As noted earlier, the computer simulation model of the Onslow PHES was operated with a simplified model of the Clutha, Waitaki, Manapouri, and Waikato hydro power schemes, with wind energy development. All water transfers and energy values are on a 30-minute timestep (trading period half-hourly data). As discussed in Chapter Four, the actual fluctuating wind energy was considered as output power per half hour in the model. However, the demand from the wind energy section of the model was considered as the annual average wind energy as a base reference in 2012. For example, taking 50 MWh as the demand (average annual output) and an actual output of 90 MWh then the surplus energy would be 40 MWh. In this case would the Onslow PHES be able to absorb the 40 MWh?
The simulation was performed using eight scenarios for wind energy generation capacity, to compare the benefits of integrating pumped storage in each case. The first scenario, with no increase in wind energy development, represented the lowest possible level of wind energy generation and the 24% increase assumed in this study is the maximum potential future development. All scenarios were conducted in conjunction with modified operation of hydro power schemes in half- hour simulation periods for 1998-2012.
5.3.1 Operation of the pumped hydro storage with and without wind energy development in the future.
The results of applying the model with and without wind energy development are shown in Table 5-1. The simulation with 24% wind energy development shows that almost 20,437 GWh, and without wind energy development 20,630 GWh per half hour could have been used and stored through avoided spill from 1998-2012. The total difference within the simulation periods is 193 GWh, which is equivalent to 1.415 MW.
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Wind energy development 0 % 1% 8% 16% 24%
Mean daily power output through avoided spill throughout New Zealand in MW between 1998-2012
168 167.97 167.81 167.3 166.58
Equivalent mean power output (MW) between 1998-2012
18.85 18.85 18.85 18.85 18.85 Energy stored at upper reservoir
GWh at the end of simulation
6412 6382 6265 6052 5782
Equivalent mean daily power output (MW) between 1998-2012
47 46.72 45.78 44.04 41.87 Energy loss due to operation of
pumped storage in TWh per half hour
10.32 10.34 10.44 10.6 10.77
Equivalent to power loss MW between 1998-2012
84.1 84.32 85.1 86.35 87.73 Energy loss from wind energy GWh
per half hour
0 2.77 4.92 7.41 10
Equivalent to power MW between 1998-2012
0 0.022 0.04 0.06 0.0814
The operation of the model with the zero wind energy development scenario shows that the Onslow pumped storage system could absorb all the extra wind energy with no wind energy development or compensate for any shortfall in the grid in the case of low wind energy availability. Similarly, there is a loss of 0.01% with a 24% development in wind energy every year. In other words, a pumped hydro energy storage of 1,300 MW can absorb all the excess energy dispatched to the grid with or without wind energy development. The simulation shows that every 1 MW of pumped storage can support another 2 MW of wind. The above results were compared with wind energy development in five scenarios, as shown in Table 5-1.
Figure 5.8 shows the operating level of the Onslow reservoir in two simulation scenarios: no increase in wind energy development and 24% increase every year from 1998-2012. The amount of water pumped and stored at the Onslow reservoir decreases proportionally with increases in wind integration levels. The two curves in Figure 5.8 illustrating the operation of the pumped storage scheme Table 5-1 Results of operating possible Onslow pumped storage for a range of wind energy senarios.
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with and without wind energy development display the same trend during operation.
Sending more wind energy to the grid reduces avoided water spill in the hydro power plants, which reduces the level of the Onslow reservoir. However, the pumped storage scheme shows it can support the goal of increasing the use of intermittent energy sources such as wind power even when wind power approaches a 20% or more generation share in the future. This would also provide a grid buffer as it moves toward renewable energy with fluctuating power outputs.
Figure 5.8 Onslow water reservoir water level (1998-2012) in two scenarios: with no increase in wind energy development (blue line); and 24% increase every year (red line). Starting point is zero storage at 720 masl.
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Chapter Six: Waitaki Valley improvement from pumped storage:
increased irrigation water
6.1 Introduction
Irrigation began in the Waitaki Valley in the early twentieth century and has developed ever since. The generally temperate climate makes the area ideal for high-production agriculture, but a reliable supply of water is needed to maintain production levels, as the lower river catchment receives only around 500mm of rainfall annually. Irrigation is essential to the existing local economy, supporting a number of primary sector industries including horticulture, viticulture, arable farming, sheep and beef farming and dairying. A 2010 report by Lincoln University concluded that the Waitaki River is the most significant river for irrigation in Canterbury [116].
Competition for allocation is fierce and often litigious, and occurs between hydroelectric power schemes and irrigation, or between irrigators themselves. This has been in evidence on the Waitaki River where Meridian Energy Limited’s Project Aqua hydroelectricity application and numerous irrigation applications prompted a Ministerial call-in, which was followed by special legislation requiring the promulgation of a water allocation plan [117].
The seasonal Onslow pumped hydro storage scheme offers a useful consequence of maintaining stable hydro lake levels so that more summer water is available in the Waitaki, which makes more irrigation a viable option.
The aim of the chapter is to demonstrate the value of extra Waitaki summer water, under the scenario of use to maximum possible extent.