Battery energy storage systems (BESS) are becoming foundational assets in European power systems, providing multi-service flexibility across energy, balancing, ancillary services, and congestion-management contexts. In parallel, regulators and network operators are redesigning network tariff frameworks to balance several objectives: cost recovery, transparent signals for network scarcity, and efficient integration of new flexibility.
A recurring challenge in the German debate, and increasingly across Europe, is that storage tariff proposals are frequently communicated as headline price thresholds (e.g., “€/MW-year” or “€/MWh”) without a consistent translation into bankability and investment viability across heterogeneous projects. This can lead to contradictory conclusions, because a single numerical tariff level can have sharply different financial impacts depending on project conditions and regulatory implementation details.
In practice, an “acceptable fee” cannot be defined in tariff units alone. The same fee can translate into materially different investment impacts depending on:
FAIR-GRID (Finance-Aware IRR-based Regulatory Grid-fee Design) addresses this gap by providing a standardised, finance-aware translation from tariff proposals into a comparable bankability metric. Rather than debating fee units in isolation, the application quantifies how any proposed design maps into an implied IRR haircut k (pp) and benchmarks that burden against an explicit WACC/hurdle. This enables transparent, scenario-consistent interpretation of fee feasibility across operating regimes and supports evidence-based discussion on fair and investable tariff design.
All heatmaps display k, the implied IRR haircut expressed in percentage points (pp). k provides a standardised translation from grid-fee units (€/MW-year or €/MWh) into an investment-relevant impact measure that is comparable across fee bases, placements, and operating conditions.
Key interpretation: - k ≈ 0 pp indicates that the proposed fee design has a negligible bankability impact under the selected operating condition. - Increasing k indicates a larger reduction in project IRR and a progressive erosion of financing headroom. - k is not itself a tariff level and should not be interpreted as a price. It is a financial impact index designed for comparability and decision support.
Red star markers denote critical points, defined as operating points where:
IRR_base - k = WACC (pp)
This equality is interpreted as a bankability breakpoint: at the associated fee level and operating condition (utilisation U or efficiency η), the grid-fee burden consumes the full financing headroom represented by the gap between the project’s baseline IRR before fee and the selected WACC/hurdle.
Practical interpretation: - Below the star (IRR_base - k > WACC): the fee impact remains within the selected financing headroom. - At the star (IRR_base - k = WACC): the fee reaches the headroom threshold. - Beyond the star (IRR_base - k < WACC): the fee impact exceeds the threshold, and investability becomes increasingly sensitive to additional increases in fee level, reductions in utilisation, reductions in efficiency, or more punitive placement.
The critical-point representation is therefore intended to support transparent discussion of “how much headroom is preserved” under different tariff design choices, rather than debate of fee units in isolation.
Network tariffs for BESS can be levied on: - imports (charging), - exports (discharging), - or both directions.
This placement choice is a first-order design variable. BESS economics are structurally asymmetric between charging and discharging because value capture depends on the interaction of market price formation, dispatch constraints, and operational decision rules. As a result, the same numerical fee level applied to import and export does not generally produce the same investment impact. Uniform placement can therefore create unequal and potentially distortive penalisation, with consequences for both bankability and operational incentives.
For each placement—import-side (charge-side), export-side (discharge-side), and bi-directional placement (both sides)—the fee is translated into the bankability metric k (pp) using calibrated sensitivity relationships developed from a broad evidence base of market and operational behaviours across multiple settings (years, regimes, and representative strategies). This enables a consistent and comparable translation from tariff units (€/MW-year, €/MWh) into an investment-relevant impact metric.
A key interpretation follows directly:
Section 4 formalises this through the fairness mapping principle: equal numerical fees across placements are not necessarily equivalent burdens in k(pp) terms, and “fair” design requires mapping fees to comparable investment impacts.
The application evaluates two policy-relevant tariff bases commonly discussed in Germany and internationally: capacity-based and energy-throughput-based. Beyond comparing these designs, the application also supports a fairness mapping principle: fee levels should be interpreted relative to their IRR sensitivity under a consistent reference.
A fixed annual charge per reserved power capacity. Its financial impact is strongly dependent on utilisation U (throughput intensity). When grid constraints reduce throughput, the same €/MW-year fee becomes effectively more punitive per unit of energy moved, increasing k.
Why it matters:
This design directly interacts with connection constraints and operational limitations. Under flexible connection agreements (FCAs) or limited activation, the same capacity fee can become disproportionately restrictive unless adjusted for reduced utilisation.
Capacity fee (Import / charge-side). Red star points indicate critical points where IRR_base - k = WACC (e.g., WACC = 9 pp in this illustration).
Capacity fee (Export / discharge-side). Red star points indicate critical points where IRR_base - k = WACC (e.g., WACC = 9 pp in this illustration).