You are right that unfortunately the smaller VS pump you got will not integrate into an automation controller.
Solar heating is best at higher flow rates. Although with only 4 panels they only need about 20ppm. You could run it as a single speed only when you have a need for solar. And run in VS mode in the winter.
Solar heating is best at higher flow rates. Although with only 4 panels they only need about 20ppm. You could run it as a single speed only when you have a need for solar. And run in VS mode in the winter.