El Hierro Renewable Energy Project – October 2015 Performance Review

The Gorona del Viento (GdV) renewable energy plant on the Canary Island of El Hierro is a flagship project designed ultimately to provide the island with 100% renewable electricity and to consign its diesel generators to history. GdV comprises a wind park with 11.5 MW capacity and a pumped hydro storage plant with 11.3MW capacity, installed at a total cost of €84 million. Since operations began in June of this year the plant has not performed up to expectations. This is the second in a series of operational updates.


According to grid data published by the Red Eléctrica de España (REE) power sent to the El Hierro grid from the GdV wind-pumped hydro plant and Endesa’s Llanos Blancos diesel plant during October 2015 was as follows:

  • Diesel: 3,225 MWh (86%)
  • Wind:      414 MWh  (11%)
  • Hydro:      90 MWh  ( 2%)
  • Total:   3,730 MWh

Renewable energy from GdV made a minimal contribution to El Hierro’s electricity demand during the month dominantly because of a lack of wind. Wind speeds on El Hierro began to decrease in late August and low wind conditions persisted through most of September and all of October. For 40% of the time during October (300 out of 744 hours based on 10-minute grid data) the wind speed was too low to turn the turbine blades and zero wind output was recorded.

El Hierro grid statistics since GdV startup on June 27, 2015 are summarized in Table 1. In 127 days of operation renewable energy from GdV has supplied 34% of El Hierro’s grid demand, contrasting with the 65% predicted by a 2012 engineering study and with the 100% anticipated by some media reports.

Figure 1 plots diesel, wind and pumped hydro generation during October 2015:

Figure 1: Diesel, wind and pumped hydro generation sent to grid, ten-minute grid data, October 2015

Figure 2 plots average daily generation since project startup on June 27, 2015. The impact of the decrease in wind speeds after late August is clearly visible:

Figure 2: Diesel, wind and pumped hydro generation sent to grid, daily averages, June 27 to October 31, 2015

Details on GdV plant layout, operation and capacities are given in the September update.

Operations to date have identified five problem areas that are causing GdV to perform below expectations: 1) extended low-wind periods, 2) inadequate wind capacity, 3) inadequate hydro storage capacity, 4) wind curtailment to maintain grid stability and 5) additional wastage of wind power caused by operating procedures. Dealing with these in sequence:

1. Extended low-wind periods

As shown in Figure 3 GdV has been in the doldrums since mid-September and only a minimal amount of wind power has been delivered to the grid since then. Are such low-wind periods common on El Hierro? No wind speed data are available for the GdV wind farm but they are available for El Hierro airport 3km to the north, and as shown in Figure 3 airport wind speeds correlate quite well with GdV wind farm generation, particularly if the GdV wind turbines have a typical ~3.5 m/s cut-in speed:

Figure 3: Wind speeds at El Hierro airport vs. Gorona del Viento wind generation, daily averages, June 27 to October 31, 2015

To investigate how common extended low wind periods might be on El Hierro I downloaded all the available airport wind speed data, which begin in January 2014. Figure 4 plots daily average wind speeds with the 2015 data superimposed on the 2014 data. The September-October lull appear in both years, as do low-wind periods in early February and to a lesser extent April, and the 2014 and 2015 March, June and October daily average wind speeds almost mirror each other:

Figure 4: Daily average wind speeds at El Hierro airport, January 1, 2014 to October 31, 2o15

These results indicate that low (and high) wind periods on El Hierro occur at about the same time every year, sometimes replicating each other remarkably closely. If GdV is to supply 100% renewable energy to El Hierro year-round it must therefore generate enough wind power to supply annual island demand and have enough hydro storage capacity to cover generation shortfalls during low-wind periods up to two months long.

2. Inadequate wind capacity

This is a difficult issue to resolve because current operating procedures are resulting in the curtailment of an unmetered amount of wind power, as discussed later. However, an approximate calculation based on airport wind speeds and GdV wind production indicates that without this curtailment the GdV wind farm would have an annual capacity factor of about 35%. This is a very respectable capacity factor for onshore wind, but with 11.5MW of installed wind capacity it will generate 35GWh/year, only about 70% of El Hierro’s annual demand. So if GdV is to supply 100% of annual demand wind farm capacity must be increased to about 17MW. This number, however, presupposes that substantially all of the power generated by the wind farm is consumed on the El Hierro grid, which as we shall see is presently not the case.

