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2012 Jim Dunlop Solar

Chapter 4

System Components and

Configurations

Major Components ● Balance-of-System ● System Classifications and Designs

Presenter

Presentation Notes

Photovoltaic systems are an assembly of electrical components that are intended to produce power suitable for operating electrical loads and appliances, or to interface with other electrical systems, like the utility grid. PV systems are versatile power generators, and the configurations and components required vary widely depending on the type of system and its intended application. Reference: Photovoltaic Systems, Chap. 4

2012 Jim Dunlop Solar System Components and Configurations: 4 - 2

Overview

Identifying major PV system components and their functions, including PV modules and arrays, energy storage, power conditioning equipment and other energy sources.

Discussing the key trends and sources of U.S. energy supply and

consumption.

Identifying the key components of the electrical utility system and the differences between centralized and distributed power generation.

Identifying the basic types of stand-alone and interactive PV systems, their operating principles and major components.

Presenter

Presentation Notes

Reference: Photovoltaic Systems, p. 89


Solar Photovoltaic (PV) Systems

Solar PV systems are electrical generators that produce energy for electrical loads and may interface with other electrical systems.

Electrical Load Energy

Source

Power Conditioning

Energy Conversion

Inverter PV Array

Power Distribution

Load Center

Battery Energy

Storage (optional)

Electric Utility

Presenter

Presentation Notes

PV systems are highly versatile and modular electrical power generation systems, and can meet very small loads on the order of a few watts up to utility-scale systems of several megawatts. PV systems can produce DC or AC power to supply any type of electrical load at any service voltage. Reference: Photovoltaic Systems, p. 90-97


Major System Components

Photovoltaic (PV) Array

An assembly of PV modules that convert sunlight to DC electricity.

Power Conditioning Equipment Inverters, chargers and controllers that process DC power from PV arrays

and produce AC power for utilization loads. Energy Storage

Batteries store energy produced by PV arrays, and are used in most stand-alone systems, but only in specially-designed grid-tied systems.

Presenter

Presentation Notes

Photovoltaic systems include an array of PV modules, and other equipment required to conduct, control, convert, distribute, store and utilize the energy produced by the array. The specific components needed depend on the functional and operational requirements for the system, and may include power conditioning equipment and energy storage. Reference: Photovoltaic Systems, p. 90-97


PV System Components

1. PV modules and array

2. Combiner box

3. DC disconnect

4. Inverter (charger & controller)

5. AC disconnect

6. Utility service panel

7. Battery (optional)

1

2

3

4

5

7

6

Presenter

Presentation Notes

Batteries are used in stand-alone PV systems, but only in grid-connected PV systems using special inverters and designed as a backup power supply for dedicated loads. Reference: Photovoltaic Systems, p. 90-97


Balance-of-System Components

Balance-of-System (BOS) Components

Mechanical or electrical equipment and hardware used to assemble and integrate major components, and to conduct, distribute and control the flow of power in the system.

Examples of BOS components include: Conductors (wiring) Raceways (conduit) Junction and combiner boxes Disconnect switches Fuses and circuit breakers Terminals and connectors Array mounting hardware

Presenter

Presentation Notes

Balance-of-system components include all equipment and materials (excluding major components) required to assemble a complete PV system. Reference: Photovoltaic Systems, p. 90-97


PV Modules and Arrays

PV modules are assembled electrically and mechanically to form an integrated DC power supply.

An array is the total DC power generating unit designed to produce a specified electrical output.

PV Array PV Module

Presenter

Presentation Notes

PV modules are assembled electrically and mechanically to form a single DC power generating unit called an array. PV arrays are configured electrically to meet the requirements of connected DC equipment, and mechanically secured to a structure. PV arrays are characterized by their electrical output, which depends on solar radiation, temperature, electrical load and other factors. PV arrays may be used to charge batteries, operate DC loads, or may be connected to inverters that produce AC power and interface with the electric utility grid. Reference: Photovoltaic Systems, p. 90 & Chap. 5


Energy Storage

Batteries are the primary type of energy storage used in PV

systems, and transform electrical and chemical energy.

