Tuesday, July 1, 2008

A photovoltaic hybrid system is better

by Charles Roring
Solar energy is another renewable energy resources which can be converted directly into electricity. In fact, all the renewable energy whether it is hydropower or biofuel come from solar energy. Traditionally, villagers have used solar energy for drying grain, clothes, and fish. Tropical countries enjoy full sun light all year long. For example, farmers make concrete floor at the front yard to dry rice paddy (as shown in the picture). By doing so, farmers can save cost and get higher profit. There are drying machines available on the market but the price of such machines are very expensive. In addition, their capacity is very limited and they still need fuel to run. Sun rays heat sea water and evaporates it into steam and then into clouds. When it is cooled, it will pur down in hills and mountains. Water flows down into waterfalls, rivers and back to the sea again. When it flows down through waterfalls its potential energy is collected, channelled to penstock that goes to powerhouse, there the water jet is converted into mechanical energy by water turbine that is coupled with electrical generator.
To produce grains, plants such as corn, soya beans need sunlight to carry out the photosynthesis. Grains contain oil which will be extracted by bio-fuel pressing machine.
The direct conversion of solar energy into electricity can be done by using photovoltaic panel or module. A photovoltaic (PV) panel consists of a number of solar cells. PV cells convert sunlight directly into electricity without polluting the surrounding environment. PV cell is a semiconductor device. Another semiconductor device which is similar to PV cell is diode. Their characteristics are similar. Diode is an electrical load whereas PV cell is a source of electricity. PV cells are made of at least two layers of semi-conductor material. One layer has a positive charge, and the other negative. When sun rays enter or hit the surface of the cells, some of the photons from the rays are absorbed by atoms in the junction of the layers. This will energized the electrons and freeing them from their negative layer to flow through an external circuit and back into positive layer.
To increase the amount of electricity, dozens of individual photovoltaic cells are grouped and interconnected in a sealed, weatherproof panel or module. If we want to double the voltage, we have to wire two panels in series. The current remains constant. The current will be doubled if we connect them in parallel. These kind of connections make photovoltaic system becomes flexible.
A PV designer can achieve a desired power, voltage and current by combining PV modules in serial and parallel connections. PV module is suitable to be deployed in remote regions where there are small cluster of homes. It is also powerful to pump water in an agriculture estate or provide electricity of communication device.
Solar panel does not need refuelling. It only needs sunlight. As long as the panel is not broken, it can produce electricity for up to 25 years. Usually, photovoltaic panels are installed on the roof or deck shade of a house.
The electrical energy a PV system produces is stored in batteries. At night, the house can still use electricity from these batteries. To ensure stable supply of electricity, a hybrid system should be considered. Such hybrid system consists of wind turbine, and PV system. Sometimes an emergency generator is added. Most PV designers prefer hybrid system when deploying electricity to remote health care or weather station, or communication centers in remote region. Hybrid system can give uninterruptible supply of electricity to people who use it.