Comparativ study regarding the energy of turbines with vertical and horizontal axis.

Dubau, Calin

1. INTRODUCTION

The comparative analysis has focused on the energy evaluations of each separate assembly. Based on these, the functional performances of the two turbines have been established. The adimentional curves have been constructed CP = f([lambda]), where these curves of reference present the association of the characteristic number [lambda] with the maximum power value CP (Bej, 2003).

For estimations of the energy production, we have analysed the energy curves of the turbines with vertical (Gyulai, 2000 a) and horizontal (Dubau, 2007) axis previously presented.

2. MATERIAL AND METHOD

There is made a comparative analysis based on the results yielded by the calculations. There will be compared: the vertical turbine V2500 (Gyulai et al., 2000) and the horizontal turbine H2500:

a) Adimentional curves:

--V2500 - CPmax = 0,45, [lambda] = 3;

--H2500 - CPmax = 0,87, [lambda] = 3;

b) Exploitation curves:

--V2500 - Parb = f (v); n = f (v);

--H2500 - Parb = f(v); n = f(v);

c) Energy curves:

--V2500 - ET = f (v); EE = f (vmed);

--H2500 - ET = f (v); EE = f (vmed)

a) The adimentional curves (of the two types of turbines) (see Fig.1.) allow the construction of the exploitation curves defined through the area exposed to the air blown by the rotor of the turbine (S) and the mode of operation (n) see (Gyulai, 2000 b; Gyulai & Bej, 2000). The characteristic number [lambda] is the same for both turbines (vertical and horizontal). The association of the characteristic number [lambda] with the maximum power value CP allows a maximization of the energy produced by the turbine, when this functions under optimum conditions CPmax and [[lambda].sub.0].

b) The exploitation curves (see Fig.2.) serve the evaluations of the annual energies, which are correlated with the areas exposed to the wind and the rotations of the turbine. We can notice from the figure that the horizontal turbine in comparison with the vertical one, accomplishes power Parb = 3500 at speed v =10 m/s, which is a smaller value than that of the vertical turbine, where v = 12 m/s.

Next, we present the dependence of the revolution according to wind speed, n = f (v), for the analysed turbines (vertical and horizontal), (see Fig.3.). It can be noticed from the representations that the horizontal turbine is more efficient than the vertical one because at smaller revolutions it reaches the values of the indices defined in the calculation for the obtaining of the axis energy.

c) Comparison of energy curves. The synthesis of the energy balance for the two turbines (at a location with an average speed of 4 ... 7 m/s) is presented in the following tables (Tab. 1. and Tab. 2.):

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

There is represented superimposed, in detail, the Parb=f(v) correlation graphic for five revolutions values of the two previously analyzed turbines (see Fig.4.). It is shown also in this graphic the fact that the horizontal turbine, vs. the vertical one, achieves for each revolution higher values of the power at the axis, in smaller wind speeds.

[FIGURE 4 OMITTED]

There is presented next the comparison between the energy curves of the two turbines which are graphically represented for the energy at the shaft of the turbine (see Fig.5.) and the electrical energy produced by the two turbines (see Fig.6.), depending on the wind speed.

[FIGURE 5 OMITTED]

[FIGURE 6 OMITTED]

3. CONCLUSIONS

A first conclusion is that from the dependence Parb = f(v), determined on a large interval of wind speeds, the horizontal turbine is more efficient in the process of exploitation than the vertical one, being able to reach the required powers at lower wind speed.

It can be seen that the assembly with horizontal axis yields an annual energy production, at a location which allows a medium speed of 4...7m/s and favourable variability, bigger than the assembly with vertical axis, which, under the same conditions of medium speed, yields a smaller annual energy production (EE=f(vmed)).

The horizontal turbine is yet again the most representative from both points of view: the production of more axis energy, as well as the production of more electric power in an energetically system (ET=f (v)).

Thus, we have accomplished the review of some objective criteria of comparison, based on scientifically, technical and economical analysis, which have been subordinated to the general aim of increasing the efficiency of low power wind assemblies.

4. REFERENCES

Bej, A. (2003). Wind Turbines, Timisoara Polytechnic Press, ISBN 973-625-098-9, Timisoara, Romania

Dubau, C. (2007). The Utilization of Micro-Wind Assemblies within Complex Systems, Timisoara Polytechnic Press, ISBN 978-973-625-408-6, Timisoara

Gyulai, F. (2000a). Contributions on horizontal axis wind turbine theory, Proceedings of the 5th International Conference on Hydraulic Machinery and Hydrodynamic, Oct. 2000, Timisoara, Romania

Gyulai, F. (2000b). Vocational Training in Sustainable Energy --Course Wind Systems

Gyulai, F. & Bej, A. (2000). State of Wind Turbines in the End of 20th Century and Proposals for Romanian Options, Buletinul Stiinfific al Universitapii "Politehnica" Timisoara, Romania, Tom 45(59), ISSN 1224-6077

Gyulai, F.; Bej, A. & Hentea, T. (2000). Contribution to aerodynamic optimization of horizontal axis wind turbines for mountain sites, ENERGEX'2000, Proceedings of the 8th International Energy Forum and the Conference of the International Energy Foundation, and Las Vegas, USA

Tab. 1. The vertical turbine--[lambda] = 3, CPmax = 0,45

[v.sub.med] 4 5 6 7

ET 2607 4110 5900 7895
EE 2103 3316 4755 6348

Tab. 2. The horizontal turbine--[lambda] = 3, CPmax = 0,87

[v.sub.med] 4 5 6 7

ET 4419 6668 9125 11627
EE 3577 5410 7403 9416