A HYBRID MODEL OF GRID INTERACTIVE SMART MICRO-GRID SOLAR (PV) HOME POWER STATION FOR RURAL INDIA

Transcription

1 A HYBRID MODEL OF GRID INTERACTIVE SMART MICRO-GRID SOLAR (PV) HOME POWER STATION FOR RURAL INDIA Dr S.N. Singh 1, Rakesh Kumar 2, Raj Ranjan Singh 3 1. Professor, Deptt. of Electronics and Communication Engineering, NIT Jamshedpur. 2. Associate Professor, Deptt. of Electronics and Communication Engg., RVSCET, Jamshedpur 3. Technical Assistant in NIT Jamshedpur. ABSTRACT Electricity is the basic need of all human being. The electrical power is obtained from conventional grid source. But the raw material of this conventional energy sources i.e. fossil fuel (coal, petroleum and natural gas) is depleting day by day. The expansion of these generating sources especially in rural sectors has become almost standstill. On the other hand, demand of electricity is increasing with growth of population very rapidly. To.meet this challenge standalone PV system, as an alternative source, were used by villagers but due to high cost and size of the system, need was felt to explore the possibility of bringing cost factor of electricity down within affordable limit. Later, PV systems were assisted by Grid supply and Load power was met from either of this energy source. But the sustainability feature could not be maintained due to frequent breakdown of grid supply sources. To overcome the above short comings a hybrid grid interactive PV system has been proposed as a new scheme and a prototype model of 300W for each station of solar power house has been developed for total 1kW loads of a cluster of rural houses. To maintain the sustainability feature (i.e. 24X7days) which was lacking in above PV systems, integration of individual standalone 300W PV energy sources of houses located in one cluster has been done by connecting these solar PV stations to a 1kW smart micro grid adopting ring topology. The power flow has been balanced with each other individual station using microcontroller. The power grid connectivity was made with smart micro grid to store the surplus power which in turn supplements the smart micro grid in case any deficit of power is encountered by any of the rural house. The impact of this sustainable power sources on rural society of our country was found an encouraging one. Index Terms - SPWM: Single Pulse width modulation, SMF: Sealed Maintenance Free, Ah: Ampere Hour, THD: Total harmonic distortion, PV: Photovoltaic Cell etc. 1. INTRODUCTION The fossil fuels (coal, petroleum and natural gas etc) used for generating electrical power are depleting day by day. As a result, Govt. of India do not find it economical to expand the existing supply network

2 further to rural villages or remote places of our country. The shortage of power especially in our rural village is revealed from the fact that only 10% to 40% of houses are connected with grid network, that too, with very poor availability of power. To meet this challenge, Scientist and Engineers looked for alternative renewable energy sources. like solar, wind, tidal and geothermal etc. Among all these solar energy has gained popularity, as it is abundant in nature, easily available, noiseless and involves simple technology to convert light energy into electrical energy. The development of solar power plant started with standalone PV system with battery as a storage device [1, 2, 3, 4] But due to high investment and cost of electricity, villagers could not adopt it. On the other hand, the demand of power was continuously increasing with rapid growth of population and people felt the need of a cost effective hybrid system, where PV was to be integrated with other renewable sources such as PV-Wind, PV-Tides and PV Bio- Mass etc. The availability of wind, tides, geothermal energy resources are restricted to specific location of our country. Further Bio Mass needs fertile land to grow plants. Hence PV-grid hybrid system became viable option for them. But this system was lacking sustainability feature, as power breakdown was encountered very frequently in these rural areas. Utility interface PV system also came to existence but surplus power saving of electrical power as generated by PV system during no load or under less load condition remains a constraint. In the proposed scheme, a prototype unit of 300W solar home power stations has been integrated with 1kW smart micro grid and controller has been designed to transfer power among each other through smart micro grid. The deficit of load power, if occurs, in smart micro grid has been supplemented with power grid. Load LG LG : Local Solar Power Generator Load LG Smart Micro Grid LG Load LG Load Fig: 1 Smart Micro grid Model Need was felt to back feed and store the power in the power grid as a storage element under the above situation, which can be utilized either during grid outage period or to meet the peak requirement of these solar power stations [5,6,7,8,9] Benefits of smart micro grid can be envisaged as follows: Smart grid connect small houses with Micro converter and share their load power among themselves in a balance way. Even on power grid failure/power outage system work as standalone PV system. It is easily expandable as individual micro converter can be added to the ring of smart micro grid and scaled up to higher rating as per future need of electrical power. The system cannot go down due to fault of any inverter even if shading or tilt of an individual solar panel is encounter. Power efficiency can be maximized as individual optimization of PV as well as Load power is possible. Power grid supplements the smart micro grid, in case deficit of power is encountered by individual system of smart grid. Demand and supply of Load power of these houses is made balanced through Wi-Fi controlling switches. 2 SYSTEMS DESCRIPTION 2.1 PV Grid Interactive system

