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Removing the isolation transformer in grid-connected photovoltaic (PV) inverters is desirable to increase efficiency and reduce the size, weight, and cost of these systems. However, it may also allow leakage current through the stray capacitance between the PV array and ground, causing a safety risk. Both efficiency and leakage current depend upon both inverter topology and modulation strategy. In this work three single-phase inverter topologies, i.e. the H-bridge, HERIC, and H5 inverters, are compared with respect to efficiency and leakage current to determine their suitability as transformerless PV inverter systems. Experimental results are presented for the most promising case, i.e. the HERIC inverter with standard sinusoidal pulse-width modulation.