This section presents the results obtained from the application of the method described in
Section 2 to the island of Gran Canaria. This island belongs to the province of Las Palmas, in the region of the Canary Islands, Spain. Gran Canaria is located in the southwest of the Iberian Peninsula, at 28° North latitude and 15°35′ West longitude. Its total surface area is 1560 km
2. Its maximum altitude is 1956 metres above sea level. It consists of a rugged volcanic landscape with an average height of 150 metres. Of the 114 “large dams” existing in the eight Canary Islands, Gran Canaria has 69, more than 60% of the total. In relation to its surface area, it is considered the area with the highest concentration of dams on the planet. The island has 172 dams, which are divided by the local authorities into 69 “large dams” and 103 “small dams”, according to the local nomenclature used by the island’s government, the Cabildo de Gran Canaria [
22]. The “large dams” are hydraulic works for the retention of water in ravines with a height of more than 15 metres or with a capacity of more than 100,000 m
3 [
22]. For simplicity of wording, the term “large dams” will be replaced by the term “dams”. It is not the purpose of this study to apply the proposed methodology to what are considered “small dams” at the local level, in order to avoid considering excessively low storage capacities. However, the methodology is designed to be applied also to sites with small capacities.
As part of the study in this document, it has been decided to divide the surface area of the island into zones delimited by ravine basins and interbasins, as detailed in previous sections. Each of these includes one or more ravine channelswhich house the different dams on the island.
3.1. Dataset Choice and Connection Detection
In our application of the method, we will use the Spatial Data Infrastructure of the Canary Islands (IDE Canarias), included in the Spatial Data Infrastructure of Spain (IDEE), belonging to the National Geographic Institute of Spain (IGN). The IDE Canarias GRAFCAN Viewer Version 4.5.1 [
39] has a maximum resolution of 10 m. This software contains all the dams to be analyzed in this study, as well as the basins, interbasins, watercourses and ravines that make up the island (see
Figure 4). All the island’s ravines start, in the first instance, from Pico de Las Nieves, the point on the island with the highest elevation above sea level and located in the geometric centre of the island. Our study aims to offer the results broken down by basin and interbasin, so these data are of vital importance. If we look at
Figure 5, we can see the distribution of the 69 “large dams” on the island in relation to the aforementioned breakdown. In addition, for further information on the dams, we have used data from the Consejo Insular de Aguas de Gran Canaria (Gran Canaria Water Board) [
22], a public body belonging to the island government of Gran Canaria. These data include surface area, volume, state of exploitation and height.
Figure 4 shows the study area divided into the different basins and interbasins existing on the island on a steep terrain. Each basin has the bed of a large gully of the island, which crosses it until it reaches the sea. It is this ravine that gives the basin its name. Some basins have more ravines in addition to the main one described above. The basins with the largest extension correspond to the ravines of La Aldea (182 km
2), Maspalomas (134 km
2) and Arguineguín (94 km
2).
Figure 5 shows the distribution of the island’s “large dams” divided into the different existing basins and interbasins, on a terrain whose relief has been highlighted in order to give an immediate idea of the height above sea level at which these dams are located, where the relief increases as we approach the highest point of the island.
With the IDE Canarias Viewer Version 4.5.1, we have also been able to locate the different environmentally protected areas on the island. Although it is true that the connections discarded because they are in these areas will be subject to an environmental impact assessment study:
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Natura 2000 Network: European ecological network of biodiversity conservation areas, either Special Areas of Conservation (SAC) or Special Protection Areas for Birds (SPAB) (see
Figure 6). 50% of the island’s land area belongs to one of the two categories of this protection instrument.
A large number of the dams analyzed in this study are located in the SAC Zone, specifically 28.99% in relative terms. Essentially, this zone is concentrated in the southwest and west, which coincides with the least populated area of the island. On the other hand, in
Figure 6, the SPAB Zone occupies a smaller area than the SAC Zone, being mainly centered in the south and west of the island and the proportion of dams included in this category is 13.04%.
However, the greater dispersion of dams in the southwest and west of the island compared to the north and east of the island reduces the proportions described.
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Canary Islands Network of Biosphere Reserves: UNESCO project to conserve biodiversity in a sustainable way. The island of Gran Canaria has 46% of its territory declared a Biosphere Reserve (see
Figure 6.). This environmental protection is quite restrictive and covers land and sea. Some 33% of the island’s dams are located in this category.
