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Incorporating Solar Home Systems (SHS) for smart grid applications

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Solar PV systems are becoming popular for powering homes, commonly known as roof top solar plants. In this paper, various ways of connecting the solar system with the smart grids has been explored. An …

Solar PV systems are becoming popular for powering homes, commonly known as roof top solar plants. In this paper, various ways of connecting the solar system with the smart grids has been explored. An effective method using DC grids has been concluded after the discussion.

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  • 1. Incorporating Solar Home Systems for Smart Grid Applications B. Alipuria (*), B. Asare-Bediako (*), R.J.W. de Groot (*), J.Sarker (*), J.G. Slootweg (*), W.L. Kling (*) (*) Eindhoven University of Technology, Den Dolech 2, Eindhoven, The Netherlands B.Alipuria@student.tue.nl; B.Asare.Bediako@tue.nl; R.J.W.d.Groot@tue.nl; J.Sarker@student.tue.nl; J.G.Slootweg@tue.nl; W.L.Kling@tue.nl Abstract- Smart Grids have been one of the prime focuses of studies for the past few years on power systems. The goal is to make the power infrastructure more reliable and effective to cater for the needs of the future. Another goal for improving the power infrastructure is to incorporate renewable energy sources in an efficient and cost-effective manner. The popularity of solar PV has increased in recent times which has lead to exponential growth in the installed solar PV. This paper compares four possible scenarios for incorporating household solar PV systems into the power grid. It discusses the properties of each scenario along with their advantages and disadvantages. An effective system layout can be obtained by choosing the suitable case for incorporation of solar home systems according to the requirements. Index Terms-- DC Micro-grids, Distributed generation, Energy management system, Smart Grids, Solar home system I. INTRODUCTION The last few years have seen considerable increase in energy demand in the world [1]. This is due to the increasing population and the rising standards of living. A concern in this regard is that the conventional resources for power generation are limited and are depleting rapidly. Additionally there is a great requirement to find alternative ways to generate power due to climate change problems and increasing anthropological CO2 levels. This has led to a major development in renewable energy sources (RES) [2]. Despite many efforts, RES are still struggling to replace conventional generation sources. One of the prime reasons is the uncertainty and “uncontrollability” of these sources. One of the solutions to incorporate renewable energy sources as a major part of power system is to have multiple buffers to compensate for their uncertainty [3]. Smart Grids is a much discussed concept for future power systems. It incorporates the functioning of components of the grid in an intelligent and flexible manner for optimal operation of the grids [4]. The various components i.e. generation sources and loads are monitored and a local or central control co-ordinates the power flow according to set rules, priorities and preferences. Information is collected, processed and managed for monitoring and controlling of various components. Such ideas are also incorporated in this paper. Keeping in mind the need for renewable energy and the need for power grids to be smart, in this paper an attempt has been made to design a system that could meet the requirements of the future. This has been primarily done by integrating the solar home systems into the power grid with effective controls and information transfer. Advanced technologies have been acknowledged that could enhance the performance of such a system to accomplish effective and competent electric power scheme. II. SOLAR HOME SYSTEM The most preferred renewable source of energy by the consumers, particularly in sunny parts of the world, is the solar photovoltaic system [5]. Due to its easy installation and almost no maintenance, it is very easy to incorporate within the home system. It provides local generation source for every household which can be used in various ways and also avoids transmission losses. The home system can also consist of batteries that store energy for future/emergency use along with the controllers and converters required in accordance to the type of use. Energy storage acts as a buffer to increase system’s reliability and improve control for the network. The conventional system layout for a Solar Home System (SHS) is shown in Fig. 1. The sizing of various components is done according the requirement of the user and its installed function [6-7]. Users can manage their energy by choosing between power from grid or PV panels as the primary source and the other as backup. The user can control the load operation to match the time of generation so include the ideas of demand side management [8]. This reduces the stress on the grid and makes it stable. In the case of excess energy during day time, it can either be stored in batteries to be used later or supplied back to the grid. The batteries are often expensive hence large power storage is difficult. Supplying back to the grid has some challenges like low feed-in tariffs, and power quality standards [9]. With generation at distribution level, often the conventional power infrastructure is challenged. On the other Fig. 1. Layout for conventional solar home system
