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Photovoltaic Training - Session 1 - Design

• Solar resource assessment
• Determination of profitability of a PV plant
• Selection and optimization of the site.
• Selection of components (Inverters, Modules, Protection and Wiring, Grounding, Transformers, Metering, Grid Connection)
• Advanced calculations : Estimated losses; Shading study, etc
• Electrical diagrams

  • Inicia sesión para ver los comentarios

Photovoltaic Training - Session 1 - Design

  1. 1. Photovoltaic Systems Training Session 1 ‐ Design Javier Relancio & Luis Recuero Generalia Group September 14th 2010 construction-operation-and-maintenance
  2. 2. PHOTOVOLTAIC SYSTEM Design, Execution, Operation & Maintenance FACILITY DESIGN Javier Relancio. Generalia Group.  14/09/2010 2
  3. 3. INDEX Evaluation of the solar resource Increasing the plant profitability from the design Choosing the components Photovoltaic facilities calculations Single-line diagram 3
  4. 4. INDEX Evaluation of the solar resource Increasing the profitability of the plant from the design Choosing the components Photovoltaic facilities calculations Single-line diagram 4
  5. 5. Solar resource evaluation Characteristics of the solar resource: random and variable Great quantity and quality of measurement stations, both the global radiation and its components: direct and diffuse These stations are insufficient to allow the evaluation of any geographical location or with changeable topography. The usage of Geostationary satellites images are a tool that can cover this gap They are more reliable than the interpolation of the data from closer meteorological stations 5
  6. 6. Solar resource evaluation: Solar Radiation maps Each day, we can find new maps, which have less uncertain measures They allow a first approach to the viability study for a solar plant location They can be considered enough for small solar facilities Source: NASA But, to get a completely certain measure, a rigorous solar radiation evaluation must be done in situ. Then, we could additionally compare them with the satellite information and the closer meteorological stations 6
  7. 7. INDEX Evaluation of the solar resource Increasing the plant profitability from the design Choosing the components Photovoltaic facilities calculations Single-line diagram 7
  8. 8. Towards the profitability of the plant from the design Resource evaluation System losses (PR) • Latitude • Shadows • Longitude • Disconnections & Breakdowns • Altitude • Panel tolerance • Data from closest • Pollution, dispersion & reflectance meteorological stations • Temperature • Data from satellites • Inverter • Cables OPTIMUM  PROFITABILITY 8
  9. 9. INDEX Evaluation of the solar resource Increasing the plant profitability from the design Choosing the components Photovoltaic facilities calculations Single-line diagram 9
  10. 10. Inverters: Trends The inverter can be considered as the heart of a solar facility Its cost, in relation to the complete installation, is between 6% - 9% Its performance is already between 95 %-97 % It is important to know about their operation principles. We can find 3 options: MULTI CONTROLLED MULTI POWER STAGES ONE POWER STAGE POWER STAGES The electrical companies can ask for galvanic isolation transformers when the connection is in low voltage 10
  11. 11. Inverters: features The inverter main features are: Maximum Input Voltage:  The PV generator voltage must be under the  inverter maximum input voltage MPPT Voltage:  It is the range where the inverter is able to get  the Maximum Power Point from the PV  generator I‐V profile. The PV generator voltage must be within this  range in the different conditions and weather  during the whole year. Source: SolarMax 11
  12. 12. Inverters: Features Other important parameters are: • Inverter efficiency: • As it is shown in the graphic, the inverter has a different efficiency depending on the load. Usually,  the manufacturers give the maximum efficiency and the european efficiency, which is the weighting  of the different efficiencies when the load is: 5%, 10%, 30%...100% • Inverter temperature range: • This is really important, as in some places the temperature can reach over 40º, and extra cooling  might be considered 12
