Grid Connection

For general information on grid-connection of renewable energy power generating systems, refer to Grid Connection section of this website.

The Technical Guidelines on Grid Connection of Small-scale Renewable Energy Power Systems of EMSD provides useful guidance on the technical considerations relevant to grid-connected PV systems. For such systems, the inverter can be considered to be the critical component for safe and reliable operation of the system and the Technical Guidelines also addresses the technical considerations relating to the inverter.

There are also many standards and guidelines covering the safety aspects, commissioning, inspection and measurement aspects of grid-connected PV systems. Some relevant standards and guidelines are given in the Solar Photovoltaic - Standards section of this website.

Inverter designed for grid-connection applications are called grid-connected inverters, grid-tie inverters, grid-interactive inverters, or utility-interacitve inverters. One important feature of grid-connected inverter is the anti-islanding function.

Grid-connected inverters manufactured in different countries usual comply with the respective national standards. For example in the US, grid-tie inverters usually comply with UL 1741 and IEEE 929.

Small grid-connected PV systems are usually built as single-phase systems. With larger systems, sometimes the PV system is arranged into three arrays, with one single-phase inverter for each array, feeding into each of the three phases. For even larger systems, three-phase inverters are used.

Modern grid-connected PV inverters for PV systems perform the following functions:

  • convert DC into AC
  • adjust the operating point of the inverter to the maximum power point (MPP) of the PV array (the maximum power point tracking function, MPPT)
  • record operational data
  • provide different protective functions and anti-islanding protection function
  • provide isolation function with an isolating transformer at the AC output

Losses occur in an inverter mainly in the semiconductor switching devices and the magnetic devices. Efficiency of 90% or above is usually achievable. A high efficiency inverter will of course help achieve maximum overall system efficiency.

It should be noted that at low loads (at less than 15% rated power), the efficiency drops significant and in some designs the inverters are switched off during low irradiance periods (from evening to early morning).

   
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