Photovoltaic (PV) systems are expected to play a major role in the Swiss energy transition, but homeowners considering installing a PV system face some key decisions, such as deciding on the size of their PV system, whether to tilt their rooftop PV panels, and whether to install a battery. The optimal system design may vary with the homeowner’s reason for considering a PV system: Whilst some homeowners might be interested in lowering their energy bill, others might be motivated by a desire to lower their emissions and thus contribute to the Swiss energy transition. Moreover, the policy landscape for residential PV in Switzerland might change, with Swiss distribution system operators calling for a limit on the electricity that PV owners can feed into local electricity grids to avoid line overloads during peak production times. Such policy changes might further impact the trade-offs in the optimal PV system design. In this analysis, we examine the optimal design of the PV system for homeowners that prioritize costs and emissions under multiple scenarios that limit the electricity exports to the local distribution grid and draw recommendations for homeowners.
Increasing shares of residential PV will likely require export limits
With increasing shares of residential PV systems, there will likely be situations where many households export excess PV electricity to the local distribution network at the same time. This could, for example, happen at 12 pm on a sunny summer day, when the PV electricity generation exceeds the households’ electricity demand at that time. Such situations can lead to congestion in local distribution networks, resulting in power line overloads and destabilizing the grid. To prevent such scenarios, Swiss distribution network operators are proposing to limit the sale of excess PV-generated electricity to the grid, in the following referred to as export limits. In Australia, for example, such export limits are common, with some distribution network operators even entirely prohibiting electricity exports by PV owners. Such export limits greatly impact the financial viability of PV systems. While it is still uncertain whether such restrictions will be implemented in Switzerland, in a recent study, we investigated how export limits influence the cost- and emission-optimal PV system designs for prospective PV owners in Switzerland.
How to identify the optimal PV system design
To examine how export limits might impact residential PV systems that are cost- or emissions-optimal, we developed an optimization model that determines the optimal rooftop and east-, west-, and southward-facing facade PV installations, and the optimal battery installation for a mixed-use building in Dübendorf, near Zurich (see Figure 1). The annual electricity and heat demand of the case study building are around 100 MWh and 200 MWh, respectively, with the heat demand fully being met by a heat pump. The model determines the optimal size of all PV installations and of the battery installation and accounts for the emissions produced in the production process of all technologies. Moreover, the rooftop PV system can be tilted. This tilt angle is important because by tilting the rooftop PV system, the timing of the electricity production can be shifted, for example, from midday to the afternoon, which might help to better align the electricity production with the local electricity consumption patterns. However, this comes at a cost. By tilting the rooftop PV system, the overall electricity production volume decreases, leading to a tradeoff between the timing of electricity production and the overall production volume.