  13. 13. Crystalline or Thin-film Panels Visual identification: Mono crystalline Poli crystalline Thin film A‐Si:H Source: Atersa Thin film panel observations: They are cheaper, but they need larger surfaces & structures The guaranteed output power is not as precise as in Mono/Poli crystalline modules There are no references from facilities producing an important amount of years 13
  14. 14. Crystalline or Thin film modules CRYSTALLINE PANEL PRICE* TEMPERATURE EFFICIENCY REQUIRED INFLUENCE SURFACE Mono crystalline Poli crystalline THIN FILM PANEL CGIS (Copper‐Gallium‐Indium  Selenide) CIS (Copper‐Indium Selenide) CdTe (Cadmium telluride) A‐Si:H triple (Amorphous silicon  triple union) A‐Si:H tandem (Amorphous silicon  double union) A‐Si:H single (Amorphous silicon) * This information can be altered depending on each manufacturer price policy 14
  15. 15. PV Module Specs The most important electrical spec is the panel efficiency The highest the efficiency is, we will require a smaller  surface to reach a certain output power Voltage and current parameters are not determinant, as we  can connect the panels in series or in parallels to fit the  inverter input. Source: Atersa 15
  16. 16. PV Module Specs The losses due to temperature affect the production  specially in countries with latitudes between 0 – 35º Among panels with the same technology: the  thermal coefficient is quite similar among the  different manufacturers & models Source: Atersa Among panels with different technologies: we can find big differences, as we can see in the technical  information below.  A: Si Polycrystalline Source: QS Solar 16
  17. 17. Concentration Panel Concentration technology is still being developed Fresnel Lens (and other kinds) Refractive optical system Concentration up to 500x Potential cost savings Source: Everphoton Improvement in cell efficiency: from actual 30% towards 40% Increasing the concentration: from actual 500x towards 1000x Hardest challenges Extremely accurate suntracking (Accuracy < 0.1 - 0.2º): High costs Optical elements degradation Cooling systems are required 17
  18. 18. Protections The protections to be installed are: DC side AC side DC AC AC DC Miniature Circuit  Miniature Circuit  Fuses Differential Breaker (MCB) Breaker (MCB) Example: ABB S800PV (Specifications) S800PV-S High Performance MCB Versions: 2P, 3P & 4P Current: Up to 80 A Voltage: 800 Vdc with 2P & 1200Vcc with 3P & 4P S800PV-M Switch-Disconnector Versions: 2P, 3P & 4P Source: ABB Current: Up to 125 A Voltage: 800Vcc with 2P & 1200Vcc with 3P & 4P 18
  19. 19. Overvoltage protections To protect the installation against overvoltage we must  install high energy varistors close to the element that we  want to protect The main aim of this device is to detect an overvoltage  within a certain period of time and then divert it to the  ground The device may be destroyed depending on the power to  be diverted to the ground Type 150 275 320 385 According to standard IEC – 61643 – 1  Maximum voltage (AC/DC) Uc(L‐N/N‐PE) 150/200V 275/350V 320/420V 385/500V Nominal discharge current (8/20) In (L‐N/N‐PE) 20/20 kA Maximum discharge current (8/20) Imax(L‐N/N‐PE) 40/40 kA Protection Level Up (L‐N) < 0.9 kV < 1.5 kV < 1.5 kV < 1.9 kV Up (N‐PE) < 2 kV Tracking current If (L‐N/N‐PE) > 100 A RMS 19 Response time tA (L‐N/N‐PE) < 25 ns / 100 ns
  20. 20. Cables Cable Requirements for PV facilities The facility has a lifetime of over 25 years From solar panel to inverter: weatherproof for outdoor conditions and suitable for indoor conditions (in houses or industries) From inverters to meters: direct burial or inside cable ducts If medium-voltage is required, it might be suitable: For underground installation (inside cable ducts) For aerial installation Source: TopCable 20
  21. 21. Cables It is recommended to use*: Specific PV usage cable RZ Cable Main features: Conductor: electrolytic copper Insulation: halogen free Cover: fireproof; low emissions (corrosive gas & toxic smokes) in case of fire To avoid health damages and device damages Obligatory in public locations A comparative table can be found in next slides Source: TopCable 21 * Based in previous slide considerations