3. Inadequate hydro storage capacity

This deficiency was noted in the September report and things have not improved since then. Between September 12 and October 31 GdV wind + hydro generation averaged 0.7MW and El Hierro demand averaged 5.1MW, representing an average shortfall of 4.4MW for 50 days. Approximately 6,600MWh of hydro storage capacity would be needed to cover 100% of this shortfall, over twenty times the ~270MWh capacity of the existing GdV hydro reservoirs. Even with twice as much installed wind capacity the storage requirement falls only to 5,600MWh. (Adding wind capacity does not increase generation when the wind isn’t blowing. Multiplying zero by any number still gives zero.)

4. Wind curtailment to maintain grid stability

Grid stability at high levels of wind penetration was recognized as a potential problem in the GdV planning phase. A 2012 study by Merino et al. claimed to have developed a plan to overcome it, but either the plan was not adopted or has not worked because GdV wind power is still being curtailed at higher generation levels. Curtailment is apparently being imposed by REE, the grid operator, who according to a recent BBC article , still “needs to be convinced that diesel output can be safely reduced.”

Figure 5 shows the impacts of wind curtailment on wind generation during July, the first full month of operation and the best “wind month” to date. Curtailment thresholds vary generally between 5 and 7MW presumably depending on grid conditions at the time, although on July 17 and 18 a threshold of a little over 1MW seems to have been applied. How much wind power was curtailed is impossible to estimate but it seems that it could have been substantial during July. Curtailment was, however, somewhat lower in August, very much lower in September and effectively zero in October.

Figure 5: Total wind generation during July 2015, ten-minute grid data

5. Additional wastage of wind power caused by operating procedures

Figure 5 above plots the total wind power delivered to the El Hierro grid according to the values shown in the REE “wind” column. However, only some of this power was consumed by grid customers. The rest was sent back to the GdV plant and used to pump water from the lower to the upper reservoir, and this power shows as negative values in the REE “hydro” column (REE has confirmed this in a response to an e-mail enquiry). Figure 6 segregates the wind output shown in Figure 5 into power consumed by grid customers and power used to pump water uphill at GdV during July. There is roughly an even split between the two:

Figure 6: Total wind generation for July 2015 segregated into wind-to-grid and wind-to-pumping, ten-minute grid data

The question now arises, what was the protocol for sending power to the GdV pumping station rather than to grid consumers? Figure 7 provides the answer. Wind power during July was allocated between grid consumers and GdV to match total generation to demand:

Figure 7: Total generation by source vs. demand, ten minute-grid data, July 2015

The same thing happened in August (the thin green streak touching zero on August 9 is the much-publicized two-hour period during which El Hierro obtained 100% of its electricity from renewables):

Figure 8: Total generation by source vs. demand, ten minute-grid data, August 2015

It’s inevitable that there will be teething troubles getting a plant like GdV up and running, but this modus operandi certainly isn’t what the project designers had in mind. Instead of using wind to displace diesel generation El Hierro has used its diesel plants to provide variable levels of baseload power and wind power for load-following, filling in the few gaps when the wind didn’t blow with GdV hydro generation. As a result a large amount of wind power that could have been used to displace diesel generation has been sent to the GdV pumping station as “surplus wind power” instead.

And what happened to this wind power when it arrived at the pumping station? According to the calculations performed by Hubert Flocard and documented in the Appendix at the end of the post approximately 80% of it was wasted. It was indeed used to pump water to the GdV upper reservoir (there was nothing else it could have been used for) but because the reservoirs did not have the capacity to handle the volumes involved the bulk of the water had to be allowed to flow straight back down into the lower reservoir, bypassing the hydro turbines because there was no room on the grid for any additional power. Hubert’s analyses further demonstrate that the amount of water pumped uphill substantially exceeded the combined capacity of the three desalination plants that supply water to GdV, that this water was sufficient to fill the upper reservoir many times over, that irrigation extraction from the upper reservoir could not have emptied it quickly enough to make room for more and that a balance between the upper and lower reservoirs when water is being added to the lower reservoir at average rates of 18,000 cu m/day can be maintained only by circulating water between the reservoirs. Hubert’s results are in fact sufficiently convincing that I have reversed the conclusion I reached in the September review, which was that almost all of the water pumped to the upper reservoir was taken for irrigation or other uses and that little or none of it came back down again.

