NEW LARGE HYDRO

Angola has an exceptional hydro resource, characterized by many rivers with high flow rates and significant slopes, particularly the slopes between the central plateau and the sea level.
Angola started to explore hydropower during the 50s and 60s when several hydropower plants were built in the country, namely Cambambe, Mabubas, Biópio and Matala, together with a number of small hydropower plants. Among these it is worth highlighting the Cambambe hydropower plant, which was built between 1958 and 1963 with a power capacity of 260 MW. Presently this hydropower scheme is under rehabilitation and expansion, which includes dam heightening and the construction of a second hydropower plant.

The Action Plan 2013-2017 gives high priority to hydropower, in particular, the heightening and construction of the 2nd central of Cambambe, and the construction of the hydropower scheme of Laúca. It is expected that by 2017/2018 the installed hydropower capacity, considering Laúca, may reach 4 GW, which will represent roughly 70% of the total installed power capacity in Angola by then.
The following map depicts the hydropower schemes included in the 4 GW power capacity that are expected to be installed by 2017 using differentiated symbology according to status: existing or in construction vs. planned. In addition to these schemes, several large hydropower investments, mentioned in the Action Plan 2013-2017, are also shown - Baynes, Caculo Cabaça, Jamba Ya Mina, Jamba Ya Oma, Cacombo and also the schemes included in the Hydrothermal project – however these will only operate after 2017. Some of the planned schemes will be built in phases in order to optimize their integration in the system.
In the long term hydropower is considered a priority both by the approved Energy Security Policy and by the 2025 country overall strategy. The strategy  expects the country to take advantage from its privileged position regarding water resources in the period between 2015 and 2025. Dispite the significant investment planned for hydro up to 2017, such investment will only result in a utilization of 30% of Angola’s full estimated potential of 18,2 GW (graph below).

EXISTING/PLANNED HYDROPOWER PROJECTS POTENTIAL

OPERATIONAL, UNDER-CONSTRUCTION AND PLANNED HYDROPOWER SCHEMES

The already planned hydropower schemes constitute the starting point for setting the 2025 vision. Still, some optimization and phasing in is considered for Caculo Cabaça and hydro projects in Benguela, Huambo and Bié (Central region) in order to optimize and adjust the schemes to the requirements of the power system in the 2025 horizon.

The current study tried to evaluate all remaining known hydro scheme candidates that are part of the 18 GW hydropower potential of the country through a Strategic Environmental Assessment, which is presented in the current chapter.
With a view to ensuring the assessment of all the existing alternatives and to avoid new project candidates from undermining the 2025 energy strategy, 159 formerly studied sites were identified through a thorough research to the Angolan and Portuguese archives (see map).
Amongst the 159 identified sites, 54 were excluded due to: a) the hydro schemes were already built, under construction or under planning; b) the hydro sites were located on international rivers; c) the schemes primary purpose was irrigation or water supply; d) there was no certainty regarding the location of the hydro site; e) there was no sufficient available data in order to carry out a technical description of the projects.

The 105 remaining sites were assessed and ranked on a preliminary basis in accordance with a multi-criteria matrix that weighted: the impact of the hydro schemes on protected areas; the impact on the navigability of rivers; the amount and cost of generated power; as well as the level of priority for regional development of the impacted Provinces. After this stage around 50 hydro sites were selected so as to undertake a second more detailed analysis.
These 50 sites were further evaluated on the overall impact of the resulting natural reservoirs on protected areas, populated places and infrastructures. The analysis also included the reservoir’s volume calculation and its impact on the watershed. Finally, the hydro schemes were also assessed on construction issues, such as the distance to the electric grid and accessibility to the hydro sites. This final assessment resulted in around 20 priority sites with a view to integrating those in the strategic environmental assessment.

MAP WITH LOCATION OF THE IDENTIFIED 159 SCHEMES AND SELECTION

THE SELECTED SITES

The selection of sites tried not only to include the most competitive run-of-the-river schemes, but also the upstream reservoirs whose main objective is to stabilize the flow and therefore increase energy generation downstream.

