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THEORETICAL FRAMEWORK AND LITERATURE STUDY
The following section will describe the necessary components for both a diesel and hydrogen system. As there exist multiple different kinds of fuel cells a brief introduction to the most noteworthy ones will be carried out. Beside the primary unit there also exist other components needed to have a fully functioning UPS. The most important ones including tanks, electronics and pressurizers. Some already existing projects will also be described to give a better understanding of the current state of the technology.
Data center classification
According to Velimirovic (2021) there are four types of different data center classifications. These are classified from tier 1-4, where 1 has the largest downtime and security while tier 4 has the smallest. Primarily tier 3 and 4 are used for larger companies and organizations which demand higher reliability and backup power. A tier 3 data center must be able to provide backup power for at least 72 hours and no more than 1.6 hours of total downtime per year. A tier 4 data center must provide a minimum of 96 hours backup power and a maximum of 26.3 minutes downtime per year. Staff must be always on site. Eska and Corneille (2018) states that equipment can either have a backup power source (BPS) or an uninterruptable power source (UPS) but for data centers of type 4 both systems must be installed.
Backup Power system
Most data centers utilize two systems for power during outages. The backup power generation system often take time before being able to operate at full power and therefor also a second system is included. This uninterruptable power supply (UPS) provides instantaneous power during outages. The backup power system need time before operating at full load and therefore an UPS is also needed. There exist multiple types of uninterruptable power systems but for data centers primarily online systems are used (FS Community, 2021). Online UPS are always connected to the data center and therefor have no response time, thus they are the preferred choice for sensitive equipment like data centers. This kind of system utilize both a rectifier and an inverter to convert between ac and dc. This creates a smoother voltage with a voltage ripple of 2-3%. Even though its primary function is to supply power during outages, the UPS can also be utilized during times of high demand on the electricity grid.
Diesel generator theory
Diesel generators can be approximated as diesel cycle. Much like a fuel cell, chemical energy is converted to electrical energy, for a diesel cycle however the fuel is combusted (Mishra, 2017). In a diesel cycle the air is compressed from point one to two with a constant entropy, which is an isentropic process. From point two to three, heat is added to the system at constant volume. From point three to four, the air expands in the system and work is produced, which in this case is used to drive an alternator, which in turn drives the generator.
Diesel storage
In temperatures of 30 degrees Celsius, diesel energy can last for 6 to 12 months according to Kendrick Oil (2015). The gasoline will also start to reply with the oxygen in the tank. Diesel may come slippery because of this interaction. However, it can block energy pollutants, causing machine problems, if diesel turns slippery. The slippery gasoline won’t burn duly, performing in a film of soot and carbon on the inside of the machine. One possibility is to apply oxidation- defying stability treatments. Declination of diesel energy can also be caused by other sources. Fungus can develop in the presence of water in the energy. Fungus can produce organic chemicals that break down diesel motes (Kendrick Oil, 2015). The gumming process can be accelerated by high temperatures. When essence like zinc and bobby meet diesel energy, they can spark a chemical response. Certain chemicals have been shown to quicken the aging process. Diesel is a combustive liquid that should be handled and stored with care. The diesel energy should be kept in a secure position. A below- ground vessel can be placed within a structure or beneath a spare- to. This placement keeps water out of the tank and prevents the diesel from sinking due to radiant heat.
It’s critical to avoid water accumulating on top of the tank. combined water may erode essence holders and promote nonentity and bacterial development on all holders. It’s also pivotal to keep an eye on the water position in the storehouse tank. Condensation will collect water, which will drop on top of the diesel energy. Accumulated water is a perfect parentage niche for bacteria, which can beget the diesel energy to break down precociously. One system is to drain the water. Using biocide complements is another option.
Diesel Price
There are different types of diesel fuel depending on factors like outside humidity and temperature, for the discussed generator diesel of type two is used as stated in the datasheet. In figure 2, price history of diesel type 2 from the US Energy Information Administration (2022) can be observed throughout the years. This is the retail price in the USA, which have different taxes compared to Sweden (EIA, 2022). EIA (2022) states that an excise tax of 24,3 cents per gallon as well as a storage fee of 0,1 cents per gallon is paid on diesel. The retail price of 5,12 USD/gallon converts to 4,876 before tax. With the assumption that one gallon equals 3,7854 Litre, this translates to 1,2882 USD/Litre or 12,95 SEK/Litre.
This is considered the production price for diesel of type 2, to which the Swedish taxes are added to. 25% of the production cost is added to the price as VAT. An energy tax of 1,06 SEK/Litre and a carbon tax of 2.29 SEK/Litre is also added. A 25% VAT is also applied for these two taxes. The total price then equals 20,37 SEK/Litre.
Fuel Cells
The basic working principle of a fuel cell is that it is a cell that convers chemical energy to electrical energy. This happens through the process of electrochemical reactions. A fuel cell consists of three different parts, an anode, a cathode and an electrolyte. The material used differ depending on the type of fuel cell used. The different types of fuel cells also use different fuels. Fuel cells suitable for backup power generation can mainly be divided into three types depending on the fuel used: Methanol, Hydrogen or Liquified petroleum gas (LPG). Depending on the fuel used, the system components also vary. The most important components will be discussed in the following section. The principle of PEM cells and their cooling as well as stacking of the cells will be covered.
