One location for information on Solar Inverters and the software to interface to them can be found on Whirlpool. This WIKI is designed to be updated as people find out more information on their inverter and the interfaces that it provides.
My particular inverter uses a MODBUS interface with an RS-232 port. Most inverters use either an RS-232 or RS-422/RS-485 interface. With an RS-232 interface, interfacing to most modern compters can be done with an RS-232 to USB adapter, or an RS-232 to Ethernet Adapter. I initially went for the USB solution, before moving to Ethernet.