Grid integration of big photovoltaic farms with energy storage support

This report deals with two types of network code requirements that apply to big
photovoltaic installations and cannot be met with the use of inverters but require energy
storage.
The first of these requirements is frequency response. It prescribes how much the active
power output of a photovoltaic installation should change when system frequency
deviates from the nominal frequency in order to support the grid.
The second requirement is the maximum ramping rate which determines by how fast the
active power output of a photovoltaic installation may vary due to changing cloud cover or
other factors.
The report classifies the network codes into three grades of severity. Two methods to size
the required storage capacity for different grades of severity are explained with
corresponding examples.
The report concludes that improved storage sizing methods should be developed as there
is clear potential for significant reductions in required storage capacity.