Sep 9, 2021

How Can We Encourage Private Households to Install Photovoltaic Systems?

While the environmental benefits of installing photovoltaic systems are clear, the costs can remain off-putting for private households. In this video, I explore the relevance of the peer effect (neighbors already having the technology) in a decision to install a photovoltaic system. Establishing an installed base and considering fixed effects alongside an instrumental variable approach, Johannes Rode (main author) and I find that peer effects are most prominent on a very local level i.e. within a distance of 100m. We also show that the visibility of an existing photovoltaic system plays a vital role in its potential influence in the neighborhood.

Aug 5, 2021

New Publication

In this new publication Stefan Tscharaktschiew (TU Dresden) and I investigate the substitution between bicycling and public transport in school travel focusing on an underrated determinant in the literature – the personal effort (e.g. energy input in terms of kcal) of students when traveling by bike (or walk).

Jun 4, 2021

EURO Excellence in Practice Award 2021 - Finalist

Our pilgrim scheduling approach to increase safety during the Hajj (published in Operations Research) is one out of six finalists in the EURO Excellence in Practice Award 2021. The joint work with Knut Haase, Matthes Koch (both Hamburg University) and Mathias Kasper (TU Dresden) presents an innovative mathematical program to guide pilgrims safely and convenient during the great pilgrimage to Makkah, Saudi-Arabia.



The Hajj — the great pilgrimage to Mecca, Saudi Arabia — is one of the five pillars of Islam. Up to four million pilgrims perform the Hajj rituals every year. This makes it one of the largest pedestrian problems in the world. Ramy al-Jamarat — the symbolic stoning of the devil — is known to be a particularly crowded ritual. Up until 2006, it was repeatedly overshadowed by severe crowd disasters. To avoid such disasters, Saudi authorities initiated a comprehensive crowd management program. A novel contribution to these efforts was the development of an optimized schedule for the pilgrims performing the stoning ritual. A pilgrim schedule prescribes specific routes and time slots for all registered pilgrim groups. Together, the assigned routes strictly enforce one-way flows toward and from the ritual site. In this paper, we introduce a model and a solution approach to the Pilgrim Scheduling Problem. Our multistage procedure first spatially smooths the utilization of infrastructure capacity to avoid dangerous pedestrian densities in the network. In the next optimization step, it minimizes overall dissatisfaction with the scheduled time slots. We solve the Pilgrim Scheduling Problem by a fix-and-optimize heuristic, and subsequently simulate the results to identify necessary modifications of the scheduling constraints. Our numerical study shows that the approach solves instances with more than 2.3 million variables in less than 10 minutes on average. At the same time, the gap between optimal solution and upper bound never exceeds 0.28%. The scheduling approach was an integral part of the Hajj planning process in 2007–2014 and 2016–2017. No crowd disaster occurred in these years. Our approach was not applied in 2015, when a severe crowd crush happened close to the ritual site. We briefly discuss possible causes and consequences of this accident.