Solar Panel Shading (Part 1): Are Optimisers and Micro inverters Worth It?

so you're almost ready to buy solar the question is should you go for a solution with optimizers or micro inverters some say that shading on one panel will affect all the other panels but others say this is a complete myth so what's the truth here let's find out [Music] hi I'm Gary and welcome back to my channel Gary does solar shading can really affect the power output of your solar array and many companies advertise products called optimizers or micro inverters they claim to counteract those effects here are some of those products from leading manufacturers solar Edge optimizers Tigo optimizers n phase micro inverters and SMA micro inverters if you're not familiar with these products check out my previous video on how to choose the right solar equipment the link for that is in the video description now there's a lot of debate as to whether it optimizers micro inverters add that much value when it comes to shading if you look at marketing material from several leading manufacturers of these products they claim that shading on one panel lowers the power output of all the other panels in the same string here are some examples in a video made by solaredge there is an animation of a bird landing on a single panel of an array which they claim will affect all the other panels but with optimizers installed the other panels are not affected in a video made by taigo there is an animation showing an array producing 400 watts essentially each panel is producing 100 watts of power at that point but when one of the panels is partially shaded the output of the whole array drops to 200 Watts they use the analogy of water flowing through a pipe where the flow is constricted by that shaded panel thereby affecting the flow through all the other panels but with optimizers installed the flow is bypassed around the Shaded panel bringing the total power output back up to 350 Watts in marketing material from end phase a leaf having fallen onto one of the panels reduces the output of all the other panels after it the image is quite dark here so I'll lighten it the first panel appears unaffected but the power output of all the other panels reduces with a micro inverter the power output of the panel with the leaf reduces again I'll lighten the image but the other panels are unaffected you could be forgiven then for thinking that optimizers and micro-inverters are essential for solar installations that experience any kind of shading throughout the day but you'll also find there are several videos out there that seek to demonstrate this is all just a myth seeking to sell you products you don't really need these videos state that in shaded conditions solar arrays without optimizers or micro inverters perform just as well as those with one of the most well-known is this video from NRG solar they constructed two identical solar arrays one with micro inverters and the other just with the fronius string inverter they then applied various equivalent types of shading on both arrays and demonstrated that there was essentially no difference in the power output between the two arrays they then went a little further with the experiments than I would have done and took a cricket bat to one of the panels as you can see despite the damage inflicted onto the panel the total output of the array was largely unaffected in order to get to the truth then let's look at how solar arrays manage shading all by themselves and then we can look at how optimizers and micro inverters might improve matters consider a solar array similar to this one a string of panels connected to an inverter with no optimizers if there is shading onto one of the panels what effect will that have on the power output of that panel and the total power output of the array to get to the bottom of this we need to look at what's going on inside a solar panel a solar panel is made up of a number of solar cells in this case 60 of them all connected in series each cell when generating electricity via the sun acts like a small battery each cell operates at around about 0.5 volts so for 60 cells connected in series we simply add up all these voltages which gives us around 30 volts in total whilst the voltage remains constant the amount of current will vary depending on the sunlight shining onto that panel that current passes through all of the cells in our example here around 10 amps the power output of the panel is simply the voltage multiplied by the current which here is 300 watts now let's say a leaf falls onto the panel covering one of the cells completely what effect will that have on the power output we can start by checking what effect covering all or part of a cell has on the current flowing through that cell using this online utility the link is in the video description to the right of the cell you can see a graph of current plotted on the y-axis against voltage on the x-axis this is called the IV curve and we'll be returning to this later as you can see when I start to shade the cell the amount of current that flows reduces in line with the amount of shading I apply if I cover half of the cell the amount of current also reduces by half to the point where if I completely cover the cell no current flows at all if you're enjoying the content in my videos one of the best ways you can help me is to like this video and YouTube will recommend it to others and if you subscribe to this channel you'll be the first to see the new videos that I'm working on many thanks so shading on a single cell clearly affects its performance but what effect will that have on other cells in the same string we can check the effect shading on one cell will have on other cells connected in series to it using the same utility any shading on just one cell reduces the current on all of the cells connected in series to it for example if I cover 30 percent of this one cell it reduces the current flow in all of the cells by 30 percent and again if I cover this one cell completely then no current flows through the string at all to use the water analogy it's like we're stepping on the hose pipe that connects all of the cells back to our panel diagram then because the leaf is covering one of the cells completely if there were no electronic protection measures in place the current