Other types of energy storage systems include:

Flywheels store kinetic energy Supercapacitors store electrical charge Fuels store chemical energy Hydroelectric dams and compressed air systems store potential energy

Presenter

Presentation Notes

Energy storage technologies are classified by the form of potential or kinetic energy that they store. Energy storage is used for many applications, and becoming a critical element for the electric utility system and transportation sectors. Reference: Photovoltaic Systems, p. 90-93


Batteries

Batteries are used in most stand-

alone PV systems to store energy from the PV array and establish the operating voltage for DC utilization equipment, such as inverters or DC loads.

Lead-acid batteries are the most common type used in PV systems.

Flooded Lead-Acid

Sealed Lead-Acid

Presenter

Presentation Notes

Because the energy production from PV arrays does not always coincide with when the load requires energy, batteries are used in most stand-alone PV systems. Some small utility-interactive systems also use batteries that provide backup power to loads when the grid is down, but require special inverters. The magnitude and duration of the electrical load is the primary factor affecting the size of battery needed for any PV system. Lead-acid batteries are typically used in PV systems, both flooded and sealed types. Nickel-cadmium batteries are used in a few critical applications, and some smaller applications are beginning to use lithium ion batteries. Reference: Photovoltaic Systems, p. 90-93 & Chap. 6


Power Conditioning Equipment

Power conditioning equipment converts, controls or processes

the DC power produced by PV arrays, for interfacing with electrical loads, utilization equipment or other electrical systems.

Power conditioning equipment includes:

Inverters Charge controllers Battery chargers DC-DC converters Maximum power point trackers

Presenter

Presentation Notes

Power conditioning equipment converts, controls or processes the DC power produced by PV arrays, to make it suitable for interfacing with electrical loads or utilization equipment. Power conditioning equipment interfaces between PV arrays, batteries, loads or other electrical systems. Power conditioning equipment includes inverters, chargers, DC-DC converters, battery charge controllers, and maximum power point trackers. Reference: Photovoltaic Systems, p. 92-96 & Chaps. 7, 8


Inverters

Stand-Alone Inverters

Operate from batteries and supply power independent of the utility grid.

Utility-Interactive or Grid-Connected Inverters Operate from PV arrays and supply power in parallel with the utility grid.

Bi-Modal or Battery-Based Interactive Inverters

Operate as diversionary charge controllers, and produce AC power output to regulate PV array battery charging when the grid is energized.

Transfer PV system operation to stand-alone mode and provide backup electric power to critical loads when the utility grid is not energized

Presenter

Presentation Notes

Stand-alone inverters operate from batteries and supply power independent of the electrical utility system. These inverters may also include a battery charger to operate from an independent AC source, such as a generator. Utility-interactive or grid-connected inverters operate from PV arrays and supply power in parallel with an electrical production and distribution network. They do not supply PV array power to loads during loss of grid voltage (energy storage is required). Bi-modal inverters are a type of battery-based interactive inverter that act as diversionary charge controllers by producing AC power output to regulate PV array battery charging, and send excess power to the grid when it is energized. During grid outages, these inverters transfer backup loads off-grid, and operate in stand-alone mode. They can operate either in interactive or stand-alone mode, but not simultaneously. Reference: Photovoltaic Systems, p. 93-94, 212-213


Inverters

Bi-Modal Inverter

Interactive Inverter Stand-Alone Inverter

Presenter

Presentation Notes

Inverters convert DC power to AC power, and are characterized by the DC power source they use (PV array or battery), their power output, operating voltages, power quality and efficiency. Reference: Photovoltaic Systems, p. 93-94, 212-213


Charge Controllers

A charge controller regulates battery

charging by limiting the charging current from a PV array, and protects a battery from overcharge.

A load controller regulates battery discharge current by disconnecting electrical loads, and protects a battery from overdischarge.

A diversion charge controller

regulates battery charging by diverting power to a DC diversion load or grid-connected inverter.

