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    2010

    Prepared by: Joss K. Mankad

    PV Inverter Systems

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    Contents

    Preface .......................................................................................................................................................... 3

    1. PV inverters introduction ...................................................................................................................... 4

    2. PV cell types .......................................................................................................................................... 5

    3. Grid tie PV inverter design .................................................................................................................... 5

    Key terms for a pv inverter ....................................................................................................................... 5

    Layout of a grid tie PV inverter system ..................................................................................................... 7

    Inversion function ..................................................................................................................................... 7

    Filters......................................................................................................................................................... 8

    Maximum power point tracking ............................................................................................................... 8

    Auto wake-up system ............................................................................................................................. 10

    Grid disconnection (islanding mode detection) ...................................................................................... 10

    4. Other protections and controls .......................................................................................................... 11

    Ground fault protection .......................................................................................................................... 11

    Ac over current detection and protection .............................................................................................. 12

    Single phase open detection ................................................................................................................... 13

    Thermal requirements ............................................................................................................................ 13

    Dc bus over voltage and over current protection ................................................................................... 13

    5. Monitoring software and metering .................................................................................................... 13

    6. Testing of a PV system ........................................................................................................................ 14

    7. Future trends ...................................................................................................................................... 15

    8. Conclusion ........................................................................................................................................... 17

    9. Appendix ............................................................................................................................................. 18

    Various standards ................................................................................................................................... 18

    Voltage requirements ............................................................................................................................. 19

    Frequency requirements ......................................................................................................................... 19

    Synchronization( IEEE 1547) ................................................................................................................... 20

    Ac current harmonics .............................................................................................................................. 20

    Efficiencies and costs of PV module ....................................................................................................... 21

    Solar map of India ................................................................................................................................... 22

    10. Index ................................................................................................................................................ 24

    11. References ...................................................................................................................................... 25

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    Preface

    The Indian economy has been growing at more than 8% since last three years. In spite of

    the expected slow down in the global economy the Indian GDP is likely to grow at about 7%.

    To grow at this rate one of the major requirement is to have uninterrupted supply of

    energy. The primary use of energy is for electricity generation followed by fuel for

    transportation. An Indian consumer consumes 512 kg of oil equivalent of energy for power,

    transportation, industrial and domestic application in cities and rural areas.

    The major source of energy is coal and oil other fuel sources contributing to produce

    energy are gas, hydro, nuclear and renewable sources. Government of India has a mission of

    power for all by 2012. Currently 44% of the 200 million Indian house holds do not use

    electricity and 75 million rural households still use kerosene for lighting. This means

    additional energy through grid interactive and distributed sources are required.

    India has about 250 to 300 sunny days in most parts of the country. Annual solar energy

    received approximately 5000 trillion KWh per year and the daily average solar energy

    incident varies from 4.6-6.4 KWh per square meter. Per day, conductive arid condition and

    minimal sun tracking, making it an ideal place for solar energy power plan.

    Solar energy can be harnessed through two routes, namely photovoltaic and solar

    thermal, by direct conversion to electrical energy and heat energy respectively. A variety of

    photo voltaic technology enables the direct conversion of solar radiation into electricity. Avariety of PV systems have been developed for centralized applications like street lights

    home lighting, stand alone PV power plants, building integrated PV systemsetc. solar

    photovoltaic has a potential for grid interactive power plants.

    The presented work reviews the working of PV inverters as a grid interactive plant, their

    advantages and drawbacks plus recent and future trends in PV inverter system.

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    1. PV inverters introductionPV cells were first used to power satellites. Through the middle of the 1990s the most

    common terrestrial PV applications were stand-alone systems located where connection to

    the utility grid was impractical. By the end of the 1990s, PV electrical generation was cost-

    competitive with the marginal cost of central station power when it replaced gas turbine

    peaking in areas with high afternoon irradiance levels. Encouraged by consumer approval, a

    number of utilities have introduced utility-interactive PV systems to supply a portion of their

    total customer demand. Some of these systems have been residential and commercial

    rooftop systems and other systems have been larger ground-mounted systems. PV systems

    are generally classified as utility interactive (grid connected) or stand-alone. Orientation of

    the PV modules for optimal energy collection is an important design consideration, whether

    for a utility interactive system or for a stand-alone system. Best overall energy collection on

    an Annual basis is generally obtained with a south-facing collector having a tilt at an angle

    with the horizontal approximately 90% of the latitude of the site. For optimal winterperformance, a tilt of latitude +15 is best and for optimal summer performance a tilt of

    latitude 15 is best. In some cases, when it is desired to have the PV output track utility

    peaking requirements, a west-facing array may be preferred, since its maximum output will

    occur during summer afternoon utility peaking hours.

