El sid pumps are good but the system has to be designed to have low head pressures so depending on how your system is designed (length of piping runs, 90s and height of panels) it might be a good pump. An alternate to the el sid is the Thermo-Dynamics pump which is bigger and more robust.
Thermo Dynamics Ltd. - Solar Pumps
This pump will run off a 20w panel and needs no controller at all. You usually don't get a digital output for DC pumps so monitoring is harder. That may not matter tho....