Resource Library Category: Netherlands (9 items)

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Documents presented here are not the product of nor are they necessarily endorsed by National Wind Watch. This resource library is provided to assist anyone wishing to research the issue of industrial wind power and the impacts of its development. The information should be evaluated by each reader to come to their own conclusions about the many areas of debate.

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Windmills increase fossil fuel consumption and CO2 emissions

Source:  Le Pair, Kees

Abstract

First we describe the models presently used by others to calculate fuel saving and reduction of CO₂ emission through windparks. These models are incomplete. Neglected factors deminish the calculated savings.

Using wind data of a normal windy day in the Netherlands it will be shown that windparks of various size cause extra fuel consumption instead of fuel saving, when compared to electricity production with modern gas turbines only. We demonstrate that such losses occur.

Factors taken into account are: low thermal efficiency at low power; cycling of back up generators; energy needed to build and to install wind turbines; energy needed for cabling and net adaptation; increase of fuel consumption through partial replacement of efficient generators by low-efficient, fast reacting OCGTs.

1. Introduction

Several countries invest heavily in the construction of windmills in order to save fossil fuel and to reduce CO₂ emission. The wind comes free, the mills do not pollute and there is no need to burn fossil fuel. However, this simple notion defended by staunch supporters of windturbines, has been criticized by critical analysts, e.g. refs 4, 5, 6, 8, 10, 11, 12.

Wind does not blow according to demand of electricity users. Sometimes there is no wind or little wind and sometimes there is a lot. It would be no problem if there was an economic way to store electricity and to use it from that storage whenever needed. Unfortunately we do not have such a storage. Batteries have little capacity and they are much too expensive. There are other possibillities but none of them comes near to anything that is economically feasible. The only exception is hydro power, i.e. lakes in mountains, that can be pumped full if there is an electricity surplus and emptied when the power is needed. Unfortunately there are no mountains in the Netherlands. (Also many other countries that do have them, do not have sufficient place there for such storage lakes.) So the current practice is to have windparks operate in connection to conventional powerplants. These generators step in when the wind fails and they can be switched off, or their output is reduced, if the wind blows. Thus, when considering wind power, one must do that normally in connection with ‘back up’ conventional systems. That is why the wind influences from minute to minute the performance of the conventional generators.

A handicap prohibiting the settlement of the dispute is the absence in the public domain of factual data of the different producing units. So the the arguments are mostly about model computations. There are exceptions. In the USA a BENTEK study used real emission data of power plants in Texas and Colorado. They became available due to the freedom of information act. Its conclusion was: wind has no visible influence on fuel consumption for electricity production and the emission of CO₂ in the atmosphere is not reduced¹³.

This shocking result did not convince decision makers. At least not in Europe. The negative result was attributed to a difference in fuel mix. Coal-, oil-, gas- and nuclear heated generators behave differently. So what might be true there, does not mean that it holds true for us.

In August 2011 Fred Udo analysed the data put on the internet by EirGrid, the grid operator in Ireland. His web page article was termed by colleagues abroad ‘The smoking gun of the windmill fraud’. He showed that the substantial wind contribution in the Irish republic caused such a small saving of fuel and a corresponding small reduction of CO₂ emission, that it shatters the whole economy of the wind policy. He also was able to show that more wind penetration caused an increase of CO₂ emission⁸.

The real situation, however, is even worse. The way EirGrid derives its data on CO₂ emission does not correspond with what is actually happening in fossil fired power plants. More over, the Irish data do not enclose some serious other factors that deteriorate the fuel saving aimed at. An indication could be, that the overall CO₂ emission in Ireland is 20% higher than the emission calculated in the EirGrid tables, as Udo showed. (His source: ref. 14. A difference of 3% might be due to import of electricity. Transport losses have been accounted for.)

In this present study we shall explain what is wrong. On the basis of existing data and new information on the behavior of conventional generators when they are cycling – i.e. ramping up and down in order to compensate for the variations in wind power – we shall show how much worse the influence of adding wind electricity to the grid really is.

2. The old model.

During the early days of modern wind turbines the argument was simple and appealing. Every kWh electric energy generated by wind replaces a kWh produced by a conventional power plant. As a result the fuel needed to produce it, is saved and the CO₂ that would be produced is not released in the earth’s atmosphere.

Different generators have different thermal efficiencies. And the CO₂ production is different for gas, coal and other fuels. Some basic data for certain generators and fuel used in the Netherlands are listed in table 1. The coal fired unit in the table is the most efficient one currently under construction. Others presently in operation do not have efficiencies better than 0,44 or 0,42. The data about CCGTs should be read as of the best units running at the moment. The newest OCGTs may under optimal conditions reach an efficiency of 0,36. But there is quite a number of older ones that will remain in operation till after 2020.

Table 1.

Thermal efficiency η of different generators1
coal fired steam enhanced gas turbine, CCGT open cycle gas turbine, OCGT nuclear	0,455 0,59 0,32 0,377
latent heat2
Gas [J/m3] coal [J/kg] Uranium [kWh/kg]	32 × 106 29 × 106 7,4 × 106
CO2 emission when burning3
Gas [kg CO2/m3] Coal [kg CO2/kg] Uranium	2,5 2,6 nihil

The old model then tells: for every kWh wind electricity we save fuel and gas as is summarised in table 2.

Table 2.
Savings according to the old model.

