10. Solar Systems.pdf

Energy Systems Engineering Technology ESET 222 Wind & Solar Energy Winter, 2022 Professor: Arun Hor. Solar Systems ESET 222: Wind & Solar Energy ( Winter 2022 ) Solar Energy Systems Wiring “Wiring” may be one of the less expensive parts of a small solar electrical system, but definitely not the leas...

Energy Systems Engineering Technology ESET 222 Wind & Solar Energy Winter, 2022 Professor: Arun Hor. Solar Systems ESET 222: Wind & Solar Energy ( Winter 2022 ) Solar Energy Systems Wiring “Wiring” may be one of the less expensive parts of a small solar electrical system, but definitely not the least important. In fact, if you make a mistake in wiring there can be big consequences, all bad, even on a small system. And, they’re easy mistakes to make. Wiring is addressed both as “wire” and also as “cable”. To eliminate some confusion, wire is smaller/thinner and cable is bigger/fatter. Technically, “wire” is a single conductor wire while cable is a group of conductors, each wrapped in insulation inside an even bigger insulator. Wiring or cable size is measured in gauge or referred to as AWG which means American Wire Gauge, A 12 “gauge”, or 12 “AWG” would carry the same meaning. Increasing gauge numbers, bigger gauge numbers, indicate decreasing, smaller, wire diameters. A 22 gauge wire is smaller than a 16 gauge wire and a lot smaller than a 8 gauge or 8 AWG heavy wire. ESET 222: Wind & Solar Energy ( Winter 2022 ) Solar Energy Systems Wiring Wire is rated according to amps, the number of amps that can safely pass along it. The higher the current (amps), the thicker the wire, the lower the gauge. Distance matters. Amps aren’t the only things that determine size of wiring. There’s also the distance of wiring between components to consider. Increased distance requires increasingly heavier wiring. This has to do with something called OHMS. The OHMS law says that when voltage goes down, which it does over distance, the current goes up. Wiring has to be able to accommodate the increase. ESET 222: Wind & Solar Energy ( Winter 2022 ) Solar Energy Systems Wiring Diagram As we don't know how our system may develop in the future, it would be a good idea to buy your panels in even numbers, making it convenient to wire pairs in series if we want to change, say, from a 24 volt to a 48 volt system. The next question to consider is the type of wire to use. The resistance offered by the wire will be proportional to the length of the cable (the longer the cable the greater the resistance), and inversely proportional to the cross sectional area (a fatter cable has less resistance). Below is a table showing approximate resistances per metre length for different sizes of copper wire. (Resistance is measured in ohms) Cable X-sectional area (mm2) App. Equivalent American gauge App. Resistance per meter length(ohm) 1.5 16 0.012 2.5 14 0.007 6 10 0.003 Green = Ground Black = Negative Red = Positive ESET 222: Wind & Solar Energy ( Winter 2022 ) Solar Energy Systems Wiring Diagram Let's suppose the cables we connect to our solar panels are going to have a 1.5mm2 cross sectional area and are going to be 20m in total length (10m each for positive and negative cables). The total resistance of our cable will be 20 x 0.012 = 0.24 ohms Let's suppose that our solar panels are going to be pushing out 20 amps of current, then we can use ohms law to calculate the "voltage drop" along these cables. From Ohm’s law, V=I x R or, Voltage Drop = Current in amps x resistance in ohms. In our case above, the voltage drop is going to be 20 x 0.24 = 4.8 volts. This means that the voltage at the charge controller end of the cables will be 4.8 volts less than the voltage produced by the panels if a current of 20amps is flowing. This voltage drop is irrespective of the voltage we are using, it is caused by the current and the resistance. If our panels are wired for a 24 volt system we would be looking at a voltage drop of 20% which is clearly unacceptable. Various different figures may be quoted as a maximum acceptable voltage drop but 2% sounds like a good target. ESET 222: Wind & Solar Energy ( Winter 2022 ) Solar Energy Systems Wiring Diagram These diagram examples could represent 12, 24, or 48 volts systems. The basic wiring configuration would be the same for any voltage system. These diagrams are meant to give a general idea of typical system wiring. ESET 222: Wind & Solar Energy ( Winter 2022 ) Annual Solar Energy Output of a Photovoltaic System? The global formula to estimate the electricity generated in output of a photovoltaic system is : E = A * r * H * PR Where, E = Energy (kWh) A = Total solar panel Area (m2) r = solar panel yield or efficiency(%) H = Annual average solar radiation on