Wind flaps Wings…
Sunday, April 19, 2015
Breeze blow…for the power to flow… and the globe to glow…
Dear readers, the team EnerzyEE believes that the time is ripe to pay our serious attention to one of the booming industries in the world: the wind power. Thus, the revealed before you is an interview we had with Eng. Mr. Manjula Perera, the CEO of WindForce (Pvt) Ltd., a giant as well a pioneer in the field of wind power generation in Sri Lanka.
Sir, today the wind power is at a boost in almost all parts of the world. What are the reasons behind this boom?
Well, the worldwide flourish in the wind power developments can be attributed to many facts. In the first place wind is a green energy source having zero carbon emission and thus is an effective means of saving our environment from pollution. Secondly, it is a massive energy source having the potential of serving twice the total energy consumption of the whole world. Hope you can imagine the size of this natural resource. So today, the world has identified the importance of tapping this vast energy resource. Most importantly, this power source is inexhaustible. No matter how much you use it, it will never be depleted like coal, crude oil or natural gas. Now the technology being developed to harness wind power efficiently, new avenues have been opened up for wind power developments.If we look at this trend in the Sri Lankan perspective, certain other facts come into play. Firstly, Sri Lanka has a quite good wind potential, especially in the North and West regions. Secondly, at the moment, we are heavily dependent on fossil fuel which comes 100% from imports. But we are freely bestowed with wind which is 100% our own. Therefore, wind power developments can safeguard us against the uncertainty of fuel supply, save our foreign currency and protect our economy from impacts of currency fluctuations.
Besides, it is our goal to achieve 20% of total electricity generation from new renewables by 2020 to assure proper energy mix. Today in 2015, what we have achieved is just 10% and there is a long way to go. Moreover, the small hydro resources of our country being almost utilized, the remaining option is tapping the wind and solar sources. Solar generation technologies are still under the development phase and thus wind has a big role to play in achieving 20% by 2020.
You mentioned that Sri Lanka has a considerable wind potential. How large is that and how much of it can be commercially utilized for electricity generation?
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| Wind map of Sri Lanka |
Yes, according to the studies carried out by the National Renewable Energy Laboratory (NREL), Sri Lanka has a wind potential of 20,740 MW. But this full potential is not exploitable due to various reasons such as land use constraints. It is conspicuous that you can’t exploit forests and residential areas. Moreover, the grid availability too plays a vital role. It is not economically viable to tap wind sources when there are no means of grid integration. Excluding all these, the exploitable wind potential is estimated to be 5,653MW, which is way higher than the present peak demand.
Okay, if harnessing wind power in Sri Lanka is economically viable, then what are the technical barriers that restrain us from fully utilizing it?
As you are well aware of, wind power is non-dispatchable and variable in nature. These drawbacks, when superimposed upon the poor load profile of Sri Lanka, give rise to a maximum limit of wind power that can be absorbed by our system.
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| The load profile of Sri Lanka |
If we can flatten our load curve using demand side management or any other means, it will definitely open up a lot of opportunities to absorb more wind power into the system.
You mentioned that wind power is variable. Isn’t there any remedy for this?
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Using the
pumped storages
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Of course there are various means to reduce the variability of wind power output. One is using pumped storages. That is, when the power output of a wind farm goes beyond a certain limit, we pump water to a reservoir at a higher elevation using this excess power. This water is later used to generate electricity by means of a hydro power plant, as the wind output drops, which is capable of compensating for the reduction of wind power output. This method is successfully implemented in various parts of the world today.
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Using an
advanced battery backup
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The next is the battery backup system. But, batteries are pretty expensive. Therefore, a lot of researches are going on in this field, so as to develop a battery backup, only to reduce the ripple in the wind power output. We are keenly awaiting good news from these researches.
Moreover, there are sophisticated wind power prediction models developed by now. Each hour they give a wind prediction for 14 days ahead, with the accuracy of ±15%. This can be used at the system control center in planning their short term dispatch schedule, such that the variation of wind power output is foreseen, and necessary actions are taken in advance to eliminate the undesirable outcomes of wind power variations. Unfortunately, the SCADA system of our system control center is incapable of adapting such advanced technologies. Yet, we will be using these advanced technologies in the near future, once the construction of new system control center is completed.
In large countries like Russia, USA and China, wind farms are scattered all over the country. When the wind power drops in one region, there is abundant power in the other regions to compensate for the loss. Thus the variation of power output is minimized.
Another method successfully practiced in the Europe is interconnectivity of grid. Today, the whole of the Europe is connected via one huge network, fed by many countries. This provides ample opportunities to exploit the renewable power sources, which are inexhaustible and purely green. Since the system is huge and fed at many locations, it has the capacity to absorb quite a lot of wind power. That’s why Germany and Spain have been fortunate to exploit so much of wind resources. (About 50% of Germany’s electricity generation comes from renewables.) Likewise, if we can interconnect our gird to that of India, then we can broaden the horizons of wind power utilization.
it is said that wind farms consume reactive power from the grid, which is considered a major drawback. What is the validity of this widespread idea?
Whether a wind farm consumes reactive power or rather generates it, depends on the type of generators that are used there. If induction generators are used, of course they consume some amount of reactive power from the grid. But synchronous generators, on the other hand, generate reactive power instead of consuming any. Nowadays, almost all the wind farms are equipped with synchronous generators and therefore, it is amiss to think that they consume reactive power from the grid any longer.
You talked about the generators used in wind power plants. Could you please elaborate them further?
Okay… Mainly there are four types of wind generators. Those are; induction generator, doubly fed induction generator, synchronous generator equipped with a full converter and multi-pole synchronous generator with a full converter (gearless).