Large fractions of wind generation have also been sent to pumping during low-wind periods. This is illustrated in Figure 9, which plots the REE generation data for October. Without reservoir inflow and outflow data it’s impossible to say what the rationale for this was, but it could be related to irrigation demands on the upper reservoir, which may well take priority over hydro generation. Despite the low wind speeds wind power used for pumping during October exceeded hydro generation by a factor of three:

Figure 9: Total generation by source vs. demand, ten minute-grid data, October 2015


Gorona del Viento is the world’s first – and so far only – megawatt-scale attempt to demonstrate that 100% generation from intermittent renewables is possible without the assistance of interconnector balancing services. If GdV succeeds the world can look forward to a 100% renewables-powered future. If it fails it won’t necessarily prove that 100% intermittent renewables generation is impossible everywhere, but it will provide valuable operational data on the limitations of intermittent renewables and the fraction of fossil generation they can reasonably be expected to replace.

So what has GdV taught us so far? First that grid stability is a potentially major concern at high levels of renewables penetration. El Hierro is a “weak” grid and Spanish regulations for island grids are reportedly among the most stringent in the world, so larger and stronger grids may not be so severely affected. But REE’s evident reluctance to make use of all of GdV’s wind power and the wastage of wind power that has resulted has significantly downgraded plant performance. Had all the available wind power been admitted to the grid renewable energy from GdV would probably have supplied over 50% of El Hierro’s electricity instead of 34%, and performance to date includes the September-October low wind period. Annual performance could be expected to be better.

Also not helping is the requirement to pump water to the upper reservoir to serve El Hierro’s irrigation demands, which has always been and still is a project priority. Exactly how much power is consumed in doing this can’t be determined until extraction data are available.

The question of whether GdV will ever be able to supply El Hierro with 100% year-round renewable energy, however, is already answered. It won’t. Previous Energy Matters posts have concluded that the enormous amounts of energy storage needed to do this are not practically achievable, and operating experience indicates that the existing storage capacity at GdV is at least twenty times too small to balance seasonal wind fluctuations. Other high-penetration intermittent renewables projects will face the same problem.

As to what fraction of El Hierro’s demand could ultimately be supplied by renewable energy, Hubert Flocard estimated in his recent post that it couldn’t exceed 80%. Hubert’s assessment, however, was based on the high-wind period between June 26 and the end of August and decreases to 54% with the inclusion of the September and October data.

And what does GdV think? As reported in the BBC article linked to earlier:

Juan Pedro Sanchez, an industrial engineer who works as an adviser to Gorona del Viento, foresees steadily increasing the length of time the plant is used to cover 100% of the island’s needs. This was done for two hours on 9 August, the next step will be to try it for 24 hours and ultimately it should be possible for weeks on end, he thinks. “I think that in a year or so, the plant could supply all the electricity the island needs for about 200, 250 days,” Sanchez says.

I don’t see much chance of that happening, but we will have to await more data to make a final judgment.


Appendix: Gorona del Viento water management
By Hubert Flocard

A) Foreword

1) Options for water to get into the upper reservoir

There are two:

– Natural cause: rain and condensation
– Pumping up from the lower reservoir

I assume that the rain and condensation is taken as compensating part of the evaporation in the balance sheet of the natural factors affecting the amount of water in the reservoirs. Thus only the pumping of water remains.

2) Options for water present in the upper reservoir

There are six:

– It seeps into the ground via a leak in the lining of the reservoir
– It evaporates
– It remains there to increase the amount of water in the reservoir
– It flows to satisfy human usage mostly irrigation
– It flows down to the lower reservoir and produces electricity
– It flows down to the lower reservoir and does not produce electricity

I assume that the first option is eliminated because the reservoir liner is new and waterproof. As said above, the negative amount of evaporation is assumed to take into account the smaller positive contribution of rain. Thus there are only five options to consider.

3) Options for water to get into the lower reservoir

There are four:

– Natural cause: rain and condensation
– It is part of a flow of water descending from the upper reservoir which both produces and replenish the level of the lower reservoir
– It is part of a flow of water descending from the upper reservoir whose only function is to make sure that the lower reservoir has still some water left for the pumping one has to effect at this moment.
– It is injected into the reservoir from the water pipeline and desalination plant system of the island

For the reason stated above I disregard the contribution of rain. Thus only three options are considered.

4) Options for water present in the lower reservoir

There are four:

– It seeps into the ground via a leak in the lining of the reservoir
– It evaporates
– It remains there to increase the amount of water in the reservoir
– It is pumped up to the upper reservoir

I also eliminate the first option for this brand new reservoir. Note that I also assume that no water is flowing back from this reservoir into the water pipeline system of the island. Thus only three options remain.

