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Photovoltaic Systems ELEG620 Solar Electric Systems University of Delaware ECE Spring 2009 S Bremner Photovoltaic Systems We will look in more detail at the components of PV systems in a little while but first we want to understand some of the larger issues involved Central issues in PV systems Characteristics of Energy Systems in General Characteristics of PV Systems Types of PV Systems Overview of systems design ELEG620 Solar Electric Systems University of Delaware ECE Spring 2009 S Bremner Central Issue We need to understand how the interaction between the components of our system affects the power produced the cost and the reliability of the system This means that we are considering the following issues Matching between components and the losses in components Possibly a large range in operating conditions variability of input temperature other factors Component reliability PV modules have 20 year warranty What about other components To provide the best solution for the application a trade off between performance availability and cost is found Therefore the analysis of a system and also a systematic method of designing systems are critical ELEG620 Solar Electric Systems University of Delaware ECE Spring 2009 S Bremner Energy Systems The central issues for any energy system are Distribution Cost Reliability Current energy systems Vast majority 99 of energy generated by mechanical generators Mechanical energy source varies 90 is thermal to mechanical and the remainder is mostly hydro Load characteristics Peak load Base line load ELEG620 Solar Electric Systems University of Delaware ECE Spring 2009 S Bremner Energy systems Need some parameters in order to effectively judge a systems performance Availability fraction of time that load is available compared to time load is required Critical availability requires availability 99 Availability of 95 for conventional applications Loss of load probability LOLP 1 A availability sometimes also called loss of power probability Capacity factor The ratio of the electrical energy generated for the period of time considered to the energy that could have been generated at cts full power operation during the same period Useful in comparing technologies and is a standard figure of merit in electrical generating systems ELEG620 Solar Electric Systems University of Delaware ECE Spring 2009 S Bremner Energy systems Parameters to judge system performance Reliability Probability of system being inoperable due to breakdown In general mechanical systems introduce reliability issues Temperature a contributing factor in reduced reliability Operating and Maintenance Complementary to reliability with a trade off between the two in many systems Cost of operating and maintenance can vary dramatically These are what might be thought of as big picture issues but there are more that influence our judgement of a system and are important particularly for PV systems ELEG620 Solar Electric Systems University of Delaware ECE Spring 2009 S Bremner PV systems Modularity and scalability Taken together these parameters determine the minimum effective system size Thermal systems are either modular or scalable PV systems are both modular and scalable Power quality Existing systems are primarily high voltage AC based Power quality refers to match to a sine wave with the voltage within specified limits Additionally for PV systems we are generating in DC but may need to produce power in AC Environmental Impact Impact on environment and other systems quantified by externalities ELEG620 Solar Electric Systems University of Delaware ECE Spring 2009 S Bremner PV systems Big issues for characterizing PV system performance Cost Initial cost typically the biggest impediment to installing PV Operating cost typically lower for PV Lifecycle cost typically lower for PV Performance parameters Peak Power Energy ratio units of Wp Wh The Wp is the rating of the array and the Wh is the energy produced during a given time period usually a year Peak Power Energy rating is substantially a measure of location and array parameters ELEG620 Solar Electric Systems University of Delaware ECE Spring 2009 S Bremner PV systems System performance parameters continued Efficiency Power Out Power In Central question is at what time and under what conditions Efficiency Energy Out Energy In Includes realistic losses and variety of conditions Need to justify time period over which system is measured Used solar fraction Total amount of the incident solar energy which is used by the load Average battery state of charge Useful indicator for the life of the batteries in general they are the most likely failure point Array to load ratio ELEG620 Solar Electric Systems University of Delaware ECE Spring 2009 S Bremner PV systems Losses Generation losses mechanisms that reduce the power generated by the PV panels compared to that available under test conditions AM1 5 room temperature Component losses losses in the components themselves such as the inverter or battery bank Mismatch losses account for the most significant losses to the power generated by a PV system Usage losses Losses due to electrical losses in components efficiencies of power conditioning batteries wiring etc Losses in the load may not be included in the design calculations unless designer also has some input or control over load ELEG620 Solar Electric Systems University of Delaware ECE Spring 2009 S Bremner PV systems Fraction of losses Losses Energy generated if this is calculated it is a good measure of the mismatch losses in the system and is a useful design parameter Energy used by load generated by system similar to losses energy generated but would include losses due to the inability to use the incident sunlight Specific applications may also have other performance indicators or may use only a subset of these indicators Availability is not a sensible parameter in residential grid connected PV system ELEG620 Solar Electric Systems University of Delaware ECE Spring 2009 S Bremner PV systems Several types of modes of operation available for a PV system Centralized power plant Large scale PV system located in optimum location feeding exclusively into the grid Distributed grid tied System such as residential PV supplying to a small system some feed in to grid possible Stand alone systems System set up for specific purpose i e water pumping communications etc not for feed in ELEG620 Solar Electric Systems University of Delaware ECE Spring 2009 S


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UD ELEG 620 - Photovoltaic Systems

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