Again, the protected territory is located in the southwest and west of the island, due to the high environmental value in terms of the number of native species, the scarce economic development in the area and the scarce or non-existent population. For all these reasons, this area has been the most unaltered area by humans over time.
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Canary Islands Network of Protected Natural Spaces: It should contain the main habitats and centres of diversity (see
Figure 6). It includes several categories: National, Natural and Rural Parks; Special and Integral Nature Reserves; Natural Monuments; Protected Landscapes; and Sites of Scientific Interest. 43% of the island’s surface area is in one of the above categories and 31.88% of the dams are located in this area. This instrument contemplates a greater dispersion in terms of the territories it protects.
In summary, it can be deduced that the island, which is relatively small in size, has a high level of environmental protection through any of the instruments described, in any of their categories This makes it a decisive factor in making decisions on the choice of suitable sites for the implementation of future pumped-storage hydroelectric power plant projects (PHES) in the aforementioned connections.
To form the initial connections, all possible pairings between two dams were established, so that for the 69 “large dams” on the island, a total of 2346 possible combinations were produced.
3.2. Distance to Grid Connections
The steep volcanic terrain of the island requires that the distance to the power grid of an inter-tie between two dams be as short as possible. This would favour the technical implementation of the PHES project and its economic viability [
16]. In addition, the environmental impact of large extensions of high and medium voltage lines would be very high [
40].
The location of the hydroelectric power plants and electrical substations, both existing and those to be built in the near future, is obtained with the software of the Spatial Data Infrastructure of Gran Canaria (IDE Gran Canaria). This software, IDE Gran Canaria Viewer Version 4.5, is complementary to the one described at the beginning of this section and in some sectors, it expands and details the information. This software integrates the data of the entities that own the electricity grids, which are: Red Eléctrica de España (REE) and Unelco-Endesa (Enel Group). In addition, Google Earth software has been used in this study to georeference the power plants and substations and manually create a shapefile (see
Figure 7).
Figure 7 shows how the new substations attempt to remedy the deficiencies in certain areas of the island, strategically located to close the circle of the electricity network. In the areas with the highest density of substations, it has been decided to extend and display them independently (see
Figure 8). On the other hand, the existing substations are clustered around the island’s main economic and tourist centres: the island’s capital, Las Palmas de Gran Canaria and the south of the island, comprising the municipalities of San Bartolomé de Tirajana and Mogán.
Figure 8 shows the two existing thermal power plants on the island and the nearest existing and future substations. Located close to the coast, they represent the two epicentres around which the electricity grids have been built over the years. However, this situation has already changed with the development of onshore wind farms, with an installed capacity of 159.3 MW and photovoltaic plants on the island, with a capacity of 40.6 MW [
20], among other environmentally friendly technologies, different to fuel combustion. In addition, in
Figure 8 we can also see an enlargement of the future hydroelectric power plant and its corresponding substation, which will be built for energy use between the Chira-Soria dams in the heart of the Arguineguín ravine basin. This will make it possible to develop electricity grids in the least exploited part of the island from the power lines associated with the power plant, since many other grid supply points will be able to be directly or indirectly incorporated into these lines.
On the other hand, no pairings have had to be ruled out in the application of the maximum distance to the grid constraint. This is due to the high number of electricity substations in a relatively small territory, to the dispersed and strategic distribution that has had to be carried out by the local authorities and to the coincidence of the location of these substations with the locations of the compatible connections obtained after having applied the optimization (see
Figure 9). However, this is valid because we assume the future implementation of power plants and substations.
Table 5 shows the frequencies of the distances of the connections to the substations. It can be seen that most of the compatible connections are between 1 and 5 km apart.
3.3. Overall Potential Results
The stored energy for the 2346 possible combinations available at the start of the methodology was calculated as described in Equation (1), resulting in 614,737 MWh (see
Figure 9). However, this figure corresponds to an initial theoretical value, as these combinations do not include any real criteria or constraints and have not been subject to optimization. This value will only serve as a reference for comparison with those obtained in the following steps of the methodological process.
