Scenarios for solar on large rooftops. Utrecht Municipality

For the Regional Energy Strategy (RES), Utrecht Municipality has submitted a draft proposal of 175 GWh/a for rooftop solar PV, based on 50% utilisation per rooftop and 15% of roofs being used. In this study CE Delft elaborated three scenarios to assess whether this is a realistic proposal:

1. ‘Probable’: the most likely scenario in terms of projected technical efficiency, available grid capacity, business connection capacity, entrepreneurs’ willingness to invest and local and provincial policies.
2. ‘Best conditions’: the most optimistic scenario, with the PV market developing better than anticipated, high cost-effectiveness and willingness to invest and positive conditions in terms of grid and connection capacity, leading to more rooftop solar than in the Probable scenario.
3. ‘Worst conditions’: the most pessimistic scenario, with unfavourable investment conditions and so less rooftop solar than in the other two scenarios.

Our analysis indicates that the draft RES proposal of 175 GWh/a is realistic or perhaps even conservative. Although we consider 50% rooftop utilisation a little optimistic, the assumption of only 15% of roofs being used in 2030 is almost certainly unduly pessimistic. In addition, the average roof surface area used will probably exceed the average area of large roofs. All in all, we estimate that the large-rooftop solar PV cited in the draft proposal lies between the Probable and Pessimistic scenarios.