5) Consequence

The algorithm must be able to follow the movement of water along the (1+5+3+3) 12 options which are kept while being coupled as a function of time to the electric energy input to the lower reservoir as defined by the negative part of hydro; a part which is entirely devoted to pumping whether useful (compensation of evaporation, later production of electricity, irrigation) of wasted (sending up water which flows back immediately only to ensure two things simultaneously, available electricity is used and there is some water left in the lower reservoir to use this electricity via pumping).

B) How much water has been pumped up ?

The period considered here is July 1st 00:00 to September 30th 23:50.
The only two pieces of uncontroversial data are

– The volume in m3 of the lower reservoir : 150 000 m3
– The energy sent to Gorona del Viento for pumping which corresponds to the absolute value of the negative part of the hydraulica column in the REE data: 3513.98 MWh.

To move further one has to introduce two further pieces of information:

– The mechanical energy equivalent of 150 000 m3 once it has been lifted to the upper reservoir. The theoretical value using (E=mgh with h=655m) is 267MWh. However, I believe it to be an overestimate as it assumes flat reservoirs and a constant height neglecting the negative effect of the drawdown on such small sized reservoirs. Still for the sake of comparison I’ll be using here the value 270 MWh.

– The electric to mechanical efficiency of the pumping system (pumps and mechanical losses in the pipe). I’ll assume that 1.18 MWh of electric energy are used to move up 1 MWh of mechanical energy. This choice of an 18 % loss corresponds to the fact that a) I have “read” (now I am not too sure, where) that the total loss of a “roundtrip” of electric energy from the pumps back to the turbines is 40% and b) I assume that the efficiency of transformation from mechanical energy to electric energy on the way down is also 18% so that (1.18)2 = 1.392.

Via pumping the mechanical energy equivalent of 3513.98 MWh of electric energy is thus 3513.98/1.18 = 2977.95 MWh.

Transformed into a volume of water leaving the lower reservoir it gives: (2977.95/270) x 150000= 1 654 418 m3, thus an average of 17982.8 m3 per day.

C) How much of this water has been used for producing electricity?

Here the uncontroversial piece of data is the positive part of the hydraulica column in the REE data: 481.25 MWh.

Because the roundtrip efficiency for electric energy is 1.3924, this means that 481.25 x 1.3924 = 670.09 MWh of surplus wind energy have been effectively used to produce hydraulic electricity thus only 19.06 % of the total energy sent by REE to Gorona del Viento have been returned to the grid.

Because the mechanical to electric energy efficiency of the (downgoing pipe + turbine) system is 1.18, to produce 481.25 MWh of electricity it has been necessary to let ((481.25 x 1.18)/270) x 150 000 = 315 486 m3.

Again one finds that 80 % of the pumped water had to find another usage among the five remaining options listed in A.2 above. Using the number produced by the El Hierro Water council, “only” 46280 m3 have evaporated. The rest, 1 292 652 m3, either served to increase the quantity of water in the upper reservoir (but not above 380 000 m3) or to irrigation or has to be wasted in useless roundtrips. Assuming that all that was really used (storing in the upper reservoir plus irrigation) requires that “new” water was always made available to the lower reservoir.

It is difficult to imagine how one could inject an average of 17982 m3/day (not to mention that it is an average while the excess wind power sent by REE to Gorona del Viento is often much larger than (3513.92/(92 x24))= 1.59 MWh over periods lasting a fortnight.

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38 Responses to El Hierro Renewable Energy Project – October 2015 Performance Review

  1. Dave Rutledge says:


    Very significant work. Thank you.


    • Thanks Dave. GdV is a very significant project, although not widely recognized as such.

      • Willem Post says:


        Are any records available regarding month-to-month diesel fuel consumption for the past 5 years?

        There should have been a decrease after making all these investments and the wind turbines, pumps, etc., went on line.

        The objective is to reduce CO2 emissions?

        At what cost, $/metric ton of CO2, was it achieved this time?

        My email and name would appear automatically in the fields, but now I have to type them in each time I comment.

        Why the change? Is it on my end or yours?

        • Joe Public says:

          Willem. I suspect it’s at your end.

          Do you submit responses via a single or alternative devices?

          Are you logged on via say WordPress etc, which ‘remembers’ your details?

          If you’ve logged out of say WordPress, or cleared the cache of your device(s), then you’ll need to re-enter them.

