Inverter Features in High-densitiy Applications: How new Inverter Designs can Help to Stabilize Electrical Grids

In the past inverters for grid-connected PV systems were considered insignificant as far as their impact on the electric grid was concerned. As a consequence standards usually required that inverters inject only active power and disconnect immediately if any signs of grid instability (voltage, frequency fluctuations) occur. No communication capabilities were needed.

In a few European countries the PV density has reached a level which led to a change of mind: it was realized that the simultaneous shutdown of inverters with gigawatts of power would catastrophically destabilize an already shaky grid. In countries like Germany new standards were adopted which ask for completely new inverter features: providing both active and reactive power (depending on actual grid conditions), supporting the grid over a wide voltage and frequency window (in contrast to shutting down as quickly as possible), being able to respond to remote control commands (regulating power output, reactive power output), actively help to keep low-voltage grids within legal boundaries etc. As a next step it can be seen that soon communication means with Smart Grid components like electricity meters will be required. First inverter designs appear which allow local electricity storage to match PV production to local electricity demand, providing valuable benefits for grid operators.

The consequences of these new rules for the US inverter industry will be discussed; microinverters may be affected heavily as it will be very complex and costly to implement the requirements into each and every inverter.