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S2 Introduction

What is S2?

S2 is the short name for the EN 50491-12-2 standard for in building energy management. It is a protocol for the energy management of energy intensive devices found in the build environment, such as photovoltaic (PV) systems, electric vehicle (EV) chargers, batteries, (hybrid) heat pumps and white goods. It is specifically designed to utilize energy flexibility. It is built in such a way that it can work with any flexible device from any manufacturer, and that it would work for any energy management use case. It is not meant to replace existing protocols for energy management, but rather to provide a universal language for energy flexibility in the build environment.

What is energy flexibility?

Most energy intensive devices have some kind of comfort target. For example, an EV charger needs to make sure the car is sufficiently charged at a certain time, and a heat pump needs to make sure the room has the right temperature and needs to make sure the shower has hot water. However, when these devices consumer or produce energy typically has some flexibility. For example, as long as the car is sufficiently charged at the desired time, an EV charger might delay charging a while or might charge with less power. A heat pump might generate a bit more heat at some point, so it doesn't have to do it later. This flexibility in when a devices can consume or produce energy, without sacrificing the comfort targets is what we refer to as energy flexibility.

Why do we need energy flexibility?

TODO

Why do we need a common protocol for energy flexibility?

TODO

What is s2-ws-json?

S2 was designed as a semantic protocol, which can have multiple, mutually compatible, implementing protocols. Different devices might prefer a different form of communication. For example, you can have a version of S2 which uses bluetooth, and another version which uses KNX. These versions differ in the transport protocol they use, but typically also in the way they encode data. Since both protocols are based upon the same S2 specification, one S2 implementing protocol can easily be translated into the other version using a simple software adapter.

S2-ws-json is a protocol specification which implements the S2 protocol using the common web technologies WebSockets and JSON. S2-ws-json can be used for:

• in-building communication between device and energy management system using a wired (Ethernet) or wireless (Wi-Fi) network
• communication between a device in the building and an energy management system in the cloud
• communication between a device endpoint in the cloud with an energy management system in the cloud
• communication between a device endpoint in the cloud and an energy management system in the building