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Building integrated PV - technical issues - part 1
 

Building integrated PV - technical issues - part 1

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Building integrated PV - technilacl issue. Part 1 ...

Building integrated PV - technilacl issue. Part 1
The presentation gives a short overview of the technical issues to be considered in designing a building integrated PV system.
Brief overview of photovoltaic materials and modules is given.

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    Building integrated PV - technical issues - part 1 Building integrated PV - technical issues - part 1 Presentation Transcript

    • BUILDING INTEGRATED PVTECHNICAL ISSUES http://www.solar-tec.comwwwenbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES The presentation gives a short overview of the technical issues to be considered in designing a building integrated PV system. Brief overview of photovoltaic materials and modules is given.www.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES Photovoltaic modules There are a wide variety of modules. Photovoltaic modules should not be confused with solar thermal panels (used to heat water or air for water and space heating).www.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES PV module construction The photovoltaic module has a sandwich structure. As a standard there is a glass sheet over the crystalline silicon PV cells embedded in a resin. At the back there is a tedlar backing sheet. Other materials in use: • Front sheets can be glass or other plastics for flexibility or impact resistance. • The PV cells can be made from a variety of semi-conductor materials • The backing sheets can be glass to provide a partially transparent module, as well as metal or plastic. www.eco-manager.comwww.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES PV module terminology Photovoltaic cell is the basic block used to make a module. The array is made up from the required number of modules. cell modules (panels) arraywww.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES Semiconductor materials - crystalline Modules are either crystalline or thin film. The most of the PV modules are made of silicon. Other semiconductors can also be used e.g. gallium arsenide which offers higher efficiency at higher costs is used for space applications. Crystalline modules use cells made from a crystalline semiconductor. Normally a large silicon crystal is manufactured and then is cut into slices to make cells. • Monocrystalline silicon, slices of a single crystal. Efficiency 12-15% • Polycrystalline silicon, slices of a ingot of crystals of silicon. Efficiency 11- 14% Monocrystalline silicon cells and moduleswww.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES Semiconductor materials - thin film Thin film modules are made of layers of semiconductor material deposited in thin layers on glass, stainless steel or plastic. They are cheaper than the monocrystalline silicon cells because less semiconductor material is required and more suitable for automated production methods however they are also less efficient. The most common material is amorphous silicon. The same material normally is used in watches, calculators, etc. but it can also be used for larger modules. Efficiency varies between 5% and 7%. Thin film modules made with cadmium telluride (CdTe) and copper indium diselenide (CIGS). amorphous silicon moduleswww.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES Design The main issues in design of a building integrated PV system: • What size of system is required? • Where on the building it could be installed? • What type of modules would be appropriate? • How to maximize the energy production of the system? • How to fix the system on the building? • The electrical design of the PV system. All these issues need to be considered to come up with the most suitable design for a building integrated PV system.www.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES Where to install the modules? How much space is needed? The first important thing is the approximate size of the PV system required, i.e. the scale of the system, and the possible areas on the building where it could be installed. Things to be known: • The maximum available surface on the roof, facade or other areas suitable for installing of a PV system; • The amount of energy required from the system; • The funding of the system (some funding programs have minimum sizes of system for funding which may dictate the minimum system size); • The visibility of the PV system – desired or not.www.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES Suitable areas • Almost any type of building surface - roof, facade, sunshades or atriums and etc. • The surface must be with an appropriate orientation and tilt to receive as much sunshine as possible and be strong enough to bear the weight of the PV modules. • The surface area must be available to provide the required power output. Average area required to install 1 kWp of PV modules: • 8 m2 - for monocrystalline silicon • 10 m2 - for polycrystalline silicon • 20 m2 - for amorphous siliconwww.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES Energy production To analyse in advanced the energy production from a PV system multiply: (irradiance on the array plane) x (size of system in kWp) x (performance ratio)www.