In November last year I wrote a post on the Gorona del Viento plant on the island of El Hierro in the Canaries, an innovative renewable energy project that uses a pumped hydro system to supply dispatchable power to the grid and surplus power from a wind farm to keep the pumped hydro reservoirs topped up. Gorona del Viento was in the news at the time because it had just been commissioned and was being hailed as an example of how renewable energy could be made to supply 100% of energy needs on a remote island. The graphic below recaps the plant layout:
Gorona del Viento plant layout. The wind turbines have a capacity of 11.5 MW and the pumped hydro plant a capacity of 11.3MW. The Llanos Blancos diesel plant, which has historically provided the island’s electricity, consists of seven diesel-fired units (one mobile) ranging in size from 0.78MW to 2MW and aggregating 11.78MW. Average demand on the island is about 5.4MW and peak demand about 7.6MW.
And after having succeeded in supplying 100% of El Hierro’s power for two consecutive hours between 12.25 and 14.25 on August 9th, 2015 (the claims of four consecutive hours are incorrect) Gorona del Viento is now back in the news:
For four hours from 12 noon on Sunday August 9, the Gorona del Viento wind-hydro power station generated all the electricity for the tiny island of 10,000 inhabitants using clean energy – the culmination of a project that began 30 years ago.
“This is a relevant fact for locals, Europe and the planet. We prove that it is possible to achieve 100% of green energy in an isolated region by boosting renewables and ditching fossil fuels.”
El Hierro, one of the Canary Islands, has turned off its diesel engines. The island is set to be run entirely on wind power from this week.
Well, El Hierro hasn’t turned off its diesel engines quite yet. On August 30, 2015, the last day for which I have data, 74% of the island’s electricity came from diesel generation. Nor is it set to be run entirely on wind power. In fact it won’t be for some time, if ever.
I never expected to come across any grid data for Gorona del Viento, so I was pleasantly surprised when I found that the Red Eléctrica de España (REE) publishes data for the El Hierro grid that includes diesel generation plus wind and pumped hydro generation from Gorona del Viento, with values at ten-minute intervals. The numbers REE gives for wind and hydro output are ambiguous but the sum of wind + hydro is not, so we are able to compare total renewables generation with total diesel generation over the life of the plant since startup. Figure 1 shows the results since July 27, 2014, the day on which Gorona del Viento sent its first renewable energy to the grid, with REE’s ten-minute data compiled into average daily generation values:
Figure 1: Daily average El Hierro generation, July 27, 2014 to August 30, 2015
The first year after plant inauguration on June 27, 2014 was devoted to “initial testing” and as a result approximately 95% of El Hierro’s electricity had to be supplied by diesel generation over this period. Full operation did not commence until late June, 2015 (I’ve assumed June 25), and Figure 2 summarizes daily generation over the two months between then and August 30. The diesel/renewables split is almost exactly 50-50, which is not too bad considering that Gorona del Viento was expected to supply only 65% of the island’s demand to begin with. It is, however, far short of the 100% renewables generation that many were led to expect:
Figure 2: Daily average El Hierro generation, June 25 to August 30, 2015
Figure 3 shows the ten-minute grid data for August 9, the day when renewables succeeded in filling all of El Hierro’s electricity demand for two consecutive hours, although for the day as a whole they supplied only 71% of it. Two features are of interest:
- There is no obvious reason why diesel generation should have been abruptly shut down at 12.25. Maybe it was simply an unscheduled outage.
- Diesel generation during the day was cut back to a low-level baseload mode, with presumably only one unit operating, and load-following was handled entirely by Gorona del Viento wind and hydro. This shows that the plant is capable of doing what it was designed to do at least for short periods:
Figure 3: Ten-minute average El Hierro generation, August 9, 2015
What it might take to upgrade the Gorona del Viento plant to the level where it produces 100% of El Hierro’s electricity? This is at least theoretically possible because the pumped hydro system provides a balancing capability that other renewables installations don’t have. So let’s briefly look into this question.