3 The hybrid grid interactive PV systems are based on their grid-tied and off-grid counterparts. The system (Fig 2) can offer both the feature of the above PV system. FIG. 2: SOLAR HOME POWER STATION MODEL Fig.3: PN Junction and Electricity generation 3 SOLAR CONVERTER FOR POWER GENERATION 3.1 PV System Solar Converter involves the use of PV array, Inverter and Battery units. The block schematic diagram of Modules is shown in Fig 3. The prototype system is designed for a maximum home load of 200W from a PV module of 300W but this can be scaled to any higher wattage of load requirement. 3.2 PN Junction The PV cells are made of semiconductor material namely (i) Si (ii) Cd S (iii) Cd Te. The cell is a light sensitive PN junction semiconductor device. A barrier potential (depletion region) is formed due to diffusion of negatively charges electrons in P side and positively charge holes in N side of PN junction resulting in neutralization of electrons and holes at the junction and thus formation of electric field (E) across junction due to immobile ions left behind. When sun radiation i.e. photon (hv) fall on the surface of device, it breaks the covalent bond existing between atoms of Si and N or P type material and activate electron leaving behind space (holes) to jump from valance band to conduction band and make the electrons free to move, thus it create electron- hole pair. The electric field E, as formed across the P-N junction, separate electron and holes. Electrons being positive charge moves opposite to direction of electric field E and holes in the same direction. As a result electrons are made available on N side, where as holes on P type, thus form a DC current source. Electrodes are formed by providing finger plate conductive material on n type layer (0.3um) and a conductive plate on p type layer (350 um) Electric current is produced while these PN device is connected together through load. The cell produces 0.5V, 0.75A and 0.33W and is connected in series and parallel to get higher voltage and current. The requirement of PN junction device to work as solar cell are as follows: Photon hv> E G Where, Energy Gap (Eg) (i) Si= 1eV, (ii) GaAs= 1.5eV,(iii) GaTd= 1.45eV High optical absorbing capability Conductive Cost-effective Availability 3.3 I-V Characteristic (Open/Short Circuit) The open voltage/short circuit current Fig 4(a) can be expressed as follows i.e. V = E - ir When I = 0, V = E (Voc) and V = 0, I = ISC The image of I -V characteristic is reflected in Fig 4

4 Fig: 4: I-V catachrestic 3.4 SOLAR Converter The Electrical power, as designed for 12V and 300W, is produced during sun hour period (8AM - 4PM) in a sunny day from 12V PV modules and stored in 150Ah Battery. The PV converter (Fig.5) consist of PV module, Battery, inverter etc [10] Fig 5: Solar Converter Circuit Model A transistorized 3 level SPWM power inverter circuit configured with Power MOSFET (IRF 540) in push pull topology convert 12 volt DC voltage, obtained from PV source and stored in Battery, in to PWM AC voltage 250V, 50 Hz with maximum 95 % efficiency and having THD value less than 5%. The intelligent unit of solar converter regulates the power flow from PV source to load and send the surplus load power to grid. The synchronization of phase and frequency of micro inverter is maintained with the grid The Wi-Fi switches establish link between solar converter and smart micro grid The intelligent battery charger unit regulate the charging current of battery at constant rate (100W) and protect it from overcharging (13.4V) as well as under charging (10.4V). This also protects the battery from deep discharging. 4 PROTOTYPE DEVELOPMENT OF PV SOLAR HOME POWER STATION A prototype unit of PV solar home power plant of 300W unit for each house of cluster has been designed in an adopted village. The solar home power station consists of PV module, battery and inverter unit. The designs of these modules/units depend on the home load energy requirement. 4.1 Load Power Profile Load energy profile, as reflected in graph (Fig 6) is taken as critical base load for designing component of PV system has been used to compute the optimal size of PV module for critical load as stated below Table 1: Power Consumption of a Rural House Fig 6: Load profile over a period of 24 Hour Electrical Appliances Rating Hours Energy (W-Hr) Remarks Fan Bulb TV Pump W@ 4Hr 800W@1Hr 300 W 300W 400 W 800 W All the load as reflected here are critical load of a House Total 1800 W-Hr 4.2. PV Sizing The empirical formula based on energy balance equation PV cell rating