          Another cause could be that your browser is set to not-remember sites visited (private browsing).

        • Willem. I have no data on fuel consumption, but according to the REE grid data El Hierro has “saved” about 4,000 tonnes of CO2 emissions over the last four months when we ignore the impacts of ramping on fuel consumption. These, however, are not going to be very large because the diesel plants haven’t been asked to do much in the way of ramping. Load following has been performed mostly by allocating wind generation between the grid and the GdV pumping station, as described in the post.

          The project’s objective is eventually to have GdV supply 100% of El Hierro’s electricity with renewable energy, but it looks as if the sights are already being lowered on that.

  2. Peter Lang says:


    I was so amazed by the figures in the first paragraph, I stopped to write this comment.

    Diesel: 3,225 MWh (86%)

    That’s amazing. Absolute stupidity. They have the choice of using diesel as a dispatchable generator to match demand or run it to store energy (at say 75% efficiency). That means the diesels are consuming 1/3 more fuel and producing 1/3 more emissions for 86% of the electricity than if they used them as dispatchable generators. By the time the capital and O&M cost of the pumped storage and wind farms are included, El Hierro’s residents are probably paying in the order of twice as much for their electricity than simply running it all on diesel without any renewables.

    However, this is just one month. To make any sense of the costs it is essential to have years of data.

    • Peter:

      As I recollect residential electricity prices are the same throughout Spain regardless of the cost of generation, so the residents of El Hierro are shielded from GdV costs. Right now I think they are paying about 25c/kWh – or it may be euros, can’t remember which.

      REE also gives data on El Hierro CO2 emissions. REE assumes a constant 0.75 tons of CO2 emitted per MWh of diesel generation and ignores ramping impacts.

      • Peter Lang says:

        Roger thank you for your reply. Sorry I should have been clearer. I was meaning actual fuel consumption, actual GHG emissions per MWh and actual costs of electricity supply, not electricity prices.

  3. Gavin D says:

    It strikes me that this project is more of an experiment than one that has been thought through from an economic point of view. It’s a nice little closed system that should show everyone the true cost of renewables if they’re required for base-load generation.

    Clearly, to make it work (technically), they need to expand it significantly by erecting more wind turbines, and by building more puddles and hydro plants (that reservoir really is a silly little thing).

    Also, I’d have thought that El Hierro must be a prime target for geothermal sources of energy.

    Throw money at it (no doubt German money if Spanish consumers aren’t paying), make it work, and then maybe we’ll have real figures to help the renewables weenies understand where these things might fit into real economies that actually run industries.

    • Peter Lang says:

      I wonder how many El Hierros would be required to power the world (without diesel generators)?

      How many similarly ideal topographic sites – with 700 m hydraulic head and already made upper reservoirs – are available in the world?

    • I’ve mentioned geothermal in previous comments. El Hierro is a volcanic island only a little more than a million years old. It’s covered in cinder cones, one of which is reportedly still active, and in 2011-12 there was a submarine volcanic eruption just off the south coast. All the island needs to supply 100% of its electricity is one piddling little 10MW geothermal plant, and if it had one the GdV hydro system could handle load balancing. There may be studies showing that geothermal is not an option on El Hierro but if so I haven’t come across them.

  4. Joe Public says:

    Thank you, Roger. More pieces of the jigsaw being slotted into place.

  5. Euan Mearns says:

    Roger, Great charts! Below is July, August and October. Its interesting to note the change in operating procedure into October when the wind stopped blowing. Do you have a chart for September that shows the transition?

  6. Rob Slightam says:

    fascinating reading

  7. Euan Mearns says:

    Rumour has it that National Grid are concerned about UK capacity today. Metered wind output has dropped to 0.28 GW and demand is running at 47.4 GW with 30 minutes to go before peak. Maybe we could import some hot air from Denmark, Germany and Scandinavia.

  8. Nador says:

    Using ‘excess’ wind power to circulate water between the reservoirs – as you write – seems incredibly stupid. So I suspect we actually miss something.

    Do we know which method the desalination plant uses?

    If I understand correctly, the desalination plant was built before the wind plants were built. So, when built it was probably assumed that there will be working diesel generators anyway, thus it could have been reasonable to use for example multi-effect distillation or membrane distillation which could use the waste heat from the diesel generators. That would mean – even if they have sufficient wind – they need to run some diesel generators to have heat for the desalination plant.

