diy solar

diy solar

Double check panel math

Is ‘PV Forecast’ related to PVWATTS?
I don’t know. Maybe? It was called PV Forecast or forecaster.
But it ain’t a very good tool.

It’s mostly like an extrapolation of a ten day weather forecast into a watts forecast. You tell it your inverter size and panel watts, location/azimuth and it tells you what your charging output might be.
I made way more than forecast most of the time especially if cloudy. If partly cloudy or partly sunny, it failed out royally with enough inconsistency that it just wasn’t a useful tool. Way more, way less, no predictability.
How I started was when I installed the 120V fridge I expected to struggle so I looked up some apps.
As it turned out the system outdid itself brilliantly until recently as the days got shorter. The app was often 50% incorrect for the five weeks it took for me to get disgusted.
 
Is ‘PV Forecast’ related to PVWATTS?

PVWATTS is a pretty fantastic tool, at least for getting a good sense of seasonal variation in production levels as well as comparing different roof surfaces / mounting options…
No. PV Watts is an annual planning forecaster.
PV Forecast is a predictor based on weather forecast for the day
 
No. PV Watts is an annual planning forecaster.
PV Forecast is a predictor based on weather forecast for the day

To elaborate, PV Watts actually computes performance by the hour.

It uses the last 30 years of weather data for each day. Then it selects the day over those 30 years that most closely matches the average and uses it to calculate the solar performance for that day. It can then break this down into hourly values that one can download and analyze in a spreadsheet.
 
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