Two-loop windmill for stable energy supply

Project substantiation

p. 5

Noting all aforesaid, for today the wind energy engineering has the following tasks:

– it needs the schemes how to create powerful windmills, not summing little power units – they lessen reliability – but creating powerful unitary windmills;

– we have to break the vicious circle of connection between the size of rotor mills and flowed-about area;

– we have to combine windmills with reliable sources of energy providing uninterrupted generation of energy. The doubling sources have to be reliable, to have not high price and to avoid hydrocarbon fuel;

– windmills have to be mounted in windy places, same as hydroelectric power stations are established not near consumers but at the water resources. This does not mean that we have to stop production and exploitation of low- and medium-power windmills at the places of consumers. The point is of ability to effectively use wind energy engineering and its ability to provide main consumption at the level of trivial sources – hydro-, thermo- and atomic stations. Only having ensured this level of energy production, we can speak of effective use of wind energy.

As the above analysis showed, to solve the mentioned problems, we have to abandon propeller-like constructions which cause unresolvable difficulties: larger power – larger mass and size of rotating parts. Experts just come up to this conclusion: “There lessens the interest to traditional propeller-like (axial) wind rotors rotating around the horizontal axis. The practical efficiency of these mills is well less than that determined in the wind tunnel; the wind direction often changes so fast that the very perfect (which means, of high cost) system of rotor turn has a delay, due to which the vane loss arises. Another thing are windmills whose orthogonal rotors rotate around the vertical axis. The main property of these mills is independence of wind direction. The vane losses are absent at all” [22]. “The wind rotors in a free flow are good for little electric power stations. The more power the more rotor, which means growing inertial forces, so it needs more massive construction. Sluggishness, which means losses of all kinds, grows faster than productivity (and this was proven by the experience of megawatt windmills in Denmark and Canada)” [22].

“So many inventors prefer constructions with the wind flow concentrators and little fast turbo-generators with high engineering and economic characteristics. Such is “The windmill”, patent number 2074980 (B.P., D.B. and G.Ya. Khozyainov). The dampers 1 installed on stationary reinforcing cage (Fig. 18) turn about in the hinges 2 between the slops 3 by the wind flow. They direct the air flow from any side to the blades of Francis turbine 4. Unavoidable head losses in the directing system are possibly compensated by high efficiency and low cost of miniature fast turbo-generator” [22].

The construction shown in Fig. 18 really breaks the vicious circle between the flowed-about area and size of windmill rotor. The constructional stability under the wind is sufficiently higher, as with the growing flowed-about area, in this construction the area of base grows, while in propeller windmills the power grows with the consol length and it makes the windmill unstable to the wind. One more merit of this construction is that the concentrators allow change of fan regime into that head and to avoid the problem of wind flow scattered in the area. Such construction also makes possible to build a multi-storey construction terminated to one generator. It sufficiently increases the compactness of construction and the output per unit of earth surface area, and the main, it offers, remaining rigid construction, to build powerful unitary windmills comparative in power with hydro electric power stations. And head-proof stability of the construction offers using the wind energy for the utmost, without limitation at some permissible speed – true, for it we have to break one more vicious relation between produced and supplied energy.

The only demerit of this construction is the presence of moving guide vanes. They disable the flow concentration necessary for powerful windmills. The mass of vanes will grow with growing power, and this will cause the vanes lagging; hence, the windmill will follow the wind direction much worse. This will cause the necessity in servo-mechanisms and automatic actuation; it will complicate the construction and control and raise the cost of service.

While there is no necessity in vanes, if we configure the guide so that it concentrated the wind flow at the centre of operation part of blade, see Fig. 19. If the number of blades is about 1,5 times less than the number of guides, the wind flow will concentrate at the central parts of blades, while the back parts of blades will work as additional concentrators.