  22. 22. Cable FV CABLE FV 22
  23. 23. Cable RZ CABLE RZ 23
  24. 24. Earthing System Typical elements (used in every electrical installation): Earth peg: different sizes depending on the required depth (from 1,5 to 2,5 meters) Cable: copper without cover >35mm2. Depending on the installation: Low-power installations: it would be enough to use several earth pegs connected by a copper cable (without cover) High-power installations: a copper cable grid is usually used (without cover). Depending on the physical measures, earth pegs can be also used. 24
  25. 25. Transformation stations Required elements for a Medium-voltage installation: Transformer: With the same power as the PV inverter output. With the following features: Mineral oil bath Accessible neutral (in low-voltage) Natural cooling Three-phase voltage reduction: MV - LV Medium-voltage cells: We can find different types, such as: Measurement cell Automatic switch cell They can be remotely controlled Depending on each connection requirement, the company might define the devices, and the cost may vary drastically. 25
  26. 26. Metering Device The meter must be certified in the country where it will be used Typical specifications to meet are: Class 1.0 ( Class B) Bidirectional Optical & RS 485 outputs Depending on the installed power the meter can be directly connected or coil inductors are to be used. Source: Circutor The most usual cases are: The grid connected PV facility exports all the generated electricity towards the grid, except the consumption of its own devices: Inverters, Monitoring & communications devices, Auxiliary services, Suntracking devices The grid connected PV facility uses the network as a battery. This type is known as “Net metering” 26
  27. 27. Grid connection point In order to avoid shadowing, MV cable will be buried underground Usual voltage will be between 15 kV – 30 kV (Although it can be a different one depending on each country) An underground to aerial link will be done, to connect with the power line of the electric company Main features for the copper cable Density g/cm3 8,89 Resistivity Ohm – mm2/km 17.241 Conductivity (%IACS) 100.0 Breaking strength Mpa 220 Elongation % 25 – 30 Corrosion resistance Excellent MT PV Facility Source: Centelsa 27
  28. 28. Grid connection point The MV cable requires a reinforcement to guarantee that the electrical distribution is homogeneous. This reinforcement is done in three layers (triple extrusion): • Conductor reinforcement • Insulation • Insulation reinforcement The cable requires also an external cover to provide resistance to: • Humidity • Fire • UV sunlight Source: Centelsa • Impact • Chemicals agents 28
  29. 29. INDEX Evaluation of the solar resource Increasing the plant profitability from the design Choosing the components Photovoltaic facilities calculations Single-line diagram 29
  30. 30. Towards the PR (Performance Ratio) definition Electric Energy (Wh) System Losses PR = 0,74 - 0.78 Radiation (Wh/m2) Considerations: 1. The values considered in the following slides are estimated values and should only be used as an approach. They may vary depending on each location. 2. A detailed Performance Ratio study is fundamental to evaluate the profitability of each solar facility 30
  31. 31. System Losses evaluation 100% 1. Temperature. (9%) +10ºC 4% received energy 91% 2. Inverter. We can consider about 6%. New inverters can reach 4% 87,4% 3. Cable: AC, DC & other electric devices: < 2% 85,6% 4. Panel tolerance. It shouldn’t be higher than 3% 83% 5. Pollution, dispersion & reflectance. 1. Fixed panel: aprox.3% 2. Suntracking system: 2%. 80,6% In urban areas, it should de increased by 2% 6. Shadowing. They should be below 4%. In case of using suntracking 77,3% systems, a shadowing study might be necessary. 7. Other losses (incidences, etc). 1. Fixed panel: 2% 75,8% 2. Suntracking system: 4%. 31
  32. 32. Keys to optimize the PR Choose cool locations, as elevated areas Select inverters with high efficiency and Maximum Power Point Tracking (MPPT) Consider extra cable sizing avoiding long traces with voltage drops Choose solar panels with tolerances between +/- 2-3% Cleaning the modules in long periods without rain Balance the separation between panel rows (to avoid shadowing) with the optimization of the surface area Minimize the impact of breakdowns, with a preventive maintenance. 32
