why are there crystals here but not on this one and how does solar panels even work let's find out you can now buy a mug and a hoodie to help support the channel links down below solar panels convert light into electricity they are photovoltaic meaning light and voltage it works with sunlight or artificial light take a small solar cell set up your multimeter connect the leads and expose it to some light we instantly see a voltage is generated the stronger the light the more electricity is produced but can this be reversed if we connect the solar cell to a power supply it produces infrared light the human eye can't see this but if we take a camera and remove the filter we can see that light is being produced from the cell light is basically just lots of particles called photons the solar cell absorbs these photons when they hit the solar cell they knock another particle called an electron out of the solar cell leaving a hole behind this is the photo voltaic effect I'll explain in detail how it works later in the video but the hole drifts down to the bottom and the electron is pulled into the top layer the electron is attracted to the hole similar to how opposite ends of a magnet attract if we provide a path using a wire the electron will flow through this to get back to the hole we place things such as LEDs in the path and that way the electron has to flow through them causing it to emit light which means it emits photons so if the LED emits photons and the solar cell absorbs photons then can the LED power itself tell me your answers in the comment section and I'll tell you the answer later in the video you have probably seen solar cells on your calculator or your garden lights they're often used in motor homes and boats we see them on houses and even vast solar arrays in fields an array is just multiple strings of solar modules connected together a string is just multiple solar modules connected together and the solar module is just multiple solar cells connected together to make a basic solar cell we start with a metal conductive plate this forms the positive electrode on top of this we find a thin silicon layer this is our semiconductor material typically this consists of a layer of silicon Boron mixture on the bottom and a layer of silicon phosphorus on top The Joint between them is known as the PN Junction on top of the Silicon we have an anti-reflective coating a metal grid is then placed over this which is our negative electrode the thin strips are known as fingers and the thicker strip strip is known as the bus bar we typically have a glass protective layer over this because solar cells are very thin and they will easily break so we need to protect them this tiny cell has the bus bar at the very edge this one through the middle and these large ones have multiple bus bars through the middle they all have fingers reaching out across the Silicon to collect the free electrons these electrons will flow along the fingers and then collect and flow to together in the bus bars we need as much light as possible to enter the silicon and so the metal conductors need to be as thin as possible more fingers make it easier to collect more electrons but it also blocks light the Silicon material is shiny which means light is reflected away so the anti-reflection coating helps reduce this but some will always be reflected we also find cells with this rough surface this helps capture some of the reflected light and direct it back into the solar cell each of these cells generates just 0. 5 volts but the larger the cell the more current it can generate to make a solar module we have a solid back sheet with a layer of Eva adhesive over this then the solar cells are stuck to this and connected together another layer of Eva film sits on top of this then a layer of glass and finally the frame is fitted on the back we have the electrical connections which connect to the cells the Eva encapsulates the solar cells insulating them from moisture and mechanical stresses which would degrade the material over time looking at the solar modules the top of one cell is connected to the bottom of the next cell and this increases the voltage looking inside this unit we have two cells both producing 0. 5 Vols if we look closely we can see the cells overlap and join to form a serious connection the ends pass through the back where we find the electrical terminals small modules use 36 cells which produces around 18 to 19.
8 Vols perfect for charging a 12vt battery because we need more voltage than the battery to charge it so we often find these used for off-grid systems but most residential install ations are grid connected and they use 60 or 72 cell modules commercial installations typically use 60 72 or 96 cell modules some can be even larger when we connect cells in series the voltage adds together but the current Remains the Same this module uses 60 cells each providing around 0. 5 Vols and 8 amps of current so it produces around 30 volt and 8 amps this gives us 240 W of power if we connected four of these modules in series we would get 120 volt and 8 amps the voltage adds together but the current Remains the Same this gives us 960 wats but if we connected four in parallel we get 30 volts and 32 amps the voltage is the same but the current adds together this also gives us 960 watt we often use a combination of series parallel connections the modules connect to a charge controller and inverter these have a maximum and a minimum voltage and current to work for example this one might be 100 to 150 volts and 25 amps our string of modules has 120 volt and 8 amps so we can't add another string in series because we will exceed the voltage limit limit therefore we connect two strings in parallel giving us 120 volts with 16 amps the system could be Standalone or grid connected we can use a solar panel to directly power a load but it only works when exposed to light for example this solar fan will automatically turn on when exposed to light the brighter the light the faster it spins but it doesn't work at night we therefore need a battery to store the energy it charges during the day and we can then use it at night that's how this very simple battery charger Works however the voltage and current will vary and the solar module can overcharge the battery which will damage it and at night time the battery can discharge back through the solar panel so we separate