The combined wind/hydro system at Gorona del Viento presently produces only about half the power El Hierro needs. (Between June 25 and August 30, 2015 it produced an average of 2.7MW, which relative to the 11.5MW capacity of the wind farm works out to a capacity factor of 23%, about what one would expect for a combination of onshore wind turbines and pumped hydro.) The obvious requirement is therefore to double wind capacity – in fact more than double it because July and August are the windiest months on El Hierro. So we will increase it to 25MW.
The pumped hydro system might also need to be expanded. At present it has a capacity of about 250MWh (I estimated 230MWh using the formula given by Stanford University and 270MWh by scaling down Dinorwig), enough to supply El Hierro demand for only about two days. Increasing the size of the lower reservoir, which is less than 40% of the size of the upper reservoir (150,000 cubic meters versus 380,000 cubic meters, which limits the effective capacity of the system to 150,000 cubic meters) to match the size of the upper reservoir would increase storage capacity to around 600MWh, enough to supply island demand for about five days. This should result in a significantly higher utilization of renewable energy. (There are in fact no limits to the size of the lower reservoir. The sea is right next door.) There is, however, no need to expand maximum hydro output because the current 11.3MW capacity is already sufficient to handle El Hierro’s 7.6MW peak demand.
And the existing diesel plants? They would have to be kept 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 expanded system would probably allow El Hierro to generate most if not all of its power from renewables for most of the time. The problem with it, however, is one common to all projects where generation comes dominantly from intermittent renewables – overcapacity and inefficiency. The island of El Hierro would be using 36.8MW of installed generating capacity – 25MW wind and 11.8MW diesel – plus 11.3MW of pumped hydro to service an average demand of only 5.5MW and a peak demand of only 7.6MW. The pumped hydro system would stay busy keeping up with demand fluctuations, but the wind turbines and diesel generators would be operating at an overall capacity factor of only 15%.
Which brings us to the question of economics. How economic is Gorona del Viento? I’ve made no attempt to estimate what its levelized cost of electricity might be, but much has been made of the fact that it will save El Hierro lots of money in imported diesel costs:
This project will avoid an annual consumption of 6,000 tonnes of diesel, which is equal to 40,000 barrels of oil that would have to be imported by boat to the island, thus creating a savings of over 1.8 million euros a year.
Diesel storage tanks, Llanos Blancos Plant, El Hierro
At the moment Gorona del Viento is cutting El Hierro’s imported diesel bill approximately in two, resulting in savings of let’s say a million euros a year. The cost of the project is given as 64.7 million euros by Gorona del Viento El Hierro SA and up to 82 million euros by other sources. Time to cash payback is therefore 64.7 to 82 years when plant operating costs are excluded and infinity when they are included (based on the 0.05 euros/kWh operating cost estimated by Hallam et al, which gives operating costs of more than a million euros a year.)
And capital costs? Calculated relative to the 11.5MW of installed wind capacity they work out to 5,600-7,000 euros/kW, roughly the same as for a nuclear plant that operates at a far higher capacity factor.
So what does the Gorona del Viento project portend for the future of renewable energy on remote islands? Here is my summation:
1. A hybrid renewable energy/pumped hydro storage system can be scaled to the level where it will provide 100% of an island’s electricity demand for most of the time and for all of the time if storage capacity can be made large enough, although in most cases fossil fuel backup will be needed.
2. Hybrid systems can be installed on any mountainous island, although not on low-lying ones, by using the sea as the lower reservoir. (Gorona del Viento had the advantage of a ready-made upper reservoir, courtesy of an old volcanic crater. On islands not so blessed the upper reservoir would have to be dammed or excavated).
3. These systems will, however, be expensive, inefficient and commercially unviable unless they are heavily subsidized.
4. Staying with fossil fuel generation would be simpler and cheaper. Fossil fuel generation with carbon capture and storage might even be competitive with a hybrid system if CO2 emissions are a concern.
Finally it must be noted in the interest of fairness that despite repeated claims to the contrary El Hierro is not the undisputed world leader in island renewable energy. The island of Eigg off the coast of Scotland has had a 100% wind/solar/hydro renewable energy system in operation since February 2008, although the result has not always been 100% renewable energy.