I wish to connect multiple arduino units attached to 50 or solar arrays. What would be the best approach to communicate between these units without wireless or ethernet.
i wish to attach all the units to a central connection where data will be collected then sent out via internet.
Yes, RS-485 would have been my suggestion. Plenty fast, units can be added and removed, relatively insensitive to ground loops. Topology allows daisy-chaining..
There are some established Arduino network things as I recall.. I'll look..
If you are having 50 'transmitters', or 'slaves', you might want to consider making some cards up - minimal design: atmega, crystal, 2 22 pf caps, 2 0.1uF (100nF) caps, RS485 transceiver, connector for your cable.
Or plop a promini onto a perfboard with the driver and connector. Whole thing in a little weather tight box.
Where is power from? Tapped off the array somehow?
The power will be coming from a supply to the trackers to run the motors and such for tracking, just going to have to regulate some voltages thats all.
Sure, use NewSoftSerial for 2nd serial port. You could make up a multiplexer board also, set of analog switches to switch the RS485 around to the different boards.
Or wire it up like a network, see Figure 9 here: