Solar Energy Storage Methods 72a3q

Solar Energy Storage Methods

Abstract Developing efficient and inexpensive energy storage devices is as important as developing new sources of energy. Energy storage can reduce the time between energy supply and energy demand, thereby playing a vital role in energy conservation. Also to reduce burden on earth and reduce greenhouse gases it is better to use solar energy which is an abundant source of energy that can be harnessed in many ways .With proper use of solar capture technology, we can harvest this untapped energy supply to fulfill the world energy demand. The storage system is being designed to store sufficient thermal energy to ensure that energy is always available on demand. This paper deals with storage of solar thermal energy in conventional way and in materials undergoing phase changes. PCMs, which include salt hydrates, paraffin’s, nonparaffin, and eutectics of inorganic, are discussed. Heat storage in phase change materials (PCM) has an advantage of compactness and heat supply at constant temperature. INTRODUCTION Energy storage is a key issue to be addressed to allow intermittent energy sources, typically renewable sources, to match energy supply with demand. Energy storage became a dominant factor in economic development with the widespread introduction of electricity and refined chemical fuels There are numerous storage technologies that are capable of storing energy in various forms including kinetic energy, chemical solutions, magnetic fields, or other novel approaches. Importance of energy storage: Thrust for Renewable Energy sources Variable outputs Energy Buffering Methods to store and extract solar energy Molten salt batteries Molten salt batteries are a class of primary cell and secondary cell high temperature electric battery that use molten salts as an electrolyte. They offer both a higher energy density and higher power density by means of a high conductivity molten salt electrolyte.These features make rechargeable molten salt batteries a promising technology for powering electric vehicles. Operating temperatures of 400°C to 700°C however bring problems of thermal management and safety. Primary batteries are the most common and are designed as single use batteries, to be discarded or recycled after they run out .

Some of the limitations posed by secondary batteries are limited life, limited power capability, low energy-efficiency, and disposal concerns. Electric grid storage Grid energy storage lets electric energy producers send excess electricity over the electricity transmission grid to temporary electricity storage sites that become energy producers when electricity demand is greater, optimizing the production by storing off-peak power for use during peak times. Photovoltaic s can avoid the necessity of having battery storage by connecting to the grid, which effectively becomes a giant battery. Solar pond A solar pond is simply a pool of water, which collects and stores solar energy. It contains layers of salt solutions with increasing concentration (and therefore density) to a certain depth, below which the solution has a uniform high salt concentration. When sunlight is absorbed, the density gradient prevents heat in the lower layers from moving upwards by convection and leaving the pond. This means that the temperature at the bottom of the pond will rise to over 90°C while the temperature at the top of the pond is usually around 30°C. The heat trapped in the salty bottom layer can be used for many different purposes, such as the heating of buildings or industrial hot water or to drive a turbine for generating electricity. With the Use of Rankine Cycle Power Generation System energy can be extracted from solar pond. e.g. Bhuj solar pond in India (1993) Completed in 1993 after a sustained collaborative effort by TERI, the Gujarat Energy Development Agency, and the GDDC (Gujarat Dairy Development Corporation Ltd). The solar pond functioned effortlessly till the year 2000 when severe financial losses crippled GDDC. Phase change materials Thermal energy can be stored in well-insulated fluids or solids. It can be generally stored as latent heat-by virtue of latent heat of change of phase of medium. In this the temperature of the medium remains more or less constant since it undergoes a phase transformation. Phase change storages with higher energy densities are more attractive for small storage. Compared to different storage techniques for solar space heating and hot water production applications the operating temperature range for PCM is large, depending on the choice of material Types of PCM’S The PCMs fall in three categories:

o Salt hydrates o Paraffin's o Non paraffin organics Heat Storage Capacities: Non paraffin organics 125-200 kJ/dm3 Salt hydrates 250 -400 kJ/dm3 Comparing one method of energy storage with another is pointless. The reason - None of them are optimal for all purposes. Different storage methods differ in capacity and maximum usable storage time. Applications Applications of Salt gradient solar pond Greenhouse heating, Process heat in dairy plants,Desalination,Power generation, Agricultural applications, Drying crops, Heating livestock, buildings, Building space heating and absorption cooling

The main applications for PCMs are when space restrictions limit larger thermal storage units in direct gain or sunspace ive solar systems. Phase change materials may be used in solar domestic hot water heating or ive solar space heating systems. Conclusion Reliable and affordable energy storage is a prerequisite for using renewable energy. Energy storage therefore has a pivotal role in the future. Energy storage is the most promising technology currently available to meet the ever increasing demand for energy.