What Is Curtailment and How Does It Affect Solar PV Energy in Spain

The widespread implementation of solar energy in Spain has been one of the great successes of the energy transition. However, this rapid expansion has also created significant technical challenges. One of the most worrying for producers, operators, and investors is curtailment: a limitation on renewable energy production that prevents its full potential from being realized.

What Is Curtailment?

Curtailment is an order from the electricity system operator —in Spain, Red Eléctrica de España (REE)— to partially or completely stop the generation of renewable energy, even when technical and environmental conditions are favorable. This phenomenon can be caused by two main factors:

Grid congestion, that is, the infrastructure cannot transport all the energy generated.
Excess supply compared to reduced demand, which can lead to zero or even negative prices.

This type of interruption, also known as curtailments, especially affects large-scale solar and wind installations, as well as certain industrial self-consumption systems.

What is the duck curve and why is it related to curtailment?

The term photovoltaic duck curve originated in California (CAISO, 2013) and graphically represents the imbalance between solar generation —which peaks at midday— and electricity demand —which increases in the evening. The result is a duck-shaped curve: low demand during solar hours and a sharp rise in the afternoon, when solar production drops.

This mismatch generates overproduction during the day which, if it cannot be stored or transported, inevitably leads to curtailment. In countries like Spain, with high solar irradiation rates and strong photovoltaic penetration, this curve becomes more pronounced during weekends or holidays, when demand is lower.

What is photovoltaic pricing (apuntamiento fotovoltaico) and how is it affected?

Photovoltaic Pricing refers to the ratio between the average electricity market price and the average price at which solar energy is sold during a specific period. When the grid is saturated and there is excess solar generation, the electricity price drops. As a result, the apuntamiento also decreases, reducing income for solar producers.

Low solar pricing is especially problematic when there are no storage systems in place, as it prevents capitalising on the most profitable hours. Without batteries, the energy produced at midday must be fed into the grid at minimal or even zero prices.

Main Causes of Curtailment in Spain

Grid saturation: many plants are located far from the consumption point and are connected to insufficient infrastructure.
Lack of distributed storage: without batteries, it is not possible to store surplus solar energy.
Low-demand hours: weekends, holidays, or vacation periods.
Delays in regulatory planning: lack of coordination between new renewable generation and evacuation capacity.

Consequences of Curtailment for Producers and Investors

Direct economic losses: unsold energy represents a drop in return on investment (ROI).
Impact on PPA contracts: in power purchase agreements, curtailment can lead to disputes or penalty clauses.
Reduction of the performance ratio: technical indicators of the plants deteriorate.
Investor uncertainty: reduces the attractiveness of the sector without clear policies supporting storage.

Technical Solutions to Curtailment

The main solutions involve providing the electrical system with greater flexibility:

Energy storage (BESS): allows absorption of solar surplus and dispatch during peak demand hours.
Digitalisation and forecasting: AI-based systems to anticipate grid congestion or price drops.
Participation in flexibility markets: buying/selling in intraday markets or ancillary services.
Smart demand management: adapting industrial consumption to hours of maximum solar generation.

What Role Do Batteries Play in Combating Curtailment?

Industrial batteries and self-consumption installations with storage are key to mitigating curtailment. They allow:

Postpone solar feed-in to periods of higher prices.
Maximise photovoltaic pricing (apuntamiento) and revenue per kWh generated.
Avoid economic losses due to forced curtailment.
Participate in new business models, such as energy communities or demand aggregators.

In addition, in industrial systems, batteries help improve power quality, reduce peak demand, and enhance system stability.

According to recent data, more than 110 GWh of renewable energy was curtailed in Spain in the first quarter of 2023 alone, mostly wind power. This phenomenon is expected to continue growing if structural solutions are not implemented.

New European regulations—such as Regulation EU 2023/1542—already include measures to promote battery storage, repairability, and eco-design. The mandatory inclusion of storage systems in new renewable energy parks is also being promoted.

Conclusion: towards a renewable system without waste

Curtailment is the direct consequence of partial success: we have installed a lot of renewable generation, but without the necessary infrastructure to take full advantage of it. If we want a clean, stable, and profitable system, we must integrate technologies such as energy storage and a smart grid that efficiently connects generation and consumption.

The solution is not to halt renewable growth, but to make it smarter and more resilient. And along that path, batteries and digitalization play a leading role.