Beyond Installed Capacity: Stress-Testing Lithuania’s 2030 Renewable Energy Targets over 35 Weather Years

National renewable energy targets are expressed in terms of installed capacity and annual energy, which do not reveal whether hourly demand can be met under adverse weather conditions. This study stress-tests Lithuania’s 2030 National Energy and Climate Plan (NECP) targets using 35 years (1990–2024) of ERA5 reanalysis data. Wind and solar photovoltaic capacity factor (CF) time series, with onshore wind and solar evaluated against observed generation, were combined with a temperature-sensitive demand model for three scenarios: NECP with non-flexible electrolysis, NECP with flexible electrolysis, and an implementation-gap scenario without offshore wind or hydrogen-related electricity demand. In all scenarios, renewable generation exceeds demand, yet multi-day deficit episodes (>48 h) account for 0.73–1.83 TWh per year, or 28–41% of deficit energy; the maximum episode reaches 467 GWh, and the longest lasts 16.5 days. Winter onshore wind droughts dominate large deficits. The flexible benchmark reduces the mean annual deficit from 4.50 to 2.20 TWh and leaves no ≥300 GWh events. During ≥100 GWh events, mean gross offshore wind CF is 2.5–2.8 times that of onshore wind; removing offshore wind from the NECP portfolio doubles the multi-day deficit. Capacity-based targets should therefore be complemented by hourly weather-based assessment of balancing needs.