Annex C: Technologies’ functionality and flexibility potential

Dispatchable generation

Dispatchable generation consists of power plants that can be controlled and adjusted in real-time to match electricity demand. These sources include hydropower, bioenergy, gas-fired power plants, and to some degree nuclear power.

Contribution to system security:

Real-time: Rapidly ramps up or down to stabilise grid frequency and voltage.
Within-day: Supports peak load management by adjusting output during morning and evening demand spikes.
Multi-day: Provides backup during periods of low renewable generation, such as dunkelflaute.
Seasonal: Reservoir hydropower and power plants using storable fuels can retain energy for months, making them crucial for securing winter supply. This is particularly important for hydropower in the Nordic region, where inflows to reservoirs are minimal during winter. To ensure a stable energy supply, stored water (representing stored energy) must last throughout the season until snowmelt fills reservoirs in spring.

Intermittent renewable energy sources (RES)

Intermittent RES, such as onshore and offshore wind and solar PV, generate electricity based on natural conditions, resulting in variable and less predictable output. As a result, they are not considered technologies suited for ensuring system stability but rather a key driver of instability. However, they are an integral part of the green transition. In a market-wide CRM, these assets can also receive capacity payments, though with a derating factor to account for their limited reliability in delivering capacity during scarcity events.

Contribution to system security:

Real-time: Limited direct contribution, but smart forecasting and curtailment strategies help mitigate short-term imbalances.
Within-day: Solar PV provides peak generation during daylight hours, while wind generation often complements night-time demand.

Multi-day: Wind and solar can reduce reliance on fossil-based generation but require backup when generation is low.
Seasonal: Offshore wind aligns well with winter demand peaks, while solar PV contributes more significantly in summer, highlighting the need for seasonal storage.

Short-duration storage

Short-duration storage solutions, such as lithium-ion batteries, supercapacitors, and flywheels, store energy for seconds to a few hours, enhancing grid flexibility. The latter two has low energy density but can deliver bursts of power within milliseconds. They are typically used to provide real-time frequency response only.

Contribution to system security:

Real-time: Provides instantaneous frequency response and grid stabilisation.
Within-day: Manages fluctuations by storing excess solar or wind power and discharging during peak demand.
Multi-day & seasonal: Limited contribution due to storage constraints; primarily used for intra-day balancing rather than prolonged shortages.

Medium-to long-duration storage

Medium- to long-duration storage covers technologies like flow batteries and sodium-sulphur batteries, which store energy for 4–24 hours. This category represents immature technologies.

Contribution to system security:

Real-time: Not optimised for fast response but can support grid balancing through controlled discharge.
Within-day: Essential for shifting excess midday solar power to meet evening demand.
Multi-day: Extends system resilience by covering short renewable droughts.
Seasonal: Limited seasonal impact due to moderate storage capacity.

Long-duration and seasonal storage

These technologies, including pumped hydro storage (PHS), hydrogen storage, iron-air batteries, and thermal energy storage (TES), can provide multi-day and seasonal energy reserves.

Contribution to system security:

Real-time: Some options, like PHS, provide fast ramping capability.
Within-day: Can discharge stored energy over extended periods, improving grid stability.
Multi-day: Iron-air and zinc-air batteries can sustain output for days, bridging renewable shortfalls.
Seasonal: Hydrogen storage and TES in district heating networks enable long-term energy shifting, addressing winter shortages.

Demand-side response (DSR)

DSR refers to mechanisms that adjust electricity consumption to match grid conditions, with participation from industrial, commercial, and residential consumers. DSR has great potential and could solve most of the challenges caused by the green transition. However, attracting demand-side to respond to price signals has proven difficult. While this is a challenge that must be addressed to fully utilise DSR flexibility, the below describes its potential.

Contribution to system security:

Real-time: Supports frequency control by reducing or shifting demand instantly.
Within-day: Helps smooth peaks by incentivising off-peak electricity use.
Multi-day: Industrial demand flexibility (e.g., electrolysis, cold storage) can help manage prolonged supply shortages.
Seasonal: Reduces strain on the grid in winter by shifting heating and industrial loads.

DSR with storage

A combination of demand flexibility and energy storage, such as electric vehicles with vehicle-to-grid (V2G) capability, industrial facilities with on-site batteries, and electrified district heating with TES or alternative fuels.

Contribution to system security:

Real-time: EVs can provide rapid frequency response via bidirectional charging.
Within-day: Enhances peak shaving by dynamically adjusting demand.
Multi-day: Batteries within DSR programmes can store and discharge power when required.
Seasonal: District heating with TES ensures reliable winter heating, reducing electricity demand.

Grid infrastructure

Grid infrastructure includes HVDC interconnectors, smart grids, dynamic line rating (DLR), and virtual power plants (VPPs), enabling efficient energy transmission and distribution.

Contribution to system security:

Real-time: Smart grids improve system monitoring and response times, reducing failures.
Within-day: HVDC interconnectors allow cross-border electricity exchange, helping meet peak demand.
Multi-day: Reinforced transmission networks can import/export energy during renewable shortfalls.
Seasonal: Enhances grid resilience by connecting diverse renewable resources across regions.