In order to achieve the calculation of a viable storage potential, we first need to establish acceptability limits that allow us to define a framework based on technically feasible connections. Two technical parameters have been chosen as limits: the maximum distance and the minimum height between dams (see
Table 1). Values have been chosen that do not excessively restrict the number of connections. In particular, connections will be formed between dams with a height between them of not less than 30 m and a maximum distance between them of 5 km. The result is a new list of compatible connections that can actually be realised from a technically and economically realistic perspective. Calculating the storage energy obtained with this new dataset we obtain 19,768 MWh, produced by 151 connections formed between 67 dams (see
Figure 9). This result corresponds to less than 5% of the previous value, obtained without applying the conditions.
Once the optimization has been applied, by means of Equations (5)–(7), we obtain a much lower result, 8443 MWh, with 26 connections and 52 dams. This result is less than half the value we had before optimization (19,768 MWh), which means that the optimization algorithm has worked. The optimized selection of connections, referred to in
Figure 9 as “Selected connections 1”, is detailed in
Table 6, which includes the basin or interbasin to which each dam belongs, in addition to the installed storage power estimated by Equation (4) and other results such as the values of distance between dams, height between dams and distance to the electricity grid. From the process optimization, the remaining technical constraints from
Table 3 are applied to the resulting dataset. Again, the figure (5996 MWh) shows a considerable decrease (28.98%), essentially due to the technical restriction of the distance-to-height ratio. This shows the significant influence of this parameter on the final result. This new selection of connections is referred to in
Figure 9 as “Selected Connections 2” and is shown in
Table 7. The application of the maximum grid distance constraint does not alter the results (
Section 3.2). This table shows the results before applying the environmental restrictions. We have considered these results as indicative of the potential because, as explained in
Section 2.5.3, the connections included in these spaces must be analyzed on a case-by-case basis.
Finally, the environmental restrictions described in
Table 4 results in a potential of zero. It must be taken into account that a single dam may belong to one, several or all the categories of protected areas. The graph in
Figure 10 shows the distribution of dams on the island in relation to each category, taking into account the condition described above.
Considering our estimated viable potential as that to which environmental restrictions do not apply, we will increase the energy stored on the island from 0 MWh to 5996 MWh. If we consider the immediate implementation of the PHES Chira-Soria, then the existing potential would be 4814.34 MWh and the studied potential would add 1181.66 MWh of storage capacity, which would be an increase of 24.54%.
If instead of taking 5996 MWh as viable potential and instead we take 8443 MWh, which is the value obtained after optimizing and without having applied the technical environmental restrictions, the storage capacity would increase. At this point, the various local development agents would have to study which restrictions to apply to each PHES, because it may happen that, for example, the higher technical and economic cost of not complying with the distance-height ratio restriction may be assumed, or that, in another case, a connection excluded in this study due to an environmental restriction may be taken into account because it represents little or non-significant ecological impact.
It is for all the reasons described in the previous paragraph that, as described in the methodology, the process of calculating the viable potential presented in this study is open-ended. We therefore consider the value of 8443 MWh as the figure from which the variations of the method begin.
Although this study does not consider the possibility of connecting one dam to two other dams, it has been detected in the course of the study that the Cueva de Las Niñas-Soria connection, added to the future Chira-Soria connection, would represent the second largest storage capacity value between two dams (specifically, 4158.82 MWh of stored energy and 189.04 MW of installed power), second only to the Chira-Soria dam connection.
Table 8 shows the distribution of the potential between the basins and interbasins of the island after optimization. To understand the values in the table, it must be taken into account that in each basin the stored energy of a connection has been included, provided that in this connection, one of the two dams, or both of them, belong to this basin. Furthermore, if the dams forming a given connection belong to different basins (or interbasins), the storage potential will be imputed to both basins, so that the total storage potential does not necessarily coincide with the above results without distribution in basins and interbasins. The purpose of
Table 8 is simply to show the ranking of basins and interbasins according to maximum stored energy. The distortion of the result for the reason described above does not alter the order of this ranking.
The Arguineguín ravine basin has the greatest potential and therefore the order in which projects are undertaken must begin there. The Chira-Soria hydroelectric power plant is located in this basin, as the two dams that make it up belong to this basin. If the option of adding the Cueva de Las Niñas dam to a power plant with three dams were also explored, the potential in this basin would almost double.
Table 9 is analogous to
Table 8, the difference being that
Table 9 is made for the viable storage potential, before applying the environmental restrictions. It may be highlighted that the same basins or interbasins in the first positions in
Table 8 are those in
Table 9.