ESSIM

ESSIM is an energy system model simulating energy balances over time and across scales. Refer to https://multimodelling.readthedocs.io/en/latest/energy_models/ESSIM/index.html for more overall information regarding the model.

General model information

General model information questions were asked regarding basic information, model versions, and point of contact for questions. The ESSIM model is developed and maintained by TNO.

Questions to ask	Answers/Explanation
Model name	ESSIM
Model owner	TNO
Model Developer	TNO
The latest model version/date
The model version used in this project
Organization	TNO
Individual

A second set of questions was asked regarding whether the model is type or token, the intended purpose of the model, and the level of decision that the model aims to support. We understand that the model can be categorized as a token model as this represents a small part of the energy system. The model’s intended purpose is to simulate network balancing and its effects in an interconnected hybrid system. Long-term planning aspects include future scenario investigation or studies. In the medium term, the model calculates optimal schedule of flexible producers and the effects of this schedule on emissions, costs, load on the network, etc.

Questions to ask	Answers/Explanation
Is the model a token model? If so, give illustration(s).	A small part of the energy system is described.
Is the model a type model? If so, give illustration(s).
Briefly describe the intended purpose of the model	1. Energy balances over time and across scales. 2. Simulates network balancing and the effects thereof, in an interconnected hybrid system.
Strategic - long-term planning; what do we want?	Future scenario investigation/studies
Tactical - medium-term; how do we approach this?	The model calculates optimal schedule of flexible producers and the effects of this schedule on emissions, costs, load on the network, etc.
Operational - short-term; regular/ day-to-day operations?

Typical questions about the model include dimensioning and balance of any hybrid system over the whole year. Similarly, questions can be asked about shortage or excess of any particular energy carrier, interactions between them, effects of adding storage, or emissions from different producers.

The model can be used to model the behavior of an aggregator (the role in the energy system, aggregating flex, dealing on markets, etc.). One of the important limitations of the model is a lack of representation of full-scale interactions within an energy system. The model has been used as a model orchestrator between multiple lower-level infrastructure models.

Questions to ask	Answers/Explanation
What are typical types of questions that can be asked to the model? provide examples of such questions	1. Is my energy system well-dimensioned and in balance during the whole year? 2. During what periods of the year do I have excess or shortage of energy, and for what energy carrier? 3. How do the different energy carriers interact with each other? 4. What is the load on the transport infrastructure over the year, and how often does overloading happen, and to what extent? 5. What is the total CO2 emission for the simulated system, and how is CO2 emission distributed over the different producers? 6. What are the effects of adding storage?
What are the strengths of this model? What is unique?	It can be used to model the behavior of an aggregator (the role in the energy system, aggregating flex, dealing on markets).
What are the important limitations of the model?	It does not represent full-scale energy system interactions.
Cases/examples where the model was used for its intended purpose	It has been used as a model orchestrator between multiple lower-level infrastructure models; Additional comments/remarks: 1. ESSIM acts as the connection between the energy carrier models (basically responsible for all ‘conversion assets’). 2. It orchestrates and simulates the behavior of the conversion.
Cases/examples where the model was not used for its intended purpose; are there any examples of model abuse or misuse?

The next set of questions is related to model documentation, accessibility, and type. The model documentation is complete and is available online in English. The Application Programming Interfaces (APIs) are online. The model is static, deterministic, and discrete.

Questions to ask	Answers/Explanation
Is the model documentation complete?	No
Is the documentation accessible? If so, how?	Yes, online https://essim-documentation.readthedocs.io/en/latest/
Is the documentation in English?	Yes
Does the model have a GUI? If so, how to access it?
Does the model have an Application Programming Interface (API) ? If so, how to access it?	Yes, APIs are also online. https://essim-documentation.readthedocs.io/en/latest/essim_api/index.html
Is the model static or dynamic?	Static Additional comments/remarks: ESSIM simulates a certain period of time with a specific resolution (so a simulation of a year on an hourly basis). Most of the time, the system description doesn’t change (the hourly values in the profiles are the things that change).
Is the model continuous or discrete?	discrete
Is the model stochastic or deterministic?	Deterministic
Is it an optimization model? If so, what type of algorithms it uses?	No

The next set of questions are regarding the modeling paradigm, implementation environment, and license. The model applies multiple formalisms, such as graph/network-based, non-linear functions, etc. Multiple general-purpose programming languages, such as Python, JAVA, etc., are used. No license is required to run the model; however, permission is required from the model owner.