Fig. 19

When large difference of input and output cross-section, the fixed guides have one more important property: from the view of gas flows this kind of guides can be thought as a simple nozzle. In the nozzles, with growing ratio of input/output pressure, the gas flow rate first grows, but at the level of critical input/output ratio (which is less than one in simple constrictive nozzles for subsonic flows), “the inside-nozzle flow stops changing. The flow rate also remains constant and equal to that critical… The flow regime in a simple nozzle cannot be changed by the change of counter-pressure after achieving the sound speed at the nozzle exit section, and it has a simple physical explanation. Perturbations and, hence, small changes of counter-pressure propagate through the particles of medium with the sound speed. But the particles at the nozzle exit cross-section have the sound speed, and perturbations cannot permeate into the nozzle, they are carried by the flow. The particles that are inside the nozzle don’t ‘know’, after they achieved the critical regime of flow, what occurs out of nozzle” [23, p. 51]. Thus, the guides are some kind of flow regulators and cut off the excessive flows, as if blocking the air within the guiding tube. This cutting off limits the utmost power achievable from one unit of the construction, as well as the utmost possible ratio between the input and output cross-section of concentrator. We can evaluate it, noting that the rate of flow will stabilise when the output air achieves the sound speed, 332 m/s. At the utmost admissible input speed – 20 m/s – the maximal ratio of cross-sections will be 332/20 = 16,6. At constant height of block, we can easily recalculate it into the ratio of diameters of the whole windmill to that of rotor. We should underline, this is a very rough evaluation, only the idea of order of numbers, and it shows at least 16-fold advantage comparing to the fan-like windmills. To damp noise and vibrations arising in the domain of subsonic speed of flow, we can lag the guides with sound-absorbing material. This lag will partly damp the wind speed of course but the sound as well, and will effectively block the wind flow at critical speed.

This effective solution is unable, however, to solve the second problem of windmills – calms. “Even best efficiency cannot remove the idle time when calm” [22]. The only way out is an additional source. If we reject known solutions like storage batteries or diesel-generators, there remains only one way – to seek this source in the excessive energy of wind. As we saw in the analysis, the efficiency of use of windmill energy falls off, beginning with the moment when the efficiency achieves its nominal power. It is caused by immediate relation between the energy production and consumption. Although in some projects – for example, in designs shown in Fig. 11 and 12 – the windmills worked, charging the batteries, the energy stored in them was consumed as needed. In other words, if production is separated from consumption and the windmill works exceptionally for production and reproduction of electric resource, then, on one hand, we will achieve utmost utilisation of wind energy, and on the other, the energy production will not depend on momentary consumption but can be spent as necessary, not as the wind offers. In this way we can reliably provide uninterrupted supply and to solve the problem of inconstant wind flow.

In this relation, it would be interesting to analyse one more invention which gives us the idea of good energy storage, though from the very other side. We are speaking of “patent 2062353 (G.I. Efimov, Sh.R. Abdurashitov). Through the accelerating air intakes 1 and pit 2, the wind comes to the blades of oppositely rotating wheels 3 and 4 kinematically connected to the armature and yoke of electric generator 5 (see Fig. 20). When the wind is quite strong, in the reservoir 6 the utilised, for example, biological gas is accumulated. If the wind power is insufficient, this gas is conveyed through the injector 7 and damper 8 and burned in the chamber of intakes 1, due to which a usual draught arises; the wind wheels and generators convert it into the commercial energy” [22].

Fig. 20

In this invention, the authors premise that the energy is generated in combination of two parallel processes: some device produces biogas and the windmill produces electricity. When calm, the auxiliary source compensates the absence of wind energy. How much attractive is this construction for uninterrupted supply, all the above demerits are inherent in it. First of all, to produce biogas, we have to permanently supply biological material, which is not always possible and convenient, the more if speaking of powerful stations. But even if it is possible, efficiency of gas energy utilisation in the double wheels construction will be well less than the utilisation degree of the same fuel in multistage turbines of thermal electric power stations; so it seems inefficient to combine windmills with biogas burning in the windmill.

At the same time, if speaking of gas fuel utilisation, the windmill can not consume fuel to support working but produce it as a cheap and environmentally harmless natural storage battery. Electricity produced by the turbine can be effectively used to produce, for example, hydrogen – perfect environmentally harmless fuel. In Fig. 21 we see two-circuit construction of such windmill complex.