tilted panels (shadings not included) PR = Performance ratio, coefficient for losses (range between 0.5 and 0.9, default value = 0.75) r is the yield (power density) of the solar panel given by the ratio : electrical power (in kWp) of one solar panel divided by the area of one panel. Example : the solar panel yield of a PV module of 250 Wp with an area of 1.6 m2 is 15.6%. ESET 222: Wind & Solar Energy ( Winter 2022 ) Annual Solar Energy Output of a Photovoltaic System? Be aware that this nominal ratio is given for standard test conditions (STC) : radiation=1000 W/m2, cell temperature=250C, Wind speed=1 m/s, AM=1.5. H is the annual average solar insolation on tilted panels. Between 200 kWh/m2 (Norway) and 2600 kWh/m2 (Saudi Arabia). You can find this global radiation value here :solar radiation database. You have to find the global annual radiation incident on your PV panels with your specific inclination (slope, tilt) and orientation (azimuth). PR : PR (Performance Ratio) is a very important value to evaluate the quality of a photovoltaic installation because it gives the performance of the installation independently of the orientation, inclination of the panel. It includes all losses. ESET 222: Wind & Solar Energy ( Winter 2022 ) Annual Solar Energy Output of a Photovoltaic System? Example of detailed losses that gives the PR value (depends on the site, the technology, and sizing of the system): - Inverter losses (4% to 10 %) - Temperature losses (5% to 20%) - DC cables losses (1 to 3 %) - AC cables losses (1 to 3 %) - Shadings 0 % to 80% !!! (specific to each site) - Losses at weak radiation 3% to 7% - Losses due to dust, snow... (2%) - Other Losses (?) ESET 222: Wind & Solar Energy ( Winter 2022 ) Annual Solar Energy Output of a Photovoltaic System? A microFIT Contract is a commercial agreement entered into between the Independent Electricity System Operator (IESO) and a Supplier for a term of 20 years. The microFIT Program was a streamlined program for small renewable energy projects under the umbrella of the Feed-in Tariff (FIT) Program, which was designed for projects generating up to 10 kW of electricity. How many solar panels do I need for 1000 kWh per month? A home consuming 1000 kWh per month would need 27 solar panels, each rated at 300 watts. This assumes an average irradiance of 4 kWh/m2/day (peak-sun-hours) and does not include PV system losses of up to 23%. ESET 222: Wind & Solar Energy ( Winter 2022 ) Solar Energy Systems Wiring Diagram Wire chart for connecting 12 Volt solar panels Correct wire sizes are essential To connect the components of a Solar Energy System, you will need to use correct wire sizes to ensure low loss of energy and to prevent overheating and possible damage or even fire. Connecting the Charge Controller After you connect the Solar Panels to the input terminals of the Charge Controller, you can use the same size wire to connect the Charge Controller output to the batteries since these wires will carry no more current than the solar panel wires and will probably be located pretty close to the batteries anyway. Connecting the Power Inverter Both the Power Inverter and the Batteries require the largest wires in the system. During operation, the AC produced by the Power Inverter draws considerable amps from the batteries. Not only are very large wires required, but they should not exceed 6 feet in length to reach the batteries. These wires are like the large battery cables in cars. Use the largest size possible. An AC appliance drawing 10 amps (like a microwave or vacuum cleaner) will require 100 amps at 12 volts DC. Even large cables will get warm. Don't skimp here. ESET 222: Wind & Solar Energy ( Winter 2022 ) Solar Energy Systems Wiring Diagram Wire chart for connecting 12 Volt solar panels Connecting the Batteries They will also require very large cables like the large battery cables in cars. The full current to the loads and also the full charging current flow thru the entire battery bank. Connect all the batteries with large high quality cables. Inter-Module Cables These cables are used to connect one solar panel, also know as a solar module, to another. Inter-Module, also called inter-connect, cables are 2-strand cables and are available in 26", 36", and 72" lengths. Output Cables These cables are used to connect your solar PV system to your electric junction box. Output cables are 2-strand cables and are available in 4' to 100' lengths. Output cables are 2-strand cables and are available in 4' to 100' lengths. ESET 222: Wind & Solar Energy ( Winter 2022 ) Solar Energy Systems Wiring Diagram Wire chart for connecting 12 Volt solar panels This chart shows wire distances for a 3% voltage drop or less. These distances are calculated for