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Arrangement of
an induction generator
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A doubly fed
induction generator
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The doubly fed induction generator is an evolution of the induction generator having higher efficiency and better controllability. Depending on the mode of operation, the grid can be fed either by both stator and rotor or stator only.
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Synchronous
generator with a full converter
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The third type comprises of a full converter added to a synchronous generator, which is used to replace the induction type generators to eliminate their drawbacks.
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Multi pole
synchronous generator
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The forth type is a multi-pole synchronous generator connected to a full converter. This generator doesn’t require a gear box and therefore eliminates all the issues and losses introduced by the gear box. Thus it increases efficiency and performance yet at the cost of increased price. Nevertheless, these are gaining popularity among the wind power developers.
Wind is different in various parts of the world. How does this effect to a wind power developer?
Yes, wind speed changes from one place to another. Moreover there are seasonal as well instantaneous changes in wind speed. Based on the wind speed, wind sites are broadly categorized into three main classes namely class 1, class 2, class 3 and classm4. The average wind speeds of these sites very from (10-8.5)m/s, (8.5-7.5) m/s, (7.5-6) m/s and below 6 m/s respectively. The majority of the wind sites of our country generally fall under class 2.
Depending on the wind class, the blade diameter of the wind turbine should vary. Class 3 type wind turbines require a higher diameter whereas class 1 type is made with smaller diameters. The match between the wind class and turbine diameter is mandatory for the proper functionality of the wind farm.
What will happen if there is a mismatch between the blade diameter and the wind class of the site?
The live example is the Hambanthota pilot wind power project. It ended up having a very low plant factor (around 17%), making the investment an utter waste.
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| A wind turbine |
P = 1/2 ρ.a.v^3
Where ρ, a and v stand for air density, swept area of the turbine blades and wind velocity, respectively. When the wind velocity is less, the blade diameter has to be large enough to capture sufficient amount of power. In Hambanthota pilot wind power project, they had used class 1 type wind turbines in a class 3 type site. Those turbines have small diameters and are unable to capture sufficient power from the slow winds.
On the other hand, if class 3 type turbines (These have large diameters) were installed at a class 1 site, where the wind speed is high, then the aerodynamic forces acting on the turbine blades and the hub are so high such that they tend to break under fatigue failure due to vibrations, reducing the the lifetime of the turbine. Therefore, care must be taken in matching the site and the wind turbine types.
The wind turbines are installed far from each other. Is there any reason behind this as well?
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Layout of a
wind farm
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Why do wind turbines have three blades? Why not one, two or four?
Who said you so? It seems as if you are greatly mistaken. Of course there are wind turbines with one, two, four and even many blades. The wind captured by a single blade turbine is less, compared to the other types and so does its power output. Turbines with two blades can capture more wind than the previous but is very vulnerable to mechanical failure due to unbalanced forces acting on the blades. The three blade is the most common and the most optimum design. It harnesses a considerable amount of wind whilst showing the highest mechanical stability. That’s why those are so much popular these days. You can also find wind turbines with four blades, but those are rare.
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Various kinds
of wind turbines
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The three
tiered tariff
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Wind power is not expensive. At least, it is not as expensive as people believe it to be. Unfortunately this is a misconception even some dignitaries have.
Wind power projects are paid according to a tiered tariff structure. During the first eight years, one unit of power is sold at about 21 rupees. Of course, wind power is expensive during this time compared to coal power, but not as expensive as oil fired power generation. (Anyway, due to the expertise we have
gained in this field and rapid technological advancement, we may be able to bring this down further.) Thereafter, one unit is sold at about 12 rupees till the 15th year, during which wind become cheaper than many other technologies. Next, the selling price drops down to somewhere around 8 rupees per unit, which is even cheaper than coal. (at the 20th year)
My argument is; whether wind power is expensive or not should be decided after paying due consideration to its lifetime costs. Can you think of buying one unit of electricity from a coal fired power plant at eight rupees, after fifteen years from now? So, what’s the point of saying “wind is expensive”?
Okay, we talked much about wind power. Let’s turn towards the wind power developers. What are the challenges they have to confront in the Sri Lankan context?
“Obtaining the approvals” I must say. You have to get 36 approvals from 24 agencies. This takes a minimum of one year and the process is extremely tiresome, no matter how much they talk about encouraging the renewable power developments. You must have a great patience and determination to pull through this initial phase.
What about the technical challenges?
Well, there are lots of technical challenges for sure. In the first place, it is not easy to find correct wind data for certain sites. You have to find them somehow. Then the are not in good condition to transport the equipment. You may have to develop those roads at your own expense. Then you have to find high capacity cranes capable of installing the wind turbines and the list drags on. But, all these are engineering challanges and we have enough competent local engineers to address those. The real obstacle is getting the approvals, as I mentioned earlier as well.
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Transporting
the equipment
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| Erecting the tower |
There are ample opportunities in our country to further exploit this huge resource, and the business is challenging as well as rewarding. So, come join our family of wind power developers to harness the full potential of Sri Lankan winds.
As the secretary of the Wind Power Association, do you have anything else to add?
Yes, now the CEB is going to call open tenders for wind power development. Then, the local developers have to compete with the international players. If by any chance, these tenders are won by those foreign contractors, they will simply utilize our own resource, make money out of it and take it away from the country. We will never develop a technology of our own and will be dependent on them forever. So, as a country, what is the big advantage we are going to achieve from calling open tenders? What I believe that, it is the country and its people that should be benefitted by any natural resource, not the foreigners coming to exploit us and our resources.
Dear sir, today we came to know many interesting facts about wind power generation. Thank you very much for your time! Team Energyzee is really grateful to you for your kind collaboration!
Dear readers, this marks the end of our interview regarding wind power generation. Keep in touch with Energyzee to explore more about electricity and related subjects!
Article By: Dilini Darmawardana
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