5 (P PV) = (P TL*S.F)/Sun Hour (watt-hour) (1) Where, Sun hour = 6.2 for adopted area Safety factor (SF) = 1.5 for cloudy weather P TL : Total load energy in watt hour (i.e. total load power consumption over a period of 24 hours assuming hourly load power (PL) as constant P TL Watt Hour (i = hour) = Sum of P L (i) (2) N = Optimal number of PV module = P PV/ Wattage of Standard PV Module (3) 4.3. Battery sizing The battery stores the energy to its maximum value as per average load energy requirement Battery Capacity (Ah) =P TL/ (12V*SOC) (4) Where, SOC (State of Charge) = 50 % 4.4 Inverter The inverter, based on PWM technology, is synchronized with power grid frequency. The control circuit regulates the input and output power flow in both directions. The load power is drawn from the power grid and surplus power is fed back to grid The Inverter capacity = Rated load /Efficiency Where, Efficiency = System Specification A prototype system has been developed with the following design specification: Load Energy : 1800 W-h (Load Fan, Bulb, TV and Pump etc ) PV module: 4 x 75 Wp (Each Module size =75 cm x 100cm) with efficiency of maximum 95 %. Sun tracking : PV module inclination at an angle of 45 degree North-South position Installation : Roof top Battery Size : 150Ah (Tubular /SMF) Converter : 300W (bidirectional ) Intelligent Controller Unit : Arduino Micro-Controller 4.6 LOAD Power Optimisation The following intelligent devices are used to reduce the power billing: a) Inbuilt Intelligent Regulator Devices in appliances like Fan, TV, Pump etc b) Power factor Regulator / Harmonic Absorber c) Soft computing Tool e.g. Fuzzy Load Controller etc 5. ADVANTAGES / DISADVANTAGES OF SOLAR PV CELL FOR POWER GENERATION The advantages and disadvantages of PV module over other renewable sources are depicted in Table 2. Table 2: Advantages and Disadvantage of PV cell 6.0 COST EVALUATION OF THE PV SYSTEM The cost of system may be computed from market value and reflected in Table 3.

6 S.No Component /Modules Cost ( s) 1 PV module 300W = Rs 25 x 300W Inverter 300W (Peak 400W) Battery 150Ah Miscellaneous (wires, cable etc) 1000 Total : 20,000 Govt. /NGO Subsidy (50%) 10,000 Net Price : Rs 10,000 Presently 100 square feet area of PV module, available in market, can produce 1kW of solar electricity costing 1 Lakh approx., if mounted on roof top of a building or on a ground plain. 7.0 PERFORMANCE OF SOLAR HOME POWER STATION 7.1 Design Verification Performance test were carried out on the prototype module to examine the computed value of capacity of the PV system with the predicted value of Load energy and was found within the deviation limit of 5 % 7.2 Battery charging The charging status of Battery was recorded under varying climatic condition and autonomy period of one day was recorded. 7.3 LOAD Sensitivity The response time of system on a sudden change of load, insolution, grid was recorded as 1.5S, 40 ms and 40 ms respectively and was found within tolerance. 7.4 EFFICIENCY PV cell Efficiency of solar cell is computed by measuring Electrical Power output delivered by the cell and Power intercepted on it and was found 14 %. The efficiency of solar converter was tested at all loads (> 20%) and was found almost constant at a value of Sustainibility The sustainability feature (i.e. 24 hours x 7 days) from PV system could be able to achieve.this has been reflected in Table 4. Table 4: Month-Breakdown Period in the year 2015 Jan 15 Feb March April May June 2 hr 3hr 2hr 3 hr 6 hr 5 hr July Aug Sept Oct Nov Dec 15 3 hr 4 hr 2 hr 5 hr 4 hr 3 hr 7.6 PAYBACK PERIOD Initially due to high cost of electricity, the payback period of solar plant is approximately 4-5 years, but in future, it is expected that price as well as size will come down with the advancement in PV module by raising its conversion efficiency from 25% to 75% using better material utilizing nanotechnology. 7.7 LIFE Cycle /Maintenance Period PV module : 20 years

