 Hello everyone and good afternoon, good evening, or good morning depending on where you're joining us from. Welcome to Engineering for Change or E4C for Short. Today we're pleased to bring you this month's installment of E4C's 2018 Off-Grid Energy Webinar Series, focusing on Generating Off-Grid Power. My name is Mariela Machado and I'm the Program Manager at Engineering for Change. I will be the moderator for today's webinar. The webinar you are participating in today will be archived on our webinars page and our YouTube channel. Both of those URLs are listed on this slide that you're seeing on your screen. Information on upcoming webinars is available on our webinars page. E4C members will receive invitations to upcoming webinars directly. If you have any questions, comments, and recommendations for future topics and speakers, please contact the E4C webinar series team at webinars at engineeringforchange.org. If you're following us on Twitter today, please join the conversation with our hashtag E4C Webinars, as you see on the screen as well. Before we move to our presenter today, I would like to tell you a bit about Engineering for Change. E4C is a knowledge organization and global community of more than one million engineers, designers, development practitioners, and social scientists who are leveraging technology to solve quality of life challenges faced by undeserved communities all over the world. Some of those challenges include access to clean water and sanitation, sustainable energy, lack of internet, improved agriculture, and more. We invite you to become a member. E4C membership is free and provides access to news and thought leaders, insights on hundreds of essential technologies on our Solutions Library, professional development resources, and current opportunities such as jobs, funding calls, fellowships, and more. E4C members also enjoy a unique user experience based on their site behavior and engagement. Essentially, the more you interact with the E4C site, the better we will be able to serve your resources that are aligned to your interests. For more, please see our website, engineeringforchange.org, to learn more and sign up. Today's webinar is the third in the Off-Grid Energy webinar series. Additional topics covered in the series are drawn from the book Off-Grid Electrical Systems in Developing Countries, authored by our presenter, Dr. Henry Louis. The future webinars in this series are listed on this slide and will be announced via our newsletter. E4C members will receive the information directly in their mailbox, so be sure to sign up. For reference, you can find examples of off-grid energy products like the Mobisol Solar Home System in the E4C Solutions Library. There, you can learn more about technical performance, compliance with standards, academic research, and user provision models of these systems. All the information is sourced by E4C research fellows and reviewed by our community of experts. This solution and many more are available to E4C members free of charge, so be sure to check out the Solutions Library. A few housekeeping items before we get started. Let's practice using the WebEx platform by telling us where you are in the world right now. So in the chat window, which is located at the bottom right of your screen, please type your location right now. If the chat is not open on your screen, try clicking the chat icon at the bottom of the screen in the middle of the slides. You can use this window to share remarks during the webinar, and if you have technical questions, just sign up private chat to Engineer for Change Admin. Let's see where you guys are joining us from. Cincinnati, Los Angeles, Denmark, welcome. Ontario, Canada, Netherlands, Uganda, UK, Ghana, what we have from all over the world today. Nashville, Tennessee, welcome everyone. I saw India earlier today too, so welcome everyone. So through this chat, you can also share remarks, as mentioned before, so be sure to do that. But during the webinar, please be sure to use the Q&A window, which is a different one, located below the chat to type in your questions for the presenter. The presenter will have 15 minutes at the end of the presentation, so be sure to type your questions there. If you don't see it, click the Q&A icon at the bottom of the screen in the middle of the slides. If you're listening to the audio broadcast and you encounter any trouble, try hitting stop and then start. You may also want to try opening WebEx up in a different browser. If you see webinars, qualify engineers for one professional development hour to request your PDH, please follow the instructions on the top of the If you see professional development page after the presentation. As you see on the link on the slide. A special note about today's webinar, we will stop, as I mentioned before, 15 minutes before the hour, so 11.45 Eastern time. But so be sure to type in your questions during the presentation. Okay. So now let's get started. But before we do that, I would like to introduce our speaker today. Dr. Henry Louis is an associate professor in the Department of Electrical and Computer Engineering at Seattle University. His research areas include electricity access in developing communities, renewable energy and appropriate technology. He's the president and co-founder of kilowatts for humanity, an unprofit organization providing electricity access and business opportunities in Sub-Saharan Africa. Dr. Louis served as a Fulbright scholar to Co-Provide University in Kidwa, Sambia. He's recognized as a distinguished lecturer of the IEEE and is an associate editor of the Journal of Energy for Sustainable Development. He's author of the book, Off-Grid Electrical Systems in Developing Countries, published by Springer Nature. So without further to say, I want to welcome Dr. Henry Louis. So over to you, Henry. Welcome and thank you for joining us, everyone. It's fantastic to be back here giving my third webinar as part of our Off-Grid Electrical System webinar series. And today we're going to be talking about how we actually supply power to Off-Grid systems. As was mentioned in my introduction, I'm associate professor at Seattle University where I teach in the Department of Electrical and Computer Engineering. I also am president of a nonprofit that works in off-grid electricity access known as kilowatts for humanity. And I've previously been on the steering committee of IEEE Smart Village and have been a Fulbright scholar. So today's webinar is going to be following a few chapters of the book Off-Grid Electrical Systems in Developing Countries. If you want to know more