Distribution Transformers -Impact of Harmonics, Estimation of Losses and Life expectancy & Mitigation of ill effects

Solar Power PlantTechnologiesM. Nageswar Rao, Sr.Mgr.(EMD)

Date: 24.10.2015Venue: EDC, Simhadri

Presentation layoutSolar radiation & resourcesSolar power technologiesGovt. policiesSolar PVSolar Thermal Solar power distribution

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Solar Radiation3

Solar energyThe surface receives about 47% of the total solar energy that reaches the Earth. Only this amount is usable.

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NTPC Solar projectsCommissioned (110 MW)

Under execution (8MW)8 MW hydro energy based project at NTPC-Singrauli in Uttar Pradesh.

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Insolation Insolation is a measure of solar radiation energy received on a given surface area in a given time. It is commonly expressed as average irradiance in watts per square meter (W/m2), orkWh/sq. m/day

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Direct insolationDirect insolation is the solar irradiance measured at a given location on Earth with a surface element perpendicular to the Sun's rays, excluding diffuse insolation (the solar radiation that is scattered or reflected by atmospheric components in the sky). Direct insolation is equal to the solar constant minus the atmospheric losses due to absorption and scattering.While the solar constant varies with the Earth-Sun distance and solar cycles, the losses depend on the time of day (length of light's path through the atmosphere depending on the Solar elevation angle), cloud cover, moisture content, and other impurities. Insolation is a fundamental abiotic factor affecting the metabolism of plants and the behaviour of animals.

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Solar radiationSolar radiation is received as heat and light.Availability of reliable solar radiation data is vital for the success of solar energy installations in different sites of the country. Solar radiation data is available in the form of 8solar radiation data ApplicationGlobal Horizontal Irradiance (GHI)for flat solar collectorsSolar PVDirect Normal Irradiance (DNI)for solar collectors/ concentrators. Solar Thermal

GHIMost parts of India receive good solar radiation 5.5- 6 kWh/sq. m/day

DNIMost parts of India receive good solar radiation 5- 5.5 kWh/sq. m/day

Solar power technologies

Solar power applicationsSolar PVRoof-topSolar farmsSolar thermalPower TowerParabolic TroughParabolic dishGrid connectivityOff-gridOn -grid

Solar power technologiesSolar PVCertain semiconductors when exposed to light produce an electric current. Efficiency of Solar PV systems range from 14% - 36%.Solar thermalHeat from the sun is used to heat large amounts of water which is then used to drive turbines. Efficiency of Solar Thermal system is around 22%. 13

Tilt of panelMaximizing exposure with direct sunlight is achieved byAvoiding shadeExposing the panels to the most direct sunlight for greatest amount of timeTilt and azimuth

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Tilt and azimuthTilt of the arrayis the angle of inclination from horizontal (0 = horizontal, 90 = vertical). installers aim for a tilt equal to the geographic latitude minus 15 degrees in order to achieve yearly maximum output of power. An increased tilt will favor power output in the winter months, which is often desired for solar water heating, and a decreased tilt will favor power output in summer months.The azimuth is the angle clockwise from true north of the direction that the PV array faces (0 or 360 = North, 180 = South). Solar installations in the Northwest should generally be designed with an azimuth within 45 degrees of true south (180) to maximize energy production. Increasing the azimuth angle favors afternoon energy production, while decreasing the azimuth angle favors morning energy production.

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Solar trackerA tracking system is one that moves to track the sun. There are two different axes that can be trackedthe tilt which would change over the course of a year, and the azimuth, which would change over the course of a day. Tracking with either a one or two axis system allows the PV production to stay closer to maximum capacity for many additional hours.Note: All modules wired to one inverter (or all modules sharing a string in the case of a multi-string inverter) should be mounted at the same tilt and azimuth. This is to maintain consistent voltage production throughout the array (or string). If voltage differences occur, energy production from the entire array may be compromised.16

Govt. Policies

JNNSMThe Jawaharlal Nehru National Solar Mission was launched on the 11th January, 2010 by the Prime Minister under National Action Plan on Climate Change. The Mission has set the ambitious target of deploying 20,000 MW of grid connected solar power by 2022 is aimed at reducing the cost of solar power generation in the country through (i) long term policy; (ii) large scale deployment goals; (iii) aggressive R&D; and (iv) domestic production of critical raw materials, components and products, as a result to achieve grid tariff parity by 2022. 18

19JNNSM - 3 phase approachApplication segmentTarget for Phase I (2010-13)Cumulative Target for Phase 2 (2013-17) Cumulative Target for Phase 3 (2017-22)Grid solar power incl. roof top & distribution grid connected plants 1,000 MW100 MW4,000 MW10,000 MW20,000 MWOff-grid solar applications 200 MW