48 V / 40 A Charge Controller

12 V / 10 A Charge Controller

Presenter

Presentation Notes

A charge controller regulates battery charging current from a PV array, and protects a battery from overcharging. Almost every PV system that uses a battery requires a charge controller for safe charging operations. Charge controllers are intended to optimize system performance and battery life, and are characterized by their method of charge regulation, set points, voltage and current ratings, and other features. Advanced charge controllers are microprocessor-based and include PV array maximum power point tracking (MPPT) functions. A load controller regulates battery discharge current to electrical loads, and protects a battery from overdischarging. Load controllers may also control the timing or duration of electrical loads, such as lighting. A diversion charge controller regulates battery charge by diverting power to a diversion load. The diversion load may be DC load, or an inverter that produces AC power and is interconnected to the utility grid. Systems using a diversionary charge controller as a primary means of control must have a second independent means of charge control to protect the battery is the diversion load fails or becomes unavailable to dump power from the battery. Reference: Photovoltaic Systems, p. 94-95 & Chap. 7


Battery Chargers

Battery chargers are commonly

used in stand-alone hybrid and UPS systems where an AC power source is available, such as a generator or the utility grid.

Many stand-alone inverters have a built-in battery charger.

Xantrex/Schneider Electric

Separate Charger

Integral Inverter/Charger

Presenter

Presentation Notes

Battery chargers operate from AC power and contain transformers, rectifiers, filters, and controls to produce suitable DC power for charging batteries. Battery chargers are commonly used in PV systems where an alternative AC power source is available to provide supplemental battery charging in addition to a PV array, such as an engine generator or the utility grid. Battery chargers can be independent equipment, or commonly an integral feature of stand-alone inverters. Battery chargers are characterized by their AC input and DC output ratings, methods of charge regulation, and efficiency. Reference: Photovoltaic Systems, p. 95


Uninterruptible Power Supplies

An uninterruptible power supply (UPS) is an emergency power

system that supplies electrical loads when the primary source of power is lost.

Typically includes a battery, charger, inverter and automatic

transfer switch. Grid-connected PV systems with battery storage are a type of

UPS system, transferring loads to the battery-inverter system when the grid de-energizes. Unlike most UPS systems, the PV array still charges the batteries and

extends load operating time.

Presenter

Presentation Notes

An uninterruptible power supply (UPS) is an emergency power supply that supports electrical loads when the primary source of power is lost. A typical UPS system includes a battery, charger, inverter and automatic transfer switch. When primary power is lost, the automatic transfer switch isolates from the utility, and powers connected loads directly from the battery and inverter. The size of the battery in the UPS system limits the magnitude and duration of electrical loads. Grid-connected PV systems with battery storage are a form of UPS system, with the PV array providing a means to recharge batteries when the primary source of power is lost, extending the load operating time. Reference: Photovoltaic Systems, p. 100


Maximum Power Point Trackers

Maximum power point trackers

(MPPTs) are electronic devices that operate PV modules or arrays at their maximum power output.

MPPT functions are included in all interactive inverters and in some battery charge controllers.

Also used at the PV module and source circuit level for some applications.

MPPT Controller

Module MPPT

Outback Power Systems

SolarMagic/National Semiconductor

Presenter

Presentation Notes

Maximum power point trackers are a type of DC-DC converter that operates PV arrays or modules at their maximum power output. All interactive inverters contain maximum power point trackers to optimize array output, as well as some battery charge controllers. Maximum power point trackers can also be utilized for water pump loads, or located at the PV source circuit or module level to optimize output of the array. Reference: Photovoltaic Systems, p. 95


Electrical Loads

Electrical loads include DC or AC appliances or utilization equipment that consumes power.

DC loads typically operate from batteries and are used in some small stand-alone PV systems, such as for lighting.

AC loads are powered by inverters, generators or the utility grid.

Electrical loads are characterized by their operating voltage (AC or DC), power and energy consumption.

where = load energy consumption (kWh/day) = load average power (kW)

= load operating time (hrs/day)

E P t

EPt

= ×

Presenter

Presentation Notes

Electrical loads are any type of device, equipment or appliance that consumes electrical power. Electrical loads are characterized by their voltage (DC or AC) and power consumption. Many types of electrical loads and appliances are rated for energy-efficiency. Direct-current (DC) loads operate from a DC source, such as a battery. DC loads are used in many small PV system applications, and avoid having to use an inverter to power AC loads. Alternating-current (AC) loads are powered by inverters, generators or the utility grid. Resistive loads or circuits are characterized by in-phase voltage and current waveforms. Reactive loads or circuits include inductance or capacitance, and are characterized by out-of-phase current and voltage waveforms. Inductive loads are most prevalent, and include common equipment such as motors and transformers. Inductive loads or circuits momentarily retard AC current in the process of building magnetic fields, and result in the current waveform following, or lagging the voltage waveform. Capacitive loads or circuits momentarily store voltage, and result in the current waveform leading the voltage waveform in time. Reference: Photovoltaic Systems, p. 97


