Solar Photovoltaics

Photovoltaics has been derived from the combination of two words, ‘Photo’ means Light and ‘Voltaic’ means electricity. It is a technology that converts light directly into electricity. Photovoltaic material, most commonly utilizing highly-purified silicon, converts sunlight directly into electricity. When sunlight strikes the material, electrons are dislodged, creating an electrical current which can be captured and harnessed. The photovoltaic materials can be several individual Solar cells or a single thin layer, which make up a larger Solar panel. The output of Solar panels will vary according to their conversion efficiency and the amount of sunlight received.

Solar Thermal - Solar thermal electricity technologies produce electric power by converting the sun’s energy into high-temperature heat using various mirror configurations, which is then channeled to an on-site power plant and used to make electricity through traditional heat-conversion technologies. The plant essentially consists of two parts; one that collects Solar energy and converts it to heat, and another that converts the heat energy to electricity.

Crystalline Solar Cell - Solar cells are made of Single Crystal or multi – crystalline silicon material. Silicon ingots made by the process of crystal growth or by casting in specially designed furnaces. Ingots are then sliced into thin wafers. Using high temperature diffusion furnaces, “impurities” like boron and phosphorous are introduced into the silicon wafers to form p-n junction (Positive – Negative junction). Silicon wafers are thus converted into Solar cells. When exposed to Sunlight, a current is generated in each cell.

Thin Film Cell – Thin film Solar Cells are made using a thin film deposition on the substrate instead of using wafers. Various materials can be used to form the thin film such as Amorphous Silicon (a-si), copper indium selenide/ cadmium telluride/cadmium sulphide, etc. These technologies are at various stages of development and have not yet reached the maturity of crystalline silicon. Production of thin-film PV modules is therefore limited. However, at the current pace of developments, thin film will contribute a major portion of the total Solar cells produced in the near future.

String Ribbon Technology - In the String Ribbon process, a set of special parallel strings are pulled continuously through a small molten pool of silicon inside a custom furnace. A thin "ribbon" is created between the two strings as the silicon cools and re-crystallizes. The ribbon is then cut into wafers, which are converted into Solar cells and used in the production of Solar panels - all under one roof.

Solar Water Heater (SWH) - In its simplest form, a SWH consists of an absorber, a storage tank, insulation, piping and a transparent cover. Solar energy heats the absorber surface and a heat-transfer fluid (indirect) or water (direct) flowing through tubes attached to the absorber. If a heat-transfer fluid is used, there is a heat exchanger that then heats the water. The heated water is transferred to the insulated storage tank either with a pump or without a pump through natural convection. A transparent cover (glass or plastic) is placed above the absorber to reduce heat losses due to radiation and also on account of wind flowing over the absorber. The bottom and sides of the absorber are covered with insulation to reduce both types of heat losses. The absorber, cover and insulation are placed within a plastic or metal container.

The Solar Water Heating System with single Solar Flat plate collector is designed for heating minimum 100 litre of water upto minimum 60º C under winter conditions. Worldwide, Solar water heaters annually deliver approximately 600 kWh per kW installed. The most common types of Solar water heaters are glazed flat plate collectors (34%) and evacuated tube collectors (44%) generally used for domestic hot water; and unglazed plastic collectors (21%) used mainly to heat swimming pools. As of 2007, the total installed capacity of Solar hot water systems is approximately 128 GW and growth is 15-20% per year. China is the world leader in the deployment of Solar hot water with 70 GW installed as of 2006 and a long term goal of 210 GW by 2020.

Solar Cookers - A Solar oven or Solar cooker is a device which uses sunlight as its energy source. A solar cooker needs an outdoor spot that is sunny for several hours and protected from strong wind, and where food will be safe. Solar cookers don't work at night or on cloudy days. A basic box cooker consists of an insulated container with a transparent lid. Solar cookers use sunlight for cooking, drying and pasteurization. Solar cooking offsets fuel costs, reduces demand for fuel or firewood, and improves air quality by reducing or removing a source of smoke. The simplest type of Solar cooker is the box cooker first built by Horace de Saussure in 1767.

Solar Lantern - A Solar Lantern is made of three main components - the Solar PV panel, the storage battery and the lamp. The Solar energy is converted to electrical energy by the SPV panel and stored in a sealed maintenance-free battery for later use during the night hours. During the day, the PV module is placed in the sun and is connected through a cable to the lantern unit. A single charge can operate the lamp for about 4-5 hours.

Solar Street Lighting – Solar Street Lighting is outdoor lighting unit used to illuminate a street or open areas in villages. A Compact fluorescent lamp is fixed inside a luminaire which is mounted on a pole. PV module is placed at the top of the pole and a battery is placed at the base of the pole. The system is designed to operate from dusk to dawn. The CFL lights up when surroundings become dark and switches off around sunrise time.

Solar Traffic Systems –Solar Traffic systems use Light Emitting Diodes (LEDs) and work without the interruption during power failures. The design of these systems depends on the number of lights operated at a junction. This system does not require any inverter. The system has programmable logic controllers for setting parameters such as through time, peak time, on/off etc.

Solar Generators – Solar Generator is a small capacity, stand alone SPV power system based on a PV array, connected to a battery bank and inverter of appropriate size. This system is designed to supply power to limited loads for a period of two to three hours daily in situation of power failure or load- shedding.