Assuming a scenario where large-scale penetration of electricity generation from wind and other intermittent renewable energy resources is achieved, it is of fundamental importance that the electricity system into which these new power generators are being integrated is able to compensate for the variability of production.

Hydropower and solar power can be used to boost production capacity – Portuguese hydropower capacity is large and significant photovoltaic development is planned – but energy storage, demand side management (DSM) and demand side-response (DR) could also play a major role in optimizing capacity for wind power production. As wind energy is stochastic in nature and essentially ruled by random meteorological changes, its ability to reach peak load requirements is the biggest problem for producers of wind energy. Therefore, wind energy should be considered an energy resource but not a peak capacity resource, as only a small fraction of wind capacity has a high probability of running consistently. Wind is, and should be, used when available and if capacity exceeds demand then this should be viewed as a bonus.

Wind intermittence can also affect the economic viability of projects, as it leads to lower value energy. Most wind generation occurs in hours when energy use is low, making it less valuable. Studies have shown that as wind penetration increases, three factors lower the economic value of wind power:

• increasing wind generation usually displaces capacity from increasingly lower cost plants
• operational losses due to repeated plant starts or partial plant loading
• unnecessary wind energy, which cannot be absorbed, due to operational constraints or excess production

Managing Intermittency

Intermittency is a long standing and recognized problem for many forms of renewable energy. Efforts to overcome the effects of variability and randomness of wind power availability has been traditionally addressed by the promotion of wind power resource studies in the industry, and the identification of solutions based on reversible hydroelectric dams, or pumped storage.

The intermittency of wind energy can also be reduced by some other estalished techniques:

• improved forecasting techniques
• grid integration
• technical distribution of the generators
• geographic distribution of the generators

The last three of these techniques can be grouped as aggregation and distribution methods. These techniques aim to increase the predictability of the production of wind power and therefore achieve a substantial reduction in system variations.

However, although those improvements bring benefits, as Table 1 (below) shows, periods of low wind production and substantial variations will remain. Thus tools to respond to short-to medium-term and long-term variability of power production are necessary in order to manage the operational and capacity reserve. For large-scale integration of wind power the provision of flexible capacity reserve is of crucial importance. To achieve this aim several options are available [as follow].

Wind Power Forecasting

In addition to being variable, it is also challenging to accurately predict wind power production within the time scales which are necessary for long-term planning. It is easy enough to predict energy production from a large wind generation facility over a long period of time – even over the life time of the plant – but over shorter time periods, production is less easy to predict. Large divergences can occur in the timing of and the wind’s amplitude.

Aggregation and Distribution

Generally, the more wind turbines which are operating in a given period, the lower the production variability is. Similarly, the more turbines which are installed across a geographical area, the more predictable production becomes, as shown in Table 2 (below).

The number of hours with zero output will also decrease when using turbines based over a large area. A smoothing effect in the system wind power production can be achieved over large areas, as the correlation between the number of wind generators and the energy produced will be lower.

Interconnection With Other Grid Systems

This will enable the export of energy in times of wind power production in excess of demand; and imports when production is reduced.

Power Plants Providing Reserve

The use of alternative power plants to provide operational capacity and reserve is the most traditional method of integration of intermittent power. Plants which can provide such system must be flexible and have short response times, in order to make up the lost capacity from wind production quickly. Hydropower is the technology which presents the most advantages. Fossil-fuel supported power plants, can be also be used. However, the biggest disadvantage associated with this method is that it is not cost effective to run extra capacity which will only operate when wind capacity is suddenly reduced. Also, the greenhouse gas emissions released by this kind of installation negates the positive benefits of using renewable wind energy.

Curtailment of Intermittent Technology

To ensure system stability and control, a minimum level of conventional generation must be maintained, even in periods of low demand. Other situations which can limit wind power may occur when the transmission and distribution capacity is congested near the wind farm. In such situations the curtailment of wind power generation can be used to reduce the overall system integration costs.

The curtailment is made by constraining the output of a group of wind generators, shutting down some or all the turbines. This will result in a loss of energy production and in economic losses. The costs also include the time taken for the wind farm to become fully operational following grid curtailment.

