Energetica India Magazine nº88 March-April 2020

36 energetica INDIA- March-April_2020 SOLAR POWER Fundamental principles for designing a mini-grid system: Appropriate system design and component sizing is a funda- mental requirement for reliable operation, better performance, safety and longevity of a solar PV Mini-grid system. Therefore, it is critical to have a correct approach towards designing of a solar PV Mini-grid system. The design of a solar PV Mini-grid system must be approached keeping the following underlying principles in mind: • The system is safe and meets regulatory requirements; • The system meets the requirement of the users; • The provision for anticipated energy demand in near future; • The design is robust and results into a reliable system. Major system parameters for designing a solar Mini-grid system are as under: • Energy supply strategy and how to manage supply of elec- tricity with respect to demand; • Whether distribution is for d.c. loads or a.c. loads; • Maximum and surge demand; • System voltage; • Days of autonomy; • In case of a hybrid system: size and optimized run time of generator; • Size or capacity of solar array; • Size or capacity of battery bank; • Ratings of major components. Accurate energy demand assessment is the key: An energy demand assessment and load profiling for a pro - posed PV Mini-grid system must be as detailed and quantitative as possible. A faulty energy demand assessment may result in incorrect sizing and system performance. The energy demand and load characteristics influence every aspect of system de - sign and must be as accurate and reliable as possible. Maximum load demand should be estimated considering the power of largest load combined with all other loads is likely to be in use at the same time. The selection should be based on an understanding of load usage patterns and load management plan. Accurate estimation of a.c. surge current is important while selecting the inverter and capacity of battery bank which should be able to supply that surge current. After estimation of a.c. surge power, one must verify and ensure that the selected inverter can deliver such surge power. Seasonal variation to the energy demand should be considered while choosing the PV array tilt angle as well as the battery ca- pacity. Provisions as per growth in energy demand should be made, considering the increase in use of electrical appliances and increase in the number of consumers connected to a Mini- grid system. Thus, it all has to be carefully considered based on budget, initial subscription, socio economic status of the present and potential consumers and economic activities in the Minigrid area. It is also very important that system designers seek the most efficient loads for PV systems. Investing in efficient loads will most often pay for itself in cost savings through reduced PV array and battery size. Demand side management may be ap- plied for reducing the maximum demand and minimizing the component size and cost. This may be implemented by the user or by automatic control. Typical demand management practices include - staggering the time of operation of high-power loads so that they do not operate concurrently; delaying or reducing the usage of energy during periods of low resource availability; or scheduling high energy use to diesel generator run time or peak PV hours whenever possible. Selecting a right system configuration: PV Mini-grid systems are generally configured either as d.c. bus system or as a.c bus system. When more than one energy gen- erating system (such as diesel generator or distribution grid) is connected at a common point for reliable power supply, these configurations are further categorized into the following based on the factors/criteria mentioned above. • d.c. bus system integrated with DG set in series configuration • d.c. bus system integrated with DG set in switch configuration • d.c. bus system integrated with DG set in parallel configuration • a.c. bus system integrated with DG set in parallel configuration • a.c. bus system integrated with DG set and distribution grid in parallel configuration System configuration should be chosen to satisfy the design cri - teria, to make it more cost effective, efficient, reliable, long last - ing and for making sure that the system qualifies for any future upgrade. Economic evaluation of different options, if required, may be carried out on the basis of the cost of the life cycle. The configuration of a PV Mini-grid system into a d.c. bus system or an a.c. bus system will be determined based on the following considerations: