Calculation mode for shading factor

[laurens]

Hello,

I got a generell question about the calculation mode for the shading factor. Is there a specific recommendation as to when to use the fast and when to use the slow mode? 
The description only states that the slow mode can be used “for not too big systems”. Is this simply a time-related recommendation or is there also a system size for which the fast mode can/should be used?   

[dtarin]

Slow can be used on any size system, but simulations will extend to multiple hours for large, complex sites. The main difference that I see between slow and fast (modeling projects in US) is that fast will have higher near shading and lower electrical loss, and for slow, it is the opposite. Not always, but I would say more often than not. In total, shading losses are typically comparable for most sites with fast being slightly higher. Sometimes difference is negligible, but depends on the site; less complex and utility scale will have closer figures. More complex sites with topography, smaller sites with severe shading, will benefit more from slow simulation and the increased accuracy with calculating electrical loss. 

As for when to use, it depends on your position, project, etc. For utility scale in development stages, fast makes sense, and then moving to slow (or at least benchmarking slow) later on when design is closer to final, prior to financing, construction, etc. If the project is small and simulation time is short, I dont see a reason not to run slow for single, one-off estimates. But if you're doing batch runs, running multiple designs, evaluating different components or weather files, in early stage and need indicative numbers, etc., fast is fine. 

What's more important is understanding the differences and impacts to simulation results (irradiance, shading, production, etc.), and deciding when to prioritize simulation speed over accuracy and vice versa (and knowing if there even exists material differences). 

Edited 34 minutes ago by dtarin