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Structure of MEDEAS-World model
MEDEAS-World model is a global, one region-aggregated economy-energy-environment model (or Integrated Assessment Model, IAM) which runs from 1995 to 2050.
MEDEAS-World model serves as framework for the development and evolution of the European model version, which is the core of the MEDEAS project.
MEDEAS-World model has been designed applying System Dynamics, which facilitates the integration of knowledge from different perspectives as well as the feedbacks from different subsystems.
The model, originally built in Vensim DSS software for Windows Version 6.4E (x32), is being translated to Python programming language (open source) - available from January 2018
MEDEAS-World model consists of a modular and flexible structure, where each module can be expanded/simplified/replaced by another version or submodel. The model is structured into 7 submodules:
- Economy: The economy of MEDEAS is modelled following a post-Keynesian approach assuming disequilibrium (i.e. non-clearing markets), demand-led growth and supply constraints. The economic structure is captured by the integration of IOA (35 industrial sectors and households).
- Energy: This module includes the renewable and non-renewable energy resources potentials and availability taking into account biophysical and temporal constraints. In total, 5 final fuels are considered (electricity, heat, solids, gases and liquids) and a diversity of energy technologies are modelled. A net energy approach has been followed.
- Infrastructures: Energy infrastructures represent the infrastructures of power plants to generate electricity and heat.
- Materials: Materials are required by the economy and MEDEAS especially tracks the material requirements for the construction and O&M of the energy infrastructures. The extraction demands are subsequently compared with the levels of available metrics of reserves and resources.
- Land Use: this is the less developed module of MEDEAS, and it mainly accounts for the land requirements of the RES energies.
- Climate Change: This module projects the climate change levels due to the GHG emissions generated by the human societies, which also feed-back through a damage function.
- and Social and Environmental Impacts Indicators: this module translates the “biophysical” results of the simulations into metrics related with social and environmental impacts. The objective of this module is to contextualize the implications for human societies in terms of well-being for each simulation.
The modules of economy and energy are the most extensive and reach the highest degree of disaggregation. Interrelations between the 7 modules: the main variables that connect the different modules are represented by arrows. Most modules have bi-directional linkages, excepting for the Land-use and Social and Environmental impacts indicators which mainly report outputs from the simulations without feed-backing to rest of the structure.
Overview of MEDEAS-World by modules and the modelled linkages between them
Novelties of MEDEAS-World in relation to the existing models in the literature
- Economic submodule following a post-Keynesian approach assuming disequilibrium (i.e. non-clearing markets), demand-led growth and supply constraints,
- Integration of Input-Output Matrices within a System Dynamics structure,
- Comprehensive analysis of the techno-sustainable potential of RES for electricity and heat generation,
- Consideration of geological availability of fossil fuel resources given stock and flow limits,
- Supply-demand closures model implementation. The energy shortage determines the feedback between the energy and the economic submodule,
- Estimations of potential mineral scarcity,
- Estimation of EROI of the system and feedback,
- The effects of climate change are feed-backed into energy consumption,
- Social and environmental impacts indicators which contextualize the implications for human societies in terms of well-being for each simulation.
This way, MEDEAS-World incorporates three limits to growth that are rather rarely considered in the literature: energy availability taking into account biophysical and temporal constraints, declining EROI levels and consistent climate change impacts.
How does the Model function?
For each time-period, households demand a certain amount of goods and services as given by the IOTs structure. This monetary demand is translated into final energy demand by fuel applying the final energy intensities by fuel and sector. The final energy demand by final fuel is confronted with the available final energy from the energy module.
The dynamic energy availability is given by stocks and flows limitations of non-renewable fuels –i.e. peak oil phenomena-, sustainable potential of renewables, realistic rhythms of technology deployment, etc. In the case that the final energy demands are lower than the final energy availability, the demand is fulfilled. If the opposite is true, the final demand adapts to the available final energy. In any case, the demand of the next time-period is estimated taking as reference the consumption in the previous time-period.
The consumption of final energy by final fuels is covered by a mix of technologies (infrastructures module), which derives in the consumption of primary energy. Special attention is devoted to the consideration in MEDEAS framework of those technologies which seem to be realistically available and with a positive net energy balance.
Material availability does not directly constrain the deployment of technologies given the uncertainty in the available metrics of reserves and resources. However, the model detect potential mineral scarcities.
The level of primary energy consumption by fuel translates into a certain level of GHG emissions. Positive emissions are absorbed by the atmosphere, leading to the worsening of climate change. A worse climate change feed-backs into the human societies through a certain level of unavoidable impacts.
The modules of land-use and social and environmental impacts indicators allow to account for the land requirements of the RES energies, as well as to contextualize the implications for human societies in terms of well-being for each simulation.
Limitations and use of the model
Despite the challenges encountered with the development of the model, there are still many limitations and uncertainties. Hence, the interpretation of the results must be done with caution. MEDEAS-World is not intended to predict the future, but rather to qualitatively guide the best options for the energy transition towards a low carbon economy. It is a tool to explore strategies, not specific policies, since the latter are applied at a different (reduced) political scale. The model obtained can still be modified and expanded, depending on the availability of new data or new information, but the current version provides a solid enough basis to serve as a framework for the European scale model.