Type generator	Per kWh conventional	Per kWh CO2 [kg]
Coal fired CCGT OCGT Nuclear	0,273 kg coal 0,191 m3 gas 0,352 m3 gas 0,358 mg Uranium	0,71 0,48 0,88 nihil

These figures have opened the market for the large size windmill introduction. Governments and the public became convinced. Wind offered a possibillity to offset the thread of climate change and depletion of fossil stocks. Even today the same numbers are often used in public debates, sometimes disguised in terms of ‘so many windmills are capable to provide for the electricity needs of so many households’.

Critics pointed to flaws in the assumption. There are several reasons why these figures are wrong. This lead to a new model, which is now accepted e.g. by the Dutch government. (Also the EirGrid uses this model in order to calculate the CO₂ emission on the basis of the amount of electricity produced by the different conventional power plants during their operation in co-operation with the windparks.) We shall therefore call it the current model.

3. The current model.

The current model acknowledges variation of the thermal efficiency of the generators. A generator is designed for a certain optimal output. If one lowers the temperature, i.e. feeds in less fuel, the electricity output does not deminish proportionally. Every conventional generator has its own ‘heat rate curve’ describing how its efficiency, η, depends on power output. With increasing wind electricity penetration conventional power generation has to be reduced and the efficiency of the units becomes less. This reduces the savings calculated with the old model. The results are presented in table 3. For data & algorithm see Appendix.

Table 3.
Comparison of savings in fuel and CO₂ emission between the old model
and the current model with resp. 20%, 40% and 60% less than
‘design power’ of the back up conventional plants.
We left out the ones not relevant: “n.a.”

savings					relative setback
old model all	current model
	Coal fired	CCGT	OCGT	nuclear	CCGT	OCGT
0% 20% 40% 60%	0% 19,1% 36,5% n.a.	0% 17,2% 35,6% 51,8%	0% 14,7% 28,9% 44,3%	0% 17,8% n.a. n.a.	n.a. 14,0% 10,9% 13,6%	n.a. 26,7% 27,8% 26,1%

The current model shows saving under the given circumstances. The Netherlands government assured parliament that the previously assumed savings had to be reduced by at most 10%. When we look at the figures in table 3, we see that it was slightly overplaying its hand. Our calculations show a relative savings reduction exceeding this for the most relevant generator types, CCGT & OCGT. OCGTs ought to be used as little as possible in view of their low efficiency. They are only needed when rapid power changes are required.

(Coal and nuclear plants are almost irrelevant in this respect as they cannot be ramped up and down sufficiently fast to follow wind variations. Nuclear plants do not produce CO₂ anyway and their fuel is virtually inexhaustible.)

4. Errors in the current model.

Unfortunately the current model does not represent what is going on in a power plant. It neglects completely other factors that reduce the supposed fuel and emission savings. We shall first list the important factors that influence the fuel consumption and the savings. After that we discuss them and show their implications.

1. Cycling, § 5.

   As we mentioned before, cycling i.e. ramping up and down of conventional generators, differs from running them at less than their designed power in a stationary mode. The latter can be dealt with using the well known ‘heat rate curves’ for that particular type of generator. For cycling there is no public data. If it exists, it is kept secret. The power industry world wide consider it ‘competition sensitive’. We have argued several times that cycling is important because it is inherent to the task of following wind energy variations. It has such a strong impact on the fuel consumption of the plants, that authorities should insist that this data becomes available before they decide on huge subsidies for the wind industry. The argument that generators did cycle also before wind electricity was added because of variations in demand, is irrelevant. The wind variations add up almost to their full extend and they are more frequent and less predictable than demand variations, see for instance figures 1 & 3 below.

   Recently we received some information concerning a fuel flow recording of a coal fired generator during cycling. The generator running stationary for some time at 100% of its optimal capacity reduced its output to 80% and up again to 100%. The whole cycle took place in one hour. The total fuel consumption during that period was 1,2% more than it would have been had the machine continued running at 100%. It was suggested that for a CCGT this outcome should have been 1%⁷. One might wonder whether this measurement is at all representative for the conventional segment? There is good evidence, that it is. A few decennia ago power companies in the Netherlands were owned by public authorities, cities or other regional entities. They were nation wide united in a co-operative association, the SEP. Within that organisation there was a free exchange of information. The SEP regulated the production of the individual plants in such a way that variable costs were minimised. Therefore the individual heat rate curves were precisely known. Please note: these were measured data, not theoretical! It turned out that the actual fuel use of the units doing the regulation and delivering the variable part of the power needed, nation wide, was always some 0,3 – 0,5% higher than that calculated with the heat rate curves. This remarkable difference was attributed to the ‘hysterysis effect’. Variations in demand required the plants to ramp up and down causing this extra fuel consumption. One should take into account that some 30% of the joint producing units took part in this cycling and provided for the extra demand above the permanent load. The demand variation was higly predictable. It consisted more or less of only two major cycles per day and yet 0,3 – 0,5% more fuel for the whole top production. This strenthens our trust in the validity of the figure of the test run.

   In our calculation later on we shall assume this behaviour as a cycling fact¹⁵.

2. Energy costs of construction and installation, § 6

   Windmills are considerable units. They require energy for their constituents, their construction, their foundation and their installation. One of the firms actually doing this type of work figured it out. (See ref. 5. Note 13.) It boils down to an amount of energy equal to the assumed production of the wind turbine during a period of 1½ year.

