Wind energy fundamentals
What does a wind turbine do? It turns the energy contained in the wind – the motion – into electrical energy.
How? Simply said, when wind hits the rotor of the turbine, the rotor starts spinning and inside the turbine a generator – like the one on a bicycle, just larger – that is connected to the rotor produces electricity.
And not so simple: when wind sweeps over the rotor blades, a vacuum behind the blade sets the rotor in motion just like an airplane lifts off the ground. The turbine constantly measures wind speed and direction. It turns the whole nacelle – the cabin on top of the tower – to face directly into the wind. Every few seconds the angle of each rotor blade is adjusted to keep the turbine at optimal performance. The generator is kept synchronous to the electricity grid at all time. The voltage is transformed up to 20 000 Volt at the turbine and later to 110 000 Volt at the substation. Optical cables connect the turbine controls with each other and a satellite link connects them to the remote control center. Exciting? We think so. For more details, here are some links to find out more.
Wind turbine manufacturers:
Wind Resource Assessment, or in industry slang wind study, basically means a detailed, scientific analysis of the wind and climate characteristics for the location of every wind turbine of the project. This serves three main purposes.
First and most importantly, it allows to accurately predict the performance of the project. This is needed to receive bank financing amongst other things.
Secondly, only with the wind resource assessment can it be determined which specific model of wind turbine will be the most efficient one to be used for a project.
Lastly, the wind turbine manufacturers need the wind study to make sure their wind turbines are suitable for the project.
Now, what does a wind resource assessment look like, how does it work? Measurements of the following wind and other weather data for a project are conducted:
Wind speed (m/s)– to forecast production and determine suitable wind turbines
Wind Direction (deg) – arrange the wind turbines optimally so they do not block the wind from each other
Air pressure and humidity (mBar / % RH) – to forecast the mass of the air, production and stress on the turbines
Temperature (deg C) – to determine whether special low or high temperature features are needed
Measurements are conducted with wind measurement masts. Those are masts that are either 10 or 60 m high. Why do they need to be so high? Because wind speed increases with height and the wind turbines will be at least 80 m high. This increase with height is called wind shear. So we need to find out, what the wind is like up there.
Lastly, experts are hired – meteorologists, specialized in wind energy – to analyze the data. For this they look at the data, inspect the locations, build 3D computer models of the terrain and then simulate the flow of wind for the project. Lastly all this is done to determine where the wind will be the strongest and just exactly how much wind there will be. Without this, you cannot build a good project. For an example of the wind resource maps that can be generated, have a look at the image below.
Links to sensor and system manufacturers:
How does the electricity produced by a wind park reach its users? Well, let’s follow the “flow” of electricity on its way. We start out in the generator, which turned by the rotor procures electrical energy. From there we run down the cables inside the tower of the wind turbine to a small transformer. Here we switch from around 690 Volt to 20 000 Volt. Why? Because the higher the voltage, the better we can transport electricity. Similar to how you use higher pressure in big, long distance water pipes and lower pressure at home. So, we come out of the transformer at 20 000 Volt and we continue through the wind park, from turbine to turbine so we collect all the electrical current together. Next, it goes to a substation. Here we meet another transformer, this time we transform up to 110 000 Volt. This is the voltage of the large power lines running through the country, operated by the National Electricity Company, and that’s exactly where we are going next, into the high voltage transmission grid of the country.
And from there we go to wherever electricity is needed at the moment - a shop, a factory, a hospital, a school, a heater, maybe your computer right now. How do we get there? Pretty much the same way but backwards. We travel along the transmission grid, to another large substation. These are usually just outside any bigger town. There we switch down from 110 000 Volt to 20 000 Volt. That makes things easier to handle and safer. From there we travel either on overhead lines or via underground cables to somewhere just around the corner from you. There, on an electricity mast or in a small transformer house, we switch down again in one or two steps to 230 Volt. Sounds familiar? Of course, because now we are at the voltage that most things at home, including your computer, run at. So now it’s just into your house, through the fuse box, to the electrical socket, into the computer and here we are.
For a graph of the whole process, look here.
One thing that is different about electricity as opposed to other power sources is this. Electrical energy cannot be stored in significant scale. You can use pumped storage but that only goes so far. This means, the amount of electricity that is being produced must always be equal to the amount of electricity that is being consumed. If there is too much electricity, voltage rises and the grid shuts down to protect your electronics. If there is too little, well, it gets dark.