    Stand-alone PV systems are used when it is impractical to connect to the utility grid.

    Common standalone systems include PV-powered fans, water pumping systems, portable

    highway signs, and power systems for remote installations, such as cabins, communications

    repeater stations. The PV modules must supply all the energy required unless another form

    of backup power. Stand-alone systems also often incorporate battery storage to run thesystem under low sun or no sun conditions.

    Utility-interactive PV systems are classified by IEEE Standard 929 as small, medium, or

    large (ANSI/IEEE, 1999). Small systems are less than 10 kW, medium systems range from 10

    to 500 kW, and large systems are larger than 500 kW. Each size range requires different

    consideration for the utility interconnect. In addition to being able to offset utility peak

    power, the distributed nature of PV systems also results in the reduction of load on

    transmission and distribution lines. Normally, utility-interactive systems do not incorporate

    any form of energy storage they simply supply power to the grid when they are

    operating. In some instances, however, where grid power may not be as reliable as the usermay desire, battery backup is incorporated to ensure uninterrupted power.

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    2. PV cell typesA solar panel (photovoltaic module or photovoltaic panel) is a packaged interconnected

    assembly of solar cells, also known as photovoltaic cells. The solar panel is used as a

    component in a larger photovoltaic system to offer electricity for commercial and residential

    applications. Because a single solar panel can only produce a limited amount of power,

    many installations contain several panels. This is known as a photovoltaic array. A

    photovoltaic installation typically includes an array of solar panels, an inverter, batteries and

    interconnection wiring. Photovoltaic systems are used for either on- or off-grid applications,

    and for solar panels on spacecraft.

    Solar panels use light energy (photons) from the sun to generate electricity through the

    photovoltaic effect. The structural (load carrying) member of a module can either be the top

    layer (superstrate) or the back layer (substrate). The majority of modules use wafer-based

    crystalline silicon cells or a thin-film cell based on cadmium telluride or silicon. Crystalline

    silicon, which is commonly used in the wafer form in photovoltaic (PV) modules, is derived

    from silicon, a commonly used semi-conductor.

    In order to use the cells in practical applications, they must be:

    connected electrically to one another and to the rest of the system Protected from mechanical damage during manufacture, transport, installation

    and use (in particular against hail impact, wind and snow loads). This is especiallyimportant for wafer-based silicon cells which are brittle.

    Protected from moisture, which corrodes metal contacts and interconnects, (andfor thin-film cells the transparent conductive oxide layer) thus decreasing

    performance and lifetime.

    Most modules are usually rigid, but there are some flexible modules available, based

    on thin-film cells. Electrical connections are made in series to achieve a desired output

    voltage and/or in parallel to provide a desired amount of current source capability.

    3. Grid tie PV inverter designKey terms for a pv inverter

    PV Production Electricity generated by a PV System. May be stated in terms of kW(Point in time power) or kWH (Power produced in a given period of time).

