The Euro-Calliope model

Short overview

Calliope is an open-source energy modelling framework. It focuses on flexibility, high spatial and temporal resolution, the ability to execute many runs based on the same base model, and a clear separation of framework (code) and model (data). Its primary focus is on planning energy systems at scales ranging from urban districts to entire continents. In an optional operational mode it can also test a pre-defined system under different operational conditions.

Euro-Calliope is a freely available instance of the Calliope framework, which models the European electricity system at a high spatial resolution. It can be built on three spatial resolutions: on the continental level as a single location, on the national level with 34 locations, and on the regional level with 497 locations. On each node, renewable generation capacities (wind, solar, bioenergy) and balancing capacities (battery, hydrogen) can be built. In addition, hydro electricity and pumped hydro storage capacities can be built up to the extent to which they exist today. All capacities are used to satisfy electricity demand on all locations which is based on historic data. Locations are connected through transmission lines of unrestricted capacity. Using Calliope, the model is formulated as a linear optimisation problem with total monetary cost of all capacities as the minimisation objective. All elements of Euro-Calliope can be manipulated either by changing the configuration in config/default.yaml or by manipulating the build workflow before building the model.

The broader Calliope framework has been used in many European projects and features in several peer-reviewed publications aimed at supporting energy policies at the national scale. For instance: Francesco Lombardi, Matteo Vincenzo Rocco and Emanuela Colombo (2019). A multi-layer energy modelling methodology to assess the impact of heat-electricity integration strategies: the case of the residential cooking sector in Italy. Energy, doi: 10.1016/j.energy.2019.01.004.

Key features of the Euro-Calliope model

Euro-Calliope's key features are the ease of use, the flexibility to variable geographical and temporal resolutions, and the high degree of transparency and internal validation, in addition to a completely open-source and fully documented release.

Building a model is easy using Calliope's flexible text-based model definition format. Existing model instances, such as Euro-Calliope can be freely manipulated and adapted to the specific needs of the study of interest. This is a key point, because several of the features currently not implemented in the model (e.g. accounting for other emissions than CO2) might be included at need.

The existing Euro-Calliope model has very high spatial detail (up to NUTS3 geographical units across all Europe) and temporal resolution (1-hour timesteps for a full year). Moreover, such detail can be flexibily adapted, allowing to compromise at need between resolution and computational tractability.

Unlike the majority of models, Calliope's code features a full set of internal tests and checks that ensure code's consistency across releases and code developments. This significantly increases the users' trust in the model and in its results, as well as the scientific robustness of the latter.

Climate module & emissions granularity

Whilst not featuring direct integration with a climate module, Calliope allows for technology-specific accounting of direct and indirect emissions. As such, it is open to the implementation of any internationally-recognised emissions inventory. Moreover, the wide gallery of model instances for several different European countries, as well as for the whole EU-28, ensures already a full and up-to-date database of technology-specific emissions on which the user can rely.

Socioeconomic dimensions

Socioeconomic dimensions are not explicitly captured by energy models, and Euro-Calliope is no exception.

Mitigation/adaptation measures and technologies

Whilst any mitigation or adaptation measure related to the energy sector can be virtually included in the model at need, the basic implementation of Euro-Calliope features key mitigation technologies, such as Direct Air Capture (DAC) in combination with methanation of green hydrogn, for the production of carbon-neutral methane to be injected in existing gas grids. In addition, the model includes bioenergy power plants, which can be easily equipped with CCS technology (if need be), leading to BECCS.

Economic rationale and model solution

The model finds the energy system configuration which minimises total (investmet + operation) annualised costs. The optimisation is performed over a 1 year horizon, for 1-hour timesteps (i.e. 8760 total timesptes). Technologies lifetime is accounted for in the annualisation of their fixed costs. This assumes that the energy sector "actors" implicit in the model behave rationally and with perfect foresight of subsequent events. Such actors include: power plants owners, aggregators of residential distributed loads (heat pumps, electric vehicles), grid operators, etc.

As an example, in each timestep the modell will have to satisfy the demand for any carrier (electricity, gas, hydrogen, etc.) at the minimum cost. However, this also needs to take into account the demand of the subsequent timesteps. For instance, the use of stored energy to meet demand might be the least-cost option in the timestep, but it may be preserved for subsequent timestep in which the model knows (thanks to its perfect foresight) that the same energy will be needed more.

As anticipated, the implict actors in the model have perfect foresight of the future. However, it is possible to re-run any energy system configuration, obtained as the cost-optimal to meet a given demand scenario, in the so-called "operation" mode. In such mode, conceived to stres-test the operational feasibility of any configuration, the actors do not have full perfect foresight. Rather, the model operates based on a rolling horizon, in which actors have knowledge only of the subsequent 48 h (with the number of hours being a customisable parameter).

Key parameters

Key scenario assumptions for Euro-Calliope include energy technology characteristics (e.g. fixed and variable costs, efficiency, direct emissions); resource timeseries, such as wind, solar and hydroelectric timeseries; demand timeseries for each carrier; and capacity expansion maximum potential per technology (i.e. how many additional GW of a given technology can be installed at each location), if available.

Key scenario results (outputs) from the Euro-Calliope model include the cost-optimal energy system configuration and the cost-optimal hourly dispatch of energy (or any other carrier) within the latter. It is worth noting that the resulting energy system configuration can be a green field result, if assuming that no existing capacity is kept in operation, or a brown field one, in which the capacity expands starting from the current one. The outcomes of the model depend on the quality of the abovementioned parameters, and sensitivity analysis is always envisaged to complement the results.

Policy questions and SDGs

Key policies that can be addressed

Several types of policies can be assessed by Euro-Calliope Emissions-related policies It is possible to impose a limit (carbon budget) on cumulative yearly emissions, as well as to modulate the budget across different energy sectors (e.g. 100% carbon-neutral power generation, 80% heat generation, etc.). It is also possible to include CO2 emissions in the objective formulation such that the minimisation of cost is weighted with the minimisation of CO2 emissions, both on a yearly and on a hourly basis. This is equivalent to assigning a price to CO2 emissions. Energy production policies It is possible to define a large variety of energy policies, such as the imposure of a certain share of renewables or biofuels in either energy generation or installed capacity. As before, this can be modulated across differnt sectors and carriers with a high detail Land use policies It is possible to limit the total amount of land occupied in any one location, even at the subnational level, if land-use values are defined for each energy technology. Or, as for CO2 emissions, it is possible to give an additional price to such land occupation and make it feature in the objective function.

Implications for other SDGs

The model can provide insights about the impact of alternative feasible energy system configurations on a number of SDGs. Clearly on SDG7, in terms of renewable penetration, use of bioenergy, etc., but also on SDGs related to climate (SDG13) and potentially to others (e.g. health) if additional emission metrics are included.

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