1. Photovoltaic (PV) Systems
ME 252
Thermal-Fluid Systems
G. Kallio

2. Photovoltaic (PV) Systems
Introduction
Electricity produced from PV modules must be properly controlled, stored, converted, and distributed to be useful
PV systems are generally divided into two major categories:
Stand-alone systems for remote power
Grid-connected systems for interacting with the utility grid
PV system loads may be DC or AC; here, it is assumed that the loads are solely AC
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Photovoltaic (PV) Systems

3. Photovoltaic (PV) Systems
Stand-Alone PV System
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Photovoltaic (PV) Systems

4. Grid-Connected PV System
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Photovoltaic (PV) Systems

5. Photovoltaic (PV) Systems
PV Components
PV array
Primary Balance of System (BOS)
Charge controller
Battery Bank
Inverter
Electrical BOS
Disconnect & protection devices
Grounding equipment
Mechanical BOS
Array support & alignment structures
Enclosures
Ventilation
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Photovoltaic (PV) Systems

6. Photovoltaic (PV) Systems
The PV Cell
Photons dislodge electrons from the silicon atoms which move as a current under the influence of the electric field set up by the the P-N junction
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Photovoltaic (PV) Systems

7. Photovoltaic (PV) Systems
I-V Characteristic
Isc = short-circuit current
Voc = open-circuit voltage
PV cell can be considered a constant-current device for a given solar irradiation
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Photovoltaic (PV) Systems

8. Photovoltaic (PV) Systems
Maximum Power Point
The maximum power point (MPP) is where the cell operates at maximum efficiency and corresponds to a load that produces the highest IV product
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Photovoltaic (PV) Systems

9. Photovoltaic (PV) Systems
Effect of Irradiation
Irradiation has a large effect on current but little effect on voltage; maximum solar irradation is about 1.0 kW/m2 without concentration
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Photovoltaic (PV) Systems

10. Photovoltaic (PV) Systems
PV Configurations
PV cell – thin, semiconductor wafer that converts sunlight to DC current
PV module – series and parallel cell circuits sealed in a protective laminate
PV panel – two or more modules assembled as a pre-wired, field-installable unit
PV array – complete power-generating unit that consists of the required number of modules/panels
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Photovoltaic (PV) Systems

11. Photovoltaic (PV) Systems
Batteries
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12. Photovoltaic (PV) Systems
Batteries, cont.
Batteries are used in stand-alone PV systems since energy supply  demand
Functions
Store electrical energy as it is produced
Supply power to loads at stable voltages
Supply power to loads at high operating currents
Primary Types
Flooded lead-acid
Captive electrolyte lead-acid
Nickel-cadmium
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Photovoltaic (PV) Systems

13. Photovoltaic (PV) Systems
Charge Controllers
Primary Function: maintain batteries at highest level of charge while protecting against overcharging by the PV array and from overdischarge by the load
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Photovoltaic (PV) Systems

14. Charge Controllers, cont.
Seven Important Functions
Prevents battery overcharge
Prevents battery overdischarge
Provides load control
Provide system status information
Interfaces with and controls backup energy sources
Diverts PV power to auxiliary load
Serves as a wiring hub
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Photovoltaic (PV) Systems

15. Charge Controllers, cont.
Two methods of charge control
Shunt regulation
Series regulation
Three-stage charge control
Bulk:: maximum preset charging current, battery voltage increases
Absorption: battery voltage held constant, current decreases
Float: voltage constant: small amounts of current as needed
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Photovoltaic (PV) Systems

16. Photovoltaic (PV) Systems
Inverters
Inverters convert battery DC power  AC load power
Often incorporate equipment to charge batteries from AC source
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Photovoltaic (PV) Systems