So what we would like to do is to extract as much of the gravitational potential energy related to the mass of the water, related to the flow rate and the kinetic energy when water fall through a large head, through a large distance. So the velocity of the water is changing as it falls. It is increasing. It's increasing almost ten meters per second every second. So if the velocity increases, the kinetic energy also increases. So we have always a combined effect of the gravitational potential energy and kinetic energy to be extracted from the flow of water, and transduced through a turbine into electrical energy. So lots of water, we know exactly what it means. It means high Q. Very high drop, we know what it means. It means a high H. What we do is that we interact with the turbine. The turbine is connected to an electrical device called an AC Alternator, AC alternating current. The alternators has the virtue of having many coils in the starter or their rotor. It depends on a builder, and therefore, it can produce very large current at low RPMs. RPMs are revolutions per minute. It's the mount, the rotational speed of the axis of that electric motor. For transducing all that gravitational potential and kinetic energy into electrical energy, we need a turbine. The turbine fundamentally possess a disk, and that disk, it's going to spin at very high angular velocities at very high rate and it's called a runner. It's just like it's a running away from you. It's the runner. The runner is a disk, so let's say, for different applications and for different turbines have different dimensions and, of course, it scales with the power. So if need a little power, is going to be real tiny, if you need a lot of powers and over the order of megawatts, then you have something that are the sides of buildings. But we're talking about really low head hydroelectric so it's really something, let's say of the order of 50 kilowatts or something less, and therefore they are very manageable and it's small and Penstock that collects the water from the Forebay and place it very close to the runner, will equip itself with several nozzles. It's just like Jets. So imagine that here, we have this disk that is the runner, and the runner has some cups or some spoons to interact with the flow, and we're going to have tangential to it. So this is the disk, tangential to the disk where we have the cups or spoons, we're going to have jets. Okay. So we can have several jets activating one of the runners, and this hardware is utilize fundamentally when you have very large heads. Okay. When your places very close to a mountain and there is a waterfall, wow, great place to try one of these turbines. Now, if you have a lot of water, you have a lot of water into your river but the height through which the water it's falling is small, you will have another turbine. They're called reaction turbines, and they're called Reaction Turbines because they look like a propeller. In the case of a propeller, the propeller the axis of the propeller is not in the vertical, it's in the horizontal and it can move a little bit like this and that is call pitch. That is what happened with the windmills although the windmills also have a yaw, but it also have a pitch. So in this case is the pitch and the pitch is a propeller that it can change the pitch, so you can change the angle of attack between the flow of the water and where the propeller is, and obtain as much lift as possible. It's an intelligent turbine that knows when to adjust so it can extract the best amount of energy from the flow. So it is called Reaction Turbine because you remember the third Newton's law of action, for each action, there's a reaction equal in magnitude but opposite in direction, so that is what happens. So imagine that there comes the flow and it produces a lift, a lift is a force because it's a pressure and the pressure is force per unit area. So for the area of the propeller, it is a force, so it is causing a motion in this direction but in order to cause a most under these directs, and there is a force that resists that motion in this direction which is a reaction force because this is connected to an axis that is connected to an electrical generating system that it's feeding energy to your load. So actually there are those two forces. So they are called reaction turbines because of the action and reaction types. So what are the important things to remember when we are trying to do the Low-Head System. Number one, it's often ignored, often ignored trigger pedal is the Penstock. It what feeds the water to your turbine. The Penstock has to be very well designed and very well constructed. It's usually in the form of a cone but the cone assume that it's axial symmetry, but it can actually be in the form of a triangle with two sides. But definitely has to be very well done. If it plastic, probably it will require some reinforcement and you will not be able to pressurize it to through a long head because it's going to fracture. Fracture, it's the weight engineers called breaking in two, well, breaking in to pieces. So for the type of turbine, it's very important that you know what is the Q and what isthe I and the H. The Q is the flow rate, you remember that, the amount of water, and the H is the height through which the water falls to the head. But you must remember that in the majority of the cases, you will have to do some structures. They call it civil works. The structures can be from a very small pool, a Forebay, or it can be a large pond or it can be a substantial lake depending on the amount of power that you are aiming for. If you live very close to a large river, so river. Okay. It can not be a lake, river. You can implement something called a Free Flow System. A Free Flow System it's where you're using the flow of water because of the difference in gravitational potential energy. The difference is in force that makes the flow going in one direction, and if there is a pylon in there somewhere or there's a bridge, you can connect your own electric motor connected to a runner in there and as long as the runner is acting, so half the runner has to be in the water. The other half has to be outside. If all the runner is in the water, it will not work. Because you're going to have forces that can be symmetric at times and you have to be careful. Or you can mount it on a floating barge. The problem with the floating barge is that you're going to be interacting with the navigation of the river and you're interacting with recreational users of the river, so you have to be careful.
