Inlägg "Here is a student question on the first partial ..." | Drift och planering av elproduktion (EG2200)

Here is a student question on the first partial exam:

Problem 2e: Please explain how the reservoirs in Land are full sometime between 1:00 and 17:00.

Notice that it is stated that the electricity market in Land has perfect competition and perfect information. This means that the power system will for a given load be operated so that the generation costs are minimised. Now, assume that the reservoirs are not full between 1:00 and 17:00. It would then be possible to reduce the hydro generation in the first hour by 200 MWh/h and increase the CHP generation by the same amount. This would increase the generation costs of the system by 200*200 = 40000 ¤, but at the same time we could use the 200 MWh hydro genration to replace the 200 MWh coal condensing generated between 17:00 and 18:00, which reduced the costs by 200*400 = 80000 ¤. As this means that we would lower the operation costs we can conclude that the assumption that the reservoirs are not full is not valid; the explanation why we do not store more water from the first hour to eliminate the coal condensing generation is that we cannot store more water, i.e., the reservoirs are full.

Compare with example 3.3 from the textbook (which was also presented in the lectures on electricity pricing).

Thank you for detail explanation. I agree with your above explanation. However I am facing with the following issues.

When the reservoir is full then Hydro should generate its maximum generation (assuming hydro generator is running perfectly) as to reduce the spillage of water. However, Hydro is not producing at its full capacity during 17.00-18.00 (considering 9.00-11.00 as the max hydro capacity).

Moreover Hydro is producing at 0 marginal cost. However during 1.00 to 6.00 and 19.00-24.00 hydro is producing less than the installed capacity allowing CHP to decide the market clearing price. Should not hydro generate more if the reservoir is full when the demand is higher? Is not that the above issues suggest hydro has reservoir that is not full yet.

Thank you very much.

It is not correct that hydro power should generate its maximal capacity whenever the reservoirs are full. That the reservoirs are full does not have to imply that we are spilling water, it just means that we would like to save as much water as possible for future use.