Co-Locating Battery Storage with Onshore Wind Projects Lifts Assets Over Investment Hurdle
Co-Locating Battery Storage with Onshore Wind Projects Lifts Assets Over Investment Hurdle
In a joint study, phelas and Fluence modelled a 25 MW wind project in Germany and show that a right-sized battery energy storage system lifts project returns above the cost of capital in every modelled price scenario.
MUNICH/ERLANGEN, Germany, July 23, 2026 — phelas, the developer of Catalyst, a techno-economic modelling platform for large-scale battery storage in Europe, and Fluence Energy GmbH, subsidiary of Fluence Energy, Inc. (Nasdaq: FLNC), a global market leader delivering intelligent energy storage systems, services, and asset optimization software, today published their joint case study that outlines the fundamental attractiveness of co-locating energy storage with wind in Germany.
The study quantifies, at the project level, how adding a battery energy storage system changes the investment case for a 25 MW wind park across five forward market price scenarios for the German power market.
The analysis combines Fluence’s expertise in grid-scale battery energy storage systems (BESS) with phelas’s techno-economic project modelling. Using phelas’s Catalyst platform, the partners simulated 125 storage configurations with durations of 2 to 8 hours and power ratings of 5 to 30 MW across the five price environments spanning 30 years and measured the impact on net present value (NPV), internal rate of return (IRR), curtailment, and revenue composition.
To date, Germany has one of the largest onshore wind fleets in the world. According to the German Federal Network Agency Bundesnetzagentur, installed onshore wind capacity reached 68.1 GW at the end of 2025 and is targeted to grow up to 115 GW by 2030 — making wind the country’s largest single source of electricity generation, at 24% of gross electricity generation in 2025. Reaching that 2030 target requires adding on average over 9 GW each year, opening up a large field of opportunity for co-location with BESS.
The full case study, including the underlying methodology, scenario definitions, and interactive results, is available below and at phelas.com.
“Co-location is no longer an optional enhancement but the structural change that keeps the wind business case future proof. This study provides an example to developers and IPPs on how much value the storage could add to a project and portfolio.”
— Leon Schwarzott, Director Business Unit Catalyst at phelas
IRR above the cost of capital in every scenario
On its own, the 25 MW onshore wind park is expected to deliver an IRR between 7.5% and 12.5%. In only 2 of the 5 market price scenarios do returns clear the 8% cost of capital. With a well-sized BESS, every modelled scenario exceeds the cost of capital, with the strongest cases approaching 14%.
BESS revenue share outweighs its CapEx share
The battery energy storage system is expected to earn 26% to 51% of total project revenue from the additional markets it unlocks (day-ahead arbitrage, intraday, and positive aFRR), while accounting for only 17% to 29% of anticipated total project CapEx.
Right-sized beats over-sized
2-hour systems at 15–25 MW are expected to be optimal in most scenarios, extending to durations of up to 6 hours only in the most volatile, heavily cannibalized scenario. Over-sized configurations are projected to under-earn their CapEx.
Minimizing curtailment is the wrong target
Sizing storage to eliminate curtailment entirely is expected to decrease NPV by an estimated €18 million to €29 million within the modelling. Accepting some economically rational curtailment maximizes expected value.
About phelas
phelas is a Munich-based climate tech company and the team behind Catalyst, the leading SaaS platform for financial modeling and asset planning of battery energy storage and hybrid renewable energy projects. Catalyst enables asset managers, project developers, and investors to benchmark tens of thousands of revenue scenarios. From early feasibility through financial close, phelas equips the energy transition with the analytical infrastructure for faster, more precise investment decisions.
About Fluence
Fluence Energy, Inc. (Nasdaq: FLNC) is a global market leader delivering intelligent energy storage and optimization software for renewables and storage. The company's solutions and operational services are helping to create a more resilient grid, from powering the next generation of AI-driven data centers to unlocking the full potential of renewable portfolios. With gigawatts of projects successfully contracted, deployed, and under management across nearly 50 markets, the company is transforming the way we power our world for a more sustainable future.
“With the accelerated build-out of the German wind fleet, storage becomes paramount to preserve wind assets’ economics and lowering energy costs through renewables. We believe that merchant price cannibalization and curtailment are hurting the investment case, but co-locating wind with BESS in Germany now makes more sense than ever before to secure strong returns for investors.”
— Julian Jansen, Vice President and Managing Director, Germany at Fluence
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