Balancing supply and demand in national energy systems with an even higher share of renewable production is an important challenge and a major issue in prospective studies. This critical need for flexibility can be met by existing or new flexible productions, storage technologies like lithium batteries or by demand-side management. Regarding the environmental impacts of PV, focusing only on its carbon footprint during the phase of fabrication is not enough. A higher share of PV in the production requires additional flexibilities and network infrastructures. Unlike the carbon footprint of PV which focuses on the manufacturing stage, these impacts are systemic: they depend on its interactions with the broader electricity system and on how it evolves over time under a range of technological, economic, and societal assumptions. It is required to scenarize and model interactions with the whole electricity system to evaluate these impacts.

We choose to focus our study on PV integrated to a residential building (an individual house) with different flexibility options: battery, demand-side flexibilities with electric vehicle charging, heating and cooling needs management. This is to limit the scope of our study and because incorporating PV generation and flexibilities at the distribution level offers several advantages, notably reducing stress on network infrastructure. The energy model of the building will be linked with an energy system planning optimization model (national scale of France) to assess the impacts of PV and flexibility integrated to a building on the decisions at the national scale. This model optimizes operational decisions like the flexible productions and storages charge and discharge as well as investment decision for new capacities. In particular, we expect to observe the increasing or decreasing needs in battery storage or flexible production at the national scale (fossil or decarbonized) that can be attributed to the building PV and flexibilities.

The building energy model is a simple power flow optimization model, a mixed-integer linear program. The use of a RC thermal model for the building allows to approximate the thermal needs of the building and to evaluate different heating or cooling demand flexibility scenarios. This model is made using the MORE-GAMS library. The national model is the open-source TiTAN model which is a multi-sectorial techno-economic model to plan the pathway of France to decarbonization until 2050, it is also an optimization model. This model includes assumptions regarding the evolution of the French energy system until 2050 defining a trajectory for both the evolution of the production mix and national demand. As a first approach, we observe the impact of variations of the residual demand simulated with the building model on the national model. The residual demand is defined as the total load minus inflexible generation. We also assess the level of flexibility required at the building scale to compensate for the imbalance introduced by PV generation. The objective function is the economic cost in both models. We test the sensitivity of the results to alternative scenarios with different electrical production mix (based on the reference scenarios of RTE) and level of acceptance of flexibilities influencing the total energy demand.