Subject: Constant Hydropower Generation – Need for Input on Reservoir Setup Posted: 4/16/2025 Viewed: 249 times
Dear All,
In my reservoir operation model, I’m observing constant hydropower generation that doesn’t vary by month. In the 'Storage Capacity' field of the reservoir, should I enter monthly varying values? Currently, I’ve used a constant storage capacity based on the reservoir’s design specifications. I’m using automatic catchment delineation and achieved very good calibration and validation results for a node upstream of this reservoir.
I’d appreciate any insights or suggestions on possible solutions.
Thank you.
Best regards,
Selam
Mr. Doug Chalmers
Subject: Re: Constant Hydropower Generation – Need for Input on Reservoir Setup Posted: 4/16/2025 Viewed: 242 times
Selam,
If you have fairly constant hydropower generation, then that would likely mean you have fairly constant reservoir storage elevation, right? The storage capacity input represents the maximum volume that can be physically held within the structure. I'd recommend to instead modify the monthly Top of Conservation, which sets the operating level of the reservoir. Another option is to use a minimum flow requirement object immediately downstream of the reservoir if you want to set a given release pattern.
Hope this helps!
-Doug
Eng. Selam Sahlu
Subject: Re: Constant Hydropower Generation – Need for Input on Reservoir Setup Posted: 4/16/2025 Viewed: 234 times
Dear Doug,
Thank you for your response. Yes, I have a constant storage elevation. How can I modify the monthly top of conservation? I’m experiencing the same problem in all the reservoirs in my catchment: the power generation does not vary by month. I would expect the energy output to vary monthly and annually, since the inflow varies on those time scales. I’ve also set a minimum downstream flow requirement for each reservoir, but the issue persists.
I would greatly appreciate your help. I’ve spent more than a week trying to resolve this, but I haven’t been successful.
Thank you for your support.
Best regards,
Selam
Mr. Doug Chalmers
Subject: Re: Constant Hydropower Generation – Need for Input on Reservoir Setup Posted: 4/17/2025 Viewed: 226 times
Selam,
The hydropower generation is a function of the outflow and the storage elevation, not the inflow. Check the results of your outflow and storage elevation. You may have to adjust your volume-elevation-curve input parameter of your reservoir, your downstream flow requirement, or your top of conservation if your elevation or outflow are giving unexpected values. To adjust the top of conservation, go to the parameter in your reservoir object under Operations, then you can assign monthly values using the If and Month functions of the Expression Builder, or using the Lookup Wizard.
Eng. Selam Sahlu
Subject: Re: Constant Hydropower Generation – Need for Input on Reservoir Setup Posted: 4/17/2025 Viewed: 221 times
Dear Doug,
Thank you for your explanation. The outflow is nearly the same as the inflow, with only a very small amount evaporated. The “Increase in Storage” variable is almost zero, which means inflow equals outflow and there are no other losses. I have adjusted the top of conservation to vary monthly, but the hydropower generation remains constant. In this case, however, there are non‑zero “Increase in Storage” and “Decrease in Storage” values. Do these values indicate what the problem might be, and how can I resolve it?
Best regards,
Selam
Mr. Doug Chalmers
Subject: Re: Constant Hydropower Generation – Need for Input on Reservoir Setup Posted: 4/17/2025 Viewed: 213 times
Selam,
If the hydropower generation is remaining constant, then likely your storage elevation (distinct from storage volume) and your outflow are constant as well. I would check the value of these in your results. Note that any outflow above the Max Turbine Flow input value (found in the reservoir hydropower inputs) will no longer increase the hydropower generation. Note too that the storage elevation is a function of the volume elevation curve input for the reservoir.
Ask yourself- is it a correct representation of my system that the storage elevation and outflow are constant? If not, then you'll need to modify your model.
-Doug
Eng. Selam Sahlu
Subject: Re: Constant Hydropower Generation – Need for Input on Reservoir Setup Posted: 4/24/2025 Viewed: 2 times
Dear Doug,
Thank you for your explanation. I found that the issue was related to the Max. Turbine Flow. When I increased this value, I observed monthly variations in hydropower generation. As you mentioned, any outflow exceeding the Max. Turbine Flow does not contribute to hydropower generation. After increasing the Max. Turbine Flow, the variations became visible.
Thank you again for your clarification.
Best regards,
Selam
Topic "Constant Hydropower Generation – Need for Input on Reservoir Setup"