  • 2. hand, it enables ‘bottom-up principl les’ by use of decentralized generation sources in the power system. It makes the system more robust and reliable. The SHS needs to . be incorporated within the future grids in nfrastructure. There are certain conditions that it must satisfy along with giving sufficient comfort to the user. III. SMART GRIDS disturbance in the main netwo ork. Then affected component will be isolated automatically a the rest of the system shall and function in limited capacity. Th would reduce the affected his area and make the network more robust. In this paper, we will ma ainly consider on designing a micro-grid with SHS acting as distributed generation. g Multiple micro-grids can be c combined to cater to a larger network bringing in stability a modularity to the system and [14]. er It is important to redesign the powe infrastructure to integrate the various new and developing technologies within IV. HOME ENERGY MANAGEMENT SYSTEM the system. These include the technologies on generation, storage and efficient use of power. Also th incorporation of he Controlling an interface of loads and grids would require communication technology within the pow system would an effective energy managemen system that would empower wer nt lead to a more efficient, versatile a and user friendly the user to control its power f flows. This unit is called the infrastructure. Hence the concept of Sm Grids is being Home Energy Management Sys mart stem (HEMS). It does not only researched to integrate such various advan ncing technologies monitor and control the power f flows but also enables the user in the infrastructure [4]. A variety of ways have been used to to customize his power accordi to his needs. The user can ing define such a system, but for this paper we have used the select what source of power he/ /she prefers. It can control the comprehensive definition of Smart grid by Smart Grid load devices using the HEMS t ds thus enabling him to prioritize dictionary [10]. the demand according to cond dition [15]. This can be done The Smart Grid is a bi-directio onal electric and using the principles of demand s management of power. side communication network that improves the reliability, s The HEMS can function in various modes according to n security, and efficiency of the electric sy ystem for small to the needs of the user and the best suitable environmental e large-scale generation, transmission, distribution, and condition. Various scenarios can be programmed in the re er storage. It includes software and hardwar applications for system to control such a powe system. It also acts as the dynamic, integrated, and interoperable optimization of intelligent centre for the house that operates on the basis of e e electric system operations, maintenance, and planning; information signals it receive from the grids and loads es distributed generation interconnection and integration; and respectively. It optimizes the power usage of the home according to the instructions of the user. HEMS plays a major feedback and controls at the consumer leve el. One of the most important distinction in a smart grids role in empowering the user. G ns General architecture for Home infrastructure is the inclusion of Informatio Communication energy management is shown in fig. 2. on n Technology (ICT) at various positions of th systems. It plays he V. INTELL LIGENT LOADS an important role to monitor system at v various points and With the advancing techno ology, loads are developed to evaluate the state of various parts of the system. It should d communicate this information to other par so the effective integrate into the evolving grid network. This would include rts action can be taken by the other parts of the system if intelligent control that would enable them to work more effectively and synchronies themselves in accordance required. se Such ICT based network ensures re eliability in power network conditions [16]. Thes devices can be controlled supply and better power exchange within the grid. Also it from the HEMS or individual controls within the device. n would be able to incorporate all kinds o generation, both Such devices would be capable of automated operation under of y small and large within the system in an effi icient manner. This required conditions. They may even have the capability to can would greatly improve the ability of inte egrating distributed store energy. Electric vehicles c be considered as one such e generation and local RES. Such an advan nced system would load that can store energy hence acting as a buffer if required need to include additional software and har rdware for efficient [17]. working [11]. In total, the system would ea the pressure on ase environment by promoting renewable gen neration sources at various points on the grid. The network would be easy to xtent autonomous. monitor and operate and to a great ex Another important feature would be to em mpower the user to participate in the power grid in an effect tive with a deeper understanding of the system [12]. In a Smart Grid are multiple se ensors and relays monitoring and operating the network Communication k. technologies shall be used to exchange required information within system for efficient operation [13]. It includes storage as energy buffers and smart load like elect vehicles. There tric is also a possibility of networks connected in such a manner d that it is possible to operate in island m mode if there is a Fig. 2. Home energy management system architecture m