about today's topic or the other topics in our other webinars, I encourage you to go and get a copy of the book. It's available on Amazon in hard copy or on Kindle. It's also available through the publisher's website Springer. And you can also access it through my website, Dr. HenryLouis.com. So the book covers many topics. And today's webinar is going to focus on three of the chapters in particular. And of course it's challenging to cover three entire chapters in a 35 or 40-minute presentation. So if you really want to know more of the details, I would encourage you to check out those chapters. It includes example problems and lots of other details that we won't be able to get into today. So today's webinar we're going to talk about the fundamental operating principles of the energy conversion technologies that you commonly encounter in off-grid systems. And the off-grid systems that I'm going to be talking about today are those that are perhaps one kilowatt to maybe 100 kilowatts in size. So nothing larger than that and nothing really smaller than that. And as you see, there's going to be quite a few types of technologies that we're going to discuss in the next while here. So to center ourselves, let's think about an off-grid system and we'll generically call it a mini-grid. You can really take an off-grid system and break it up into three subsystems, an energy production system, a distribution system, and the in-use system. In our last webinar, we did talk a bit about distribution systems and then this webinar we're really going to focus on the energy production system, in particular the energy conversion technologies. So the technologies that generate the electricity that the users of the system consume. Off-grid systems generally are supplied by one or more of these five types of energy conversion systems. Generator sets, hydroturbines, photovoltaic arrays, wind turbines, or biomass systems. There's actually quite a few different ways of using biomass. So we're going to talk about each of these types of energy conversion technologies in this webinar. Now with the exception of photovoltaic arrays, all of the other energy conversion technologies ultimately rely on some sort of generator to produce electricity. So we're going to talk a little bit about generators. Now there's two types of generators. There's AC generators and there's DC generators and there's several subtypes within those two categories. Now in most off-grid systems you see AC generators rather than DC. You might see DC generators in specialty wind turbines, but for the most part we see AC generators in off-grid systems. Within AC generators there's two types. There's synchronous generators and then there's induction generators. And both of these are used at off-grid systems. However induction generators are I would say less common. Remember that an induction generator requires some source of reactive power to be able to function. And so you end up having to either have another generator like a synchronous generator that can supply that reactive power or you might have some capacitors. So although induction generators are used, typically it's synchronous generators that are used. And so that's going to be the focus of our discussion here over the next few minutes. So synchronous generators are always powered by some sort of prime mover. And that prime mover can be a combustion engine, a wind turbine, a hydro turbine. In other words something that can provide mechanical power input to that generator. Now shown on the right hand side of the slide is a cutaway of a synchronous generator. Synchronous generators are really composed of two parts. We have a stator and we have a rotor and they're separated by a small air gap. The stator is a stationary part of the generator so it doesn't move. Inside that stator are a bunch of coils of wire and these coils of wire are going to be ultimately connected to the load to supply electricity. The rotor itself contains either a permanent magnet or an electromagnet. And voltage is induced in the coils in the stator when the rotor rotates according to Lenz's law. So briefly what Lenz's law tells us is that the voltage that we get in a coil is proportional to the number of turns of coils multiplied by the rate of change of the magnetic flux. So that rotor is producing a magnetic field and so flux is passing through those coils. And as the flux passes through those coils the voltage is induced. Now there's a few consequences from Lenz's law that are important to our discussion today. The first is that we can adjust the induced voltage by adjusting the strength of the magnetic field. So if we have an electromagnet on our rotor we can adjust the strength of the magnetic field by adjusting the current to that electromagnet. And then we are able to control the voltage. The second consequence of Lenz's law is that it's the rate of change of flux that ultimately induces a voltage. So if we spin the rotor faster, if our hydro turbine or wind turbine rotates faster, we're going to get a higher voltage induced. Which may be a good thing but it could also be a bad thing. Now related to this is that as we rotate our rotor faster the frequency of the voltage will also increase. And so this can be a challenge because for the most part when we supply AC power to a load we want to do it at constant frequency and constant voltage. So if we have an energy conversion technology whose speed can't be regulated very well what we're going to end up with is a frequency and voltage that fluctuates with that rotor speed. And so this obviously is something we don't want to do. And so really when we think about energy conversion technologies we really need to use those that are capable of being governed in some way. So in other words they need to have their speed to be able to be controlled. And we see that with gensets and microhydro it's very easy to control their speed. Something like a wind turbine unfortunately it's very difficult to control the speed. You know if the wind isn't blowing then you will have a very difficult time making that wind turbine rotate. And so what we see is we see wind turbines used in systems where we have batteries and so we convert the electricity they produce to DC anyway. So we're less concerned about the frequency. Now we also have a similar constraint with our voltage. We want the voltage supplied to the load to be relatively constant. However as the current flows through the coils of the generator and it encounters resistance and inductive reactants associated with those coils. And what that means is the voltage that we get at the