Energy Sources

Basic forms of energy include thermal, chemical, electrical,

kinetic and potential energy sources: Solar radiation Fuels (biomass, fossil and alternative fuels) Radioactive materials Hydro and geothermal

Energy sources can be converted from one form to another with various energy conversion devices. Steam, combustion and wind turbines Electrical generators Fuel cells PV devices

Presenter

Presentation Notes

Energy sources are basic forms of energy. Many forms of energy including fossil fuels, wind power and ocean energy sources are ultimately derived from solar energy. Most energy sources require conversion in several steps to produce electricity. Direct energy conversion devices convert a basic form of energy to electricity with no intermediate steps. PV devices, fuel cells, and thermoelectric generators are examples of direct energy conversion devices. Reference: Photovoltaic Systems, p. 98-101


The Energy Dilemma

Presenter

Presentation Notes

The issues involving energy resources and consumption are compelling.


U.S. Energy Consumption

U.S Energy consumption is growing at extraordinary rates.

The turning point: production peaks, consumption exceeds production

DOE/EIA

Presenter

Presentation Notes

Since 1950, U.S. annual energy consumption has increased three fold to over 100 quadrillion Btu (Quads), accounting for 25% of total world consumption (U.S. has about 5% of the world population). Since 1970, U.S. net energy imports have grown from zero to 30% of total consumption. Reference: U.S Dept. of Energy - Energy Information Agency: www.eia.doe.gov


U.S. Energy Flow

DOE/EIA

Quadrillion Btu [2007]

Presenter

Presentation Notes

The U.S. is heavily dependent on fossil fuels, which are integral to every facet of our economy. Fossil fuels account for 85% of total U.S. energy consumption, with the remaining 15% mostly hydro and nuclear sources: Petroleum 37% Coal 22% Natural gas 24% Nuclear power 8% Renewables 7% (hydro, biomass, wind, and solar) Reference: U.S Dept. of Energy - Energy Information Agency: www.eia.doe.gov


U.S. Electricity Flow

Quadrillion Btu [2007]

DOE/EIA

Presenter

Presentation Notes

There are approximately 5,400 power plants in the US (65 nuclear with 104 reactors). The total generation capacity is about 1100 GW, with about 4100 million MWH of electrical energy produced. The average residential energy use in the U.S is approximately 30 kWh per day. Reference: U.S Dept. of Energy - Energy Information Agency: www.eia.doe.gov


Central Power Generation

Most power generation is centralized in remote areas and

transmitted over the grid to consumers in population areas. A large percentage of the energy content in the fuel goes unutilized.

Electricity 33% Fuel 100%

67%

Waste Heat

CO2 + Pollution

Power Plant

(Remote from thermal users) Thomas Casten

Presenter

Presentation Notes

Conventional thermal power plants convert only 30-40% of the energy content in the fuel source to electrical energy, while the remaining 2/3 is wasted as heat. Since most power plants are located remote from population centers and thermal energy users, this excess energy goes largely unutilized. Reference: Photovoltaic Systems, p. 3-5


Combined Heat and Power

Combined heat and power (CHP) systems utilize waste heat from

electrical power generation for other purposes.

Fuel 100% Steam

Electricity

Chilled Water

90%

10% Waste Heat

CO2 + Pollution

CHP Plants

(located close to thermal users)

Thomas Casten

Presenter

Presentation Notes

Combined heat and power (CHP) systems use smaller distributed power systems located closer to end users and thermal loads, where waste heat can be recovered and utilized. While many CHP technologies rely on fossil fuels, their value lies in utilizing the fuel more efficiently and providing power where and when it is needed.


Electrical Generators

Most electrical power is

produced from synchronous generators that are mechanically driven by turbines or engines.

A typical generator consists of an electromagnet, called the field or rotor, which rotates inside a coil of wire with an iron core, called the stator.