   This energy investment has to be ‘written off’ during the whole life time of the installation. This according to wind supporters is supposed to be around 25 year. We have seen recently that a whole windpark in the Netherlands with that supposed life time had to be renewed after 12 year. Subsidy regulations applied by the government are based on a write off in 15 year. That is the period we deem realistic.

   We shall incorporate the energy costs factor in our subsequent calculations with a life time of 15 years. To appease the wind fans, we’ll add a line based on 30 year.

3. Energy costs of connection and adaptation to the grid, § 7

   The same as in b must be assumed for the extra cables and the adaptation of the wind generators to the grid. Germany has to construct for instance 2700 km extra high power lines. The Netherlands for that reason was connected by under water cables to Norway and to the UK. The Norwegian connection had already to be renewed partly two years after initial construction. The new to be built off shore windpark in Denmark ‘Gwynt y Môr’ will cost ~ 2 G€. 1,2 G€ of that is required for the wind turbines, 0,8 G€ for the connections etc.

   We shall include in our calculations a similar ‘write off’ for this purpose as for the energy costs in b above.

4. Need for more OCGTs, § 8

   There are two types of gas fired generators fit to co-operate with the wind turbines: CCGTs and OCGTs. CCGTs are beautiful effective machines. Their efficiency might before long reach a thermal efficiency of 60%. However, their ability to ramp up and down is not suited for very rapid variations. It is in the order of ½ hour. But frequent ramping is unlikely because of the damage in terms of wear and tear (see g. below) it causes. OCGTs on the other hand can deal with variations within minutes. But their efficiency is sadly low. It is about 32% while running at design power. The wind variations may sometimes come sudden.

   The centralised grid regulation is to a large extend done on the base of frequency regulation. This requires sophisticated manipulation of the available units. As a consequence units are often condemned to operate on less than their design power with less than optimal fuel efficiency.

   Therefore it is necessary to make more often use of the OCGTs than would be the case without wind power. More use of OCGTs means more fuel. It reduces the savings the wind might give.

   In our calculations we have made a moderate estimation for this factor.

5. Quasi static ramping, § 5 (cycling)

   In the current model it is assumed that there is an instantanious transition in a cycle from one stationary state to the next with different η. In reality there is a transition that takes time. In our calculations we have used a slightly more sophisticated approach. We assume the transitions to take place as a quasi static proces. (The cycle loss is taken into account separately.) This means that at any time during the transition we account for conditions pertaining to those at the power level at that moment. The results as shown in table 3 are not significantly altered. In a more frequently occurring ramping up and down in which the transiton time becomes more important with respect to the time in which the generator is in a stationary state, there is a difference.

6. Self consumption of electricity

   Windmills do not only produce electricity, they also use it. Electricity is needed to start them, and to heat some of their parts. The power regulation electronics consume electricity all the time. It is not known, whether the actual production data provided by the national statistics bureau, CBS, are nett figures. We suppose that the turbines, while running, provide for their own needs. But when they are not producing, that cannot be the case.

   For the time being and by lack of information we have not included this element in our calculations.

7. Extra wear and tear

   Life time and maintenance of conventional plants depend largely on the ramping activity. More than on the number of stationary running hours. Ramping is a fact of life in the electricity business because of variations in demand. However, the connection with wind power adds extra to the normal, that is according to demand variation, cycling routine. Also the wind varations are often less predictable. This issue was reason for the government to ask for a special assessment. The report¹ of a research group at Delft University of Technology came out in April 2009. It contains serious warnings about this phenomenon. In the USA there are firms active, which make their business by consulting power producers about more efficient ways to deal with ramping in order to save on extra fuel costs and to protect their costly equipment against faster wear and tear than what is absolutely necessary. The extra maintenance and life time shortening must have consequences in terms of energy costs.

   We have to omit this factor in our calculations by lack of sufficient information.

8. Spinning reserve

   In actual situations it happens that conventional units must be turned off because of the wind electricity preference. In such cases normally these units remain spinning idle and thus are using fuel without production of electric energy. Data there about is also not available.

   We also have to omit this factor in our calculations by lack of sufficient information.

-o-o-o-o-o-o-o-

Towards an integral savings assessment of windturbines.

(Details of the calculations can be found in the Appendix.)

5. Cycling.

The biggest CCGT presently in operation has a maximum capacity of 440 MW. In our model we use a hypothetic gas fueled plant with a capacity of 500 MW. In combination with a 100 MW windpark 3% or 15 MW of this is supplied by an OCGT. In that case the remainder has to be supplied by two smaller CCGTs. For a mainly CCGT based plant with a design capacity of 500 MW the cycle properties as described in § 4a implicate that the assumed fuel saving during one hour with a cycle 100% – 80% – 100% and a ramp rate of 12 MW/min actually becomes a loss in stead:

assumed saving	~ 16 400 m3 gas
actual loss	~ 950 m3 gas

The substantial difference is not so surprising; think of a car in town and on an express way. The fuel use of a normal diesel engine while driving at a constant speed of 100 km/h is normally about 50 – 60% of its consumption in a city with continuous speed variation. This happens also with power generators that have to adjust their output continuously following the variations of their wind powered counterparts.

