At the end of June 2017 Gorona del Viento completed two years and four days of full operation. Over this period it supplied 39.1% of El Hierro’s electricity demand – far short of the 100% promised by its backers – and 9.0% of its total energy consumption. (In June 2017 it supplied 61.2% of El Hierro’s electricity and 14.1% of its energy.) Since startup GdV has made progress integrating wind generation with the grid without compromising stability, and it can now fill El Hierro’s electricity demand with 100% renewables for periods of days, but only during periods of strong and sustained winds. These periods could be lengthened if the performance of the pumped hydro system could be improved, but there is no certainly that this can be done. The likelihood is therefore that GdV will continue to be capable of supplying El Hierro with renewable electricity only when wind conditions are favorable, which they are for only a fraction of the time.



Figure 1 shows daily mean percent renewables generation since full operations began on June 27, 2015. The data are from Red Eléctrica de España (REE):

Figure 1: Daily average percentages of diesel & renewables (wind plus hydro) sent to the El Hierro grid since startup. The dark green lozenges show monthly means. The month scale is not exact.

The Table below updates the monthly grid statistics since project startup on June 27, 2015 through April 30, 2017:

Figure 2 plots the REE 10-minute generation data for June. The month began in spectacular fashion with an uninterrupted 8-day (192 hour) period of 100% renewables generation, eclipsing the previous record of 76 hours (3.2 days) set in July/August 2016. But because of the period of lower wind generation that followed (during which GdV generated no electricity at all for 56.5 hours) the month did not set a new renewables record – that honor is still held by July 2016:

Figure 2: Generation by source, June 2017

Total wind generation during June, including wind sent to the grid and wind used for pumping, is shown in Figure 3. The mid-month decrease shows that lengthy wind lulls can occur even in months when winds are normally high and sustained. Also of note is the fact that the level at which wind generation is curtailed has increased significantly since project startup. In June/July 2015 output was commonly curtailed at around 7.5MW. On June 30, 2017 it exceeded 10MW for several hours. As discussed in the next section, however, this will have little if any impact on the amount of electricity GdV sends to the grid:

Figure 3: Total wind generation, June 2017

GdV’s performance to date:

With less than 40% renewables penetration in its first two years of operation GdV has come nowhere close to fulfilling its pre-development goal, which was to cover 100% of El Hierro’s electricity demand with renewable energy. “El proyecto tiene como objetivo el diseño, desarrollo, construcción y puesta en servicio de un sistema hidroeólico capaz de cubrir la demanda eléctrica en la isla de El Hierro, convirtiendo esta isla en un territorio autoabastecido eléctricamente solamente por energías renovables.”

Another complicating factor, although not one confined to El Hierro, has been an inability to distinguish between electricity and energy. Despite GdV’s poor performance to date it seems to be generally believed that the plant will ultimately supply 100% of El Hierro’s energy, only about a quarter of which is supplied by electricity. And although GdV has so far supplied only 9% of El Hierro’s energy it also seems to be generally believed that 100% (or more) is just around the corner. The recent call for bids to install EV charging stations to take advantage of a non-existent energy surplus admits of no other explanation.

Some progress has nevertheless been made towards increasing GdV’s level of renewables penetration over the last two years, with the main advance having taken place in grid stability. Confidence in the ability of the system to maintain 100% renewables generation at high levels of wind output without compromising grid stability has clearly increased, and as a result we are now seeing more extended 100% renewables tests for as long as the wind keeps blowing. (One is in progress as I write.)

However, the decision as to when to start and stop a 100% renewables test is still left up to the judgment of REE staff, who are responsible for grid stability but also under pressure from GdV to admit as much wind as possible. (The 192-hour test at the beginning of June started at 4.00am on June 1 and ended at 4.00am an June 9 when wind generation had dropped to about a megawatt and the resulting demand deficit was being filled by hydro – I can almost hear the GdV people pleading with REE at 3.00am on June 9: “C’mon guys, give us eight days.”) A run-up period of sustained high wind speeds, presumably backed up by weather forecasts predicting that they will continue, is also needed before a 100% test is initiated, although as shown earlier in Figure 3 REE is more adventurous when it comes to resuming a test when the wind picks up again.

