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Automating self-powered reserve %

I've automated several aspects of my PV/PW setup with the one remaining being to automatically set the PW reserve % based on expected solar production. For background, I'm typically running in self-powered mode with storm watch off and have no TOU; I'm separately metered for incoming vs outgoing from/to the grid with incoming costing more that what I am paid. Currently, I'll look at the weather.gov sky cover forecast for the next couple of days and determine where to set the self-powered % to ensure if the grid goes out there's enough power in the PW to carry over until the next solar producing day. Curious whether anyone has automated this and what data sources or algorithms are in use?
Tough to do, unless you have an accurate sun forecast for the next 3-5 days...

Below is a sky cover forecast example. It's for 2 days at a time and includes 2 more steps (i.e., 6 days total). Haven't dug into it too much but am guessing it's available in machine-readable format from the weather.gov API. Just trying to avoid figuring it all out if someone else has already automated things.

I have not used it, but your question got me googling, and I found this: Rooftop solar forecasting API

Once completed, this will trigger the creation of a new ‘site’ in our API system, which you can use to instantly retrieve both live (real-time back through 7 days) and forecast (present time to 7 days ahead) power output estimates at 30 minute time resolution.

And, it is supposedly "Free for your verified home residence."

Seems like this might solve the problem without having to do your own modeling work, and they may have access to more/better data.


Grid Specialist
Supporting Member
Mar 4, 2018
Arcadia, CA
Thanks @wjgjr, will check it out. Still hoping someone may have an end-to-end PW solution using the local API.
I'm using api.weather.gov for the sky cover. I have a program to hit it every 8 hours and get up to 6 days data. I process the data and use it to generate coverage levels.

Attached are some files that may help you. The sky.bat runs the API call from a command prompt and put the result in sky.txt. The sky.c program then parses the data and creates two more files, sky.log and sky.dat. The sky.log file show the interpretation of the sky.txt data, and does a conversion on the data (inversion so 100% is no sky cover, 0% is full cover) as I prefer the data that way. So note the values are opposite of the API at this point. The sky.dat file is the final result, with a rolling month of values by hour. Since I haven't run this on my laptop recently, the sky.dat file has mixed data from last October and this March. The real file on my system is current though.

I don't make a direct correlation between sky cover and reserve %, but I do use it to monitor for upcoming days when the solar production will be low and adjust accordingly.

Note the API call in sky.bat needs to be changed for your location. You can get the gridpoints for your area from the API with another call.


  • sky.zip
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