Now how do you achieve this balance? First of all, you predict how much electricity is going to be consumed. All in all, we are quite a predictable bunch. Most of us cook our coffee, turn on our TVs and shut off the light at round about the same time. So grid operators can predict consumption fairly well. Next, you plan how much electricity what power station will produce accordingly. For wind and solar you have a look at the weather forecast so you know what to expect from those. And then for the fine details of balancing that are left, you turn on and off small power stations, like small gas turbines, or you let more or less water flow out of a hydro dam to produce more or less electricity. And there you go, you have balanced your electricity grid.
For more details of how this works and what it looks like when this goes wrong, look here:
How do wind park projects benefit the environment? They produce electrical energy using wind without burning any coal, oil, gas or anything else and without producing nuclear waste. And they will produce lots of it!
What does that mean for the environment? Well, take a conventional power station. Power stations need to burn something – coal, oil, gas, nuclear fuel – to create heat to turn a turbine. We use wind. The more wind we turn into electricity with our wind turbines, the less fuel needs to be burned by conventional power stations. Most of Bulgaria’s energy comes from burning coal. With wind parks every year tons of coal can be saved from being burned. Interested in the math? Click here.
More information on clean energy production:
Wind Power (Wikipedia)
Reduction in Carbon Dioxide Emissions: Estimating the Potential Contribution from Wind Power (By Industrial Wind Action Group)
|Water consumption for electricity production|
How do wind parks help fight climate change?
Simple. They produce energy without burning things.
Whenever coal, oil or gas is being burned, we do not just use up limited fossil resources, we all produce a whole bunch of dirt.
We produce green house gasses. Most famous is Carbon Dioxide (CO2) but also quite a few more. And when these are released into the atmosphere, they trap more heat on the planet – by reflecting it back to earth on its way to outer space - which results in rising temperatures.
In addition, we emit a bunch of smog or micro dust into the air. This stuff does a whole list of bad things. For example the dirt from coal power stations travels around the globe and settles on the ice of the Arctic and Antarctic where it turns white ice into grey ice. Why is this important? White ice reflects almost all light and heat right back out to the sky and outer space. Grey ice absorbs light and heat, melts the polar ice caps and leads to rising sea levels.
Melting multi year pack ice (Reuters)
For some calculations, click here.
Grams of CO2 per KWh of energy
Wind park projects have an impact on the environment from four separate sources. Roads are built to transport and maintain the wind turbines, cable lines are installed to carry the electricity, foundations are needed for the wind turbines, and lastly every turbine needs a crane pad for its installation. Let’s talk about these one by one.
To each turbine an access road is needed, so the components can be transported there and the wind turbine can be maintained and serviced. Much of the roads are simply improvements of the currently existing roads. Lastly, some new roads might have to be built, in as minimum amount as possible. That is both the best for the environment and it reduces costs. Also, the roads are made of gravel, no large asphalt or concrete roads. That means they let water through, avoid erosion and can be removed and recycled easier at the end of a project.
All the wind turbines in a project need to be connected to each other and then to the national electricity grid, so that the produced electricity can reach its users. This is done by underground cables or small overhead power lines. Wherever possible the lines follow the roads to minimize impact and they are as short as possible. This reduces losses of electricity; it reduces costs and minimizes the impact on the environment.
Each wind turbine, like a house, needs a foundation to stand on. The foundation for a single wind turbine is approximately 20 m in diameter and no more than 3 m deep. The foundations are, of course, made out of concrete and steel. And, at the end of a project’s lifetime, they can be removed just like the foundations of a house with pneumatic hammers.
The wind turbines need a crane for their installation and this crane needs a carefully prepared area to stand on. That’s the crane pad. Essentially, crane pads are very similar to the roads which need to be built. They are made of gravel and can be removed and recycled the same way.
After a project's lifetime, the land that had been used for it could be restored to its initial condition. This means that all wind turbines, cable lines, foundations, roads and crane pads are removed from the site of the project. Of course, improvements of existing roads could stay for the public to use.
In the past, there have been problems with noise and shadows from wind energy projects. This happened when projects were built too close to the next houses.