a 12 volt system. Multiply distances by 2 for a 24 volt system. Multiply distances by 4 for a 48 volt system. ESET 222: Wind & Solar Energy ( Winter 2022 ) Solar Energy Systems HOW TO CONNECT TO AC GRID FROM A SOLAR-WIND DC OUTPUT A grid-tie inverter (GTI) is a special type of inverter that converts direct current(DC) electricity into alternating current(AC) electricity and feeds it into an existing electrical grid. GTIs are often used to convert direct current produced by many renewable energy sources, such as solar panels or small wind turbines, into the alternating current used to power homes and businesses. The technical name for a grid-tie inverter is "grid-interactive inverter". They may also be called synchronous inverters. Gridinteractive inverters typically cannot be used in standalone applications where utility power is not available. ESET 222: Wind & Solar Energy ( Winter 2022 ) Solar Energy Systems HOW TO CONNECT TO AC GRID FROM A SOLAR-WIND DC OUTPUT Residences and businesses that have a grid-tied electrical system are permitted in many countries to sell their energy to the utility grid. Electricity delivered to the grid can be compensated in several ways. "Net metering", is where the entity that owns the renewable energy power source receives compensation from the utility for its net outflow of power. So for example, if during a given month a power system feeds 500 kilowatt-hours into the grid and uses 100 kilowatt-hours from the grid, it would receive compensation for 400 kilowatt-hours. In the US, net metering policies vary by jurisdiction. Another policy is a feed-in tariff, where the producer is paid for every kilowatt hour delivered to the grid by a special tariff based on a contract with distribution company or other power authority. ESET 222: Wind & Solar Energy ( Winter 2022 ) Solar Energy Systems HOW TO CONNECT TO AC GRID FROM A SOLAR-WIND DC OUTPUT OPERATION: Inverters take DC power and invert it to AC power so it can be fed into the electric utility company grid. The grid tie inverter must synchronize its frequency with that of the grid (e.g. 50 or 60 Hz) using a local oscillator and limit the voltage to no higher than the grid voltage. A high-quality modern GTI has a fixed unity power factor, which means its output voltage and current are perfectly lined up, and its phase angle is within 1 degree of the AC power grid. The inverter has an on-board computer which will sense the current AC grid waveform, and output a voltage to correspond with the grid. ESET 222: Wind & Solar Energy ( Winter 2022 ) Solar Energy Systems HOW TO CONNECT TO AC GRID FROM A SOLAR-WIND DC OUTPUT Grid-tie inverters are also designed to quickly disconnect from the grid if the utility grid goes down. This is an NEC requirement that ensures that in the event of a blackout, the grid tie inverter will shut down to prevent the energy it produces from harming any line workers who are sent to fix the power grid. Properly configured, a grid tie inverter enables a home owner to use an alternative power generation system like solar or wind power without extensive rewiring and without batteries. If the alternative power being produced is insufficient, the deficit will be sourced from the electricity grid. ESET 222: Wind & Solar Energy ( Winter 2022 ) Solar Energy Systems How to Test a Solar System? Sometimes you will want to check that your solar system is performing properly, or you may simply want to know what output your panel is giving. In this section we outline how to do this using a multimeter to measure current (amps) and voltage. Before you start: Find the voltage (V) and current (A) ratings of your panel (you can usually find these written on the back of the panel). Check that sunlight conditions are suitable for producing readings on your system. To obtain the rated output of your panel you will need full, bright sunlight falling directly onto the panel. Remember, no sun no power. Make sure you understand how to use the multimeter, and that you are using appropriate settings for the power you expect to measure. If you are testing a charge controller you will need to make sure that the battery is NOT fully charged otherwise it will not be able to accept current. The first two measurements use the solar panel on its own. When disconnecting the solar panel, regulator and battery, take care to disconnect the panel from the regulator first, and then disconnect the regulator from the battery. When reconnecting, connect the regulator to the battery first, and then connect to the solar panel. This will avoid causing damage to the regulator. ESET 222: Wind & Solar Energy ( Winter 2022 ) Solar Energy Systems How to Test a Solar System? CAUTION: Observe polarities when connecting solar