Because of higher wind speeds in the second half of the month GdV supplied 40.8% of El Hierro’s electricity in May, up from the 27.5% achieved in April. As at the end of May renewable energy from GdV had supplied 38.2% of El Hierro’s electricity demand since project startup, up marginally from 38.1% at the end of April. The percentage of El Hierro’s primary energy consumption supplied by GdV remains the same at 8.8%. A recent video on the project (inset), which attempts to tell both sides of the story, is of general interest.



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 month scale is not exact.

The Table below updates the monthly grid statistics since project startup on June 27, 2015 through April 30, 2017, a total of slightly over 22 months of operation.

Figure 2 plots the REE 10-minute generation mix for May. The impact of higher wind speeds in the second half of the month is evident. For a total of 208 hours during the low-wind period between May 3 and May 12 GdV generated no electricity at all. (Since project startup GdV has generated 100% renewable energy for 3.4% of the time and no electricity at all for 11.3% of the time.) The 100% renewables test on May 19 and 20 is discussed below.

Figure 2: Generation by source, March 2017

Total wind generation during May, including wind sent to the grid and wind used for pumping, is shown in Figure 3. Wind generation remains highly variable, but there is less curtailment during high-wind periods than there used to be. For five hours on May 16 total wind generation consistently exceeded 10MW:

Figure 3: Total wind generation, May 2017

Figure 4 plots the 10-minute REE generation data for May 18 through May 20, which includes the 32-hour 100% renewables test period on May 19 and 20. Wind speeds at El Hierro airport, which are now given at hourly intervals, are superimposed:

Figure 4: Generation by source, May 18, 19 & 20th, 2017

Figure 4 shows the following features of interest:

The 100% renewables test started promptly at 0000 hours on May 19. It was preceded by an extended period of sustained high wind generation, indicating that REE/GdV need some assurance that the wind is going to keep blowing before they turn the diesels off.

Wind generation dropped abruptly from 8MW at 0320 to zero at 0520 on May 20, but hydro took up the slack without the grid crashing. The 4.6 MW of hydro generation at 0520 and the 4.8MW at 0530 in fact supplied 100% of El Hierro’s electricity demand for maybe 15 minutes.

Airport wind speeds show a decrease that coincides with the decrease in GdV wind generation early on May 20. But while GdV wind generation fell from 8MW to zero airport wind speeds fell only from 8m/s to 5m/s. This suggests either that wind speeds at the airport are much less variable than wind speeds up on the hill at the GdV wind farm, or that GdV deliberately reduced wind generation to zero, possibly to run a check on hydro performance.

The diesels were restarted at 0800 on the 20th even though the wind had begun to blow again.

Comments are solicited.

The video referred to in the introduction was posted on the web by Deutsche Welle. It’s well worth watching…

… but for those who would rather read the book here are some of the comments it contains:

Voiceover: The energy shift has cost 83 million euros and ran 20 million over budget. Critics say that’s far too much.

Juan Pedro Sanchez, El Hierro Island Council: Today it’s a project that works. One that creates jobs and brings in money. In the next few years it’ll turn a profit.

Voiceover: The wind turbines provide more than enough energy to meet the island’s own needs. (The hydro reservoirs provide) a steady, unbroken string of power even when nature doesn’t play along.

Voiceover: But things haven’t worked out quite as planned. Providing the island with 100% renewable energy was always an ambitious goal, and it still hasn’t been reached. Last year the facility generated only 40% of the power consumed on El Hierro. That disappointed many of the island’s residents. They hoped electricity bills would fall. Instead, just like in the rest of the country, costs for power have actually gone up. Lots of people now say the project was all wind and no substance.

GdV engineer: What really threw (our plans) out of kilter was the lower water basin, which we couldn’t build to the size we wanted. That now could be a hindrance to producing the sustainable energy we want.



Man in the street: They announced that our island would now be provided with 100% sustainable energy, and that hasn’t happened. We ask why not and don’t get any answers. Somebody needs to explain to us why it’s not working.

Voiceover: The developers once wanted to shut down the old diesel-driven power plant. But no one talks about that any more. A fuel tanker still makes regular trips to the island. And the old plant’s smokestacks still blow lots of carbon dioxide into the atmosphere.

Cristina Morales, GdV’s PR person: Despite speed bumps El Hierro’s energy mix is now much more environmentally friendly than it was in the past. In the first year of operation we saved nearly 7,000 tons of diesel. That means we emitted 14,000 tons less CO2. And other islands have profited from the pioneering work we’ve done. It’s in the nature of things that pioneering projects are experimental.

Voiceover: The engineers are certain they can improve efficiency in their sustainable energy mix. But they’ve grown much more careful about what they promise.