Two-loop windmill for stable energy supply

Project substantiation

p. 3

As the characteristics show, vertical-axis windmills are more adjusted for low speeds of wind and better work in turbulent and inconstant in directions flows. �The horizontal-axis windmills of the Megawatt class are not very good for roofs of buildings, because of required large space and turbulence of the wind bending around the building. Small (<50 kW) turbines with vertical either horizontal axis do not give sufficient energy to think them effective. The vertical-axis enhanced turbine of 100-500 kW in power is an optimal solution for urban conditions, as limited space, wind direction and turbulence make no trouble for these all-round-directed turbines� [14]. The general appearance of the working part of Aeol turbine and its disposition on the building are shown in Fig. 9 [14], [15].

a

b

Despite �in 1988, in the joint project of industry, government and municipal powers, the Hydro-Quebec company in Canada has developed, produced and evaluated the Aeol � 4-Megawatt vertical-axis windmill of the class of Darrieus. Aeol was (and remains) a record-holder in size, working life, reliability among the horizontal- and vertical-axis turbines. During their being in charge, three experts of company Dermond have provided several operational improvements that succeeded to make much better the values of turbine Darrieus, with lessening of capital and exploitational expenses. These improvements (forty of which have been patented) along with multidirected ability to cope with turbulence of wind, made the windmill Dermond a perfectly adjusted to be mounted on the roofs of buildings� [14], � the existing types of windmills are unable solving the main problem of wind-power engineering � variability of wind load. �The wind has two essential demerits: its energy is much scattered in space and we are unable forecasting it � it often changes direction, disappears even in the most windy places of Earth, and sometimes it develops such power that simply destroys the windmills� [1], see Fig. 10..

By the way, the risk that the windmill will be fallen down because of long consoles is considerable and it grows with growing power of mills. Just so the windmills NEG Micon block blades, according to the Table 2, at the wind speed more than 25 m/s. This causes the necessity to additionally strengthen the base of mill, which raises the price of construction and, hence, lessens the economical indexes of windmill.

The first two factors � scattered and non-forecasted wind energy � are the most difficult problems of wind energetics.

As we could see when analysing the Aerolla windmill, more than 62 % of time it works under its optimal load and about 41 % of working time the speed of wind is less than 3 m/s, i.e. lower of the initial working level. Such long pauses in working have an influence of course on the stability of produced energy. The more that windmills can generate energy only when the wind flow is present, which far from always coincides with the peaks of consumption. So practically all contemporary models, from low-power to powerful, are furnished by doubling power supply and energy transformation. As an example, see in Fig. 11 a simple diagram of combined power supply of consumer used in the mills on antenna supports [2].

In the diagram we see several little-power generators connected in parallel to the battery to charge it. The authors of Aeol use similar but more complicated design circuit, only as the storage they take lithium and lithium-vanadium batteries (see Fig.12 [14]).

This design circuit shows, how complicated is the storage-wind mill.

First of all, storage batteries cost much, the more if the power of mill is several dozens kilowatt and consumed energy is same..

Second, the number of charge/discharge cycles for accumulators is not big: the authors of project evaluate it as about one thousand of cycles [14]. Though the authors believe this number sufficient for 10-15 working years, if the battery charges/discharges at least 3-4 times daily, it will work 5 years for utmost. And �storage batteries need utilisation, they are not harmless� [15].

Third, we see in the diagram that windmill produces direct voltage which is converted into that alternating before consumption. On one hand, this is a necessary condition for stable energy supply, but on the other, this causes additional financial and energetic expenses for power converting equipment, the more that integrator has to cope with many functions of service and control: �This �intrinsic� integrator of the system has been developed for following functions necessary, the systems of renewable energy to have competitive price on the energetic market (see Fig. 12). It

- automatically chooses and distributes consumer less-expensive power;

- controls multiple digital input signals from different DWTs and storage battery and/or other sources, to the individual analogue connection for distribution;

- controls the quality of supplied energy, at the point of analogue connection;

- controls the energy production from individual energy sources through the remote and/or wire coupling;

- signals to controllers of individual turbine for power mill either codes of maximal power of each DWT it to meet the requirements of consumer;

- establishes and controls a safe storage of available energy to support stable energy supply when abrupt changes of the load;

- at the same time it is the point for data input/output to the central desk� [14]. It is also seen from this list that when large number of small windmills, there arises a great difficulty how to match their phases of which we will speak further. The more if the matter is of some giant system with the total power 75 Megawatt: �The windmill for 75 MW (50 turbines per 1,5 MW from General Electric for $100 million) will be built in Leningrad district� [15].

As the last drop, inconstant wind load and misfit of load peak and of maximums of wind energy cause the fact that �if we connect the storage battery to the windmill, it can exhaust before the end of calm� [1]. Just so the company that developed the Aeol windmill warrants not the uninterrupted energy supply but virtually continuous secure with minimal inconvenience in case of discharge of doubling storage batteries: the consumer �sees immediate profit at the very first day as the WindStor is switched on, and enjoys being protected against the growing prices and increased scope with the help of quasi-uninterrupted energy supply for all devices as a bonus� [14]. At the same time the company warrants that �If the WindStor is produced, as expected, with the perfectly configured battery, the consumers will enjoy of correct switching off of all their devices, lest people were blocked on the upper storeys and in lifts in the office buildings while long-term disconnection� [14].

With regard to above demerits, besides the considered project Aeol, the storage batteries are mainly used for small power stations, though we all understand now that the doubling energy source is necessary..