would stop flowing throughout the entire panel and because power is voltage times current the power output would also go to zero now you might be thinking okay that leaf might take out the panel it landed on but the other solar panels in the same string will surely be unaffected well again if there were no electronic protection measures in place you can see that the other panels are simply lengthening the string of cells here we have three panels each panel is 30 volts so collectively they are generating 90 volts we simply add the voltages together the current Remains the Same at 10 amps flowing through all of the panels let's drop our Leaf again on the middle panel this would stop the current flow through the entire string of panels and with no current flowing there would be no power output now we simply cannot have the situation where a single leaf falling on a panel takes out the whole array so the good news is that solar panels do indeed have electronic protection measures in place to prevent that and those measures are surprisingly simple yet very effective each panel has a number of what are called bypass diodes added to the Circuit like so without getting into the detail on how these diodes work they essentially re-route current around cells if they detect what would otherwise be a reduction in that current in the event of shading this is actually to protect the cells from damage because when the cells are shaded they can overheat and fail what's great for us is that a side benefit of this protection is to help maximize power output in the event of localized shading of the panels theoretically you could have a bypass diode for every cell on the panel but to keep costs down it's practical enough just to have three bypass diodes for the whole panel as you can see here let's see how they work with our Leaf scenario then so in normal operation our panel is generating 300 watts when the leaf falls onto the panel the current would normally stop flowing and the power output of the panel would fall to zero but here the third bypass diode detects a change in current in the cells it is managing and decides to root all of the current away from those affected cells this maintains the 10 amps of current flowing through the panel however we've lost about 10 volts worth of cells so the overall voltage of the panel reduces to 20 volts that means the power output of the panel also reduces from its original 300 watts to 200 Watts losing a third of the power output to a single leaf still feels like a lot but the real benefit of bypass diodes with respect to power management is seen with an entire string of panels here is our three panel system again producing 900 watts let's introduce some shading this time from a chimney or something if there were no bypass diodes the current would stop flowing and the power would drop to zero this is because at least one of the cells is completely covered but one of the bypass diodes detects the shading and re-routes the current around the affected part essentially maintaining it for the other panels in the string this means that although we lose a third of the power from the affected panel the other panels are not affected at all so the overall power output only drops by 100 watts to 800 watts roughly 11 percent if the shading increases on that panel another bypass diode kicks in to maintain the current flow so we're only losing 200 Watts from the original 900 watts generation so hopefully you can see without any optimizers or micro inverters solar panels already have capability built in to minimize the effects of localized shading I found a brilliant YouTube video from Paradise Energy Solutions that demonstrates this capability in action they took a single solar panel and wired it up so they could monitor voltage current and power the monitoring equipment being used was able to show a graph of voltage against current like we saw before this IV curve as it is called is an important Concept in solar especially for string inverters using a capability called mppt or maximum PowerPoint tracking the string inverter is able to modify the voltage slightly in order to determine the maximum amount of power it can extract from the hull array remembering that power is voltage multiplied by current the string inverter will essentially choose a point along the curve where the area under the curve is greatest in this case where there is no shading the maximum power output was achieved when the voltage was roughly 35 volts and the current roughly 6 amps we'll be talking about mppt capability later on when we come to optimizers and micro-inverters the guys then applied some shading to the left bottom of the panel I think you can already predict what kind of effect that shading will have on the power output let's have a look at the results yes the power has dropped by a third and this is because the first bypass diode has kicked in the guys then applied that shading to two-thirds of the bottom of the panel and yes as expected the power had dropped to one third of its original level when there was no shading this is because two of the three bypass diodes in the panel have kicked in to prevent any damage to the Shaded cells just to complete the picture then the shading was applied right across the bottom of the panel and sure enough the power output dropped to zero this is because all three bypass diodes kicked in to prevent cell damage the guys then went further and looked at what the effect of shading might be if there was a shadow from a cable or TV antenna pull across the panel can you guess what happened to the power in this scenario feel free to pause the video for a few moments while you work it out okay here was the power output for the unshaded panel and here is the change in that output with the pole shadow the performance indicator shows a drop in power of around four percent but looking at the graph it looks to me to be more like 10 to 15 either way the amount of current drop in the affected cells was not enough to trigger any of the bypass diodes and so the string inverter simply adjusted its mppt to minimize the loss in power there is a consequence though for any other panels in the string however because there is a reduction in current and from what we've learned earlier that drop in current translates into the same drop in power