    http://en.wikipedia.org/wiki/Solar_cellhttp://en.wikipedia.org/wiki/Photovoltaic_arrayhttp://en.wikipedia.org/wiki/Inverter_%28electrical%29http://en.wikipedia.org/wiki/Battery_%28electricity%29http://en.wikipedia.org/wiki/Off-gridhttp://en.wikipedia.org/wiki/Solar_panels_on_spacecrafthttp://en.wikipedia.org/wiki/Photonshttp://en.wikipedia.org/wiki/Photovoltaic_effecthttp://en.wikipedia.org/w/index.php?title=Load_carrying&action=edit&redlink=1http://en.wikipedia.org/wiki/Superstratehttp://en.wikipedia.org/wiki/Coatinghttp://en.wikipedia.org/wiki/Waferhttp://en.wikipedia.org/wiki/Crystalline_siliconhttp://en.wikipedia.org/wiki/Thin-film_cellhttp://en.wikipedia.org/wiki/Cadmium_telluridehttp://en.wikipedia.org/wiki/Crystalline_siliconhttp://en.wikipedia.org/wiki/Crystalline_siliconhttp://en.wikipedia.org/wiki/Hailhttp://en.wikipedia.org/wiki/Brittlehttp://en.wikipedia.org/wiki/Thin-film_cellhttp://en.wikipedia.org/w/index.php?title=Transparent_conductive_oxide&action=edit&redlink=1http://en.wikipedia.org/wiki/Layerhttp://en.wikipedia.org/wiki/Series_and_parallel_circuits#Series_circuitshttp://en.wikipedia.org/wiki/Series_and_parallel_circuits#Parallel_circuitshttp://en.wikipedia.org/wiki/Series_and_parallel_circuits#Parallel_circuitshttp://en.wikipedia.org/wiki/Series_and_parallel_circuits#Series_circuitshttp://en.wikipedia.org/wiki/Layerhttp://en.wikipedia.org/w/index.php?title=Transparent_conductive_oxide&action=edit&redlink=1http://en.wikipedia.org/wiki/Thin-film_cellhttp://en.wikipedia.org/wiki/Brittlehttp://en.wikipedia.org/wiki/Hailhttp://en.wikipedia.org/wiki/Crystalline_siliconhttp://en.wikipedia.org/wiki/Crystalline_siliconhttp://en.wikipedia.org/wiki/Cadmium_telluridehttp://en.wikipedia.org/wiki/Thin-film_cellhttp://en.wikipedia.org/wiki/Crystalline_siliconhttp://en.wikipedia.org/wiki/Waferhttp://en.wikipedia.org/wiki/Coatinghttp://en.wikipedia.org/wiki/Superstratehttp://en.wikipedia.org/w/index.php?title=Load_carrying&action=edit&redlink=1http://en.wikipedia.org/wiki/Photovoltaic_effecthttp://en.wikipedia.org/wiki/Photonshttp://en.wikipedia.org/wiki/Solar_panels_on_spacecrafthttp://en.wikipedia.org/wiki/Off-gridhttp://en.wikipedia.org/wiki/Battery_%28electricity%29http://en.wikipedia.org/wiki/Inverter_%28electrical%29http://en.wikipedia.org/wiki/Photovoltaic_arrayhttp://en.wikipedia.org/wiki/Solar_cell
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    PTC Performance Test Conditions. Testing standard for modules that wasdeveloped to more closely represent conditions likely to be found in the field. 1000

    W/M2, 20C Ambient Temp. (AKA PVUSA Test Conditions)

    STC Standard Test Conditions. Laboratory testing standard for modules. 1000W/M

    2

    , 25C Cell Temp. Nameplate Rating of Module or Array. Manufacturersadvertise and sell modules based on this value. (AKA Peak Power Rating)

    Combiner Circuit Termination Equipment that connects multiple PV SourceCircuits, generally in Parallel. Have fuses or breakers for over current protection of

    individual circuits.

    Disconnect Switch. Turns electrical circuit on & off. Inverter Converts DC to AC. Module An individual assembly of PV cells. Often called a panel by unfamiliar

    folks.

    Voc Open Circuit Voltage at STC. Vpeak(Vmpp) Voltage at Maximum Power Point at STC. Isc Short Circuit Current (Amps) at STC. Ipeak(Impp) Amperage at Maximum Power Point at STC. Max Power(Wpeak) Watts at STC. Max DC Short Circuit Current Maximum Array Isc at STC. DC Voltage Range Minimum to Maximum DC Voltage Input for the Inverter to

    operate. Array must be electrically connected to provide voltage in this range.

    Output Power Rated AC output capacity in Watts. AC Voltage Range Minimum to Maximum AC Voltage Input for the Inverter to

    operate. Grid Voltage.

    Efficiency Efficiency of the DC-AC conversion in terms of watts. Ratings are basedon X % of capacity.

