۱- Introduction

۲- Heat storage material type based TES systems

۳- Storage cycle frequency based TES systems

۴- Delivery scheme based TES systems

۵- Heat storage mechanism based TES systems

۶- Operating temperature range based TES systems

۷- Design and performance parameters for TES systems

۸- Operational issues management in TES systems

۹- Conclusions

References

Abstract

Due to humanity’s huge scale of thermal energy consumption, any improvements in thermal energy management practices can significantly benefit the society. One key function in thermal energy management is thermal energy storage (TES). Following aspects of TES are presented in this review: (1) wide scope of thermal energy storage field is discussed. Role of TES in the contexts of different thermal energy sources and how TES unnecessitates fossil fuel burning are explained. Solar power generation, building thermal comfort and other niche applications of TES are presented. (2) Insight into classes of TES storage materials with details like their physical properties, cost, operational performance and suitability to application requirements is provided. (3) Insight into types of TES systems is presented. TES systems are classified using different types of criteria. Most common TES systems like seasonal TES systems, CSP plant TES systems, TES systems of domestic solar thermal applications, heat and cold storages of building HVAC systems etc are described. Active TES systems like thermocline, packed bed, fluidized bed, moving bed etc are analyzed. Passive TES systems implemented in buildings, textiles, automobiles etc are presented. TES systems operating in cold, low, medium and high temperature ranges are listed. Design parameters, operational issues and cost model of TES systems are discussed.

Introduction

Discovery of fire is regarded as the most important milestone in the evolution of mankind. Simple activity like cooking food is one of the first applications that humans discovered for thermal energy. Thermal energy was readily available in nature even before human existence. Our bodies require a minimum ambient temperature to be alive. Due to such realities of our life, a strong need for thermal energy exists. Freely available solar thermal energy from sun helps to maintain the favorable ambient thermal condition needed to sustain our lives on earth. However the availability of solar radiation varies across different locations on the planet resulting in extreme cold ambient conditions in the high latitude regions to extreme hot ambient conditions near the equator. Since humans are expanding their presence across the planet into places with such extreme local conditions, need for thermal energy management arises. Moreover our modern lifestyle has created plenty of new applications for thermal energy which further increase the demand for thermal energy. Today our main energy consumption forms at the usereend are electricity, heat and mechanical work. International Energy Association (IEA) publishes the usereend energy consumption details as ‘Final consumption’. The usereend energy forms like electricity, heat and mechanical work are produced from energy conversion of multiple energy sources which include both natural sources and fuel sources. International Energy Association (IEA) [1] publishes the energy source details as ‘Primary energy supply’. International Energy Association (IEA) in its world energy statistics report for year 2014 estimated that, world’s annual ‘total primary energy supply’ is 573 EJ (13,699 million tonnes of oil equivalent) and the annual ‘total final consumption’ is 394 EJ (9425 million tonnes of oil equivalent). During the conversion process from ‘Primary energy supply’ to ‘Final consumption’ certain amount of energy (z31%) is lost which is huge due to the sheer amount of energy involved. World is now facing challenges in meeting its energy demand through burning fuels. Rapid burning of fossil fuels results in emission of greenhouse gases like CO2. Elevated level of CO2 in the atmosphere is contributing to climate warming. This has serious consequences like rising sea levels due to melting of ice in the polar region. World realized the importance of renewability of energy sources during the energy crisis of the 1970s. Fossil fuel reserves are limited in supply and are nonerenewable. Therefore there is an urgent need to conserve energy and move towards clean and renewable energy sources. Thermal energy storage is a key function enabling energy conservation across all major thermal energy sources, although each thermal energy source has its own unique context.