  33. 33. Shadowing evaluation Depending on the type of installation, the shadowing study and the surface optimization, the project profitability may vary. The main aspect to study are: Azimuthal deviation from the south (North hemisphere) or north (South hemisphere) Tilt of the solar panel Shadows of extern elements Shadows of own elements FIX - GROUND SUNTRACKING-GROUND FIX - ROOF INTEGRATION 33
  34. 34. Fix - Ground 1. Distance between panel rows A basic rule would be to avoid shadows during the 4 central hours of the day, in the day of the year with less radiation. This implies calculating the angle of the sun (height regarding the line of the horizon) to +/-2 hours regarding the solar midday. This angle will vary depending on the latitude The objective is to avoid that the top of the front panel projects a shadow to the lowest part of the panel that is placed behind. d= h / k Latitude 29° 37° 39° 41° 43° 45° 34 k 1,600 2,246 2,475 2,747 3,078 3,487
  35. 35. Fix - Ground 2. Tilt angles The optimum tilt angle of the solar panel can be expressed by the following simplified formula: Tilt = Latitude – 10º In Spain, tilt angles from 30 to 33º is considered as optimum, but tilt angles between 20 – 40º don’t mean considerable system losses Tilt angles below 15º in urban areas may cause system losses due to pollution and dirt accumulation on the panels. Local land slope will be logically taken into account, which can help reducing distance between the panel rows to improve the surface profit. (Obviously, the opposite effect can happen) 35
  36. 36. Fix - Ground 3. Orientation angle The most favorable orientation is 0º South (North hemisphere). An orientation deviation below 20º (East or West) cause negligible system losses. The following graph (which is valid for a 40º latitude) shows how additional losses may appear depending on the combination of orientation and tilt angle. 36
  37. 37. Suntracking - ground …Placement optimization A practical example: Solar Plant in Valdecarabanos (Spain) 37
  38. 38. Suntracking - ground …Location optimization Previous tasks: Environmental conditions Urban conditions Topography External elements shadowing study (trees, electrical posts, etc) Own elements shadowing study: direct & crossed (in suntracking cases) Definition of the distance between suntrackers (or panel rows) 38
  39. 39. Suntracking - ground …Location optimization. Shadowing study 39
  40. 40. Fix - Roofs As grid connected solar facilities are considered as an investment, we have to choose between the following cases: To place the solar panels at the optimum tilt and orientation angle. To adapt the solar panels to the roof shape OPTIMUM ANGLE & ORIENTATION We should take into account: Impact of angle orientation. Impact of tilt angle. Impact of shadows Comparison between adapted VS optimum Roof geometrical limits ROOF ADDAPTED Remarks: be careful with panels from the same “row” in different planes 40
  41. 41. Architectural integration Two possibilities: To avoid visual impact, adapting the solar panels to the roof shape To integrate the panel as a constructive element with a certain function: Electricity generation Sunshade effect: special panels which allow some sunlight to go through Innovative design: usually special structures are required, and this may increase the installation costs In architectural integration, the solar facility is not considered as just an profitable investment, but also as an image and design element 41
  42. 42. Annual production We will consider that the radiation, in the south of Madrid (Spain), for a certain year can be around 4.77 kW-h/m2 (Average) 42
  43. 43. Annual production Production by kWp (installed) Hmed − day × PR × finc × days / year × Pinst Eannual / kWp = ISTC (4.7 kW-h/ m2 –day x 0.74 x 1.15 x 365 day x 1 kW) / 1 kW/m2 Hmed-day Average solar radiation per day PR Performance ratio for the solar installation. Dimensionless F inc Tilt coefficient: a ratio normally obtained from the optimum tilt for a fixed panel (Which optimizes its performance). In Spain (Latitude = 40º) it is 1.15 Pinst Installed solar power ISTC Average irradiance in the horizontal plane Expected production for this horizontal radiation, with a PR = 0.74, would be: 1460 kW-h 43
