During September the hybrid wind-hydro Gorona del Viento (GdV) plant achieved 58.2% renewables generation, comparable to the 55.6% achieved in August and far higher than the 19.9% achieved in September 2015. This was largely a result of the fact that the wind didn’t die early in the month as it did in September 2015. Total renewables generation since full operations began at GdV on June 27, 2015 is now 40.1%, up from 38.7% at the end of August. Data on GdV plant layout, operation and capacities are given in the September 2015 review. Previous posts on GdV are accessible through the El Hierro portal.

Figure 1 shows daily mean percent renewables generation since June 27, 2015 (data from Red Eléctrica de España (REE). Aided by sustained winds and by occasional “100% renewables” tests GdV has been able to supply 58.4% of El Hierro’s electricity demand with renewables generation over the last four months:

Figure 1: Daily mean percent renewables generation since June 27, 2015. The monthly divisions are approximate

The Table below updates the monthly grid statistics:

Figure 2 shows the REE 10-minute generation data for September. Hydro is still being fed to the grid in small spurts when wind generation is inadequate to meet demand. Two 24-hour 100% renewables tests, both of which seem to have been terminated because of decreasing wind speeds, were conducted during the month. Approximately 40% of GdV’s gross wind generation during the month was curtailed by sending it to pumping, and this does not allow for the additional curtailment caused by limiting the 11.5MW wind farm to a maximum output of 7.5MW:

Figure 2: 10-minute REE grid data for El Hierro, September 2016

Figure 3 compares 3-hour wind speed readings at El Hierro airport with GdV’s gross wind generation. There is a generally good match except around September 6, when wind generation fell to zero even though the wind continued to blow.

Figure 3: Wind speeds at El Hierro airport compared with GdV gross wind generation, August 2016

Figure 4 is an XY plot comparing mean monthly airport wind speeds with GdV’s mean monthly gross wind generation since July 2015, the first full month of operation. The 0.79 R squared value for the trend line confirms that GdV’s wind generation is correlated with airport wind speeds and that wind speed is a dominant control on GdV generation, as would be expected. (The May 2016 value shown in red is non-representative because of GdV’s unsuccessful experimentation with a different operating approach in this month, as discussed here.)

Figure 4: XY plot comparing mean monthly airport wind speeds with mean monthly gross GdV wind generation since project startup. The regression line gives an R squared value of 0.79 with May 2016 (the red dot) excluded.

Discussion:

GdV’s improved performance over the last four months once more raises the question of how much renewable energy GdV might ultimately be capable of delivering. The answer depends on two imponderables:

First wind speed. At the end of the August update I stated:

If history repeats itself September 2016 will inaugurate an extended period of low-wind conditions during which GdV’s renewables output will fall drastically.

This comment was based on the El Hierro airport wind records for 2014 and 2015, which track each other quite well – almost exactly in some cases – with both showing a decrease in wind speed starting in mid-August (Figure 5):

Figure 5: El Hierro daily mean wind speeds for 2014 and 2015

Well, history declined to repeat itself. Neither wind speed nor GdV’s output fell drastically in September. Superimposing the 2016 wind record on Figure 5 shows September 2016 wind speeds about 2m/s higher on average than they were in September 2014/15 (Figure 6), although to compensate they were about 4m/s lower in the second half of January 2016. Average wind speeds from January through September were in fact about the same in all three years (6.84m/s in 2014, 7.05m/s in 2015 and 6.96m/s in 2016). The average for all 1,004 days between January 1, 2014 and September 2016 is 6.75m/s.

Figure 6: El Hierro daily mean wind speeds for 2014, 2015 and 2016

Now if we go back to Figure 4 and project up from 6.75m/s on the X-axis we intersect the trend line at about 42% renewables. However, three recent months with average wind speeds of around 6.9m/s (June, August and September) give an average value of 56% renewables, suggesting that ~55% is perhaps a better estimate of future GdV renewables production, all other things being equal. This is a few percent higher than Hubert Flocard’s June 2016 estimate of 51.33%.

The second imponderable is how much 100% renewables generation can ultimately be achieved. The two 100% renewables tests conducted in September lasted for 48 hours, or for 6.6% of the time. Can the number and/or duration of these tests be increased? This question is impossible to answer without knowing why the tests start and finish when they do (I sent an email to REE some months ago requesting clarification on this issue but never received a response). According to Figure 7, however, there has been no increase in test length or duration during the last four months, when wind speeds were high enough to support testing for most of the time. The implication is that little progress is being made:

Figure 7: Timing and duration of 100% renewables tests, June through September 2016. Tests are plotted on the day they started.

It now remains to be seen whether the wind will drop off in October. It seems to be heading in that direction. Around midday on September 30 the wind at the airport decreased to a gentle breeze (5m/s) and since then it’s been back to diesel generation.