The hydropower schemes represent a total power capacity of 4 GW and they are located in watersheds with the largest hydro potential within Angola (Kwanza, Queve, Longa, Catumbela and Cubango watersheds). Considering the remaining existing, on-going or planned projects, the present strategy considered more than 50% of the country’s hydro potential.

These hydro schemes were studied and updated with a considerable increase in the level of detail relative to prior studies. In some cases new construction technologies and equipment were applied, in others location and implantation of main structures were adjusted. For all, the numerical simulation of operation along the water cascade was carried out together with the pre-design and estimative budget associated with the main hydraulic infra-structures.
In the following pages a summary of the main features is presented, as well as an example of some of the main technical drawings of some of the plants selected in the Cuanza basin, Longa basin, Queve basin, Cubango basin and Catumbela basin.

EXAMPLE OF PAST STUDIES UPDATED FOR THE 20 SITES

SELECTED HYDROPOWER PLANTS AND CAPACITY

STRATEGIC ENVIRONMENTAL ASSESSMENT

The Strategic Environmental Assessment is an impact assessment tool that works at the strategic level and contributes to the integration of  environmental and sustainability issues and objectives into the plans where it is applied.
Given the significant environmental impact of a hydropower plant and the relevance of this energy source for Angola, it is of strong concern to ensure that the alternatives by 2025 also take into account environmental criteria, thus seeking to mitigate the risk of non-viability at the later stages.
The hydropower schemes with large reservoirs, whose main objective is to regulate the downstream water flow, present different features in comparison with other schemes.
Despite the higher investment and impact on environment from schemes with large reservoirs relative to run-ofriver schemes, one has to consider also their benefit to all downstream hydro schemes. Therefore, the study included not only an individual assessment of each hydropower scheme, but also the evaluation of combinations of downstream schemes operating with upstream reservoirs.
As for the Catumbela river, only the Cacombo hydropower scheme was assessed as a reservoir, whose main objective was to regulate water flow, together with the remaining downstream hydropower schemes.

The hydropower schemes or the groups of hydropower schemes were assessed and compared according to several parameters, along 3 main dimensions:

• Hydropower potential: which includes an assessment of the installed and firm power capacity, levelized cost of energy, profitability and distance to the supplied consumption center.
   
• Watershed potential and regional development: which assesses the potential of the capacity to regulate water flow – by taking into consideration the storage capacity of the reservoir, the regulation coefficient, the possibility to implement reversible schemes and also the existing downstream power capacity -, the potential for human consumption and agricultural usage, the level of geographical interiority and the potential for the development of new consumption centers within the country.
   
• Environmental impact and constraints: which takes into account the flooded area of each reservoir and its impact on environmental protected areas; on several identified wildlife species (particularly the threatened and/or endemic mammals, reptiles, fishes and amphibians); on existing settlements, on archaeological, historical and architectural heritage; on existing infrastructures – such as roads, bridges and channels - and on the economic activities of the mining and agricultural sectors.

 
ADOPTED CRITERIA FOR THE ENVIRONMENTAL STRATEGIC ASSESSMENT

Three scenarios with different weights for each of the criteria were established for ranking the hydropower schemes on the horizon 2025. All the three scenarios assume the same weight for the environmental component and varying weights for the hydropower potential and the regional development.
In the first scenario – designated “Economic optimization” - there is an emphasis on the hydropower potential. In the second scenario – designated “Economy-territory balance” - the hydropower potential and regional development are given the same weight. In the third scenario, there is a particular focus on the regional development.

DIFFERENT ASSESSMENT SCENARIOS AND RESPECTIVE WEIGHTING OF CRITERIA

The ranking of the different hydropower schemes for each scenario as shown in figure 30, included not only the individual scores - which are depicted on the map – but also the score of the different groups of hydropower schemes along the cascade.
In the Economic optimization and Economy-territory balance scenarios, the hydropower scheme of Calengue in the Catumbela river is considered to have top priority for its competitiveness, integration in the cascade and little environmental impact.

