From the wikipedia article on grid_tie_inverters technology subsection
Grid-tie inverters that are available on the market today use a number of different technologies. The inverters may use the newer high-frequency transformers, conventional low-frequency transformers, or even use no transformer. Instead of converting DC current directly to 120 or 240 volts AC, high-frequency transformers employ a computerized multi-step process that involves converting the power to high-frequency AC and then back to DC and then to the final AC output voltage.[1] Transformerless inverters, which boast lighter weight and higher efficiencies than their counterparts with transformers, are popular in Europe. However, transformerless inverters have been slow to enter the US market. Until 2005, NEC code required all solar electric systems to be negative grounded, an electrical configuration that interferes with the operation of transformerless inverters. The issue at stake currently is that there are concerns about having transformerless electrical systems feed into the public utility grid since the lack of galvanic isolation between the DC and AC circuits could allow the passage of dangerous DC faults to be transmitted to the AC side.[2]
Most solar grid-interactive inverters on the market include a maximum power point tracker that enables the inverter to extract an optimal amount of power from the solar array by tracking the array's maximum power point.
The references were:
1 ^ Solar Energy International (2006). Photovoltaics: Design and Installation Manual, Gabriola Island, BC:New Society Publishers, p. 80.
2 ^ Ton, Dan and Ward Bower (2005). "Summary Report on the DOE High-tech Inverter Workshop", sponsored by the US Department of Energy, prepared by McNeil Technologies.
