From a structural perspective, an energy system is like any
system and is made up of a set of interacting component parts, located within an environment. These components derive from ideas found in
engineering and
economics. Taking a process view, an energy system "consists of an integrated set of technical and economic activities operating within a complex societal framework". The identification of the components and behaviors of an energy system depends on the circumstances, the purpose of the analysis, and the questions under investigation. The concept of an energy system is therefore an
abstraction which usually precedes some form of computer-based investigation, such as the construction and use of a suitable
energy model. Viewed in engineering terms, an energy system lends itself to representation as a
flow network: the
vertices map to engineering components like
power stations and
pipelines and the
edges map to the interfaces between these components. This approach allows collections of similar or adjacent components to be aggregated and treated as one to simplify the model. Once described thus, flow network algorithms, such as
minimum cost flow, may be applied. The components themselves can be treated as simple
dynamical systems in their own right.
Economic modeling Conversely, relatively pure economic modeling may adopt a sectoral approach with only limited engineering detail present. The sector and sub-sector categories published by the
International Energy Agency are often used as a basis for this analysis. A 2009 study of the UK residential energy sector contrasts the use of the technology-rich
Markal model with several UK sectoral housing stock models.
Data International
energy statistics are typically broken down by carrier, sector and sub-sector, and country.
Energy carriers ( energy products) are further classified as
primary energy and
secondary (or intermediate) energy and sometimes final (or end-use) energy. Published energy datasets are normally adjusted so that they are internally consistent, meaning that all energy stocks and flows must
balance. The IEA regularly publishes energy statistics and energy balances with varying levels of detail and cost and also offers mid-term projections based on this data. The notion of an energy carrier, as used in
energy economics, is distinct and different from the definition of
energy used in physics.
Scopes Energy systems can range in scope, from local, municipal, national, and regional, to global, depending on issues under investigation. Researchers may or may not include demand side measures within their definition of an energy system. The
Intergovernmental Panel on Climate Change (IPCC) does so, for instance, but covers these measures in separate chapters on transport, buildings, industry, and agriculture. Household consumption and investment decisions may also be included within the ambit of an energy system. Such considerations are not common because consumer behavior is difficult to characterize, but the trend is to include human factors in models. Household decision-taking may be represented using techniques from
bounded rationality and
agent-based behavior. The
American Association for the Advancement of Science (AAAS) specifically advocates that "more attention should be paid to incorporating behavioral considerations other than price- and income-driven behavior into economic models [of the energy system]". == Energy-services ==