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES Outline design Base on the issues mentioned above a designer can define an outline design of the PV system, with a choice on: • the type of modules required, • the size of the system required and the place on the building where to be installed. Ex a m p le : O ne build ing o wne r m a y ha ve a la rg e a re a a va ila ble a nd m a y wis h to p ro d uc e the m a x im um p o s s ible a m o unt o f re ne wa ble e le c tric ity p ro d uc tio n but to be unc o nc e rne d a bo ut the vis ibility o f the s y s te m . A the r build ing o wne r m a y wis h to g e ne ra te re ne wa ble e le c tric ity a nd no to m a ke a vis ible s ta te m e nt o f his e nviro nm e nta l c o m m itm e nt. I this n c a s e a fa c a d e s y s te m m a y be m o re s uita ble a nd m a y re q uire c us to m m a d e s e m i-tra ns p a re nt m o d ule s .www.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES Maximum energy production Maximum energy production from a PV system maximizes the cost effectiveness of the installation and the amount of the conventional energy displaced and hence CO2 emissions avoided. • Orientation and tilt of the PV array reflect to the amount of solar energy collection and respectively to the total annual amount of electricity production; • Minimize the shade on the modules. If some shade cannot be avoided the good electrical design can minimize their effect on the energy output of the system; • Allow ventilation behind the modules so that they don’t get too hot. Module efficiency drops with increases in temperature.www.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES Optimal orientation and tilt The orientation and tilt of the modules reflect to the total amount of solar radiation received and therefore to the amount of total annual electricity production. In the northern hemisphere the best orientation is south. In the southern hemisphere the best orientation is north. The optimal tilt angle (deviation from the horizontal) is derived from the degree of latitude of the building location. If it’s considered the direct solar radiation only the optimal tilt angle for maximum energy production over the year would be equal to the latitude of the location. In many locations, a major part of the incident irradiation comes as diffuse radiation from other directions than the sun. This moves the optimal tilt angle towards the horizontal so that the modules “see” more of the sky.www.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES Optimal orientation and tilt To optimize energy production in winter time can be used a steeper tilt angle. To optimize energy production in the summer time can be used a shallower tilt angle. The optimal orientation dependent on local weather conditions and topography. i. e . m o rning fo g c o m m o n o rie nta tio n is s lig htly we s t o f s o uth. I f the re is a la rg e m o unta in, o r ta ll build ing e a s t o f the s ite the o p tim a l o rie nta tio n o f the PV m o d ule s is g o o d to be s lig htly we s t o f s o uth.www.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES Acceptable orientation and tilt Often is not possible to positioned the PV modules at the optimum orientation and tilt. The range of orientations and tilts that provide acceptable levels of solar energy capture are presented of the diagrame bellow. The diagram illustrates the percentage of the optimum energy capture that can be expected for a range of orientations and tilts. www.eco-manager.com solar radiation and building orientation in Europewww.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES Shading Shading on the array occure a great difference to the annual amount of energy production. Due to the electrical characteristics of PV modules even a small amount of shade can cause a disproportionally large effect. The shading reduces the output of the shaded cells. The shaded cells show an increased resistance to the flow of electric current which reduces the flow of electric current through all the cells joined to that module. If some shade cannot be avoided it effects can be minimized by good electrical design. It is worthwhile designing so as to avoid even small areas of shade such as that cast by vent pipes or chimneys.www.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES Shading Po s s ible c a us e s o f s ha d ing to be c o ns id e re d a nd a v o id e d . A) Shading influence due to other buildings www.eco-manager.comwww.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES Shading Po s s ible c a us e s o f s ha d ing to be c o ns id e re d a nd a v o id e d . B) Shading influence due to roof obstacles www.eco-manager.comwww.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES Shading Po s s ible c a us e s o f s ha d ing to be c o ns id e re d a nd a v o id e d . B) Shading influence due to roof obstacles www.eco-manager.comwww.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES Shading Po s s ible c a us e s o f s ha d ing to be c o ns id e re d a nd a v o id e d . C) Shading influence due to trees www.eco-manager.comwww.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES Shading Po s s ible c a us e s o f s ha d ing to be c o ns id e re d a nd a v o id e d . D) Shading influence due to windows www.eco-manager.comwww.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES Ventilation The efficiency of PV cells decreases with temperature increases. For crystalline silicon cells the efficiency decrease is almost linearly by 0.4% for every degree rise in temperature. For amorphous silicon cells the effect is less depending on the specific production process. High module temperatures could cause problems for the roof materials. Two types of the most offten problems: • the roof material could melt • the difference in the coefficient of expansion between the PV and the roof might induce stress that causes tears, leaking or breaking of the PV laminate. www.eco-manager.comwww.