7 Converter/ Inverter : 20 years Battery : 3-5 Years Maintenance : 1 year 8.0 SOCIAL IMPACT ON THE RURAL SOCIETY The impact of Home Solar Power Plant may bring many changes in the social parameters as follows: Education (30%) Employment (40%) Health Services (30%) Social function (20%) Migration (-10%) Agriculture Yield (30%) Economic status (50%) Women Empowerment etc The data, as acquired from the survey done in adopted village of Jharkhand state of our country and its analysis, reveal that the expected outcome will be as follows: a) The socially economically backward section of the society will be benefited in raising their economic status and may start living with their children and other family members happily. b) Potential youth will be trained in vocational skill formation trades in solar powered community centers even during night period and could be able to get self/wage employment in near future. c) Women will be empowered and they could be able to move late in the evening from one place to another place d) Agricultural yield will increase e) Migration of youth outside their home place will stop. 9.0 GOVT. OF INDIA INITIATIVE FOR SETTING UP SOLAR POWER STATION Govt. of India (MNES) has taken much initiative during the last three years to promote the use of solar PV module by individuals/organization. Subsidy in the range of 30-75% is being given to rural masses as well various organizations by Govt. on setting solar power plant. Delhi metro railway is one such example that can be cited here, where PV modules have been placed on roof top of the building. Solar lantern is being distributed in villages for lighting by Govt. of India through state nodal agency like JREDA (Jharkhand)/NGO. Govt. of India has a mission to install total MW in various capacity of power plant in near future in different state of our country. The subsidy provided to solar module manufacturer has reduced the cost from Rs 200 (2014) to Rs 25 (2016) per watt. All University/Technical Institutions have been sanctioned and asked to install rooftop solar plant to meet their additional demand of electricity and also to generate electricity for national grid network. Govt. of India has also taken initiative to set up solar park in different state of our country to create awareness among the people to use renewable source of energy emphasizing solar (PV) energy for their home use CONCLUSION A prototype module has been developed for 300W Home Solar Power Plant, integrating it with smart grid for rural house. The PWM technology as adopted give rise to an efficient system and maximum number of villagers expressed their satisfaction with the availability of power in their home. Although slow adoption of technology was observed by the villagers in the past, but this was only due to high cost of system and villagers could not afford for the same. Thus sustainability feature i.e. 24 x 7 days in the PV system was found except in case of prolonged power failure that occurred at site from time to time. This PV interactive PV system model can be applied to urban area for sustainable power need of organization. The Grid interactive PV power supply can be operated in standalone mode of operation which may find its application in Street lighting, Mobile Tower power supply, Boat lighting, Space Station Power Supply etc.the performance of PV system depend on many factors including material and manufacturing process and also on the selection of places and climatic conditions etc. Reference

8 [1]. Saha et al grid interfaced urban domestic power pack proceeding of 29 th IEEE photovoltaic specialist may Neworlians 2003 pp [2]. S.N. Singh, A.K.Singh & Anumeha : " Modelling and Dynamics of a PWM Sinusoidal Inverter for water pumping system for use in agriculture and household applications". Journal of IEEMA January 2008,Vol-28, pp [3]. Lindgreen, A 110 W Inverter for Photovoltaic Application, Published in international Journal of Renewable Journal of Renewable Energy Engineering, April [4]. Sopitpan. S, PV system with / without grid backup for housing applications, Photovoltaic specialists conference, IEEE (2000). [5]. S.N. Singh and A.K. Singh: "Solar Power System- An effective Tool for sustainable socio-economic Development of Indian Villages: A Case Study " Journal of ARISER, Vol-5,No-1, March 2009, pp [6]. S.N.Singh and A.K.Singh : "Techno-economic viability of the Hybrid Solar(PV)-AC Utility Interfaced Power System for Rural India". The Journal of CPRI, vol 5, No 1, March 2009, pp 1-7 [7]. S.N. Singh et al "FGPA based Sinusoidal Pulse width Modulated Waveform Generator for Solar (PV) Rural Home Power Inverter". Journal of Telecommunication (Canada), vol-1, Issue-1.February 2010, pp: [8]. S.N.Singh, A.K.Singh: "Simulation of Grid-assisted Solar Power converters: an effective solution for power crisis in rural India" Asian Journal on Energy and Environment. 2010,2011 (02), pp , [9]. S.N.Singh and A.K.Singh "Solar (PV)-Grid/DG Green Power Supply for Rural India"JEE, Vol-10 (2010), pp [10]. M.H. Rashid Power Electronics circuits, devices and Application. Pearson education (2004)