We now consider a region to be served by a windpark in combination with a conventional system. We assume a constant demand of 500 MW. The conventional system, we choose, consists of the most efficient generator units (CCGT), only when necessary assisted by a small fraction of OCGT. In order to cope with lulls in the wind, the conventional power system has a design capacity of 500 MW. For the wind park we shall look at 100, 200 and 300 MW name plate capacity. To approach average conditions, we’ll choose a normal windy day, picking the wind record of Schiphol Airport on August 28, 2011.

Figure 1.

A wind turbine depends for its power on the flow of the wind energy, i.e. it varies with the 3d power of the wind speed, v. If v ≤ 5 kn (= 2,5 m/sec) the turbines do not produce electricity. (Their wings may still be rotating. That is better for the bearings, but there is no output.) At 19 knots they reach their maximum capacity, i.e. P = 100 MW (or 200, or 300 MW).

In between the power must be interpolated by:

P = 0,03644 × (v − 5)3 (or 2x, or 3x)

(1)

as depicted in

Figure 2.

This implies a loss that depends on the wind speed. At that site on August 28 this means a varying wind contribution shown in

Figure 3.

If we would calculate the total power contribution using the old model, on that day the 100 MW wind park would have saved 4,2% of the use of the conventional power plant. Details of the arithmatic can be found in the Appendix. Wind power experts attribute a ‘capacity factor’ of 25% to wind mills in the Netherlands. That is to say with a name plate capacity of 100 MW the average contribution over the year would be 25 MW, which means 5% saving. However, in 2008 the overall capacity factor of the wind turbines in the Netherlands was 22,63%¹⁶. Thus an average wind day in 2008 would have saved 4,5%. We found 4,2% which means that August 28 was just slightly less than an average wind day that year.

But, because of the cycling effect the real result is appreciably different.

The Schiphol record tells us the wind speed every half hour (i). With (1) we find the wind power, P_w,i, and the power of the adjusting CCGT+, P_GT,i.

PGT,i = 500 − Pw,i

(2)

We calculate the fuel consumption during that half hour with the quasi stationary method. That is we split the 30 minutes in a part in which the CCGT+ produces stationary and a part at which the system is ramping from the previous level P_GT,i-1 to P_GT,i. For the first we part we use: η_i and for the second: 0,5 × (η_i-1 + η_i).

For details see Appendix.

We know what cycling does in the case of 100% – 80% – 100% for a 500 MW generator. During a full cycle there are three phases: up, down & stationary. In a cycle during a full hour with 12 MW/min, these last ~8,3 min, ~8,3 min and ~43,4 min. During the 43,4 min there is saving. During the two times 8,3 min there is saving while going down and extra fuel consumption going up. The nett cycle cost in the example is the same whether it happens during an hour or during a half hour as long as the ramp rate remains 12 MW/min. Only the stationary minutes are less.

The net cycle costs will depend on the amplitude of the cycle and to some extend on the power level at which the CCGT operates. Also the duration of cycling depends on the amplitude.

We assume:

1. The net cycle loss does not depend on the power level. (Probably the loss at low power i.e. with high wind penetration increases, because the relative diferences are bigger and the CCGT has a lower efficiency there.)
2. The nett cycle loss is proportional to the amplitude. It is zero if the amplitude = 0 (stationary) and at amplitude = 100 MW the loss is as in the example.
3. During the half hours we only see half cycles. We assume that they require also only half the nett loss. Because the wind speed over a longer period always returns to its earlier value, our CCGT ramps as much up as down, which justifies this assumption.

Now we are able to compute for each half hour the savings of the system. (Quasi stationary saving minus the pertaining cycle loss.) Summing them up and comparing them with the fuel use of our CCGT at full power, we obtain the percentage fuel (and emission) saving over the 21½ hour period.

6. Energy costs of construction and installation.

We use the data of the energy costs for construction and installation of the research department of Volker Wessels Stevin, a major installer of windturbines⁵: 1,5 year windmill production to recover the needed energy. If we then assume the life time of a windmill to be 15 year, it means that 10% of its production must be deducted to compensate for the earlier loss. We shall also do our calculation for a life time of 30 years, meaning a 5% deduction.

7. Energy costs of connection and adaptation to the grid.

Here wil work with the same deductions as in § 6, see § 4c.

8. Need for more OCGTs.

OCGTs are the best generators to compensate for rapid variations. Their thermal efficiency is about half of that of a CCGT. OCGTs are always used because of fast changes of demand. Now the variations of wind power add to the variations of demand, which requires more often production with their low efficiency and accompanying more fuel use.

We assume that with windparks of 100 MW, resp. 200 MW and 300 MW the participation of OCGTs has to be increased by resp. 3, 6 and 10%. That we are not dealing here with a negligible complication can be illustrated with a comic remark by the CEO of the Gas Union, the main natural gas supplier in the Netherlands. While he was being interviewed on Dutch TV about the huge activity of constructing new gas pipe lines, he said: “It is because all that wind takes so much gas.”

In our computations we reduced the effective η of the conventional plant according to the said percentages with the η of the OCGTs, for which we took η_OCGt = 0,32.

The other factors mentioned in §§ 4f, 4g & 4h we leave out.

9. Results & conclusions.

The result of our calculations are summarised in table 4. One must keep in mind that the conventional plant by itself is capable to fullfil the whole electricity demand. So all costs for buying the wind equipment, the costs of installation and those of the extra cables and net adaptation are extra. (See Appendix for the algorithmes.)

