A study by French scientists warns: solar and wind farms with accompanying storage reduce the EROI factor from 25 to only 2.3.

The scientific paper titled “Energy Return on Investment of the electricity mix: the impact of intermittent sources” (Energy Return on Investment of the electro-energy mix: impact of intermittent sources), published in the prestigious journal of the French Academy of Sciences, presents significant findings that shed new light on the sustainability of scenarios of a complete energy transition based solely on renewable energy sources

Authors, among whom are French scientists Marc Fontecave from the prestigious Collège de France and Jacques Treiner, analyzed the evolution of the energy return on energy investment (EROI – Energy Return On Investment) for two possible scenarios of the French energy mix for 2050. EROI is a key indicator that measures the ratio of the total energy supplied (over the lifetime of the plant) and the total energy invested in its construction, operation and decommissioning.

The main and most striking conclusion of the study is that the massive introduction of intermittent energy sources, such as solar panels (PV) and wind power plants, drastically reduces the overall EROI factor of the entire electricity system. Today, the EROI factor of the French energy mix (which relies heavily on nuclear and hydroelectric power) is about 25.5. This means that for every unit of energy invested, the system generates 25.5 units of delivered electrical energy that go to consumption and are used.

Analyzing alternative scenarios, Fontecave and Treiner conclude that in a hypothetical 50% RES and nuclear energy scenario the EROI factor would be approximately 6.6. The second scenario with 100% renewable energy sources has an EROI factor dropping to a very low value of about 2.3.

Such low values raise a serious question about the sustainability of the proposed scenarios for developed societies. The authors remind that the literature indicates that for the functioning of a reasonably developed country a certain minimal EROI factor is required, and they ask whether a system with an EROI of 2.3 is even “sustainable for our society”.

The authors emphasize that the low EROI factor in scenarios with a high share of renewable energy sources is not primarily a consequence of lower efficiency of solar panels or wind turbines (which indeed are lower – the capacity factor of solar panels, for example, is about 20%, while in nuclear power plants it is often higher than 90%), but is essentially the result of the impact of energy storage systems.

Unlike previous studies that analyzed the EROI of intermittent sources considering only daily storage (such as batteries), Fontecave and coauthors conducted detailed simulations of the entire flexibility system necessary for the operation of the grid throughout the year (i.e., not just during a single daily cycle).

They argue that, since solar and wind energy have seasonal and random fluctuations (for example, solar production is four times lower in winter than in summer in France), the grid requires massive interseasonal storage systems.

The simulations carried out by Fontecave and Treiner revealed the following:

• Storage is crucial: In the scenario 50% Nuclear/50% RES, the total Ein (energy invested) in the storage system amounts to 64.4 TWh, which constitutes more than half of the total energy invested in the entire electrical system.
• High hydrogen losses: The main driver lowering the EROI factor is the use of hydrogen for interseasonal storage (in the 50% scenario). Because the extremely low conversion efficiency of “power-to-gas-to-power,” which is only about 30%, losses in the storage system are enormous.
• Required additional production: Losses in storage (reaching 32.2 TWh in the 50/50 scenario, or 87.6 TWh in the 100% RES scenario) must be compensated by additional electricity production to maintain grid balance.

Therefore they conclude that the enormous losses associated with this storage account for 75% of the total energy investment (Ein) in that scenario, reducing the EROI to 2.3.

The study concludes that systems relying on high shares of intermittent sources are inseparable from large storage systems, whose low efficiency not only requires large energy investments in construction but also generates enormous energy losses.

These results contradict claims that renewable energy sources are inherently more efficient. The authors suggest that comprehensive EROI-factor studies must include the entire flexibility chain – including seasonal storage – in order to avoid misestimating the sustainability of the energy transition.

For a society aiming to maintain a high level of economic development and living standards, an EROI factor significantly higher than 2.3 is needed, which strongly calls into question the feasibility of a complete energy transition scenario based on solar and wind energy.

You can read the original study here.