  • 3. VI. SYSTEM DESIGN To design the system for SHS integration, multiple cases were formed and evaluated. The formation of the cases is based on possible combination of various components that could be used in a SHS. These cases are compared with each other primarily based on the following parameters: 1. 3. Technology Efficiency 2. 4. Complexity Flexibility A HEMS has been considered as a control unit in every home and an interface to the network. Case1: Utility grid connected to the load along with the HEMS. Storage is personal and no energy is fed back to the grid. The case is formulated simply by combining the SHS with utility grid infrastructure along with ICT enabled controls monitored by HEMS as shown in Fig. 3. Due to private storage availability, the house can work on island operation if the grid fails. There are no changes in the operation of the network and the smart features are extensively applied within the home. • Technology: The technology for the system is well developed and is already in application. • Complexity: There is some degree of complexity involved in the operation. Various sources like PV power input, battery SOC, load power and grid quality can be variables for operation. • Efficiency: The system is not very efficient due to the need for a very large battery in order to store all the excess energy for the household. There is limited need for conversion of power between AC/DC. • Flexibility: Limited flexibility for the user due to limited storage and singular power source. No additional flexibility is gained for the network. Case2: There is no storage in the system. Any excess power generated is fed back to the grid. This case is formed by removing the storage from the SHS to analyze its effects as shown in Fig. 4. Due to lack of Fig. 4 System layout for case 2 - There is no storage in the system. Any excess power generated is fed back to the grid storage and unpredictable RES it becomes difficult to operate the network with high efficiency. It can be overcome by the prediction of RES and load as accurately as possible. • Technology: The technology for the system is developed to a great extent. The power quality at grid level is affected adversely due to inverters but can be improved. • Complexity: The system is really simple to manage as there are not a lot of components reducing the number of variables for operation. The complexity for operation is prediction of load and generation accurately which can be overcome by having a variable load or buffer system. • Efficiency: It is difficult to predict the load and generation precisely and with lack of storage. Any mismatch in energy is influences power quality of the utility grid. • Flexibility: There is no flexibility for the user or network operator. The generation must meet the demand at all times which is often difficult to predict. Case3: Utility grid is connected to community storage and the HEMS. Excess energy generated by PV is fed back to the grid. This case is formed by using communal storage at grid level thus reducing the need for private storage as shown in Fig. 5. The use of communal batteries is more effective compared to individual batteries [18]. It provides a larger storage to every household hence ensuring optimized usage. These can be collectively maintained and the operation can be monitored by the network operator, providing more flexibility. Also, the storage can be used as a fast charging station for electric vehicles or other purposes that requires high power for short term. The grid becomes more robust and certain parts can operate in islanded mode if there is a fault. The storage helps the network to integrate RES within the system with a higher efficiency in comparison to a network with no storage [18]. Fig. 3. System layout for case 1 - Utility grid connected to the load along with the HEMS. Storage is personal and no energy is fed back to the grid. • Technology: There is a developed technology available for this scenario as well. The power quality of the utility grid is affected by the numerous feed-in inverters during excess generation. • Efficiency: System efficiency is reduced due to multiple conversions of power between AC and DC at various
  • 4. Fig. 5. System layout for case 3 - Utility grid is connected to community storage and the HEMS. Excess energy generated by PV is fed back to the grid. levels of the grid. Many economically viable converters are used that also affect the power quality. • Complexity: The system is relatively easy to operate at user as well as network level. There are not many variables that need to be taken into account thus making the system simple. • Flexibility: The user has limited flexibility. Network operator gains the needed flexibility for an efficient operation due to the presence of storage. Case4: Excess power is not fed back to the grid but stored in a communal storage which is connected to the HEMS using a DC network. The case is formulated by adding an additional DC grid that connects the HEMS to the communal storage as shown in Fig. 6. This configuration allows the additional DC technology to be integrated within the grid. It provides a lot of advantages that DC has to offer along with making the system more reliable by providing dual voltage network. These have been discussed further in the paper. • Technology: The technology involved in the system would be new and needs to be perfected with time. The technologies that are in play for the network already exist but have to be improved upon according to the needs. • Flexibility: Due to multiple power sources, the system has a high degree of flexibility. Both AC and DC power are available for the user to choose from. There is a storage system for excess generation. There is a lot of freedom for both the network operator as well as user within the system. • Efficiency: The presence of both AC and DC encourages reduced power conversions. This improves the efficiency of the system. Power quality for the grid is enhanced. Incorporating storage allows efficient integration with RES. • Complexity: The operation of the system can be really complex due to the large number of variables in the system. This is a trade-off between flexibility of the system. This can be overcome using effective ICT control strategies by both user and network operator. With the advancement in power electronics, it might be important to consider DC systems as a part of the network. There has been great progress in electronics technology. Various modern day devices work on DC. With only AC networks, there is a need to convert the power to DC for such devices that reduces system efficiency. A DC-powered local grid can reduce the conversion