The work on a simple high efficient solar pump equipped with a piston pump with a matching valve, reported at the Solar World Congress in Budapest, has been continued. Quasi-static and dynamic models of the solar pump have been derived with which the operation of the system is simulated. A test rig has been built at ECN in Petten (The Netherlands) to perform some preliminary measurements. These tests show that the piston with a matching valve indeed ensures a good matching of the system components over a wide range of solar insolations. Daily average solar panel maximum power point tracking efficiencies of over 80% were measured. Daily average subsystem efficiencies (solar panel power output to hydraulic power output) measured were about 40%, which is lower than expected. These low efficiencies were caused by substantial power losses in the motor, transmission and pump. The losses can easily be reduced by appropriate design of each component; subsystem efficiencies of 50% should be attainable.