Concerning the Economic optimization scenario, the Kwanza’s hydropower schemes (Zenzo 1 and Túmulo do Caçador) followed by the Queve’s hydropower schemes (Cafula, Dala and Balalunga/Quilengue), assume high priority. As for the Economy-territory balance scenario, the hydropower schemes of the Queve river assume top priority over the Kwanza river.

Finally, the regional development scenario prioritizes the hydropower schemes of Cubango (Mucundi) and High Kwanza (Quissonde), which are located within the country and, despite having higher costs and environmental impacts, are known to have the greatest benefits regarding the agriculture sector. Moreover, the hydropower scheme of Cafula in the Queve river, with a strong agricultural benefit, also takes priority.

RANKING PROCESS OF THE HYDROPOWER SCHEMES IN  EACH OF THE THREE SCENARIOS

SCORE OF EACH HYDROPOWER SCHEMES PER CRITERIA

HYDROLOGICAL VARIABILITY AND OPTIMIZATION/PHASING IN OF THE PROJECTS

The main rivers of Angola, in particular the Kwanza river, are characterized by high hydrological variability not only along a water year, but also between different years. The previous table depicts the mean annual flow observed in the Kwanza river, upstream the hydropower scheme of Capanda, over
11 consecutive water years, whose average is roughly 650 m3/s. However, the peak of the mean annual flow is known to have already exceeded 1000 m3/s in opposition with the water year of 1971/72 when the mean annual flow did not exceed 312 m3/s.
The Lauca, Capanda and Cambambe hydropower schemes will allow to store approximately 7,500 hm3 - only about a third of the Kwanza river’s flow during a regular water year.
These reservoirs allow Angola to take advantage from the water resources of the Kwanza river on a more stable way throughout the year or during the peak hours, particularly in dry years. However, the storage capacity is not sufficient for inter-annual regulation of the river.
Therefore, Angola will need other supplementary alternatives and reserves to face dry water years, on the horizon 2025, such as the 1971/72.

If there was no water storage in Kwanza river and power plants had to dispatch as run-of-river, the available capacity during an extreme dry year would not exceed 1,200 MW out of a total of roughly 3,500 MW of installed power capacity by 2017/2018.

CUANZA RIVER ANNUAL FLOW VARIABILITY (Kangandala gauging station)

However, because consumption of power does not occur consistently during a day or year, but with variable loads, which in Angola peak on the early evenings of summer days, it is possible to use the high storage capacity of Kwanza’s reservoirs to concentrate operation and available power of hydropower plants during the hours of higher need. This is one of the most important advantages of the Lauca and Capanda large reservoirs during dry years.
The advantage of using the hydropower plants, located in the Kwanza river, during the dry water years in order to meet the peak energy requirements of the system is limited to 3.4 GW in 2025 (estimated difference between the peak power capacity of the system and the off-peak power capacity) - corresponding roughly to the installed power capacity without Caculo Cabaça.

The Caculo Cabaça hydropower scheme, with a power capacity of 2,000 MW, has a design flow considerably greater than the water flow running on an average water year in the Kwanza river, which implies that the scheme will only operate at 43% of its total capacity during average water years. During a dry year the hydropower plant would only be able to guarantee 450 MW to the system. A phased approach starting with the dam and other civil works together with the implementation of 1000 MW would allow the system to defer a significant investment with the benefit of a larger and more stable production per MW (the scheme would operate at full power equivalent 77% of the time on an average year) and the same firm power capacity in dry years as in the final solution.

In the central region of the country, several new projects are expected to be implemented not only in the Queve river but also in the Catumbela river and in the Andulo region, particularly in the province of Bié (Cutato, Cune and Cunhinga rivers). The timing for the implementation of the new schemes in this region should be adjusted to the evolution of the system’s requirements. The hydrothermal project, because of its modularity, provides a greater capacity for phasing and optimization.

HYDROPOWER PLANTS CAPACITY FACTOR ON AVERAGE AND DRY YEAR