Distributed Generation

The use of other types of distributed generation can provide several benefits in the network, such as: alleviating congestion, reducing transmission losses and providing ancillary services. Distributed generation can also help in wind power integration, providing reserve capacity as a substitute for conventional power plants. However, wind power is normally a form of distributed generation and has the same requirements for grid connection. Several other types of distributed generation technology can also have intermittency problems, like solar power for example.

Synergy Between Renewable Sources

Hydropower and solar power are also intermittent resources, due to their dependence meteorological conditions. However, the variables affecting these three different forms of renewable resource are independent of each other and do not necessarily occur at the same time. They can therefore be partially mutually compensated.

Analyzing 50 years of data on wind velocity in Portugal shows high variation relative to the average year, with a consequent impact on the yearly variation curve.

The wind velocity and the water inflow have average variations through the year which follow a similar pattern and their two curves have a high correlation (0.98). The solar radiation varies almost inversely, relatively to the wind velocity and the water flow (correlations of −0.7 and −0.66, respectively). That observation indicates that the complementary relationship between solar energy and wind/hydro is favourable. Solar energy can therefore be used to smooth seasonal variations of wind power. Hydropower is not complementary to wind power, but due to similar variations it is the ideal means to store excess wind energy in order to cope with the intermittence, using the storage, dispatchable power and dynamic response capacities. Also, other dispatchable energy technologies, such as biomass, can have a positive contribution, reducing the intermittent power requirements.

Demand-Side Management

Most critical situations occur in periods with high energy consumption. Thus, demand side management technologies could play a major role in avoiding critical situations due to intermittent power generation resulting from the increasing use of wind in the national generation portfolio. One of the most serious peak load problems is the need for elevated electricity production due to the increased use of air conditioning on summer days with high temperatures and reduced wind velocities. Therefore DSM technologies in space conditioning are important.

The European Union Energy Services Directive in Portugal aims to achieve a consumption reduction of 9% between 2008 and 2016. A variety of DSM technologies were considered in order to execute the plan. The aggregated impact in the load diagrams of the selected technologies in the residential (lighting, appliances and space conditioning), services (lighting, office equipment and space conditioning) and industrial (lighting, power factor, energy efficient motor systems and drives) sectors was determined. It was found that the application of DSM measures will reduce the amount of investment needed to integrate intermittent power and will lead to a large reduction in peak power demand.

Demand Side Response

DR is another technology which can play a major role in the integration of renewable intermittent power. With these technologies it is possible to direct or indirectly force a consumption reduction in critical situations, over a short period of time.

In the past, the grid has been planned and operated under the presumption that the supply system must meet all customer’s energy needs, and that it is not possible to control the demand. However, that is starting to change due to the creation of opportunities for customers to manage their energy use in response to signals, such as those coming from prices or load contracts.

If the marginal peak load price is higher than the value that a consumer gets out of the services derived from the electricity, they may be willing to modify the demand, if paid the peak price or slightly less. A grid operator can obtain a greater economic benefit by providing incentives for a customer to reduce their consumption rather than paying a power producer to supply more output. Traditionally the DR technologies were typically used to attend to economic concerns. However, they can now be used to improve the system reliability, instantaneously reducing the energy consumption to prevent the most unbalanced situations, like the problems that result from the large space conditioning consumption on days with reduced wind velocity. As more customers practice automated price-responsive demand or automatically receive and respond to directions to increase or decrease their electricity use, system loads will be able to respond to, or manage, variability from wind power production.

Energy Storage

Energy storage has crucial importance in the electricity sector, because the energy demand has relatively large hourly, daily and seasonal variations. Additionally, as energy generation from renewable energy sources also has significant variations, either in the short term (periods of a few seconds) or in the long term (hourly, daily and seasonal), storage is becoming increasingly important.

Energy storage is an appropriated option for allowing the large-scale integration of intermittent renewable sources. Energy storage in electric energy generation systems enables the adjustment between energy production and demand. The energy produced by intermittent renewable sources can be transferred to be released in low production or high consumption times. Storage technology has the advantage of generally not using fossil fuel generation, so storage facilities do not directly contribute to greenhouse gas production. One disadvantage of energy storage are the inherent losses due to the efficiency of energy conversion (about 75%–80% typically), as Table 3 (below) shows.

