Skip to 0 minutes and 6 seconds In this lecture, we want to get an overview of different storage technologies. Also, we will take a closer look at some specific battery technologies to understand better why they have different technical characteristics and performance.
Skip to 0 minutes and 20 seconds Generally speaking, storage technologies can be categorised into 4 main groups: 1.Chemical 2. Mechanical 3. Electrical 4. and Electro-chemical. Chemical storage stores energy in a chemical which are in form of gaseous, liquid or solid and releases that energy through chemical reactions. Mechanical energy storage combines several storage principles. For example, it uses from the energy of water behind the dams in hydropower storage (PHS) and the volume and pressure of the air in a compressed air energy storage (CAES). Mechanical storage was traditionally the most utilised type of storage at a grid. Electrical energy storage stores electrons in an electrostatic field between two electrodes. The energy capacity of this storage group is limited but the reaction time is very fast.
Skip to 1 minute and 17 seconds Finally, Electrochemical storage stores chemical energy and converts that to electrical energy through electro-chemical reactions. Different available options for electrodes and electrolytes materials lead to different characteristics of these storage technologies. Battery storage technologies belong to this group. Now that we have learned about the main groups of storage technologies, let’s have a look at their different characteristics.
Skip to 1 minute and 45 seconds The main characteristics of storage technologies are the following: First, Energy storage capacity (kWh) which refers to the amount of energy that could be stored in a storage technology. Second, Energy density (kWh/kg) or power density (kW/kg) that reflect on the amount of energy or power per unit volume of the technology. This characteristic is particularly important for the application with restricted space. Third, charge and discharge rates (kW) define how fast energy can be charged or discharged. Fourth, response time refers to the time that is needed for a storage technology to respond. This is normally in terms of milliseconds to seconds, minutes, or even hours. Lifetime of a storage technology shows the potential number of years or cycles of a storage technology.
Skip to 2 minutes and 39 seconds Efficiency is the ratio of energy discharged by a storage technology to the energy needed to charge it at each cycle. It accounts for energy loss during each storage cycle. These characteristics determine the services that batteries can provide in the electricity industry. Characteristics such as energy or power density or lifetime affect whether a technology is suitable for a particular application or not. Now let’s have a closer look at battery technologies. As I said previously, battery technologies belong to the electrochemical storage group. Batteries are among the most deployed storage technologies in the electricity industry. This is because of their favourable technical characteristics.
Skip to 3 minutes and 23 seconds In this lecture, we will go through 3 specific storage technologies: Lithium-ion batteries, flow batteries and lead-acid batteries. Let’s start with, Lithium-ion (Li-ion) batteries. This battery has a cathode made of lithiated metal oxide and an anode made of graphitic carbon or intercalation compound. The electrolyte is a non-gaseous liquid which contains lithium salts. Li-ion move from the negative electrode to the positive electrode during discharge and back when charging. Li-ions are a good candidate for many applications. Nowadays li-ion batteries are used in most of the electric devices in our households. For example, they are in our mobile phones, toothbrush or laptops. Li-ion batteries are suitable for different applications because of their high energy density and short response time.
Skip to 4 minutes and 17 seconds Besides, the cost of Li-ion has been decreasing dramatically over the past years. On a negative side, Li-ion batteries’ lifetime is limited because they can degrade during each charge and discharge process. Li-ion batteries can also overheat in undesirable site conditions. It is interesting to mention that in 2013 the largest share of Li-ion batteries was utilised in the end-user segment, for example, in our mobile phones. But, this is changing and now the share of Li-ion batteries at grid or in mobility sector is on a rise. Now let’s have a look at Flow batteries. This battery technology consists of two liquid electrolytes. The electrolytes are separated using an ion selective membrane.
Skip to 5 minutes and 9 seconds During each charge and discharge the membrane allows selected ions to pass and complete chemical reactions. What is interesting about this technology is that this battery allows total decoupling of power and energy ratings. The power rate is determined by the active surface of the membrane and hydraulic pump management. The energy rating of flow batteries depends on the number of electrolytes and the size of the tanks. The storage capacity of flow batteries can be increased by simply utilising larger tanks for electrolytes. Flow battery has the potential to reach an infinite number of cycles. It does not impose any constraints on environment, health or safety and they mainly use abundant materials on earth.
Skip to 5 minutes and 58 seconds Given their long lifetime and the ability to decouple power and energy, flow batteries are suitable for services both requiring high power and energy. But flow batteries are not suitable for applications with space constraints due to their low energy densities. Besides, the cost of this battery is still high and shall be decreased in the coming years. Now let’s have a look at one of the oldest type of batteries, lead-acid battery. Lead-acid is a mature and fully developed battery. For this battery technology, there are advanced recycling facilities available. The lead-acid battery has a positive electrode that contains lead dioxide (PbO2) and a negative electrode that contains spongy lead (Pb).
Skip to 6 minutes and 42 seconds It stores energy through electro-chemical charge and discharge reactions that occur between the electrodes. Both electrodes are merged in an electrolyte of sulphuric acid which participates also in the charge and discharge reactions. The biggest issue associated with lead-acid is its low energy density and short lifetime. The lead-acid technology used to be utilised in many applications and services except small portable systems. But slowly the share of Li-ion batteries is becoming more dominant and overtaking the share of lead-acid battery in the market. Now that we learned about battery technologies, let’s also have a look at a competitive or you may say complementary storage technologies to get a broader view. Here we focus on supercapacitors. Supercapacitors are a form of electrical storage technology.
Skip to 7 minutes and 35 seconds They can have numerous charge and discharge cycles at high power. The short charging time, long life, lower need for maintenance and high round-trip efficiency create competitive advantages for this technology. On a negative side, supercapacitors have low energy density and their price is still higher than batteries. The technical features of supercapacitors make them suitable for short term and frequent services requiring high power discharge. For example, in the transport industry, supercapacitors could be utilised in electric vehicles for starting the engine. This is because starting an engine requires high power that can exhaust batteries fast and shorten their lifetime. Another interesting utilisation of supercapacitors has been seen for public transport. The public transport buses powered by supercapacitors are called Capa vehicles.
Skip to 8 minutes and 35 seconds These buses drive often in the same route. The Capa buses can be charged during each stop in about 30 seconds when the passengers are leaving or entering the bus. The short charging time, long lifetime and almost 95% round-trip efficiency make Capa vehicles competitive. We can already find Capa vehicles and have a ride on them in countries such as China and Germany. To conclude this lecture, I hope you have now a clearer view of different groups of storage technologies. I also hope you understood that storage technologies follow different principles and have varied technical characteristics. Unique characteristics of the storage technologies are what make them suitable only for specific applications and services.
Skip to 9 minutes and 21 seconds So, it is important to know and learn about different storage technologies in order to use them in a right place and in a right time.
A closer look at battery storage technologies
In this step, we will learn about different groups of energy storage technologies, in particular batteries.
We will take a closer look at 3 battery technologies and at supercapacitors to better understand the chemistry and basic principles of storage technologies. You will learn why batteries have different technical characteristics, and thereby different performance levels.