Solar Photovoltaic PDF - Centennial College - ESET 222

Solar Photovoltaic ESET 222 Wind & Solar Energy Winter, 2022 Professor: Arun Hor. Solar Photovoltaic Photovoltaic Photovoltaic (PV) is a solar energy technology that uses the unique properties of certain semiconductors to directly convert solar radiation into electricity. Photovoltaic systems use wa...

Solar Photovoltaic ESET 222 Wind & Solar Energy Winter, 2022 Professor: Arun Hor. Solar Photovoltaic Photovoltaic Photovoltaic (PV) is a solar energy technology that uses the unique properties of certain semiconductors to directly convert solar radiation into electricity. Photovoltaic systems use wafers typically made of crystalline silicon, that are sensitive to sunlight and produce a small direct current when exposed to light with no moving parts, noise, or emmissions. A photovoltaic (PV) system is an electrical system consisting of a PV module array and other electrical components needed to convert solar energy into electricity usable by loads. A load is a piece of equipment that consumes electricity. A utility is a company that produces and/or distributes electricity to consumers in a certain region or province. A grid is the utility’s network of conductors, substations, and equipment that distributes electricity from its central generation point to consumer. Photovoltaic A utility connected PV system with various electrical components control, condition, and distribute the power to on-site loads. A distributed generation of electricity power. This require the power delivery system to be smart to store and share energy in an on-demand manner. In the future, solar energy will have a huge role in personal transport – such as recharging electric vehicles. Distributed Generation Distributed generation, also distributed energy, on-site generation (OSG), or district/decentralized energy, is electrical generation and storage performed by a variety of small, gridconnected or distribution system-connected devices referred to as distributed energy resources (DER). Conventional power stations, such as coal-fired, gas, and nuclear powered plants, as well as hydroelectric dams and large-scale solar power stations, are centralized and often require electric energy to be transmitted over long distances. By contrast, DER systems are decentralized, modular, and more flexible technologies that are located close to the load they serve. Distributed Generation Typically producing less than 10 megawatts (MW) of power, DER systems can usually be sized to meet your particular needs and installed on site. DER systems typically use renewable energy sources, including small hydro, biomass, biogas, solar power, wind power, and geothermal power, and increasingly play an important role for the electric power distribution system. Microgrids are modern, localized, small-scale grids, contrary to the traditional, centralized electricity grid (macro-grid). Microgrids can disconnect from the centralized grid and operate autonomously, strengthen grid resilience, and help mitigate grid disturbances. Behind the Meter What does behind-the-meter really mean? A BTM system provides power that can be used on-site without passing through a meter, while a front-of-meter system provides power to off-site locations. The power provided by a front-of-meter system must pass through an electric meter before reaching an end-user. BTM systems can provide energy directly to a home without interacting with the electric grid. Photovoltaic Major Photovoltaic technologies Modules Crystalline Silicon (Si) Mono Crystalline Silicon (Si) Poly Crystalline Silicon (Si) Mono Crystalline Silicon Module Thin Film Solar Cells Amorphous Si CdTe Thin Film Module Poly Crystalline Module Photovoltaic Always look for 3 things before selecting a solar panel. -- Panel efficiency -- Panel technology -- Temperature coefficient High efficiency panel is smaller in size than low efficiency panel. So it takes less space. Warranty: Two types. Performance efficiency (25 years) Product efficiency (12 years) This is the real efficiency you should look for. Photovoltaic Mono Crystalline Silicon Module Right now, these are the most efficient type of solar panels. In other words, when sunlight hits these panels, more of it turns into electricity than the other types. As a result of their high silicon content, they’re also more expensive, but you need fewer of them. That’s why they’re ideal for roofs. You can tell if you have a monocrystalline solar panel by its square-ish