Table 4.
Fuel saving and CO₂ emission saving through windparks according to different models and including other relevant factors.
Results for a 500 MW production provided by a modern gas fired plant with design capacity of 500 MW together with a windpark with name plate capacity, V, near Schiphol on a normal windy day.

V	100 MW wind	200 MW wind	300 MW wind
Old model	4,2%	8,3%	12,5%
Quasi stationary ≈ current	3,5%	7,1%	10,7%
Including ‘cycling’	1,4%	2,9%	4,4%
Ibid. incl. lifetime 30 yr.	1,0%	2,0%	3,1%
Same lifetime 15 yr.	0,6%	1,2%	1,9%
Same (30 yr.) + OCGT	−0,3%	−0,5%	−1,0%
Same (15 yr.) + OCGT15	−0,8%	−1,4%	−2,3%

It is clear. The alleged savings provided by windparks that could cover 20%, 40% or 60% of the electricity demand during favourable winds are not just negligible, they are even negative, when the most relevant factors are taken into account. As we remarked before, there is substantial evidence that a life time of 15 year is not an exaggeration. We mentioned the park that had to be renewed after 12 year. That was an on shore park. The parks to be constructed off shore operate under more difficult circumstances. Therefore we conclude:

NON-SUSTAINABLE. A 300 MW nameplate windpark near Schiphol on August 28, 2011, a normal windy day, during 21,5 h would have increased the amount of natural gas needed for the electricity production of 500 MW with 47150 m3 gas. This would have caused an extra emission of 117,9 ton CO2 into the atmosphere.

The windparks do not fulfill ‘sustainable’ objectives. They cost more fuel than they save and they cause no CO₂ saving, in the contrary they increase our environmental ‘foot print’.

A decision to invest thousands of millions Euros in the construction of windparks ‘to save fossil fuel and to reduce CO₂ emission’ is irresponsible. There are no savings, THERE IS LOSS!

We do not consider it likely that more knowledge of the factors influencing the present outcomes would change our results appreciably.

Nieuwegein, October 7, 2011.

Click here to go to APPENDIX

References & notes.

• This web page article is aimed at readers with some background knowledge. It is a short version of the Dutch report Gas, Wind en CO₂ op Schiphol. De crash van de windmolens. (The Dutch report tries to explain the subject to the laymen.)

1. Dijkema, Z. Lukszo, A. Verkooijen, L. de Vries & M. Weijnen: De regelbaarheid van elektriciteitscentrales; quickscan in opdracht van het Ministerie van Economische Zaken; TU Delft, 20 April 2009.
2. Oscar Vlijmen.
3. CO₂-PROFIEL
4. K. de Groot & C. le Pair: The hidden fuel costs of wind generated electricity. Also: SPIL 263 – 264 (2009) p.15 ff.
5. C. le Pair & K. de Groot: The impact of wind generated electricity on fossil fuel consumption.
6. F. Udo, K. de Groot & C. le Pair: Wind turbines as a source of energy.
7. KEMA: priv. comm.
8. F. Udo: Wind energy in the Irish Power System.
9. Wind record Schiphol
10. Kent Hawkins: Wind Integration Realities: Case Studies of the Netherlands and of Colorado.
11. W. Post: Wind power and CO₂ emissions.
12. Hugh Sharman: Wind energy, the case of Denmark.
13. BENTEK Energy: How less became more: Wind power and unintended consequences in the Colorado energy market.
14. SEAI.
15. In discussions among us (De Groot, Udo and myself) it has been asked whether the data of ref.7 should not be interpreted as ’1% more than the current model’? We think not. Remember the ‘car in city’ argument above. Nevertheless, we have also done the calculations using that assumption. In this case the outcomes taking into account the other factors as well are for a 15 years life time:

    savings of resp. 1,2%; 2,6% and 3,7% for 100 MW wind, 200 MW wind and 300 MW wind, i.e. 20%, 40% and 60% of the total demand capacity in the form of windmills.

    These are also absurd low savings in the view of the economics of electricity production.

16. CBS Statline.

Click here to go to original paper (which may have been updated since posting here).



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Date added:  June 4, 2010
Aesthetics, Netherlands, Noise •

Response to noise from modern wind farms in The Netherlands

Source:  Pederen, Eja; van den Berg, Frits; Bakker, Roel; and Bouma, Jelte

Abstract: The increasing number and size of wind farms call for more data on human response to wind turbine noise, so that a generalized dose-response relationship can be modeled and possible adverse health effects avoided. This paper reports the results of a 2007 field study in The Netherlands with 725 respondents. A dose-response relationship between calculated A-weighted sound pressure levels and reported perception and annoyance was found. Wind turbine noise was more annoying than transportation noise or industrial noise at comparable levels, possibly due to specific sound properties such as a “swishing” quality, temporal variability, and lack of nighttime abatement. High turbine visibility enhances negative response, and having wind turbines visible from the dwelling significantly increased the risk of annoyance. Annoyance was strongly correlated with a negative attitude toward the visual impact of wind turbines on the landscape. The study further demonstrates that people who benefit economically from wind turbines have a significantly decreased risk of annoyance, despite exposure to similar sound levels. Response to wind turbine noise was similar to that found in Sweden so the dose-response relationship should be generalizable.

