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बारावीसाठीही फेरपरीक्षा लवकरच पुणे - यंदा दहावीची फेरपरीक्षा ऑक्‍टोबरऐवजी जुलै-ऑगस्टमध्ये घेऊन विद्यार्थ्यांचे वर्ष वाया जाऊ नये, यासाठी प्रयत्न करण्यात आले. या प्रमाणेच पुढील वर्षी बारावीची फेरपरीक्षादेखील लवकरात लवकर घेऊन विद्यार्थ्यांचा "बारावी नापास‘चा शिक्का पुसण्याचा विचार राज्य पातळीवर सुरू आहे. महाराष्ट्र राज्य माध्यमिक व उच्च माध्यमिक शिक्षण मंडळातर्फे जुलै-ऑगस्टमध्ये दहावीची फेरपरीक्षा झाली. या परीक्षेचा निकाल मंगळवारी लागला. त्यात उत्तीर्ण झालेल्या विद्यार्थ्यांना यंदाच्याच वर्षी अकरावीत प्रवेश दिले जाणार आहेत. या प्रकारचा हा पहिलाच प्रयत्न होता. त्यानंतर पुढील वर्षी दहावीबरोबरच बारावीच्या विद्यार्थ्यांसाठीदेखील अशी फेरपरीक्षा घेण्याबाबत सरकार विचाराधीन आहे. यासाठी दोन्ही फेरपरीक्षा लवकर घेण्यासाठी तयारी दर्शविली आहे, अशी माहिती मंडळाचे सचिव कृष्णकुमार पाटील यांनी दिली.

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SOLAR POWER – A GUIDE FOR SIZING A SOLAR POWER SYSTEM ARPIT JUNE 25, 2015RENEWABLE ENERGY, SOLAR ENERGY Increasing demand of energy in the world is waiting to be replaced by clean and cost effective sources of energy. Clean and cheap sources of energy are available as wind power, solar power, hydropower, tidal power with initial cost for setup. SOLAR POWER Sun the power house of the universe is providing energy free of cost to us. Rays coming from sun have packets of energy called photons. Heat energy from sun is also used to produce electricity, but in a totally different manner by conversion of heat energy into electrical energy. The setup is known as Concentrated Solar Power(CSP) or Concentrated Solar Thermal Energy. We will discuss it later. Here we are talking about conversion of solar energy into electrical energy with the help of PV module known as Photovoltaic cell. The initial investment is little more but one will get pay back between 3-10 years depending upon the sun rays intensity, sunshine hours and days in a year. In past decade the solar power systems are widely adopted as a clean and cheap energy source. As a result number of solar power plants are working across the globe. Here is a guide for sizing an off-grid solar power system ESSENTIAL COMPONENTS FOR A OFF-GRID SOLAR POWER SYSTEM 1. Array of PV Modules 2. PV Module Combiner 3. Charge Controller/ Voltage Regulator 4. DC to AC Inverter 5. Storage Bank (Batteries) SIZING A SOLAR POWER SYSTEM For a solar power system, to full fill the specific electrical requirements, calculations are needed in order to select optimum size of components for the system. It is a primary requirement to save energy in order to design a cost effective solar power system. Instead of using a big costly solar power system, a small optimum system would work well if we save electricity by altering our bad habits of wasting energy. Some common bad habits like keeping the screen ON while leaving the PC, Keeping lights and fans on without any purpose, Using lights & fans instead of using natural ventilation (If available) etc. Energy saving LED lights are replacing all old energy consuming tube lights and bulbs. LED lights consume very less as compared to tube lights and bulbs. If all these measures are taken then it will show a considerable cut off in energy consumption over a big span of time. Let us take an example to setup a home off-grid solar power system for following home appliances for given intended period of operation every day. This illustration is for knowledge purpose and such big system is capable to full fill energy requirements of a big house. An off-grid solar power system is the system which withdraw energy from sun through PV modules during day time, while utilize stored energy from storage bank during no sun shine or evening. Off-grid systems are not tied with available public grid. These systems are used where power from grid is not available or grid fails most of the time like in rural areas. For sizing the system first step is to calculate the electrical energy required by different appliances for intended period of use at home. Before calculation we have to understand basic terms, electrical power and electrical energy. POWER Rate of generation or utilization of electrical energy is termed as Power. Unit of Power is Watt or Joule/sec. 1 Watt = 1 Joule/sec Power rating of appliances is given in Watt. Home electricity is billed by KW consumed per month also called unit consumed. 1KW = 1 unit = 103 Watt Electricity generation capacity of power station is calculated as megawatt (MW) 1 MW = 106 Watt ELECTRICAL ENERGY Power generation or utilization over a period of time is termed as Electrical Energy. Unit of energy is Watt-Hour. For example- Power rating of tube light is 40W. So a tube light will consume 40WH in one hour, 80WH in two hours, and 160WH in four hours. ENERGY CONSUMED EVERY DAY For designing a home off-grid solar power system, first step is to calculate the energy consumption by different appliances every day at home on the basis of power rating and intended period of use. At home all appliances have different power rating and are used for specific period of time. Thus with the help power rating and intended period of operation, overall