Recent Advances in Renewable Energy

To date, concentrated solar power is the only type of renewable energy that allows for long term energy storage over sufficiently long periods of time and at large scales to completely eliminate the intermittent nature of the solar resource. It is a proven and mature technology as shown by its widespread deployment. However, cost reduction is essential in order to compete with alternative sources. Existing technologies are described in detail highlighting improvement opportunities. Increasing the overall solar-to-electric energy conversion efficiency by developing new power conversion pathways and looking for alternative markets for Concentrated Solar Power such as desalination, process heat, enhanced oil recovery or hybridization appear to be the best options for the future.

Modern societies are called upon to face the consequences of their persistence on using fossil fuels. Energy resources shortage and environment pollution urge us to find alternative advanced technologies for viable and sustainable growth. Thermal Energy Storage (TES) systems supported by renewable energy sources (mainly solar energy) can be viewed as an effective means of achieving the aforementioned goal. This study reviews the available TES systems. In this context, sensible TES systems which utilize liquid and solid storage media and their applications are presented. Furthermore, the usage of ice and other solid-liquid phase change materials in latent heat storage systems is investigated in terms of materials, applications and future trends. Finally, the utilization of thermochemical reactions in TES systems is presented.

Solar energy is one of the most promising renewable energy sources. Building sector is one of the most suitable candidates for utilizing this energy source because of its abundance. More specifically, solar energy is able to be used for electricity production, as well as for covering the heating and the cooling loads of the buildings. In this chapter, new and innovative ideas about the adoption of solar energy systems in buildings are presented. Simple and low cost solar collectors which can produce heating in low and medium temperatures levels are analyzed. Emphasis is given in the utilization of Phase Change Materials, as well as in the utilization of solar assisted heat pumps. Moreover, innovative passive heating systems, as Trombe wall are presented with detail.

Due to the necessity for the reduction of the utilization of fossil fuels, the share of renewable energy sources is expected to further increase in the near future. Energy from biomass, alternatively defined as bioenergy, already provides the majority of the renewable energy worldwide. In this chapter, the use of solid, liquid and gaseous biomass as an energy source is presented, with particular emphasis being given to biogas production by anaerobic digestion. The chapter is divided into six parts: In the first, a brief description of the global energy consumption and the expected trends are given. In the second part, the advantages and disadvantages associated with the use of biomass as an energy source are discussed. Furthermore, the sources of biomass (forestry, agriculture residues and energy crops, waste), along with its properties are investigated. In the third part, potential fields for the utilization of the three forms of biomass (solid, liquid and gaseous) for energy production are described, along with ways for biomass upgrading. In the fourth part, the process of Anaerobic Digestion is described in detail. Anaerobic Digestion is a popular method of biological treatment that is suitable for many types of wastes (sewage sludge produced by wastewater treatment, animal waste, the organic matter of municipal solid waste) and leads to biogas production. Then, a common model for the modeling of the process is presented. ADM1 (Anaerobic Digestion Model No. 1) is applied on two wastewater treatment plants operating in Stockholm and in Athens. In the fifth part, the factors that mostly affect Anaerobic Digestion are discussed and the effect of selected parameters (temperature, digester volume, inflow rate and number of digestion stages) is practically examined with the use of ADM1. In the sixth part, the modification of ADM1 to enable its use on the treatment of olivemill waste (wastewater and solid waste) is presented. The model is then applied to the combined treatment of wastewater and solid waste of a small rural olive-mill. Finally, in the Appendices, the suggested values of ADM1 parameters and the effect of selected parameters of the model in biogas quantity and energy content are presented, along with the suggested modification of the model parameters for its application on olivemill waste.

The exploitation of wind energy dates thousands of years of history, where societies used wind as solution for many of their daily applications. During the last century, globally electricity needs were covered almost exclusively from fossil-fuel based technologies resulting in a negative impact on the environment. Since 1980, wind energy applications acquired great interest from the global community in order to cope with security of energy supply and environmental issues. This study presents the evolution of wind energy throughout the last 30 years, along with its prospects for covering a considerable percentage of the future global electrical demand. Furthermore, available information concerning the major wind energy markets has been analysed and revealed in general the existing trends of wind energy for the next years to come. In this context, technology and financial aspects along with environmental issues arising from wind power projects’ implementation are investigated in order to provide all the necessary data for acquiring an integrated view of the wind energy future.

Given the environmental concerns over the use of fossil fuels, the search for non-fossil energy sources to cover the increasing energy demands is gathering a lot of interest. Hydrogen fuel, being CO2 neutral and non-pollutant, is one of these sources. The main scope of this chapter is to provide a comprehensive review of hydrogen production and storage technologies. Firstly, various hydrogen production methods are discussed, including the utilization of various primary sources. Apart from the conventional natural gas and coal based hydrogen production, more recent technologies, including solar, photobiologic electrolysis and supercritical water gasification are presented. In the second part of the chapter, hydrogen gaseous and liquid storage methods are discussed. Regarding gaseous hydrogen storage, several types of commercially available steel and composite tanks are presented. Furthermore, the option of storage via glass microspheres is briefly presented. For liquid hydrogen storage, two of the most common options are analyzed: cryogenic liquid hydrogen and NaBH4 solutions. In the last section of the chapter, the most recent advances in hydrogen storage in solid materials and its storage via conversion to other fuels are discussed with an overview of the challenges of these options.

The main objective of this chapter is to provide a fully and comprehensive introduction to geothermal systems that exploit normal (or swallow) geothermal energy including construction and designing guidelines. The necessity to decrease power consumption and consequently cost led to the integration of these systems to cover heating, cooling and domestic hot water loads in domestic or even industrial facilities. Basic operational and construction guidelines concerning all possible geothermal plants (closed or open loop) are provided along with representing drawings. The chapter is divided into various sections focusing on certain issues. It begins with basic geological information regarding the ability of the subsoil to absorb or supply heat via the integrated heat exchanger. Subsequently, a summary on the operation of heat pumps in general and the advantages of geothermal pumps is provided. Then, the two main categories of geothermal loops are analyzed: closed loop horizontal or vertical geothermal exchangers and open loop system installations. Finally, the proposed methodology to follow when such a system should be designed is discussed, containing cost elements issues of such systems.

Renewable Energy Systems are designed to take benefit of the outdoor natural conditions. Their efficiency and long life depend on them (air flow, air velocity, solar radiation, temperature etc.). Continuous monitoring of outdoor natural qualities is essential for optimizing operation, preventing small and large scale damages and adapting design according local conditions. Common requirement for such applications is saving data for a long period of time and/or the ability to send them on line. This is why most of the instrumentation presented in this chapter is based on transducers: Flow transducers, temperature transducers, solar radiation transducers, humidity transducers, etc.