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Solar Photovoltaic Systems Introduction
Photovoltaic ( PV ) effect was first described in 1839 by a French physicist Edmond Becquerel. It was further studied by Heinrids Hertz in 1870s. Initially, selenium PV cells were used for converting light to electricity at 1 to 2 % efficiency. PV was first used commercially in 1940s. In the early 1950s, Czochraiski process was developed for producing highly pure crystalline silicon. The first crystalline silicon PV cell was developed in 1954 with 4 % efficiency. The PV devices used now have efficiencies in the range of 13 16 %. How is electricity produced ? When the light rays fall on a solar cell, they penetrate into the solar cell and create a flow of electrons throughout the crystal structure. The crystal structure of silicon contains empty spaces ( hole ) which accept these electrons. As one electron moves to fill a hole, it creates another hole and it is this flow of electrons which produces electricity. Cells, Modules, Arrays There are different types of silicon cells such as: (a) Mono crystalline silicon (b) Poly crystalline silicon (c) Amorphous silicon The most common types of silicon cells are mono crystalline with efficiency of about 12% Since typical silicon solar cells produce only about 0.5 V, many cells are connected together to give higher and useful voltages. Usually 3036 cells are connected together in a circuit to give a final voltage of about 15 to 17 V, which is sufficient to charge a 12 V battery. If the voltage or current from one module is not enough to power the load, then modules can also be connected together, just as the cells. Manufacturers usually build modules with convenient junction boxes that allow inter connection in series or parallel. Module: refers to set of solar cells connected in series and parallel for required power (voltage and current). Array: refers to set of modules connected in series and parallel for higher power output especially in kilowatts. Different methods of use of solar PV (i) Instantaneous: Under this method, electricity is produced whenever there is sunshine and is used instantaneously and no storage is involved in this mode. This mode is useful only when there is sunlight and can not be used at night. Example : Solar water pumping (ii) Store and Use In this method, electricity produced during day time is stored in a battery and used either simultaneously or at night for lighting applications or traffic signals. Example : Solar home lights, street lights, radio, traffic signals etc. (iii) DC to AC conversion Solar module produces DC electricity, which is stored in the battery and converted as AC electricity through an inverter and used for domestic AC appliances such as conventional lights, fans, TV etc. (iv) Hybrid systems SPV power plant in conjunction with a diesel generator set or small aerogenerators could be used as hybrid system to increase the availability of power during day and night. Components of the Solar PV system The SPV systems generally consist of the following components : (i) SPV Modules / Panels SPV module / panel is made of number of solar cells connected together in parallel and series to produce electricity from sun light. (ii) Battery D.C. electricity produced during day time is stored for use at night. Mostly, lead acid batteries are used. Nichel cadmium batteries are also suitable but are expensive. All batteries used for P.V. applications are deep cycle i.e. designed to discharge down to 50 % or more without damage so that they can supply power over a long period of time unlike a car battery which is usually discharged to about 3 - 5 % only. The life time of battery varies depending on factors such as usage, maintenance and proper charging. Normal life is about 5 years. (iii) Balance of System / Power Conditioner It helps maintain the battery at as high a charge as possible and provides the required quantity of electricity, at the same time protecting the battery from deep discharge or over-charge. Power conditioners consist of
(iv) Power/electrical load Luminaires or electrical appliances such as fan, TV, pump etc. form the electrical load in S.P.V. system. Types of Solar PV Systems (i) Solar Lantern Configuration
Potential for use
12,398 lanterns have been supplied in Tamil Nadu with subsidy from MNRE / State Govt. Cost A lantern with SPV panel of 10 Wp costs about Rs.3000 (tentative) each. Subsidy is not available. (withdrawn from 2002 03 ). But soft loans are available through select banks and IREDA (ii) Solar PV Home lights / Office lights Configuration This is a fixed indoor lighting system and consists of solar PV, module, battery and balance of systems. It is supplied under the following configurations as per specifications of MNRE : * 1 light * 2 lights * 1 light & 1 fan * 2 lights & 1 fan * 4 lights. The luminaires used in the above systems comprise compact fluorescent lamp (CFL) of 7 W / 9 W / 11 W capacity which consume less energy but give illumination equivalent to 25 / 40 / 60 W capacity conventional incandescent lamps respectively; The fan is of DC type with less than 20 W rating. One Battery of 12 V, 40 / 75 Ah capacity is also provided with SPV modules of 37 Wp / 74 Wp as required. The system will work for about 4 hours daily, if charged regularly. The capacity and rating of different models are as follows:
Potential for use:
Cost and Subsidy Tentative cost of the systems range from Rs.8,000 for model-1 to Rs.25,000 for model-5. MNRE provides subsidy of 50 % of cost subject to a maximum of Rs.2,500 for model-1 and Rs.4,800 for model-2 to 5.
