About theground screw, different countries have different application, Different places have different factors to consider. Existing soil conditions, along with and perhaps more importantly, soil upset conditions from the installation of the foundation screws, and all that resulting uncertainty.

ground screws are used to anchor manufacturer and modular homes here in Florida and must meet some pretty high wind loading due to hurricanes.

Ground screw piles are quite popular for big fields in Mass.Customer used the same rigs under a house to resupport the footings on some marginal soil, worked great.Not so good in Northern NH where the soil is 90%rocks.

Also, for a lot of analyses, often the structure's dead weigh will offset a good portion of a pullout load from a wind/seismic induced overturning moment, usually adding a bit of comfort/safety factor to the analysis as well as that larger mass acting as a bit of a vibration dampener, reducing any occasional load impulse(s) perhaps a bit before it gets to the screw. So unless those ground screws are in clay or are very very deep, concrete makes more sense to anchor a pv system.