across the whole array not just the one panel okay all of that was a bit techy but hopefully now you've got a fairly good understanding of how solar panels handle shading without the aid of optimizers or micro inverters let's look now then at how it optimizers and micro inverters might improve matters with regard to shading optimizers are small electronic units that attach directly to the solar panels like so some Brands like taigo allow you to install optimizers on selected panels other brands like solar Edge require all of the panels attached to the inverter to have optimizers installed micro inverters are very similar in operation to optimizers but they are also inverters hence the name they convert DC voltage into AC at the panel so there is no need for a string inverter you can think of a micro inverter as being an inverter and Optimizer all in one unit for the analysis then we'll concentrate on optimizers as that covers both the optimizer essentially performs the same maximum PowerPoint tracking that we saw before but this time on a pair of panel bases instead of the whole array what does that mean in practice well we're shading in a panel would normally cause one or more of the bypass diodes to kick in the optimizer on that panel may decide instead to reduce the current flow just for that panel in order to stop the bypass diodes kicking in resulting in a slightly higher power output from that panel without affecting any of the other panels let's see that in action so with no shading our panels are generating 300 watts each totaling 1.8 kilowatts for the whole array note that with no shading there is no difference in output with or without optimizers being fitted let's introduce some shading then and we'll start with the poll or service cable shading over two panels so we know already that without optimizers there is not enough shading to cause the bypass diodes to kick in but there will be a small drop in current and therefore power for the two affected panels let's assume 10 for the sake of argument we know already though that that small drop in current will also reduce the power output for the four remaining panels what about the same situation with optimizers though well the two shaded panels will still have reduced current and therefore reduced power output the optimizers cannot fix that but the four remaining unshaded panels will operate as they did before why is that it's because the two optimizers on the Shaded panels root the extra current around those panels in this example here this brings about a nearly nine percent increase in power output from the array let's increase the level of shading on those panels then this could be the shadow of a chimney for example this Shadow is large enough that it covers several cells right across the widths of those two panels and from what we know earlier this will cause all of the bypass diodes in those panels to kick in meaning there will be no current flowing through the cells in those panels so without any optimization the power output of those two panels drops to zero but the remaining four panels will not be affected with optimization the first four panels will also not be affected but what about the last two will there be any Improvement well actually no because the bypass diodes have already kicked in and there is no current in those panels for the optimizers to work with by the way if you'd like to support my work live in the UK and are thinking of moving your energy supplier over to octopus if you phone them with my referral code we'll both get 50 pounds credited to our accounts that 50 pound will help me buy better recording equipment thank you are there any other shading scenarios then where optimizers might improve matters over non-optimized panels here is another scenario then where the Shadow from a nearby tree partially Shades some of those panels what's important here is that the shading would need to be relatively diffuse remember if any one of the cells becomes completely shaded it will stop the flow of current for all of the cells managed by the same bypass diode in our example here let's say the diffuse shading from the tree reduces the light onto those shaded panels by half if those shaded panels didn't have any optimization the reduced current flow in those panels compared to the unshaded panels would cause the bypass diodes to kick in meaning the power output from those panels would reduce to zero now if those panels were optimized the optimizers would automatically limit the amount of current passing through the panels using mppt so as not to trigger the bypass diodes and therefore generate power the remaining current is simply bypassed around the panels preserving the power output of the non-shaded panels hopefully you've seen them that solar panels without any optimizers or micro inverters already do a pretty good job at managing shading but there are situations where having optimizers or micro inverters can marginally improve the output of your array if I were to drop a list of the pros and cons of optimizers and micro-inverters it might look like this as we have seen they can improve the power output of your array under certain situations for example where there is a shadow from a pull or service cable or where there is diffuse shading from a tree and they allow you to monitor the performance of each of your solar panels which might be important to you but optimizers and micro inverters come at significant extra cost with each unit costing perhaps as much as the panel itself as we saw earlier solar panels are extremely simple electrical devices there's not much to go wrong which is just as well because it will likely be costly to access your roof in order to fix any problems now adding optimizers or micro inverters onto your roof dramatically increases the complexity up there much more that can go wrong and you may not be comfortable with that you'll need to make your own assessment as to whether optimize as a micro inverters are worth it but hopefully I've been able to provide you with more insight which will allow you to make an informed decision as always thanks for taking the time to watch my videos [Music]

Channel: Gary Does Solar

Views: 178,823

Keywords: solar, panel, shading

Id: 9GvhDhCSJgo

Length: 19min 49sec (1189 seconds)

Published: Tue Oct 18 2022