Eligible beneficiaries : Individuals and non-profit institutions in rural areas Systems installed so far: No. of Solar home lights installed with subsidy : 1296+5190=6486 New initiative: TEDA took a major initiative to provide SPV home lighting systems for the group houses constructed by DRDAs under Indira Awaz Yojana (IAY). 429 nos of model-2 were installed during 2003-04 in 10 districts and 59 nos. in 2006-07. (iii) Solar PV Street Lights Configuration
Advantages
Potential for use
Cost and Subsidy : Tentative cost of solar street lights range from Rs.25,000/- to Rs.35,000/- depending upon period of warranty. MNRE provides subsidy of 50 % of cost subject to a maximum of Rs.9,600/- for non-commercial institutions in rural areas. MNRE subsidy is also available for Municipal corporations only. Details given separately. No. of systems installed in Tamil Nadu No. of SPV street lights installed with subsidy as on 31.03.2008 :6378 (6095+283) New initiatives TEDA carried out awareness campaigns in the districts through DRDA and local bodies are coming forward to install SPV street lights in large numbers. MNRE sanctioned 3387 Nos. of SPV street lights for 2003-04 which have been installed in village panchayats in 28 districts and 6 municipal corporations. During 2006-07, 244 Nos. have been installed in the Districts and corporations. (iv) Solar PV Power plant Configuration SPV power plant consists of SPV modules in arrays (total wattage being 1 kW or more), re-chargeable battery bank, power conditioning unit (inverter & charge controller) etc. When sunlight falls on the SPV module, DC current is produced, which is stored in a battery bank. The inverter converts the DC current from the battery into AC current which, in turn, is used for operating various loads, such as, lights, fans or other electrical appliances in the building, subject to the total load (watts) being restricted to the capacity of the module (Wp). Advantages
Potential for use:
Cost and Subsidy Tentative cost of SPV power plant of 10 kWp capacity is Rs.32.0 lakhs. MNRE provides subsidy at 50 % cost subject to a maximum of Rs.1.25 lakhs / kWp for capacity more than 1 kWp and Rs.1.50 lakhs / kWp for capacity more than 10 kWp for non-commercial institutions in rural areas. Systems in use: Standalone SPV Power Plants have been installed so far in the following places :
(i) MS Swaminathan Research Foundation, - 20 kWp
(ii) TEDA, Chennai - 4 kWp (iii) Residential Houses - 5 x 1 kWp SPV power plant may also be grid connected and power generated could be exported to the grid. PCU senses the grid voltage frequency and modifies the PV array output voltage and frequency so as to synchronize with the grid and feeds the AC power generated from PV array to the grid. Grid interactive solar power plants can also be installed for voltage support in rural areas of the grid, peak shaving in urban centres and diesel saving in islands or remote locations. Cost for grid interactive plant: Tentative cost of a 100 kWp grid interactive SPV power plant is about Rs.3.5crores. The grid connected power plants are installed in the following locations:- (i) Udaya Semi Conductors, Coimbatore - 2 x 25 kWp (ii) NEPC, Coimbatore - 100 kWp (iii) TEDA, Kayathar - 15 kWp (v) Building Integrated Photovoltaic ( BIPV ) Systems Configuration: Under this scheme, SPV panels are integrated with the roof or faηade of building instead of glass. These panels while serving as building materials, also generate electricity during day time, which is used for meeting part of the energy needs of the building at night. It is thus feasible to construct energy efficient and a esthetically appealing buildings using this concept. A typical BIPV system consists of the following:-
Cost & Subsidy: The tentative cost of the system including panels, batteries etc is about Rs 3 Lakhs per kWp. MNRE subsidy details given separately (subject to changes). Subsidy is available upto 80 % of the cost of SPV panels. (Battery cost is not included) New Schemes under MNRE assistance A. Municipal Corporations 1. Solar Street / public garden lights (112 Nos.) Dusk to dawn systesm 74 / 75 wp SPV modules and 11 W / 18 W CFLs - 50 % of the cost or Rs.10,000/- for 11 W CFL / Rs.12,000/- for 18 W CFL which ever is less upto 100 per Municipal Corporations. 2. Street light solar control systems (10 Nos.) Dusk to dawn systems of 5 wp SPV module capacity 25 % cost or Rs.5,000/- which ever is less. Upto 20 systems (100 street lights per system) per Municipal Corporations. 3. Illuminated Hoardings Systems upto 1 Kwp of SPV module capacitu illuminating, a minimum of 2 sq.m. hoarding are atleast for 6 hours. 50% of the cost or Rs.15,000/- per 100 wp hoarding which ever is less. Upto 20 per Municipal Corporations. B. Traffic Police Department
C. For implementation through SNAs
(a) Preparation of DPR CFA @ 50 % of the cost of the DPR, subject to a maximum of Rs.2.00 lakhs will be provided for preparation of CDPR, including detailed building plan and architectural drawings for public / private institutional buildings. A maximum of 10 DPRs will be supported in each state with CFA being released on reimbursement basis. (b) Demonstration of Solar Buildings Support for construction of demonstration solar buildings will be provided upto 10% of the cost of construction subject to a maximum of Rs.50.00 lakhs for each project. The support will be available for the buildings of SNAs and other public / Government buildings will not be covered under the scheme. Two buildings will be supported in each state. (vi) Solar Water Pumps Configuration:
Types of Solar Power pumps: SPV water pumping system uses the SPV array mounted on a stand and includes one of the following motor pump sets compatible with the PV array.