Presenter

Presentation Notes

Most power generation uses synchronous generators that are mechanically driven by turbines or engines. A typical generator consists of an electromagnet, called the field or rotor, which rotates inside a coil of wire with an iron core, called the stator. As the rotating magnetic field passes the conductors in the stator, it induces a voltage in the coils which varies sinusoidally as the field rotates, and can be tapped to draw electrical power from the machine. When multiple coils are spaced equally around the rotating magnetic field, multiple voltage outputs can be obtained, as with three-phase generators. A generator field or rotor consists of magnetic poles-pairs each having a north and south pole. A two pole field has one pole pair, a four pole field has two pole pairs and so on. The number of poles in a generator field establishes the speed at which the machine must rotate to produce output at a prescribed frequency. For example, to maintain an output of 60 Hz, a 2-pole generator must rotate at 3600 RPM, while a 4-pole unit must rotate at 1800 RPM, while an 80-pole field would need to spin at 90 RPM.


Engine Generators

Engine generators use internal

combustion engines to drive electrical generators, and are often used in conjunction with off-grid PV systems.

Presenter

Presentation Notes

Engine generators are commonly used in hybrid PV systems as an alternative source. Generators may be controlled directly by the power conditioning equipment in a PV system, and used to support battery charging and AC loads. Internal-combustion engines (ICEs) use reciprocating pistons to compress an air-fuel mixture, which is then combusted in cylinders. The pistons are connected to a crankshaft and flywheel and produce mechanical power to drive an electrical generator. Four-stroke ICEs include spark-ignition and compression-ignition (diesel cycle) types. Spark-ignition engines use a highly volatile fuel (gasoline), and use an ignition source (spark plug) to combust the air-fuel mixture. Diesel engines use a low-volatility fuel which vaporizes and combusts more slowly, and use higher compression ratios to combust the fuel without an ignition source. Diesel engines are well-suited for constant loads, and run slower, are more robust, have longer life and require less maintenance that spark-ignition engines. Prime-duty generators generally use diesel engines, and designed to operate in continual service. Standby generators are designed for backup and temporary power applications of limited duration. Reference: Photovoltaic Systems, p. 98-99


Combustion Turbines

Combustion turbines are large power generators that are similar to jet engines.

Caterpillar/Solar Turbines

Presenter

Presentation Notes

Gas or combustion turbines use axial air compressors, combustion chambers and expansion turbines to produce mechanical shaft power to drive electrical generators. Gas-turbines are essentially jet engines developed for stationary applications, and have become quite popular for peak utility power generation, and are available in sizes up to several hundred MW. Gas turbines can operate from natural gas, liquefied petroleum or even vaporized diesel or kerosene fuels. Reference: Photovoltaic Systems, p. 99-100


Microturbines

Ingersoll-Rand

Microturbines are small gas turbine generators adapted for distributed power and CHP applications.

Presenter

Presentation Notes

Microturbines are small gas-turbine generators use for distributed power and demand-side applications, as opposed to central power plants. Microturbines are available in size up to a few hundred kW, and incorporate heat exchangers for CHP applications. CHP microturbines may be installed in commercial facilities and interconnected with the electrical system to supply peak loads, and or to provide utility backup. Reference: Photovoltaic Systems, p. 99-100


Wind Turbines

Small wind turbines are sometimes used in stand-alone off-grid PV applications. Large turbines and wind farms are becoming increasing popular for utility-scale power generation.

Southwest Windpower

Presenter

Presentation Notes

Wind turbines extract the forces in the wind to drive a rotating mechanical shaft and electrical generator. Most wind turbines use horizontal-axis rotors with variable yaw and pitch, and electronic clutch mechanisms to load and unload the machine and for stowing during excessive winds. Small wind turbines from 1kW to 20 kW peak output and higher are often used in conjunction with PV systems for agriculture, and rural commercial or residential applications. Large wind farms with individual turbines 1 MW and larger are becoming increasingly popular, but their deployments have been limited by transmission capacity and infrastructure in some remote regions where good wind resources exist. Reference: Photovoltaic Systems, p. 100-101


Stirling Engines

Stirling engines use an external heat

source, such as concentrated solar energy, to compress a gas which expands to produce mechanical shaft power to drive an electrical generator.

NREL/Bill Timmerman

Presenter

Presentation Notes

Stirling engines use an external heat source unlike internal combustion engines, and produce no emissions when using concentrated solar energy as the heat source. Stirling engines are simple designs with few moving parts, and have low maintenance and high reliability. Stirling engines are produced in sizes up to 25 kW, but are expensive and have limited commercial deployment.


