OPINION /
By Cyril Champier | Paris, France, Thursday 14 August 2025
Why flexibility is essential for renewables
The shift toward a fully decarbonized, electrified future demands a complete transformation of our energy systems. The key to this transformation lies in a concept that was once peripheral and is now central: flexibility.
In France, the future will need five times more flexibility than today to ensure a stable, resilient, and economically viable power grid. Let’s explore what flexibility really means, how France’s electric system will evolve from 2000 to 2050, and why simple choices, like how we manage transportation depots, could make all the difference.
If you’ve ever flipped a breaker at home, then you’ve engaged with a simple aspect of grid operation. Electricity supply and demand must continuously be balanced. If it doesn’t, the grid destabilizes, and blackouts happen. On a national scale, this balancing act must be maintained constantly across the entire grid. Earlier this year, Spain failed to maintain that balance, for just a few seconds, resulting in a cascading event that left the country without power for nearly 12 hours.
But balancing supply and demand isn’t just a moment-to-moment challenge. It’s also a matter of scale. Electricity demand varies widely between day and night — and even more drastically between seasons. Winter evenings are the toughest: people come home, turn on heaters, lights, and ovens, and demand surges. Building generators to handle just these peak moments would mean creating an overbuilt, underutilized system — costly to operate and mostly idle. In fact, some nuclear plants might only run for a few days a year, just to cover these spikes.
At the dawn of the millennium, France’s energy system was a highly centralized and controllable model. The means of production (nuclear, hydroelectric, or coal power plants) all used large rotating turbines – physical machines in continuous rotation. These moving masses kept spinning even if a sudden imbalance occurred. For example, in the event of a line failure, the mechanical inertia would slow the collapse of the grid, thus giving the system a few precious seconds to react.
Nuclear offered inertial stability, and adjustable output between 40-100%, and planned maintenance shutdowns during summer. Whereas Hydro enabled rapid adjustments, notably thanks to pumped storage (STEP) and huge storage capacity. Fossil fuel plants filled gaps. Even consumers helped – industries agreed to shut down during emergencies, and households used off-peak electricity thanks to pricing incentives.
Most flexibility was built into the generation infrastructure:
Two trends have clearly taken root in the past two decades: the rise of renewable energy generation and the spread of electric vehicles (EVs).
While much of the legacy infrastructure remains and key metrics are still close to those of 2000, the exponential growth of these trends is poised to become a major game-changer in the coming years.
For example, last year in France, because of solar energy overflows during the afternoon, electricity spot prices were negative during 4% of the hours, meaning people were actually paid to consume electricity!
By 2050, everything changes. Forecasts like “Futurs Énergétiques 2050” from RTE (the French TSO) describe a radically transformed electricity system: dominated by renewables and with electric vehicles accounting for nearly 25% of total demand. France’s electricity system will no longer be defined by central control or big spinning machines.
Instead, it will be shaped by renewables. EVs will make up nearly a quarter of total demand. Wind and solar will dominate electricity generation. Nuclear will shrink, and fossil fuels will be completely gone. This sounds green – and it is.
But it also introduces major risks. Without turbines, the grid loses its built-in inertia. Wind and solar can’t stabilize the system the way big machines once did. That means we need four times more safeguard flexibility – fast, reactive systems that can react to unforeseen events and prevent blackouts. And since solar and wind follow the weather, not human needs, we’ll need six times more strategic flexibility, to shift supply and demand across hours, days, and even seasons. Nuclear is no longer dominant. Hydro can’t scale further. The old stabilizers are gone. Even standalone batteries and new time-of-use tariffs help only so much.
Without new solutions, the 2050 grid may be green but unstable.
What happens at the depot level mirrors what will happen to the grid. Regulation is pushing hard: these sites are being outfitted with photovoltaic (PV) solar panels and fleets of electric vehicle (EVs). In France alone, there are over 4,000 depots, covering nearly 100,000 m² of rooftop space. Left unmanaged, these could overwhelm the grid:
It’s a mismatch that creates instability, inefficiency, and rising costs. The very depots meant to green the system could instead strain it further.
Now, imagine a different path – powered by smart integration of BESS (Battery Energy Storage System), EMS (Energy Management System), and V2G (Vehicle-to-Grid). Suddenly, depots evolve from passive energy burdens into active, flexible energy hubs:
The Depot of the Future
Unlike EVs scattered across homes, depots are centralized, predictable, and manageable – perfect candidates for transformation into controllable energy assets. Drop in a containerized battery, plug in the software… and give the fleet manager a financial nudge. Trucks now create value even while parked.
And the impact is massive: depot flexibility could eventually provide up to 50% of France’s grid flexibility needs by 2050.
The French energy system of 2050 will not be an evolution of the 2000s: it will be a completely new creature, powered by the wind and sun, destabilized by their intermittency and lack of inertia, and reshaped by EVs. The same will happen for all countries where the generation will largely shift for large turbines generating AC to renewables generating DC.
According to the RTE, to make this system work, we will need five times more flexibility.
Fortunately, we don’t need to reinvent everything. Sometimes, the answer lies in overlooked places: like transportation depots. With the right tools and strategies, they can provide massive flexibility, helping us build a clean, resilient, and future-proof grid.
Because when it comes to renewable energy, flexibility is not an option.
Together, Decade Energy and Siteboost are showing how battery storage can strengthen France’s energy system while turning underused land into assets for the clean transition.
From finance to fleet electrification, Aymeric Leenhardt leads sales and partnerships at Decade Energy to help make depot electrification a reality.
As renewables reshape the grid, flexibility becomes the backbone of stability. By 2050, France will need five times more of it, and transport depots could provide half, turning into powerful...