In my experience, there isn’t a customized theoretical calculation.
I started with my best guess, measuring and invariably adding more panels until I reached about 90% of MPPT’s capability at noon.
(This is what I did for my charge controller type of MPPT).
So put up a representative East and West string and measure, only then pull the trigger on the inverter sizing.
I use East strings paralleled with West strings.
I don’t know how many MPPTs your inverters will have at that size.
I adopted a similar but different strategy for my grid-tied inverters. For example, my ABB inverter has a 3.6kW overall power rating, but it has two MPPTs of 2kW capacity.
Because an East array’s power peaks earlier than a West array, I can take advantage of this by loading both MPPTs with 2kW of generation.
This means I can maintain 3.6kW output for longer in the day.
If I were to dedicate an inverter to East or West arrays, I would need a 4kW inverter for the same number of panels.
Something to consider doing in your configuration.
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Your Fimer PVS-100-TL has 6 trackers. The 50kW Tauro has 3 trackers, but interestingly the larger models have just 1. The large 50kW Solis has 4 trackers. The Huawei SUN2000 has 6 trackers as well.
For a 150kW plant, I would think you are probably looking at 3 x 50kW units anyway.
It seems to me, that to get to the full power, you pretty much have to max out every tracker in terms of both voltage and current. Just playing around with the Tauro, for example, it has a max voltage of 1000V, but to be safe on a very cold morning you are probably looking at around 700V per string nominal, times the 22A it can handle per tracker, which puts you at just around 45kW over the three strings.
For ease of installation, a higher voltage is going to mean less cables. Here a 600V MPPT (Huawei) will limit you more. The Solis is rated 1000V but wants to operate closer to 600V, and both the Fimer and the Tauro is rated 1000V.
Just tossing around some ideas. This is why you need the consultant. To work out all these details.
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100% agreed!
I’ll have a list of hardware soon enough. Maybe it is interesting for you experts 
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Oh yes and to add to your comment, I guess the sales pitch calculation would be way off if we are only able to power one of the 50kw heat pumps. Think I’ll definitely raise that question. What can we actually power in the real world and not just using the max PV output. Coz that’s not the real world.
Put it this way: get as many panels as you can fit. This is the part of the set-up that will be paying you back.
Cool, asked them to do another proposal with the entire roof covered in panels.
Also, spoke to the consultant about heat pump and he had the following to say:
That’s good news, seems we could cover all 3 with 107kw system.
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