Sunday 29 May 2016

New Report : The Reduction in Gas Savings Due to Wind Energy 2012 to 2015

MAY 2016


  • Ireland increased it’s wind generation by 11% between 2012 and 2013. This resulted in additional gas savings of 7%, a saving of 360 m3 of gas per MW of wind installed during 2013.
  • Between 2013 and 2015 wind generation increased by 44%. This resulted in additional gas savings of 16%, a saving of 160 m3 per MW of wind installed during 2014 and 15.  
  • This means that over double the wind farms had to be installed during 2014 and 2015 to achieve the same fossil fuel savings as in 2013.
  • The expected fossil fuel savings from high levels of wind energy do not materialize because back up plant are forced to run more inefficiently.
  • Without large levels of hydro to connect to as in Denmark, gas powered stations will be forced to run less efficiently negating most of the savings from wind.
  • At some point, the high costs associated with installing more wind energy will outweigh the increasingly diminished benefits (saturation point).
  • It is likely that we are approaching that point now.
  • The Irish Government needs to place a moratorium on wind energy until a full assessment is carried out on other options.


Most commentators in the energy debate here in Ireland assume that 1MW of wind energy displaces equivalent fossil fuels required to generate 1MW of conventional power in the electricity system. Last year, wind energy contributed 23% to the electricity generation fuel mix[1]. The conventional view is that this resulted in equivalent fossil fuels savings and associated CO2 emissions. The problem with this view is that it ignores back up plant having to run less efficiently during high penetrations of wind. Joe Wheatley was among the first to question the conventional view in his 2012 paper[2]. Up until 2014, this was the stated position of SEAI, the agency set up by the Irish government to advise them on renewable energy. Then in 2014, SEAI issued a report which claimed to include all of the inefficiencies in the grid from high penetrations of wind energy[3]. In 2016, a report prepared by Danish researchers showed quite clearly that back up gas plant (CCGT) ran more inefficiently during high penetrations of wind[4]. This resulted in increased specific CO2 emissions and fuel consumption during these periods.

This report now examines precisely what the gas savings were for the years 2012 to 2015. The EPA publish annual gas consumption figures for Ireland’s CCGT and OCGT. Due to omissions in the 2014 data, that year will be left out of this report and I will only look at 2012, 2013 and 2015. This omission does not have any bearing on the results.

No analysis like this has been carried out for Ireland’s electricity system since large scale wind energy was deployed. It is based on real data from the power stations rather than models. Most, if not all reports on wind energy use models which, while instructive, may not reflect all factors which this report will include such as reserves. The analysis refers to the Republic of Ireland only and does not include Northern Ireland as the two systems are not connected.


It is widely agreed that wind energy mainly replaces gas in Ireland’s electricity system.
Gas is consumed in either Combined Cycle Gas Turbines (CCGT) power stations or in their less efficient relations Open Cycle Gas Turbines (OCGT). There are eight CCGT power stations and nine OCGT in Ireland. Generally, CCGT run more frequently than OCGT which are mainly used for peaking. Some OCGT use oil instead of gas.

Gas consumption data for the CCGT in Aghada are not separated from the OCGT situated at the same site so it is not possible to show separate results for both CCGT and OCGT. Therefore, the figures for gas in this report are a combined OCGT / CCGT figure.  

No data was available for the two OCGT at Sealrock, however these run as baseload (they have priority dispatch) so again the omission of these gas power stations doesn’t have any bearing on the results as they will run similar each year. Likewise, there is no recent data available for the two OCGT at Edenderry but these run on oil anyway.

So this report will include the three OCGT at Aghada, Marina OCGT and North Wall OCGT. So does the inclusion of these not affect the overall conclusions as some will argue that it is CCGT which back up wind rather than OCGT ? Well, the answer is No. Bord Na Mona, who operate the two OCGT at Edenderry state the following [5] :
  • There is a need for flexible thermal units with fast response times to complement the increasing amount of wind capacity on the Irish electricity network

OCGT are far more flexible and respond much quicker than CCGT and therefore they are a necessity during high periods of stochastic wind penetration. For this reason OCGT are often used as reserve and replacement reserve. A report prepared by Eirgrid in 2007 stated the following [6] :

  • "Generally, the demand for replacement reserves increases with increasing wind power capacity installed.

