Subject: buffer coefficient and energy demand Posted: 7/26/2012 Viewed: 19609 times
I am trying to solve a problem regarding the management optimization of three reservoirs in cascade.The first reservoir has a total storage capacity of 800 million m3,the second of 92 million m3 and the third of 16 million m3. I am trying to calculate the releases from the first reservoir.I have also two demand sites and a flow requirement with priority 1.The hydropower priority is 2. I have set the top of conservation zone of the first reservoir equal to the top of buffer zone,so that WEAP considers both conservation zone and buffer zone as buffer zone.I expected that by using different values of the buffer coefficient would lead to different results in reliability and hydropower generation.Nevertheless, i noticed that whatever the value of the buffer coefficient is, there is change neither to the reliability of the system nor to the hydropower generation. It seems as the system has no sensitivity to the buffer coefficient.
I have also determined a value for the "energy demand" variable for each reservoir.By changing these values, i noticed that the hydropower generation is maximized when no energy demand is required,and starts to drop as the values of energy demand are increasing.
Do you have any idea why is this happening?
Subject: Re: buffer coefficient and energy demand Posted: 7/26/2012 Viewed: 19607 times
Try setting the Buffer Coefficient (BC) to 1.0 in one scenario and 0.0 in another scenario and compare the results. Is the reservoir volume the same in both scenarios? BC=0 means that WEAP will not release any water that was in the Buffer Zone at the beginning of a timestep--in other words, the reservoir level cannot go down. However, it can any release water that flows into the reservoir that timestep.
I do not know why your hydropower results are this way. Remember, because the downstream demand sites and flow requirement have a higher priority than the hydropower demand, the reservoirs will release water first to satisfy the downstream demands, and then second for the hydropower demand. Perhaps when the energy demand is low the downstream demands are higher, so that more water is released, which generates hydropower. Perhaps when the Eenergy Demand is higher, the reservoir level has been drawn down (from previous releases for downstream demands), and there is not enough water left to meet the hydropower demand. Check the reservoir volume in those months--is it at the Top of Inactive (TOI)? If so, no more can be released. Otherwise, the Buffer Coefficient could limit how much is released for hydropower.
Subject: Re: buffer coefficient and energy demand Posted: 7/28/2012 Viewed: 19579 times
I would like to ask you something else.I set all the priorities 1 (demand nodes, flow requirement and hydropower priority).I assumed also that energy demand for each reservoir is 0 throughout the year. The flow requirement is 6 m3/s all over the year.Also, the demand nodes values are 0 for the winter period (October to March).Initially,i expected that the hydropower generation for the winter period would correspond to the constant discharge of the permanent flow requirement and that spilling during the winter months would take place.However, I noticed that the real production is very much higher.I also noticed that the storage elevation never exceeds the top of conservation zone.So, I concluded that WEAP uses the volumes of water that would be part of the flood control zone or would overflow as a release through the turbines thus increasing the hydropower generation.Could you please confirm that WEAP adopts this approach or otherwise comment?
Subject: Re: buffer coefficient and energy demand Posted: 7/28/2012 Viewed: 19578 times
You are right--WEAP will always release water from a reservoir so that the end of month storage will not exceed top of conservation (except if you have added an optional maximum hydraulic outflow (MHO) on the reservoir, in which case the outflow cannot exceed the MHO). This water will all pass through the turbines to generate hydropower (up to any maximum turbine flow you might have set).
Subject: Re: buffer coefficient and energy demand Posted: 8/2/2012 Viewed: 19572 times
I would like to ask you some questions. I have set monthly constant values to the energy demand of each reservoir and i want to calculate the reliability of energy demand for each reservoir. Actually, i want to do the same thing that you have done with the reliability of demands nodes, but in the place of demand of demand nodes there will be the energy demand of the reservoirs. Correct me if i' m wrong, but i think that the only way to do this is by creating a new user defined variable. I think it should be an annual result variable with minimum value 0 and maximum value 100. I also think i have to tick the section "sum across branches". I would like to ask you some questions. Firstly, is there any other way to calculate this result than creating a new result variable? Secondly, which would be the correct expression of this new variable i should put in order to do that in current accounts and scenarios? Thirdly, should it be an annual variable? The unit section must be left blank? Finally, where should i put this new variable? Under the variable tab "reservoir" (one variable for all reservoirs) or do i have to create one variable for each reservoir?
Thank you very much for your help!