Photovoltaic Systems Engineering Residential Scale – Part 2 SEC598F17 Photovoltaic Systems Engineering Session 20 Grid Tied PV Systems Residential Scale – Part 2 October 31, 2017

Session 17 content Grid-Connected Residential PV Systems Wrap-up of Residential PV System Example Balance of Systems Considerations

Grid-Tied PV Systems – The Design Process Design Steps in any Residential Scale System Examination of site and estimation of performance Securing financing Carrying out PV system engineering and design Securing relevant permits Construction Inspection Connection to the grid Performance monitoring

Grid-Tied PV Systems – The Design Process Step 3 - PV system engineering and design Evaluation of solar availability and electrical consumption PV array sizing Inverter selection Module selection Balance of system

Step 3 - PV system engineering and design Part 3: Inverter Selection The PV system output is expected to be 4000W (Part 2). This is the peak DC power output If we use a PV system design that employs one inverter, it must be able to accept DC electricity with power of 4000W. Representative inverter characteristics Inverter AC power Max array power Max DC Vin Vin MPPT Range Max DC Iin Vout Iout 1 3500 W 3800 W 600 V 200 – 500 V 20 A 240 V 16 A 2 4400 W 500 V 200 – 400 V 24 A

Step 3 PV system engineering and design Part 4: Module Selection The PV system output is a combination of all the separate modules’ power outputs Both the open circuit voltage (Voc) and the voltage at maximum power (Vm) vary with temperature; the ranges are shown in the following table Representative module characteristics Module Voc (nominal) (max) Isc Vm (min) Im Pm 1 33 V 37 V 8 A 27 V 20 V 7 A 189 W 2 44 V 49 V 5.5 A 36 V 5 A 180 W

Step 3 PV system engineering and design Parts 3 and 4: Inverter and Module Compatibility Inverter #1 [Vin(max) = 600V] Module #1 [Voc(max) = 37V] : 600/37 = 16.21  16 modules Module #2 [Voc(max) = 49V] : 600/49 = 12.24  12 modules Inverter #2 [Vin(max) = 500V] Module #1 [Voc(max) = 37V] : 500/37 = 13.51  13 modules Module #2 [Voc(max) = 49V] : 500/49 = 10.20  10 modules

Step 3 PV system engineering and design Parts 3 and 4: Inverter and Module Compatibility, cont. Inverter #1 [VMPPT(min) = 200V] Module #1 [Vm(min) = 20 V] : 200/20 = 10  10 modules Module #2 [Vm(min) = 27 V] : 200/27 = 7.4  8 modules Inverter #2 [VMPPT(min) = 200V]

Step 3 PV system engineering and design Parts 3 and 4: Inverter and Module Compatibility, cont. Number of modules based on inverter requirements Circuit Number of modules Inverter #1, Module #1 10 - 16 Inverter #1, Module #2 8 - 12 Inverter #2, Module #1 10 - 13 Inverter #2, Module #2 8 - 10

Step 3 PV system engineering and design Parts 2 and 4: Required PV array power and modules Module #1 [Pm(nominal) = 189 W] NMod1 : 4000/189 = 21.16  22 modules Module #2 [Pm(nominal) = 180 W] NMod2 : 4000/180 = 22.22  23 modules

Step 3: PV system engineering and design Part 2 and 4: Reconciling the module number calculations Consider the Module #2 + Inverter #1 combination: To meet the array power requirements, 23 modules are required But if the 23 modules are connected in series, forming one source circuit, their combined voltage would exceed the allowed inverter voltage input: 23 x 49V = 1127V >> 600V Another approach is to split the modules into two source circuits, each containing 12 modules in series, and then combining the two source circuits in parallel to meet the power requirement. 12 x 49V = 588V < 600V This does, however, double the total current, and it must be verified that it does not exceed the allowed inverter current input: 2 x 5.5A = 11A < 20A Success!

Step 3 PV system engineering and design Modules (15 in series) Representative single source circuit

Step 3 PV system engineering and design Modules (2 parallel strings of 8 in series) Representative two source circuit

Step 3 - PV System Engineering and Design Recap of Inverter/Module selection (Parts 2, 3, and 4) Inverter selection Pin (DC, array) Pout (AC) Vin (DC, max) & Iin (DC, max) Vin (DC, MPPT range) Vout (AC) = 240V & Iout (AC) Module selection Voc (DC) & Isc (DC) Vmp (DC) & Imp (DC) Temperature Range -> Voc (max) & Vmp (min) Module Range Maximum -> Vin (max)/Voc (max) Minimum -> Vin (MPPT,min)/Vmp (min) Power -> Psystem/Pmodule

Grid-Tied PV Systems – The Design Process Shaded max power point Original max power point