As noted earlier, the productivity of the 11.5MW of wind turbines has been increased to the point where they are now capable of sustained generation at the ~10MW level during high-wind conditions. An across-the-board improvement in turbine productivity would of course be of benefit at lower wind speeds, but increases at generation levels that exceed demand will achieve nothing because the extra generation would have to be wasted by uphill pumping, there being nowhere to store it.

Which brings us to the pumped hydro system. The dismal performance of this system since project startup is summarized in Figure 4. The Y scale is the same as that used to plot wind generation in Figure 3:

Figure 4: Generation from pumped hydro, daily averages since project startup. The numbers show the megawatt-hour totals for selected hydro generation intervals when there was no recharge from uphill pumping

Calculations based on reservoir volumes peg GdV’s pumped hydro storage capacity at about 270 MWh when fully charged – still only about a twentieth of what would be needed to cover annual storage requirements – but the most energy it has ever sent to the grid without being recharged was 125MWh in March 2016, less than half of its design capacity and enough to supply El Hierro with electricity for only a day.

There are also reasons to believe that the capacity of the hydro system has degraded further since March 2016. Figure 5 zooms in on the recent interval of hydro generation on June 17, 18 and 19, which dribbled 46MWh of stored energy into the El Hierro grid in 1-2MW doses over a two-day period (Although the hydro system can deliver more megawatts when the need arises. At 5.20 and 5.30am on May 20, 2017 it sent 4.6 and 4.8MW to the grid, thereby supplying all of El Hierro’s electricity demand with hydropower for about twenty minutes):

Figure 5: Diesel, wind and pumped hydro generation, hourly REE data, June 16 through 19, 2017.

Figure 5 shows hydro releases, supplemented by increasing diesel generation, beginning when wind generation started to drop on the 17th. This was a logical step. What wasn’t a logical step was shutting hydro down on the 19th and allowing 100% diesel to take over. There can in fact be only one explanation for taking it – the hydro system had run out of charge. Assuming that the system was charged to begin with (and all the uphill pumping that preceded the releases suggest that it was) then its current storage capacity is only about 50MWh, less than half what it was as recently as March and less than a fifth of design capacity, which as noted earlier is already at least twenty times too small.

This shortfall in hydro capacity significantly lowered GdV’s June generation. Diesel generation on June 17, 18 and 19 totaled 275.5MWh, and if the hydro system had been working at its 270MWh design capacity instead of at 50MWh another 220MWh of diesel could have been replaced by hydro over this period (numbers approximate). This alone would have increased the June renewables percentage from 61% to 67%, and there were other periods during the month when hydro could have made a similar contribution. Such wholesale replacement of diesel by hydro is of course only possible during windy periods, but it makes it clear that GdV’s first priority if it wishes to increase renewables generation should be to get the hydro system working the way it’s supposed to.

Which brings up the question of why it isn’t. The straight answer is “we don’t know”, but there seem to be two possibilities. Either GdV can’t fill its reservoirs because El Hierro’s farmers are taking all the island’s fresh water, or there are serious concerns regarding reservoir stability. In the second case there is nothing much to be done and in the first – well, farmers on a desert island aren’t going to give up any of their fresh water without a fight. GdV’s best hope is probably to install its own dedicated desalination plant, but this option has surely already been considered. And these assessments may of course be dead wrong. The problem could be something entirely different.

Overall it seems that we can look forward to continued incremental improvements in GdV’s performance over the next year or two as it struggles toward supplying 50% of El Hierro’s annual electricity demand, which in terms of ultimate potential is still the most I am going to give it.

A brief word on project economics:

GdV has a contract with the Spanish Ministry of Industry, Tourism and Trade under which it gets paid a small amount for the electricity it generates but a large amount (€12 million in 2015) for capacity availability whether the capacity generates any electricity or not. Estimates based on GdV’s total annual income and its total annual megawatt-hour output yield electricity prices of up to €1.38/kWh, but because electricity rates in Spain are the same everywhere El Hierro consumers continue to pay ~€0.25/kWh. And because revenues greatly exceed operating costs GdV, which is two-thirds owned by the El Hierro Island Council, ended 2016 with a €14 million surplus. GdV is clearly a sweet deal for El Hierro, but not for the Spanish taxpayer.