A Grid Tied Inverter
or a (GTI), allows a direct connection between the DC solar array and your homes AC power grid. This means that PV system can operate without batteries. From there the DC power generated by the solar modules is inverted to higher voltage AC and its either used directly by your AC appliances or its sold back to your utility company which lowers your monthly electric bill. Having a grid tied solar setup also lowers the cost of going 'green', and is more efficient than using a conventional system which uses a battery power bank.
Grid tied inverter work just like a conventional DC-AC inverter. They will take the input DC power, step it up, filter it into a pure sine wave, and feed it back in to the AC grid. The step up is done via high frequency DC-DC converter (PWM controlled inverter), and the filtration is done via inductors and capacitors. The electricity flows back the other way because the output voltage is slightly higher than the AC grid voltage.Effects on the grid power quality
In order for grid tie inverters to comply with utility electrical standards, the output power needs to be clean, undistorted and in phase with the AC grid. Typical modern GTI's have a fixed unity power factor, which means its output voltage and current are perfectly lined up, and its phase angle is within 1 degree of the AC power grid. The inverter has an on board computer which will sense the current AC grid waveform, and output a voltage to correspond with the grid.
There are currently around 22 company around the globe that manufacture grid tied inverters. However the US and European markets are dominated by two brands SMA (Sunny Boy) and Xantrex.
Attached is the data sheet of a 6KW Sunny boy 6000U inverter.