What is the intermittency of renewable energies?

For some time now, the world has gradually become aware of the danger represented by fossil fuels for our environment. In the context of sustainable development, making an energy transition to less polluting sources is now on the agenda. While the task does not seem impossible, it is still not easy since renewable energies such as solar and wind are often accused of a nasty defect: They are intermittent, which could be a barrier to electricity production.

What is intermittent energy?

By definition, intermittent energy is energy whose availability fluctuates enormously without it being really possible to regulate it. This concept is relatively new, as it applies primarily to renewable energy sources.

The intermittency of these energies has its origin in the flows on which they are based. Sun (dependence on luminosity) for photovoltaics, wind for wind power, reservoirs for hydroelectric... As a result, their production depends greatly on weather conditions and the alternation of day/night cycles. It is therefore discontinuous, variable and not programmable.

When addressing the problem of energy intermittency, two sources are often singled out. The first is solar/photovoltaic energy, which is only available during the day, especially when the weather is nice. As for the second, you may have guessed it, it is Wind energy. It can only be produced when the wind is blowing.

On a global scale, intermittent renewable energies still represent a small percentage of global production. However, the trend should be reversed given the transition policy initiated by several countries and the production costs which are tending to fall.

The intermittency of renewable energies: is it a problem?

The observation is clear: renewable energies occupy an increasingly important place in The energy mix many European countries facing fossil fuels. And for good reason, they already represent more than half of investments in electricity production. In 2019 alone, Denmark, one of the best students in this category, managed to cover 75% of its energy expenses using renewable energy.

Renewable energies are not necessarily at the top of the list of energies preferred by suppliers who need constant sources at all times and in predictable quantities. Renewable energies do not seem to pass this test at the moment.

They pose two main problems that are far from being unsolvable.

A demand that is difficult to meet

The intermittent nature of renewable energies seems to raise many questions about their availability. For example, how do you heat households in winter when the days are excessively short and the weather is freezing cold? Likewise, should we wait for the wind to be strong enough to have enough energy? What do we do on windless days we manage without electricity ?

While these questions are legitimate and come to mind, solutions exist and involve, in particular, electricity storage during peak production periods. What's more, Not all renewable energies are intermittent.

The disruption of electrical networks

Another important point is that the production of intermittent energies can vary drastically in a very short time. Numerous tangible examples are also available. Thus, in France in 2019, the power of wind energy oscillated between 46.7 GW and 0.4 GW. In a few hours, we even recorded falls from 10 GW to less than 3 GW.

Likewise, between winter and summer, the energy provided by the photovoltaic panels oscillated between 1.3 GW and 33.6 GW. Even more incredible, on the night of January 24, 2019, wind and solar combined provided only 0.65 GW, or less than 1% of the energy consumed at that time.

According to some experts, Intermittence could increase the speed of network wear and lead to increased maintenance costs. Likewise, an increase in intermittent energies could disturb the balance of electrical networks.

However, these various problems can be solved with the emergence of new electrical systems such as intelligent networks or smart grids. Their promise: to ensure better management of electricity distribution by facilitating the exchange of information between network operators and consumers.

Intermittent or variable renewable energy?

The problem of the intermittency of renewable energies has arisen due to the rise of these energy sources. Wind and solar power are often the renewable energy sources singled out. But it is clear that for the time being, in France, the first source of renewable energy remains Biomass. It is by no means intermittent.

Likewise, other renewable energy sources such as dam hydraulics are not intermittent and can be easily programmed. Geothermal energy and heat pumps can also be used to smooth the production of so-called intermittent energies.

Intermittence is a rather pejorative term that seems to imply that the functioning of all renewable energies depends on a kind of switch that could switch to off mode without warning.

Even with wind energy, there is no sudden stop, especially when you consider the entire production park. This is why some players such as RTE, the French electricity transmission system operator, consider electricity production from photovoltaic or wind energy to be “variable”.

How to compensate for the intermittency of energies?

Undoubtedly, intermittency can be a problem, but it is not inevitable. According to a German study published since 2007, Ensuring fully renewable electricity production despite the intermittency is entirely possible. The secret would lie in the combination of complementary energy sources.

In practice, for electricity mixes based entirely on renewable energies to be a reality, a large-scale development of scalable green energy production technologies (geothermal, biomass, hydroelectricity...).

Similarly, across the country, energy production sites are far enough apart for weather conditions to be different. This disparity, far from being a weakness, is rather a real advantage. Variable productions from one site to another will generally be more consistent at the national level.

Thanks to this abundance, deficits in one production area can be offset by excesses in another area. Enough to ultimately smooth out domestic production.

For example, France benefits from three independent wind regimes on the territory: oceanic, continental and Mediterranean. As a result, despite the significant disparities observable at the park level, they are more smoothed out at the national level.

In short, the intermittency of renewable energies refers to the fluctuation of their production, which jeopardizes their constant availability. However, this does not apply to all forms of renewable energy. And even for those that are singled out, such as wind and solar, solutions remain possible.

If you're going to turn to these energy sources, don't worry, your lightbulbs won't start flashing. In absolute terms, you are thus limiting the use of fossil fuels, which is perfectly in line with the ecological and energy transition that has begun.

To go further, do not hesitate to consult our article that answers the question: Why is energy storage necessary?