High-efficiency transformers are always preferable.

Due to high PV array string voltages (up to 1,500 VDC), step-down transformers are required to connect to the grid.

Multi-megawatt PV plants require a transformer to connect to the appropriate grid level.

Transformers should be avoided because they are heavy and bulky

With some thin film PV modules, a transformer between the grid and PV array DC circuits is required.