Discussing energy storage technology- PHS vs CAES

What energy sources are available and how is the energy from these stored?

Current energy sources are primarily divided into two categories, fossil fuels and renewable energy sources. The fossil fuels are a chemical form of energy, and are energy derived from organic material deposited on the seabed for several million years. The renewable energy sources reap the energy that hits the Earth from the sun. Wind energy, for example, also reaps the energy of the sun just indirectly as it extracts the kinetic energy of the atmosphere created by the solar warming of the earth. Or it may be solar energy that extracts the radiation energy from the sun and converts it directly into electricity. Common to the two renewable energy sources is that there is no control over production. In order to meet periods of deficit in electricity generation, energy must be saved in periods of surplus in production. There are several stages of energy, and in order to save it, you must have converted the energy you have extracted from, for example, solar cells to potential energy. This can be done by a Pumped Hydro Storage (PHS) system, which acts to pump water into a reservoir and let the water flow through a turbine when you need power. Thus, you use excess electrical energy to drive a pump that pumps the water and thereby transforms the electrical energy into potential energy. The potential energy can be calculated by epot = mass * thin acceleration (9.82 m / s) * height. However, you can also save excess energy using a compressed air energy storage (CAES) system. This system functions in its basic form in the way that a compressor is operated with excess energy and pumps air into a container and thereby creates a pressure difference. When the energy is to be used, let the air run through a turbine and thereby generate power. The energy thus goes through an energy chain that is the following: electrical-> potential-> kinetic-> mechanical-> electrical. However, it must be borne in mind that some of the energy is transformed into thermal energy during the compression of air. This form of storage usually has an efficiency of about 70-75%. The PHS systems, on the other hand, have an effect of about 80%.

What options are there for alternative energy storage different geographic locations in the world?

Looking at the two systems PHS and CAES systems require different conditions for it to function. The PHS systems require that you have the difference in height to convert the energy into potential energy. The problem can be described by the graph below:

(Anex a)

Looking at a map of where PHS systems are located, you also see that they are located in areas with mountains. This excludes countries with very small height differences such as Denmark and the Netherlands from being able to use these systems. If listed on the CAES systems in Europe, some of these systems are located in areas where there are not necessarily mountains. This is because the CAES systems only need a porous mountain species and a sealing mountain species to work. This means that CAES systems can also be used in old oil tunnels, which opens the possibility of storing energy, in areas with no major differences. So it can be seen from the map that CAES systerme is a more flexible alternative to natural conditions than the PHS systems are. From the map it can also be seen that CAES systerme also lies in the mountains, which is because old mines can also be used as pressure vessels for the compressed air. Looking at old oil tunnels, which just have the prerequisite of a porous reservoir mountain and a low porosity sealing beam, there are several qualified places in areas without prerequisitesfor use of PHS systems. An example of this is Switzerland, where there is a test facility that uses an old mine. If you generally look at maps in areas surrounding dams, as PHS systems require, you also see that it occupies large areas. Therefore, in the use of PHS systems, housing and vegetation in the various areas must also be taken into account. Height difference is therefore not the only thing necessary for establishing PHS systems.

The pictures below show different locations for respectively PHS and CAES systems in Europe:

(Anex B- PHS)

(Anex C- CAES)

How can the CAES and PHS systems be alternative energy storage options?

CAES and PHS systerme are both possible solutions to the storage problem. CAES uses compressed air for storage. The benefits of CAES systerme are that they have a relatively small impression on the nature around them, they also have a relatively high effect of about 70-75% percent. However, this is slightly lower than the PHS systems, which have an effect of about 80%. One disadvantage of CAES systerme is also that air has a much lower density than water. This causes the systems to have long-term storage problems due to air leakage. For example, CAES systems can range from maintaining the required air from 40 days to up to 1 year. However, this is lower than the PHS systems, which in theory can keep the energy as long as needed. The primary disadvantage of CAES systems comes from the fact that some of the energy is transformed into thermal energy when the air is compressed. There are several different ways in which this issue can be solved. The PHS systems are primarily divided into two different types. There is the closed cycle and the open. The advantage of the open is that it is not so expensive in construction costs and there is a smaller evaporation. The disadvantages of the closed system are also that land is being occupied, but the water is not useful to the population as it is in open reservoirs. The open system is exposed to more loss of energy in the form of evaporation, but as it said, it may be useful to the population. Generally, there are consequences for nature using PHS systems as they occupy large land areas to keep the water. However, they have a higher efficiency than the CAES systems. In addition, already built dams, relatively cheaply converted to a PHS system, can only be installed by a pump.

Conclusion:
So for renewable energy sources to be useful, new alternatives to storage of the excess energy are needed. The CAES and PHS systems are two alternative storage options that have not been seriously thrown through, but which in the future create the opportunity to save excess energy until it is used. Both types of storage have advantages and disadvantages and are useful under different circumstances. Both systems are part of a comprehensive solution to one of the biggest issues associated with renewable energy sources.

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