energy consumption is calculated as Energy Consumption (WH) = Power Rating of Appliance x Qty x Hours Used Refrigerator energy consumption depends upon the size and efficiency. Here the refrigerator fully working for 1/3rd period for producing refrigeration effect for 24 hours. Energy consumption for one day is 19300 Watt-Hour ~ 20000 Watt-Hour SIZE AND QUANTITY OF SOLAR PANELS TO PRODUCE REQUIRED ENERGY Time for sunshine and intensity of sun rays are the main factors to determine the solar panel size and quantity. Intensity of Sun rays is more near to the equator while moving towards the pole intensity decreases. Also at noon rays are more intense as compared to other time of day. Power rating of solar panel is given for 1kw/m2 solar radiation intensity. Assuming average sunshine time in winter and summer as 8 hrs every day. Power rating of solar panel is also given in Watts. Example- 100W solar panel, 300W solar panel. A 100W solar panel will produce 100W in one hour when exposed to sun. Thus in 8 hours, the energy panel will produce Energy Produced By Panel = Power Rating of Panel x Hours Exposed To Sun = 100 x 8 = 800 WH SIZE OF PANELS Panel size will be evaluated with the help of total energy consumption every day and time for sunshine in hours Required Power Rating of Solar Panel = Energy Required For One Day (24 Hours) / Time For Sunshine in Hour = 20000/8 = 2500 Watt Solar panels are not 100% efficient, their efficiency lie between 80-90%. Considering efficiency of panel as 85% Thus, Actual panel rating required = 2500/.85 = 2941 Watt ~ 3000 Watt QUANTITY OF PANELS Single Panel with 3000 Watt power rating is not available. Instead of using one big panel to produce 3000W, we will use the array of panels. Number of panels in the array would be Number of Panels = Power Required To Be Produced By Array of Panels/Power Rating of A Single Panel Selecting a suitable panel on the basis of availability, space efficiency, energy efficiency & service life. We are using polycrystalline panels of 500W rating. Thus Number of Panels Required = 3000/500 = 6 Panels So 6 panels of 500W will produce 3000 Watt power every hour And energy in 8 hours as 3000 x 8 = 24000 Watt-Hour (with 100% Efficiency) And 3000 x 8 x .85 = 20400 Watt-Hour (with 85% Efficiency) These panels can be connected in series, parallel or mixed connection in the array according to the battery battery bank output voltage, Output voltage of panel array should be more then battery bank voltage. Current always flow from low voltage to high voltage, therefore panel array should have to produce more voltage than battery bank in order to charge the batteries. SIZE AND QUANTITY OF BATTERIES REQUIRED ENERGY NEEDED TO BE STORED Energy generated by the array of panels is required to be stored for night or for period of no sunshine. During 8 hours of sunshine the energy is drawn directly from the inverter but during no sunshine, stored energy is drawn from the storage bank. Calculating the average power required every hour 19300/24 = 804.3 Watt ~ 805 watt Since, energy drawn from the system during sunshine will be 805 x 8 = 6440 Watt-Hour (Depends upon the appliances in use during sunshine hours, more energy is drawn during summers in day time.) Then energy needed to be stored for backup will be Energy consumption for one day – Energy drawn during sun shine 20000 – 6440 = 13560 Watt-hour 13560 WH is required to be stored in batteries in order to utilize it during no sunshine hours. Before calculating the size and quantity of batteries. Let us understand how much energy a battery can store. Battery is specified by Voltage and Ampere-Hour rating. Capacity of battery is measured in ampere-hour (AH). Ampere-Hour rating of a battery denotes the amount of current which a battery allows to flow across the terminals for an hour. A deep cycle battery with 70 AH capacity will able to supply 70 ampere current for one hour, 35 ampere for 2 hours, 5 ampere for 14 hours. Voltage rating of battery is the voltage difference between the terminals of the battery. There is a difference between deep cycle battery and an automobile starter lead acidic battery. Deep cycle lead acidic batteries are designed to produce a steady power over extended period of time, thus maximum of their stored energy is utilized, while an automobile battery is designed to produce large amount of power for short period of time, for cranking the engine. These batteries will not produce more than 40-50% of their stored energy. While deep cycle batteries can produces 80% of their stored energy. Energy stored in the battery can be calculated as the product of voltage and AH rating of battery. To know more about batteries available for storage system check this article TYPES OF BATTERIES FOR SOLAR STORAGE SYSTEM A 12 volt battery with 105 AH rating can store 12 x 105 = 1260WH Similarly A 12 Volt 200 AH battery can store 12 x 200 = 2400 WH Size of battery bank is calculated with the help of system AH requirement. System AH requirement is calculated as System AH Requirement = Energy required during backup/Battery Volts = 13560 WH/12V (Taking 12 Volt batteries) = 1130AH Selecting a 12 volt battery