terminals of our generator is different than the voltage that's induced. And depending on the load that voltage at the terminals could be higher but most likely lower than the induced voltage. And this will depend upon the amount of current that is flowing and this is a bad thing that we want to avoid. So how we correct for this is we can adjust the strength of the magnetic field to our rotor. And we can adjust the induced voltage and we can correct for any voltage drop that might occur. And so we use a device called an automatic voltage regulator to do that and those are found in most gensets and micro hydropower systems. But the real bottom line is only we can only directly couple an energy conversion technology to an AC load if that the energy conversion technology is capable of having its speed and voltage regulated. If you can't regulate the speed or the voltage then most likely you're going to actually have to convert to DC before using an inverter to convert to an AC load. So let's talk about our first energy conversion technology and that's gensets. Now gensets are I would say by far the most common off-grid power source. Certainly there are hundreds of millions of gensets that are around installed around the world. They can be small, maybe just a few hundred watts as shown in the top figure, or they can be quite large and permanently installed and they can be hundreds of kilowatts in size for sure. Now gensets are popular because they're relatively inexpensive at least to purchase. The challenge is they have high operating costs because they rely on a fuel source. There's a few different types of gensets depending on the nature of its internal combustion engine like a spark ignition like in a petrol generator common in most cars or it can be compression ignition which is found in diesel cars. So the basics of how a genset works is we have some sort of fuel and air that we feed into an internal combustion engine. After combustion we get mechanical power on the engine's crankshaft which we is coupled to the generator's rotor and again rotating that rotor will provide electrical power connected to a load. Because we can regulate the flow of fuel and air into the internal combustion engine we are able to moderate its speed and so we can take a genset and directly couple it with an AC load. Now when we talk about gensets the fuel source really matters and you can design a genset to take petroleum, diesel, but also biofuels like biofuel or even biomass derived syngas and biogas but also things like methane and hydrogen can be used in different types of gensets. Now like I said the fuel consumption of a genset is one of our biggest concerns because it can be expensive so it's important that we operate a genset in a way that minimizes the fuel consumption or maximizes the efficiency. So that top diagram shows the allocation of fuel to different categories depending upon the loading of the generator. So at very low load most of the energy, most of the fuel that you provide that genset goes into the exhaust or heat transfer or friction. As you start to load the generator supplying more power the efficiency of the generator increases more and more power is provided to the generator and less as a proportion to friction and the other sources. So this tells us that we should always operate a genset at high loading if possible. The other thing we need to consider is the size of the genset. So gensets are reliant thermodynamic cycles and when we have a larger genset we'll be able to operate more efficiently. So a 100 kva genset will be more efficient than say a 10 kva genset. So basically we'd rather have fewer but larger capacity gensets than a bunch of small capacity gensets if possible. So this also impacts how we might load our genset. So if we have a genset that needs to supply for example of 100 kWh over the course of a day and we are able to dictate when that energy is provided, one strategy would be to load the genset at a low level and provide consistent power throughout the day. The other option would be to maybe load it fully and supply power, high power for a few hours. So this could be a scenario where we're pumping water or something where it doesn't necessarily need to be on demand as long as we pump a certain volume of water over the course of the day we're happy. So given these two options, which one should we pick in order to minimize fuel costs? Well the one on the right is really the one that we should pick because we're going to be loading our generator at near full capacity and so it's going to operate more efficiently. So we can save quite a bit of fuel using a strategy like this if possible. It also means that the genset is operating fewer hours a day so there's less noise and the operational hours are decreased so that genset is actually going to last longer. So some considerations about gensets, we really like them again because they're relatively inexpensive. They range in capacities from hundreds of watts to megawatts even. You can start up a genset on demand and this is a big advantage over solar or wind because a wind turbine can't produce wind if it's not windy and either can a solar panel if it's not sunny. So the fact that we can on demand produce electricity is a big advantage of gensets. They're also pretty easy to control. A lot of the controls is automated and smaller gensets are portable. Now balancing those advantages are several disadvantages. And most of these are related to the fact that you have to supply fuel to the genset. So fuel is expensive. You also have to manage the whole fuel supply chain. You have to store it on site. You have to make sure that you have a supply of fuel that's dependable. And in some communities they're so rural that you spend more money on transporting the fuel to your site than the fuel itself. And so the cost can increase significantly. Gensets also have a relatively short lifespan, so maybe 20 to 30,000 hours before they need to be refurbished. And so this can be consideration as well. Now like I said earlier, gensets can be provided with fossil fuels, but they can also be fueled with biomass more generally. Biomass is distinguished from fossil fuels in that the organic material in biomass was recently alive. And so when we think about biomass, we think of crop residue, animal waste, animal manure, even food and human waste. Also forest products from cutting down trees and so forth. So these are all different biomass feedstocks. So of course we can't just take crops and feed it directly into an internal combustion engine to power it. We have to process it. And so when we