    Maximum Input Current Maximum current of the Array at Max Power Point. Max DC Short Circuit Current Maximum Array Isc. BOS Balance of System. Equipment & hardware required to build a PV system

    other than Modules & Inverters.

    AC Disconnect Switch in the AC Circuit. Disconnects AC source from Inverter. Maybe integral or external to Inverter. Multiple AC Disconnects are often required.

    DC Disconnect Switch in the DC Circuit. Disconnects DC source from Inverter. Maybe integral or external to Inverter.

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    Layout of a grid tie PV inverter system

    Above figure shows the basic layout of a grid tie pv inverter system. The main

    components of this system are PV arrays, inverter and other control accessories. First the PV

    arrays convert the solar power in to dc electricity. Then the DC output of PV arrays is given

    to the inverter which converts the DC form into AC. As most of the inverters are based on

    PWM technique their output is not purely sinusoidal. So a filter is connected with the

    inverter to produce purely sinusoidal electricity.

    To utilize the output of this system more efficiently other control systems like

    maximum power point tracker, auto wake up systems and other control accessories are also

    connected with this system which are discussed in detail further.

    Now, let us understand the functions of PV inverter system in detail.

    Inversion function

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    The method by which dc power from the PV array is converted to ac power is known

    as inversion. Other than for use in small off-grid systems and small solar gadgets, using

    straight dc power from a PV array, module or cell is not very practical. Although many things

    in our homes and businesses use dc power, large loads and our electrical power

    infrastructure are based on ac power. This dates back to the early days of Edison versus

    Tesla when ac won out over dc as a means of electrical power distribution. An important

    reason that ac won out is because it can be stepped up and travel long distances with low

    losses and with minimal material. This could change in the distant future if more of our

    energy is produced, stored and consumed by means of dc power. Today, the technology

    exists to boost dc electricity to high voltages for long distance transfer, but it is very complex

    and costly. For the foreseeable future, ac will carry electricity between our power plants,

    cities, homes and businesses. In an inverter, dc power from the PV array is inverted to ac

    power via a set of solid state switchesMOSFETs or IGBTsthat essentially flip the dc

    power back and forth, creating ac power. Diagram shows basic operation in a single-phase

    inverter.

    Filters

    As most of the inverters work on the bases of PWM technique filters are essential

    part of a PV inverter systems. These convert PWM output of an inverter into pure sinusoidal

    output. Filters are also used to filter the noise and spikes from semiconductor components.

    Other filters required in this system are EMI/RFI (electro magnetic interference/ radio

    frequency interference).

    Maximum power point tracking

    Maximum Power Point Tracking, frequently referred to as MPPT, is an electronicsystem that operates the Photovoltaic (PV) modules in a manner that allows the modules to

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    produce all the power they are capable of. MPPT is not a mechanical tracking system that

    physically moves the modules to make them point more directly at the sun. MPPT is a fully

    electronic system that varies the electrical operating point of the modules so that the

    modules are able to deliver maximum available power. Additional power harvested from

    the modules is then made available as increased battery charge current. MPPT can be used

    in conjunction with a mechanical tracking system, but the two systems are completely

    different.

    PV modules have a characteristic I-V curve that includes a short-circuit current value

    (Isc) at 0 Vdc, an open-circuit voltage (Voc) value at 0 A and a knee at the point the MPP is

    foundthe location on the I-V curve where the voltage multiplied by the current yields the

    highest value, the maximum power. Diagram shows the MPP for a module at full sun in a

    variety of temperature conditions. As cell temperature increases, voltage decreases. Module

    performance is also irradiance dependent. When the sun is brighter, module current is

    higher; and when there is less light, module current is lower. Since sunlight intensity and cell

    temperature vary substantially throughout the day and the year, array MPP current andvoltage also move significantly, greatly affecting inverter and system design.

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    The above figure shows the characteristics of current and power versus the terminal

    voltages.

    MPPT shall be fast enough to increase the energy extraction by following the

    isolation level closely but not too fast to cause the instability. Tracking along the left slopeof the power curve is not stable so should be avoided. MPPT shall take the grid voltage into

    account while tracking lower. If DC bus voltage drops too low but grid voltage is higher, the

    quality of the current to the grid will suffer.

