Medeas vs Times & Leap

Summary of models’ cross-comparison and qualitative evaluation

Introduction

The MEDEAS project developed and subsequently uses a suite of computer models, which are characterised by different geographical focusses, scopes and aims. It was therefore important to undertake a qualitative comparison to highlight strengths and weaknesses for each of them on which the project can strategically build. The models being compared and presented here are: MEDEAS-World, TIMES-Austria and LEAP-Bulgaria. The qualitative comparison involved a literature review of the models and a survey that was distributed to the modelling teams part of the MEDEAS project (i.e. UVa, AEA and BSERC). The survey was aimed at gathering information about different characteristics of the models and helped to develop the comparison tables presented here.

Definitions and descriptions of the models

MEDEAS-World is a global aggregated energy-economy-environment simulation model (or Integrated Assessment Model, IAM) that has been developed as part of the MEDEAS project. Through the development and simulation of transition pathways (i.e. scenarios) to a decarbonised energy system and their requirements, the model aims at informing policy decisions. It is developed using a System Dynamics (SD) approach, which facilitates the integration of interdisciplinary subsystems and dynamics, as well as interactions between them, therefore allowing capture of non-linearities in the energy system. MEDEAS-World is a hybrid top-down and bottom-up model that combines the two different approaches, i.e. macroeconomic perspectives on the energy system and partial equilibriums, respectively.

TIMES-Austria is a model specification of the TIMES model generator that is focussed on Austria. The model uses linear optimisation to produce a least-cost energy system, optimised according to a number of constraints. The main output from TIMES are energy system configurations, which meet the end-use energy service demands at least cost while also adhering to various constraints set by the user (e.g. 80% emissions reduction, 40% renewable electricity penetration). TIMES-Austria was developed to create medium to long-term scenarios for the Austrian energy system to answer questions such as: Is the target feasible? If yes, at what cost?

LEAP-Bulgaria is one of the applications of the LEAP model generator, with structure and data tailored to the Bulgarian energy system. Similarly to the other models studied here, LEAP-Bulgaria focusses on scenario analysis, as part of which the model simulates future scenarios under different assumptions and dynamics. The main and default output from LEAP-Bulgaria are ‘energy balances’, which is the standard format followed by the International Energy Agency and several national energy agencies. In LEAP-Bulgaria many dynamics can be run in ‘historical’ or ‘simulation’ mode: in the former the user specifies key data for use in the model, therefore bypassing some of the model’s dynamics. In the latter, dynamics are simulated endogenously.

Comparison tables

The tables below summarise some of the general differences between the three (types of) models that are used in the MEDEAS project. In particular the tables specify types and purpose of the models and the sectors included in the simulations.

Table X : Types of model (for definitions refer to Connolly et al. (2010, p. 1063))

Table X : Purpose of the models. The definitions/examples provided are based on van Beeck (2000), Natalini (2016) and Epstein (2008).

Table X : Sectors included in the models.

It is interesting to note that each model has a slightly different combination type, and purpose. In particular, MEDEAS-World clearly has a stronger research-oriented policy-information focus, as opposed to TIMES-Austria and LEAP-Bulgaria, which are more focussed on policy. All three models include similar sectors, although with different levels of aggregation, with MEDEAS-World having the most disaggregated simulated economy.

Results from the qualitative comparison

The main difference between MEDEAS-World and the other models used in the project is the innovative approach implemented in the development of MEDEAS-World, especially as regards the economic theories upon which its economic module is built, the environmental and biophysical constraints introduced and, most importantly, the connection between the two. 

Indeed, the qualitative comparison showed that the models differ greatly in terms of modelling approach, economic assumptions, complexity, account for social and environmental issues, biophysical limits, flexibility and access. In particular, MEDEAS-World shows a clear step forward in the comprehensiveness of the simulations by not assuming clearing markets (i.e. not imposing general equilibrium) in the economics module, by including the evaluation of the effects of climate change on the economy and the effects of (economic) development on depletion of natural resources, all in the context of simulations for the transition to a decarbonised energy system. Although other general equilibrium models like TIMES-Austria and LEAP-Bulgaria do not account for these dynamics, these models still provide invaluable information for infrastructural, investment and capacity requirements for the transition, especially when specified at the national level. 

TIMES-Austria and LEAP-Bulgaria being more focussed on the components of the energy system and in optimising, minimising or maximising some sort of energy function undoubtedly put more emphasis on detailed simulations, e.g. by providing results at higher time resolutions and, usually, for smaller geographical areas. MEDEAS-World is instead focussed on simulating dynamics and interactions within the global energy system and its dependencies and interactions with other social-environmental systems (e.g. climate change, GDP). In addition, MEDEAS-World is the only model amongst those used in the project that can simulate non-linearities in the system. Therefore, MEDEAS-World is the only model that is able to provide a comprehensive, cross-system perspective to support planning for the necessary energy transition to a decarbonised energy system.

One clear distinction between MEDEAS-World and TIMES-Austria and LEAP-Bulgaria is the approach used to simulate limited availability of natural resources, whereby in MEDEAS-World energy is not “magically” generated within the energy system, but it is converted into a usable form by technologies and extracted from a limited amount of resources available. The other two models do not account for the limited availability of fossil fuels.

The different modelling techniques that each model analysed here implements also greatly influences their use: TIMES-Austria and LEAP-Bulgaria as linear optimisation models are most suited to develop scenarios to hypothesise what a specific part of the energy system will look like in the future, with a clear focus on infrastructure and finding optimal results. MEDEAS-World as an SD model is instead most suited to explore broader, more aggregated, long-term dynamics and trends, explore the interconnections between different topics and systems and, finally, simulate systems out of equilibrium. MEDEAS-World is therefore the only model suitable to simulate medium- and long-term transitions.

Findings from the cross-comparison and qualitative evaluation highlight a clear difference between the models used and developed in the project, with MEDEAS-World being able to provide more comprehensive simulations by allowing us to account for disequilibrium dynamics in the economics module, effects of climate change on the economy and the effects of (economic) development on depletion of natural resources, all in the context of simulations for the transition to a decarbonised energy system. TIMES-Austria and LEAP-Bulgaria do not account for these dynamics, however they still provide information for infrastructural, investment and capacity requirements for the transition, especially when specified at the national level. 

References

Connolly, D., Lund, H., Mathiesen, B.V. and Leahy, M. 2010. A review of computer tools for analysing the integration of renewable energy into various energy systems. Applied Energy, 87(4), pp.1059-1082.

Epstein, J.M., 2008. Why model? Journal of Artificial Societies and Social Simulation, 11(4), p.12.

Natalini, D., 2016. Estimating the role of scarcity, prices and political fragility in food and fuel riots: a quantitative and agent-based modelling approach (Doctoral dissertation, Anglia Ruskin University).

van Beeck, N., 2000. Classification of energy models. Tilburg University, Faculty of Economics and Business Administration.