with suitable AH rating, we are using a deep cycle lead acidic 12 Volt 200AH battery (with 80% available rated power) Then, Number of Batteries Required = System AH Requirement/(Battery AH Rating x Available rated power) = 1130 x 100/200 x 80 (Using deep cycle Batteries with 80% Rated Power) = 7 Batteries. System requires 7 batteries connected in series, parallel or mixed configuration to produce 1130 AH. Batteries should be connected in series, parallel or mixed connection such that the battery bank voltage should be lower then panel array voltage. So to make current to flow from panels to batteries, from high voltage to low voltage. It is strongly recommended to design a storage bank with batteries working with 50% depth of discharge(DOD) instead of 80%. This increase the battery cycle life up to twice and decreases the per KW cost over a long period. Now finally we need a DC to AC Inverter to convert direct input current to alternating current for home appliances. POWER RATING OF INVERTER Generally power rating of power consuming equipment is indicated in Watt as Real Power, while power rating of power supplying equipment is indicated in VA (Volt Ampere Rating) as apparent power. The reason beyond this is the power losses in the power supplying equipment. In other words we can say because of power factor. Power factor is the ratio of real power to the apparent power. Simply we can say the equipment is not 100% efficient. Thus supply is little less as expected. This will clear more Real Power (W) = Apparent Power (VA) – Power Losses Or Power in Watts = Power in VA x Efficiency of Equipment Power of Inverter is specified by Volt Ampere Rating or VA rating, it is the capacity of inverter to supply apparent power to number of appliances simultaneously. Suppose 5 tube lights(40W each) and 3 fans(100W Each) are required to run all together, then power required from inverter would be 5 x 40 + 3 x 100 = 500W So theoretically we need an inverter of 500VA rating but the inverter of this capacity will not produce 500W to appliances because of lower efficiency or losses. Efficiency of an inverter lie between 60-80% or we can say Power factor lie between 0.6-0.8. To get a supply of 500W, actual rating of inverter should be VA Rating of Inverter = Power Required/ Efficiency of Inverter Thus VA Rating = 500W/0.7 (Considering Efficiency as 70%) = 714.2 VA (714.2 is the actual power rating, Apparent power. While 500W is the real power it will produce after power losses) So Inverter of available standard rating as 750 VA or 800 VA can be used. Now a days inverter manufacturer are claiming efficiency up to 90% for specially designed solar inverters. For home solar power system we need a DC to AC Inverter to supply AC power to appliances at night. For a hassle free power output without any overload breakdown, we are assuming that for a certain period, maximum number of appliance works together. So power required from inverter would be calculated as Power Rating of Appliance (W) x Qty = Power Required (W) All the above equipments working together will require 8126 Watt power from inverter. Although it never happens that we use appliances all together like Microwave, Water Heater, Laser Printer, Washing Machine, Iron, Mixer Grinder, Hair Dryer and Motor Pump. This is an illustration to design a home solar power system. Further it is a personal choice to select system components according to the need. Let us consider a 2500 watt power output from inverter is sufficient for hassle free operation. Power Rating of Inverter would be VA Rating of Inverter = Power Required/ Efficiency of Inverter = 2500/.85 (Using a Solar Inverter with 85% Efficiency) = 2941 VA ~ 3000 VA So Inverter with equal or more than 2941 VA rating is required. 2941 VA is not a standard rating for Inverter, so we can use a 3000VA or 3KVA Inverter. Finally two essential components are required as solar panel combiner and a charge controller. Solar Panel Combiner combines the output of all panels in the array as parallel, series or mix connection and delivers a single input supply to Charge Controller. Charge controller controls the amount of current and voltages produced by panels, and supply it to the batteries in order to prevent the batteries from damage. Charge Controller also restricts the reverse flow of current from batteries to panels during no sunshine. Energy Meter is an additional optional component used in the system in order track the system data like, Storage available, Solar Panel supply Voltage and Current, Charging Rate, load etc. POINTS TO REMEMBER 1. Intensity of sun rays and sunshine time should be analysed properly for better performance. 2. Superior quality panels with better efficiency should be used for better performance and long service life. 3. Batteries should be of superior quality with high efficiency and long service life. 4. Inverter should be high efficient to reduce energy losses. 5. Over all system losses are needed to be considered to keep the design optimum for hassle free operation. 6. Power rating of appliances should be checked with manufacturer data.

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