Successful implementation of the energy transition requires more than just electricity from renewable sources. Sustainable power generators, smart grids and flexible electricity storage systems are equally important for success. Efficiency is an important factor in the interaction of all components. But how can a statement be made about what is efficient and what is not? And how can the efficiency of individual power generation technologies be measured and quantified? The efficiency factor provides information on this. What do you mean by efficiency? The following section provides answers to the question of what efficiency is all about. How it comes about and what it has to do with fuel cells. Fuel cells also have an efficiency factor. And, let us reveal at this point, they are particularly efficient when compared with conventional energy generators. But more about that later. Let’s start with what is probably the most important question: What is the efficiency of a fuel cell?
Efficiency in general makes the efficiency of technical systems comparable. For this purpose, it is given as a ratio or percentage. So the efficiency of a fuel cell has to be calculated? Yes, but don’t worry: In this context, no in-depth knowledge of mathematics is necessary. And the efficiency of a fuel cell is calculated in the same way as that of other units. A car engine, for example, has an average efficiency of about 0.2 or 20 percent.1 So the combustion engine converts only 20 percent of the 100 percent fuel used into locomotion energy. The remaining 80 percent is lost in the form of heat. Is an internal combustion engine efficient? It doesn’t look like it. A comparison sheds light on this. For example, with an electric motor. Vehicles with electric motors have efficiencies of 90 percent and sometimes even more.23 So the electric unit generates 0.9 kilowatts of mechanical drive power from one kilowatt of electrical power. As with the gasoline engine, the remaining 0.1 kilowatts are referred to as power loss and are released as heat.
How high are the efficiencies of fuel cells? A distinction must be made here. There are two definitions of fuel cell efficiency. For example, the energy efficiency of fuel cells is the ratio of the electrical energy obtained to the energy stored in the volume of fuel consumed (hydrogen, methanol). The ideal efficiency of fuel cells or the theoretical efficiency of fuel cells, on the other hand, indicates how much electrical energy can theoretically be used in relation to the total energy released. It is immediately obvious that we are talking about ideal conditions, such as may only be found in the laboratory. In practice, the ideal efficiency of fuel cells can hardly ever be achieved. However, it plays a more decisive role for research.
When looking for the efficiency of fuel cells, a further distinction is necessary. Namely, that of the type of unit. The most commonly used fuel cell technology or type is the polymer electrolyte fuel cell (proton exchange membrane fuel cell; PEMFC) versus the solid oxide fuel cell (SOFC). The electrical efficiency of the PEM fuel cell ranges from 32 percent to 37 percent.4 In contrast, the efficiency of the SOFC fuel cell ranges from 33 percent to 60 percent.5 Although the efficiency of this type of fuel cell is higher than that of the PEM fuel cell, the latter has longer life cycles. On average, they last ten years or more.6This is due to their comparatively lower operating temperature of 80°C.78 This makes the PEM fuel cell particularly interesting for mobile applications. SOFC units, on the other hand, are used more frequently in stationary applications. For example, for combined heat and power plants and micro combined heat and power plants. The EFOY JUPITER hydrogen fuel cell by SFC Energy is based on PEM technology. It covers high power ranges and provides reliable and durable environmentally friendly energy for a wide range of applications. Among other things, it functions as an emergency power generator in mobile phone masts.
So there is a suitable fuel cell solution for every application. And that’s a good thing. Because in the course of the ambitious climate protection goals of the Paris Climate Agreement, major challenges have to be overcome. Electromobility is therefore moving back into focus on the path to more sustainable concepts. As mentioned, fuel cells can also be used as energy generators for electric vehicles, in addition to numerous other areas of application. More precisely, this also involves the hydrogen fuel cell. The efficiency of a hydrogen fuel cell is also above average compared to conventional combustion engines. The efficiency of the fuel cell in a car is around 60 percent.9 This is almost three times that of the previously preferred internal combustion engine. With ranges of up to 700 kilometers, vehicles powered by fuel cells are also on a par with their gasoline and diesel counterparts. The disadvantages, however, are that the network of filling stations is not yet widely available and the production of the fuel hydrogen is still expensive.
What is the efficiency of hydrogen? What is the hydrogen fuel cell efficiency? To answer these questions, it should first be noted that although hydrogen is the most abundant element in the universe, it is not present in the earth’s crust like oil, for example. Accordingly, hydrogen cannot be easily mined like oil. On the other hand, hydrogen is comparatively easy to produce. In principle, it can be produced in any quantity, since it is contained in water. In principle, it can be produced by adding fossil fuels such as natural gas. This is a so-called reforming process. An alternative is electrolysis. In this process, water is broken down into its constituents hydrogen (H2) and oxygen (O2) with the aid of electricity. Electrolysis has an efficiency of 60 to 70 percent.1011 And energy is also lost when the hydrogen is converted into electricity. The efficiency of the fuel cell is 60 to 80 percent, depending on the application.12
What does this mean? Over the entire process from the generation of energy, its storage, possible transport and the renewed conversion of hydrogen into electricity, only about a quarter to a third arrives in the application.13 This point of criticism is often cited. However, it has nothing to do with the efficiency of the fuel cell or, in this case, the efficiency of the hydrogen fuel cell. In fact, this circumstance has no influence on the efficiency of the fuel cell. In addition, the issue recedes into the background in the case of so-called "green hydrogen". This is because this form of hydrogen is produced in a climate-neutral way. Only electricity from renewable sources is used in its production. For example, from wind and sun. Electrical energy is subsequently converted into chemical energy. Electricity can be stored. This storage option is an essential building block in the finalization of the energy transition. With electricity storage, energy is delivered to where it is needed. This makes the supply more decentralized.
Fuel cells do not necessarily rely on hydrogen as a fuel. Direct methanol fuel cells are just as much in demand. They are operated with methanol, which gives them their name. The efficiency of direct methanol fuel cells is also in the range of 40 percent. With the EFOY, EFOY Pro, EMILY, and JENNY, SFC Energy offers methanol fuel cells with high efficiencies, which are used by industrial as well as governmental organizations, e.g. for traffic control systems, measuring and weather stations, or civil surveillance technology. In the consumer sector, they are used in motor homes and boats. It is impressive to see how versatile fuel cells are. The efficiency of the fuel cell is just one of its many advantages.
12 Töpler, Johannes; Lehmann, Jochen (eds.): "Hydrogen and Fuel Cell – Technologies and Market Perspectives"; Springer-Verlag Berlin, Heidelberg 2014.