Questions to ask	Answers/Explanation
What modeling paradigm or formalism does the model use?	Graph/network-based, code is object-oriented, heavily data-driven, assets dynamics are non-linear functions, etc.
Is it implemented in a General purpose programming language?	1. ESSIM is implemented in JAVA. Some extensions are written in Python (KPI modules) 2. The internal component uses the NATS message bus interface, other projects use MQTT, and others use Rabbit MQ.
Does it use a modeling/Simulation environment/package?	No
Is it implemented in a spreadsheet?
Is any license required to run the model?	No license is required. Permission is required from the model owner, however.

Model content

A preliminary set of model content questions were related to energy system integration and scope. The model represents an integrated energy system. Though, the user has to define and scope them. Essential elements and concepts included in the model are energy carriers, production, conversion, transport, and storage. The model focuses on flexibility in energy and time for different technology options.

Questions to ask	Answers/Explanation
Does the model represent an integrated energy system?	Yes The user has to define and scope them, though.
What important elements and concepts are included in the model?	Describes energy carriers, energy production, consumption, conversion, transport, and storage.
What elements and concepts are currently not included in the model, but in your opinion, those shall be included?
Specific attention to flexibility options: What type of flexibility options are included in the model?	Yes, it focuses on flexibility in energy and time for different technology options, for example, gas heaters (energy flexible, time inflexible), batteries (energy and time flexible), etc.

The next set of content-related questions included scale and resolution. There is no specific spatial scale of the model. The model has an annual temporal scale. The model has no specific spatial resolution. The input file can have spatial information included. Temporal resolution is an hour.

Questions to ask	Answers/Explanation
What spatial (or geospatial) scale does the model have?	Not specific
What temporal (or time) scale does the model have?	Annual
Spatial resolution	Not specific Additional comments/remarks: ESSIM can be used to model the energy system of a single house or the world’s energy balance. The ESDL that goes into ESSIM contains geographical information 99% of the time, but ESSIM doesn’t do anything with this information.
Temporal resolution	hourly

The next set of questions is related to model assumptions, model inputs, parameters, and outputs, and data sources related to the model. The model follows an internal algorithm to determine the order of solving various commodity networks. The model follows flexibility-based demand-supply matching algorithm that uses the costs of energy production as a means to grade the desirability of producers. The model does not fully enforce energy or mass conservation, which might be contested by others. The input and output file format is Energy System Description Language (ESDL). Important model inputs are household demand and supply, related technology options, energy network infrastructure, large-scale energy supply options, etc. Important model outputs are production/consumption time series at each node, total production, total costs, imports/exports, full-load hours, etc.

Questions to ask	Answers/Explanation
What critical assumptions does the model have?	1. The model follows an algorithm to determine the order of solving various commodity networks. 2. A flexibility-based demand-supply matching algorithm that uses costs of energy production as a means to grade the desirability of producers. 3. A tree-based transport network solver that calculates the load on various transport elements based on the demand-supply solution determined above.
Which ones are likely to be contested by others? Why?	1. Infrastructure cycles/loops are “randomly” cut to make a directed tree. 2. Energy conservation is not fully enforced (conversion losses can be ignored or made explicit) Transport losses are not considered Mass conservation is not enforced
What is/are the model input format(s)?	ESDL
What is/are the model output format(s)?	ESDL
What are the important model inputs?	Topological city household demand and supply, related technology options, energy network infrastructure, large-scale energy supply options, etc.
What important parameters does the model have?	Parameters related to the inputs mentioned above Additional comments/remarks: There are no internal parameters in the model. All necessary data is in the input data files.
What are the important model outputs?	1. Mainly time-series (hourly profiles for consumption/production) at each node 2. CO2 output profiles (for each producer or each energy carrier) 3. KPI modules (metrics: energy neutrality, total (local) production/consumption, total import/export, full load hours, etc.)
What are the data sources used by the model?
Any data that can be shared? If so, what and how to access them?

Continuing with the model content, there were questions regarding verification, validation, and test, and uncertainty descriptions. There is no specific test coverage of the model. Units and data consistency checks are held manually. The results and inputs are validated by experts. Over-production and system failure are other method of validating and verifying.

Questions to ask	Answers/Explanation
Can you comment on the test coverage of the model?	There is no specific comment on the test coverage of the model.
What is being verified, validated, or tested in the model?	1. Unit and data consistency checks, including conversion units - manually Results consistency
What methods are used for the model verification, validation, and testing, if any?	Experts validation Overproduction and system failure
Can you comment on the uncertainty in model parameters?
Can you comment on the uncertainty in model input?
Can you comment on the uncertainty in the model structure?