Transformerless Inverter
An inverter that converts DC to AC without a galvanic isolation transformer between the array and the grid. Removing the transformer raises efficiency and cuts weight and size, and it is the dominant design in modern residential equipment.
The transformer used to provide galvanic separation between the DC and AC sides; without it, the array floats with respect to earth and capacitive leakage currents can flow through the module frames. Transformerless designs therefore depend on continuous residual current monitoring and insulation resistance testing at start-up, both built into the inverter. Two practical consequences: the array must not be functionally earthed on one pole unless the manufacturer explicitly allows it, and damp or poorly sealed connectors show up as insulation faults that stop the inverter starting on humid mornings.