panels and batteries. Photovoltaic panels produce electricity when exposed to light, so it is recommended that you cover the front of the solar panel if outdoors to help avoid shocks. This is particularly important for higher voltage panels. Do not short circuit either the panel or the battery. To measure open circuit voltage Voc Disconnect the solar panel completely from the battery and regulator Angle the solar panel towards the sun Ensure that the multimeter is set to measure Volts To measure Short Circuit Current Isc Disconnect the solar panel completely from the battery and regulator Angle the solar panel towards the sun. Ensure that the multimeter is set at 10A, at least to start with. You can change the setting later if required. ESET 222: Wind & Solar Energy ( Winter 2022 ) Solar Energy Systems How to Test a Solar System? To measure the Operating Current, IL Connect the panel to the controller and battery. Ensure that the multimeter is set at 10A, at least to start with. You can change the setting later if required. Disconnect the positive cable between the battery and the controller Measure the operating current by connecting the +ve from the multimeter to the positive cable from the controller, and the -ve from the meter to the positive battery terminal. This measures the current that the panel (and charge controller) are passed to the battery. If you connect the meter the wrong way round then you will get a negative current showing. Remember, if the battery is full it may not be accepting current, resulting in a low reading ESET 222: Wind & Solar Energy ( Winter 2022 ) Solar Energy Systems How to Test a Solar System? To Test the Controller Measure operating current as described above. Re-connect the solar panel directly to the battery without the controller. Disconnect the positive cable between the battery and the panel. Measure the operating current by connecting the +ve from the multimeter to the positive cable from the panel, and the -ve from the meter to the positive battery terminal. If you measure current without the controller, but not with the controller, then the controller may be faulty. Remember, if the battery is full it may not be accepting current, resulting in a low reading. ESET 222: Wind & Solar Energy ( Winter 2022 ) Solar Energy Systems How to Test a Solar System? Some Final Checks Check the condition of any fuses that might be in the power path. Verify the system wiring is correct and intact. Check all the connections and terminals for good electrical contact. Should your system for whatever reason not be giving the results you expect, please contact us for further advice. ESET 222: Wind & Solar Energy ( Winter 2022) BALANCE OF SYSTEM The balance of system or BOS encompasses all components of a photovoltaic system other than the photovoltaic panels. This includes wiring, switches, support racks, an inverter, and batteries in the case of off-grid systems. ESET 222: Wind & Solar Energy ( Winter 2022) BALANCE OF SYSTEM ESET 222: Wind & Solar Energy ( Winter 2022) BALANCE OF SYSTEM PV Mounts ESET 222: Wind & Solar Energy ( Winter 2022) Roof Rack Mounts ESET 222: Wind & Solar Energy ( Winter 2022 ) PV Installations ESET 222: Wind & Solar Energy ( Winter 2022) BALANCE OF SYSTEM Wiring Termination The positive and negative leads from the solar cell string are brought through the back surface of the module and terminate in a junction box. Two wires extend directly from this junction box and have standard connectors attached for easy connection to other panels or to extend the wires to another junction box. Most of today’s PV modules use the MC (Multi-Contact ®) connecter, which are good for 30 Amps. ESET 222: Wind & Solar Energy ( Winter 2022 ) BALANCE OF SYSTEM Multi-Connectors used in PV module attachments Female Connector MC4 Male Connector ESET 222: Wind & Solar Energy ( Winter 2022) BALANCE OF SYSTEM COMBINER BOX / OVERCURRENT PROTECTION Combiner Boxes A combiner box is similar to a junction box (J-box). The wires of PV array come into this box. There they are connected via a power distribution block to the larger conductors that run to the charge controller or inverter. The goal is to carry the electrical energy from the PVs to the charge controller or inverter with a minimum of voltage drop. ESET 222: Wind & Solar Energy ( Winter 2022) BALANCE OF SYSTEM COMBINER BOX / OVERCURRENT PROTECTION A combiner box also permits the combining of multiple photovoltaic source circuits (sub-arrays, panels, or series strings), and provides a method of removing a module or sub-array/panel from the array without interrupting the rest of the array. Combiner boxes can have fused protection or breakers. ESET 222: Wind & Solar Energy ( Winter 2022 ) Solar Energy