cells. Photovoltaic Poly Crystalline Silicon Module “Poly” panels have lower silicon levels than “mono” panels. In general, that makes them less expensive to produce, but they’re also slightly less efficient. The good news is that their overall construction design can often make up for the efficiency loss, so they’re also good for roofs. You can tell poly-silicon panels by their groovy mélange of silicon woven through thin rectangular conduit wires. Photovoltaic Amorphous Solar Module The word “amorphous” literally means shapeless. The silicon material is not structured or crystalized on a molecular level, as many other types of silicon-based solar cells are. Most pocket calculators are powered by thin film solar cell made out of amorphous silicon. For a long time, the low power output of amorphous silicon solar cells limited their use to small applications only. Photovoltaic Thin Film Monocrystalline Photovoltaic Module Thin film (amorphous silicon, cadmium telluride, copper indium gallium (di)selenide) Everyone talks about “thin film” because they’re really inexpensive to make and they don’t mind the heat, which is all cool. Except right now, they’re very inefficient, which means you’ll see them in big solar farm projects with a lot of land, but not on your roof. Photovoltaic Amorphous solar panels contain no cells but are created through a deposition process which actually forms the silicon material directly on the glass substrate. To understand this a bit clearer, think of it as spraying the silicon onto the glass in very thin layers. Amorphous panels (thin film) are in the 8-9% efficiency range. Amorphous cells can withstand higher temperatures without output being affected compared to crystalline cells. Polycrystalline solar cells are manufactured by taking raw silicone and forming it into a block or "ingot". Once this ingot is formed, the cell slicing process begins. Polycrystalline cells are generally 13-15% efficient. Monocrystalline panels are made from a single-crystal silicon. Because the cell is composed of a single crystal, the electrons that generate a flow of electricity have more room to move. The cells are usually 16 -18% efficient. Photovoltaic Bifacial solar panel Power generation from both sides of module Bifacial solar panel captures sunlight from both sides of the panel simultaneously. The photovoltaic module of bifacial type has two glass layers, which allow a portion of sunlight to pass through the panel. The sunlight that has passed though the solar panel along with the light reflected off surrounding surfaces, is captured by the back face of the panel, increasing the amount of energy produced by up to 30% compared to single-sided panels. Photovoltaic BIPV (Building Integrated Photovoltaics) Thin film (amorphous silicon, cadmium telluride, copper indium gallium (di) selenide). Everyone talks about “thin film” because they’re really inexpensive to make and they don’t mind the heat, which is all cool. Except right now, they’re very inefficient, which means you’ll see them in big solar farm projects with a lot of land, but not on your roof. Photovoltaic Fundamentals The working principle of solar cells is based on the photovoltaic effect, i.e. the generation of a potential difference at the junction of two different materials in response to electromagnetic radiation. An illustration of the photovoltaic effect Photovoltaic Fundamentals A very simple solar cell model. ❶ Absorption of a photon leads to the generation of an electron-hole pair. ❷ Usually, the electrons and holes will combine. ❸ With semipermeable membranes the electrons and the holes can be separated. ❹ The separated electrons can be used to drive an electric circuit. ❺ After the electrons passed through the circuit, they will recombine with holes. Photovoltaic Fundamentals P-Type and N-Type Semiconductors Silicon in its pure crystalline state is not a good conductor of electricity A small amount of doping of either Boron (group III) and Phosphorous (V) drastically enhances its electrical properties Doping of Boron into Si produces p-type semiconductors (hole is charge carrier) Doping of Phosphorous into Si produces n-type semiconductors (electron is a charge carrier) Pure Silicon N-Type Photovoltaic Fundamentals Cell Voltage and Current Voltage: proportional to temperature for crystalline silicon – When temperature decreases, voltage increases Current: proportional to cell surface area – When surface area increases, current increases Cell voltage: Cell surface area