On the role of districts as renewable energy hubs

Although inevitable, the process of transforming urban areas into sustainable living environmentspresents many challenges. The decentralization of the energy system, the interconnection ofmultiple energy carriers, and the need to account for conflicting interests renders it a complex task.As key stakeholders, authorities often lack appropriate decision tools to frame and encourage thetransition and to monitor the impact of implemented policies.This work aims to provide useful insights into the role of districts as renewable energy hubs byshowing requirements and highlighting constraints, leading to an increase in renewable energypenetration. The benefits and trade-offs between centralized and decentralized renewable energyhubs are emphasized to contribute to the ongoing discussion regarding sustainable urban planning.Mathematical programming is used to build a multi-objective optimization platformthat integratesseveral renewable technologies with a special focus on solar integration. Specifically, this approachincludes the role of the orientation of photovoltaic (PV) panels and the use of facades, includingmounting partly shadowed PV panels and receiving solar heat gain. A decomposition algorithm(Dantzig–Wolfe) is used to bypass the computation effort associated with centralized energy hubs atthe district scale.The results highlight that a low-emission electrical gridmix has a high impact on sustainable designof renewable energy hubs at the building scale and led to less independent system configurations.Optimally integrating of solar systems had a significant impact on their interaction with the electricalgrid: rotating the panels 20° westwards reduced the grid exchange peak by 50% while increasing costby only 8.3%. Moreover, the studied district could achieve carbon neutrality based on PV energyalone, whereas self-sufficiency is more ambitious that confirmed the importance of storage systems:even with 100% round-trip efficiency of storage systems, the required ratio of area covered in PVmodules to the energy reference area (ERA) was A_pv /A_ERA =0.44 and 16% of available facadeswere needed to be covered with PV modules. However, energy demand reduction through thermalrenovation would allow self-sufficiency with half of the PV and storage capacity. Overall, this workdemonstrates thatmoving froma decentralized to coordinated and centralized design strategy allowsa higher electrification rate and an increased integration of renewable energy in the district forthe same total expenses. The centralized investment strategy differed most from the decentralizedstrategy for PV panels; using the centralized strategy, a wide range of PV installation on less–optimalsurfaces became economically interesting. The most economically convenient solution to overcome transformer limitations were district storage for peak shaving and photovoltaic curtailment. Thecost increase were around 600 CHF per kWyr annual capacity shortage, regardless of the considereddistrict energy system.