Journal of the Acoustical Society of America 126 (2), August 2009, pages 634-643



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Date added:  December 18, 2009
Emissions, Germany, Grid, Netherlands •

Hidden fuel costs of wind generated electricity

Source:  de Groot, K.; and le Pair, C.

Summary

Wind generated electricity requires back up capacity of conventional power stations. This capacity is required to deliver electricity to consumers when wind supply is falling short. To have the non-wind power stations ramp up or down to compensate for the stochastic wind variations causes extra efficiency loss for such power stations. How much efficiency is lost in this way and how much extra fuel is required for this extra balancing of supply and demand is unknown. In this article we attempt to make an educated guess.

The extra fuel required for the efficiency loss must be added to the fuel required building and installing the wind turbines and the additions to the power cable network. While these extra requirements may be too small to notice when the installed wind power is a small fraction of the total capacity, matters change when wind capacity becomes significant. Based on the German situation with 23 GW installed wind power we show that it becomes doubtful whether wind energy results in any fuel saving and CO₂ emission reduction. What remains are the extra investments in wind energy.

Introduction.

Wind energy comes for free, but it does not follow that electricity generation using wind is also free. The hardware costs money and energy to build. The energy required for this is typically derived from fossil sources. More importantly, one needs to maintain a conventional back up power generator capacity roughly equal to the installed wind power capacity.

The wind may be free of charge, but it is not provided in the desired doses. Wind varies. The variations do not match the electricity demand. Because there is as yet no economically viable method to store electricity, the variations in wind generated electricity levels that do not match demand levels have to be met by adjusting the output of conventional power stations. In his recent thesis¹ Ummels concludes on the basis of computer modelling studies that such adjustments can be made “without problems” even when wind would generate electricity equivalent to 33% of the Dutch demand.

Others are less positive. We quote from the study² ”De regelbaarheid van elektriciteitscentrales” (The adjustability of electric power stations) which was published in Dutch in April 2009:

“Increasing the rate of reaction of the power station assembly can only be achieved by using inefficient open-cycle gas turbines or by cannibalising on the reliability and lifetime of large and efficient power stations. This means that flexibility translates into inefficiency and higher fuel consumption and CO₂ emission than one can expect on the basis of average efficiency. (our note: i.e. without the additional requirements of adjusting for wind fluctuations).

A further quote:

“Controlling the output level costs money: every output variation of a power station creates extra wear. This reduction of useful life is larger as the rate of output change increases. In addition, variations in output cause reduced energy efficiency which translates into additional costs and increased environmental impact.” (translation: ours).

While this report identifies the problem of reduced efficiency, it does not indicate the magnitude of the efficiency decrease, nor the amount of the required additional fossil fuel use. Both studies only provide assumptions on the effect of increased wind turbine power, but no field data.

The Dutch wind energy capacity is still far from the 6 GW (gigaWatt) goal set by the Dutch government. The control problems will most likely only become evident when the wind turbine capacity is a significant fraction of the total generating capacity. Therefore we have made our estimates on the magnitude of this effect on the basis of German data, where now about 23 GW is installed, and where extensive pertinent datasets have been published.

Germany.

In support of the government policy of support for sustainable energy, the country has chosen for large-scale application of wind energy. Achievements in this respect are regularly reported on³. The wind turbines are spread out over all of Germany, from Bavaria in the South to offshore in the German Bight in the North. Since the beginning of this century the amount of installed power has increased almost fourfold, from 6 GW in 2000 to 23 GW in 2008. The latter amounts to the equivalent of some 20 conventional power stations. The Germans have published on both the installed capacity and the actual annual electricity yield, as is shown in table 1. All data are from “Wind energy report 2008³”




Table 1.

Year	Power [ MW ]	Yield [ TWh ]	Wind turbine duty factor4
2000	6050	8,8	17%
2001	8680	10,9	14%
2002	11850	17	16%
2003	14500	19,2	15%
2004	16480	26,8	19%
2005	18290	27,1	17%
2006	20470	31,2	17%
2007	22090	40	21%

Table 1. The installed wind power in Germany and the actual yearly electricity production in TWh (terawatthour) and the derived wind turbine duty factor⁴ (= ratio effective power / installed power).


Over the given years the wind turbine duty factor (defined as the ratio of what was delivered to the net and the amount that would have been delivered with design capacity of the wind turbines⁴ was on average 17% or 17,5% (weighted average). When considering these figures one has to keep in mind that by law wind-generated electricity has absolute priority over all conventionally generated electricity. When wind generated electricity is available, it must be used. The output of other power stations has to be reduced commensurately.

The data in table 1 cover wind turbines all over the country, so the effect of wind variability over the country is taken into account. Firstly, we observe that the contribution of this large “name plate” (design) capacity is rather modest. Secondly, the effect of spreading the turbines over a large geographical area did not solve this problem. This does not just hold for Germany, as has been observed in a report to the British House of Lords⁵. But then, every sustainably generated unit of electricity counts, and this means a saving on fossil fuel use and a reduction of CO₂ emission, one would presume. Anyway, this was and is the reason to invest in wind turbines in the first place.

Wind and electricity

In the introduction we mentioned the issue of wind supply variability and the lack of an acceptable method for electricity buffer storage to cope with this variability. That variability is a huge issue as is demonstrated in the figure.