Today the understanding of these issues is much better. The law requires suitable minimum distances and there are detailed studies and specialized software that we use to make sure we do not disturb residents with noise or shadows. Let’s talk about these two concerns now.
When the sun is behind the rotor of a wind turbine you can get a so called “strobe effect” from the rotor blades passing in front of the sun. It is possible to calculate very precisely whether a flickering shadow will in fact fall on a given location near a wind farm, and how many hours in a year it will do so. Therefore, it should be easy to determine whether this is a potential problem.
Wind turbines, just like cars, have become much more quiet over the past 15 years. All new wind turbines now come with sound insulation and the rotor blades are designed to minimize noise. Specialized software can calculate the exact amount of noise a project would make depending on the strength of the wind. For examples of the noise produced by a wind turbine at different wind speed and distances from the turbine, have a look at the table below.
|Distance from Turbine (km)||Sound Power Level at 4 m/s (dB)||Sound Power Level at 6 m/s (dB)||Sound Power Level at 8-12 m/s (dB)|
|Jet aircraft, 50 m away||140|
|Threshold of pain||130|
|Threshold of discomfort||120|
|Chainsaw, 1 m distance||110|
|Disco, 1 m from speaker||100|
|Diesel truck, 10 m away||90|
|Kerbside of busy road, 5 m||80|
|Vacuum cleaner, distance 1 m||70|
|Conversational speech, 1 m||60|
|Quiet bedroom at night||30|
|Background in TV studio||20|
Do wind turbines harm birds or other animals? No. This may be hard to believe and it has been a concern of activists for a long time, which is precisely why a lot of research has been done on this subject. The result of these has been that wind turbines do not hurt birds, do not disturb bird migration and do not negatively affect other animals. In fact, birds avoid wind turbines, simply flying around them like they do with other obstacles. And most other animals seem not to care too much. Wind turbines operate throughout the world in the middle of cattle farms, in tulip fields, fruit plantations in areas with sheep herds and even in the middle of the sea without disturbing the animal kingdom.
Don’t take our word for it, have a look at these studies:
|Causes of bird mortality
Did you know, that Bulgaria must develop renewable energy projects? Why? The European Union, in its effort to battle climate change, has set mandatory goals for every member state of how much renewable energy it must produce by 2020. For Bulgaria this means that by 2020 a total of 16% of the energy produced in the country must come from renewable energies.
And what happens if this target is not met? There will be penalties and regulation imposed by the European Union. And this, for sure, will be a bad use of money that can otherwise be invested for the benefit of the country.
Is wind energy too expensive? No. Here are two reasons why:
Wind Energy is already competitive as an energy source. It is cheaper than many other energy sources like gas or oil.
The feed-in tariff that a project receives for the produced electricity is set and adjusted every year by a state regulatory commission here. And the job of this commission is to make sure that the feed-in tariff is just high enough to encourage investment in projects like this one, to help meet the EU climate targets but still as low as possible to keep energy affordable.
When you look at a wind energy project as a financial investment, it is pretty similar to investing in an apartment to rent out. At the beginning of a project you make a large investment in the wind turbines and infrastructure. And over the next 15 to 20 years you receive a steady stream of income from the sale of the produced electricity. To keep the investment in the beginning manageable, you finance part of the project – something like 70 % - with a bank loan, which you then pay back over the next 10 to 12 years or so. Big differences to real estate? You do not need tenants, you need wind, which is why every wind energy project comes with multiple, detailed expert studies of the wind potential. Without that it would not be a very wise investment and no bank would grant a loan for the project.
In summary, wind energy projects are not speculative high income investments. We believe Bulgaria has had too much of those already anyway. Wind energy projects are stable, reliable long term investments with very little risk.
Wind energy projects generate large amounts of investment in Bulgaria and in the respective region. Much of the investment volume, including the construction of roads and crane pads, electrical lines and components, is sourced within Bulgaria. This creates further investments and jobs in the country. Analogically to this, experts and consultants are hired in the country. Also, this type of projects attract follow-on investments bringing more investment, more income and more jobs to the region.
RES LEGAL - website on legislation on renewable energy generation
Renewable energy website of the European Commission
Directive 2009/28/EC of the European Parliament and of the Council of 23 April 2009