Fig. 21

As we can see from the scheme, the electric generator works out direct current which feeds the gas-generator station producing hydrogen. The windmill works in the optimal regime of load, fully utilising the wind energy; if we mount such complexes, say, near Novorossiysk, it can protect the town from the destroying power of bora. The thermoelectric station is separated from the inconstant wind load, and it is not subject to calms. It works on time-stable source and provides all required parameters of voltage, irrespectively of wind energy variation and consumption peaks. The only requirement is, the average productivities of thermoelectric station and windmill have to be equal. Or rather the peak power of thermal station can be more but the average productivity has to be matched with the windmill. Otherwise we have to provide transportation of excessive hydrogen to the consumer either to blow it off. This last would be undesirable as worsening the economical characteristics of the station. And if the power of thermal station is more than that of windmills, the thermal station will stop working from time to time, which is also undesirable, though the mount of additional windmills can solve the problem by growing amount of hydrogen in the storage.

The possibility to connect the thermal station with several windmills is an additional advantage, we will need only to match powers of sources and consumers but will not need, as conventionally, to match parameters of generated current. Such autonomy well simplifies windmill control. The unitary source working for consumers is the thermoelectric station; with the stored energy of hydrogen it provides stable match, irrespectively of different working conditions of windmills. Such connection remains windmills autonomous and they can be connected to one or several gas-generator stations, and if connected to a common gas-generator station, can merge with other sources in the output of production cycle, but remain independent cycles of hydrogen production having only a common collector of hydrogen fuel. Such independence provides maximal efficiency without losses that would be unavoidable if matching of electric parameters of windmill nets.

One more issue for effective exploitation of such complex is to place them in windy regions. As this complex can provide considerable power comparable with powers of today thermal and even hydro stations, we need not place it near the consumer. It will be even better to place it in thinly populated places useless for other human activity – for example, in a mountain locality where wind load is much higher. The windmills can be placed on the ridges, other parts of a complex – in the valleys near the water sources, as shown in Fig. 22.

Fig. 22

1 is the windmill, 2 is the compressor station and storage of hydrogen fuel, 3 is the water intake station, 4 is the gas-generator station, 5 is the thermal electric station

In Fig. 22 we see several windmills with concentrators gathered into a multistage tower in a thinly populated windy region, on the ridge. Such compact construction that effectively uses wind flow can dissociate the water of natural source (in this case the water of a lake) immediately at the place, using the produced direct current. This lifts the problem of area necessary to produce energy that bothered British colleagues [21]. With correct calculation of produced voltage, the windmill can be some separated from the rest of complex. Direct voltage is transmitted to the valley by wires. From the gas-generator station, hydrogen is carried through the compressor to the reservoir from which it is taken to burn at the thermal station, producing the alternating current. This gives really, not virtually uninterrupted energy supply without any storage batteries and costly diesel-generators.

Broadening the scope of this construction, we can add, not only lakes and rivers can be thought as the water source but glaciers also – true, with some lower efficiency because of loss to melt ice. It will not reflect on productivity but only will require to mount additional windmills which will compensate the additional energy expenses.

The hydrogen fuel is ecologically harmless and chemically low-active, as opposite to, for example, hydrocarbons; this is of high importance because of seismic activity in the mountain regions. Due to this property, it is not risky to store hydrogen in hermetic reservoirs. Hydrogen thermal electro station will not disturb the environment. The water produced in burning can be returned to the natural hydrological cycle, doing not exhausting the local supply. And we can effectively produce cheap hydrogen fuel for cars and airplanes.

The only demerit of this scheme seems to be that to produce the final product, we propose double-circuit transformation of energy, which lessens the efficiency. It will not affect the energy cost, as additional expenses to mount windmills and gas-generator complex have to be compared with expenses to supply hydrocarbon fuel to the today thermal stations. Noting the level of contemporary fuel cells using hydrogen, expenses to produce hydrogen fuel are lower in time than growing expenses for hydrocarbon fuel, including exploration, mining, transport, processing, burial of waste, restoration of environment. While hydrogen fuel is produced at the place and utilised without waste and any harm for environment. As we showed in the analysis of Table 1, even on existing constructions of windmills, financial economy on fuel is about a half of cost of energy produced by windmills. This makes windmills efficient and realisable. In this version, windmill energy engineering is competition-able in effectiveness with traditional energy sources and is superior to them all in the least harm to environment.

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