El principio del reconocimiento mutuo

Option B of intervention Phase 4 builds upon Option A by adding a pump storage scheme between Evinos and Mornos reservoirs instead of including only the small hydropower plant at the outlet of Evinos – Mornos tunnel.

UWOT implementation

The analysis of the specific intervention was examined by developing a separate UWOT model than the one used for the other four intervention phases and baseline scenario. The new model uses a finer time step that is more appropriate for this type of application rather than using a monthly time step so that it will be able to capture the associated processes more accurately. The developed model, which could be considered as a modelling experiment for the initial assessment of the pump storage scheme, extends up to Giona location including the two parallel small hydropower plants, the existing Giona HPP and the proposed for Phase 3 Giona extension HPP (Figure 9.17).

Mornos and Evinos reservoirs are represented as in the previous models by a single “lumped” reservoir, but in this model an extra reservoir, Evinos control, has been added that represents the upper control reservoir used for solely the pump storage operation. Evinos control is a virtual reservoir that stores only the water from pump storage and doesn’t receive the inflows of Evinos reservoir.

As in the model developed for Phase 4 / Option A Evinos inflow timeseries passes through the Evinos-Mornos hydropower plant before becoming inflow for the Evinos – Mornos lumped reservoir. In this case, a new inflow to the reservoir has been added that represents the extra inflow coming from the upper control reservoir, i.e. the water used for the pump- storage operation only. This inflow also produces an extra amount of renewable energy and the water amount transferred from the upper to the lower reservoir is controlled by the signal entering the pump component Hydropower Plant.

Regarding the demand signal of Mornos-Evinos reservoir besides the existing Athens water demand coming from Mornos main aqueduct, a new demand signal has been added. This demand refers to the water being pumped up from the lower to the upper reservoir via the pump component Pump (Wind turbine). This demand signal and pump operation are controlled by the input timeseries entering the pump component.

Figure 9.17: UWOT schematisation for the pump-storage scheme (Phase 4 / Option B)

The model was setup with a daily time step using historic data for the period 01/08/2002 to 24/01/2007. The input data used for the specific model have been defined as follows:

• For Evinos inflow that represents the inflow from Evinos to Mornos reservoir via the Evinos-Mornos a daily timeseries of reservoir outflow data was used from Mamassis et al. (2011).

• Mornos runoff daily timeseries was created from the corresponding monthly timeseries (from reservoir balance, Mamassis et al., 2011) by stochastic disaggregation using a uniform model.

• The daily demand signal at Giona location representing the Athens water supply demand was estimated from the average monthly demand of the model developed for the previous modelling scenarios that simulates the entire external water supply system.

• A daily timeseries of wind speed data from Mornos meteorological station was used for the assessment of the local wind energy potential (Mamassis et al., 2011). • The daily wind velocity timeseries was converted to power output using an

appropriate power curve (turbine efficiency) and this in turn was converted to daily generated energy. Using the available generated energy the daily volume of water pumped to the upper reservoir was calculated and used as the input signal for the pump operation.

• The creation of the input signal for the turbine operation was based on the daily flow timeseries of pumped water using a moving average.

Model results

Figure 9.18 displays separately the estimated average monthly energy production from the Evinos-Mornos small hydropower plant and the Evinos-Mornos pump-storage scheme as a result of the pump storage modelling experiment on the Athens external water supply network.

However, it should be noted that these results should be considered as indicative results of a preliminary modelling approach and assessment. It is suggested that the specific model needs further refinement in order to make a more accurate estimation of friction losses as a function of reservoir water level. For this purpose Mornos and Evinos reservoirs should be modelled as separate reservoirs and further appropriate modifications should be implemented within UWOT. Furthermore the entire Athens external hydrosystem should be put in a common modelling framework and run with a daily time step so that a direct comparison of all modelling scenarios is feasible.

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 1 2 3 4 5 6 7 8 9 10 11 12 Av er ag e M ont hl y Ene rg y Pr oduc tio n (G W h) Month Evinos pump- storage Evinos-Mornos HPP

Figure 9.18. Average monthly energy production from Evinos-Mornos HPP and pump-storage scheme

Other considerations

The initial analysis has indicated that the pump storage option is feasible; however there are various technical and financial considerations that need to be taken into account and further explored:

• During the renewable scheme design special attention should be given to the fact that the pump operation does not intervene with the normal operation of the tunnel that is used for water supply purposes, which obviously has the highest priority.

• Since Mornos water level has a significant seasonal fluctuation a possible design solution for minimisation of the head for pumping would be the construction of a small control reservoir possibly at the outlet of Evinos-Mornos tunnel at the bottom of which the pump outlet will be located. The reservoir will always be the first to receive the diverted water from Evinos reservoir and the water will go to Mornos reservoir with overflow.

• Detailed analysis is needed for the selection of the most appropriate pump and turbine for the proposed scheme; either the selection of a combination of two separate units or a single reversible pump-turbine.

• The most significant issue for the proposed pump storage scheme is the relatively low elevation difference between the two reservoirs (the total head assuming Evinos mean water level is less than 60 metres) and the long horizontal length between them (30 km). This in effect means high friction losses and a relatively low hydropower production potential. A detailed analysis and modelling taking into account head variability and friction losses variability is therefore necessary.

• Due to high losses and low head it is presumed that pump storage with conventional fuels probably wouldn’t be a financially attractive option. However, the combination with renewable energy sources seems more promising but a detailed cost benefit analysis is required to assess the financial feasibility of such an investment.