This paper presents the mathematical deduction of models for LCL filters with and without the damping resistor, the criteria for designing LCL filter, a systematic procedure for designing LCL filter and experimental tests with an isolated load. Experimental tests demonstrate the relevance of propose procedure for the design of LCL filter. Usually, power inverter is the interface between renewable energy sources such as wind, solar and hydrogen fuel cells, and utility grid. However, high frequency PWM modulation generated in power inverter causes harmonic injection to the utility grid and reduces quality of the injected energy. LCL filter can reduce harmonic injection to the utility grid. Inappropriate design of LCL filter can cause excessive voltage attenuation at the output of the power inverter, resonances and oscillations that can increase total harmonic distortion, instability in power system and slow dynamic response.