them using a charge controller now when the sun shines the controller charges the battery we can switch the light on and and the controller sends power to the load with any excess energy going to charge the battery at nighttime the controller protects the solar panel from the battery but it still allows us to use the energy stored in the battery and that is how these solar powered phone chargers work you can see from this simple garden light that inside we have just a solar cell connected to a basic charge controller this separates the battery and the led the solar cell charges the battery and when charging stops the light is powered we can also control the light with the switch the solar panel and the battery provide DC electricity if we connect this multimeter to a battery we see a constant Flatline voltage that's because the electrons are flowing in One Direction much like the flow of water down a river we can use this to power small DC motors lights and USB devices perfect for motor homes and boats but many of our appliances require AC electricity which works differently if I connect to this power circuit we have a wave pattern the electrons are flowing backwards and forwards it is alternating Direction much like the tide of the sea flowing in and out to power these devices we need an inverter this will convert the DC into AC inside we basically just have some electronic switches which turn on and off extremely fast to control the path of the electrons you can watch our detailed inverter video to learn more but using an inverter allows us to use both AC and DC devices from this system however the battery will run out of energy if it isn't recharged for domestic and Commercial installations we therefore often connect to the electrical Grid in a simple system we have just the solar panels connected to an inverter this feeds the breaker panel and the AC loads in the property the electrical grid connects via a meter to the panel also the inverter must therefore synchronize with the Grid at night time no solar energy is generated so we buy electricity from the Grid on a sunny day the solar panels will be enough to power a few items within the home and so no electricity will pass through the electrical meter on very sunny days the panels provide more energy than we can use within the home so the excess is sold back to the grid this is net metering more advanced systems will use a battery bank which requires a charge controller the solar modules will charge the batteries and power the appliances but when the batteries are full the Excess power is solded back to the Grid at night time the batteries power the home until they are empty at this point electricity needs to be purchased from the Grid in the event of a power cup the batteries will power the home until they are empty and then in the daytime they will recharge solar Farms will have multiple rows of solar panels generating much higher voltages these will then combine and Connect into a large inverter and then feed into a Transformer substation here the voltage is increased and it is then exported to the grid the problem with solar is that the Sun keeps moving it moves from east to west every single day and in the summer it's high in the sky but in the winter it's low in the sky assuming you're in the northern hemisphere solar panels work best when perpendicular to the sun we can see with this torch that the light is strongest here but as it tilts the light is spread over a larger area so it is less intense ideally we would just move the solar panels with the Sun but this is difficult and expensive to do so we need to assess the location for the altitude and the azth of the Sun at that Latitude then we have to check for shading and then we choose the best orientation and tilt angle for the module this involves a lot of data tables and maths which is very time consuming but with PV case our sponsor you can simulate the actual location using the Next Generation AutoCAD based PV software which incorporates 3D topographical data points so you can prototype the design as well as the electrical cabling rout and cable trays and assess the placement of the inverter the stringing and cabling can be automated or manually designed and with their shade analysis you can find and remove overshadowed modules to ensure optimal sun exposure design and even compare different designs side by side of course you can then export the projects you can design ground and commercial or industrial roof mounted projects and automatically produce Construction docum documentation as well as a bill of materials this helps you save time from the initial design all the way through to the procurement phase perfect for large commercial industrial or even utility scale projects click the link in the video description to learn more do check them out you might have noticed the solar cells look different there are crystalline types and thin film types where have you seen them used let me know in the comment section down below one of the most common is the polycrystalline cell it typically has these blue flakes although we can get other colors like this Emerald version these flakes are individual silicon crystals poly meaning many and crystalline meaning crystals they look beautiful but each crystal is a separate group of atoms in different orientations the boundaries of the crystals are defects and they actually reduce the efficiency of the cell these are very common for hobby electronic IC solar powered products and also in solar panels they are relatively cheap but have an efficiency of around 13 to 17% to make them we basically take some silica sand and some carbon such as coal and melt it in an electric Arc furnace it cools down and forms these large chunks of raw silicon this is a piece of raw silicon in my hand it's very lightweight and you can see it's very shiny I'll leave a link in the video description for where to bis some these chunks are crushed into a powder they are mixed with hydrogen chloride and boiled into a gas the gas is then distilled to remove the impurities and it then enters a reactor and slowly collects on the surface of rods forming pure silicon the pure silicon rods are then broken up they are melted and then cooled to form Ingot blocks as the material cools the atoms join and form crystals the blocks are then cut up into thin sheets and used as solar cells this is a monocrystalline