Connecting Decentralized Renewable Energy Sources

Author: Oliver Janke, OMICRON electronics, Germany

Legal Regulations

According to the Electricity Feeding Act the network operators in Germany were bound to connect renewable energy sources to their grid since 1st January, 1991. This law also stipulates minimum remunerations for the injected energy. It was replaced by the Renewable Energies Act in 2000 which was last revised in 2009.
The current version determines the rates for injected electrical energy into the grid in dependency on several factors such as the type of energy source, the date of connection to the grid, or the nominal power. These rates are guaranteed for a specified period. Therefore, the guaranteed rates for plants connected in earlier years are higher than for those connected later. This takes into account the higher investment cost for the new technologies and supports further research and development (for example in regards to efficiency, reliability etc.). It also specifies a system service bonus of 0.5 cent/kWh for wind energy power plants that are put into service before the 1st of January 2014, and are meeting a number of requirements mentioned in the Ordinance on System Services by Wind Energy Plants.
According to this regulation, Directional Reactive Power Undervoltage Protection (Q->& U<) must be installed.
As a guide for developers of such protection devices the FFN (committee for grid technologies and operations within the VDE, Federation of Electro Technology Electronics Information Technology) developed detailed requirement specifications.
The Q->& U< protection's setting  values can be derived from the Technical Guideline for Generating Plants of the Medium-Voltage Power Grid.
This document specifies the requirements according to safety and reliability for connecting electrical energy sources to the medium voltage network.  One requirement is the dynamic grid support during voltage dips within the high voltage network. The electrical energy source must be able to:

  • Stay connected to the grid during network faults
  • Support the system voltage by injecting a reactive current during the fault
  • Receive the same amount of reactive energy or less from the network after the fault was cleared

This must be proven to the network operator with a certificate for each single unit and another certificate for the whole plant.
In summary, the legal regulations state that renewable energy sources connected to the medium voltage network must support the system voltage during network faults (verified by certificate) and should they not do so, for any reason, must be disconnected from the grid by a Q-->& U< protection.

BeijingSifang June 2016