talk about biomass systems, we're really talking about processing biomass into a fuel that's more convenient than the raw biomass itself. And I'll also point out that biomass, most of the biomass systems that you see out there aren't used ultimately for electricity generation. They're used for perhaps heating and cooking instead, but nonetheless there are still many examples where biomass is used as a feedstock to a generator to produce electricity. So there are a few ways that we can convert biomass into a fuel that can be used in an internal combustion engine. We can use anaerobic digestion. So this is basically using microbes to digest like wet biomass. So for example manure and over time it will produce a combination of methane and carbon dioxide, which we can burn or combust in an engine. We can also make synthesis gas or syngas and I'll talk about that on the next slide here. And also we can just take the biomass directly, we can dry it, we can chop it up and then we can burn it and for example create steam that we can use in a steam turbine. So this would be more common in larger industrial facilities where we might use this solid biomass directly. So syngas is biomass that has been turned into a combination of hydrogen, carbon monoxide and a little carbon dioxide using a thermochemical reaction. So what we do here is we take a vessel called a reactor, it's a big metal tank and we put dried biomass up at the top. So this could be like sugar cane stock for example we put in the top and inside the vessel it's quite hot due to several of the reactions that are occurring within. So the biomass begins drying because of the heat and as the temperature increases pyrolysis occurs. Pyrolysis is the same reaction that occurs when we make charcoal. So basically you take organic material, you heat it to a high temperature in the absence of oxygen so it doesn't, it doesn't combust. And under these conditions you basically end up with char which you can think of as mostly just carbon. So you take those organic compounds and you are able to just convert it to straight carbon. Now a little bit further down the vessel we introduce air and also maybe some steam and that carbon is going to combine with the air through oxidation yielding carbon dioxide. Now a little bit further down we'll actually have reduction that occurs so that carbon reacts with the water in the steam or the water in the air and it splits the H2O into hydrogen and carbon monoxide. So we're able to get hydrogen H2 out of the vessel and that's really where the energy in our syngas comes from. So we can take this syngas and we can use it, we can input it into an internal combustion engine saving on the diesel that it would have consumed. So you can fire this internal combustion engine using a mixture of hydrogen and diesel and you also ultimately reduce the diesel consumption by maybe 80% or so. So syngas is used in many places. I think India is probably the leader of using syngas based electricity production. So some of the practical considerations about biomass, you know, biomass depending on how you produce it, the byproduct could be used as a fertilizer. So that's particularly biogas. You can store the biomass fuel on site. You don't have to wait for the sun to rise or the wind to blow. Biomass can create employment in rural areas collecting the crop waste and so it can improve cash flow. But there are several disadvantages. So you still require a gen set. So all the advantages and disadvantages of the gen sets that we just talked about also apply here. You also have to maintain the flow of your feedstock. And so this can be a challenge, especially if the feedstock is based on a crop that might be seasonal. You also have to be careful not to compete with crops that might be grown for food. So generally speaking, we don't want to replace food crops with energy crops that can have some very, very negative effects to local communities. And just because the crop was considered waste, so you might be using stocks of corn, for example, or maize, it doesn't mean that it's always going to be free to you. And there's many cases that have been documented about gasification plants assuming that their feedstock is going to be free. And then people understand that they figure out that their crop waste is making somebody else money and so they want to start charging people for it. So managing that supply chain is quite important. Moving on now to talking about wind energy conversion systems. These work basically by converting the kinetic energy and air to electrical energy. Now unlike biomass or fossil fuel fired internal combustion engines, wind output is variable and uncertain. You can't just start up a wind turbine whenever you want. It really depends upon the wind resources being there. In addition, wind turbines need to be in windy locations, which sounds obvious, but I think it needs to be reiterated that the wind resource is so important. You need to put it in an area that you know is windy. And this often requires a tall tower being there. So a typical small wind energy conversion system is shown on the left there. It's three blades that rotate along the horizontal axis. Many wind turbines of this size will use just a permanent magnet on the rotor. And that means we can't control the frequency or the magnitude of the voltage very well. And so we can't connect a wind turbine directly to an AC system, at least in an off-grid sense. So that means that most wind turbines we actually use to charge batteries. So we'll take the AC power out, we'll rectify it to DC, and we'll use it to charge a battery. If we want to supply power to an AC load, we might use an inverter. So the basic principle of operation for a wind turbine is moving air interacts with the blades of the turbine. The blades have been aerodynamically designed to impart lift on the hub. So this torque causes the hub to rotate, which is connected to the generator shaft. And of course, once we have a rotating generator shaft, we can produce electricity. If we want to look at the equations that govern this, we can imagine that the wind turbine interacts with this cylinder of air that passes through its swept area. That cylinder of air is going to have some kinetic energy, and that kinetic energy is going to be one-half times its mass times its velocity squared. If we want to figure out the power, then we can take the derivative of the air accounting for the speed of the wind. And we get an equation that says the power that's in the air is one-half times the swept area times the density of the air times the velocity cubed. Now, this is