Fuel Cells

Fuel cells convert chemical to electrical energy directly. Most fuel cells combine hydrogen and oxygen to produce heat, water and DC electricity.

Fuel Cell

Water

DC Electricity

Heat

Hydrogen

Oxygen

Presenter

Presentation Notes

Fuel cells are electrochemical devices that convert the chemical energy in a fuel to electrical energy in a direct process without combusting the fuel. A fuel cells combines hydrogen and oxygen to produce DC electricity, and water and heat are generated as byproducts. Although similar to batteries, fuel cells are different because they require a continual replenishment of the reactants (hydrogen and oxygen). A typical fuel cell element consists of a cathode and anode separated by a membrane material. As hydrogen gas flows across the anode, electrons are stripped from the hydrogen and flow through an external circuit where they then re-enter the fuel cell at the cathode. Meanwhile, positively charged hydrogen ions migrate across the membrane to the cathode, where they combine with oxygen and the returning electrons to form water and release heat. Reference: Photovoltaic Systems, p. 101


Electric Utility System

The electric utility system

consists of three principal parts: Generation Transmission Distribution

Presenter

Presentation Notes

The electric utility system consists of three principal parts - generation, transmission and distribution – collectively referred to as the “grid”. The generation system consists of power plants and equipment that convert basic fuels or energy sources into electrical energy. Lower voltages from generators are then stepped up to higher voltages with transformers. The transmission system is used to transfer power from central generating facilities to large substations outside populated areas, at high voltages from 230 kV to 765 kV. Subtransmission is used to transfer power from transmission substations to distribution substations interior to populated areas, at voltages between 46 kV and 161 kV. The distribution system supplies power to feeders in residential and commercial areas at voltages between 2.4 and 38 kV. Industrial customers may use distribution or even transmission level voltages within their facilities. At most buildings, distribution voltages are stepped down to service voltages, typically either 120/240 split-phase for residential and small commercial facilities, or 480 V three-phase for larger facilities, which is usually reduced further by transformers on site to 208/120 V to power smaller loads. Reference: Photovoltaic Systems


Types of PV Systems

Stand-Alone Systems

Operate autonomously off-grid. Typically use batteries for energy storage. Sizing is based on electrical loads.

Interactive Systems Operate in parallel with the electric utility grid. Intended to supplement site energy use from utility. Operation is independent of electrical loads. Do not generally use batteries or provide backup for utility power.

Presenter

Presentation Notes

PV systems are categorized based on the loads they are designed to power, or their connections with other electrical systems. Stand-alone PV systems operate independently of other electrical systems, and are commonly used for remote power applications, including lighting, water pumping, transportation safety devices, communications, off-grid homes and many other electrical loads. Stand-alone systems may be designed to power DC and/or AC electrical loads, and with few exceptions use batteries for energy storage. A stand-alone system may use a PV array as the only power source, or additionally may use wind turbines or an engine-generator as a backup source. Stand-alone systems are not intended to produce output to the electric utility system. Interactive PV systems operate in parallel, or interconnected with the utility grid, and supplement utility supplied energy to a building or facility. Interactive PV systems are required to disconnect from the grid during utility outages or disturbances for safety reasons. Only special interactive inverters using batteries can provide stand-alone power independent from the grid. Reference: Photovoltaic Systems, p. 102-110


Direct-Coupled Stand-Alone Systems

Direct-coupled PV systems are the most basic type of stand-alone

system. A DC load is matched and directly connected to a PV module or array. Uses no energy storage. Load only operates when sun is shining.

PV Array DC Load

Water Pump or Ventilation Fan

Presenter

Presentation Notes

Direct-coupled PV systems are configured with the output of a PV module or array directly connected to a DC load, without any interconnecting power conditioning equipment or batteries. They are only appropriate where the power produced by the PV array can be utilized by the load when it is generated – when the sun is shining. DC motors are a common load for direct-coupled systems, including water pumps and ventilation fans. Direct-coupled PV systems are also used to power and control DC circulation pumps for solar water heating systems. In this application, the requirement to circulate hot water from a solar collector to a storage tank is coincident with and varies with PV output. Matching the impedance of the electrical load to the maximum power output of the PV array under varying conditions is a critical part of designing a well-performing direct-coupled system. Maximum power point trackers may be used between the PV module and DC load in some direct-coupled applications. Reference: Photovoltaic Systems, p. 102-110


Stand-Alone PV System with Battery Storage

Most stand-alone PV systems use batteries to store energy

produced by the array for use by loads as required.

