Alternative and renewable energy by power of WIND

Hybrid PV-Wind systems There are some places where wind speeds are often low in periods when the sun resources are at their best. On the other hand, the wind is often stronger in seasons when there are less sun resources. That can make solar PV-wind hybrid solutions an alternative to consider. Even during the same day, in many regions worldwide or in some periods of the year, there are different and opposite wind and solar resource patterns. And those different patterns can make the hybrid systems the best option for electricity production. Hybrid PV-Wind system is the combination of PV and wind turbine for the generation of electricity. Picture: Hybrid PV-Wind systems Grid-connected PV systems DC power generated by PV is converted into AC and is supplied to the national grid. Energy storage is not necessary in this case. On sunny days, the solar generator provides power, e.g., for the electrical appliances in the house. Excess energy is supplied to the national grid. During the night and overcast days, the house draws its power from the grid. In this way, the electricity grid can be regarded as a large “storage unit”. In the case of a favorable rate-based tariff for PV electricity, as in force in some countries, it is more advantageous to feed all solar electricity into the grid. Grid-connected PV systems can be subdivided into two kinds: Decentralized Grid-connected PV systems: Decentralized Grid-connected PV systems have mostly a small power range and are installed on the roof-top of buildings (roof-top or flat-roof installation) or integrated into building facades. For example, in Germany around 80% of the more than 50,000 existing grid-connected PV systems are installed either on the roof-top of a building or integrated into a building façade. The benefit of the installation of a PV system into or onto a building is that no separate area for the solar generator is needed. Centralized Grid-connected PV systems: Central Grid-connected PV systems have an installed power up to MW range. With such central photovoltaic power stations it is possible to feed directly into the medium or high voltage grid. Mostly central photovoltaic power stations are set on unused land, but in some cases an installation on buildings, mostly on the flat roof of greater buildings, is also possible. Single phase less than or equal to 25kW. Three phase less than or equal to 300kW. Grid-connected PV System can also be classified according to size : Small – Power from 1 to 10 kWp. Typical applications are: rooftops of private houses, school buildings, car parks etc. Medium size – Power from 10 kWp to some hundred of kWp. These kind of systems can be found in what are called building integrated PV (BIPV) systems, in roofs or facades. They may operate at higher voltages than smaller systems. Large size – Power from 500 kWp to MWp range, centralized systems. Picture: Grid-connected PV Systems (a) Decentralized (b) Centralized These systems are normally operated by electric companies. In general a grid-connected PV system consists of the following two main components: 1) PV Module; 2) Inverter The complete system consists of a support structure, cabling, and other conventional components. Besides the modules, the most important part of a system is the inverter. Inverters for Grid-connected PV power systems can be subdivided into the following classes; a) Line-commutated grid-connected inverter; b)Self-commutated grid-connected inverter. Line-commutated grid-connected inverter: In this inverter the AC output generated is dependent on the utility interconnection. The system will not work if the utility interconnection is lacking (e.g. during grid black-out). This system is able to feed the grid only. Self-commutated grid-connected inverter: In self-commutated inverter, the AC output generated is independent of any utility interconnection. Thus this system can operate in the stand-alone mode. Picture: Line-commutated Grid-connected PV power system Written by: Sahriar Ahamed Mirpur1, Dhaka, Bangladesh