Category CONGRESS

ЕЗ/ Wind Turbine Generator Model

A full characterization test of the hybrid system’s wind generator machine has been carried out. The test was divided into two parts. In the laboratory the generator efficiency was determined for a variety of rotational speeds in the range 150[rpm] – 1100[rpm] and the characteristics of the generator efficiency n™e against the output power Pout for the whole range of rotational speeds were plotted in the form

(7)

A wind tunnel test was organized in order to simulate realistic wind

[8] Reliable hourly climatic data were not provided. For sensitivity studies, we selected U. S. SOLMET station Bakersfield, CA whose climate is closest to that of Sede Boqer.

[9] The phase of the project with the longest lead time was construction of the combiner box requiring about 10 weeks.

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THE SECOND-LAW APPROACH

Thermodynamics heavily dwells on a variety of phenomena which in­volve the generation of useful work (electricity for our purpose); in particular, "the maximum work that can be extracted from a given system in a given state by a process which brings it into equili­brium with its environment". That maximum work is termed the avall- ibitv or exerav. The lower heating value of fossil fuel comes out ti be quite close to 100% exergy (AIP, 1970; Krenz, 1984) (therefore wi use the symbol Wir» for it). We can see that the power-engineering approach closely relates to the exergy (second-law) concept. If we use a coefficient k, such that for a particular fossil-fired power plant

^OUt — kWln,

then the power-engineering and the exergy approaches become usefull correlated...

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THE POWER-ENGINEERING APPROACH

The power-plant engineer recognizes that new, modern fossil-firing power plants will have conversion efficiencies in the range of 33­40/., depending on the specified fossil fuel, size of plant and local environment. For some specific conditions, it may be 33X, i. e.,

0. 33 kWh(e) net electricity will be produced per 1 kWh(t) of fuel <Lo. ht. val. ). Therefore, in a solar hybrid plant, the solar electri­city contribution should be obtainable by substraction, as follows :

Solar electricity = W„ut! – 0.33 x Win = 36.67 x 10* kWh(e)

Hence,

Solar fraction = (Wou« – 0.33 x Wi„)/Weut = 0.569

and

Solar Efficiency = (Solar electricity)/А x I = 7.8X

With this approach the value of the obtained solar fraction repre­sents the fuel displaced and pollution obviation in a much more justifiable ma...

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THE FIRST-LAW APPROACH

With this approach one may try to define the amount of solar kilo­Watt-hours electricity contribution as follows, using the numerical values of the above example :

Solar electricity = Wou« x 0/(0 + Wirl) = 45.516 x 10b kWh(e)

The ratio 0/(0 * Wlr)) will thus represent the solar fraction, i. e., the part of the total output <W, ut) assigned to the solar source, yielding for our case :

Solar fraction = 0/(0 + Wi„) = 0.706

Finally, this will yield.

Solar Efficiency = (solar electricity)/<A x I) =9.6%

The first-law approach invokes an equal rank to a unit Joule inde­pendently whether it is heat at 200°C, 300°С or higher, or whether it is a Joule of work (or fuel), which is a pronounced weakness...

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A NUMERICAL EXAMPLE

For a conventional fossil-fired power plant, one of the major pei— formance indicators is the percentage of conversion, or fuel utili­zation efficiency, e. g., in a typical modern Rankine-cycle power plant, 37% of the heat of combustion of the fuel used (the "low heating value" — the enthalpy of combustion for gaseous product water) appears as electricity output. The customary "heat rate" is an inverse value. The net conversion value (allowing for power plant in-house energy consumption, or "parasitics") should generally be specified...

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THE SECOND-LAW AND POWER-ENGINEERING ANALYSIS OF. HYBRID (FOSSIL-ASSISTED) SOLAR-THERMAL POWER PLANTS

Aharon S. Roy

Dept, of Chemical Engineering, Ben-Gurion Univ. of the Negev, Beer-Sheva, ISRAEL

ABSTRACT

When a solar power plant is assisted by fossil fuel-firing, the question is often legitimately asked as to the actual magnitude of the contribution of the solar resource vs. that of the fossil, or as to the real savings in fossil fuel brought about by the solar part of the hybrid plant. In addition, it may be of interest to assess the fossil-saving potential of the hybrid, in face of advanced-cycle power plants based on fossil fuel alone. A closely related issue is the assessment of the overall efficiency of the solar subsystem (solar to electricity) of the hybrid...

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RECENT SOLAR THERMAL DEVELOPMENTS

Luz International Corp., developer of solar energy generating stations on the mainland, has been contracted by the state government to conduct a feasibility study for the islands. Site visits have been made and discussions held with local utilities. Luz will examine facility sizes from a 1-30 MW range, and possibly up to 200 MW capacity. Land availability (80 MW require 400 acres), utility interface, energy storage, and other factors are conditions Luz will consider in this project.

In addition, inter-island electrical connections will be addressed if the systems are proposed away from population centers. A final report is due in late 1991 (M. Sloan, personal communication, 1991).

Bechtel Corporation, in response to a USDOE initiative, is leading a group of solar Stirling dish manufacturer...

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POTENTIAL CONCENTRATING SOLAR THERMAL SITES

Solar insolation data have been recorded in Hawaii from as early as 1932, at 140 observation stations over various periods. Almost all of the data were collected by the sugar industry, which maintains a network of roughly 100 stations located on the four sugarcane-growing islands, for the evaluation of solar energy available for photosynthesis. The use of several types of instruments limits the accuracy of radiation observation to 10% (How, 1978). Because the data are used for agricultural purposes, only global insolation is collected and reported.

Scientists at the University of Hawaii have also monitored solar insolation values for a number of years...

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