01A BESS diversifies the revenue stack.

Wind alone earns from one price curve. The battery energy storage system brings in three additional revenue streams — day-ahead arbitrage, intraday, and aFRR positive capacity — which dilutes exposure to any single market and stabilises cash flow.

02Wind alone barely clears the cost of capital.

Standalone wind delivers IRR between 7.5% and 12.5% — and lands within 100 bp of the 8% hurdle in three of five scenarios. With the right-sized BESS, the co-located project earns IRR between 8.5% and 13.9% — every scenario clears the 8% hurdle and four of five deliver IRR ≥ 9%.

03BESS and wind operate complementarily.

The BESS generates 26%–51% of total project revenue from just 17%–29% of the CapEx. It absorbs energy when wind cannibalises its own price and releases it when the market values it most, while also reducing exposure to redispatch costs.

04Well-utilised, right-sized systems beat oversized ones.

Across all scenarios the NPV-maximising BESS is well utilised at 15–25 MW — 2 hours in four of five scenarios, extending to 6 hours only in the most heavily cannibalised (disorderly) scenario. Capital efficiency is the driver: a 2 h system already captures the full daily peak-to-trough spread where almost all arbitrage value sits.

05Minimising curtailment is the wrong target.

Sizing the BESS to eliminate curtailment destroys €18M–€29M of NPV. To avoid curtailing the last surplus MWh, the system would have to charge defensively at low-value hours, sacrificing higher-value arbitrage and aFRR cycles. The economic optimum is reached well before all curtailment is removed.