NTUA has developed a set-up for lab testing of off-grid system controllers using a combination of Controller-HIL and Power-HIL testing. The setup allows for exhaustive testing of the actual controller in realistic conditions, before field deployment. For example the operation and control of battery-less hybrid systems for off-grid power supply. The load demand of the system was covered by a diesel-driven generator and photovoltaic arrays. Hardware controllable loads are activated by a hardware controller in order to respect the minimum load ratio of the diesel-driven generator at times of high PV production. Similarly, instead of controllable loads a hardware PV inverter curtails its active power production to deal with the same problem. The HIL simulation results show that both methods are effective to reduce the frequency deviation of the system and maintain the power output of the diesel-driven generator above the predefined minimum requirement. The tests were performed with a combination of Controller HIL and Power HIL simulation leading to more realistic testing than Controller HIL simulation or pure digital simulation. This type of testing can be the final stage of lab testing, before field deployment of the controller.