In this video, we assess hydropower resources. We'll be taking a look at global hydropower resources, critical factors for hydropower, types of hydropower, impoundment dams including power and energy calculations with an example, run-of-river and diversion dams, again, power and energy calculations with an example, and we'll be talking about upgrading non-power dams using unused hydropower resources. The picture at the right is a wild river in Alaska. Rather than trying to build impoundment dam and ruin the river, a run-of-river plant was put in. You can barely see it. Here's the intake up above the waterfall here, and at the bottom of the falls is a discharge. It's a 1.5 megawatt run-of-river power plant that services a very small local community. Hydropower represents some of the largest unused renewable energy resources in the world. This map shows river power in red, and diversion canal power in blue and major rivers in, well, those are the blue lines. But you get the picture that there's a lot of opportunities for hydropower in the world. Then here's another assessment; the bigger the circle, the greater the hydropower resource. The blue are calculated existing use the dark blue, and light blue is remaining resources. We can see that South America has enormous hydropower resources unused as to Southeast Asia and much of Africa. Factors for calculating hydropower and energy resource estimates include the following. Two critical factors. Hydraulic head or pressure is shown here, the height of the hydropower resource, and volumetric flow rate, how much water is flowing, as shown by this waterfall. Other factors include the seasonality of the flow. Water flows very differently, different times of the season depending on where we are. Uncertainty of the flow and restrictions on the flow such as water conservation restrictions or ecological constraints. Finally, geology and engineering is important. If we're going to build a dam, there has to be a valley where we can conserve the water, or if it's a run-of-river, or a diversion dam, we have to have perhaps a reservoir or a pie, and certainly need to be able to run conduit or piping from the high levels to low levels. Types of hydropower dams. We've already talked about some of these impoundment dams are large dams with a lot of water behind them in a reservoir. Diversion dams often have a high reservoir, but then pipe the water down to the turbine generator at the bottom of the hill or the bottom of the mountain. Finally, run-of-river dams, less powerful than the first two. This is where we actually divert a stream or part of a river, not the whole stream but part of a stream, through a pipe to a downstream and lower-level turbine houses to generate power. One of the most important assessments we need to make for hydropower resources is how much water is flowing in the stream or river. There are many ways to do this calculation, but a simple way is the float method. First off, we calculate the cross-sectional area of the stream or river, call it A, a downstream location L_2 is shown in the diagram. We drop a float in an upstream location in location L_1, and we measure the flow time T from L_1 to L_2, Distance D, that's the distance that the flow takes. To calculate the mass flow rate, we multiply Phi, we'll talk about that in a moment, times the cross-sectional area times the distance the flow travels, times the density of water divided by T. Now, Phi is a float friction coefficient. You can imagine that based on what's on the bottom of the river, water will flow faster or slower. Phi is 0.8 for this gravel and rock bottom, or 0.9 for a sandy or mud bottom. The density of water is about one ton per meter cubed, we've seen that before. In our example, let's suppose that the Phi is 0.8 for this gravel and rock bottom. We calculate the cross-sectional area to be 10 meters squared. The float is 10 meters, and the time it takes is 10 seconds. When we do the calculation, we get eight meters cubed per second, which is eight tons per second. That's an estimate of the mass flow rate for this particular stream. Let's look at assessment of power dams. We're going to look at power and energy calculations. First off, power. If H is the effective height in meters of the dam, we're going to achieve the gravitational constant 9.81 meters per second. F is the mass flow rate in tons per second, and Eta is the turbine efficiency. Seventy-five to 95 percent is typical with a 90 percent average for hydropower dams. The power calculation is the head times gravity times flow rate times Eta in kilowatts. Then the energy production follows. We know the power already, and so what we need to calculate is the capacity utilization. This typically varies between 40 and 60 percent for hydropower dams, with perhaps 25 percent as an average. Then the energy produced is simply the utilization k times power times 8,760 hours a year to give us kilowatt hours. The photograph to the right is the Enguri Dam in New Republic of Georgia in South Asia. It's 272 meters high and produces 1,300 megawatts maximum power. It's a