# Flexible here-and-now decisions for two-stage multi-objective optimization: Method and application to energy system design selection

## TL;DR

This paper introduces the flex-hand method for automatically selecting a single, flexible design in two-stage multi-objective energy system optimization, accommodating uncertainties and changing decision priorities.

## Contribution

The paper presents a novel flexible here-and-now decision approach that automatically identifies a single robust design from multiple Pareto-efficient options in multi-objective optimization.

## Key findings

- The method effectively identifies a flexible energy system design.
- The approach accommodates uncertainty through a robust extension.
- Real-world case study demonstrates adaptability to changing objectives.

## Abstract

The synthesis of energy systems is a two-stage optimization problem where design decisions have to be implemented here-and-now (first stage), while for the operation of installed components, we can wait-and-see (second stage). To identify a sustainable design, we need to account for both economical and environmental criteria leading to multi-objective optimization problems. However, multi-objective optimization leads not to one optimal design but to multiple Pareto-efficient design options in general. Thus, the decision maker usually has to decide manually which design should finally be implemented. In this paper, we propose the flexible here-and-now decision (flex-hand) approach for automatic identification of one single design for multi-objective optimization. The approach minimizes the distance of the Pareto front based on one fixed design to the Pareto front allowing multiple designs. Uncertainty regarding parameters of future operations can be easily included through a robust extension of the flex-hand approach. Results of a real-world case study show that the obtained design is highly flexible to adapt operation to the considered objective functions. Thus, the design provides an energy system with the ability to adapt to a changing focus in decision criteria, e. g., due to changing political aims.