has little effect, Solar irradiance has an effect until 200W/m2. After that there is little effect. Voltage almost remains constant at 0.5V-0.6V. Cell material and cell temperature have major effects on voltage. Voltage is inversely proportional to temperature for c-Si. If cell temperature decreases (gets colder), cell voltage increases. A typical commercially-available silicon cell produces a current between 28 and 35 milliamps per square centimeter. Photovoltaic Fundamentals Effect of Insolation on the I-V curve The electrical current in the cells/modules is directly proportional to solar irradiance The change in voltage is negligible with solar irradiance The maximum power increases with solar irradiance i.e., P ∞ S ∞ I Photovoltaic Fundamentals Cell current: Cell current is directly proportional to cell surface area (sq. meter) and to solar irradiance. Temperature has very little effect on cell current. If Isc is 6A at 1kW/m2 irradiance for a 1 sq. meter cell, the Isc will be 3A for a ½ sq. meter cell and 1.5A for a ¼ sq. meter cell. Example-1: A string of cells is connected in series. The string consists of 100 cells at 0.52Voc per cell. Find the total Voc and the load (RL) for maximum power if MPP is [email protected] Symbol of a PV cell Example-2: Four modules are connected in parallel to a load. If Voc for each module is 52VDC and Isc per module is 2.6A, what are the output Voc and Isc? If the MPP for the array is 49V@10A, what is the value of load to operate the MPP? Photovoltaic Fundamentals Example-1: A string of cells is connected in series. The string consists of 100 cells at 0.52Voc per cell. Find the total Voc and the load (RL) and maximum power if MPP is [email protected] Sloution: ??? Example-2: Four modules are connected in parallel to a load. If Voc for each module is 52VDC and Isc per module is 2.6A, what are the output Voc and Isc? If the MPP for the array is 49V@10A, what is the value of load to operate the MPP? Solution: ??? Photovoltaic Fundamentals Single-crystalline silicon – Grown as a single crystal Multi-crystalline silicon – Cast into an ingot of multiple crystals Ribbon Silicon – Drawn out and allowed to cool and solidify as a continuous multi-crystalline strip Amorphous Silicon – Deposited as a thin film A comparison of solar cell, module, panel, & array Photovoltaic Fundamentals Other Solar Module Types Copper indium gallium selenium (CIGS) Cadmium telluride (CdTe) Gallium arsenide (GaAs) Photochemical cell Photovoltaic Fundamentals PV Module Performance Characteristics I-V curve – Representation of all voltage and current values for a specific module – Voc – open circuit voltage Maximum voltage available when no current is being drawn – Isc – short circuit current Maximum current output with no resistance Photovoltaic Fundamentals PV Module Performance Characteristics An I-V curve for a common PV module size. PV Module Performance Characteristics MPP – maximum power point – Maximum output of the PV module – Maximum voltage x maximum current Solar cells work most efficiently at the MPP – Electrical load or battery bank will determine actual operating point PV Module Performance Characteristics The voltage of this 12V DC nominal module decreases as the cell temperature rises. The current output changes very little. PV Module Performance Characteristics The effect of shading on a PV module The effect of shading on a common 12-volt PV module. Photovoltaic Fundamentals Open circuit voltage of solar cells The open-circuit voltage (Voc) is the maximum voltage on an I-V curve. There is no current and power output on Voc The open-circuit voltage measured by a voltmeter or a multi-meter Photovoltaic Fundamentals Short circuit current of solar cells The current flow is maximum when the leads of positive and negative terminals of cell are connected together, There is no voltage drop and this current is known as short circuit current The power output is zero at this point The short circuit current is measured by ammeter Photovoltaic Fundamentals Electrical properties of solar cells are understood in terms of I-V curves Every cell or module has unique I-V curve under set of operating conditions The I-V curve consists of short circuit current, open circuit voltage and maximum power point The maximum power point is at the knee of the curve Current-Voltage (I-V) curve of solar cells Photovoltaic Fundamentals Effect of Temperature on the I-V curve The electrical current in the cells/modules is not affected much with the temperature The voltage is decreasing with increasing temperature The maximum power is also decreasing with increasing temperature The effect of temperature on thin film cells is relatively less Photovoltaic Fundamentals Cells, Module and Arrays One c-Si cell generates about 0.5 volt and a current between 28 and 35 milliamps per square centimeter. 