cell it is rigid and it typically has a black or very dark blue color with no visible crystals mono means one the atoms form a very orderly structure monocrystalline is more efficient at around 15 to 19% but it's also more expensive to produce as it is more refined the pure silicon chunks are placed into a crucible and melters a seed crystal is lowered into this and the silicon atoms start to stick to it this is then slowly extracted and as it cools it forms an Ingot the atoms structure themselves perfectly in this process forming one giant crystal the Ingot is then cut into blocks and then into thin slices to form the solar cells we can also get thin film types this monocrystalline version is flexible and so is this polycristalline version these are often used for curved roofs or Vans and boats it has a shorter lifespan and is less efficient this garden light and this calculator use thin film amorphous silicon which has this brown color the atoms have a random structure with no defined pattern they are very cheap to produce but only around 5 to 8% efficient when we talk about efficiency we mean the energy from the Sun and how much is converted into electricity the energy travels in waves the waves are different sizes from Tiny But high energy gamma rays to large low energy radio waves but most of its emitted energy is in the ultraviolet visible and infrared region the visible spectrum is what the human eye can see the wavelength determines what color light the eye will see if we measure the energy per area by wavelength in space we see a curve like this but down at sea level it looks more like this and that's because the atmosphere has absorbed abbed and also deflected some of the energy remember inside the solar cell we need a photon to knock an electron off of it silicon atom we use silicon because the electron in the outer veence band only needs to receive around 1. 1 electron volts to make the jump to the conduction band and then become free from the atom that is equal to a photon with a wavelength of around 1,127 nanom which is here on the spect any wavelength Beyond this therefore can't be used to generate electricity with this material but all the wavelengths below this can be used however the wavelengths have more energy than is needed and so this excess energy is going to be wasted by heating the solar cells and so there is only around 30% left that can actually be used to generate electricity with silicon some of this energy will be reflected away dust and dirt on the solar panel will also block some energy and additionally as solar cells heat up from the wasted energy the efficiency will decrease and after we've generated all that energy we then also have energy losses from the inverter and also the wires so this red LED cannot power itself it has a wavelength of around 705 nanom providing 1.
75 electron volts we only need 1. 1 and so the rest of this energy will be wasted as heat but to produce the light we are consuming 4 Ms and only around 10% of that is going to be converted back into electricity so we would need around 10 LEDs to power Just One LED I have tried it here and 9 LEDs is just enough to produce light LEDs also use silicon and so do diodes a solar cell is basically just a giant flat LED working in Reverse we can actually shine light into an LED and it will produce a voltage check out our LED video to learn how they work in detail when we look at silicon atoms they have 14 electrons with four in its outermost shell known as the veent shell silicon atoms are most stable when they have eight electrons in their veence shell but they only have four and so they will share an electron with each of their neighbors to achieve this so where did the threee electrons and the holes come from for the electrons we add some phosphorus to one side because it has five electrons in the outermost shell four of these will be shared and there is now one spare electron which is free to move around the material for the holes we add some Boron to the other side because it has just three electrons in its outermost shell there isn't enough electrons to share and so there will now be a hole where an electron can occupy so we now have a layer with too many electrons and also a layer with not enough electrons this joins to form the PN Junction n stands for negative because the electrons are negatively charged and P stands for positive because the holes are therefore considered positively charged at this Junction we get a depletion region some of the electrons move across and some of the holes also move across but this will form a barrier with a slightly positively charged region and a slightly negatively charged region this creates an electric field which prevents more electrons or holes from moving across and that is what forms the depletion region where no free electrons or holes can exist when light shines on the solar cell the photons penetrate through the Thin N type layer and reach the PN Junction if the photon has enough energy it can knock an electron off of an atom in this region setting it free and leaving an electron hole behind remember no free electrons or holes can exist in this depletion region so the electric field pulls the free electron up into the N type layer the atoms share electrons so another will move from the ptype layer to fill this hole but this just leaves another hole behind it this is also quickly filled and so the hole drifts down through the ptype layer a large amount of electrons and holes will build up in the two materials at their terminals this causes a buildup of positive and negative charge and this is what creates the voltage the free electrons are attracted to the electron holes think of them like opposite ends of a magnet being attracted together so if we provide a path the electrons will then flow through the wire to get to the other side of the solar cell where it can recombine with a hole the light hitting the solar cell will cause a vast amount of electrons to break free these all flow through the wire and a current develops as soon as light hits the solar cell electrons will flow continuously we have therefore generated DC electricity and that is how a solar cell works check out these videos to learn more about engineering and I'll catch you there for the next lesson don't forget to follow us on Tik Tok Facebook Instagram LinkedIn and of course the engineering mindset.
