Department of Mechanical and Aerospace Engineering AN EXPERIMENTAL INVESTIGATION OF AN ELECTRICAL STORAGE HEATER IN THE CONTEXT OF STORAGE TECHNOLOGIES Author: Ignacio Becerril Romero Supervisor: Dr Paul Strachan A thesis submitted in partial fulfilment for the requirement of the degree Master of Science Sustainable Engineering: Renewable Energy Systems and the Environment 2013 Copyright Declaration This thesis is the result of the author’s original research. It has been composed by the author and has not been previously submitted for examination which has led to the award of a degree. The copyright of this thesis belongs to the author under the terms of the United Kingdom Copyright Acts as qualified by University of Strathclyde Regulation 3.50. Due acknowledgement must always be made of the use of any material contained in, or derived from, this thesis. Signed: Ignacio Becerril Romero Date: 22nd September 2013 Abstract This project is divided in two different parts: an investigation of energy storage and an experimental analysis of a storage heater. The “20 20 20” targets dictate that the share of renewables in EU’s energy consumption has to be increased to a 20% by the year 2020 (European Commission, 2012). More flexibility needs to be added to the grid in order to integrate the increasing amount of variable generation. Energy storage is especially well suited to respond to this challenge (Teller et al., 2013). However, the role that storage is to play in the future grid needs to be evaluated meticulously. A detailed investigation of the services that storage can provide to the grid and of the main storage technologies is carried out in this thesis. The analysis shows that storage is a very valuable element of the energy grid since it can provide numerous services at the same time. It plays a fundamental role within the integration of renewables and is particularly useful combined with wind power to avoid curtailment and minimum generation constrains. In addition, it is realised that only a combination of different storage technologies can deliver all the services that energy storage will need to provide in the future. State-of-the-art storage heaters can provide demand side management (DSM) services in small isolated grids with significant wind generation. The charging periods of the heater can be scheduled by the utility provider based on wind output and demand forecasts. At the same time, storage heaters can also provide frequency response. However, they present some features that may affect their performance. No relevant publications were found about the topic, so an experimental analysis of the thermophysical properties of the storage medium and of the temperature distribution inside the core of the heater is performed. The first shows that the specific heat and conductivity of the storage material are higher than expected with values of CP = 1.58 J/g·K and k = 4.3 W/m·K. It is concluded that the storage material presents good qualities for heat storage. On the other hand, the temperature distribution is shown to be very inhomogeneous during a standard charging cycle. Nevertheless, the method used overestimates the average temperature of the core of the heater by a 50% showing that a 3D approach is necessary to study absolute temperatures. Likewise, the data obtained are insufficient to study the performance of the heater as DSM and, due to the lack of time and equipment, this is left as future work. cxcxcxcxcxcxcxcxcxcxc i Acknowledgements I would like to express my gratitude to the following: My supervisor, Dr Paul Strachan, for his kind support, encouragement and guidance over the course of the project. My ‘second supervisor’, Katalin Svehla, for her kindness, support, guidance, and for all the effort she put into having a new insulation panel delivered. Chris Cameron, for securing the heater to the wall, cutting samples from the bricks and, in general, for his help and approachability. Fiona Sillars, for performing the analysis of the samples and giving me valuable information about the results and the experimental procedure. Jim Doherty, for his continuous good mood and his efficient work ordering and supplying everything I needed throughout the project. A very special thanks goes to John Redgate for his priceless help. The technical part of this project would have been impossible without him. He has fixed the heater every time anything failed (something that, unfortunately, has happened too often in this project), made lots of thermocouples and installed new controls in the heater in addition to ‘a long etcetera’; and he has always done it with a smile in his face. I would also like to thank: My parents, José Luis and Elda, for supporting me in everything I do and giving me the opportunity to study this MSc. My grandmothers, Aurora and Ángeles, for their unconditional love; and, although they are not here anymore, I also want to thank my grandfathers, Pepe y Pascual, for all the love they gave me and all the things I learnt from them. The rest of my family and my friends in Spain. I could not have got so far without them. My friends in Glasgow for making this year a wonderful experience. My dear friend Preet, for sharing so many late nights with me at the Livingstone Tower and for his help and support in the last days of this project. And, finally, my girlfriend, Anita, for her love and for dealing with my stress and bad mood during this stressful project and for trying to help and support me always in every way she can. ii Contents 1. Introduction ............................................................................................................... 1 2. Energy Storage .......................................................................................................... 4 2.1 Applications of Energy Storage within the Energy Grid ................................... 4 2.1.1 Introduction ................................................................................................ 4 2.1.2 Electric Supply Applications ...................................................................... 5 2.1.3 Ancillary Services Applications/Frequency Response Services ................ 5 2.1.4 Grid System Applications ........................................................................... 9 2.1.5 End User Applications .............................................................................. 11 2.1.6 Renewables Integration Applications ....................................................... 13 2.2 Storage and Wind Power ................................................................................. 17 2.2.1 Introduction .............................................................................................. 17 2.2.2 Wind uncertainty ...................................................................................... 18 2.2.3 Minimum generation constrains ............................................................... 19 2.3 Location of storage .......................................................................................... 20 2.3.1 Separated generation and storage ............................................................. 21 2.3.2 Co-location of generation and storage ...................................................... 22 2.3.3 Bottom line ............................................................................................... 23 2.4 Energy Storage Technologies .......................................................................... 24 2.4.1 Introduction .............................................................................................. 24 2.4.2 Mechanical energy storage ....................................................................... 24 2.4.3 Chemical energy storage .......................................................................... 31 2.4.4 Electrochemical energy storage - Batteries and supercapacitors.............. 33 2.5 Conclusions ...................................................................................................... 39 2.6 Thermal Energy Storage (TES) ....................................................................... 41 2.6.1 Introduction .............................................................................................. 41 iii 2.6.2 Sensible heat ............................................................................................. 42 2.6.3 Latent heat ................................................................................................ 44 2.6.4 Thermo-chemical storage ......................................................................... 47 2.6.5 Applications .............................................................................................. 48 2.6.6 Conclusions .............................................................................................. 49 2.7 Summary .......................................................................................................... 52 3. Storage Heaters ....................................................................................................... 54 3.1 Storage heater basics ........................................................................................ 54 3.1.1 Introduction .............................................................................................. 54 3.1.2 Structure, types and operation of storage heaters ..................................... 56 3.2 Storage heaters as demand side management (DSM) ...................................... 60 3.2.1 Demand side management .......................................................................