For many years El Hierro, the most westerly of the Canary Islands, obtained its electricity from an 11.36 MW diesel-fired plant that supplied erratic and expensive (€0.242/kWh) power to the 10,920 residents of this scenic tourist destination:
El Hierro landscape
Then on June 27th of this year, culminating a process that began in 1997, the island proudly inaugurated its new renewable energy system, which will replace the diesel-fired generation with hydro and wind and eliminate 8,700 tonnes of CO2 emissions and save €1.8 million in fuel costs each year. Renewable energy enthusiasts were predictably ecstatic. Even ENEL, Europe’s second largest utility, hailed El Hierro as an example of how sustainable development can be made to work:
El Hierro has realised its dream of achieving a sustainable ecosystem. The island, which was designated a UNESCO Biosphere Reserve in 2000, has actually become a global model of sustainable development in which technology, renewable energy and protection of the environment come together in a single project, one that is set to become a benchmark for the global energy market.
But will it?
El Hierro location
The El Hierro system is still in the start-up/testing phase so no operational data are as yet available. The operating concept, however, is a novel one that combines wind power and pumped hydro storage in the opposite sense to the way they are usually combined. Instead of the pumped hydro being used as load-following backup for the wind power, the wind power will be used to keep the pumped hydro reservoirs full, allowing the hydro plant to function as a baseload and load-following generation source.
The system has three basic components – an 11.5 MW wind farm, a 380,000- cubic-meter upper pumped hydro reservoir in a conveniently-located inactive volcanic crater at 709.5 meters elevation and a lower 150,000-cubic-meter reservoir at 56 meters elevation. The system layout is shown below. The Spanish labels will hopefully be interpretable:
Hydro/wind plant layout
And here are the individual components:
The upper reservoir, in an inactive volcanic crater
The lower reservoir and the hydro plant
The wind farm
On the face of it the El Hierro plan looks workable, even elegant. Hard numbers on exactly how it’s going to work, however, are difficult to find, although one thing we do learn from the quote below is that the system is designed to provide only about two-thirds of the island’s electricity, not 100% as some articles claim:
A production study has been carried out for the hybrid hydro-wind plant. The results obtained are that total demand on the island is 47.4 GWh. Available wind energy is 49.6 GWh. Wind energy that can reliably be produced during periods of demand is 25 GWh, with 9.2 GWh for pumping and 1.8 GWh for synchronous compensation. Hydroelectric production is expected to be 5.6 GWh, and in the end the hydro-wind plant is expected to provide 30.6 GWh during periods of demand, for a total of 64.56% of total energy needed for the island.
Below is my summary of facts, assumptions, deductions and suppositions gleaned from the information that is available. Selected data sources (as is usual in cases like this there are a large number of articles that say the same thing) are listed at the end of the post.
Cost: The system was expensive. Capital costs are given as either €64.7 million (€5,600/kW installed) or $US112 million ($9,700/kW installed) depending on which source one consults. Between a third and a half of the cost was financed by the Spanish government, again depending on the source of information.
Hydro storage capacity & duration: I can find no published storage capacity estimates for El Hierro, but scaling down the Dinorwig pumped hydro plant in Wales (7 million cu meters of reservoir storage, 500 meters head, 1.72 GWh) to El Hierro dimensions (0.15 million cubic meters, 650 meters head) gives approximately 50 MWh, or about half the island’s average daily electricity consumption. If this estimate is correct the hydro system will be able to supply the island’s needs for only about twelve hours after the wind stops blowing, assuming it was fully charged to begin with.
Wind generation: According to the italicized quote above annual “available wind energy” is 49.6 GWh, and since this is in line with the 47.4 GWh annual demand I am assuming that 49.6 GWh is what the 11.5 MW wind farm is expected to generate. But it has to run at a 49% load factor to generate this much electricity in a year, and while the Canary Islands are indeed windy this seems a little optimistic. As illustrated in the graphic below the Canaries experience periods when the wind doesn’t blow, just like the UK, and it blows twice as hard there in the summer as it does in the winter – the opposite of the UK, but still creating a seasonal balancing problem:
And with only five wind turbines in operation we can also expect that breakdowns and scheduled maintenance will make significant dents in output from time to time. The fact that the pumped hydro system is only ~80% efficient also implies a further ~20% loss of input wind energy.
There may well be factors I haven’t considered, but based on the available information it’s questionable whether the El Hierro wind farm will generate enough electricity to keep the hydro plant running year-round.
Water availability: No information is provided as to where the water to fill the pumped hydro reservoirs and keep them topped up will come from, although it’s obviously coming from somewhere or the photos wouldn’t show the reservoirs with water in them. The reservoirs aren’t in major catchments so natural inflow will be minimal. Fresh water is also in short supply on El Hierro and much of it comes from sea water desalination plants that burn a lot of electricity. Hopefully the reservoir water isn’t coming from them.
The capacity differential between the upper and low reservoirs: As far as I can see the productivity of the hydro system is limited to the 150,000 cubic meter capacity of the lower reservoir – unless the plan is to drain this reservoir into the ocean after it’s full, whereupon the problem becomes how to replace the lost water. And if this isn’t the plan then 230,000 cubic meters of the 380,000 cubic meters of water in the upper reservoir is effectively unusable. Am I missing something here?
Performance of the hydro plant: The hydro plant has a capacity rating of 11.3MW, comfortably in excess of peak demand (7.6 MW), and to generate the 47.4 GWh needed to satisfy annual consumption it would have to operate at a load factor of 48%, which is not beyond the bounds of feasibility. So if the wind turbines can generate enough power to keep the reservoirs topped up the hydro system should be able to fill demand.
Finally comes the question of the fate of the 11.36 MW diesel-fired power plant that has historically supplied the island’s electricity. It’s going to remain in service “to be used in exceptional or emergency situations, when there is neither sufficient wind nor water to produce enough electricity to meet demand.” This sounds like a wise precaution.
Although the locals don’t expect they will ever have to fire it up:
The island of Hierro supplies itself entirely with renewable energy. We’re 100% ecological!!