Centrifugal pumps are suitable for areas where water is available at shallow depths such as open wells / stream / ponds / canals etc. They are driven by a DC motor. The total head is 14 m and maximum suction head is 7m. Better performance in the form of higher water output can be achieved when the suction head is kept at the minimum. Submersible pumps are recommended where water table is available at higher depth ( more than 14 m ). It is highly efficient and rugged multistage pump. Pumps can be conveniently placed under water so as to lift water from up to 50 m depth. The normal discharge rates of water for different types of pumps are given below :
Advantages:
Potential for Use: SPV pumps are more suitable for remote areas with no or unreliable grid or as an alternative to diesel pumps. Some of the most popular applications are :
Cost & Subsidy : Tentative cost of solar water pumps range from Rs.2.10 lakhs to Rs.5.10 lakhs depending on type and capacity of pumps. For 2006 - 07, MNRE subsidy was available at the rate of Rs.30 per Watt peak subject to a maximum of Rs.50,000/- per system for community applications such as drinking water are to be given priority over individuals. IREDA will provide loans to eligible users and the inter med arise at the rate of 5% per annum respectively for the remaining price subject to a maximum of 90 % repayable in 10 years (subject to changes). No. of systems installed with subsidy : 285 pumps Limitations:
New and emerging uses of Solar PV systems: (i) Electrification of unelectrified remote habitations Electrification of 128 remote unelectrified habitations in 12 Districts (which could not be electrified through grid supply, as they are located in or near forest areas) has been completed by providing 5190 Nos. Solar PV home lighting systems and 283 nos. solar PV street lighting systems with the entire cost including 5 years maintenance should between MNRE and State Govt. View list of districtwise habitations electrified through Solar lighting systems. (ii) Solar Fencing Solar fencing is useful particularly in remote areas where elephants, or other wild animals from nearby forests destroy agricultural crops. A 37 W solar panel can charge a 12 V battery and an energizer will convert the charge into 8 000 V, 150 mA current. Whenever the wild animals come in contact with the fence, they get a heavy shock for 1/10 second and due to very low milli amps current flow, no harm is caused to the animal; but they are scared away. It can be used particularly to prevent entry of wild animals in the farms near forest areas. It costs about Rs.1 lakh per km or Rs.20,000 per acre. The total cost will come down with the increase in the area covered. (iii) Solar Traps / pest catchers Solar lantern with some minor modifications are used as solar traps and pest controller which trap the pests causing damage to the crops. It is very useful to farmers not only as an emergency light but also for protecting the crops from pests. It costs about Rs.3 500 / each. (iv) Solar Traffic Signals Solar powered traffic signal system uses SPV panel to produce current, which is stored in a battery and used for operating the LED signal lamps for required hours of operation. (v) Police wireless system in remote areas Police Department uses batteries for continuous operation of communication equipment which is vital for linking their operations throughout the state. Solar energy can be used for charging of batteries for more effective and long term use and to reduce recurring cost. SPV charged batteries are useful for transmitters in rural / remote areas ( RASI ) where grid supply may not be available all the time. (vi) Telecommunication network In remote locations which are not electrified or face frequent power interruptions, working of telecom systems would get affected. Solar charged batteries would be of great help to maintain uninterrupted operation. (vii) Solar T.V. and other devices Solar energy can also be used for running T.V. sets or radios or charging mobile phones or a fan or any other electrical appliance depending upon power required for these devices. Solar powered refrigerators can also be used for storing of life saving drugs, vaccines etc in remote places. Manufacturers View the list of manufacturers / suppliers of SPV system Electrification of Remote Habitation Phase -ITamil Nadu Energy Development Agency has implemented the Electrification of remote unelectrified habitations in 12 districts by using Solar Photovoltaic lights under phase - I through M/s. Bharat Electronics Ltd., with full funding assistance of MNRE and State Government.
Total Project Cost Rs. 825.23 lakhs
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