Germany-based solar power company SMA Solar Technology’s Sunny Central CP XT-Inverters meet the requirements that were stipulated in November by the Grid Connection Code for Renewable Power Plants (RPPs) for photovoltaic (PV) inverters in South Africa.

The regulations have been adopted by the National Energy Regulator of South Africa (Nersa) and stipulate the technical and design requirements that must be met and implemented by all renewable-energy power plants.

Together with SMA’s plant control system, complex requirements and control functions can be implemented, especially for multi- megawatt power plants. Intelligent algo- rithms facilitate a quick reaction to changes in individual grid parameters, such as voltage or frequency, ensuring grid integration of power-plant-scale PV systems.

Global product MD Thorsten Ronge explains that compliance with the grid code applies to the RPPs, depending on their rated power and, where indicated, the nominal voltage at the point of common coupling (POC).

RPPs are grouped into three categories – A, up to 1 MVA connected to the low-voltage grid; B, 1 MVA to 20 MVA connected to the medium-voltage grid; and C, 20 MVA and higher connected to the high-voltage grid.

RPPs must be able to support the network grid frequency and voltage stability in line with the requirements of the grid connection code. Those that are grouped under categories B and C, which are often PV projects for which SMA inverters are used, must be designed to operate within the voltage range of about 10% around the nominal voltage at the POC.

“Furthermore, the RPP must be able to withstand voltage peaks of up to 120% of the nominal grid voltage, measured at the POC, for at least two seconds without dis- connecting,” says Ronge.

The RPP must also be equipped with reactive- power control functions to deal with the reactive power supplied at the POC.

The SMA power plant controller is connected to the POC. It measures and tracks the medium-voltage grid parameters and controls each inverter in the field to either deliver reactive power or curtail the maximum power to stabilise the grid frequency.

Ronge says that the challenge for smaller RPP companies in meeting the grid connection code is that the regulations are complex and entail extensive software knowledge about the inverter and a holistic approach to RPP. Subsequently, the inverter needs to have built-in grid support functions and these need to communicate with a power plant control system that regulates the grid inter- action of the RPP.

Last year, SMA solar technology was awarded the contract to supply 84 Sunny Central 800 CP XT inverters to the 75 MW Kalkbult project, in the North West. This PV power plant will be connected to the utility grid by midyear and will provide electricity for about 35 000 households.