36 cells are put together in a module of 12 volts In an array, number of modules are put together to generate system voltage Photovoltaic Fundamentals Efficiency of solar cells Efficiency is simply ratio of power out to solar energy input Efficiency is different for various technologies Real efficiency is different from tested module efficiency Where, Pmax= maximum power (W) Vmp=Voltage at maximum power (volt) Imp= Current at maximum power (amp) E= Solar irradiance (W/m2) A= Surface area of cell/module(m2) Photovoltaic Fundamentals Fill Factor (FF) Fill factor is ratio of maximum power (Pmp) to the product of Isc and Voc Most commercial c-Si solar modules have FF more than 70% Thin film cells have FF less than 70% High fill factor indicates: Maximum power current near Isc Maximum power voltage near Voc Where, Pmax= maximum power (W) Voc=Open circuit voltage (volt) Isc= Short circuit current (amp) A decreasing Fill Factor over time indicates degraded performance usually of the cells and/or system wiring Photovoltaic Fundamentals Fill Factor (FF) Adjoining figure indicate higher and lower fill factors FF is another indicator other than efficiency about the quality of modules A decrease in FF overtime means there is problem in the module Photovoltaic Fill Factor (FF) Example: what is the fill factor of a PV device with a maximum power of 167 W, an open-circuit voltage of 29 V and a short-circuit current of 7.9 A? Most commercial crystalline silicon PV cells have fill factors exceeding 70%, while the fill factor for many thin-film materials is somewhat less. Photovoltaic Fundamentals Effect of solar irradiance on efficiency Efficiency is varied with the amount of solar irradiance Efficiency vs Solar Radiation 18.5 Where E= Solar Irradiance (W/m2) ηop= Nominal cell efficiency (ex.18%) 18 Efficiency (%) 17.5 17 16.5 16 15.5 15 100 200 300 400 500 600 700 800 90010001100 Solar irradiance (W/m²) Photovoltaic Effect of Temperature Solar panels, like other electronics, perform their best when they are kept cool (ideally around 250C (770F). You can use the temperature coefficient to get a sense of how your panel’s performance will change during hot sunny summer days. For every degree above 250C (770F), your solar panel’s electricity production will decrease by its temperature coefficient. For example, a panel has a temperature coefficient of -0.5%/0C. This means that, if the panel’s temperature increases by one degree from 250C (770F) to 260C (790F), its electricity production will be reduced by -0.5%. If its temperature increases all the way to 350C (950F), electricity production will decrease by 5%. Photovoltaic Temperature Coefficient All solar cells have a temperature coefficient. As a solar panel increases in temperature, the power output of the solar panel decreases. Generally, monocrystalline solar cells have a temperature coefficient of -0.5%/degC. This means a mono solar panel will lose half of once percent of its power for every degree the temperature rises. Solar panels are all rated at 25degC, however, when solar panels are installed on a roof, they generally reach much higher temperatures. EXAMPLE Lets say a 250W monocrystalline solar panel installed on a roof is at 650C. The solar panel’s power loss can be calculated as follows: 650C – 250C = 400C i.e., 400C x -0.5% = 20% Therefore panel power loss = 20% x 250W = 50W Therefore panel power = 200W Rule of Thumb: Efficiency drops half a percentage per degree increase of temperature from 250C Photovoltaics Both Monocrystalline and Polycrystalline cells temperature coefficient between -0.45% to -0.50% Amorphous based thin film between -0.20% to -0.25%. panels have a have a rating of The Hybrid solar cells currently on the market sit in the middle with a temperature coefficient between -0.32% Photovoltaic Fundamentals Effect of temperature on efficiency Efficiency is varied with temperature of cell/module 25 20 15 10 5 0 Efficiency of Cell Temp c-Si where ηop= Nominal cell efficiency (ex.18%) Tcel= Cell Temperature (°C) Ct= Temperature coefficient Photovoltaic Fundamentals Module to array (In-series) Number of modules put in-series to build voltage The negative terminal