Ok, after digging some more, I found that there is Sol, Eco-Sol, and Eco-Sol MAX. (We have only ever used MAX)
I found these tidbits of info:
SOL INK (CMYK+LcLm) has a unique, low-volatile chemistry that allows signmakers to print durable graphics without having to purchase special ventilation or environmental equipment. Odor and drying time are minimal. Signmakers can produce signs, banners and exhibits that last up to three years outdoors.* SOL INK is water and UV resistant.
ECO-SOL MAX has been formulated to enhance the performance of all Roland eco-solvent inkjets including popular VersaCAMM and SOLJET models. ECO-SOL MAX replaces Roland Eco-SOL Ink in these powerful inkjet printers and integrated printer/cutters.
I found a supplier closing out the SOL ink line. Just wondered if it was worth messing with at $20 a cartridge.