    Or the less likely case: the desalination plant is using reverse osmosis, hence needs a lot of electricity, so the wind energy sent to the pumping station is not only used to pump water, but to desalinate as well.

    • Using ‘excess’ wind power to circulate water between the reservoirs – as you write – seems incredibly stupid. So I suspect we actually miss something.

      To begin with it struck me as incredibly stupid too and for a long while I didn’t believe that it was happening either. But Hubert Flocard eventually convinced me that this is the only way things can be made to fit.

      The reason it’s happening is that the plant isn’t operating the way it was designed to operate. The original concept was that all the wind power generated at GdV would displace diesel, giving a power distribution like this on a windy day:

      Demand 5MW, wind 4MW, diesel 1MW, no surplus

      But what’s happening in practice is that REE is keeping the diesel plants running and admitting only a fraction of GdV’s wind power to the grid because of grid stability concerns, giving a power distribution like this:

      Demand 5MW, wind 4MW, diesel 3MW, surplus wind 2MW (REE has confirmed by e-mail that all diesel power is consumed on the grid)

      Where is this surplus wind to go? It can only go to pumping. This is where the operating plan says it will go and there’s nowhere else to send it anyway. The problem is that there’s far more of it than anyone ever expected and it overwhelms the capacity of the reservoirs. So GdV has to waste it by pumping water up the hill and letting it run straight down again. I’m sure they would prefer not to be doing it this way but I don’t think they have much alternative.

      Hubert, do you have any comments? Hubert, ou êtes-vous?

      • A C Osborn says:

        Sorry, this bit does not make sense “The problem is that there’s far more of it than anyone ever expected and it overwhelms the capacity of the reservoirs.”
        The whole system was supposed to be 100% wind, so are you saying that if it produces 100% that they will still run the generators?
        Surely they can’t be runnuing it that for from it’s design, because if they are they shouldn’t have bothered at all.

      • Nador says:

        I see.
        Nevertheless desalination still needs some source of energy. It might be totally independent from the rest of the system, but I it seems even in the past there had to be reasons to not use such a system.
        Using waste heat would have been reasonable even before starting to build a green folly. If they need heat for desalination – installing an electric water heater should be very cheap and would be a better usage than circulating water.
        Or, if they use reverse osmosis I really can not see why they do not use it directly for desalination – and why not mention it as saved fuel for the desalination plant. At 4-5 kWh/m^3 that would mean ca. 700 MWh for filling the lower reservoir. Pumping it up is another 270 MWh. Although that is less then Hubert’s 3500 MWh wasted in 3 month, but there sure must be some consumption during summer.

        El Hierro has 10k people. There must be some tourist there as well. If I use 0.2 m^3 /person/day, the consumption would be 180k m^3 for the 90 days in question. And that usage was certainly very conservatively guessed, without agriculture. Do you have any data on this – my short search did not turn up anything usable [just green PR]?

        So I suspect that electricity sent to “pumping station” includes not just pumping but desalination as well.
        If you say that they explicitly stated that all of the energy in question goes to pumping then I have to accept it. But using it for desalination seems to be easy, so I would assume this unless explicitly stated otherwise.

        • Flocard says:

