Smart Energy For The Zero Emission Century

Smart Energy Home Promo
ICON -Eco Circle

We need energy flexibility to overcome major challenges in the energy transition in the best possible way.

S2 is a communication standard for energy flexibility in homes and buildings, designed to keep you comfortable.

You can jump to the Github or Whitepaper immediately, or keep reading for an introduction in the S2 Standard.

FLEXCON2024 - Green Transparent Background

SAVE THE DATE! Want to see S2 in action? Join us at the upcoming FLEXCON2024 conference in Amsterdam 26-27 September.

1_Simple House Flexible battery

What is energy flexibility?

Energy flexibility is the ability to alter the use of energy without a significant impact on comfort. PV systems, EV chargers, batteries, and (hybrid) heat pumps are very suitable for this purpose, especially when they are combined in a smart approach.


Some examples of energy flexibility:

  • As long as an electric vehicle is sufficiently charged an EV charger might delay charging to a later moment.

  • A heat pump might generate a bit more heat at some point, so it needs less energy later.

Why do we need energy flexibility, and a standard for it?

2_5 Time More Energy

We need energy flexibility to overcome major challenges in the energy transition.

Take for example all-electric homes: they can easily generate 5 x as much energy flows compared to conventional homes.

Electrification of transportation, heating, and industry is also surging. This boosts electricity demand and peak load, stressing the grid. Despite growing sustainable electricity production, the energy system faces challenges meeting rising demand and supply. Grid upgrades lag, forcing grid operators to seek alternative solutions.

Using the flexibility within the energy system, where users adjust consumption or store energy, can ease grid strain. It also allows us to integrate more renewable energy into our power grid.  However, lacking a standard for managing millions of devices complicates this and raises costs. A standardized approach to energy flexibility is crucial.

S2 is such a standard. S2 is a communication standard for energy flexibility and energy management. S2 helps to simplify the use of energy flexibility of smart devices in homes and buildings. 

S2 works with energy usage characteristics, which makes it a particularly future-proof standard. It gives prominence to user convenience and manufacturer choices.

The S2 standard                                                               

3_Intro S2

In S2, there are two entities that communicate with each other. The Customer Energy Manager (CEM), which orchestrates the flexibility provided by the appliances in the building. 

Based on optimisation targets and additional external information and incentives, it decides how to use that flexibility by sending instructions to these devices. These instructions are sent by using the S2 communication protocol.

The CEM does not connect directly to the devices, but to the Resource Managers (RM) of these devices. This Resource Manager communicates the energy flexibility information of the device to the Customer Energy Manager (CEM), and only that. Resource Managers can be integrated into the smart appliance, but they can also work remotely, for example in a cloud service.

"In S2, the Resource Manager is concerned with how a flexible device can behave.

The Customer Energy Manager is concerned with why it should behave a certain way."

Focus on Energy Management

S2 focuses on the exchange of standardised energy flexibility information between energy management systems (EMS) and energy equipment in buildings. It has been a conscious decision not to extend that scope to include other functionalities such as device configuration and remote maintenance functionality.

S2 works with eight so-called 'Energy Flexibility Patterns', rather than relying on specific use cases for each type of device. Limiting the scope to energy flexibility makes it easy to implement and maintain S2. Because the energy management capabilities are generic, it is easy to add devices in the future, making it energy transition-proof.




Artboard 42

S2 benefits for manufacturers (OEM’s)

S2 is not meant to replace existing protocols, but rather to provide a universal language for energy flexibility.

S2 offers freedom and security for manufacturers of Energy Smart Appliances. 

Both the Customer Energy Managers (CEM) and Resource Managers (RM) can be integrated into the (firmware of the) smart energy devices, but can also run alongside them, for example in cloud services, in the meter box or smart meters, or on smart home controllers such as Apple TV. 

This flexibility also means that phased implementation is possible: start with the cloud and integrate later in the firmware.

CEM system

The S2 approach also ensures the integrity of OEM devices and OEM business approaches. S2 does not overwrite or interfere with internal logic and security of devices, nor does it require other OEM information such as runtime, or maintenance information.

S2 is not a replacement for existing OEM protocols. S2 is modelled in SAREF, which is a shared model of consensus that facilitates the matching of existing assets in the smart applications domain. S2 can also be easily integrated with other protocols.

Resource managers can be created for all kinds of smart energy devices, such as EV chargers, heat pumps, inverters, batteries / storage devices, white goods, as well as swimming pools and commercial cold stores.

S2 is published as an official European standard under the reference EN 50491-12-2. The management of S2 is open and well managed by the standardisation body CENELEC.

The S2 consortium has published a position paper calling for future-proof and interoperable demand-side flexibility that serves the energy transition. You can find it on the ECOS website or download it directly below
demand-side flexibility Icon

Navigating the future of renewable energy demand

A call for future-proof and interoperable demandside flexibility that serves the energy transition

S2 Consortium

The S2 consortium is working hard on the adoption of S2 by manufacturers, utilities, grid operators and other parties in the energy system.

Github Resources

ICON - GitHub Cat White

S2 Implementation in JSON

The S2 standard describes what information should be exchanged between devices and the CEM, but not how this information can be exchanged. This approach allows different communication technologies for different situations that are mutual compatible. This makes sure that S2 is independent from communication technologies and makes it future proof to communication technologies that might become obsolete in a few years.

The s2-ws-json project describes how S2 should be used when using the current popular technologies for internet and in-home communication: WebSockets and JSON. It describes in detail how to connect devices, how data is exchanged and how this data exchange is secured. The schemas defined in this project allow developers to generate their own S2 implementation for their favorite programming language.


S2 analyzer backend

The S2-analyser is a software solution to test the communication between devices and energy management systems that implement the s2-ws-json specification. The software inspects the communication, validates all messages for correctness and common mistakes, and makes the message exchange insightful for developers. This facilitates error finding and debugging and improves working with S2.


S2 python implementation

Based on the s2-ws-json project, everybody can create an S2 implementation using their own favorite technology. However, developers that use the popular Python language can use this project as a starting point for their implementation. S2-python makes sure an S2-based connection is created, checks messages automatically for possible errors and gives the developer feedback in a Python-friendly manner.