losses [19-20]. Apart from the load devices, there are also DC generation sources like PV panels which are really simple to implement. The formulation of a DC power network would reduce the need for many AC/DC conversions improving the efficiency of the system. The absence of frequency function makes a DC network simpler to control, monitor and operate. Power transmission with DC is also more effective than AC transmission [21]. Another major advantage that incorporation of DC lines could provide for the network would be their ability to carry information signals along with DC power [22]. Since DC current is a constant voltage line, information signals can be easily superimposed on the line. Telecom technology like Asymmetric digital subscriber line (ADSL) technology can be used for transmission of data in the network over short distances on these DC lines. This reduces the need for separate channels for data transfer making the communication more secure [23]. DC networks are already applied in various niche areas. Many ships and submarines are powered by DC networks [24]. People have started employing total DC technology to power off-grid house [24-25]. Many commercial data centres have also been suggested to switch to DC power mode which can be up to 20% more efficient than using AC power [20]. Even though the use of DC has many advantages, there are still many barriers it must overcome. The most important one would be standardization of DC. There are no standards of DC voltages, so manufacturers can’t products to connect to a DC grid network directly. Another concern is the safety and regulatory aspect of DC networks. Since it is a new technology, large scale implementation must be regulated to safeguard society. Once standardization is done, the technology on networks can advance much faster. Fig. 6. System layout for case 4 - Excess power is not fed back to the grid but stored in a communal storage which is connected to the HEMS using a DC network
  • 5. Fig. 7. Proposed system layout – Integrating solar home systems to smart grid infrastructure (Exten nsion of Case 4) A micro-grid can be formed by c connecting various HEMS systems to the communal storage to ogether as shown in Fig. 7. This could even enable large renew wable sources like wind farms and solar farms to be conne ected to the grids without any problem. The ICT infrast tructure could be embedded within the network omitting t need for extra the communication network. The system would be reliable, more flexible and futuristic. VII. REFERE ENCES [1] [2] [3] CONCLUSION The Solar Home Energy Managemen System can be nt easily incorporated in the new Smart Grid design giving the d user multiple options to choose from. The system keeps the e user informed about the state of the netw work so he/she can make intelligent decisions regarding opera ation. It is possible to include DC technology and a communal battery within the l design which makes the system more flex xible and robust in use. ICT incorporation within the system m makes it smart and futuristic. Standardization of DC is requir for mass scale red integration in the system. With advancing technologies, the g system can be used to its best capacity m making the power infrastructure much more reliable and versatile. Comparison of various cases for integration of SHS wit thin the system has been given in Table I. [4] [5] [6] [7] [8] [9] IEA, “World Energy Outlo ook”, 2010 – Available Online: (http://www.iea.org/publication ns/freepublications/publication/name, 18027,en.html), April 2012 M. Wolsink, ”The research agenda on social acceptance of rt distributed generation in smar grids: Renewable as common pool resources”, Renewable and Su ustainable Energy Reviews, vol. 16.1, pp 822-835, January 2012 J. Liantao, Z. Jiancheng, “An e effective hybrid energy storage system based on battery-EDLC for d distributed generation systems”, 5th IEEE Conference on Indus strial Electronics and Applications (ICIEA), pp 819-824, June 2010. J.G. Slootweg, M.M.A.M. Van der Meijden, J.D. Knigge, mart grids – Different concepts and E.Veldman,, “Demystifying sm connection with smart metering CIRED, June 2011 g”, Live Science Survey y – Available Online: (http://www.livescience.com/en nvironment/090417-top10-alternativeenergy.html), March 2012 ye, M. Bond, R.J. Fuller, L. Ay “Sizing solar home systems for optimal development impact” Elsevier-Energy Policy, vol. 42, ”, pp.699-709, March 2012 M.M.H. Bhuiyan, M.A. Asgar, “Sizing of a stand-alone photovoltaic vier-Renewable Energy, vol. 28.6, pp. power system at Dhaka”, Elsev 929-938, May 2003 M. Castillo-Cagigal, et al., “A semi-distributed electric demand-side management system with PV generation for self-consumption enhancement”, Elsevier-Energy conversion and management, vol. 52.7, pp. 2659-2666, July 2011 S.K. Kim, J.H. Jeon, C.H. Cho, E.S. Kim, ”Modeling and simulation neration system for electromagnetic of a grid connected PV gen transient analysis”, Elsevier-So Energy, vol. 83.5, pp. 664-678, olar TABLE I COMPARISON OF CASES FOR SHS INTEGRATION Case Main Components Advantages Disadvantages 1 PV Modules + HEMS + Grid + Individual storage • • • Developed technology Simple operation High efficiency • Private battery leads to high cost y • Limited flexibility 2 PV modules + HEMS + Grid • • • Simple operation Developed techolgoy Cost effective operation • Difficult to operate with RES • Limited flexibility • Grid power qu uality affected 3 PV modules + HEMS +Grid + Communal storage • • Operational flexibility at grid level Effective integration with RES • Efficiency loss due to multiple conversions ses • Grid power qu uality affected 4 PV modules + HEMS +Grid + Communal storage + DC network • • • Backup DC grid structure High flexibility Higher efficieny • Developing tec chnology • Complex opera ation • High investme cost for the DC-network ent
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