1,000 MW

2,000 MW

Solar collectors 7 million sq meters15 million sq meters 20 million sq meters

JNNSM- RPOThe key driver for promoting solar power is through a Renewable Purchase Obligation (RPO) mandated for power utilities, with a specific solar component. This will drive utility scale power generation, whether solar PV or solar thermal. The Solar Purchase Obligation will be gradually increased while the tariff fixed for solar power purchase will decline over time.As per the National Tariff Policy, it is envisaged that the targets for Solar RPO shall be 0.25% by 2012-13 extending to 3% by 2022

JNNSM- RPOSolar Power Capacity Requirement By 2022

JNNSM- RECAnother mechanism being used by the Government is the REC. Renewable Energy Certificate (REC) mechanism is a market based instrument to promote renewable energy and facilitate the compliance of RPOs. Through RECs, states that do not have sufficient potential for renewable energy can trade with those that have surplus of such resources. One REC is treated as equivalent to 1MWh. RECs are available for solar as well as non solar applications. Revenue for the renewable energy generator can come from the sale of electricity as well as from the sale of environmental attributes in the form of these certificates. The RECs shall be exchanged through Power Exchanges authorised by CERC.The price range shall be within the band of floor price and forbearance price to be determined by CERC from time to time.

JNNSM- RECForbearance Price: It is the highest difference between the CERC tariff and the APPC across states.Floor Price: This is the price to keep the project viable in terms of meeting the O&M expenses, Interests on loan and working capital, principal repayment etc. It is taken as the highest difference between the minimum requirement for project viability and respective state APPC of pervious year.The proposed downward revision is in line with the practices in other countries (say Germany) where the Feed-in-Tariff (FiT) is periodically reduced. It is known as digression and is done to ensure that the subsidy (offered as FiT) follows the falling market prices of the renewable energy systems.

Average Power Purchase Cost (APPC): The APPC for a state represents the weighted average pooled power purchase by distribution licensees (without transmission charges) in the state during the financial year 2011-12.

JNNSM- REC

Solar PV

Solar PV powerRoof-top applicationSolar farms 26

PV module27

Solar array wiring28

How does power produceSunlight is composed of photons, or bundles of radiant energy. When photons strike a PV cell, they may be reflected or absorbed (transmitted through the cell). Only the absorbed photons generate electricity. When the photons are absorbed, the energy of the photons is transferred to electrons in the atoms of the solar cell.Solar cells are usually made of two thin pieces of silicon, the substance that makes up sand and the second most common substance on earth. One piece of silicon has a small amount of boron added to it, which gives it a tendency to attract electrons. It is called the p-layer because of its positive tendency.The other piece of silicon has a small amount of phosphorous added to it, giving it an excess of free electrons. This is called the n-layer because it has a tendency to give up negatively charged electrons.

PV cell typesCrystalline-Silicon Solar PanelsThin-Film Solar Panels

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Crystalline-Silicon Solar PanelsAdvantages stable, efficiencies in the range of 15% to 25%, relies on established process technologies proven to be reliable most common solar cells in use. Disadvantagespoor absorber of light, it needs to be fairly thick and rigid.ConstructionA basic c-Si cell consists of essentially seven layers. A transparent adhesive holds a protective glass cover over the anti-reflective coating that ensures all of the light filters through to the silicon crystalline layers. N layer sandwiches against a P layer and the entire package is held together with two electrical contacts: positive topside and negative below.31

Thin-Film Solar PanelsPotentially cheaper less efficientTypes of thin-film solar cells: amorphous Silicon (a-Si) and Thin-film Silicon (TF-Si); Cadmium Telluride (CdTe); Copper Indium Gallium Deselenide (CIS or CIGS); andDye-sensitized Solar Cell (DSC) plus other organic materials.Constructionconsist of about six layers. a transparent coating covers the antireflective layer. These are followed by the P- and N-type materials, followed by the contact plate and substrate. And, obviously, the operating principle (photovoltaic) is the same as c-Si cells.

