Microgrid

The island grid is a form of power distribution, which often consists of only one or a few power plants, supplies a defined area and has no connection to public (or other) power grids.

The counterpart to the island grid is the grid, for which the public power grid is the most famous example. The transition from off-grid to the grid is blurred, because larger islands in a real grid structure can be constructed. Technically, the definition of an island network that, in an island grid the secondary control is only designed for the stabilization of the grid frequency. In interconnected networks, the secondary control additionally assumes the task of transferring power to so-called interconnectors, which are interconnections between individual network segments to hold in certain areas.

Types of isolated networks

In an off-grid, it can be a real island or to independent power networks on the mainland. In West Berlin, there were, for example, a separate network at the time the division of Germany. Large national island networks exist today mainly in developing countries and countries that want to enter into any alliance with neighboring countries or physical reasons can not enter. For example, the power grid in Fairbanks, Alaska, operated as a stand-alone grid with no direct connection to adjacent North American interconnections within the North American Electric Reliability Corporation. This is due to the large spatial distances and sparsely populated region, resulting in a combined operation with neighboring North American electricity networks does not allow economically.

Small or very small island networks ( off grid ) are found in areas that are poorly accessible by the general supply grid. So island networks are for example often found on mountain huts, and at most not located near the coast islands. Especially in hard to reach areas, such as in high mountains and in polar regions, renewable energies play an important role in island grids. The reason is to avoid the costly transport of fuel, as would be the case with fossil-fueled power generation plants.

Even the electrical system of vehicles or aircraft constitutes a separate network

Some traction power networks show certain similarities with isolated networks, although coupling exists for public grid via Bahnstromumformerwerke. Also special traction power networks such as the Mariazell Railway is coupled via the power plant Erlaufboden with converters to the grid and therefore not fully be understood as stand-alone grid.

A special feature as stand-alone grid, the Electric Power Supply on ships dar. This board power is fed into the rule of auxiliary diesel generators, wave generators, or more rarely of turbo generators.

Supply and operation of isolated networks

The disadvantages of island networks lie in the reduced reliability, increased frequency and voltage fluctuation and the high cost of the holding of power reserves. The cost of electricity reserves arise, for example, if have multiple redundant turbines operating at part load running with an unfavorable efficiency in large power plants.

Frequently small island networks and stand-alone systems are operated with diesel generators, but can be operated for example it with photovoltaic systems, wind turbines, small hydroelectric power plants, fuel cells or combinations. In some isolated networks are also memory such as battery storage power plants or flywheel storage device integrated with.

Stand-alone grid with high voltage direct current transmission

There are also isolated networks that are associated with a larger power supply by means of high -voltage direct current (HVDC ) in conjunction. This is consistently to power grids on islands, such as on Gotland. If such a connection is restored, this often represents the only technical option for coupling with another power supply represents a such a connection increases the security of supply and may allow the export of electrical energy. However, a pure power from the HVDC is only possible with a self-commutated HVDC converters.