The storage devices do not need to be located in the wind farms and can be installed at any point on the grid. Several energy storage technologies can mitigate over-generation problems, absorbing the surplus energy in a few seconds. Each technology has its response rate, varying from a few seconds to some minutes, but all can quickly connect to the system and ramp up to add load to the system. Hydro storage facilities, whether in the form of pumped-hydro or hydro reservoirs, have played a key role in providing several grid balancing services. Large pumped storage hydropower plants can be switched from generation mode to pumping mode within a few minutes, storing the excess energy produced by the installed base of wind power capacity and releasing the energy for use meeting demand when wind production decreases.

This kind of storage has potential for large-scale electricity storage, fast response times and reduced operating costs.

Some storage devices can provide regulation services and frequency control. Hydropower can ensure such a requirement due to having fast ramp rates and can maintain maximum power for several hours. However, other technologies can be used, such as NaS (sodium-sulphur) batteries or flywheels. Storage systems that incorporate an inverter can also deliver reactive power, supporting voltage regulation.

Of the storage energy technologies available (as shown in Table 3 above), only hydropower has been used for many years and is well established in the market. The other storage technologies present non-competitive costs and reduced commercial availability. The major barrier for construction of new storage facilities is not the technology but the absence of market mechanisms which recognize the value of the storage facilities and financially compensate them for the services and benefits they can provide. Certain storage systems such as flywheels, flow cells and certain battery types could become viable. Another viable technology is compressed air depending on available locations, which is stored in geologic structures under the ground and released when necessary.

Integrating Wind

All of these options have the same aim: to balance supply and demand continuously. The first course of action when ensuring the effective integration of variable energy sources into an electricity grid should be various project techniques, including grid integration, technical distribution of the generators, geographic distribution of the generators and improved forecasting techniques. However, with large-scale integration of wind power, periods of large intermittence will remain. Therefore it is important to integrate other technologies alongside these project techniques. The complimentary relationship between renewable sources, demand side management and demand side response are all important, and energy storage technologies are rapidly improving, becoming more available. The diversity of these options means there is great potential for wind energy to be successfully integrated into domestic electricity grids, if proper planning is implemented.

Sidebar: Extreme Variations in Wind Power Ramp

Several extreme ramp rates have been recorded during storms:

• Denmark – 2000 MW (83% of capacity) decrease in 6 hours or 12 MW (0.5% of capacity) in a minute on 8 January, 2005.
• North Germany – over 4000 MW (58% of capacity) decrease within 10 hours, extreme negative ramp rate of 16 MW/min (0.2% of capacity) on 24 December, 2004.
• Ireland – 63 MW in 15 mins (some 12% of capacity at the time), 144 MW in 1 hour (29% of capacity) and 338 MW in 12 hours (68% of capacity).
• Portugal – 700 MW (60% of capacity) decrease in 8 hours on 1 June, 2006.
• Spain – 800 MW (7%) increase in 45 minutes (ramp rate of 1067 MW/h, 9% of capacity), and 1000 MW (9%) decrease in 1 hour and 45 minutes (ramp rate -570 MW/h, 5% of capacity). A generated wind power of between 25 MW and 8375 MW has occurred (0.2% and 72% of capacity) in a single year.
• Texas, USA – loss of 1550 MW of wind capacity at the rate of approximately 600 MW/hr over a 2.5 hour period on 24 February, 2007.

Pedro S. Moura is a researcher at the Institute for Systems and Robotics (ISR), at the University of Coimbra in Portugal. Anibal T. de Almeida is professor of Electrical Engineering and Computers, and a director of the ISR.

This article was adapted from a paper which was first presented at the Renewable Energy World Europe conference in Cologne, May 2009.

Background. Noise is a major factor in many military environments. Usually the concern is with the higher frequency bands (>500 Hz) that cause hearing damage or interfere with speech. Protection against noise is thus focused on these higher frequencies, while the bands of lower frequencies (<500 Hz) are neglected, and non-audible bands, infrasound (<20 Hz) are ignored. In reality, long-term exposure to low frequency noise (<500 Hz, including infrasound) (LFN) can be quite detrimental to one's health.

LFN-Induced Pathology. The disorders associated with occupational exposure to LFN have been described for aeronautical technicians and pilots. Diagnostic tools and methodologies for monitoring and controlling the development of LFN-induced pathology, have already been outlined. Immediate effects of LFN-exposure can include a) decreased capacity for cognitive functions, which implies a decline in performance, the consequences of which can be minor to devastating; b) sudden onset of acute respiratory problems, neurological disturbances, and mood alterations, such as, rage reactions. Cumulative effects of LFN-exposure can include triggering of early aging processes, and the development of vibroacoustic disease in susceptible (70%) individuals. Early compulsory retirement is a frequent situation.

