BKCHAP13-2011 - Chapter 13 ENERGY STORAGE SYSTEMS 13.1...

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Chapter 13 ENERGY STORAGE SYSTEMS 13.1 Introduction Storing some form of energy that can be drawn upon at a later time to perform some useful operation is basically known as Energy storage . Storage of primary energy such as coal, oil, gas etc. is also a form of energy storage; however, the term ‘energy storage’ generally applies to secondary energy (e.g. electricity, secondary fuels such as hydrogen etc.) rather than to primary energy. Therefore, means of storing secondary energy in a readily recoverable form when the supply exceeds the demand for use at other times is known as energy storage . In contrast to fossil fuel and nuclear fuel based energy, the initial input power of renewable energy source is outside our control. The use of renewable energy supplies constitutes a diversion of a continuing natural flow of energy; there are problems in matching supply and demand in time domain, i.e. matching the rate at which energy is supplied and used. The mismatch varies with time, on scales of months (e.g. house heating in temperate climate), days (e.g. artificial lighting) and even seconds (e.g. starting motors). Renewable energy systems need energy storage to adopt the intermittent, seasonally and daily varying supply to the demand. There are a number of factors on the basis of which the performances of an energy storage system may be evaluated. The importance of a particular performance factor depends on the application at hand. Some of them become deciding factor for a particular application. Some important performance factors are discussed below. (i) Rate of energy storage / retrieval, MJ s -1 or response time of the system It is the maximum rate at which the energy can be stored-in and drawn-out of the storage system. It is very important in applications requiring absorption of repetitive pulses of energy. But it is difficult to estimate. (ii) Energy storage per unit volume, MJ m -3 It is also known as energy density. It is very important where space is prime consideration e.g. indoor applications. (iii) Energy storage per unit weight, MJ kg -1 This factor as well as the previous one is very important for portable storage systems. (iv) Efficiency
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The fraction of input energy recovered from the system for useful work. (v) Duration of storage The duration for which energy can be stored without significant losses. (vi) Installation cost of the energy storage system, $ per MJ (vii) Operation and maintenance cost, $ per MJ per year (viii) Monitoring, control and safety considerations (ix) Lifetime of energy storage system, years 13.2 Significance of Energy Storage 1. The effective utilization of intermittent and variable energy source such as solar, wind etc. often requires energy storage. 2. Optimal use of fuel cell in cogeneration requires energy storage.
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BKCHAP13-2011 - Chapter 13 ENERGY STORAGE SYSTEMS 13.1...

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