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Photovoltaic Systems – Utility Scale Part 1 April 7, 2014

Photovoltaic Systems – Utility Scale Part 1 April 7, 2014. Learning Outcomes. A comparison of the design process for utility scale PV projects vs smaller scale projects. Value to participants. A review of the importance of technical vs non-technical components of utility scale projects

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Photovoltaic Systems – Utility Scale Part 1 April 7, 2014

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  1. Photovoltaic Systems – Utility Scale Part 1 April 7, 2014

  2. Learning Outcomes • A comparison of the design process for utility scale PV projects vs smaller scale projects

  3. Value to participants • A review of the importance of technical vs non-technical components of utility scale projects • A review of utility scale projects both commissioned and in development

  4. Grid-Connected Utility-Scale PV System Design Steps in a Utility-Scale System • Examination of site and estimation of performance • Determining financing model • Carrying out PV system engineering and design • Securing relevant permits • Construction • Inspection • Connection to the grid • Performance monitoring

  5. Grid-Connected Utility-Scale PV Systems Comparison of PV system engineering and design for different scales • Evaluation of space availability, solar availability, and electrical consumption • PV array sizing • Module selection • Inverter selection • Balance of system

  6. Grid-Connected Utility-Scale PV Systems System sizing by AC Power • Small: Up to 10kW (Residential) • Typically, 240V AC, single phase • Medium: 10kW to 500kW (Commercial) • Large: 500kW to 5MW • Typically, 208V AC, three phase • Very Large: 5MW to 1GW (Utility) • Typically, 480V AC, three phase

  7. Grid-Connected Utility-Scale PV Systems Properties of a 3-phase system: • The phase currents tend to cancel out one another, summing to zero in the case of a linear balanced load. This makes it possible to reduce the size of the neutral conductor because it carries little to no current; all the phase conductors carry the same current and so can be the same size, for a balanced load. • Power transfer into a linear balanced load is constant, which helps to reduce generator and motor vibrations. • Three-phase systems can produce a rotating magnetic field with a specified direction and constant magnitude, which simplifies the design of electric motors

  8. Grid-Connected Utility-Scale PV Systems Recall the circuit diagram for a 3-phase system (Y-connected)

  9. Grid-Connected Utility-Scale PV Systems Before looking at a utility-scale system, consider a smaller (21kW) 3-phase system, with these components: • Modules with nameplate 305 Wp output • VOC = 64.2 V; VOC(max) = 73.7 V • VP = 54.7 V; VP(min) = 47.0 V • ISC = 5.96 A • Inverters with 7000 W output • VIN(max) = 600 V • 250 V < VMPPT < 480 V • IIN(max) = 30 A

  10. Grid-Connected Utility-Scale PV Systems • Module upper and lower bounds: • VIN(max)/VOC(max) = 600/73.3 = 8.13  8 modules • VMPPT(min)/VP(min) = 250/47 = 5.32  6 modules • Array Power

  11. Grid-Connected Utility-Scale PV Systems • Best Choice: • 3 source circuits, 8 modules in each circuit Higher voltage operation • 3 inverters One for each phase • 3 sets of 3 source circuits  9 source circuits, 72 modules 72 x 305W = 21,960W

  12. Grid-Connected Utility-Scale PV Systems 21kW three-phase PV system THWN – Thermoplastic Heat and Water Resistant Nylon-Coated

  13. Grid-Connected Utility-Scale PV Systems To build a utility-scale system, one can construct subarrays (similar to the 21kW system), then combine them to achieve a much larger power output. So to construct a 250kW system, we can use: • The same modules with nameplate 305 Wp output • VOC = 64.2 V; VOC(max) = 73.7 V • VP = 54.7 V; VP(min) = 47.0 V • ISC = 5.96 A; IP = 5.6 A • An inverter with 250 kW output • VIN(max) = 600 V • 320 V < VMPPT < 600 V • IIN(max) = 814 A • VOUT = 480 V • IOUT(max) = 301 A

  14. Grid-Connected Utility-Scale PV Systems • More on the inverter • Large inverters are not quite as efficient as smaller units, and may have a inversion efficiency of 96% • Therefore the array power should have: PARRAY = 250kW/0.96 = 260kW • Using again an 8 module source-circuit • PSOURCE-CIRCUIT = 2440W • Therefore the number of source-circuits PARRAY = 260,000/2440 = 106.6 • Even more on the inverter • It is preferable to combine source circuits to produce a balanced set of output currents, matching (or compatible with) inputs on inverter

  15. Grid-Connected Utility-Scale PV Systems • Dividing the source-circuits • 100 source-circuits is a nice round number with many ways for division (10x10, 20x5), but the produced power would be less than 260kW • A better choice for this example is 108 source-circuits, producing 263.5kW, and dividable into: • 12 groups of 9 source-circuits • 9 groups of 12 source-circuits • Any division must match the inverter current and voltage ratings: • Each source circuit has a maximum voltage output of 8x73.3 = 586V • Each source circuit has a peak current of 5.6A, so 108x5.6 = 603A, which is less than the inverter maximum of 814 A • Source-circuit combiner boxes that can combine 12-source circuits are available

  16. Grid-Connected Utility-Scale PV Systems 250kW three-phase PV system: physical layout

  17. Grid-Connected Utility-Scale PV Systems 250kW three-phase PV system: electrical layout

  18. Grid-Connected Utility-Scale PV Systems 250MW three-phase PV system:

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