Grid-Tied PV Systems – The Design Process A new approach to combatting the effects of shading has emerged recently – the use of “microinverters” A microinverter is a compact inverter installed directly on the back of a PV module Therefore in a PV array, each module has its own inverter – the PV modules now have an AC output, not a DC output Each module is separately operated at its own MPP – they are connected in parallel, so the current loss from shading is eliminated The wiring and the connections are simplified, and high DC voltages are eliminated A typical microinverter has a 25 year expected lifetime – a dramatic increase over the expected 10 – 12 year lifetime of a high power central inverter

Grid-Tied PV Systems – The Design Process Block diagram for AC PV system

Grid-Tied PV Systems – The Design Process Microinverters installed on back of modules

Grid-Tied PV Systems – The Design Process Module VOC = 44V ISC = 5.3A Vmp = 36V Imp = 4.9A Pm = 175W Microinverter Vin(max) = 54V Iin(max) = 8A MPPT voltage range -> 25-40V Vout = 240V (AC) Iout = 750mA Pout(max) = 175W

Grid-Tied PV Systems – The Design Process Part 5: Balance of System (BOS) component selection Module extension wires Junction box and/or Combiner boxes Wire and Conduit to connect JB or CB to inverter DC and AC disconnects at inverter Wire and Conduit from inverter to Point of Utility Connection (PUC)

Grid-Tied PV Systems – The Design Process Block diagram of two source circuit PV system

Grid-Tied PV Systems – The Design Process Wiring of service panel

Grid-Tied PV Systems – The Design Process

Grid-Tied PV Systems – The Design Process

Grid-Tied PV Systems – The Design Process PV wiring THHN – Thermoplastic, High Heat, Nylon Coated – 90C THWN – Thermoplastic, High Heat, Water resistant, Nylon Coated – 75C USE-2 – Underground Service Entrance PV – https://www.youtube.com/watch?v=dDbaJQBdpbc

Grid-Tied PV Systems – The Design Process Voltage drop and wire sizing NEC requirement: Total voltage drop in feeder and branch circuits less than 5% (combined) or 3% (either) Size 18 (s) 10 (s) 4 (str) 0 (str) Rdc (W/kft) 7.77 1.21 0.31 0.12 Imax (A) 14 40 95 170

Grid-Tied PV Systems – The Design Process Branch circuits are source circuits that connect PV arrays to power conditioning Feeder circuits are PV inverter output circuits that connect to the utility (service panel) Rule of thumb: Don’t allow voltage drops to exceed 2% in any circuit

Grid-Tied PV Systems – The Design Process Ampacity and wire sizing NEC requirement (690.8): Ampacity > (1.25) * (1.25) * ISC = 1.56 ISC Temperature derating from Tambient > 300C (NEC 310.15) 3 hrs of max current flow Focusing effects of clouds T (0C) 26-30 31-35 41-45 Correction 1.00 0.96 0.82

Grid-Tied PV Systems – The Design Process M&A Example (modified) ISC = 8.05A -> 1.56 ISC = 12.6A Case 1: Wire size 10 AWG 300C ampacity -> 40A Suppose the ambient temperature will rise to 380C Derating factor is 0.91 Derated ampacity -> 36A >> 12.6A Case 2: Wire size 14 AWG 300C ampacity -> 25A Suppose the ambient temperature will rise to 600C Derating factor is 0.71 Derated ampacity -> 17.5A > 12.6A

Grid-Tied PV Systems – The Design Process 1. Solar PV Inspection Walkthrough - Introduction https://www.youtube.com/watch?v=APrbl0Ngp8o 2. Solar PV Inspection Walkthrough - Inspector Safety https://www.youtube.com/watch?v=UfQvlpi-8Es 3. Solar PV Inspection Walkthrough - The Array https://www.youtube.com/watch?v=L5ilShww9h4 4. Solar PV Inspection Walkthrough - Combiner Boxes https://www.youtube.com/watch?v=nohKIGN4FxU 5. Solar PV Inspection Walkthrough - Wiring Methods https://www.youtube.com/watch?v=hbw5bUHf87Q 6. Solar PV Inspection Walkthrough - Inverters https://www.youtube.com/watch?v=kKy8Qg4FFZE 7. Solar PV Inspection Walkthrough - Interconnection https://www.youtube.com/watch?v=NvlVfEcmUZE 8. Solar PV Inspection Walkthrough - Following Up https://www.youtube.com/watch?v=ibgUZrvUdcE Penn State Solar Center

Grid-Tied PV Systems – PV system engineering and design AC disconnect between PV modules and service panel

Grid-Tied PV Systems – PV system engineering and design AC disconnect between PV modules and service panel

Grid-Tied PV Systems – PV system engineering and design Second AC disconnect between PV modules and service panel

Grid-Tied PV Systems – PV system engineering and design Wiring of service panel

Grid-Tied PV Systems – PV system engineering and design Service panel, PUC

Grid-Tied PV Systems – PV system engineering and design Service panel, PUC

Grid-Tied PV Systems – PV system engineering and design Service panel, PUC