          I come in rather late in the discussion. I am not very reactive sorry.
          Still I believe that anyone can check by him(her)self that there is a problem.
          First the desalination plants are hooked to the grid. They are outside Gorona del Viento (GDV). Before GDV started operating (end June 2015) they were using grid power. Then grid power was entirely provided by the diesel plant. After GDV started nothing has changed in the average or peak grid power. The desalination plants are now using that fraction of the wind power that is sent to the grid (dark green zone in Roger’s picture 7 or 8) not the fraction that appears in light green in those pictures.
          What one has to clarify is how the light green area is being used.
          In its answer to Roger’s set of questions, REE makes it clear that the excess wind power (the negative part of Hydro: H-) is used for pumping. The only hydraulic energy that comes out of GDV is the positive part of the column “hidraulica” (H+) the blue zone in Roger’s drawings”
          It means that it is up to GDV pumping to take care of using the H- part of the “Hidraulica” curve.
          Roger was nice enough to extend his contribution by adding at the end a text I had sent to him. The calculations it contains are simple they only involve few additions and multiplications which are detailed.
          Using two REE and GDV data and two assumptions which are explained (mechanical energy capacity of the lower reservoir 270MWh and efficiency loss of 18 % in pumping ; you are free to change these with numbers if prefer other values), one finds (subsection how much has been pumped up) that over three months 1 654 500 m3 of water have been pumped up.
          Using now the H+ part one finds (subsection how much of this water was used to produce electricity) that “only” 315 500 m3 have been sent down to produce electricity.
          One can then try to figure out how the remaining (1 654 500 – 315 500) = 1 339 000 m3 which have not come down to produce electricity are being used over these three months. That is part of the algorithm I have built. One could compare this number (1.6 Mm3) with the size of the upper reservoir (380 000 m3) or the quantity of water which according to the water council of el Hierro has evaporated from the upper reservoir (~16 000 m3). For the water pumped up to be really entirely used one would have to have sent about 1 000 000 m3 to irrigation or other water usage. That’s a lot but why not ?
          But in such a case (no wind energy is wasted) the real problem comes when one asks oneself where does this water (1 339 000 m3 plus the 30 000 m3 which according to the water council have evaporated from the lower reservoir) which has been pumped up and didn’t come down, comes from. Of course it has to come from outside, from the desalination plants. Then over 92 days these plants should have been able to provide every day 14 900 m3 to GDV. If one reads the technical documents of November 2013 one understands that only a maximal capacity of 2400 m3/day was specifically built for GDV. Its load factor is certainly 100 %. In addition if the sole task of all the desalination plants of the islands (most of them were not built for the service of GDV) was to provide water to the lower reservoir of GDV they could only muster 11 000 m3/day. More over 14 900 m3/day is an average over the period. If one really follows the algorithm one finds that some days in July there is so much wind excess sent back to GDV pumping station that an injection capacity of 24 000 m3/day would be necessary.
          The only way out of this dilemma that I could find is to assume that some water is circulating without creating power for the grid (REE does not want it) just to make sure that there is enough water in the lower reservoir to be pumped.
          Except for few figures, I have only been paraphrasing what Roger is saying. Discussion with French electric engineers convinced me also that “stability of the grid” enforced by REE is the key issue.
          In my calculations where ALL possible wind energy (dark green and light green zones) is being used to displace the diesel production (and where grid stability issues are neglected), there is no problem with the management of water. The size of the reservoirs is OK The injection of sweet water is only needed to compensate evaporation in both reservoirs (typically (550 m3/day in summer). This is because if all possible wind energy is sent to the grid, there are only few hours that there is a wind excess over demand which is sent to GDV for pumping.
          I have tried to explain how the water management is done in my calculations. If something is missing. I welcome a suggestion.
          In my opinion the GDV system as it is built can function, only if a minimal activity request is made to the most expensive part of GDV, the hydraulic part. El Hierro would have been much better off financially it had only built the wind turbines.

          • Günter Weber says:

            I am really curiouse why the wind generators are not stopped if there is much more energy generated than can be used. The lifetime of the machinery (also the pumps of the hydro plant) would be extended by simply shutting down some wind generators.

          • Roger Andrews says:

            Hubert: Thanks for that explanation.The only comment I would make is relative to your statement that:

            In my calculations where ALL possible wind energy (dark green and light green zones) is being used to displace the diesel production (and where grid stability issues are neglected), there is no problem with the management of water. The size of the reservoirs is OK

            Starting with the reservoirs “charged” the existing 270GWh of storage is adequate to cover island demand for about two days. As I write there has been little or no wind generation for 54 days.

    • And the desalination plants obtain their power from the grid so they would be included in the 5MW demand.

      • Nador says:

        Somehow I did not see your comment before sending my previous…

        • No problem. I’ll add one thing though. Some of the water pumped to the upper reservoir is being taken for irrigation use – we don’t know how much – so the wind power consumed in pumping it up – again we don’t know how much – isn’t wasted. GdV should receive credit for this wind power but it doesn’t show up in the REE grid data.

  9. Flocard says:

    An unperfect reply to Günter Weber

    The answer that REE sent to Roger makes it clear that the wind turbine production is curtailed. Roger’s drawing such as in figure 5 makes it also clear that the wind production curve does not have the profile it would have if there were no curtailment. Roger discusses this point in the text.

    In a sense it is wasted wind energy which does not show up in any set of data as if it had never existed. Its only effect is to reduce the effective load factor of the wind park whose maximal power exceeds by almost a factor two the average demand power.

    I suppose that curtailing the wind turbine production to fit excatly the needs of the grid plus the water resources of GDV would lead to a complex management of the wind turbines which would have to be stopped and restarted at second or minute notice.

    Presently wasting wind energy in this pumped-up and useless flow-down schene may be the easiest technical way to handle the mismatch btween wind production, water resource, operation of the diesel plant and the wind park and stability of the grid.