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES PV efficiency and temperature www.eco-manager.comwww.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES Ventilation The temperature of the PV modules depends on how well they can dissipate the heat. If the PV is insulated at the rear side, it can occure only lose heat at the front side. If an air gap is provided at the rear of the module it allows a convective air flow and lowers the PV temperature. The optimum air gap is 15cm.www.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES PV ventilation & installation no efficiency about 5% about 10% loss efficiency loss efficiency loss www.eco-manager.comwww.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES Building energy consumption The design of building integrated PV systems should be considered to minimize the energy requirements of the building. The investment would be better spent in improving the energy efficiency of the building if the energy consumption of the building is known. The best BIPV designs consider all aspects of building energy use in an holistic way.www.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES PV design installation www.eco-manager.comwww.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES Installation method The choice of installation method have to be base on the usual issues for buildings i.e. strength, corrosion resistance, ease of installing and maintaining, wind loading, snow loading, fire resistance, etc. It’s important to check that any methods and products chosen meet the local building regulations.www.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES Electrical design There are 3 main areas of electrical design of building integrated PV systems: • System design (selection of inverters, etc) • Array wiring • Interconnection to the utility grid Designers need to take into account the national requirements and standards and the characteristics of the products being used.www.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES System components The main component is the inverter which converts the dc power, generated from the PV array, into ac power. The system requires fuses, wiring, junction boxes, isolator switches, earthing and 2 electric meters to measure the electricity flow into and out of the building. A choice needs to be made between a centralized inverters, string inverters or module integrated inverters. A conventional PV system has an array of modules connected to a centralized inverter which feeds power into the building distribution board.www.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES Central inverter Central inverter www.eco-manager.comwww.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES System components The most of the building integrated PV systems have used string inverters rather than a single centralized inverter. i.e. a number of small inverters are installed, one for each string of modules in the array. Because of a standard range the string inverters can be used for any size of system standards. This cost less money in compare with the centralized inverters. In this case the amount of dc wiring is kept to a minimum.www.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES String inverters String inverters www.eco-manager.comwww.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES Module inverters Another approach is to have one small inverter for each PV module. Module inverters www.eco-manager.comwww.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES Electrical design – array wiring An array is wired up to join modules in series and parallel to produce the required current and voltage. In case the modules are connected in a string - the same output current as a single module but the output voltage is the total ammount of the individual module voltages. A number of identical strings can be joined in parallel to produce an array. In this case the total current is the sum of all the string currents. There cannot be any number of modules in an array, there has to be a multiple of the number of modules in a string. The resulting array has to have an output current and voltage within the acceptable input range for the inverter being used.www.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES Electrical design – array wiring If part of the array is likely to be shaded at certain times of day it is best to arrange the array so that the minimum number of strings are affected. A shaded module in a string will reduce the output of the entire string. If there was a vertical strip of shade down one edge of the roof every morning the strings should be wired to run vertically rather than horizontally.www.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES Local utility grid In grid-connected systems the PV operates in parallel with the grid. It is not necessary to store energy e.g. in batteries which are expensive, bulky and have limited lifetimes. Technically connection to the grid is extremely straightforward. Any system connected to the building electricity distribution system is connected to the local grid and excess power will automatically flow out of the building into the grid. If the building loads require more power than is being supplied by the PV it will flow from the grid. The local electricity company has various requirements that a PV system must comply with.www.enbc.eu
    • BUILDING INTEGRATED PV-TECHNICAL ISSUES Contact details t. +359 885222471, +359 882909105, +359 888435561 e. office@enbc.eu http://www.enbc.euwww.enbc.eu