Photovoltaic (PV) SystemsIntroductionStand-Alone PV SystemGrid-Connected PV SystemPV ComponentsThe PV CellI-V CharacteristicMaximum Power PointEffect of IrradiationPV ConfigurationsBatteriesBatteries, cont.Charge ControllersCharge Controllers, cont.Slide 15InvertersPhotovoltaic (PV) SystemsME 252Thermal-Fluid SystemsG. Kallio01/13/19 Photovoltaic (PV) Systems2Introduction•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 AC01/13/19 Photovoltaic (PV) Systems3Stand-Alone PV System01/13/19 Photovoltaic (PV) Systems4Grid-Connected PV System01/13/19 Photovoltaic (PV) Systems5PV 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–Ventilation01/13/19 Photovoltaic (PV) Systems6The 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 junction01/13/19 Photovoltaic (PV) Systems7I-V Characteristic•Isc = short-circuit current •Voc = open-circuit voltage•PV cell can be considered a constant-current device for a given solar irradiation01/13/19 Photovoltaic (PV) Systems8Maximum 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 product01/13/19 Photovoltaic (PV) Systems9Effect of Irradiation•Irradiation has a large effect on current but little effect on voltage; maximum solar irradation is about 1.0 kW/m2 without concentration01/13/19 Photovoltaic (PV) Systems10PV 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/panels01/13/19 Photovoltaic (PV) Systems11Batteries01/13/19 Photovoltaic (PV) Systems12Batteries, 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-cadmium01/13/19 Photovoltaic (PV) Systems13Charge Controllers•Primary Function: maintain batteries at highest level of charge while protecting against overcharging by the PV array and from overdischarge by the load01/13/19 Photovoltaic (PV) Systems14Charge 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 hub01/13/19 Photovoltaic (PV) Systems15Charge 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 needed01/13/19 Photovoltaic (PV) Systems16Inverters•Inverters convert battery DC power  AC load power•Often incorporate equipment to charge batteries from AC