An Investigation of Integrated Reservoir and Power System Operation, an Optimal Dispatch of the Ethiopian Electric Power System
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Date
2015-06
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Addis Ababa University
Abstract
Ethiopian Electric Utility (which is born from EEPCo) has been running a Load Dispatch
Center (LDC), which is tasked with the responsibility of an optimal power dispatch from an
operational point of view. However, to date most operational decisions (including reservoir
management) are done manually. Under such circumstance, integrated reservoir management
and power system dispatch become more challenging as more and more plants with different
technologies are to be added in coming years. Thus, it is very important to perform high
resolution system dispatch to identify short term challenges, opportunities and potential
solutions. This study was performed using two parallel, linear optimization, models that have
been developed using MATLAB optimization toolbox. The first one, which is termed as
energy model, deals with year round reservoir operations subject to the energy requirement
of the power grid. This model has 73 time steps, with each time step representing a block of
successive five days. The second one uses the output of the former model to test the hourly
power balance and hourly reserve needs subject to the requirements of hourly water balance
in reservoir and power systems operation over the selected days. The second model has 120
time steps, with each time step representing an hour. The result for the reference scenario
shows that hydropower contributes significant amount of energy (approximately 90%) to
meet 2017’s annual demand at least cost. It also indicates that this could be achieved while
maintaining steady state reservoir level and fulfilling the power reserve requirement.
However, vulnerability related to heavy reliance on hydropower puts the power grid at
significant risk that would lead to high cost of electricity due to shortage of water during dry
year and high demand conditions. It was also shown that 3 GW capacity of GERD power
plant should be available at the beginning of 2017 in order to avoid high cost of electricity
generation and unserved energy that could occur if the construction is delayed. The result
shows that depending on scenarios’ the increase in cost of electricity, including cost of
unserved energy, was approximately 6.3 to 8.75 fold the cost at the reference scenario. The
major causes of this cost increase are the direct cost related to the use of more expensive
electricity generators, and the indirect cost due to unserved energy (lost GDP per kWh). In
short, it is concluded that integrated reservoir and power system operation leads to efficient
resource utilization (Especially water and power system infrastructure), which should be
given due attention during hydropower power resources development and operation. Future
mitigation of the observed vulnerability should look into the following four solutions. These
are: (i) implementing an optimal integrated operation; (ii) emphasizing the use of diverse
generation resources; (iii) implementing strategies that enhance water inflows to reservoirs;
(iv) designing power plants with higher capacity factors.
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Keywords
Power system operation, optimal reservoir operation, optimal dispatch