Problems of wind power plants from point of view of grid RADIL LUKAS, BARTOSIK TOMAS, MASTNY PETR

Department of Electrical Power Engineering Faculty of Electrical Engineering and Communication

Brno University of Technology Technicka 2048/8, 616 00 Brno

CZECH REPUBLIC lukas.radil@phd.feec.vutbr.cz, xbarto36@stud.feec.vutbr.cz, mastny@feec.vutbr.cz

http://www.ueen.feec.vutbr.cz

Abstract: High costs of oil and fossil fuel result in the idea to start use hydrogen and other supporting means for energetic secure of every state. Wind power plants and other renewable sources are best candidates for the production of hydrogen because of their position - low cost of their operating expanses. Key-Words: Vanad redox battery, Hydrogen, Oxygen, EESTOR, Prediction, Wind power, Black out 1 Introduction The power generated by wind turbine is dependent on wind speeds, air density, humidity, etc. As the wind speed can change at any time, input power is fluctuating. Wind turbines are quite intermittent and not dispatchable. Before, wind power plants didn't have wide share of electricity production, but it has been changed recently. A large wind park over the Europe has grown in past several years, and further wind parks are still being constructed. Wind energy share has dramatically risen and dispatching problems has occurred. In November 2006 high generation at North German wind parks caused overload of transmission lines. This caused several network failures and European grid was split into three separate areas. Power imbalances in these grids finally resulted in blackout, which affected industry and over 15 million people. [1] 2 Problem Formulation To keep wind energy under control there are three following options. • transmission line development • wind power prediction • energy accumulation 2.1 Transmission line development New transmission lines are being built and existing lines are being reconstructed recently. However development of transmission line will have positive effect on whole grid system, it cannot be used just by itself. Necessity of good dispatching at low costs needs accurate wind prediction.

2.2 Wind power prediction The wind turbine power dependence on wind speed is expressed by power function (1), where ρ is wind mass density, D diameter of windmill, v wind speed, cp. is correction coefficient.

(1) Wind speed derivation of Pm function provides next equation (2).

(2) This equation expresses how much wind speed changes the output power. If the prediction model is based on meteorological speed of wind, small changes of wind speed results in higher changes of produced energy. Next figure (1) was obtained by numerical derivation of function Pm / Pmax. Where Pm is power function, Pmax is maximum value. Prediction models based on meteorological wind speed prediction could be reached satisfactory results for small applications. Although meteorological prediction of wind speed is quite accurate, small derivations of wind speed could cause relatively big derivations of turbine power. From figure (2) we can see, that difference of 1 m.s-1 could results in 18 % change of wind turbine power. That makes meteorological prediction itself unsatisfactory at large application.

Proceedings of the 3rd WSEAS Int. Conf. on RENEWABLE ENERGY SOURCES

ISSN: 1790-5095 369 ISBN: 978-960-474-093-2

Fig.1: Wind speed derivation of Pm/Pmax ratio function, function Pm is for turbine RE power MD70 [2]

Fig.2: Distribution function and frequencies of supplied power from German distribution network Vattenfall wind parks (hour averages from the year 2007)

In recent years Germany uses developed models, which synthesize meteorological prediction, numerical and stochastic methods. Though these prediction models bring satisfactory results, there are still some larger sporadic mistakes, which bring danger for grid system. 2.3 Accumulation Wind parks produce different power during the year, which is illustrated in following figure (2). Red curve expresses how frequent was supply at specific power and

black curve is its distribution function. Wind capacity factors are typically 20 to 40 %, which is quite low. Higher capacity factors are for offshore wind turbines, lower values are for onshore. Therefore power lines are not appropriate. Large grid system reserve is expensive and low reserve can result in serious failures. In both cases transmission lines operate at lower efficiency. Accumulation can reduce costs of transmission system development and also could make it more efficient.

Proceedings of the 3rd WSEAS Int. Conf. on RENEWABLE ENERGY SOURCES

ISSN: 1790-5095 370 ISBN: 978-960-474-093-2

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Proceedings of the 3rd WSEAS Int. Conf. on RENEWABLE ENERGY SOURCES

ISSN: 1790-5095 371 ISBN: 978-960-474-093-2

SCADA interface. Modbus, Profibus, Canbus or other interfaces are available for interconnection to auxiliary systems. 2.4.5. Hydrogen – Oxygen systems These systems will be used in the future. If we will connect wind power plant as source of energy to electrolytic process, producing hydrogen and oxygen will be very interesting. This system seems to have two possible applications: a) Producing hydrogen and oxygen, and their sale

(mainly for medical usage) b) Producing hydrogen and oxygen, their storage and

later usage for electricity production and its sale The backward converse on electric energy is possible with two ways: a) thought fuel cells b) in combustion turbines or using of co generation units In the second case speaks in favour the economy of construction and well-known qualities of these sources. Present-days turbines can be used with minimal changes. Modern machines have a great reliability and lifetime to general overhaul is about 20.000 hours.