the power in the air, and we're not able to harness all of that. Instead, we only are able to harness some fraction of that, so we multiply this equation by C sub P, which is a power coefficient. Now, I'll note, and this is quite important, that the mechanical power in that the turbine harnesses is related cubically to the speed of the wind. So in other words, if we double the velocity of the wind, we actually get an eight-fold increase in the power. So again, putting the wind turbine in a very high wind area is extremely, extremely important because of that cubic relationship. Now, the power that we're able to harness, the mechanical power that we're able to harness from that massive moving air really depends upon the aerodynamics of the blades. And so that power coefficient is going to vary based upon several factors, including like the angle of the blades, the number of blades, but also importantly, the tip speed ratio. So the tip speed ratio is just the speed of the tips of the blades compared to the speed of the oncoming air. And typically, we want a tip speed ratio between about six and eight for most three-bladed wind turbines. Now, just because we design our wind turbine to operate at a tip speed ratio that's between six and eight doesn't mean it actually will. So we have to actually consider the electrical side as well. And so designing wind turbines is actually a bit challenging because you have to co-design the mechanical system and the electrical system. But basically, we want to find where the electrical generator's power curve intersects the wind turbine's mechanical power curve. And that's what's shown on the upper right. So in order for the generator to produce power at steady state, the mechanical power needs to equal the electrical power. And you can see that the two lines, the dashed lines and the colored solid lines don't always intersect at the maximum of the colored line. So in other words, if we look at that 12 meters per second mechanical power curve, we see that we're actually over speeding with this generator. So the generator is not well matched for the blades for the wind turbine part for this particular example. But nonetheless, a well-designed turbine will have a power curve, which is shown at the bottom, and that power curve relates wind speed to power output. And so even though there might be some wind, it doesn't mean that the wind turbine is actually producing power. There has to be a minimum amount of kinetic energy to get the blades to rotate. And then finally, for the wind turbine to be able to produce a high enough voltage for the rectifier to be able to charge the battery. So I think maybe the biggest drawback to using wind turbines is assessing the wind resource. Wind is affected by local conditions. And so you really don't know if an area is windy until you've actually gone there and taken some measurements. And so measuring the wind speed over a period of time is recommended. And doing that over the course of about a year is really what you need to do in order to have a good sense of how windy it is. So obviously this adds time and adds a lot of expense. And I think this is probably the biggest drawback to using wind. You also have to have towers. And so this takes some engineering to figure out how tall the tower and the civil works associated with it. I'll just point out that the cost of the tower is often about the same cost as the turbine. So don't underestimate the cost of the towers. Just to recap here, using wind for powering off-grid systems, we like wind because there's no fuel costs, no emissions. It's possible that it's windy in the evening, which is great if your load is also heaviest in the evening. It's really hard to steal a wind turbine. There's a big tower there. It's actually possible to construct a wind turbine using local materials. And there's a few references that you see there if you want to know how to make your own. I would say the disadvantages for using wind is that it's a relatively high upfront cost, particularly with solar decreasing. The wind resource, again, is difficult to assess ahead of time. You really need to take on-site measurements. Wind turbines are also quite conspicuous. We've worked up with some wind turbines, and you can see those wind turbines from miles away. And so that might draw unwanted attention to your system. In addition, there could be some bird or bat strikes, which could be an issue. And then towers require maintenance and can also be safety risks. So we'll move on to microhydro, and I'll speed things up here just to make sure that we have enough time for questions. But in my opinion, if you have a location where there's an adequate hydro resource, microhydro is what you should go with. Microhydro systems, they last a really long time. They can be easily controlled. Maybe one drawback is that you have to require some civil structures be built to harness the water. But in general, they're going to be the most cost-effective type of off-grid power source. So typically how they work is we find a location where there's a river and there's steep terrain. And high up in the mountains or the hills, we divert a portion of the water away from the river into a penstock. In a penstock, you can think of as just being a pipe. And so the water flows through this penstock all the way down to our powerhouse, which is located down river where it interacts with the turbine, and then the water is returned to the river. So two things to note here. First is that we only use a portion of the river. We don't divert the whole river. The second is that the turbine itself isn't immersed in the river. We don't immerse the turbine in the river itself because there's lots of debris and there's lots of challenges. So we're only using a portion of the water and then the turbine itself is just fed by the penstock. We don't place it, we don't submerge it in the river itself. You can think of a hydro turbine operating based upon the potential energy of the water at its intake. So a volume of water at elevation has potential energy and that potential energy is a function of the distance between the turbine and that water, the density of the water, the volume of the water, and of course the gravitational constant. Now, typically the actual measured distance between the turbine and the elevated volume of water, we call that the total head. And generally speaking, the energy available to the turbine isn't based on the total head, but it's based on the effective head. And so we reduce the total head by some percentage based upon losses that we expect to incur within the penstock