A self-regulating PV system does not use charge control, but the battery is susceptible to overcharge and overdischarge.

DC Load PV Array Battery

Maximum charge must be limited, typically lower voltage modules are used.

Load must be well-defined, operate daily and not subject to user control.

Battery must be oversized in relation to PV array charge rates and daily load energy.

Presenter

Presentation Notes

Most stand-alone PV systems use batteries for energy storage. The PV array produces energy (income) that is stored in the battery (bank account) for later use by loads (expenses) as required. A self-regulating PV system uses batteries without charge control. These designs must have a well-defined load, the battery must be oversized, and the PV array must be designed to limit output current as the battery reaches full state-of-charge. The U.S. Coast Guard commonly uses self-regulating PV systems for navigational aids. Reference: Photovoltaic Systems, p. 102-110


Stand-Alone PV Systems with Charge Control

A charge controller is required in most PV systems using

batteries to protect from overcharge and overdischarge, and may also provide load control functions.

DC Load PV Array

Battery

Charge Controller

Presenter

Presentation Notes

Active means of protecting a battery from overcharge is required for most stand-alone PV systems using batteries. A charge controller is equipment that regulates battery charge by controlling DC voltage or DC current, or both. Wherever the battery and PV array have been sized to minimize costs, and wherever the load is variable or uncontrolled, charge control is usually required to prevent damage to the battery and consequently shortening its life. Any PV system employing batteries must use equipment to control the charging process unless the maximum PV array charge current multiplied by one hour is less than 3% of the rated battery capacity in amp-hours. For example, a 100 amp-hour battery would require charge control if the maximum PV array charging current exceeds 3 amps.


Stand-Alone PV Systems with Charge Control

Battery is not protected from overdischarge by load.

Charge controller protects battery from overcharge by PV array

PV Array Charge

Controller Battery

DC Load

Presenter

Presentation Notes

Battery charge controllers are most commonly used to protect the battery from overcharge by the PV array. This involves either interrupting or limiting the current flow from the array when the battery reaches a voltage corresponding to full state of charge. Reference: Photovoltaic Systems, p. 102-110, 177-178


Stand-Alone PV Systems with Charge and Load Control

This controller protects battery from overcharge

This controller protects battery from overdischarge

PV Array

Battery

DC Load Load Controller

Charge Controller

Presenter

Presentation Notes

Charge controllers are also used to protect a battery from excessively deep discharges that can damage the battery and shorten its life. Typically, the controller disconnects DC loads at a predetermined battery voltage, corresponding to low state-of-charge conditions. High-current DC utilization equipment like inverters are usually connected directly to batteries rather than through charge controllers, and have integral low-voltage disconnect means. A charge controller may protect a battery from both overcharge and/or overdischarge with the same unit or separate equipment. Reference: Photovoltaic Systems, p. 102-100, 179-180


Stand-Alone PV Systems with Multiple Charge Controllers

PV Subarray #1 Charge Controller #1

One subarray may be directly connected to battery without charge control if charge rates <= 3% of battery capacity.



PV Subarray #4

Battery

DC Load or Inverter

Presenter

Presentation Notes

For larger arrays having multiple source circuits, multiple independent charge controllers are often used as opposed to a single, larger controller. These designs provide redundancy in the event of a single controller failure. In some cases, one source circuit in a larger array may be left unregulated as long as the charge rate for that circuit is low enough, and sometimes used to help promote finishing charge on the battery.