of one module is connected to the positive terminal of next module The voltage of all the modules add up in the string The current will be the same in each module Photovoltaic Fundamentals Module to array (In-parallel) Number of modules put in-parallel to build the current The negative terminal of all modules are connected together and the positive terminal of all modules connected together The voltage of all the modules will be same The current is equal to the sum of current of each module Photovoltaic Fundamentals Module to array (Series-parallel) Number of modules put in-parallel to build the current Number of modules put in-series to build voltage Photovoltaic Fundamentals PV Module Standards and Codes PV modules must conform with UL 1703 Safety Standard for Flat Plate Photovoltaic Modules and Panels The CSA Code applies to installation Manufacturer determined – Standard performance ratings – Clearly labeled on each module Polarity of connections Maximum fuse or circuit breaker rating Voc, Vpmax, Ipmax, Isc, Pmax Photovoltaic Fundamentals Obstruction Shading c-Si modules are very sensitive to shading Shading obstruction can be semitransparent or opaque Some of the possible cause of shading: Trees, Buildings, Chimney, wires, etc Opaque obstruction cut-off light completely over a part of module or array Photovoltaic Fundamentals Blocking Diode The diagram to the right shows a simple setup with two panels charging a battery (for simplicity no controller is shown) with a blocking diode in series with the two panels, which are also wired in series. When the sun shines, as long as the voltage produced by the two panels is greater than that of the battery, charging will take place. However, in the dark, when no voltage is being produced by the panels, the voltage of the battery would cause a current to flow in the opposite direction through the panels, discharging the battery, if it was not for the blocking diode in the circuit. Blocking diodes will be of benefit in any system using solar panels to charge a battery. Blocking diodes are usually included in the construction of solar panels so further blocking diodes are not required. Photovoltaic Fundamentals Bypass Diode What happens if one of the panels in the diagram is shaded. Not only will that panel not be producing any significant power, but it will also have a high resistance, blocking the flow of power produced by the unshaded panel. This is where by-pass diodes come into play as shown in the diagram to the right. Now, if one panel is shaded, the current produced by the unshaded panel can flow through a by-pass diode to avoid the high resistance of the shaded panel. By-pass diodes will not be of use unless panels are connected in series to produce a higher voltage. They are most likely to be of benefit where an MPPT Controller or String Inverter involves panels connected in series to produce voltages well above that items minimum input voltage. Some solar panels are constructed with the cells divided into groups, each group having a built-in bypass diode. Shading of part of a panel may be cuased by a tree branch, debris, or snow. Photovoltaic Fundamentals By-Pass & Blocking Diode The diagram to the right shows a simple setup with two panels charging a battery (for simplicity no controller is shown) with a blocking diode in series with the two panels, which are also wired in series. This are also two by-pass diodes shown in the diagram to the right. So, if one panel is shaded, the current produced by the unshaded panel can flow through a by-pass diode to avoid the high resistance of the shaded panel. Photovoltaic Fundamentals A simple solar system Q: On a bright sunny day which two components could you take out and still power the a/c load? Photovoltaic Fundamentals Nominal operating cell temperature (NOCT) NOCT is defined as the temperature reached by open circuited cells under the conditions as listed below: Irradiance = 800 W/m2 Air Temperature = 20°C Wind Velocity = 1 m/s Mounting = open back side. The best module operated at a NOCT of 33°C, the worst at 58°C and the typical module at 48°C respectively Photovoltaic Fundamentals Standard Test Conditions (STC) STC is an industry-wide standard to indicate the performance of PV modules and specifies a cell temperature of 25°C and an irradiance of 1000 W/m2 at an air mass of 1.5 on a sunny day without clouds. STC is a benchmark for comparing different types of PV modules, even if they are not from the same provider. Photovoltaic Fundamentals