very big dam. Let's now look at an example of a hydropower impoundment dam with numbers. Let's suppose we have a dam that's 100 meters in height, that's the head height. We know the gravitational constant of 9.81 meters per second squared. We've measured the flow rate to be 120 tonnes per second and efficiency of the turbine at 90 percent. Then the power of this dam is the head height times gravity times flow rate times efficiency. When we plug in the numbers, we find that the power of this dam is 106 megawatts. The expected annual energy if the efficiency is 50 percent typical for hydropower dams, then the energy turns out to be 464,000 megawatt hours per year, which translates to 464 gigawatt hours per year. That's a lot of energy. Now, let's calculate water flow through pipes. This is really important for diversion dams and run-of-river dams. The reason for that it's important and difficult is that there's a lot of friction in the pipe water flowing through a pipe, as this diagram shows, water in the center moves much faster than water adjacent to the sides of the pipe. This calculation gets difficult. Happily, there are websites out there that'll help us out. We need the pipe diameter. We need the type material for erupts factor plastic is smoother than say, cast iron. We need to know the pipe length and we need to know the elevation drop or the head. We can go to an online calculator shown here. There are several online. This one's from omni calculator. When you have the pipe diameter by assumption 25 centimeters, that's about 10 inches for those of you without the metric system. The material is plastic so it determines the roughness coefficient force inside the website. We say the pipe length is 200 meters, the drop is a 100 meters. It's coming down pretty steeply. The flow velocity then the website gives us is 15.27 meters per second and the flow discharge is 0.75 meters cubed per second. We can then calculate the flow discharge, knowing the flow velocity in the flow discharge as follows. Power is equal to the flow discharge time the flow velocity squared. We get in this case, when we plug in those numbers, 750 kilograms per second times 15.27 meters per second. That's just from the online calculator. Run the arithmetic and we get 174,880 watts or 175 kilowatts. This is how you calculate the power of water flowing through a pipe. Now let's look at power and energy calculations for run of river and diversion dams. The variables we need are the mass flow rate, the flow velocity, turbine generator efficiency, and capacity utilization. Suppose the flow rate we know to be perhaps from an online source, 750 kilograms per second. The velocity is 15.27 meters per second, and the efficiency is 90 percent. From that, we can calculate power simply as efficiency times flow rate times velocity squared. When we plug in the numbers, we get 157 kilowatts is the output of this dam or the maximum output of this run of river diversion dam. Annual energy then is simply the utilization, let's say 75 percent. The energy then out is the 8,760 hours per year times efficiency of 75 percent times power of 157 kilowatts, and we get 1,034 megawatt hours per year, which would be about one gigawatt hour per year. A lot of energy. That's enough for about 20 homes. Another often overlooked source of hydro-power is upgrading existing non-power dams for hydro-power. Many dams are built for flood control, for irrigation, or for drinking water, and they are perfectly suitable with upgrades for generating electricity. We add hydro-power to existing dams, under utilized hydro-power resource. There are many dams in the world that could have hydro-power that don't. Large and small dams can be upgraded. Many cases it's pretty easy to small dams, much harder with very large dams. Although here's an example. This is the Red Rock dam in the United States, dams in Missouri River. The Missouri River is known for its great floods over time. The dam was constructed in 1969, mostly for flood control. You can see the original dam here to the right, and in 2000, a 55 megawatt power plant was added. Again, is shown in the picture at the right. This was a major project. It took several years, but it's now generating a lot of energy where none was being generated before. In summary, we've looked at global hydro-power resources, critical factors for hydro-power, types of hydro-power including empowerment dams. We've looked at power and energy calculations with an example. We've looked at diversion and run off river dams with power and energy calculations as well. Now this interesting picture at the right is a very small hydro-power run of river generator. You can see water comes down from above in a simple flexible tube. There's this compact hydropower generator, that's dumping water into the stream and generating 1.5 kilowatts of energy. Hydropower can be a very small application and of course going to be very large. Then when we talked about upgrading non-power dams and unused hydropower resources. In the next video, we take a look at geothermal energy, and we'll see you there.