Figure. (E.ON Wind Report 2005) Fraction delivered wind of total delivered power. Wind delivery varied from 0,2% to 38% of total power delivered to the grid.

E.ON is the largest German wind-generated electricity provider. They demonstrate in the figure the significant engineering challenge they had to cope with over the time span of a year, as the fraction “wind” in the electricity they delivered varied from 0,2% of the total to as much as 38%. In the year this figure relates to, E.ON had as much wind power capacity as the Dutch government target for the future. The strong variation in yield over time is partly the result of the given unfavourable physics of wind energy: the energy yield varies with the 3rd power of the wind velocity. In practice: when the wind blows at half the wind turbine design speed, the electricity yield is only one eighth of the design output, some 12% of the design capacity. Furthermore, there are days when there is no wind at all over almost the whole geographical area. In both cases, a very significant amount of energy must come from the conventional sources.

The effect of giving sustainably generated electricity priority in Germany has the following obvious consequences: when the wind turbines operate at design capacity, up to 23 GW is produced. When there is now wind, up to 23 GW of electricity must be largely or fully provided from non-sustainable sources. In the German practice this means that now up to 23 GW must be in stand-by mode. Prof. Alt from the Technische Fach Hochschule Aachen⁶ has concluded that this is indeed the practice, even when the German Wind Energy Report³ states that this standby power is only 90%. It is obvious that there is an extra capital charge involved in

• Maintaining this backup power, and
• Making the additional investments in the high tension network and
• Coping with the wind fluctuations.

However, we will not discuss these economic aspects here.

Estimating the adverse effect of the wind-induced inefficiency of conventional power stations.

We want to focus on the effect of the wind induced extra variability on the efficiency and thus the power use of conventional power plants. So far, we have been unable to find data on this additional fuel use. If these data are gathered, they have not been published. The conventional power stations, meanwhile, do what they are asked and provide the supply security that wind cannot provide. In view of the lack of data on this effect, we have gone out on a limb and made some estimates on the effect of wind variability on fuel efficiency of the back up power stations. We hope to connect with the experts that have the real data or who can significantly improve on our estimates. We must make the following assumptions for our estimate:

1. The installed wind capacity operates several times a year at design capacity. It follows that the back-up units must provide this capacity when there is no wind. This assumption is supported by the observation of Prof. Alt, that after installing the wind turbines in Germany (and Denmark) no conventional power station has been decommissioned. As we mentioned in the previous chapter, he also believes that the full 100% back-up power (“Spinning reserve”) is required.
2. Only a fraction of the back-up power stations are open cycle gas turbines. By careful planning part of the stochastic wind supply variations can be balanced by ramping up or down of large-scale efficient conventional plant. Only the most rapid and or unexpected unbalances are taken up by switching gas turbines on or off. (We remind the reader that extra balancing effort even when planned always means extra wear and fuel use for the large power stations).
3. The electrical efficiency of a modern conventional power station is set at 55%, and that of an open cycle turbine 30%.

4. We know that 1 kWh electrical energy requires 270 grams of hard coal³, so that 1 kWh wind generated power saves 270 gram hard coal, excluding the effect of back-up inefficiency.

We now consider the production of 100 kWh electricity for which wind turbines have been built. After a year it turns out that on average 17,5 kWh have been supplied by wind, and the rest from conventional power plants, effectively serving as back-up. Assuming that these conventional plants delivered under optimum conditions, this required 82,5 x 270 = 22 275 g of hard coal, and 17,5 x 270 = 4 725 g of coal is saved producing this 100kWh.

However, the wind generated production has priority and forces the conventional stations to reactively ramp up and down. In the extreme case of the use of rapidly reacting open-cycle gasturbines only to achieve this, the efficiency falls from 55% to 30%.

Table 2 shows how the decreasing efficiency influences the saving of conventional fuel. At an overall efficiency rate for the back-up system of 45% the fuel saving already becomes negative and there is an extra fossil fuel demand. Wind electricity generation in this case produces extra CO₂, which is a truly counter intuitive result. If this level of inefficiency is truly the result of wind energy use, a cynic could observe that Putin and OPEC might want to promote wind energy in countries like Germany in order to increase its dependency on fossil fuel.

Please note that the reduced efficiency only applies to the back-up power stations. The other conventional stations operate at their regular efficiency.

Table 2.

Efficiency conv.station	Consumption [ g coal ]	Extra consumption	Ultimate saving [ g coal ]	Visible efficiency
55%	22275	0	4725	55%
53%	23116	841	3884	54%
51%	24022	1747	2978	53%
49%	25003	2728	1997	52%
47%	26066	3791	934	51%
45%	27225	4950	−225	50%
43%	28491	6216	−1491	49%
41%	29881	7606	−2881	48%
39%	31413	9138	−4413	48%
37%	33111	10836	−6111	47%
35%	35004	12729	−8004	46%
33%	37125	14850	−10125	45%
31%	39520	17245	−12520	44%
29%	42246	19971	−15246	43%
27%	45375	23100	−18375	42%
25%	49005	26730	−22005	41%

Table 2. The primary fuel saving (column 4) at assumed reduced efficiencies due to wind variation (column 1) and overall decrease in efficiency of all conventional power stations taken together (column 5). (100 kWh).

