A study puts 150 GW of extra PV behind 1,313 German rural substations
Serguey Asael Shinder2 min readFraunhofer IEE has published a study, commissioned by the German solar association BSW-Solar, estimating that around 150 GW of additional PV capacity and 60 GW of battery storage could be connected at 1,313 rural substations between the medium- and high-voltage grids, if storage absorbs generation peaks so that existing transformers are used better over time.
The method is worth stating precisely, because it bounds the claim. The analysis rests on actual operating data from 20 transformers at 13 substations, extrapolated to the larger group through similarity analysis. In the reference scenario, existing renewable plant plus new PV reaches 200% of a transformer's rated capacity, with batteries sized to take the peaks whenever the transformer would otherwise hit its load limit. Under those assumptions the average curtailment of the additional PV is about 1% across the transformers studied — on condition that substation, storage and PV are operated as one system, with power flows monitored and limited dynamically and storage adjusting to the actual flow at the substation.
The study says clearly what it does not establish: the 150 GW should not be read as that much verified, immediately available connection capacity. It contains no detailed calculation of grid bottlenecks and does not assess the condition of the grid sections above or below the substation. The authors' claim is narrower — that better use of existing transformer capacity could reduce or postpone some grid expansion.
⚠ Commissioned research, and the client is an interested party. BSW-Solar is using the findings in the debate over the federal government's grid package, arguing against long-term designation of large areas as grid bottleneck zones where renewable deployment could be restricted under a planned redispatch provision.
What it means
The premise is the right one even if the number is soft: transformers are sized for a peak they rarely see. Any asset dimensioned for a worst case spends most of its life with headroom, and the reason that headroom cannot be sold today is that nothing controls the peak. A battery at the substation is a way of buying utilisation instead of copper.
Note what the 1% curtailment figure is conditional on. It assumes dynamic, coordinated operation of substation, storage and generation. Without that coordination — with each asset optimising separately against market prices — the same physical equipment gives a different answer. The number describes a control regime, not a piece of hardware.
Twenty transformers, extrapolated to 1,313, is the load-bearing weakness. Similarity analysis is a reasonable method and it is a long way from a measured national figure. Read the study as an argument for a pilot at a real substation, which is a testable proposition, rather than as a national resource estimate.