    Auto wake-up system

    The PV inverter shall be able to wake up when the available power is more than the

    total loss of the inverter system. Pre-mature wake up will cause negative power flow from

    the grid thus hampers the energy production. Delayed wake up also hampers the energy

    production. Since the available power changes with weather condition, the wake up

    algorithm has to be adaptive in nature.

    Grid disconnection (islanding mode detection)

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    As required by UL 1741 and IEEE 1547, all grid-tied inverters must disconnect from

    the grid if the ac line voltage or frequency goes above or below limits prescribed in the

    standard. The inverter must also shut down if it detects an island, meaning that the grid is

    no longer present. In either case, the inverter may not interconnect and export power until

    the inverter records the proper utility voltage and frequency for a period of 5 minutes.

    These protections eliminate the chance that a PV system will inject voltage or current into

    disconnected utility wires or switchgear and cause a hazard to utility personnel. If an

    inverter remained on or came back on before the utility was reliably reconnected, the PV

    system could back feed a utility transformer. This could create utility pole or medium

    voltage potentials, which could be many thousands of volts. A significant battery of tests is

    performed on every grid-tied inverter to make certain that this situation can never occur.

    The figure shown here represents the islanding operation of an inverter. Upper

    waveform shows the output voltages of inverter and the waveform shown below represents

    the line or grid voltages.

    Scale:

    Vertical- 200V/div.

    Horizontal -100ms/div.

    After 650 ms the inverter shuts down this is in the permissible limits declared by IEEE 1547.

    4. Other protections and controlsGround fault protection

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    For a grounded system, the ground fault occurs when DC terminal of PV array touches

    the chassis. Current flows through the ground to the negative terminal first then goes to the

    positive through the PV cells. The current sensor on the wire between the negative and the

    ground terminal will pick up the fault. Inverters shall shutdown and disconnect itself from

    the grid as well as the PV array as soon as the ground fault is detected. The ground fault

    current shall be interrupted.

    Ac over current detection and protection

    Grid Transients or grid faults can cause over current condition. Fault in transformer

    or line filter can also cause over current condition. Faulty switching devices can cause dead

    short circuit. Over current fault shall shutdown the unit and disconnect from the grid. For

    this purpose proper protective devices must be connected with the system.

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    Single phase open detection

    Loss of any phase of the grid shall be detected and the inverter shall be shutdown to

    avoid possible safety hazard. Loss of a phase can be detected by using current sensors on

    each phase. If the output transformer is external to the inverter, the single phase open shall

    be detected on both sides of the transformer.

    Thermal requirements

    The inverter system and components shall not attain a temperature at any operating

    condition so as to result in risk of overheating, fire, or insulation damage. Junction

    temperature of switching devices shall be maintained below maximum allowed value (e.g.

    120 C). Solar inverters are generally installed outdoor so shall handle extreme temperature

    conditions like40 C to 50 C. Solar power is not generated uniformly through out the day so

    the cooling system does not have to be turned ON all the time. A power output basedcooling system control shall be designed to improve the efficiency.

    Dc bus over voltage and over current protection

    When DC bus exceeds the designed maximum voltage (e.g. 600V), the inverter shall

    shutdown and array shall be disconnected from the DC bus to protect the DC bus

    Capacitors, Disconnects and Wire Insulations. Also, inverter shall be able to identify the

    reverse polarity of the DC connection and warn the installer and remain in sleep state.

    Over current can be caused by too low DC bus voltage, higher AC grid voltagetransient, and enhanced solar condition or due to some hardware failure/short circuit in DC

    bus circuitry or wrong DC bus connection. The inverter shall be shutdown and isolated from

    the grid as well as the PV array when the over current condition occurs.

    5. Monitoring software and meteringTo reliably control the inverter, the software designed to run on the inverters digital

    signal processor or microcontroller is developed over years of code writing and debugging.

    The most critical control is the one driving the power stage. This creates the PWM

    waveforms that generate the sine waves ending up on the utility grid and at the buildings

    loads. Software also controls the inverters interaction with the grid and drives all the

    appropriate UL 1741 and IEEE 1547 required controls and events. Another part of thesoftware controls the MPPT function that varies the dc voltage and current level as required

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    to accurately and quickly follow the moving MPP of the PV array. All of these major

    functions, as well as a multitude of others, are carried out in unison like an orchestra.