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Crystalline vs. thin film33Cell TechnologyCrystalline SiliconThin FilmTypes of TechnologyMono-crystalline silicon (c-Si)Poly-crystalline silicon (pc-Si/ mc-Si)String RibbonAmorphous silicon (a-Si)Cadmium Telluride (CdTe)Copper Indium Gallium Selenide (CIG/ CIGS)Organic photovoltaic (OPV/ DSC/ DYSC)Voltage Rating (Vmp/ Voc)(Higher is better as there is less gap in Voc and Vmp)80%-85%72%-78%Temperature CoefficientsHigherLower(Lower is beneficial at high ambient temperatures)I-V Curve Fill Factor(Idealized PV cell is 100%)73%-82%60%-68%Module constructionWith Anodized AluminumFrameless, sandwiched between glass;lower cost, lower weightModule efficiency13%-19%4%- 12%Inverter Compatibility and SizingLower temperature coefficientis beneficialSystem designer has to considerfactor such as temperature coefficients,Voc-Vmp difference, isolation resistance due to external factorsMounting systemsIndustry standardSpecial clips and structures may be needed. In some cases labor cost is significantly savedDC wiringIndustry standardMay require more number of circuit combiners and fusesApplication TypeResidential/ Commercial/ UtilityCommercial/ UtilityRequired AreaIndustry standardMay require up to %50 more spacefor a given project sizeExample BrandsKyocera, Evergreen, Sanyo,Schuco,Canadian Solar, Sharp,Yingli, ET Solar, Solon, Schott, Conergy, REC, SolarworldFirst Solar, Solyndra, UniSolar, Konarka, Dye Solar, Bosch Solar, Sharp, Abound Solar

I-V characteristics34The usable voltage from solar cells depends on the semiconductor material. In silicon it amounts to approximately 0.5 V. Terminal voltage is only weakly dependent on light radiation, while the current intensity increases with higher luminosity. A 100 cm silicon cell, for example, reaches a maximum current intensity of approximately 2 A when radiated by 1000 W/m.The output (product of electricity and voltage) of a solar cell is temperature dependent.Higher cell temperatures lead to lower output, and hence to lower efficiency. The level of efficiency indicates how much of the radiated quantity of light is converted into useable electrical energy.

I-V characteristics35

P-V characteristics MPPT36

Growth in India PV production 37

Status of PV in India38

2600 MW : 53,00,000 SYSTEMS

Grid solar PV in India 1044 MW capacity new Grid Solar Power projects commissioned by September, 2012 in 16 States.

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PV Capital Cost & CERC Tariff Trends40

Proposed cost target for PV by 2017 PV Module : < Rs. 30 per Wp

BoS : < Rs. 25 per Wp

Cost of Electricity : ~ Rs. 4 - 6 per kWh

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Projection for Grid Parity in India42

Efficiency and disadvantagesEfficiency is far lass than the 77% of solar spectrum with usable wavelengths.43% of photon energy is used to warm the crystal.Efficiency drops as temperature increases (from 24% at 0C to 14% at 100C.)Light is reflected off the front face and internal electrical resistance are other factors.Overall, the efficiency is about 10-14%.Underlying problem is weighing efficiency against cost.Crystalline silicon-more efficient, more expensive to manufactureAmorphous silicon-half as efficient, less expensive to produce.

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Solar Thermal

Reflector/ Collector typesLinear Fresnel reflectors with Linear collector tubes Heliostats with Central receiverParabolic dish with receiverParabolic trough with Linear collector tubes

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Parabolic trough46

Parabolic trough47

Parabolic Trough

Sunlight focused on heat transfer fluid (HTF), which then runs steam turbine

48See http://www.powerfromthesun.net/chapter1/Chapter1.htmImage taken from http://www.trec-uk.org.uk/images/schott_parabolic_trough.jpgDiagram taken from http://www1.eere.energy.gov/solar/csp.html

Parabolic Trough power plant49

Parabolic Trough power plantAll the collectors track the path of the sun on their longitudinal axes. The mirrors concentrate the sunlight more than 80 times on a metal absorber pipe in the line of focus. This pipe is embedded in an evacuated glass tube to reduce heat loss. A selective coating on the absorber tube surface lowers emission losses. Either water or a special thermal oil, runs through the absorber tube. The concentrated sunlight heats it up to nearly 400 C, evaporating water into steam that drives a turbine and an electrical generator. After passing through the turbine, the steam condenses back into water that is returned to the cycle .

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Parabolic Trough power plantA fossil burner can drive the water-steam cycle during periods of bad weather or at night. In contrast to photovoltaic systems, solar thermal power plants can guarantee capacity. This option increases its attractiveness and the quality of planning distribution over the grid. Thermal storage can complement or replace the fossil burner so that the power plant can be run with neutral carbon dioxide emissions. In this case, heat from storage drives the cycle when there is no direct sunlight. Biomass or hydrogen could also be used in the parallel burner to run the power plant without carbon dioxide emissions.

