The purpose of Part B is to present the Smart Energy state-of-the-art research. To create a comprehensive overview, state-of-the-art research was gathered from a wide range of experts. Based on the expert input, numerous research areas have been described for the technical and non-technical aspects of Smart Energy and these include:
- Electricity grids, infrastructures and technologies - Thermal grids, infrastructures and technologies - Gas grids, infrastructures and technologies
- Cross-cutting interaction between the three energy sectors - Social, socio-economic and political dimension
Parts of the transport sector and the consuming and producing units have also been described. For example, the demand side of Smart Energy in housing, industry, etc.
The results from the review are presented below but firstly the state-of-the-art definition of Smart Energy is described.
2. State of the art definition Smart Energy Systems
The state-of-the-art definition of Smart Energy is presented here with the aim to clarify what Smart Energy encompasses. Smart Energy arises as a solution to the fact that the future energy system will rely on renewable energy resources such as wind and solar power. These resources do not contain large amounts of stored energy, but instead the energy from the wind, sun, waves and tides must be captured and used immediately. This is one of the key technological challenges facing energy systems in the future. The question is: Based on renewable energy how can the future energy system operate without the flexibility currently being provided by large amounts of stored energy in fossil fuels? While simultaneously providing affordable energy and utilising a sustainable level of the resources available. The solution will be to find new forms of flexibility within the energy system which are affordable and utilise renewable energy resources in an efficient manner. This is called a smart energy system or Smart Energy.
In recent years, a number of new terms and definitions of sub-energy systems and infrastructures have been promoted to define and describe new paradigms in the design of future energy systems such as Smart Grid [32], 4th generation district heating [33],Vehicle-2-Grid [34] and power to gas [35]. All these infrastructures are essential new contributions and represent an important shift in paradigm in the design of future renewableenergy strategies. However, they are also all sub-systems and sub-infrastructures which cannot be fullyunderstood or analysed if not properly placed in the context of the overall energy system. Moreover, theyare not always well defined and/or are defined differently by different institutions.
The issue of sub-systems versus overall energy systems is carefully analysed in [36] and [37] and are here referred to as the concept of smart energy systems. As opposed to, for instance, the Smart Grid concept, which takes a sole focus on the electricity sector, smart energy systems include the entire energy system in its approach to identifying suitable energy infrastructure designs and operation strategies. One main point is that in order to do a proper analysis of any Smart Grid infrastructure, one has to define the overall energy system in which the infrastructure should operate. Another main point is that different sub-sectors influence one another and one has to take such an influence into consideration if the best solutions are to be identified.
A smart energy system consists of new technologies and infrastructures which create new forms of flexibility, primarily in the ‘conversion’ stage of the energy system. This is achieved by transforming from a simple linear approach in today’s energy systems (i.e., fuel to conversion to end-use), to a more interconnected approach.
In simple terms, this means combining the electricity, thermal, and transport sectors so that the flexibility across these different areas can compensate for the lack of flexibility from renewable resources such as wind and solar. The smart energy system is defined in [38] and is illustrated in Figure 35 and Figure 36 and uses technologies such as:
Smart Electricity Grids to connect flexible electricity demands such as heat pumps and electric vehicles to the intermittent renewable resources such as wind and solar power.
Smart Thermal Grids (District Heating and Cooling) to connect the electricity and heating sectors. This enables the utilisation of thermal storage for creating additional flexibility and the recycling of heat losses in the energy system.
Smart Gas Grids to connect the electricity, heating, and transport sectors. This enables gas storage to be utilised for creating additional flexibility. If the gas is refined to a liquid fuel, then liquid fuel storages can also be utilised.
Figure 35: Smart energy system flow diagram [2,39,40]
Figure 36: Energy-flow-diagrams of the grids (a) and storages (b) in Smart Energy Systems[38]
In Figure 36 grids and storages in Smart Energy Systems are illustrated. By combining the electricity, thermal, and transport sectors, the grids and storages in these sectors can improve the energy system flexibility and compensate for the lack of flexibility from renewable resources such as wind and solar. In the three grids, the storage and connections between sectors is comprised of smart electricity grids, smart thermal grids and smart gas grids.
Smart electricity grids are electricity infrastructures that can intelligently integrate the actions of all users connected to it – generators, consumers and those that do both – in order to efficiently deliver sustainable, economic and secure electricity supplies.
Smart thermal grids are networks of pipes connecting the buildings in a neighbourhood, town centre or whole city, so that they can be served from centralised plants as well as from a number of distributed heating or cooling production units, including individual contributions from the connected buildings. _
Smart gas grids are gas infrastructures that can intelligently integrate the actions of all users connected to it – suppliers, consumers and those that do both – in order to efficiently deliver sustainable, economic and secure gas supplies and storage.
Based on these fundamental infrastructures, a Smart Energy System is a design in which smart Electricity, Thermal and Gas Grids are combined and coordinated to exploit synergies to achieve an optimal solution for each individual sector as well as for the overall energy system. Short and long term storage options, such as batteries and large thermal storages, as well as solid, gaseous and liquid storages are key components in 100% renewable energy systems and so are the infrastructures and grids that enable such storage.
The smart energy system concept described above was the first definition of Smart Energy on a system level encompassing all energy sectors. Other definitions of Smart Energy exist today; however, there is less research done on a system level for these definitions than has been done for the concept defined here. The definition of Smart Energy defined here should not be seen as an isolated research area but it is broad and encompasses a wide range of technological solutions and research areas which are described below.