  • The occurrence of high demands for replacement reserves is mainly driven by a high number of simultaneous forced outages that happens simultaneously to relatively high wind power or load forecast errors. The value of these peaks tends to increase with increasing wind power capacity installed."

So OCGT should be included in a study of this kind to get an accurate picture of actual gas savings due to wind. As it turns out, two of the OCGT (at Aghada) had increased running during 2015 while the other three had reduced running.

There was one new CCGT commissioned during this period - Great Island in the South East in 2014. This replaced an old heavy fuel oil power station. It’s important to note that the old station only ran between 4 and 6% of the time whereas the new station ran approx 50% of the time in 2015. Along with increased wind generation, this surely contributed to the lower running of neighbouring CCGT in the South Region and / or lower electricity imports. For the purposes of this report it is assumed that Great Island contributed to lower electricity imports in 2015.


Demand increased by about 1 TW during the period 2012 to 2015 (Figure 1) [7].
Imports increased in 2013 (from zero) and decreased in 2015 [8]. Coal output dropped slightly in 2013 but increased to it’s highest level since 2007 in 2015 [9].


Presumably, this was due to the flood of cheap American coal in the market, a consequence of the fracking boom.


During this period, wind energy grew from about 4,000 Gw to 6,500GW, an increase of 60%. Gas consumption in Ireland’s power stations fell from approx 2.2 billion m3 to 1.8 billion m3, a reduction of 20% (Figure 2).


The objective of this report is to calculate the year on year (or marginal) gas savings, taking all of the above factors from Figure 1 and 2 into account, from the additional wind added to the system each year.

THE YEARS 2012 TO 2013

To accurately calculate this, the East West Interconnector (EWIC) must be taken into account. The EWIC came into operation at the very end of 2012 and because of it’s location generally displaces generation in the Dublin region. Between 2012 and 2013, although demand did not fall, gas consumed in the four Dublin CCGT fell by 11%, about 166 million m3. However, it is assumed that for 2013 that Huntstown 2 reduces it’s output when EWIC is exporting to Ireland with the other reductions in Dublin due to wind energy [10]. Gas consumption in Huntstown 2 fell by 105 million m3 between 2012 and 2013.

Because the EWIC was running in 2013 and not in 2012, it means that an adjustment is required in 2013 for the reduced running of Huntstown in the system. This means that actual gas savings due to increased wind energy between 2012 and 2013 was not 267 million m3 as per Figure 2 but instead 162 million (267m less 105m). So a 446GW increase in wind output (or 11%) during 2013 resulted in additional gas savings of 162 million m3 or 7% [Figure 3].

So for each GW of additional wind, an additional 360,000 of gas was saved or in megawatt terms, 1MW of wind energy added during 2013 resulted in savings of 360 of gas.


Note: There was reduced coal output and increased demand in 2013 but there was more than sufficient surplus EWIC imports after accounting for the reduced Huntstown capacity factor to cover these.

THE YEARS 2013 TO 2015

We now proceed to the years 2013 and 2015. The first point to note is that the EWIC is now in operation for both years but an adjustment is still required for the reduced imports during 2015. Secondly, demand increased by approx 0.7TW but it was assumed that this was met by increased coal generation also of 0.7TW [Figure 1]. There was no increase in other renewables worth talking about [11].

Great Island came into operation during 2014 and it is assumed that this, along with higher levels of wind, resulted in the lower imports of 0.7TW [12]. Great Island had an increase in output and gas consumption of 1.2TW and 244 million m3 respectively. This meant that 1m3 of gas gave an output of 0.52MWh. I have decided to work on the conservative side and attribute all of the lower imports to the increased generation from Great Island. This means that 136 million m3 of the total gas for 2015 can be attributed to the lower imports [13].    

