To the east of the Canary island of El Hierro, where the Gorona del Viento wind-pumped hydro project has attracted international attention, the island of Gran Canaria is developing a wind-solar-pumped hydro project of its own that has so far attracted very little attention outside Gran Canaria. This is surprising because the project is many times larger than Gorona de Viento and has one distinguishing feature that so far as I know makes it unique. The €300 million pumped hydro storage plant is scheduled to be constructed first. The wind farms and PV panels will come later.
Why is the pumped hydro plant being built first?
According to Antonio Morales, President of the Gran Canaria Island Council, because A massive implantation of renewables is necessary to achieve energy sovereignty. Chira-Soria, whose dams will act as a battery that stores wind and solar energy and transforms it into a continuous and stable electricity supply, is the key.
According to the Red Eléctrica de España, because It represents essential infrastructure for integration of renewables on the island.
And according to a resolution recently passed by the Gran Canaria Island Council, because It will allow Gran Canaria to obtain up to 70% of its energy production from renewables.
This innovative approach looks good on paper but makes sense only if Chira-Soria has sufficient storage to handle a “massive implantation of renewables” and in particular up to 70% renewables generation, which in the case of Gran Canaria (population 840,000) works out to about 2.8 terawatt-hours a year. Here we look briefly into the question of whether it does.
First some details on the Chira-Soria pumped hydro plant. It will connect the existing Chira and Soria fresh water reservoirs as shown in the graphic below:
Figure 1: The Chira-Soria pumped hydro system
Plant specifics are:
- Chira (upper reservoir): Volume 5.2 million cubic meters, maximum elevation 903.5 meters
- Soria (lower reservoir): Volume 32.8 million cubic meters, maximum elevation 620m
- Head at maximum elevation: 283.5 meters
- Generation/pumping capacity: 200 megawatts
- Efficiency after generation and pumping losses: 68%
- Storage capacity: approximately 5,000 megawatt-hours (limited to the capacity of the smaller Chira reservoir).
5,000MWh of storage capacity will, however, be available only when Chira is at its full 5.2 million cubic meter capacity, and according to the graphic from this link reproduced below as Figure 2 it will rarely if ever be at that level (the brown curve shows reservoir volume before irrigation water extraction and the blue curve what’s left over). The link further concludes that only half of the total capacity of the Chira reservoir, i.e. 2.6 million cubic meters, could be used for pumped hydro because of irrigation extraction, evaporation losses and other constraints. If so then the effective storage capacity of the Chira-Soria plant decreases to 2,500MWh:
Figure 2: Predicted variations in water storage volume with time, Chira Reservoir
Next some details on Gran Canaria electricity supply and demand. Data for the year 2011 from the Local Energy Management Agency of Las Palmas of Gran Canaria are summarized in Table 1:
In 2011 Gran Canaria generated 93% of its electricity from thermal plants (a mixture of CCGTs, gas turbines, steam turbines and diesel units) and 7% from renewables, most of it wind. Renewables generation would therefore have to be scaled up by a factor of ten from 2011 levels to achieve the 70% penetration the Island Council expects.
Is Chira-Soria capable of supporting 70% renewables generation year-round ? I didn’t have the time to perform a full evaluation so I picked a single day at random (October 19, 2015, which was the last day for which complete data were available at the time I did the work. I believe this will qualify as a random selection). Figure 3 shows Gran Canaria’s demand curve for the day (data from Red Eléctrica de España) with the wind and solar generation curves plotted below. Solar contributed about what it would be expected to contribute but wind generation was at or close to zero for most of the day. This, however, is a common occurrence during September and October, which are typically low-wind months in the Canaries:
Figure 3: Gran Canaria demand, wind and solar generation, October 19, 2015.
Eyeball estimates indicate about 10,000MWh of total demand offset by about 100MWh of renewables generation, and factoring up renewables generation by ten to analog a 70% renewables scenario still leaves a deficit of about 9,000MWh. Clearly Chira-Soria is not large enough to supply Gran Canaria demand even for one windless day. And low-wind periods in the Canaries can go on for weeks at this time of the year.
Although this is not to say that Chira-Soria is worthless. It does have the capacity to follow demand to the point where Gran Canaria’s thermal plants could have run continuously at around 410MW while maintaining the reservoirs in balance, as illustrated in Figure 4. (The pumping and generation cycles each represent about 1,000MWh). But this benefits only the thermal plants, which are ultimately scheduled to be replaced in their entirety by renewables. The benefits will also be at least partially offset by the 32% loss incurred in cycling power through the hydro plant:
Figure 4: Hydro pumping and generation needed to maintain thermal generation constant at 410MW, Gran Canaria, October 19, 2015
So how much storage is needed to balance 70% renewables generation on Gran Canaria? I have no specific estimates for Gran Canaria, but scaling up “windless period” estimates from the Gorona del Viento plant on El Hierro yields numbers in the hundreds of GWh range, two orders of magnitude larger than the storage capacity of Chira-Soria. There are other reservoirs on Gran Canaria with pumped hydro potential but there is no way anything like this amount of storage could ever be developed on the island.
In summary, Chira-Soria emerges as yet another example of an ambitious renewable energy project that has no realistic chance of working simply because no one involved in the planning process seems to have realized – or is willing to admit – that it’s impossible to install the huge amount of energy storage needed to make it work. Moreover, the project is still being justified by the alleged success of the €84 million Gorona del Viento wind-hydro plant on El Hierro, which as will be discussed in the October performance update is beginning to fray at the edges after only four months of operation.
With Chira-Soria Gran Canaria is heading down the same blind alley as El Hierro, although potentially a far more costly one. Up to €300 million is already allocated for the pumped hydro facility, and expanding existing wind and solar capacity by a factor of ten or more will raise costs to well over a billion – if wind and solar ever expand to that level, that is. Crunch time will come when Chira-Soria comes on line and its storage limitations become apparent. Will wind and solar construction grind to a halt at that point, or will it continue regardless? The only thing we can be certain of is that Gran Canaria’s fossil-fuel plants will be keeping the lights on for a long time yet.