and so forth. But as that volume of water moves down the penstock, we actually have a flow of water and so we can calculate the power in that water. And that power in that water then is just related to the density, the gravity, and the head and the flow rate. So it's the head and the flow rate that really dictate the power that we have available in our turbine. Now there are many turbines types that we can use in our micro hydropower system. And each turbine is going to be designed to operate at a certain head. So most micro hydropower operate at high and medium head, meaning Pelton, Crossflow, Francis, and Tergo turbines are going to be the types of technologies that we use. Pelton and Crossflow are very, very common. So when I say high and medium head, I'm talking about 10 to maybe 100 meters in head. Now it's really important that you pick the right turbine. If you pick the wrong turbine for your application, that turbine is really not going to operate very efficiently. So most turbines are going to have some sort of efficiency curve which is based upon a certain RPM that they operate at. Now that RPM might or might not be the RPM that the generator that's coupled to the turbine needs to be driven at. And so if there's a mismatch there, basically you're going to be operating your turbine at an inefficient level or an inefficient operating state. So to make sure that you operate your turbine at an efficient state, there's a couple of approaches. One is calculating the specific speed, the specific speed of your water resource given the rotational requirements of your generator. And you compare it to like a table which is shown or a chart or a table like is shown on the bottom left. Another way is to use a turbine application chart. So you enter your flow and your head and you see where those coordinates lie. So to that red X, that's for one particular site. And given the flow rate of slightly under 10 liters per second and ahead of maybe 20 meters, for this one kilowatt system, we'd be wanting to use like a Pelton turbine. So these application charts really are useful in matching up the right generator or the right turbine with the application. Now a huge advantage of using microhydro is the fact that we can connect them directly to an AC load. So by diverting just a portion of the river, we can ensure that the penstock is always full of water. And so we can always supply mechanical power to our turbine and rotate the generator 24 hours a day. To maintain a constant frequency, we can either use a spear valve to adjust the amount of water into the turbine or we can use an electronic load controller which basically balances any change in the electrical load with power to a resistive load. So I'm not going to go into that more details. The book has more details of that if you're interested. And this is just a picture of a microhydro system. You can see there are water coming from penstocks and two pipes. So this is a multi jet Pelton turbine. There is a spear valve. The turbine itself is enclosed. You can't see it, but you can see the generator, which it's coupled to through a drive system there. Microhydro power we like because it's relatively inexpensive. The fuel is free. These can last for a really long time because they operate consistently and at low temperature. So they last a really long time. They can be AC coupled or DC coupled. It's a very, very mature technology. Now balancing those advantages or a few disadvantages. Mostly, you know, they have to be custom designed for the water resource. Adequate water resources aren't everywhere. And you really are impacting a broader community. Anybody downstream, you're going to be affecting in some way. So there's a lot more stakeholders involved. Now I'll wrap up with talking about PV arrays. And I'll be fairly quick here because there's a whole bunch of resources about solar online. But solar panels are increasingly common. You can find them, you can find them everywhere. They're becoming cheaper. They also inherently output DC. So if we have a battery system, we don't need rectifier or anything like that. Many places that struggle with access to electricity are in places where there's adequate solar radiation. But like wind, you know, power from solar is variable and uncertain. So we don't have that on demand aspect of solar. So how a solar panel works, it's actually just a diode. It's a dope silicon. It's a dope piece of silicon that has a PN junction within it. And it relies on the photovoltaic effect where we have photons, exciting electrons within that PN junction. These electrons jump up from the tightly held valence bound band to the more free conduction band. And a PN junction has a built-in electric field, which will separate these electrons and voltages produced. And so actually a circuit model for a PV cell is shown on the right. And it's, you can see a diode representing the PN junction and a current source that represents the current that's produced by the photon. What we need to know about solar is that their output is approximately proportional to the amount of sunlight. So yes, solar does work on a cloudy day, but its power output will be reduced significantly. In addition, the higher the temperature, the lower the power output. So we really like sunny, cool areas for solar. An important aspect of solar is that there is a unique operating point where its power output is maximized. So if we look at the current and voltage curve of a solar cell, which is shown at the top, when we multiply the voltage and current at every point along that curve, we get that dashed blue line, which is shown at the bottom. And we note that there's a unique point in which the power is operated, the power is maximized, I should say. And so that means there's a unique voltage that the power is optimized at. And that unique voltage may or may not correspond to the battery voltage. In fact, it's most likely will not. So if we take our PV panel and connect it directly to a battery, we're probably not going to be optimizing the power output of that panel. Even if it's really sunny, it still means that we're operating in a suboptimal way. So one way around that is to use what's called a maximum power point tracker. And a maximum power point tracker is a device that sits between the PV array and the battery. And what it does is it decouples the PV voltage from the battery voltage. And how this works is you can look at the curve at the bottom. And basically, if we didn't have the maximum power point tracker, the PV panel would be operating at point B, which is the battery voltage. But because we have