Without this adjustment gas savings for 2015 are 180m m3 compared to 162m m3 saving in 2013 for a 44% increase in wind generation. Quite clearly an adjustment is required for the lower imports which have been replaced by gas generation. Otherwise, I would be understating the gas savings due to wind.

Figure 4 shows the actual savings due to wind. After the above adjustment, gas savings are 316m m3 (180+136), about double the savings made in 2013 although for four times as much additional wind energy.


So we have gone from 1GW wind for Gas saving of 360,000 m3 to 1GW wind for Gas saving of 160,000 m3. We now have to install twice the amount of wind farms to achieve the same fossil fuel savings as achieved before. [Figure 5].


Clearly, the CCGT are frequently running on low loads, behind the high levels of wind, well below the rated output that they were designed to run at. They are also cycling more often. This has lead to significant inefficiencies and lower fossil fuel savings as more wind is added to the system.

Another contributing factor is the requirement for five large power stations to be on load at all times to maintain voltage control [14].  The majority of these are CCGT. So these power stations can’t be shut down during long periods of high wind. Also, it’s possible that reserves and replacement reserves have increased due to increased wind generation further reducing fossil fuel savings.

One can see from Figure 5 that we are soon reaching a saturation point of wind energy. This is the point at which installing an additional MW of wind will result in net gas savings of zero. At the same time, the costs of installing this extra wind will increase with additional grid requirements and increased maintenance costs of CCGT [15].

This report does not include changes in the generating mix since large scale deployment of wind energy. For example, off grid diesel generation capacity (known as Demand Side Units) now stands at 230MW, a 40% increase on the previous year [16]. There was a 6% increase in oil consumption at Ireland’s power stations between 2013 and 2015 [17].


Clearly, the CCGT have run more inefficiently since 2013 due to the large increase in wind generation.

Generating 23% of electricity from wind, whilst a good achievement on paper, does not result in equivalent fuel and associated CO2 savings of anywhere near that. Going from a wind penetration of 17% (2013) to 23% in 2015 has resulted in fossil fuel savings of 0.16 million m3 per GW of additional wind, yet when we moved from 15% (2012) to 17% (2013) there were savings of over twice as much (0.36 million m3 per GW of wind). Clearly, the fossil fuel savings are decreasing exponentially with each new MW of wind installed.

The Irish government’s commitment to wind energy needs to be re-assessed in light of the above findings. Most of the significant fossil fuel savings from wind energy have already been achieved. Without a hydro back-up system such as Norway to connect to, the savings from each new wind farm diminish until the costs clearly outweigh the negligible benefits. Running gas power stations behind high levels of wind does little to de-carbonise Ireland’s economy or reduce it’s dependence on fossil fuels in the long term.

If the job of the Irish wind energy industry is to put the fossil fuel industry out of business, then based on this analysis, it will ultimately fail.

A moratorium should be placed on all new wind energy installations until a full analysis of all options and alternatives is carried out.


Data taken from EPA Annual Environmental Reports for each power station

CCGT gas m3
Huntstown 1
Huntstown 2
Dublin Bay
Great Island


*Aghada includes 3 OCGT of 90MW each, 430MW CCGT and steam turbine of 260MW steam turbine all run on gas (just small amount of light fuel oil is used)

OCGT gas m3
North Wall



Source: SEAI


[6] Wind Variability Management Studies (P.Meibom et al) 2007
[9] All coal figures in this report come from Moneypoint Annual Environmental Reports
[11] There was 5MW increase in biomass which replaced peat and only 10MW of solar PV.
[12] EWIC had lower imports of 713,000 MW. Given the fuel / mw ratio of 0.52% for Great Island, 713,000 / 0.52% = 136 million m3 of equivalent gas attributable to EWIC
[13] Great Island is now the most efficient gas generator on the grid hence why it would make sense for it to run alongside lower imports
[17] From EPA  Annual Reports for each power station

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