  44. 44. System configuration Once the modules and inverters are selected, the configuration of the system allows to maximize the produced energy It is possible that in some cases we should consider the use of a different module or inverter in order to improve the system performance. The configuration of the systems takes into account: Maximum input voltage of the inverter Maximum input current of the inverter Voltage and current at Maximum Power Point When designing the solar panel configuration in series and parallels, we must take into account that the voltage and current of the branch will change depending on the temperature. Therefore it will be necessary to choose extreme values of the region for the calculation. 44
  45. 45. System configuration A configuration example of a designing software for Solar Plants (PVSYS screen shot ) 45 Source: PVsyst
  46. 46. Electrical calculation It is very important to take into account: Maximum current in the cables Maximum allowed voltage drop. If there is a long distance the main factor to determine the cable section will be the voltage drop. If there is a very short distance the current that flows along the cable will determine the section of the cable Tramo Seccion estandar (mm2) Sección calc. (mm2) Imax_admisible ∆V max (%) ∆V max (V) V nom (V) Conduct. Inom (A) Long. Wp inst (kWp) Seccion (mm2) 100% 70% 30% 100% 70% 30% ZA01 93 541 72 50 22 133 93 40 35 1,0 5,4 131 92 39 97 150 338 ZA02 97 541 72 50 22 133 93 40 35 1,0 5,4 136 95 41 101 150 338 ZA03 115 541 72 50 22 133 93 40 35 1,0 5,4 162 113 48 120 150 338 ZA04 133 541 38 27 12 71 50 21 35 1,0 5,4 100 70 30 74 95 245 46
  47. 47. Electrical design In order to do a simplified earthing calculation, we can start with the following formulas depending on the soil resistivity and the electrode characteristics Electrode Soil resistivity (Ohm) Buried plate R = 0,8 ρ/P ρ, soil resistivity (Ohm x m) Vertical peg R = ρ/L P, Plate perimeter (m) Buried conductor R = 2 ρ/L L, Peg or conductor length (m) The average values of the resistivity, depending on the type of soil are: Type of Soil Soil resistivity (Ohm) Cultivable and fertile soils, compact and wet soils 50 Cultivable non fertile soil, or other soils 500 Naked rock soils, and dried and permeable soils 3.000 47
  48. 48. Electrical calculations The cable sizing is based on the following formulas: • Considering: •Three Phases • P = Power • L = Cable length • γ = Cable conductivity •One Phase • E = Allowed voltage drop • U= Line voltage • For example, for LV in Europe: • 400V in Three-phase • 230V in One-phase TABLE OF CONDUCTIVITY DEPENDING ON THE TEMPERATURE Material γ 20 γ 70 γ 90 Copper 56 48 44 Aluminium 35 30 28 Temperature 20 ºC 70 ºC 90ºC 48
  49. 49. Over Voltage A lightning may produce a transitory overvoltage of short duration, with a huge amplitude. TRANSITORY OVERVOLTAGE The overvoltage produced due to network unbalances is a permanent overvoltage, with a longer duration and a lower amplitude. In order to protect our installation against overvoltage, electrical dischargers can be connected at the input and output of each device to be protected. PERMANENT OVERVOLTAGE There are three different protection levels: High Middle Low DEVICE PROTECTION LEVEL INVERTER METER Source: Cirprotect CC CABINET 49
  50. 50. Transformers connection topology In installations where more than one Medium Voltage transformer is required, it is important to define the correct topology for the connection between all the MV transformers and the main grid (Power line). The possible connections options are: STAR RING PRODUCTION  LOSSES CABLE BREAK DOWN NO PRODUCTION  LOSSES 50
  51. 51. INDEX Evaluation of the solar resource Increasing the plant profitability from the design Choosing the components Photovoltaic facilities calculations Single-Line diagram 51
  53. 53. End of Session 1 Thank you for attending construction-operation-and-maintenance 53