the maximum power point tracker there, the PV is able to operate at point A. It's maximum power point and the battery voltage on the, excuse me, the maximum power point tracker on the battery side is operating at point C. Point A and point C correspond to the same power. So in other words, the maximum power point tracker isn't producing power. It's simply making the solar panel operate in a more efficient way. So there are several methods possible. If you're interested in maximum power point tracking, you can look at references seven and eight. So to summarize PV, you know, there's no fuel costs. It's quiet. There's low maintenance. They're very modular, so you can easily expand systems. The supply chains are becoming more mature. On the downside, though, the power, you know, it varies with the radiance and temperature. You often need charge controllers and batteries. They're more expensive, at least in terms of capital costs and gen sets and some of the other technologies. And there's relatively low power density, so you actually need a lot of real estate for PV arrays. Now, most of the time we think of well engineered systems for mini grids, but if you travel around many of these communities, you'll find a lot of improvised systems. So I just wanted to show a few examples of that. The bottom left is an improvised wind turbine that I came across in Zambia. Sort of in the middle there, you see a hydro turbine where these are soda bottles that are used as nozzles. And you can see the turbine rotating just above the gentleman's hand there. A PV system is shown at the bottom. You can't see the panel. You can see the inverter and battery. And then on the right you see a battery charging scheme. Speaking of batteries, our webinar on January 16th, it's going to be all about batteries. So many engineers, if you're not a chemical engineer anyway, batteries are this big black boxes of chemicals. We don't really understand how they operate. So I'm going to do what I can to demystify batteries. I'm going to try to communicate how we can interpret spec sheets and basically provide you with the knowledge you need to select the proper battery for your off-grid system. So I'm happy. Here are the references. And you can view these when the webinar is archived, if you want to write down the specific details. But I'm happy to take questions. So thanks for listening. And I'll turn it back to the moderator for questions. Thanks. Thank you so much, Henry. This was incredible as always. I will try to pass along some of the questions. I know there's, it was a heated conversation while you were presenting, which is always great. And I will try to pass the ones that were written. If you guys have any other questions, aside from the ones I'm asking, please write them on the Q&A chat. Okay. And I will be sure to pass along. So from Bill Radcliffe, he says, as a mechanical power source, gas turbine and genes are apparently not included. Nor are they hydrogen fuel cells. Are they recent purely financial or are there any other considerations? Yeah, that's a great question. So let me kind of clarify the context of what we're talking about here. Absolutely microgrids that you see in Europe, Asia, the US. Yeah, absolutely. You can use fuel cells. You can use gas-powered turbines. In rural areas, however, I don't know that I've ever really come across a mini-grid that used a fuel cell. Natural gas turbines, sure. I think they're relatively uncommon. Just the supply chain is difficult to manage. So I'm sure that there are some that use gas turbines or probably larger systems, more sophisticated microgrids. Certainly the smaller ones are more likely to use diesel or petrol. Of course, there's other energy sources that in theory could be used to power off-grid systems, but we really don't see, for example, geothermal used in off-grid systems. Those are much larger in scale. You wouldn't see a little community using a geothermal power plant. It would be very rare. It probably doesn't even exist. But great question, yeah. Thank you so much. Okay, that's great. I saw during the conversation in the chat, they were asking about your open source turbine. And I think we answered them, but they were still asking. So if you have the link there, Henry, we can post it here or pass it along afterwards. Sure. So I'm not sure what exact link is being referred to. I haven't been following the chat while I was talking. But yeah, I've worked on open source wind turbines. Really, there's a lot of resources on this. Hugh Piggett is really the person that popularized this wind, you know, do-it-yourself wind turbine. So if you look up Hugh Piggett, he's the person behind all of it. There's also a book called Homebrew Wind Power, which is written by two gentlemen out of Colorado that does a step-by-step instruction on how to build your own wind turbine. In my experiences with wind turbines, there are, I think, a bit of a novelty. I mean, you can do it. It's fun. It's rewarding to do it. You can show that it can be done with local materials. But I think they struggle with being able to manufacture them at scale, and the maintenance can be challenging. So I wouldn't recommend, for example, a group of people in the U.S. building their own wind turbine, bringing it to Kenya and installing it, and then leaving because wind turbines do require quite a bit of maintenance, especially homemade wind turbine. It's interesting if I had a cabin in the U.S. that was off-grid, I would consider making my own wind turbine there. But if you're going to power a whole community whose livelihood depends upon that wind turbine being operational, I would have second thoughts. And there's actually quite a bit of research where people have gone back and they've looked at different wind turbines, commercially made wind turbines, too. And the overall success hasn't been too promising. There's quite a bit of maintenance that's required. Okay, but theotherpower.com, is that from you, Henry? Other power, I believe, and no, that's not me. I believe that's the people that wrote the Homebrew wind power book, Dan Fink and Dan Bartman. I believe that's the other power. But yeah, you can order many of the wind turbine parts from them. So yeah, I've ordered stuff from them, so you can check them out. You can get the magnets from them. You can get, like, the templates. So if you're interested in building your own wind turbine, sure, go check them out. Great. Thank you for clarifying, because it was a heated discussion around this topic. So if you guys have any further questions, please let me know. Okay, I will pass along to another