Solar system solution to electricity crisis

Today's photovoltaic modules are extremely safe and reliable products, with minimal failure rates and projected service life-times of 20 to 30 years. With the PV modules, the solar systems and electricity generating solutions are developed. These solutions can be different in category. 1. Stand-alone PV systems: (a) Simple single module DC system (PV Home system); (b) Large DC PV system; and (c) PV system for DC and AC power. 2. Hybrid PV systems: (a) Hybrid-PV diesel: (i) Hybrid PV-Diesel system for DC and AC power; (ii) Hybrid PV-Diesel system for DC and AC with generator for rectified DC; (b) Hybrid PV-Thermal systems; and (c) Hybrid PV-Wind systems 3. Grid-connected PV power systems; (a) Self-commutated and (b) Line commutated. Simple single module DC PV systems (PV Home systems) are used for low cost rural electrification. Usually a single module is connected to the load for sunny day use. Simple single module DC PV system (PV Home system) is connected to a single low cost battery through a simple charge controller as the regulator that is connected to a CFL. The regulator may have a relay that could turn off the light if the battery voltage became too low. The user would have to wait until the module charged the battery back to an acceptable intermediate voltage before they could turn on the light again. Large DC PV power system consists of a large number of modules and large number of batteries to drive heavy DC loads. A large heavy duty controller, having high current driving capability, is required. Usually loads are connected through the charge controller via DC circuit breaker distribution box. PV system for DC and AC power consists of large number of modules. Charge controller regulates the charging and discharging of the battery and the DC loads are supplied power through controller. Inverter generates AC power for the AC loads such as computers, fax machine, radio, TV, VCR and CD players. Hybrid PV-Diesel system: (i) Hybrid PV-Diesel system for DC and AC power: Instead of relying purely on PV system for power, a system can be designed with other generators available as well. A common choice is a diesel generator. This generator produces AC power for AC loads which can be passed directly on to AC loads through transfer switches. Generator power can also be used after (converting AC to DC) rectification to charge batteries or to supply required DC input to the inverter. (ii) Hybrid PV-Diesel system for DC and AC with generator for rectified DC: A hybrid system can be designed to have the generator act only as a battery charger. AC power is not used to run the AC loads. All AC loads are driven by the power, generated by the inverter only. The generator is turned on when the battery voltage is very low or weather is bad. After rectification generator output is used to charge the battery. The generator needs to operate only for few hours to recharge batteries. Generator is operated at its full rated output for maximum output and long life. When batteries are sufficiently recharged, the generator is turned off, and the finishing charge is supplied by the solar modules. If the bad weather continues, the generator is turned on again for a few days, and repeats the charging process. In this way the battery is kept fully charged having longer useful life. (iii) Hybrid PV-Thermal systems: Hybrid PV-thermal systems, sometimes known as hybrid PVT systems or PVT, are systems that convert solar radiation into electrical and thermal energy. These systems combine a photovoltaic cell, which converts electromagnetic radiation (photons) into electricity, with a solar thermal collector, which captures the remaining energy and removes waste heat from the PV module. Photovoltaic (PV) cells suffer from a drop in efficiency with the rise in temperature due to increased resistance. Such systems can be utilised to carry heat away from the PV cells thereby cooling the cells and thus improving their efficiency by lowering resistance. 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. 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 favourable 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: Decentralised Grid-connected PV systems and Centralised Grid-connected PV systems Single phase less than or equal to 25kW Three phase less than or equal to 300kW Decentralised Grid-connected PV systems Decentralised 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 per cent 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. Central 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. The main equipments in a solar home and commercial system connection set-ups are: i) PV solar panelsmodule; ii) Battery for storing the electricity; iii) Charge controller for the battery indicator; iv) Inverter for converting the DC current to AC out put usage equipment; and v) Accessories as cable, switch board, switch, clip, array junction box for large system, main junction box, and steel frame structure to set-up the PV panels and some more as required to design and looking the solution in descent shape. The writer is Manager, Bangladesh of Xenergeia International Ltd. He can be reached at e-mail: sahriarahamed@yahoo.com