Photovoltaic Systems Engineering Session 21 SEC598F17 Photovoltaic Systems Engineering Session 21 Grid-Tied Residential Systems BOS components Battery Backup PV Systems Design Considerations, part 1 November 01, 2017

Session 21 content Wrap-up of Session 20 Battery Backup PV Systems Design Basics Standby Loads Inverter and Battery Selection BOS components

Learning Outcomes An examination of the design of a grid-connected battery-backup photovoltaic system leading to a recognition of the complexities in large-scale expansion of this technology

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 – System 01 with microinverters AC disconnect between PV modules and service panel

Grid-Tied PV Systems – System 01 with microinverters AC disconnect between PV modules and service panel

Grid-Tied PV Systems – System 01 with microinverters Second AC disconnect between PV modules and service panel

Grid-Tied PV Systems – System 01 with microinverters Wiring of service panel

Grid-Tied PV Systems – System 01 with microinverters Service panel, PUC

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

Grid-Tied PV Systems – System 01 with microinverters Service panel, PUC

Grid-Tied PV Systems – System 02 with string inverter Typical module data sticker (nameplate)

Grid-Tied PV Systems – System 02 with string inverter Modules and Junction Box

Grid-Tied PV Systems – System 02 with string inverter DC input from PV array AC ouput from inverter Inverter and DC disconnect

Grid-Tied PV Systems – System 02 with string inverter Vin = 600 V Iin = 18 A 250<VMPPT<600 PAC = 4000 W Inverter data label

Grid-Tied PV Systems – System 02 with string inverter DC disconnect data sticker

Grid-Tied PV Systems – System 02 with string inverter PV meter To PUC From inverter PV meter and AC disconnect

Grid-Tied PV Systems – System 02 with string inverter Main panel and Point of Utility Connection

Grid-Tied PV Systems – System 02 with string inverter Main panel and Point of Utility Connection

Battery-Backup PV Systems – The Design Process Design Steps in a battery backup PV system Examination of site and estimation of performance Securing financing Carrying out PV system engineering and design Standby loads Connection to charge controllers and batteries Altered inverter design Securing relevant permits Battery housing Inverter operation Construction Inspection Connection to the grid Performance monitoring

Battery-Backup PV Systems – The Design Process

Battery-Backup PV Systems – The Design Process Step 3: System Engineering and Design Evaluation of solar availability, electrical consumption, essential electrical loads PV array sizing Inverter selection Module selection Charge controller selection Battery selection Balance of system

Battery-Backup PV Systems – Engineering Issues The Battery-Backup Grid-Connected PV System resembles the Grid-Connected PV System in that the grid and the PV source work together to supply electrical power to the residence – when the grid is available When the grid is unavailable, a grid-connected PV system is automatically disconnected from the grid – for safety considerations But a battery-backup system continues to provide electrical power to the residence through the battery/PV portion of the system

Battery-Backup PV Systems – Engineering Issues When there is a utility outage, the inverter in a conventional grid-tied system disconnects from the grid, but continues to monitor the status of the grid, and automatically reconnects when the grid is stable The inverter for a battery-backup system is more complicated and serves several purposes: It supplies AC power to the grid, when available It serves as the conduit to charge the batteries with grid electricity if the PV system cannot do this It supplies AC electricity to the “standby loads” in the residence when the grid is down

Battery-Backup PV Systems – Engineering Issues Block diagram of battery-backup system (dc)