question here from Pranav. Can we also burn plastic indirectly and then heat the water and process the blue gases like an incinerator? No, probably, but again, I think it comes down to scale. I mean, certainly there are countries in sub-Saharan Africa that have a waste to energy conversion facilities where they burn essentially trash and create steam and run steam turbines. It's really tricky to run a steam turbine at a very small scale. You need to have some sort of manufacturing facility, something that aggregates a lot of trash and has a large facility where it makes sense to have a steam turbine. It's hard to make a steam turbine efficient at a very small scale. I mean, there's so many considerations there. Okay. Great. We have another question here. How do you feel like the small module or nuclear reactors work that are connected to local grids? I mean, you certainly hear... Yeah, you hear more and more about these small nuclear reactors like five megawatt or smaller size. I think it's going to be a while before those find their way into rural communities. And I think if they... I think their bigger contribution would actually be to be grid connected and then use grid extension to power these communities. I would think that there would just be so many other considerations in installing a nuclear reactor in a remote village. You'd probably want to put it in a more secure location and then just run power lines to the village from it or provide power to the whole grid. Okay. Got it. We have another interesting question regarding the recycling of solar panels. Is it possible to manufacture green panels last polluting? Have you seen any examples? There's certainly a lot of talk now about what we're going to do when panels... I mean, worldwide there's just so many solar panels that are out there and solar panel lasts for maybe 20 years. And so at some point we're going to have a whole bunch of solar panel waste that's going out there. Solar panels themselves aren't the easiest thing to recycle. I mean, there is some aluminum and maybe some copper in there but it takes a lot of effort to actually recycle it. So it's a problem. I think it's an open problem and I think we need better solutions for it. Now, it's a village scale. Waste collection in general is a problem in villages. I mean, if you walk around many of these villages it's not like there's a trash collector that comes by once a week and picks up the trash. I mean, water bottles just sit there, you know, plastics just sit there on the ground. So waste disposal and recycling is a big issue in these communities in general, you know, independent of the energy production side. Yeah, that's a big issue that we should really start figuring out, correct? Okay, so we have, where can we get more info on micro-hydro or mini-hydro? Yeah, so of course I'll say my book has some information. There are quite a few resources, practical resources that are available. So I would look up, I think I have one here on my desk. There's a book called Serious Microhydro by Scott Davis. That's a good book that describes micro-hydro power systems. There are a few books out there by Practical Action that describe how to actually make your own micro-hydro power using like Pelton turbines. So there's actually quite a few resources that are out there. I would encourage whoever asks that question if you want to contact me or if you look at the book there are several resources that I cite within that book that describe micro-hydro in more detail. Great, yeah, and I think your book would be the best answer because can you repeat the name and where can they find them, Henry? Yeah, so well the name of my book is Off-Grid Electrical Systems and Developing Countries and if you just Google that you'll come up with the place to get it. You can get it on Amazon for about $90, a hard copy on Kendall. I think about $70, something like that. But there are books that are dedicated just to hydropower. One author that I like is his name is Scott Davis and he has I think two books that are related to practical experiences in micro-hydro. It won't necessarily tell you how to design the system but it'll give you a feel for what goes into systems and it'll give you a bunch of different real practical examples. And then there are quite a few books that are out there that go into detail about how to design the penstock, how to design the intake structures. So, you know, I consult your library or do a Google search or you feel free to email me and I can pass on a short list of other references that I found helpful. Great, Henry. So we have two more minutes and I just wanted to ask you in general so that we close up the webinar. Which generate system is the most common in the world and which one do you think should be given the sustainability, maybe the continuous fuel of energy or source? Which one do you think we should be moving towards? Yeah, great question. Well, I think globally there's a lot of advantage to solar. I would say hydro but there's only, that only works in relatively few places. Like you have to have a good hydro resource to try it. But one great thing about solar is it's really easy to tell if a community has an adequate solar resource. I mean, there's open access databases that can tell you for any square meter on Earth, any meter on Earth, you know, any location, what the solar radius is going to be like and it'll be fairly accurate. We don't have databases like that for wind. I mean, the closest you get is maybe a kilometer or two kilometers in resolution. And it varies so much locally. So I like wind, excuse me, I like solar. It's coming down in price. It's easy to design a system based upon available solar radiance data. I would say that perhaps the most common system though is probably gensets. I mean, in Nigeria there's like 100 million just in Nigeria. So there's still quite a few of those that are out there. And of course there's lots of challenges with that pollution and fuel costs and so forth. Great, Henry. I think that's a great end to our webinar. I want to thank you for this great presentation. The chat, we still have many questions there. They're asking for reference. They're asking for more information. So be sure to check Henry's book out and be sure to, if you have any other questions, be sure to reach out to him. The information about how to obtain a PDH. And if you have any further questions about the webinar, it's on the slide right now. So thank you so much for attending. Thank you, Henry, for a great presentation. And be sure to check our next webinar around off-grid energy. Thank you. Thank you.