Energy Storage Systems Lecture 3 - Mansoura University PDF

Electrical Engineering Department Faculty of Engineering Mansoura University Energy Storage Systems LEC. 3 Dr/ Mohamed Elgamal HYDROGEN STORAGE  Energy Storage Based on Hydrogen ❑ Hydrogen can be used for energy storage as energy carrier, due to its...

Electrical Engineering Department Faculty of Engineering Mansoura University Energy Storage Systems LEC. 3 Dr/ Mohamed Elgamal HYDROGEN STORAGE  Energy Storage Based on Hydrogen ❑ Hydrogen can be used for energy storage as energy carrier, due to its high energy density of 33 kWh/kg. This high value makes hydrogen a possible candidate for mid and long-term storage, as typically the so-called seasonal storage in the context of renewable energy sources (RES). ❑ Compared to other fuels, hydrogen contains 3 times more energy than diesel fuel, and 2.5 times more than natural gas. ❑ Hydrogen can be produced from electricity using electrolyzers, and the reverse transformation from hydrogen to electricity can be carried out using a fuel cell. ❑ However, hydrogen is difficult to store, due to its very low weight density. 1 kg of hydrogen needs a storage volume of 11 m3. ❑ Hydrogen is usually compressed at a high-pressure level of between 350 and 700 bar. ❑ Hydrogen is suitable for long-distance transmission. ❑ It is accountable for around 830 million tons of CO2 emissions per year due to traditional sources such as thermal and gas generating sources. ❑Hydrogen is considered a clean fuel that produces zero emissions during use (except for water vapor), if it is generated by RES. ❑But its production is currently neither clean nor sustainable because it is generated by fossil fuel-based sources. ❑In the future, water electrolysis powered by RES would be a clean way to produce Hydrogen. ❑At the current market cost, this is still considerably more expensive than the route from fossil sources such as gas. ❑ The next figure shows the different energy densities of important energy vectors such as hydrogen, natural gas, propane, diesel fuel, and ethanol. ❑ Typically, a powerful Li-ion battery appears with “only” 0.15 kWh/kg.  Various forms of hydrogen ❑ Three main techniques can be used for the volume reduction: 1. Storage of hydrogen as compressed gas (350–700 bar) 2. Storage of hydrogen in its liquid phase (-253°C) 3. Storage of hydrogen in a solid form (metallic hydride) or chemical form. where different metals can be used with hydrogen, such as, Mg, Al.  Various forms of hydrogen ❑ The energy needed to compress hydrogen to high pressure level corresponds to around 10%–15% of its energy content. ❑ For the liquid form of hydrogen, note that there is a high amount of energy needed to cool it down to −253°C. ❑ Liquid hydrogen requires a 64% higher amount of energy than that of compressed gas. ❑ Metal hydrides (such as MgH2) are one of the most common types of hydrogen chemical storage. ❑ Metal hydrides have the ability to store hydrogen at high densities that can exceed that of liquid hydrogen. ❑ But hydrogenation process requires high temperature and pressure. Hydrogen applications Hydrogen color: 1. Grey (polluting) 2. Blue (grey + carbon capture and storage) 3. Green (using renewable energy sources (RES)) Proton exchange membrane  Power-to-Power Storage System ❖ Power-to-power storage system based on hydrogen can be carried out using a water electrolyzer and a fuel cell for the intermediate conversions. In addition to these intermediate conversions, hydrogen and oxygen conditioning systems are needed to increase the energy density. ❖ The following figure shows the elementary structure of an ESS based on hydrogen. Between the electrolyzer and the storage reservoir, a hydrogen conditioning device is represented (CH2s), as well as between the storage reservoir and the fuel cell resource (CH2r). The oxygen path is represented in dotted line as the oxidation can be achieved using ambient air directly. For this purpose, an air compressor is represented (K).  Electrolysis of water ❖ Around 50% of hydrogen produced around the world is obtained from reforming of natural gas. ❖ The other 50% of hydrogen is produced from coal or oil. ❖ Electrolysis of water is a more expensive process and represents today only a few percent of the total hydrogen produced. ❖ However, electrolysis of water (or power-to-gas plants) allows converting of electric power into a chemical carrier characterized by a high specific energy. ❖ Electrolysis of water is a well-known process for producing high-purity hydrogen. ❖ An electrolyzer is a device for the chemical decomposition of water by circulation of an electric current. It comprises two electrodes, the anode and the cathode, separated by an electrolyte. ❖ The electrodes are connected to a DC current source (i.e., photovoltaic/solar generation) allowing the circulation of the current, and the electrolyte is the internal ionic conductive means. Electrolysis of water  Types of water electrolyzers 1. Alkaline Electrolysis (AE) The principle of electrolysis in an alkaline medium is based on the circulation of an electric current to produce oxygen and hydrogen. AE is a well-established technology, and its energy efficiency is about 70-80%. The electrodes are metallic, and they are separated by a ceramic membrane. AE demands an important quantity of electricity: around 4 kWh/m3 of hydrogen. AE operates at low temperatures such as 30–80 °C.  Types of water electrolyzers 2. Proton exchange membrane (PEM) electrolysis For the PEM electrolysis, a proton (H+, a positive electric charge +e, hydrogen ions) exchange membrane is used that serves as electrolyte and separator between the two electrodes. The electric power demand is similar to that for the alkaline electrolysis (4.5–7 kWh/m3 of hydrogen). PEM operates at lower temperatures such as 20–80° C. PEM has an energy efficiency of about 80-90%. PEM has a high rate of hydrogen production with a high purity of gases 99.99%.  Types of water electrolyzers 3. Solid oxide electrolysis (SOE) A new process of production of hydrogen is SOE or high- temperature electrolysis, where steam is injected on the cathode and carried out on the base of membrane (O2-, oxide ion, oxygen ions). For the electric power demand, SOE is indicated with a consumption of 3.2 kWh/m3 of hydrogen. SOE operates at high temperatures such as 500–850° C. SOE has a higher energy efficiency of about 90-100%. Fuel Cell Generation