Abstract
In this Chapter, a hybrid Photovoltaic-Fuel Cell (PV-FC) generation system employing an electrolyser for hydrogen generation is designed and simulated. The system is applicable for remote areas or isolated loads. This system has been simulated via a developed general dynamic mathematical model which analytically describes the electric subsystems. Some interesting simulation results are presented in this chapter. Specific attention is paid to the investigation of the dynamic analysis of the photovoltaic, fuel cell, and electrolyser system at the connection. The objective of this study is to evaluate the performance of an autonomous stationary power generation and thermal coupling a PV array and a storage system for hydrogen, consisting of an electrolyser, a storage unit of gas, and a fuel cell of high temperature. Hydrogen is the only means that stores electricity. Stationary applications of a few kilowatts are evaluated by numerical simulation in MATLAB/SIMULINK.
TopIntroduction
The development and use of renewable energy have experienced strong growth in recent years. In the near future, all sustainable energy system will be based on the rational use of traditional sources and increased use of renewable energy. Naturally decentralized, it is interesting to exploit the place of consumption, transforming it directly into electricity as needed. Decentralized electricity production by renewable energy sources provides greater security of supply for consumers while respecting the environment. However, the intermittency of these sources requires the use of multi sources that enable a continuous electricity production.
The depletion of fossil fuel resources on a worldwide basis has necessitated an urgent search for alternative energy sources to meet to the present day demands. Alternative energy resources, such as solar and wind energies, are clean, inexhaustible and environment friendly potential resources of renewable energy options. It is prudent that neither a standalone solar nor a wind energy system can provide a continuous supply of energy due to seasonal and periodical variations (Borowy et. al., 1994, 1996; Celik, 2002).
To solve these drawbacks conventional battery storage has been used. But batteries can store a limited amount of power for a short period of time. For long term storage electrical power produced by PV arrays can be converted into hydrogen using an electrolyser for later use in fuel cell. So these conventional batteries can be replaced with fuel cells as non-polluting and high efficiency storage devices (Esmaeili et. al., 2012).
A management system is designed for a PV-Fuel cell hybrid energy system to manage the power flow between the system components in order to satisfy the load requirements (El-Shatter et. al., 2006). A simple and economic control with DC-DC converter is used for maximum power point tracking and hence maximum power extraction from the wind turbine and photovoltaic arrays. In order to insure continuous power flow a fuel cell was also proposed in this chapter (Das et. al., 2005).
The main objectives of this study are to investigate and develop an autonomous system of clean energy to power of about 5 kW (Figure 1) (Ulleberg, 1998). Using hydrogen as the sole energy storage medium. This PV-FC is solar hydrogen systems without batteries. In this chapter, a methodology to design each configuration analytically is proposed. It is found that panels solar photovoltaic modules in parallel and in series, each of 5 kWP along with a 5 kW electrolyser and a 5 kW SOFC fuel cell unit. The integration of solar photovoltaic, electrolyser and fuel cell system with greenhouse can pave the way for sustainable cultivation in self-sustained greenhouses even in remote areas where probability of getting conventional grid connected electricity at a steady. Excess energy, after meeting the requirements of the greenhouse during peak sunshine hours, is supplied to the electrolyser bank to generate hydrogen gas, which is consumed by the fuel cell stacks to support the power requirement during energy-deficit hours. The simulation modeling approach is presented in the next section. The results are discussed and an optimization is introduced.
Figure 1. Concept of an autonomous system of energy based on hydrogen technology
TopBackground
Hybrid Renewable Energy Systems (HRES) are becoming popular for remote area power generation applications due to advances in renewable energy technologies and subsequent rise in prices of petroleum products. A hybrid energy system usually consists of two or more renewable energy sources used together to provide increased system efficiency as well as greater balance in energy supply (Deshmukh et al., 2008).
Key Terms in this Chapter
Hybrid Renewable Energy Systems (HRES): Hybrid power systems combine two or more energy conversion devices, or two or more fuels for the same device, that when integrated, overcome limitations inherent in either. Hybrid systems can address limitations in terms of fuel flexibility, efficiency, reliability, emissions and/or economics.
Photovoltaics (PV): Is a method of generating electrical power by converting solar radiation into direct current electricity using semiconductors that exhibit the photovoltaic effect. Photovoltaic power generation employs solar panels composed of a number of solar cells containing a photovoltaic material. Materials presently used for photovoltaics include monocrystalline silicon, polycrystalline silicon, amorphous silicon, cadmium telluride, and copper indium gallium selenide/sulfide.
Buck Converter: Is a step-down DC to DC converter. Its design is similar to the step-up boost converter, and like the boost converter it is a switched-mode power supply that uses two switches (a transistor and a diode), an inductor and a capacitor. Converts DC to AC power by switching the DC input voltage (or current) in a pre-determined sequence so as to generate AC voltage (or current) output.
PV Batteries: Batteries accumulate excess energy created by your PV system and store it to be used at night or when there is no other energy input. Batteries can discharge rapidly and yield more current that the charging source can produce by itself, so pumps or motors can be run intermittently.
Maximum Power Point Tracking: Frequently referred to as MPPT, is an electronic system that operates the Photovoltaic (PV) modules in a manner that allows the modules to produce all the power they are capable of. MPPT is not a mechanical tracking system that “physically moves” the modules to make them point more directly at the sun. MPPT is a fully electronic system that varies the electrical operating point of the modules so that the modules are able to deliver maximum available power. Additional power harvested from the modules is then made available as increased battery charge current. MPPT can be used in conjunction with a mechanical tracking system, but the two systems are completely different.
Mathematical Model: Is a description of a system using mathematical concepts and language. The process of developing a mathematical model is termed mathematical modelling. Mathematical models can take many forms, including but not limited to dynamical systems, statistical models, differential equations, or game theoretic models. A model may help to explain a system and to study the effects of different components, and to make predictions about behaviour.
Electrolysis of Water: Is the decomposition of water (H 2 O) into oxygen (O 2 ) and hydrogen gas (H 2 ) due to an electric current being passed through the water.
Methods of Hydrogen Storage: For subsequent use span many approaches, including high pressures, cryogenics, and chemical compounds that reversibly release H 2 upon heating. Underground hydrogen storage is useful to provide grid energy storage for intermittent energy sources, like wind power, as well as providing fuel for transportation, particularly for ships and airplanes.
Solid Oxide Fuel Cell (SOFC): Is an electrochemical conversion device that produces electricity directly from oxidizing a fuel. Fuel cells are characterized by their electrolyte material; the SOFC has a solid oxide or ceramic, electrolyte. Advantages of this class of fuel cells include high efficiency, long-term stability, fuel flexibility, low emissions, and relatively low cost.