Stable and Renewable: Assessing the Reliability of a Fully Renewable European Energy System

The transformation of the energy system has raised concerns about the reliability of fully renewable energy systems. We address this question for a 2050 European energy system using an economically optimal adequacy assessment. Our results show that a cost-optimal, fully renewable European system can be as reliable as a fossil-based one, with an average loss of load of only 0.03% due to variability in renewable generation. Outages primarily affect industrial and service sectors, while household supply remains largely uninterrupted. Regional differences in supply security emerge, with outages concentrated in countries with a low Value of Lost Load (VoLL). We demonstrate that system reliability can be fully ensured at negligible additional cost (+0.17%) by modestly increasing hydrogen turbine (+10%) and battery capacities (+15%) beyond the cost-optimal levels. We conclude that well-designed renewable energy systems are stable, with hydrogen-based backup being a key enabler of reliability.

💡 Research Summary

The paper investigates whether a fully renewable European energy system can achieve the same reliability as today’s fossil‑fuel‑based system. Using an economically optimal adequacy assessment based on the VoLL/CONE/RS framework, the authors model a 2050 Europe with 250 sub‑national regions at hourly resolution. The model (ETHOS.modelBuilder) includes on‑shore wind, solar PV, hydrogen electrolysis, hydrogen storage, hydrogen gas turbines, Li‑ion batteries, and transmission (both electricity and hydrogen pipelines). All capacities are endogenously expandable, constrained only by technical and geographic limits.

Value of Lost Load (VoLL) is derived from EU CEPA 2018 data, projected to 2050 using national GDP and electricity demand trends, and disaggregated by sector (agriculture, households, industry, services, transport). The average VoLL for 2050 is 7.3 €/kWh, with considerable country‑level variation.

The cost‑optimal solution is dominated by wind (≈60 % of generation) and solar (≈39 %). Installed capacities reach 2 709 GW PV, 2 585 GW on‑shore wind, 1 116 GW PEM electrolyzers, and 501 GW hydrogen gas turbines—roughly ten times current EU capacity. Annual system cost is 91.6 €/MWh, split as 44 % wind, 14 % PV, 22 % hydrogen infrastructure, 15 % grid, and 1 % batteries. Hydrogen storage accounts for 98 % of total storage, while batteries contribute only a marginal share.

Reliability results are striking: the average loss‑of‑load expectation (LOLE) is only 0.03 % of total demand, comparable to today’s fossil system. However, regional disparities arise. Countries with low VoLL (≤ 3 €/kWh) – mainly in Eastern Europe (Bulgaria, Hungary, Romania, Ukraine, etc.) – experience the highest loss rates, up to 0.54 % of annual demand. High‑VoLL Western nations (Germany, France, UK, etc.) see losses below 0.001 %. Outages are predominantly partial, lasting 5–10 hours; the average region experiences 2.2 such events per year, and events longer than 10 hours occur only once every 12 years per region. The maximum instantaneous unmet load is 7 %, and a 5 % system‑wide shortfall persists for about 20 hours per year on a 20‑year average.

Two characteristic outage patterns are identified. In the “Western” pattern, a wind lull over the Iberian Peninsula and northern Britain reduces exports to Central Europe; low‑VoLL regions such as Portugal and France incur partial blackouts, while high‑VoLL England remains supplied. In the “Eastern” pattern, a wind lull in Eastern Europe creates a large residual load in Central Europe; excess generation in the East is converted to hydrogen and shipped west, but limited hydrogen‑to‑electric conversion capacity prevents its use, exacerbating the deficit.

Crucially, the authors show that a modest oversizing of flexibility assets—10 % more hydrogen turbines and 15 % more batteries—eliminates all loss‑of‑load events at an additional cost of only +0.17 % of total system cost. This demonstrates that hydrogen‑based backup is the key enabler of reliability in a 100 % renewable Europe.

Policy implications include: (1) targeted investment in hydrogen turbine capacity and battery storage to hedge against multi‑day wind lulls; (2) consideration of country‑specific VoLL when designing capacity markets or reliability standards; (3) continued reinforcement of cross‑border transmission to alleviate regional congestion; and (4) recognition that, with modest additional spending, a fully renewable system can match or exceed the reliability of today’s fossil‑fuel system. The study thus provides a robust, cost‑effective pathway toward a stable, fully renewable European energy future.