1

Photovoltaic Components and System Configurations

Dave ClickFlorida Solar Energy Center

January 26, 2009

2

Solar Photovoltaic System (SPS)

Solar Photovoltaic System (690.2) The total components and subsystems that, in

combination, convert solar energy into electrical energy suitable for connection to a utilization load.

loadutilization

energysource inversion &

conditioning

energyconversion

InverterCharger

Controller

PV Arrayenergydistribution

loadcenter

batteryenergystorage

electricutilitynetwork

3

Solar Photovoltaic System (SPS) Components

PV Array: An electrical assembly of photovoltaic modules that convert sunlight to DC electricity.

Inverter: A device that converts DC power from batteries or PV arrays into utility-grade AC power.

Energy Storage: Electrical or other storage devices sometimes used to store energy produced by PV arrays for later consumption.

System Charge Control: A device used to protect batteries from overcharge and overdischarge, and sometimes to provide load control functions.

Load: Energy consuming electrical appliances served by the system.

Balance of System (BOS) Components: Other equipment required to control, conduct, protect, distribute power and structurally support the system.

4

The basic building blocks for PV systems include cells, modules, and arrays.

Cells, Modules and Arrays

5

Solar Cell

Solar Cell (690.2) The basic photovoltaic device that generates DC electricity

when exposed to light. A typical silicon solar cell produces about 0.5 volt and up to 6 amps and 3 watts for larger area cells.

electrical load

typical crystalline silicon photovoltaic cell

(-)

(+)

phosphorous-doped (N-type) silicon layer ~ 0.3 x 10-6 mboron-doped (P-type)

silicon layer ~ 250 x 10-6 m

DC current flow

sun

6

Single crystal (or monocrystalline) silicon wafers are sawn from grown cylindrical ingots.

Single Crystal Cells

7

Polycrystalline (or multicrystalline) silicon wafers are sawn from cast rectangular ingots.

Polycrystalline Silicon

8

Several steps are involved in turning silicon wafers into PV cells.

Cell Fabrication

9

Diffusion of phosphorous gas creates a thin n-type semiconductor layer over the entire surface of a p-type wafer.

Establishing the P-N Junction

10

The different materials, processes, and manufacturing steps produce a range of PV cell types.

Variety of Cell Types

11

An I-V curve illustrates the electrical output profile of a PV cell, module, or array.

Cell Current and Voltage Output

12

Photovoltaic Modules

Module (690.2) A complete, environmentally protected unit consisting of solar

cells, optics, and other components, exclusive of tracker, designed to generate DC power when exposed to sunlight.

60-Watt polycrystallinemodule

75-Watt monocrystallinemodule

13

Modules are constructed from PV cells surrounded by several layers of protective materials.

Module Packaging

14

Modules are available in several sizes and shapes, including squares, rectangles, triangles, flexible units, and shingles.

Module Shapes and Sizes

15

PV Module Markings

690.51 Modules Modules shall be marked with identification of

terminals or leads as to polarity, maximum overcurrent device rating for module protection, and with the following ratings:

(1) Open-circuit voltage (2) Operating voltage (3) Maximum permissible system voltage (4) Operating current (5) Short-circuit current (6) Maximum power

16

Module nameplates must include performance ratings for the module and may include other information used to design a PV system.

PV Module Nameplate

17

Module Performance Specifications

Module performance only has meaning when the rating conditions are specified.

All PV modules are rated at Standard Test Conditions (STC): Irradiance = 1000 W/m2

Cell temperature = 25oC Module I-V parameters at STC must be on the

module listing label per NEC 690.51.

18

Irradiance

Effect of Irradiance

0

1

2

3

4

5

6

0 100 200 300 400 500 600 700 800 900 1000 1100

Mo

du

le C

urr

ent (

amps

)

Irradiance (W/m2)

Cloudy, indire

ct sunlight

Clear, dire

ct sunlight

19

Temperature and PV Voltage (Example)

Module Voltage at 25 degrees: 17.1 volts Temperature Coefficient: -0.077 V/deg C Module Voltage at 55 degrees: 14.8 volts

20

Similar PV Devices in Series

When similar devices are connected in series, the voltages add and the current is the same as one device.

Pos (+) (-) (+) Neg (-)

Pos (+) Neg (-)

A B

Voltage (V)

Curr

ent (A

)

A, B A + B

V = VA + VB

I = IA = IB

21

Similar PV Devices in Parallel

When similar devices are connected in parallel, the individual currents add, while the voltage is the same as for one device.

A

B

Pos (+)Neg (-)

V = VA = VB

I = IA + IBA, B

Voltage (V)

Curr

ent (A

) A + B

22

Photovoltaic Panels

Panel (690.2) A collection of modules mechanically fastened

together, wired, and designed to provide a field installable unit.

23

Several modules may be connected together to form a panel, which is installed as a preassembled unit.

PV Panel

24

Photovoltaic Arrays

Array (690.2) A mechanical integrated assembly of modules or

panels with a support structure and foundation, tracker, and other components, as required, to form a direct-current power-producing unit.

25

An array is a group of PV modules integrated as a single power-generating unit.

PV Array

26

Photovoltaic Cells, Modules, Panels and Arrays

cell module

panelarray

27

Solar cells

Module

Panel

Array

Fuses

Photovoltaic source circuits

Photovoltaicoutput circuit

Identification of Solar Photovoltaic System Components

28

Inverters are available in many different configurations and ratings.

Variety of Inverters

29

Alternating Current Waveforms

square wavesine wave

modified square wave

Time

Am

plitu

de

One Cycle

30

Stand-alone inverters are connected to the battery bank.

