The solar inverter has a RS232 port that needs to be connected to the Raspberry Pi. There are basically two possibilities:
- use a USB-RS232 cable, the simplest solution.
- use the Raspberry Pi UART and a Converter from 3.3V UART to RS232. Those converters can be purchased at very low cost, as low as 1 EUR per piece. They measure 9.4 x 15.9mm, rumor says they are so small they can be accommodated in a DSUB9 Plug. I haven’t tried it though.
There are many tutorials on the internet regarding the hardware connections between a RS232 device and the raspberry pi. One good example is elinux.org (the embedded Linux pages) which links to this tutorial. It demonstrates the hardware setup using a breadboard – I prefer the solid solution however and purchased some of the pre-mounted adapter boards shown here, which require some basic soldering skills of course. First thing I did when the boards arrived was to build a UART to RS232 cable so I could connect my PC directly with the Raspberry Pi by means of a normal USB-to-serial cable.