    Software is used to drive the contactor that places the inverter on the grid in the morning

    and off the grid at night. Software controls temperature limits and optimizes cooling system

    controls. Software, its development history and robustness, is a critical element in any

    inverter.

    The metering aspect will form part

    of the Connection Agreement. "Net

    metering", where exported units run

    the meter backwards (making the PV-

    generated unit selling price effectively

    the same as the purchase rate for

    utility- supplied electricity), is seen as

    the most attractive option for PV

    system owners and gives quite anattractive rate of return (some

    estimates have shown that this

    method can contribute approximately

    15% of the PV system cost recovery).

    However, for any electricity

    import/export arrangement, a meter

    with two separate metering registers is required. It is not satisfactory to allow the meter to

    simply run backwards for exported units, since this leaves the meter open to fraudulent

    abuse. In any case, the commonly used Ferraris electro-mechanical meter is mechanically

    damped to prevent the meter from rotating backwards. Also, modern electronic meters can

    be programmed to run only in one direction (i.e. only forwards), again to combat meterfraud. A more conventional approach is to use a PV-generated unit selling price equivalent

    to the electricity pool price (approximately1

    /3of the domestic purchase rate). However, the

    cost of the two-way import/export meter becomes a major cost factor for smaller PV

    installations. For smaller systems the value of units exported is likely to be small and so it

    may be beneficial to ensure that as much of the PV output as possible is used within the

    house.

    6. Testing of a PV systemVarious tests on PV systems are performed to check its performance under various

    conditions. Here some of the tests recommended by underwriters laboratory are

    mentioned. The main tests are

    a) Normal safety related tests

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    b) Abnormal safety related testsc) Performance related tests

    In normal safety related tests the dielectricstrength, over current capacity, thermal stress

    capacity, ground fault detection, anti islanding mode

    testsetc are conducted. For the testing of islanding

    mode a dummy load of parallel R-L-C network is

    connected with the pv inverter systems.

    In abnormal safety related tests overload capacity tests, short circuit tests, single

    phase tests; dc reverse polarity tests.etc are conducted. And in performance related tests

    harmonic tests, maximum power point tracking tests and wake-up strategy tests are done.

    7. Future trends

    Future advances in central grid-tied invertersand eventually string inverters as wellwill likely also include some type of utility interaction to support the grid in times of distress.

    This might include the inverter remaining online during a brownout or other voltage events,

    even during frequency events, giving the utility more time to make adjustments or isolate

    circuits to remedy the problem and preventing even larger grid instability or a propagated

    blackout. Currently, if the grid voltage or frequency goes outside of the windows specified in

    IEEE 1547, all grid-tied inverters must go offline, which likely accelerates grid failure. Utility

    control of PV inverters and other discontinuous sources might make it possible to remedy

    some grid problems. Because inverters draw their sine wave current waveforms in many

    increments, the differential control of these increments can help specifically to adjust the

    grid voltage waveform, minimizing or correcting power factor or other problems created bycertain loads in the area. Another area for the advancement of inverters and grid tied

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    renewable energy systems will likely involve energy storage. As a larger portion of our

    power generation capacity comes from discontinuous sources of energy, like PV and wind,

    storage becomes more important. A future component of large commercial PV systems

    might include on-site energy storage with utility control or based on time of use costs for

    electricity. With increasing amounts of PV power processed by DSP-controlled inverters,

    there are many critical functions that inverters can incorporate as the industry progresses.

    As these potentials are realized, PV power will become an increasingly widespread and

    important portion of our energy infrastructure.

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    8. ConclusionWe can conclude that in the rising era of usage of renewable energy sources, solar

    energy is abundantly available energy, so usage of solar as a renewable will increase in

    future. PV inverters are the easiest method to convert solar energy than the other

    methods. The installation of a PV system is easy and it can be installed near the load, so

    negligible transmission losses. Even PV systems can be installed inside the houses so we

    can reduce the electricity bills and if we are connecting these systems to grid then we

    can get compensation in electricity bills.

