It's an RS485 serial output according to this doc:
http://www.oynot.com/files/fronius_ig_system-install.pdf which also includes the wiring pinout. You need the RS485 'datcom' converter card in the IG30 for isolation (It may be possible to make it work without this but that's probably a lot harder). Each device has an ID you set with a switch.
What is not described is the protocol details of the messages it outputs, and indeed whether it does anything at all without being interrogated by the datalogger you are supposed to use. The protocol can probably be worked out but if you need to send interrogatory commands then finding out what they are without a working system to analyse is going to be very hard. The serial data is in fronius' proprietary 'localnet' format. Five mins on the net didn't find any info on that. Clearly an opportunity there...
Aha! looks like there is a simpler version, the 'Interface card easy':
http://www.fronius.com/cps/rde/xchg/SID-8738AFE6-0DEB949F/fronius_usa/hs.xsl/2714_1456.htm which outputs RS232 serial data in an open protocol, and this is the recommended kit for a simple one-inverter system. The protocol is documented in here:
http://www.fronius.com/cps/rde/xbcr/SID-0A5B333B-9C311726/fronius_usa/4204101343_BA_0108_fronius_ig_interface_card_easy_de_en_fr_it.pdfIt looks nice and simple and several people here could knock up some software to talk to it if some doesn't already exist. There should be a place for this sort of info (how to talk to a TDC3, how to talk to an IG30, etc). But I'm not quite sure where that place is. Perhaps home-automation codebases...