Costs. Almost all military equipment require training programs for the operator. Long-term exposure to LFN can severely decrease the cost-return ratio for these operators, i.e., investment in training programs has little or no return. Accident/incidents can also damage the equipment itself, potentially jeopardizing missions. Waste of ammunition and other resources is another consequence of unmonitored LFN-exposed operators. The cost of ignoring LFN as an agent of disease is ultimately more expensive than the prevention, protection and, above all, selection of personnel for noise-environment positions.

Col. Nuno A.A. Castelo Branco, MD (PoAF, res.)
Center for Human Performance
Alverca, Portugal

Download original document: “Low Frequency Noise: A Major Risk Factor in Military Operations”

Introduction. This team has been systematically studying the effects of infrasound and low frequency noise (ILFN, <500 Hz) in both human and animal models since 1980. Recently, yet another source of ILFN has appeared: wind turbines (WT). Like many other ILFN-generating devices, WT can greatly benefit humankind if, and only if, responsible and intelligent measures are taken for their implementation. Vibroacoustic disease (VAD) is the pathology that is acquired with repeated exposures to ILFN environments (occupational, residential or recreational). This can be considered a scientific fact because there are 27 years of valid and robust scientific data supporting this assertion.

Goal. To evaluate if ILFN levels obtained in a home near WT are conducive to VAD.

Methodology. Case 1: documented in 2004, in-home ILFN levels generated by a port grain terminal, 2 adults and a 10-year-old child diagnosed with VAD. Case 2: isolated farm in agricultural area, four 2MW WT that began operation in Nov 2006, located between 300 m [984 feet] and 700 m [2297 feet] from the residential building, 3 adults and 2 children (8 and 12-years-old). ILFN levels of Case 2 were compared to those in Case 1. In both, ILFN was assessed in 1/3 octave bands, without A-weighting, (i.e. in dB Linear). In Case 1, the lower limiting frequency was 6.3 Hz, while in Case 2, it was 1 Hz.

Results. ILFN levels in the home of Case 2 were higher than those obtained in the home of Case 1.

Discussion. ILFN levels contaminating the home of Case 2 are amply sufficient to cause VAD. This family has already received standard diagnostic tests to monitor clinical evolution of VAD. Safe distances from residences have not yet been scientifically established, despite statements by other authors claiming to possess this knowledge. Acceptance, as fact, of statements or assertions not supported by any type of valid scientific data, defeats all principles on which true scientific endeavor is founded. Thus, widespread statements claiming no harm is caused by in-home ILFN produced by WT are fallacies that cannot, in good conscience, continue to be perpetuated. In-home ILFN generated by WT can lead to severe health problems, specifically, VAD. Therefore, real and efficient zoning for WT must be scientifically determined, and quickly adopted, in order to competently and responsibly protect Public Health.

Professor Mariana Alves-Pereira
ERISA-Lusofona University, Lisbon, Portugal

Nuno A. A. Castelo Branco, M.D.
Center for Human Performance, Alverca, Portugal

vibroacoustic.disease@gmail.com

Abstract: Legislation regarding low frequency noise (LFN, <500 Hz including infrasound), when existent, is highly deficient. Not only is it expressed in dBA, actually defeating the purpose of evaluating LFN, but no concrete measures are prescribed if excessive LFN is identified. The status quo notion that acoustical phenomena are only harmful when perceived by humans cannot be sustained given current scientific facts. The purpose of this report is to demonstrate just how inadequate legislation is regarding LFN control, and how ubiquitous LFN is in locations common to the general public. Methods. Noise assessments were conducted in homes, clubs, public transportation and common automobiles, in 1/3 octave bands and with a lower limiting frequency of 6.3 Hz, measured in dBLin. Overall average noise levels are reported in both dBA and dBLin. Results. Comparative frequency analysis among acoustic environments that possess the same dBA levels show that it is not scientifically valid to presume the existence of comparable acoustic environments merely based on a dBA level, i.e., equal dBA levels does not mean equal acoustic environments. Neither the dBA nor the dBLin parameter adequately reflect the presence of LFN components. Discussion. LFN is ubiquitous in modern society, and yet it is not adequately legislated. Noise-related studies do not take LFN in account and thus yield results that are deemed controversial, contradictory, and inconclusive. No effort is made to control LFN in the homes, nor in other locations of common use to the general public. The implications of ignoring LFN as an agent of disease for the public health is detrimental to us all as a human society, and a nightmare for future generations.

