The PV ecosystem
The frontend of the PV ecosystem are the PV modules that are made up of cells connected to each other in series or parallel. These cells are made up of semiconductor materials (primarily Si) that absorb light energy from the sun and convert them to electrical energy at efficiencies that typically range from 10 – 30 percent, depending on the cell and module complexity. The power extracted from the module is DC power. This needs to be converted to AC power, regardless of whether the PV system is grid tied or off-grid. The reason is that, even though home and business appliances use DC power, large loads and electrical infrastructure are based on AC power to reduce I2R losses.
The method of converting DC to AC power is called inversion. This happens in the back end of the PV chain in a system called the PV inverter. PV inverters generate a sinusoidal AC waveform at a fixed level from a DC source – PV module(s) with varying voltages. The output voltage and frequency need to be at a certain level, for example: 230 V at 50 Hz in Europe. If the inverter is connected to the power grid, voltage and frequency need to be synchronized with the power-line. Single-, two- and three-phase types are available for different applications. In addition to power management controls, the inverter performs other collateral task functions, such as maximum power point tracking, monitoring, protection and communication.
In general, there are three inverter configurations. Each depends on the power levels. A low-power configuration below 350W is called a micro-inverter. A medium power configuration between 1 kW to 20 kW is called a string inverter, and a high-power configuration greater than 20 kW is called a central inverter.
All inverter configurations follow the same methodology for power conversion. However, there are variations in the power conversion topology among the inverter configurations. The reason for this variation is for inverter efficiency maximization.