Renewable sources AC/DC converter

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other chemical adducts. 2.4.6. EESTOR capacitor EEStor is a company based in Cedar Park, Texas, United States that claims to have developed a revolutionary new type of capacitor for electricity storage, which EEStor calls 'Electrical Energy Storage Units' (EESU) – see Table 1. The capacitance of the device described in the patent is 30.693 farads. To achieve such a high energy density the capacitor has a very high breakdown voltage and uses an operating voltage of 3.475 kV. In the absence of dielectric saturation the formula for stored energy of a

capacitor is Producer claims [10]: a) Nontoxic and non-hazardous b) Non-explosive c) For a 52 kWh unit, an initial production price of

$3,200, falling to $2,100 with mass production is projected. [9] This is half the price per stored watt-hour as lead-acid batteries, and potentially cheap enough to use to store grid power at off-peak times for on-peak use and to buffer the output from intermittent power sources such as wind farms.

d) No degradation from charge/discharge cycles e) 4-6 minute charge time for a 336 pound (152 kg), 2005

cubic inch (33 L), 52 kilowatt hour (187 MJ), 31 farad, 3500 volt unit, assuming sufficient cooling of the cables.

f) The unit will come equipped with a built in Buck-boost converter (DC-DC voltage converter) to provide the proper input/output voltage

g) A self-discharge rate of 0.1% per month.

Table 1 Producer claims

4 Conclusion The problem of renewable sources is unsteadiness of the supplement of electric power output. For effective incorporation of these sources into the grid is necessary to predicate wind at least 6 hours in advance. We avoid having power plant or peak gas turbine in reserve. Accumulation itself is not able to handle with all discrepancies. It serves for short term changes. Maximum accumulation time is usually about 8 hours nominal output of a source. Models, which predict winds, are today on high level and together with appropriate accumulation resources. These resources especially wind power plants and photovoltaic can be equal to classic resources of electric energy.

Prototype /Low Volume

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606 700 1513

Specific energy 273 450 682

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$61 n/a $40

Proceedings of the 3rd WSEAS Int. Conf. on RENEWABLE ENERGY SOURCES

ISSN: 1790-5095 372 ISBN: 978-960-474-093-2

Acknowledgments: This paper contains the result of research works funded from project No. MSM0021630516 of the Ministry of Education, Youth and Sports of the Czech Republic.

References: [1] ABB - The grid of the future

<http://www.abb.com/cawp/db0003db002698/55622466a2d2c488c12572c700568a95.aspx> date of citation 13.5.2009

[2] Zelezny, V. Wind power plant – more question. [online], 4 pages., <http://www.csvts.cz/cns/news/031210v.pdf>, date of citation 13.5.2009

[3] Wikipedia, <http://en.wikipedia.org/wiki/Intermittent_power_source#Wind_energy>, date of citation 13.5.2009

[4] Wikipedia, <http://en.wikipedia.org/wiki/Wind_energy>, date of citation 13.5.2009

[5] VRB Power Systems Inc., <http://www.vrbpower.com/technology/index.html>, date of citation 4.12.2008

[6] Sumitomo Electric., <http://www.electricitystorage.org/pubs/2001/IEEE_PES_Summer2001/Miyake.pdf>, date of citation 3.3.2009

[7] BELOV, A., CUPR, V., LIST, V.: Cells galvanic, accumulation, fuel and physical Publisher SNTL, Prague 1968. Pages 174 – 180. ISSN: 04-528-68

[8] BALAJKA, J.: Hydrogen and the other new carrier energy. Publisher ALFA, Bratislava 1982. Pages 38 – 40, 177-184. ISSN: 63-128-82

[9] HUSEK, J.: Pumped storage hydro plants. Publisher SNTL 1963, Prague 1963. Pages 10 – 30. ISSN: 04-243-63.

[10] Wikipedia, EEstor, <http://en.wikipedia.org/wiki/EEStor>, date of citation 24.2.2009.

[11] Internet <http://www.sei.ie/Publications/Renewables_Publications/VRB-ESS-Energy-Storage-Rpt-Final.pdf>, date of citation 2.3.2009.

[12] Internet <http://www.windpoweringamerica.gov/pdfs/workshops/2004_wind_diesel/company/vrb.pdf>, date of citation 2.3.2009

[13] Internet < www.eas.asu.edu>, date of citation 20.5.2009

Proceedings of the 3rd WSEAS Int. Conf. on RENEWABLE ENERGY SOURCES

ISSN: 1790-5095 373 ISBN: 978-960-474-093-2