Feasibility Study of Hydropower

Part 1:  Calculating the Potential of Hydropower

In order to know the potential of power that can be generated by a river, it can be calculated by the following equation:

Where:

   P    = potential of power (kW)

   ρ     = water density (1 kg/m³)

   g     = gravity acceleration (9.8 m/s2)

  Q     = river discharge (m3/second)

  h      = hross head (m)

So, when your client or government agencies asked you to calculate the potential of hydropower, you can simply use that formula as preliminary analysis.

If the river has a record of water levels, then it is a little bit easier to calculate. However, at the preliminary stage usually they don’t have any records. Therefore this can be done by visiting the site and take some measurement using current-meter. If you don’t have current-meter, then this method can be applied on how to find the discharge of the river:

1.  Go to the site and find the location where the river morphology is straight, the flow is uniform, the slope is flat and the cross sectional area is almost the same (e.g. rectangular or trapezoid).
2. Use a stick gauge to measure the dimension of river cross-section A to B.
3. Find floating material such as wood chip, leaf, or anything can float and make sure your hand phone has installed stopwatch.
4. Drop the float at point A and account the time until the float reach the point B.
5. Repeat on the step 4 for several times.

Tabulate the record of river cross section data as follows:

Location	Width (m)	Water Depth (m)	Area (m)
A	x1	y1	z1
B	x2	y2	z2

Tabulate the time for the float flow as follows:

Distance Point A to Point B	d1 m
Measured Time	t1 second	t2 second

You can do more cross section measurement in between point A and B and time measurement if you like. Finally, use Manning Equation to calculate the flow:

Where:

   V     = average velocity (m/s)

   n      = friction coefficient (uniform linear stream: 0.028)

   R     = hydraulic radius: A / P

   A     = sectional area of flow (m²)

   P      = wetted perimeter (m)

   S      = slope (assumed 0.001 m/m for almost flat river)

River discharge (Q) is calculated by multiplying flow (V) and Sectional area of flow (A).
       

Q = V x A

Gross head is the height of water drop from the intake to the outlet. For hydropower that will be constructed using dam, it can be based on how much high the dam will be constructed. However, comprehensive analysis on hydrology and hydraulic must be carried out to know the exact water level. If the hydropower will constructed using run-of river scheme, it will be based on topographical level from intake to power house. Google Earth can be used to estimate the elevation roughly or the other available data (e.g. SRTM).

Finally, you can calculate the potential of hydropower that could be generated by river. Of course this is just a simple analysis when your client suddenly asked you at least this is what I have done. More detail analysis for sure need to be carried such as to find the effective generated power, detailed hydrology and hydraulic analysis, and layout plan design. 

Next to Part 2