In Germany about 9% of the total electricity consumed is provided by wind. In case the turbines work at design capacity, this would yield (100/17,5) x 9% = 51,4 % of the electricity demand. Therefore only 48,6% of the electricity can be conventionally produced under optimum conditions with say 55% efficiency. The remainder of the produced electricity, being 100-9-48,6%= 42,4% is being generated in a non-optimal manner.

Thus, at lower efficiencies, according to the list of table 2, the overall, visible efficiency of all conventional stations together is

42,4 × (reduced efficiency) + 48,6 × 55/91%

This result is shown in the last column of table 2. A reduction of overall efficiency say from 55 to 50% does not appear dramatic. But it does mean that the total wind turbine and auxiliary investment is useless in the sense that no emission reduction or fossil fuel saving has been achieved. The fact, that the investment in the hardware has meant a significant amount of extra fossil energy that will never be recuperated, aggravates the situation.

One can question whether a reduction in conventional generating efficiency by wind turbine involvement has been noticed at all, because this reduction is spread out in a random manner over the many providers and types of power stations.

We like to stress again that our estimate is only concerned with the operational phase of wind turbines. Extra energy and labour costs resulting from the need to have 90 to 100% back up and the energy and expense required for bringing wind electricity to and on the high tension network have not been considered.

The back up issue will with high certainty remain below the radar in the Netherlands for as long as the amount of wind power is modest. It certainly has not yet been noticed by the environmental movement nor the Dutch environmental minister Jacqueline Cramer or minister of Economic affairs Maria Van Der Hoeven.

Finally

We disregarded the economic aspects of wind turbine generated electricity. However, if it turns out that large-scale use of wind turbines only adds fossil fuel use and CO₂ emission, every Euro spent goes to waste. If however the back up efficiency is such that some fuel and CO₂ emission is avoided, then a hard economic assessment is called for. We therefore refer to a very recent study” Economic impacts from the promotion of renewable energies⁸”. This study concludes that from an economic point of view the use of wind and solar energy production is an enormous waste of resources.

Conclusions:

1. It is necessary to establish on the basis of data, rather than model predictions, the level of extra fuel use caused by decreased efficiency of fossil back-up for wind power, before countries translate large investment plans in wind energy into reality.
2. Wind energy easily costs more than it yields, not only in monetary terms, but also in non-sustainable energy use and thus it will easily increase rather than decrease CO₂ emission.
3. Electricity companies must urgently provide the real data on extra fuel required to back up for wind.

References & notes.

1. B.C. Ummels: Power System Operation with Large-Scale Wind Power…, Diss. TU Delft, februari 2009.
2. G. Dijkema, Z. Lukszo, A. Verkooijen, L. de Vries & M. Weijnen: De regelbaarheid van elektriciteitscentrales. Een quickscan in opdracht van het Ministerie van Economische Zaken, TU Delft, 20 april 2009.
3. Windenergy Report Germany 2008, ISET , Univ Kassel, Deutschland.
4. We use ‘duty factor’ in stead of ‘efficiency of wind turbines’, because we focuss in this paper on the efficiency of the spinning and standing back up reserve of conventional power generation.
5. Brits Hogerhuis, Select Committee on Economic Affairs, Report ‘The Economics of Renewable Energy, 2007-08’: “…The wider the area of interconnectedness, the more likely it is that variations in wind patterns will cancel out, although the weather may sometimes be similar over even a wider area. For example, we received some evidence that low wind speeds in the UK could coincide with similar conditions in Germany, Ireland and even as far away as Spain.”
6. H. Alt: Hardhoehengespraeche Siegsburg 30 sep 2009
7. Even that is not completely correct. Part of the wind produced electricity is surplus to demand. Professor Alt describes what happens in Germany. The surplus wind electricity is exported for free and high fines are levied. The bill goes to the tax payer.
8. M. Frondel, N. Ritter & C. Vance: Economic impacts from the promotion of renewable energies: The German experience; Rheinisch-Westfälisches Inst. f. Wissenschaftsforschung, October 2009. http://www.instituteforenergyresearch.org/germany/Germany_Study_-_FINAL.pdf

K. de Groot & C. le Pair
(Formerly of Shell & STW, The Netherlands)
kenjdegroot@mac.com
clepair@casema.nl



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Date added:  October 22, 2008
Health, Netherlands, Noise •

Response to wind turbine noise in the Netherlands

Source:  Pedersen, Eja; Bouma, Jelte; Bakker, Roel; van den Berg, Frits

Abstract: A cross-sectional study with the objective to explore the impact of wind turbine noise on people living in the vicinity of wind farms was carried out in the Netherlands in 2007. A postal questionnaire assessing response to environmental exposures in the living area, including wind turbine noise, was answered by 725 respondents (response rate: 37%). Immission levels of wind turbine noise outside the dwelling of each respondent were calculated in accordance with ISO-9613. The risk for being annoyed by wind turbine noise outdoors increased with increasing sound levels (rs = 0.501, n = 708, p<0.001). The risk for annoyance was decreased for respondents who could not see wind turbines from their dwelling and for respondents who benefited economically from the turbines. No statistically significant correlations between immission levels of wind turbine noise and health or well-being were found. However, noise annoyance due to wind turbine noise was associated with stress symptoms, psychological distress and lowered sleep quality.

Halmstad University/School of Business and Engineering (SET)

Proceedings of the 7th European conference on noise control, EURONOISE, June 29th — July 4th, 2008, Paris, France



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