Fuel Cell Function
A fuel cell utilizes an electrochemical process to generate electricity from fuel, much like a battery (Smithsonian Institute, 2017). In this way it’s more like a battery. The difference between a fuel cell and a battery is that a battery is a closed system with a finite quantity of fuel to convert whereas the fuel cell can be observed as an open system where fuel is injected from an external source. Much like a battery, a fuel cell consists of an electrolyte in between two electrodes in the form of an anode and cathode to chemically convert fuel to energy and electricity (Nice & Strickland, 2000). When a fuel comes into touch with the anode, the process begins. The anode contains a catalyst that oxidizes the fuel, separating it into positively and negatively charged ions and electrons. The positive ions travel through the electrolyte to the cathode after the split. The electrons are unable to flow through the electrolyte and must go to the cathode through a wire, resulting in DC current electricity that may be used to operate a device like as a motor. When the ions and electrons reach the cathode, they are reunited in a reduction process by a catalyst and an oxidant. As a result, a waste by-product is produced, which always contains some heat. Water is a waste by-product in hydrogen fuel cells (in which hydrogen is the fuel).
Power Conditioners
A fuel cell must be coupled with a power conditioning system to adjust the electricity which includes regulating its voltage, frequency and current as stated by (Hydrogen and Fuel Cell Technologies Office, n.d.). The current provided by the fuel cell is direct current (DC) and therefore must be converted to alternating current (AC) to be used for applications like data centers.
Stacking of fuel cells
As stated by Song et al (2022), the voltage of a single fuel cell is typically very low and thus multiple cells are assembled which forms a stack. One of the most important in a fuel cell power system’s is the fuel cell stacking. Office of energy efficiency & renewable energy(n.d.) states that it uses electrochemical processes in the fuel cell to create power in the form of direct current (DC). The output of a single fuel cell is less than 1 volt, which is inadequate for most applications. Therefor individual cells are connected in series which creates a stack. Usual stacks consist of a few hundred cells. The quantity of power generated by a fuel cell is determined by several parameters, including the fuel cell type, cell size, operating temperature, and the pressure of the gases fed to the cell.
Proton Exchange Membrane (PEM)
The fuel cell consists of a membrane that allows the protons of the hydrogen to pass through to the cathode side of cell. As the electrons cannot pass through the membrane they are thus forced through an external passage, which generates electricity.
As stated by Faghri et al (2005) proton exchange membrane fuel cells (PEMFC) primarily consist of three components, bipolar plates, gas diffusion layers and membrane electrode assemblies (MEA). The MEA itself consist of two electrodes with a proton exchange membrane between the electrodes. Oxygen from the air is reduced in the cathode and the hydrogen is oxidized in the anode. The hydrogen enters through the flow channel in the anode, then passes the gas diffusion layer before reaching the catalyst layer.
The reverse process occurs for the air, which is first introduced to the cathode channel before passing the gas diffusion layer and then reaching the catalyst layer.
An advantage of PEM fuel cells is their low operating temperature of around 60℃ (Nedstack, 2021). The start-up time can be as low as two minutes, making sure that the UPS battery do not have to run for a long time before the fuel cell system operate at full power. Nedstack also state that the low temperature is optimal to use for heating with residual heat from the fuel cell.
Table of contents :
1. INTRODUCTION
1.1. Background
1.2. Purpose/Aim
1.3. Research questions
1.4. Delimitation
2. METHOLOGY
2.1. Literature study
2.2. Calculations
3. THEORETICAL FRAMEWORK AND LITERATURE STUDY
3.1. Data center classification
3.2. Backup Power system
3.3. Diesel generator theory
3.3.1. Diesel storage
3.3.2. Diesel Price
3.3.3. Expected Lifetime
3.3.4. Diesel system Maintenance
3.4. Fuel Cells
3.4.1. Fuel Cell Function
3.4.2. Power Conditioners
3.4.3. Stacking of fuel cells
3.4.4. Proton Exchange Membrane (PEM)
3.4.5. Humidifiers
3.4.6. Cooling methods for PEMFC
3.4.6.1. LIQUID COOLING
3.4.6.2. PHASE CHANGE COOLING
3.4.7. Fuel Cell Design and Function
3.4.8. Existing Projects
3.4.9. Degradation and Lifetime
3.4.10. PEMFC UPS Maintenance
3.5. Hydrogen
3.5.1. Types of hydrogen
3.5.2. Hydrogen storage
3.5.3. Alkaline Water Electrolysis
3.5.4. Polymer Electrolyte Membrane Electrolysis
3.5.5. Solid Oxide Electrolysis Cells
3.5.6. H2 Market
3.6. Carbon trading systems
4. CURRENT STUDY
4.1. Diesel generator
4.2. Key Performance Indicators (KPI)
4.2.1. Capital Cost
4.2.2. Operating and Maintenance Cost
4.2.3. Payback time
4.2.4. Net Present Value
4.3. Data Collection
4.3.1. Diesel production cost
4.3.2. Fuel cell operating cost
4.3.3. Carbon Tax
4.4. Scenarios
4.4.1. Runtime
4.4.2. Fuel Cell Price
4.4.3. Hydrogen Price
4.4.4. Carbon Price
4.4.5. Diesel Price
4.4.6. Lifetime
5 RESULTS
5.1. System costs and emissions
5.2. Sensitivity analysis
5.2.1. Runtime
5.2.2. Fuel Cell Price
5.2.3. Hydrogen Price
5.2.4. Carbon Price
5.2.5. Diesel Price
5.2.6. Lifetime Analysis
6 DISCUSSION GÖR UNDERRUBRIKER
7 CONCLUSIONS
8 SUGGESTIONS FOR FURTHER WORK
REFERENCES
