to expect for output and didn't know if anyone knew much about what they are using..

 

[sunshine_eggo]

This is what WU gives me for my location:




Looks like about 50% cloud cover average.

It's supposed to be more accurate due to crowdsourced data from personal weather stations.

This is what it looked like today:



WU said snow and 100% clouds.

 

[rhino]

Okay.. I'll see how accurate mine is.. hopefully it is not correct with it showing it being cloudy forever

 

[teal95]

Weatherbug forecast has said the next day would be sunny every morning this week. Every day by the evening the next day forecast was cloudy or snow. We did get about 30 minutes of sun very late this afternoon...

 

[sunshine_eggo]

View attachment 186979View attachment 186981

I'd bet it will be pretty cloudy in this part of Minnesota tomorrow.

You know, I completely spaced on this... I have used that site before for light pollution, and I didn't know it had cloud cover data. We're in the circle, and the observatory is at the arrow:



This is about 9 miles from me:



It shows much more favorable conditions than WU... I hope it's right!

 

[TommySr]

MisterSandals said:
Astronomers plan observing conditions with : https://www.cleardarksky.com/csk/

I think there is a way to get data thru an API.

MisterSandals, Sweet resource, even seems gives the sun's azimuth.

Tommy
SE Wisconsin
(very new to solar)