The islanded network

What is the islanded network ?

In all industrialized countries where the electricity grid (EDF, Jirama, ...) is available for almost all homes, the network injection system is used for the installation of solar panels. This is called the islanded network. This is a technique that is used to connect the solar system to the network to use his power or, in many countries, to inject energy to the network in order to sell.

This technique was derived for the electrification of big isolated of the grid sites. The principle is simple : direct injection inverters convert the solar panels current into alternating current 220V (the same as the network). This energy is then sent to a network management system that is itself connected to the batteries and possibly a generator. The Network Manager is the heart of the system, it is used to recreate a distribution network for the site form an energy source to another without interrupotions (solar, batteries, group). This method can significantly reduce the various losses from 70% to 98% return during the day.

Operation of the plant :

During the day, as there is sun, the installation uses only solar energy. The group may be started when using high power equipment. It is often wise to scale the installation to use the group at peak times, it reduces the cost of installation.

The surplus produced by the solar panels is used to charge batteries. When the sun goes down, the batteries take over.

Here is a complete cycle. It starts every days.

With this system, the battery bank may be lower capacity than in a single-grid system (with controller), the price of the battery bank is a lower cost but often offset by the cost of the rest of the material installed. The main disadvantage of this type of installation is the fact that a labor skilled for the installation and the maintenance is needed.

Diagram of a plant

Islanded network with a three-phase generator as backup for powering a business.

We recently completed a project of this type. He helped electrify a school in Ste Marie.

This project was conducted in collaboration with AMADE Monaco association which invested to help the new school access to electricity.

The installation comprises :

  • 20 kWp of solar panels on two roofs
  • 8 injection system inverters Sunny Boy (Brand SMA) 2500VA each
  • 3 managers Sunny Island (Brand SMA) 5000 VA each
  • 48 batteries 2V - 1700 Ah (Brand Exide) what makes a bench 48V - 3400Ah

Here are some pictures of the installation :

10 kWp solar field, there are two indentical roofs

Implementation of solar panels

Wiring injection network Inverters SMA Sunny Boy 2500

Managers SMA Sunny Island 5048, they manage the system

Exide battery bank of 3500Ah 24V

Solar panels' junction box with surge protection DC

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