2. Background and Theoretical Framework

The concern about the environmental degradation and the awareness of decreasing dependence on energy import and increasing security of supply are some of the factors that have encouraged the use of renewable energies, which can provide technical and economic solutions to the problem of energy supply.

The access to energy has an important meaning in current society as well as how energy is extracted.

Today we must be aware of the importance of sustainable development, which means that global changes in the future must be minimal or even zero for future generations, in order to make this a reality we need to make the world aware of the use of renewable energies (solar energy, hydropower energy, tidal energy, biomass energy, wind energy, etc) and leave aside conventional energies (fossil and nuclear fuels).

This project will be supporting and will be part of Interreg, one of the key instruments of the European Union (EU) supporting cooperation across borders through project funding. It aims to jointly tackle common challenges and find shared solutions in fields such as health, environment, research, education, transport, sustainable energy and more.

The global project deals with the future construction of a smart city in Hvaler powered by renewable energies, including the installation of a wind farm (250 kW each one). For this reason we will describe what a smart city is and also we will talk about windmill (global history, how to work, elements…).

  • Smart city

In general terms, a city can be defined as “intelligent” or “intelligent efficient” when social investment, human capital, communications and infrastructure coexist harmoniously with sustainable economic development, relying on the use and modernisation of new technologies (ICT), and resulting in a better quality of life and prudent management of natural resources, through participatory action and the commitment of all citizens.

In relation to our project, we can say that the city obtains 100% renewable energy.

Smart city, Burlington

Smart city, Burlington

  • The windmills and wind turbines

However, first we will make a brief summary about the history of windmills in the world.

The windmills began to emerge in the 7th Century A.D. in Persia (today Iran), these used to irrigate and grind grain, although were ineffective, begins to spread throughout China and the Middle East.

In Europe they appeared in the 12th Century in France and England, thus spreading around the continent. The tower mill was developed in France in the 14th Century.

In addition to irrigation and grain milling, mill built between 15th-19th Century had other applications, such as water pumping, wood sawmills, paper mills seed pressing to produce oil…

At the end of the 19th Century, wind turbines began to be used to generate electricity, and in 1973, as a result of the first oil crisis (price increases), a period of wind energy exploitation began, sharing the leading role with solar energy.

A wind turbine has the following elements:

In the field of wind turbines we find two different terms, onshore (on ground) and offshore (at sea).

The advantages of Windfarms Offshore are:

  • There are no obstacles at sea that can reduce wind speed. This favours wind circulation at higher speeds.
  • There is less environmental turbulence, which reduce the fatigue of a wind turbine and consequently increases its services life.
  • They have enormous spaces for wind turbine, which offers the possibility of installing much larger parks than on land.
  • It reduces the visual impact on the landscape as it is further away from urban centres.
  • This distance also means that noise is no longer a problem, so that the blade’s top speed can be increased, with the corresponding reduction in weight and structures, making it possible to reduce manufacturing cost.

However, Offshore Windfarms also have significant disadvantages compared to onshore wind farms:

  • Wind resource assessment is more complex and much more expensive than onshore.
  • There is no electricity infrastructure to connect the areas with the greatest wind resources in the middle of the sea with the consumption centers.
  • The cost of the foundation and electrical networks of these facilities make offshore technology more expensive.
  • It is much more difficult to access and work in the middle of the sea. The cost and difficulties increase as they enter the depths of the sea.
  • The machines require more separation between them, which implies an increase in investment. This is because the low roughness of the sea causes turbulence to spread more rapidly and the wake of the machines influences other, thus reducing the service life.

As this project is developed in the aspect of Mechanical Engineering, we talk about the foundations.

Onshore foundation

The types of foundation that have been carried out to support onshore wind turbines are basically: surface foundation and surface foundation with piles. Depending of the soil conditions, one or the other type will be chosen.

The surface foundation is characterized by a great extension in plant, based on transmitting the loads it receives and its own weight to the ground. Its geometry is always circular or polygonal and the material used is mainly reinforced concrete.

Offshore foundation

Unlike the onshore case, the existing offshore foundations are very diverse. Depending on the depth of the site and the properties of the land, one or the other typology is chosen and the greater the separation from the coast, the greater the cost involved. These foundations must be designed to withstand additional loads to those specific to the onshore case, as they are also affected by waves, pressure distribution at depth and there is an increased risk of instability due to the constant erosion of the submerged soil.

  • Gravity foundation:

This type of foundation is based on the same principle as onshore surface foundation, the dimensions are usually larger. It is not usually solid to facilitate transport by ship and is then filled by land. They are used at depths of less than 20 m and are more expensive from 10 m (left). In places prone to frost, a wider area is usually available to protect against icebergs (right).

  • Tripod-shaped:

This type of foundation is used for depths of 30 and 40 m. The tripod is anchored to the bottom by means of steel piles; it is more expensive than the previous one (gravity foundation).

  • Type Jacket:

This type of structure comes from the offshore oil industry and is used up to depths of 60 m. High manufacturing costs. This system is anchored to the seabed using piles and is transported and installed in one piece and requires special boats.

  • Suction Buckets foundation

It consists of a design similar in appearance to the gravity foundation. The (steel) foundation is deposited on the seabed and suction is applied to the base so that it penetrates into the ground.

  • Foundations of floating supports

This type of lift is very avant-garde and it remains to be seen what its real scope will be. It seems that for intermediate depths the costs could be similar to those of fixed structures and, in addition, it would significantly expand the potential locations. In its favour, the construction process plays a role in reducing the visual impact and making it more flexible. The complexity of its design is much greater than for any other case, as it is necessary to model the coupled movement of the support structure and the turbine. Electricity infrastructure is also a new challenge.

How does a wind turbine work?

Generating energy from wind is simple; the wind flows over the blades of the wind turbine and causes a rotational force. The blades spin an axle inside the nacelle, which enters in gearbox. The gearbox increases the rotation speed of the rotor axle and drives the generator that uses magnetic fields to convert rotational energy into electrical energy.

Generator power goes through a transformer to adapt it to the necessary voltage of the distribution network, usually between 20 and 132 kV. Regional electricity distribution networks distribute energy throughout the country, both for households and businesses.