Stand-alone Inverters

31

Interactive inverters are connected to the PV array.

Utility-Interactive Inverters

32

Utility-Interactive Inverters:Power Conditioning Units

PV array maximum power point tracking (MPPT) Power inversion from DC to AC Wave-shaping and voltage regulation Synchronous utility interfacing System control and monitoring Protective and safety features

Fuses, disconnects and surge arrestors on AC and DC sides.

Automatic disconnect when the utility is down. Must comply with IEEE 1547 and UL 1741.

33

Power conditioning units are inverters that also perform other power control and conversion functions.

Power Conditioning Units

34

Most sine wave inverters maintain high efficiency over a wide operating-power range.

Inverter Efficiency

35

Inverter enclosures may include protective devices such as disconnects.

Inverter Disconnects

36

Inverter interfaces include on-board screens, remote data monitors, and computerized data acquisition and processing software.

Inverter Data Displays

37

AC modules include small inverters in place of the DC junction box.

AC Modules

38

Batteries are collections of cells that produce electricity through electrochemical reactions. Cells can be configured into batteries of many different shapes and sizes.

Batteries

39

Many components are common to various battery designs.

Battery Packaging

40

Electrochemical reactions within a cell produce a flow of electrons from the negative terminal to the positive terminal.

Battery Discharging

41

The charging reaction within a cell is the reverse of the discharge reaction.

Battery Charging

42

Batteries are divided into classes based on discharge and cycle characteristics.

Variety of Batteries

43

AGM batteries include fiberglass mats to absorb the electrolyte and separate the plates.

Absorbed Glass Mat Batteries

44

Connecting batteries in series increases system voltage.

Batteries in Series

45

Connecting batteries in parallel increases system capacity.

Batteries in Parallel

46

Series and parallel connections can be combined to produce a desired system voltage level and capacity.

Batteries in Series and Parallel

47

Charge controllers manage interactions and energy flows between a PV array, battery, and electrical load.

Charge Controllers

48

Charge controllers protect batteries from over charging by terminating or limiting charging current.

Protecting the Battery via Charge Regulation

49

Charge controllers protect batteries from over discharging by controlling discharging current.

Protecting the Battery via Load Management

50

Most charge controllers include displays or LEDs to indicate battery voltage, state of charge, and/or present operating mode.

Status Displays

51

Shunt charge controllers control charging current by short-circuiting the array.

Shunt Control

52

Series charge controllers control charging current by opening the circuit from the array.

Series Control

53

Photovoltaic System Types & Configurations

Stand-Alone Systems Operate independent of the utility grid and include

hybrid systems.

Utility-Interactive Systems Sometimes called grid-connected or grid-tied

systems. Operate connected to (i.e., in parallel with) the utility

grid. A bi-directional interface is required.

Bi-Modal Systems May operate in either utility-interactive or stand-alone

mode, but not concurrently.

54

The simplest type of stand-alone PV configuration is the direct-coupled system, consisting of only an array and a DC load.

Direct Coupled Configuration

55

Self-regulating stand-alone PV systems avoid the complexity of adding charge control components by precisely sizing the battery and array.

Self Regulated System Configuration

56

Systems with charge control regulate the charging current into the battery. Regulation may involve disconnecting or dissipating the current inside the controller or diverting the excess current into an auxiliary load.

Regulated Configurations

57

Stand-Alone PV System with Batteries and Charge Control

Charge control is required whenever the load is variable and the battery is not oversized.

Protects the battery from overcharge and overdischarge, and may provide load control functions.

DC LoadPV Array

Battery

ChargeController

58

Stand-alone systems with AC loads must include an inverter, which draws DC power from the battery bank and changes it to AC power for distribution.

Stand-Alone Configurationswith AC Loads

59

Hybrid systems include power sources other than the PV array and do not interact with the utility grid.

Hybrid Systems

60

A utility-interactive system is controlled by the inverter, which adds AC power converted from DC power to the utility grid power at the main AC power distribution panel.

Utility-Interactive System

61

Interactive System

Interactive System (690.2) A solar photovoltaic system that operates in parallel

with and may deliver power to an electrical production and distribution network. For the purposes of this definition, an energy storage subsystem of a solar photovoltaic system, such as a battery, is not another electrical production source.

62

Basic Utility-Interactive or Grid-Connected PV System

DistributionPanel

PV Array Inverter/Power Conditioner

AC Loads

ElectricUtility

63

Utility-interactive systems have either net-metering or dual-metering arrangements for exporting electricity to the utility grid.

Net and Dual Metering

64

Interactive System

Electric production and distribution network connection

Inverter

Photovoltaic source circuits

Photovoltaic output circuit

Inverter output circuit

Inverter input circuit

65

Bimodal systems can act like either a utility-interactive or a stand-alone system.

Bimodal System Configurations

66

Sun Paths for 30o N Latitude

North

PointO

East

West

Zenith

June 22: 12 noon

September 23 and March 21: 12 noon

December 21: 12 noon

10 am

8 am2 pm

4 pm

4 pm

4 pm

8 am

8 am2 pm

2 pm

10 am

10 am

South

67

Sun Position - Definitions

North

Point O

East

West

Zenith90 deg altitude

South0 deg azimuth

Altitude Angle ( )

Azimuth Angle ( )

68

Array Orientation

Ideally: face array south at (Latitude * 0.9) degrees

(Not critical to face south at 27 for Gainesville)

69

Solar Pathfinder

70

Shading Concerns

71

Shading Concerns

Same tree, four years later!

72