These Use Cases play a central role in the project, as through their application in diverse situations, the WHY Toolkit and models will be tested and validated.

The design of all Use Cases has been greatly benefited from the active engagement of stakeholders and end-users, including policy makers, public authorities, and utilities. This has taken various forms, depending on the specificities of each Use Case ranging from the organisation of (online and in-person) workshop to interviews, focus groups on online questionnaires. In all cases, stakeholders helped to
define the most important aspects, questions, and policy-relevant insights to be assessed in each Use Case.

In this Use Case the aim is to develop an implementation concept for a residential neighbourhood, and in case the decision is that the Plus-Energy-District is feasible, with a positive energy balance for both electricity and heat and to subsequently implement it. n this use case, the WHY toolkit can demonstrate one of its main strengths, namely the finely granulated simulation of household consumption, and thus provide the data basis for a more detailed examination of the consumption side

Energy retailers want to know consumer demand with high precision in order to help optimize the purchase of energy, reduce risks and associated penalties. In this Use Case, the Spanish energy cooperative Goiener will perform better estimations and load demand
forecasts using the WHY Toolkit, considering not only the climatic factors but also other non-climatic factors that are difficult to simulate on a massive level.

Energy communities can be instrumental in changing the energy landscape and enabling the clean energy transition at the local and citizen level. Energy communities can bring increased flexibility and resilience to the main energy grid, and they can also be seen as socially innovative enterprises, engaging in economic activity that lowers energy costs while providing financial returns to the local community.

The European Use Case explores the impact of EU-wide and national policies on achieving the EU goals on climate change mitigation and energy efficiency. This will be implemented by re-assessing EE policies and measures consistent with the pathway to climate neutrality by 2050, using the improved WHY modelling capabilities.

In the Global Context use case the WHY Toolkit is linked to the integrated assessment model TIAM-ECN and PROMETHEUS, a global ESM, based on the widely used TIMES model generator, in which the world is disaggregated in 36 distinct regions. TIAM-ECN has been used in several research projects (e.g. TRANSRISK, LIMITS, CLIMACAP) to investigate long-term energy and climate scenarios in diverse regions in the world including the EU.

The WHY tools developed will be validated in 5 very different Use Cases that ranges from a small microgrid to a global model. Every Use Case has a unique combination of geographic scope, temporal framework and policy objectives. Use Cases share a similar use context. The basic idea to develop WHY use cases is that a person (modeler) that is interested in defining a set of interventions (like a policy maker, a think tank, a manager of funds or a practitioner at an energy provider or Energy community) wanted to assess the final impact in the energy system before introducing a certain policy on energy system changes for the residential areas.

To support policy decisions, the modeler is going to support such policies by using the WHY results before the policy is implemented. First, this modeler will define the scenario:

• the geographic and temporal scale,
• the interventions to consider,
• the households segments that are going to be affected
• and any other information needed to run de model.

Then, the modeler retrieves all of this information and configures both the Energy System Model (ESM)  and the WHY Toolkit.

Finally, the modeler runs the simulation. The simulations are iterative. First, the energy system model asks the WHY Toolkit for an estimation of the load profile of the residential segments under the set of interventions defined in the scenarios and provides them a price signal. Then, the WHY Toolkit performs an estimation and provides to the ESM with a load profile. Next, the ESM performs the simulation of the rest of the energy system and finally, it is advance the time step and repeated until reached the end of the simulation. At this point, the modeler will retrieve the results of the simulations in terms of a series of KPIs for the final and intermediate status of the system.