Potential of Photovoltaic Panels on Building Envelopes for Decentralized District Energy Systems

Abstract

The expected increase of the penetration of distributed renewable energy technologies into the electricity grid is expected to lead to major challenges. As a main stakeholder, authorities often lack the appropriate tools to frame and encourage the transition and monitor the impact of energy transition policies. This paper aims at combining relatively detailed modeling of the PV generation potential on the building’s envelope while retaining the energy system optimization approach. The problem is addressed as a multiobjective, mixed-integer linear programming problem. Compared to the existing literature in the field, the proposed approach combines advanced modeling of the energy generation potential from PV panels with detailed representation of the district energy systems, thus allowing an accurate representation of the interaction between the energy generation from PV and the rest of the system. The proposed approach was applied to a typical residential district in Switzerland. The results of the application of the proposed method show that the district can achieve carbon neutrality based on PV energy alone, but this requires covering all the available district’s rooftops and part of the district’s facades. Whereas facades are generally disregarded due to their lower generation potential, the results also allow concluding that facade PV can be economically convenient for a wide range of electricity prices, including those currently used by the Swiss grid operators. Achieving self-sufficiency at district scale is challenging: it can be achieved by covering approximately 42–100% of the available surface when the round-trip efficiency decreases from 100 to 50%. The results underline the importance of storage for achieving self-sufficiency: even with 100%, round-trip efficiency for the storage, very large capacities are required. However, energy demand reduction through renovation would allow reaching self-sufficiency with half of the PV and storage capacity required.

Decomposition Strategy for Districts as Renewable Energy Hubs

“…The MILP problem formulation of the renewable energy hub is based on the modeling technique of BES by Stadler et al [5], which was further developed by Middelhauve et al [19]. Three types of energy demands are considered: space heating, domestic hot water and electricity.…”

“…The advantage of this method is that it exploits the natural structure of a district energy system and single buildings can be included with their own characteristics. Furthermore, this structure conveniently allows for using the decentralized approach, which is detailed in [19]. Only the objective functions have to be adjusted in order to formulate the SPs.…”

“…One major advantage of the DWD is that the decentralized MILP formulation can be used, with an adjustment of the objective functions, to formulate the SPs. The basis of the BES is described in [5], individual orientation of the roof surfaces are detailed in [20] and shadow casting among buildings and solar integration is considered according to [19]. In the following, the modified objective functions are detailed.…”

“…These can be used to generate pathways and analyze trade-offs to reach an ultimate goal. In the decentralized approach, the MOO is an algorithm which uses -constraints to generate a Pareto curve [19]. While the first objective is optimized, -constraints serve as incrementally increasing upper bounds of the second objective function.…”

“…All roof surfaces of the district were integrated with their individual orientation as described in [20]. The sources of the buildings and weather data have been further detailed in [19]. The four termination criteria were set to 1) a maximum of 9 iterations 2) a maximum runtime of 20 minutes 3) an improvement of less than 0.005% during the last 5 iterations and 4) the reduced costs of all SPs greater or equal 0.…”