What does a self-sufficient neighbourhood cost, and when does new-build beat renovation?

That depends on two things: how self-sufficient, and what seasonal storage costs. For eight all-electric homes in Breda, the Netherlands, sized robustly across the weather years 2018, 2021 and 2022: at 70% self-sufficiency € 365 per home per year; at 80% € 1,431; at 90% € 8,090 with seasonal storage at €100 per kWh, and € 2,285 at €20 per kWh. These are scenario euros for bare technology: not a quotation, excluding fixed grid charges and subsidies.

That is the winter wall. Up to roughly 80% the neighbourhood gets by on solar panels and a community battery: summer surpluses cover the daily gaps. Above it, energy has to move from summer to winter, and a day battery is the wrong tool for that. The model then builds seasonal storage (8.1 MWh at 90%), or it keeps stacking batteries. In that case 90% costs € 20,722 per home per year instead of € 8,090.

Under these assumptions yes, across the whole price band tested. At 90% self-sufficiency the battery route costs € 20,722 per home per year; with seasonal storage it is € 2,285 at €20 per kWh and € 11,646 at €150 per kWh. So the direction holds, but the word "cheap" rests entirely on that price per kWh.

That is not a date but a function of the ambition. In this model the life-cycle costs cross around 2040 at a 70% ambition under aggressive construction automation; at 90% with realistically priced seasonal storage only around 2051, and then only in the aggressive scenario. Without automation the curves do not cross at all before 2055 at high ambitions. This is a scenario explorer, not a forecaster: the learning curve for construction automation does not exist in the literature and is an explicit assumption here.

For this all-electric neighbourhood it is 2021, the grey year, not 2018 or 2022. That is less obvious than it looks: 2018 becomes the binding year as soon as the heat pumps are taken out of the model. What matters is not annual irradiation but the deepest continuous deficit the storage has to bridge.

The robustness premium. At 90% self-sufficiency that is € 582 per home per year on top of a neighbourhood sized on the record-sunshine year 2022 alone. Without that premium the same neighbourhood reaches 89.1% instead of 90% in the grey 2021. And that is still the generous reading, because it assumes perfect foresight.

The physics is hard: the energy balance closes to machine precision every hour, and the optimum is a proven global optimum of a linear program, not a heuristic. The economics is soft: investment costs are market indications for 2025 and 2026, and the price of seasonal storage is explicitly labelled low-confidence. That is why it is a control. Every assumption is listed with source and confidence in the lab's public assumptions register.