    If anyhow energy has to be wasted, the simplest way of doing it is the best. I do not believe that in the present early phase of the installation questions such as lifetime of machinery takes precedence. After all Gorona del Viento is before all a show today. It may become an industrial demonstration later.

    Anyhow a more complete integration of REE requirements, of the adjustment capacity of the diesel plant, of the producing capacities of the desalination plants and the inner working constraints of GDV is probably the key to make a better usage of the wind production.

    This is what the engineer Sanchez had probably in mind when he mentionned a learning curve. It certainly would be very interesting if GDV had a more open attitude as concerns its way of functionning. In a sense it should have since it is essentially public money which has financed it.

    Note however that if all the wind of the past 4 months had been used to displace diesel first and then the remaining wind excess to store up water for later electricity production, the renewable fraction would nevertheles not have been higher than 54 %

    On the other hand the wind curves that Roger displays in figure 3 and 4 tell us that September and October are probably the worst months for GDV. One should expect the system to become more efficient over the next eight months.

  10. Flocard says:


    You wondered about the sentence in my text
    “In my calculations where ALL possible wind energy (dark green and light green zones) is being used to displace the diesel production (and where grid stability issues are neglected), there is no problem with the management of water. The size of the reservoirs is OK”

    When I say that there is no problem with the water management do not forget that over these 4 months the maximum maximorum renewable fraction is only 54 %. The rest is diesel.production.

    I only wanted to say that if all the wind power that can possibly be sent to cover demand is used, the excess of wind power over demand is so small both in volume and duration that one does not have any problem using it to pump water as there is always water in the lower reservoir. There is also no problem using this water later as there are many moments when the wind does ris up to demand.

    When there is no wind for a long period, there is certainly a problem with electricity management (diesel is the only recourse) but there is no problem with water management. The water just stays where it is and a there is always a large fraction of the lower reservoir which has water waiting for the next gust of wind.

    It corresponds to the last sentence of my comment: GDV’s hydraulic component dimensions are perfectly adjusted for a situation when you do not have to use it or just for a minimal fraction of electricity production. Said otherwise the money spent on the hydraulic component of GDV is money wasted.

    I’ll send you directly two pictures directly.which depict the “optimal” usage for the four months from July to October. One calculation corresponds to the situation when only exists the wind park (renewable fraction 50 % and a small amount of excess wind power is lost) and one where the windpark is coupled to the hydraulic system (renewable fraction 54 % and no wind power is lost).

    All the money for the pumps, the reservoirs, the two pipelines and the turbines was spent for a few % gain in the renewable fraction. It was already the case (few % gain) when I considered only July and August.


    • As I noted in an earlier comment the GdV pumped hydro system would be just about ideal for load-balancing if it were coupled with a geothermal plant delivering a steady 5.5MW of power rather than a wind farm.

  11. Olav says:

    If increased wind production is considered then..

    The installed wind farm location is selected do to closiness to grid/pumps while also beeing a “windy” location. In this case it is probably “windy” for the windiest part of the year. From the graps I can se that it is newer zero wind but we have longer periods with low wind. Then the following can be investigated. Locate the windiest place on the island during the low wind period. It can very well be on the oposite side of the island. Then istall typcal wind turbines which is used on low wind locations in southern Germany. (Longer wings compared to generator) Then the cut in speed is lower and low wind will produce more due to larger swept area. The cut otff speed is also lower (to protect the turbine) which doesnt matter as that wind production is constrained anyway.
    The gain is a more evenlywind production which is good both for direct wind utilazion as well as power management of grid.

  12. Daniel says:

    This recently published report features several island renewable microgrids:

    El Hierro is profiled as a 100% renewable grid, which shows how this narrative has become entrenched in spite of not being true.

    Other issue: in Spain electricity prices are the same no matter where you live. So people from El Hierro are not going to pay a higher electricity price. More than half of the cost was financed by the Spanish Industry Ministry and the regional government, so that means that all the Spanish taxpayers are going to pay.
    The Ministry approved a subsidy of 35 million € for this installation and a special tariff framework. The plant company receives 15,57 €/MWh for the generated energy plus a payment for “power guarantee” calculated on an annual basis through a formula. This payments are included in the Orden IET/1711/2013 – Articles 3 to 6.

    By the way, I thank you, Roger, for your thorough reports about this installation. Here in Spain we do not have anything similar.

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