Today I am restating some definitions of terms, reflecting how my own understanding has changed over time.
Transactive Energy
Transactive Energy (TE) is the term for an energy balancing approach using economic techniques for dynamic balance of supply and demand within energy and power grids.
TE is a particular case of Transactive Resource Management which uses markets to allocate any commodity (resource) whose value is determined solely by its time of delivery. Transactive Resource Management was first described at the Xerox Palo Alto Research Center. The GridWise Olympic Peninsula Testbed Demonstration Project was the first transactive active energy field experiment in 2008.Transactive Energy was described by Edward Cazalet in a number of papers and talks culminating in the reference book “Transactive Energy: A Sustainable Business and Regulatory Model for Electricity” (Barrager & Cazalet, 2014).
Transactive techniques allow dynamic balance of supply and demand where energy is in surplus or shortage, in contrast to traditional techniques which address surplus less effectively. Transactive Energy (TE) is seen as a fundamental organizing principle of future smart grids.
Microgrids & Micromarkets
Microgrids are independent systems that manage the distribution of power. Microgrid components may supply, consume, or store electric power. TE can be paired with microgrids to make decisions about power management and distribution without constraining technology choice or technology evolution inside each microgrid component.Micro-markets require physical delivery of the product or service. Micro-grids allow (and in fact are defined by) the ability to shift energy and power within them. There is a useful symmetry of managing the balance of supply and demand in a micro-grid by means of a co-extensive micro-market.
Participants in more than one micro-grid must be able to deliver and receive the products bought and sold. North American markets typically distinguish between transmission (longer distances) and distribution (shorter distances, more end points) with different regulatory regimes. Micro-grids (composed or standalone) can be structured to allow avoidance of complex regulations designed for much larger scale enterprises.
Common Transactive Services
The interactions of Transactive Energy were defined in the Energy Interoperation Specification (OASIS, 2012). The Common Transactive Services (CTS) refers to a minimal set of standardized services originally developed as part of the NIST Transactive Energy Challenge.
The Market Code resource uses CTS-defined messages for all interactions between components. CTS defines a restricted profile of Energy Interoperation that can interoperate with each of the transactive systems within a microgrid. CTS includes minimal extensions and is at an architectural level appropriate to the semantics of all transactive systems minimized for local micromarkets, and able to enable decoupled evolution. A recent project of NIST and the Energy Mashup Lab made the first use of CTS. The Energy Mashup Lab (http://www.theenergymashuplab.org/) (EML). The Lab is a non-profit (501C3) whose purpose is the development and promulgation of microgrids through promoting open source software for TE based microgrids.
Cyber-Physical Systems
Cyber-physical systems (CPS) are systems built around co-engineered interacting networks of physical and computational (IT) components. The term CPS includes the overlapping technologies referred to as the Internet of Things (IoT), the Industrial Internet, and Operational Technology (OT). CPS applications in specific economic sectors are referred to with the terms smart manufacturing, smart transportation (including autonomous vehicles), smart healthcare, and smart energy. (NIST Cyber-Physical Systems Public Working Group , 2017).
Many CPS applications are inherently distributed and equipped with wire-bound or wireless communication facilities. When their components are largely autonomous, the organizing principle is coordination rather than control. A CPS providing critical services such as dynamic and prospective traffic safety, factory and process control, or healthcare needs to be highly dependable requiring the availability of reliability performance, availability, safety, and security.
Any consideration of CPS always includes the physical. Whatever software they run, their physical actions are constrained by physics: mass, momentum, chemistry, biology, and, for TE, electricity. When CPS are deployed in infrastructure, they will likely operate in place longer than typical IT systems. With long-life comes diversity; even if one built a CPS monoculture, with common ownership and a single vendor, the evolution of products and technology over time would lead to diversity of components.
This inevitable necessary internal diversity of components within a CPS rewards an abstract or service-oriented model for CPS integration. Service-Oriented Architectures (SOA) coordinate systems not by orchestrating processes, but by coordinating effects. For TE, one can understand this not as “turn off pump #3” but instead “use less power for 10 minutes”, not as “charge battery” but as “power is currently available”. This consideration points to the desirability of integrating CPS using abstract coordination such as CTS.
Many CPS are social systems. Autonomous cars drive to human chosen destinations. Autonomous domotic power systems must balance domestic services while they balance power and price. Even factory systems may respond to labor shifts and human-provided maintenance schedules. The social component means that few CPS can be “set-and-forget” after install, but instead must respond to and provide services to humans.