1) Output to the grid is dependant upon consumption, no inverter can tell you that on its own, you would need to install an export meter also
It is dependant upon how it is all wired in you need to monitor both generation and consumption simultaneously, and as such the inverter will need to be wired in with its own CU, otherwise it is almost impossible to measure consumption as most of the meters don;t know which way the current is flowing, (import / export)
Solution - Current Cost we are working with them to develop a system that continuosly monitors generation and consumption, then hooked up to the web you be able to see generation, import and export. tada!
If you only want to monitor generation, then a lot of inverters offer that, SMA and there SunnyBoy inverters have a free PC tool (you'll need Bluetooth if not built in) and a handy desktop display (Sunnybeam), or connect to the web with their webbox. I can't comment about fronius.
Re Roof trusses,
There are simple rules (Building regs)
4 x Screw diameter (both edges + screw) = 9 x screw diameter = 4mm Screw on a 35mm rafter
This is actually very diffcult to achieve, and the only system we know currently available in the UK that complies is the Hilti one, others may know others.
Otherwise they will have to strengthern each rafter by widening it with suitably bolted strengthening pieces.
Most of the nationals are ignorant of this requirement, anyone active on this forum knows about it!.
If they don't, the system doesn't comply with Building Regs and de facto hasn't been installed in compliance with the MCS standards and as such is ineligble for the FiTs