Download original document: “Low frequency noise legislation”

Abstract: Noise exposure is known to cause hearing loss and a variety of disturbances, such as annoyance, hypertension and loss of sleep. It is generally accepted that these situations are caused by the acoustical events processed by the auditory system. However, there are acoustical events that are not necessarily processed by the auditory system, but that nevertheless cause harm. Infrasound and low frequency noise (ILFN, <500Hz) are acoustical phenomena that can impact the human body causing irreversible organic damage to the organism, but that do not cause classical hearing impairment. Acoustical environments are normally composed of all types of acoustical events: those that are processed by the auditory system, and those that are not. It is generally assumed that acoustical phenomena not captured by the human auditory system are not harmful. This is reflected by current noise assessment procedures that merely require the quantification of the acoustical phenomena that are audible to human hearing (hence the dBA unit). Thus, studies investigating the effects of noise exposure on public health that do not take into account the entire spectrum of acoustical energy are misleading and may, in fact, be scientifically unsound. Two cases of in-home ILFN are described [one of them near 4 wind turbines].

Download original document: “Public health and noise exposure”

Professor Mariana Alves-Pereira, School of Health Sciences (ERISA), Lusofona University, Portugal, and Department of Environmental Sciences & Engineering, New University of Lisbon, Portugal

Nuno Castelo Branco, MD, Surgical Pathologist, President, Scientific Board, Center for Human Performance (CPH)

Excessive exposure to infrasound and low frequency noise (ILFN, defined as all acoustical phenomena occurring at or below the frequency bands of 500 Hz) can cause vibro-acoustic disease (VAD). [1]

Research into VAD has been ongoing since 1980, conducted by a multidisciplinary team of scientists led by pathologist Nuno Castelo Branco, MD.

In March 2007, for the first time, the Portuguese National Center for Occupational Diseases gave 100% professional disability to a 40-year-old flight attendant who had been diagnosed with VAD since 2001. Two other VAD patients also have been given a similar disability status.

Initially, only ILFN-rich occupational environments were investigated. However, over the past several years, many individuals and their families have approached our team because of the ILFN contaminant in their homes. The sources of residential ILFN vary from industrial complexes, to large volume highways, to public transportation systems, etc.

In a case study published in Proceedings of Internoise 2004 (an annual scientific meeting dedicated to all aspects of acoustics), one of the first documented cases of environmental VAD was reported in a family of four, exposed to the ILFN produced by a nearby port grain terminal. [2]

Over the past three years, several families have contacted this team complaining of noise caused by the proximity of industrial wind turbines (windmills). However, only within this past month (April 2007) has this team obtained detailed acoustical measurements within a home surrounded by four recently installed industrial windmills.

This acoustical data was essential in order to compare in-home, windmill-produced acoustical environments with the residential, ILFN-rich environments that are known to be conducive to VAD.

The levels of ILFN inside the windmill-surrounded home are larger than those obtained in the home contaminated by the port grain terminal.

The scientific report on this will be formally presented at Internoise 2007, to be held on 28-31 August in Istanbul, Turkey. [3]

These results irrefutably demonstrate that wind turbines in the proximity of residential areas produce acoustical environments that can lead to the development of VAD in nearby home-dwellers.

In order to protect Public Health, ILFN-producing devices must not be placed in locations that will contaminate residential areas with this agent of disease.

[1] Castelo Branco NAA, Alves-Pereira M. (2004) Vibroacoustic disease. Noise & Health 2004; 6(23): 3-20.
[2] Castelo Branco NAA, Araujo A., Joanaz de Melo J, Alves-Pereira M. (2004) Vibroacoustic disease in a 10-year-old male. Proc. Internoise 2004, Prague, Czech Republic, August 22-25, 2004: No. 634 (7 pages).
[3] www.internoise2007.org.tr

Download original document: “Industrial Wind Turbines, Infrasound and Vibro-­Acoustic Disease”

See these authors’ 2004 paper describing vibroacoustic disease here at National Wind Watch.