Finding 20% IRR Hydropower Sites With a 5-Cent Tariff

Part 2 - Designing a Project

we are now going to design a hydropower plant around the pink and yellow segments we found. In a HydroDesk Project Folder, there are many structures you need to fill in before you can Simulate a project. In this post, only the following structures are discussed in detail:

the Headrace
the Dam
the Access Road / Transmission Line

Water Conveyance Heuristics 1 - Contours Layer

Let’s check the slopes of the banks to see if they are crazy. First we turn on the Contours Layer Let’s assume there will be no tunneling and we will be placing all structures on the surface.

It seems the contours are not that dense between 550m to 600m, which is where our pink segment begins. However the left bank (right side of image) has a valley. So on a glance it seems our headrace will be on the right bank.

Water Conveyance Heuristics 2 - Terrain Slope Layer

Second, to see what kind of slopes our headrace might pass through, we draw a sketch line along the 575m contour and turn on the Terrain Slope layer. We can easily see what kind of challenges we face within seconds:

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Choosing a Headrace Path

Let’s remove the Satellite basemap so that we can see a clean white canvas. Then turn Contours back on again.

Its becoming more evident that the right bank (left side of image) is better. The left bank (right side of image) has at least 2 to 3 valleys and hills. Furthermore, farther downstream the contour veers off “into the mountain” (see X symbol on image below):

Seems like the right bank is the right choice!

Drawing the Headrace Alignment

We are going to try a covered channel as our primary headrace (also called a box culvert). In HydroDesk, we don’t have to draw this manually! We use a tool called Flattest Path for this purpose.

You place two points of the same elevation, click the “Run” button and HydroDesk will automatically finds the flattest path for you between these two points:

You can also easily get the elevation and excavation profile of your headrace by just clicking on the respective tabs in the toolkit:

Elevation Profile

We see that Flattest Path managed to find a flat path within a +/-2m tolerance.

Cross Section Excavations

The cross section excavations will eventually lead to calculating of the largest cost components of our project: Earth Works. On the bottom right corner of each section, you will find the cut fill volumes needed. After you have “Simulated” the project (in Part 3), you can adjust the benching parameters in great detail.

There are many more things we can do by analyzing the cross section excavations, including changing the alignment of the headrace. However, for this exercise, we will move on to site the dam.

Choosing a Dam Location

We are going to turn on the Contours Layer again. There are two possible locations where the river flattens out for a little bit. There seems to be nothing particularly special about either so I will choose the one downstream for now:

Once you draw the dam (by crossing the river line), HydroDesk will immediately ask you for the Dam Height. After that, the inundation and catchment is immediately generated. If your dam height is very tall, the inundation could take a while. I placed only 10m in this case:

Inundation

One of the features that is a work in progress is to show you visually whether the dam inundation a) affects communities upstream due to flooding and b) how it affects downstream communities in a PMF (probable maximum flood) dam breach situation. This uses artificial intelligence methods on satellite imagery to detect homes, structures and farms.

Catchment

In addition to just finding out what the catchment area shape is, HydroDesk also works in the background to perform rainfall-runoff calibration against known flow gauge stations in our proprietary database together with decades long historical satellite rainfall data.

We are working on some features that will soon be able to provide you insights into the catchment area’s Land Use Pattern using AI based computer vision on satellite images, as this affects the integrity of our Flow Duration Curve over the years to come.

Access Road and Transmission Line

Previously we used the Flattest Path tool which insisted on a grade of 0 (flat) for concrete channels. However, for roads and transmission lines, they don’t need to be on a flat grade. Roads can be up to up to 20 degrees (or 10 degrees if turbines are passing through) and transmission could go as far as 60 degrees.

We have a tool called Least Cost Path for this particular situation. Below you can tweak your maximum slope as well as whether you would like to minimize distance or slope. Sometimes if you put the maximum slope value too low, HydroDesk will complain that it found no viable paths with such aggressive parameters.

The animation below shows permutations of several access road candidates with different slopes:

The access road is only about 1km, the Least Cost Path tool works for very long lines too. For example, a transmission line to the nearest city could be 40km long:

Simulating the Project

The other project structures do not impact CAPEX severely so we will skip them for this post. Now we can simulate the entire project to view the financial results of this project!

A Simulation in HydroDesk will perform the following:

Calculate dam costs from the ground up based on the river profile
Calculate headrace, penstock, access road, transmission line structure costs
Calculate earth works costs (cut and fill) of all structures
Calculate power generation based on the river flow and catchment (including rainfall and flow gauge station calibrations)
Gather all the intermediate outputs and put it into a project finance model with reasonable default assumptions

When the Simulation completes, it will ask you to go to the “Optimize” page to view the results.

Part 2 Summary

We are going to stop here for Part 2. Here’s a summary of what we did:

Turn on the Contours layer to check for obstacles along both banks of the river.
Draw a candidate headrace line, turn on the Terrain Slope layer and check for more obstacles.
Draw a covered channel headrace using the Flattest Path tool.
Check out the cut and fill excavation profiles along the headrace.
Generate the catchment and inundation characteristics of our dam.
Generate some transmission line and access road permutations.
Put everything together into a Project and Simulate it.

In Part 3, we review the results of our simulation and tweak some inappropriate default values to the correct ones. Part 3 is the most exciting part as we finally see what the project returns are going to be like.

Read Part 3 now.

Disclaimer: Any resemblance to any schemes or projects under development in the particular area used in this post is entirely a coincidence.