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Intermittency of renewables: the challenges to make them competitive
Balancing and storage technologies are key to managing the discontinuity of solar and wind energy.
Luca Longo
Non-dispatchable renewables like solar and wind are central to the transition to a sustainable future. However, their main challenge is variability. Solar energy relies on irradiance (dependent on time, season, weather), which is highly variable, while wind intensity also fluctuates. This variability means power from these sources cannot be available in a continuous or programmable way. Such fluctuations, if not adequately balanced, can create imbalances between supply and demand and this can become a serious challenge for both users and distribution networks.
In energy systems increasingly characterised by a high presence of non-dispatchable renewables, aligning production with demand thus becomes more complex. During periods of high production and low demand, there is a risk of excess energy that cannot be used, whereas during periods of low production and high demand, energy shortages can occur.
The situation is further complicated by significant variations in energy demand between day and night, weekdays and weekends, and across seasons, as well as differing climate control needs.
Eni data on renewable sources
Some figures on our installed capacity and our electricity production targets
The role of distribution networks
Distribution networks are increasingly crucial in balancing energy imbalances.
In current energy systems, equilibrium is maintained in real time through market participation mechanisms involving various energy sources. Some of them, such as gas and nuclear fission (in the countries where it is present), can provide a stable production level to the grid, known as "baseload." Others, like gas generation, when it participates in the market with this specific aim, are capable of rapidly responding to imbalances.
Additionally, interconnections between regional networks help stabilise the system by transferring energy from areas with excess production to those with deficits. This exchange smooths out local variations in renewable energy production and is notably effective, for example, in connecting different European regions.
To maintain balance, increasingly sophisticated transport and distribution networks, known as ‘smart grids’, are starting to use and will increasingly use advanced technologies to monitor and manage real-time production and demand, automatically regulating distribution.
An effective strategy will involve ‘demand response’, where energy demand can be adjusted based on availability. According to this strategy, consumers can be encouraged to use energy during periods of high renewable production through dynamic rates or incentive programmes. Conversely, they could provide stored energy, possibly from their electric vehicle, during high-demand periods and receive direct billing rewards.
The development of smart grids, however, is still in its early stages almost everywhere, as it requires a profound transformation in the role of consumers, who need to be enabled (from a technological, regulatory, and contractual point of view) to become active participants (the so-called ‘prosumers’) in a market and distribution system that must increasingly accommodate these advanced forms of participation. These include ‘energy communities’, where groups of users can aggregate their surplus renewable production to feed into the grid, further optimising the balance between supply and demand even at the edges of the system.
Network stabilisation levers
To effectively address variability, it is essential not only to increasingly and more intelligently interconnect production, distribution and consumption networks of growing size and complexity, but also to integrate energy storage systems. These systems store excess energy produced during periods of high availability and release it when production is insufficient.
Electrical storage
The primary method of electrical storage is batteries. Lithium-ion batteries, for example, are widely used due to their high energy density and efficiency. However, other technologies, such as sodium-sulphur batteries and flow batteries, are emerging as promising solutions.
Batteries not only store energy for future use but can also provide grid stabilisation services, such as frequency regulation and voltage adjustment. This helps maintain the reliability of the energy system, also in this case compensating for the gradual reduction in capacity provided by thermal power plants so far.
Effective electrical storage, when deployed on a sufficient scale, can balance instantaneous imbalances between supply and demand.
Electrical storage
Thermal storage
Thermal storage is another stabilisation lever that is likely to become increasingly important. Systems such as hot water or hot oil storage tanks, or phase change materials (PCMs), can store energy as heat. This thermal energy can be used to heat buildings, provide domestic hot water, or support industrial processes during periods of low renewable production.
An example of this technology is the TES (Thermal Energy Storage), which Eni is developing at its laboratories in Novara. It consists of a concrete cylinder with specially designed openings through which a heat-carrying fluid flows. The system enables efficient heat storage and release, offering lower costs compared to other solutions, and features a modular design that can operate over a wide range of temperatures and accumulation times.
Thermal storage
Towards a more sustainable energy system
Renewable energy variability represents a significant challenge, but with the right technologies and management strategies, it can be overcome. Smart distribution networks and energy storage systems will become increasingly effective for balancing supply and demand, ensuring stable and reliable energy supply.
Investing in these technologies and promoting policies to incentivise their development is crucial for accelerating the transition to a sustainable and resilient energy system, capable of fully harnessing the potential of renewable energies.
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