Princess Elisabeth Research Station in Antarctica: The most Isolated and Clean Microgrid on the Planet
In the quest to reduce the environmental impact caused by human economic and industrial activities, innovative projects have emerged to present sustainable solutions to include environmental preservation as a basic requirement. In this context, one of the main fields where it is possible to obtain significant advances is in the generation of energy, through the adoption of renewable sources.
Based on that, the non-governmental organization International Polar Foundation (IPF) based in Brussels, responsible for spreading and educating society about polar science and research, decided in 2004 to announce a project to build the first “zero-emission” greenhouse gas research station, named Princess Elisabeth Antarctic (PEA).
There are indeed other research stations in Antarctica, but none has been designed and built to operate entirely with wind and solar energy. The concept of “zero-emission” consists of meeting the entire energy demand of the station, from solar and wind energy sources. And if there is a punctual emergency, diesel generators would be activated. The challenges for the project to be successful were significant. Starting with the choice of the construction period of the Station (summers 2007/08 and 2008/09), so as not to limit access and transport of supplies (1).
However, what draws the most attention is the level of complexity and intelligence of this system, also called Microgrid. There is a complex arrangement of systems and equipment that allows you to collect energy from renewable sources, store it when it is convenient, promote the efficient use of energy to avoid waste, and ultimately control the electrical stability of the system through a local PLC, given the inherent variability of renewable generation.
In this article, we will review the technical characteristics of this Microgrid, focusing on the production of renewable energy. With this, it is possible to show that if in such an extreme environment it is possible to have zero-emission of greenhouse gases, in other parts of the world it will be too.
What is a Microgrid?
According to definitions made by the Microgrid Knowledge organization, a Microgrid is a self-sufficient energy system, serving a defined geographical area. Additionally, within the Microgrids there are one or more types of distributed energy sources (2).
The term Microgrid has been widely used and often incorrectly. However, there are some criteria that serve to clearly define the framework of such systems. The first is that the microgrid is a local network that serves a specified amount of local loads within a well-defined geographical area. The second requirement is that it can operate independently of the main power distribution network, in other words, it can serve its loads even if in a limited way, without having a connection to the main power network. This operation mode is called an island or off-grid. And third, this system is smart, which means that it can define its mode of operation based on the countless generation options and system states.
A system composed of photovoltaic panels and inverters installed in a residence, for example, is not necessarily a micro-network because, in the case of disconnection from the main network, it cannot meet its loads and must be turned off.
In this case, a real Microgrid could enter the island operating mode, acting independently of the main distribution network to serve local loads, even if in a limited way. Likewise, simple diesel generators, operating as a backup, also do not constitute a microgrid because they work only in island mode. In summary, these three requirements establish a very peculiar class of systems, showing the complexity of the engineering involved.
Modern microgrid systems may also have energy storage devices such as batteries to complement periods when generation is reduced. In networks where it is necessary to guarantee the operation of the network in extreme situations, such as when there is no generation combined with no stored energy or external supply, diesel generators are installed to be operated under determined conditions.
The Princess Elisabeth Station Case
The station’s micro network is made up of different systems, all customized to meet the operating conditions of the site. The diagram below (3) summarizes the sources of generation, distribution, storage, and end-use of energy at the station. The electric energy sources are integrated into a single system that allows controlling demand and energy storage. The thermal energy generated is stored in the form of hot water in a thermal reservoir and is distributed for use in other systems.
The following diagram (3) shows the diagram of the electrical Microgrid network at the station.
How do they generate energy?
Microgrids should prioritize the use of resources available on-site, including renewable energies such as sun, wind, and water resources or fossil fuels such as gas or biomass. In the case of Princess Elisabeth Station, the natural resources available are solar energy and wind. As they are renewable energies, the station is considered zero-emission or simply ‘clean’.
The following figure was taken from the study of the Chinese station Zhongshan (3) and represents the availability of these resources during the year in the region: Graph (a) shows the wind speed. In (b) we see solar irradiation, an extreme case due to the latitude of the region where there are practically 6 months of sun during the summer and 6 dark months during the winter. It is interesting to note the complementarity of the two sources as the wind speed tends to be higher in winter, a period in which solar generation practically does not exist.