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Power tower52

Power towerA solar thermal plant consists of mirror reflectors called heliostatsProduces electricity by reflecting sunlight on to the central receiver.

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HeliostatsThey direct and concentrate the solar radiation onto a central receiver.Many parameters must be optimized, in the design of a solar thermal plant The parameters areLocationShading andBlocking

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Shading & blockingShading occurs when a heliostat casts its shadow on another heliostat located behind itBlocking occurs when a heliostat in front of another heliostat, blocks the reflected suns energy on its way to the receiver.55

Power towerGeneral idea is to collect the light from many reflectors spread over a large area at one central point to achieve high temperature.Example is the 10-MW solar power plant in Barstow, CA. 1900 heliostats, each 20 ft by 20 fta central 295 ft towerAn energy storage system allows it to generate 7 MW of electric power without sunlight. Capital cost is greater than coal fired power plant, despite the no cost for fuel, ash disposal, and stack emissions.Capital costs are expected to decline as more and more power towers are built with greater technological advances.One way to reduce cost is to use the waste steam from the turbine for space heating or other industrial processes.

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Power tower power plant57

Power tower in Barstow, California.

Power tower power plantThe solar field of a central receiver system, or power tower, is made up of several hundred or even a thousand heliostats, placed around a receiver at the top of a central tower.A computer controls each of these two-axis tracking heliostats with a tracking error of less than a fraction of a degree to ensure that the reflected sunlight focuses directly on the tower receiver, where an absorber is heated up to temperatures of about 1000 C by the concentrated sunlight. Air or molten salt transports the heat and a gas or steam turbine drives an electrical generator that transforms the heat into electricity.

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Parabolic dish59

Parabolic dishBecause they work best under direct sunlight, parabolic dishes and troughs must be steered throughout the day in the direction of the sun.

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Solar Power distribution

Off-grid/ On-grid PV

Solar Generated Electricity Distribution ApproachesCentralized (CSP)Distributed (PV Roof Installations)

CentralizedAdvantagesTraditional model of distributionNo fuel costsDisadvantagesNon-Constant PowerVulnerability

This PV Array is part of the Sacramento Municipal Utility District, generating 3.2 MW, enough for 2,200 homes.

See http://www.smud.org/news/multimedia.htmlImage taken from http://www.smud.org/news/media%20gallery/otherimages/PV_anniv.jpg

Distributed Solar (PV)AdvantagesNet-meteringGrid StorageFlexibilityReduced vulnerability to terrorist attackAlmost no maintenanceNegligible environmental impactDomestic Production (?)DisadvantagesCostExtensive Individual InvestmentLow Conversion EfficiencyCCRsIntermittency

http://www.iea-pvps.org/pv/index.htmhttp://www1.eere.energy.gov/solar/pv_important.html

Roof top grid connectedThe cost of setting up a 5-KW unit is around Rs 7.5 lakh and requires 2,000 sq feet of roof space.After signing a Power Purchase Agreement with the discoms, the house owner will pay Rs 3 lakh, on which he will get returns of close to Rs 60,000 per annum.

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Net-MeteringPeak generation from PV occurs during the dayNet-metering allows users to bank electricity they generate, and credit it against the electricity they useMost states wont pay users if they generate more electricity than they use, but they can zero-out their accountsAs of 2007, net-metering is offered to some degree in 41 states and D.C.California, New York, TexasNet-metering is offered in Illinois by one or more individual utilitiesEPAct of 2005 requires all states to offer net-metering by 2008

See P.Denholm and R. Margolis, Very Large Scale-Scale Deployment of Grid-Connected Solar Photovoltaics in the United States: Challenges and Opportunities, Conference Paper (April 2006), published by National Renewable Energy LaboratorySee http://www.eere.energy.gov/greenpower/markets/netmetering.shtmlhttp://www.dsireusa.org/documents/SummaryMaps/NetMetering_Map.ppthttp://www.eere.energy.gov/states/alternatives/net_metering.cfm

Grid-Connected PV

Graphs taken from P.Denholm and R. Margolis, Very Large Scale-Scale Deployment of Grid-Connected Solar Photovoltaics in the United States: Challenges and Opportunities, Conference Paper (April 2006), published by National Renewable Energy Laboratory

String inverter69

Central inverters70

Thank you all71

Chart11718.4416.917.9114.4215.391010.39

CAPEX Cr/MWTariff Rs/kWh

Sheet1CAPEX Cr/MWTariff Rs/kWh2009-101718.442010-1116.917.912011-1214.4215.392012-131010.39

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CAPEX Cr/MWTariff Rs/kWh

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