    The costs of PV cells are higher but they are reducing gradually. Research work in

    various organizations is in progress to increase the efficiency and reduce the cost of PV

    cells.

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    9.AppendixVarious standards

    IEEE 1547 2003 ~ Standard for Interconnecting Distributed Resources with ElectricPower Systems

    IEEE Std. 519 1992 ~ IEEE recommended practices and requirements for harmoniccontrol in electrical power systems

    PV systems

    IEEE 929 2000 ~ Recommended Practice for Utility Interface of Photovoltaic (PV)Systems (Superceded by IEEE 1547)

    IEEE 1374 1998 ~ IEEE guide for terrestrial photovoltaic power system safety US National Electrical Code (NEC) Article 690 ~ Solar Photovoltaic Systems

    Power factor (IEEE 1547-2003)- The PV system should operate at a power factor > 0.85 (lagging or leading) when

    output is > 10% of rating

    - PV inverters designed for utility-interconnected service operate close to unity

    power factor

    NEC Code 690

    - 690.13(A) ~ Disconnect means shall be provided between photovoltaic power system

    output and other building conductors, no disconnect in grounded conductor

    - 690.2 ~ DC operating voltages of 12 volts up to 600 volts, with AC outputs from 120 V

    single phase to 480 V three phase

    - 690.2 ~ Inverters for PV systems in sizes from 100 W to custom designs of up to 1 MW or

    more

    - 690.8 ~ Conductors and overcurrent devices to be sized such that over current devices

    shall not be operated continuously at more than 80%

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    Voltage requirements

    - For normal conditions and the required regulation is +/- 5% on a 120-volt base at the service

    entrance

    Frequency requirements

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    Synchronization( IEEE 1547)

    Ac current harmonics

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    Efficiencies and costs of PV module

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    Solar map of India

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    10. IndexAC over voltage-15

    Auto wake-up-9,12

    DC over current-15

    DC over voltage-15

    Disconnects-8,15

    Filters-10

    Harmonics-22

    Islanding-13,17

    MPPT-11,12,16

    PV inverter-5,6,8,9,10,17,18,19,20

    PV module- 6,12

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    11. ReferencesPapers

    1. Grid inter active solar inverters and their impact on power systems, Dr. Anil Tulafhar2. How Inverters Work,By James Worden and Michael Zuercher-Martinson3. Islanding of grid connected PV inverters-by H. haeberlin andCh. Beutler4. An improved Active Islanding Detection Technology for Grid-connected Solar

    Photovoltaic System by H. T. Yang, P. C. Peng, T. Y. Tsai, and Y. Y. Hong

    5. Scenario of renewable energy potential in india by Sagar N. Patel, Ishan P. Joshi,B.S.Pillai

    Website links

    1. http://www.sandia.gov/pv/docs/Design_and_Installation_of_PV_Systems.htm2. http://photovoltaics.sandia.gov/docs/Design_and_Installation_of_PV_Systems.htm3. http://www.teriin.org/index.php?option=com_content&task=view&id=624. http://www.teriin.org/images/Solar-desalinationMAP.jpg5. http://www.india-reports.com/summary/map-solar.aspx6. http://www.energy.ca.gov/reports/2001-09-04_500-01-020.PDF

    http://www.sandia.gov/pv/docs/Design_and_Installation_of_PV_Systems.htmhttp://photovoltaics.sandia.gov/docs/Design_and_Installation_of_PV_Systems.htmhttp://www.teriin.org/index.php?option=com_content&task=view&id=62http://www.teriin.org/images/Solar-desalinationMAP.jpghttp://www.india-reports.com/summary/map-solar.aspxhttp://www.energy.ca.gov/reports/2001-09-04_500-01-020.PDFhttp://www.energy.ca.gov/reports/2001-09-04_500-01-020.PDFhttp://www.india-reports.com/summary/map-solar.aspxhttp://www.teriin.org/images/Solar-desalinationMAP.jpghttp://www.teriin.org/index.php?option=com_content&task=view&id=62http://photovoltaics.sandia.gov/docs/Design_and_Installation_of_PV_Systems.htmhttp://www.sandia.gov/pv/docs/Design_and_Installation_of_PV_Systems.htm