Characteristics of Wind generation
Due to the difference in solar energy that the Earth’s surface receives, there is a difference in temperatures between the regions causing a different atmospheric pressure. As a consequence of these pressure differences, there is a mass flow of air, resulting in the wind. Wind turbines take advantage of this phenomenon, converting the kinetic energy of the air into electricity, from wind turbines. The PEA station is at the top of a hill called The Utsteinen, in the Queen Maud Land region. Wind generation is the main source of all year round but in winter it becomes practically the station’s only renewable energy source, with the following generation profile (3):
Wind generation has been used for many years in the Antarctic continent due to the practically constant and unidirectional wind speed (3). Commercially available equipment, however, cannot be used in local conditions and needs to be adapted to withstand low temperatures, ice accumulation in the blades, and so-called catabatic winds which, as defined by Wikipedia is “… the technical name given to a wind which carries high-density air from an elevation down the slope due to the action of gravity ”. The catabatic winds can reach speeds of up to 70m / s, more than 5 times the rated speed of the wind turbines.
The alternating current generated by the wind turbines is rectified in direct current by means of rectifiers and subsequently inverted back to alternating current using inverters. Interesting to note that the number of turbines (9 units) is a multiple of 3 to keep the three-phase distribution system balanced from the point of view of generation;
The output of the turbines (300V wild AC) is transported to a section of the station where the power electronics equipment is installed. In addition to being more protected from the environment, the heat generated by them contributes to maintaining the ideal temperature in the equipment room.
The rectifier output goes through overvoltage protection to prevent damage to the inverter.
The towers were built to withstand a negative temperature of -60ºC and wind gusts of up to 65 m / s (4). They are also equipped with a mechanism that limits the speed of rotation of the blades and allows them to continue operating even in severe wind conditions.
Characteristics of Solar generation with photovoltaic panels
Photovoltaic panels convert the solar energy present in photons of light into electrical energy from photovoltaic cells. Each photovoltaic cell is formed of two layers of semiconductor materials, usually silicon. Photons can contain different energy levels, as well as wavelengths. Depending on the wavelength of the photons of light, they can be absorbed, reflected, or go through the material.
For the purpose of generating electricity, only absorbed photons will be used. The source of photovoltaic solar energy is the second main means of obtaining electricity due to the extreme conditions of the environment, it was necessary to include reinforced glass protection in the cells (1). Here is the profile of the photovoltaic solar system present at the station:
Characteristics of Thermal Solar generation
Solar energy can also be used to heat water for use and storage. In the case of PEA, the water heating system has the function of reducing the electrical demand of the microgrid. The installed system can heat water at low or medium temperatures, up to 90ºC.
Diesel backup Generators
Diesel generators play an important role in the reliability of load handling. The operation of diesel generators is initiated in two situations:
- In emergency situations to guarantee the power supply of the station;
- Planned situations to allow full charge cycles of the battery banks to meet their performance.
The system features are:
Diesel generators are preferred over gasoline generators because of their robustness and because diesel can be stored for longer periods (4). The maximum diesel consumption was fixed during the initial stage of the project at around 1500 liters/year (4).
Battery and Thermal Storage
To enable the storage of surplus renewable energy generation, a battery system was considered. In addition to having the role of storing energy, this system also allows for greater control in meeting the load, due to the inherent variability of renewable generation sources. The system features are:
Each battery cluster is connected to a 15kVA inverter (5kVA for each phase). These converters are intelligent and control the DC / AC conversion in the discharge process and the AC / DC in the discharge process. These converters also have the role of network builders, controlling the quality of the energy supplied (voltage and frequency) by controlling the power electronics systems associated with wind and solar generation (4).
Regarding Thermal Solar Panels, PEA is equipped with 24 m of TUBO 12 Compound Parabolic Concentratorpanels. They use a vacuum to absorb sunlight and collect heat (5).
Unlike photovoltaic panels which are lined with a semi-conductor, thermal panels use an absorbing dark surface plate to recuperate the energy and generate heat.
The hot water is stored in three vertical tanks in the technical room.
References
1 INTERNATIONAL POLAR FOUNDATION. The Technical side of the Princess Elisabeth station.
2 MICROGRID KNOWLEDGE. What is a Microgrid?, 2020. Disponivel em: <https://microgridknowledge.com/microgrid-defined/>. Acesso em: 14 Dezembro 2020.
3 YINKE DOU, G.; CHANG, X.; YAN, C. A Study of a Standalone Renewable Energy System of the Chinese Zhongshan Station in Antarctica. [S.l.].
4 HALLGREEN, C. Assessment of green power production in Antarctica. [S.l.], p. 2. 2013.
5 INTERNATIONAL POLAR FOUNDATION. TECHNICAL SHEET 3: THE PRINCESS ELISABETH STATION’S ELECTRICAL SYSTEM. [S.l.]. 2008.