Stand-Alone PV Systems with Diversionary Charge Control

PV Array Charge Controller Battery

Diversion Controller

Diversion Load

This controller protects the battery when the diversion load is unavailable

Diversionary controller protects the battery from overcharge by diverting

power to a diversionary load

Presenter

Presentation Notes

A diversionary charge controller diverts excess PV array power to auxiliary loads when the primary battery system is fully charged, allowing a greater utilization of PV array energy. Whenever a diversionary charge controller is used, a second independent charge controller is required to prevent battery overcharge in the event the diversion loads are unavailable or the diversion charge controller fails. The additional charge controller uses a higher regulation voltage, and permits the diversionary charge controller to operate as the primary control. Reference: Photovoltaic Systems, p. 184-185


Stand-Alone PV Systems with AC Loads

DC Load PV Array

Battery

Charge Controller

Inverter/ Charger

AC Load AC Source (to Charger Only)

Presenter

Presentation Notes

An inverter is used in stand-alone PV systems to power AC loads, and is connected to the battery. Many inverters also include a charger, which allows this inverter input to be connected to a generator or other AC source to charge batteries or supplement the AC load. The inverter charger AC input is separate from the AC output of the inverter. The AC output of stand-alone inverters operating from batteries is never connected to the grid, only to the dedicated AC loads served by the system. The inverter must be sized to meet the total connected AC load, for both continuous loads and surge requirements. Reference: Photovoltaic Systems, p. 102-110


Hybrid System

DC Load PV Array

Battery

Charge Controller

Inverter/ Charger

AC Load Engine/Wind Generator

Presenter

Presentation Notes

Hybrid PV systems are stand-alone systems that rely on other energy sources in addition to a PV array in meeting system loads. Common energy sources used in hybrid PV systems include engine generators, wind turbines, or small micro-hydro generators. Hybrid systems offer several advantages over PV-only or generator-only systems, including lower costs, greater system reliability, and flexibility in meeting variable loads. With an additional energy source, the size of the battery and PV array in a hybrid system can be minimized compared to a PV–only system. Reference: Photovoltaic Systems, p. 102-110


Utility-Interactive PV System

Load Center

PV Array Inverter

AC Loads

Electric Utility

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Interactive PV systems operate in parallel with and are interconnected to the electric utility grid. Sometimes called grid-connected or utility-interactive PV systems, these types of systems are perhaps the simplest and least-costly of all PV systems that produce AC power. They require the fewest components, and most do not use energy storage. The primary component in interactive PV systems is the inverter, which directly interfaces between the PV array and electric utility network, and converts DC output from a PV array to AC power and synchronizes with the grid. Interactive PV systems make a bi-directional interface at the point of utility interconnection, typically at the site distribution panel or electrical service entrance. In a sense, the utility acts as a large storage battery that accepts the power produced by an interactive system. This allows the AC power produced by the PV system to either supply on-site electrical loads or to back-feed the grid when the PV system output is greater than the site load demand. At night and during other periods when the electrical loads are greater than the PV system output, the balance of power required is received from the electric utility. Reference: Photovoltaic Systems, p. 102-110 & Chap. 12


Utility-Interactive PV System with Energy Storage

Inverter/ Charger

Critical Load Sub Panel

Backup AC Loads

Main Panel

Primary AC Loads

Electric Utility

Bypass circuit

Battery PV Array

AC Out AC In

DC In/out

Charge Control

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Bimodal systems are utility-interactive systems that use battery storage. They can operate in either interactive or stand-alone mode, but not simultaneously. These types of systems are used by homeowners and small businesses where a backup power supply is required for critical loads such as computers, refrigeration, water pumps and lighting. Bimodal PV systems operate in a similar manner to uninterruptible power supplies, and have many similar components. Under normal circumstances when the grid is energized, they inverter acts as a diversionary charge controller, limit battery voltage and state-of charge. When the primary power source is lost, a transfer switch internal to the inverter opens the connection with the utility, and the inverter operates dedicated loads that have been disconnected from the grid. An external bypass switch is usually provided to allows the system to be taken off-line for service or maintenance, while not interrupting the operation of electrical loads. Reference: Photovoltaic Systems, p. 102-110


Bi-Modal System

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Other applications for bi-modal systems include demand-side load management such as shifting peak times for power or energy consumption by utilizing the battery storage. Reference: Photovoltaic Systems, p. 102-110


Summary

Major components used in PV systems include modules and

arrays, inverters, batteries, chargers and controllers.

Balance-of-system components include electrical and mechanical equipment needed to construct a complete PV system and integrate the major components.

Stand-alone PV systems operate off-grid and are designed to power specific electrical loads.

Interactive PV systems are connected to the utility grid and supplement site electrical loads.

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Reference: Photovoltaic Systems, p. 111-113


Questions and Discussion

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Reference: Photovoltaic Systems, p. 111-113

system components and · pdf filesystem components and configurations major ... chargers and...

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