Adequacy Assessments

Resource Adequacy Assessments are performed to estimate the ability of an energy system to meet demand over the near future (a few to several years). These assessments take into consideration the demand forecast, generator availability, and transmission constraints including scheduled and unscheduled outages of system facilities. It assesses if, how and at what cost the system will be able to provide the energy corresponding to consumption for a given time frame (Figure 1). Usually, the assessment is done regularly (e.g. every year or every two years) evaluating each time the adequacy of the power system up to 10 years ahead. Due to climate change there is an increasing need to include climate projections in Adequacy Assessments.

Figure 1. Results from an Adequacy assessment for the European community. LOLE (Loss of Load Expectation) values for the scenario ‘National Estimates 2030’. Circles for bidding zones with LOLE values smaller than 0.1 hours/year are not represented. Source: ENTSO-E

For countries that are just starting to install renewable plants, early action in developing RE forecasting and implementing regular Resource Adequacy Assessment can help to integrate RE into the grid in a more manageable, efficient and effective way.

Adequacy studies are performed to:

Determine the supply/demand balance
Identify the amount, timing, location, and duration of capacity needs
Assess the ability of different resource types to meet capacity needs
Guide the scope and timing for resource acquisition and investment decisions, by providing information on how market mechanisms and regulations, such as energy storage and demand response, are developed and put into place to facilitate the integration of renewable energy resources with other technologies
Provide recommendations on outage management and capacity export decisions
Adequacy studies can be used to identify and solve the gaps and obstacles in developing a dependable and resilient grid, as well as to plan and run the power system with high levels of penetration from renewable energy.

Adequacy Assessments are becoming more challenging due to the growing intricacy of the highly interconnected systems (with other regional or international grids) and their complex hybrid energy mixes with increasing contribution from renewables – some of which are decentralised energy systems, which in turn create a need for storage. They also need to account for a rising influence of demand side management, changing electricity demands (e.g. electric vehicles, heat pumps, etc) and evolving policies (like those promoting phasing out fossil-fuels). Although some of these elements are not directly about generating electricity, they certainly influence system’s dynamics.

What

More than ever, Adequacy Assessments need to consider and give answers to various aspects of the energy system, especially accounting for future climate variations. This is why it is no longer sufficient to perform energy system modeling based on historical climate data: climate projections are therefore required to create different scenarios of energy generation and demand, and identify the appropriate measures and technologies to ensure the reliability and resilience of the electricity supply. With these being the basis upon which adequacy assessment simulations are run (see below the HOW section for a more detailed description of the methods used), the simulations allow to:

Determine the supply/demand balance at a given time step (usually hourly)
Identify resource adequacy concerns (and their causes including amount, timing, location and duration) and – where regulated – assess if these issues (e.g. when load and duration of demand are not met) are within the regulation values.
Determine the optimal level of generation capacity which need to answer the following questions:
- Promote (local) generation or increase interconnection capacity?
- Promote generation or promote demand response?
Identify the optimal mix of different technologies:
- In terms of residual load (also called net demand)—given by the power demand minus non-dispatchable energy generation (mainly, wind and PV)—featuring unpredictable trends which need deeper ramp-up and ramp-down requirements. In this context the solution should be the optimal mix of base and peak generators, cross-border capacity, storage and changing demand (e.g. seasonal changes)
- In terms of energy mix – magnitude of the different risks associated with their supply and assess the ability of different resource types to meet capacity needs
Evaluate the optimal sustainability of the solution.
Assess System flexibility for unexpected strains on the system
Evaluate cross-border and interregional interconnections – they also play a fundamental role in the integration of renewable energy, participation in the generation adequacy among interconnected countries and support of peak demand hours with power imports and provide guidance for capacity export decisions
Include change in generation capacity – each renewable source needs to be modelled to forecast its generation variability and to assess its ability to meet capacity needs, which is location and time-of-the-year dependent. Important to consider climate change scenarios influencing (change in) local generation capacity
Consider planned network development during the evaluated period – due to new renewable power plants, end-of-term of old assets, mothballing (deactivation and preservation of equipment or production facility to reassess its use in the future), and decommissioning of plants using fossil fuels. Provide guidance on the scope and timing for resource acquisition and investment decisions. Provide recommendations on outage management.
Provide insight into the amount of incremental new capacity needed in the future – over and above what existing resources can provide and give guidance on the scope and timing for resource acquisition and investment decisions.
Evaluate relevant sensitivities on extreme weather events and, hydrological conditions
Provide recommendations on outage management and capacity export decisions – for example predicting service interruptions allows to optimize system decisions like redirecting transmission or distribution through alternative network paths

How

Evaluates each electricity system separately in those cases where grids are interconnected
Applies probabilistic calculations (like Monte Carlo simulations)
Applies a single modelling tool

Estimations are based on various climate years, which can be derived from historical reanalysis or from stochastic simulations (which allow to extend the sample to ~200 years). Extending the sample with simulations allows to better detect extreme conditions, and therefore, assess if demand can be met under such harsh conditions. Each climate year represents a consistent set of:

Temperature-dependent demand time series;
Wind and solar load factor time series;
Time series for hydro-generation, inflows, minimum/maximum generation or pumping capacity, and minimum/maximum reservoir level (where applicable);
Climate-dependent time series for other RES and other non-RES generation.

Simulations consist of a large number of scenarios, each representing a random realisation of probable events for the electricity grid such as unpredictable outages for both generation and transmission assets. These unpredictable outages are then combined with the climate years, which results in a large set of possible system states to be modelled. Results can then be assessed probabilistically, complying with the requirement of volatile modern power systems.

It is based on appropriate reference scenarios of projected demand and supply considering planned changes in assets/network evolution, installed capacity, energy storage, demand management, interconnection targets (imports and exports) and very importantly sensitivities on extreme weather events and hydrological conditions.

Outputs

An Adequacy Assessment identifies the sources of possible resource adequacy concerns, in particular whether it is a network constraint, a resource constraint, or both. Typically, it includes the following indicators:

EENS (Expected Energy Not Served; Number of GWh not delivered)

LoLE (Loss of Load Expectation; Average power not delivered)

LoLD (Loss of Load Duration; Average number of hours not served)

Engagement

For a useful Adequacy Assessment there is a need for a broad engagement with stakeholders and communities across the region, critically including transmission system operators. It is an iterative process that must consider short-, medium- and long-range electricity needs as well as impacts on cost, reliability, the environment and others. A good stakeholder engagement should allow to collect data, compile databases, compare scenarios and benchmark solutions.

Also, the increasing use of Smart technology and automated applications are providing valuable meteorological and energy demand data from the energy user. This can increase the predictive power of the models, therefore maintaining, or even improving, customer engagement and satisfaction levels.

Figure 2. Diagram showing the European Energy Resource Assessment (EERA) roadmap for the recent EERA implementation. Source: ENTSO-E

References

IESO (2020) APO-Resource Adequacy and Energy Assessments Methodology Independent Electricity System Operator (IESO) Annual Planning Outlook, Ontario, Canada
ENTSO-E, 2015 Guidelines for Cost Benefit Analysis of Grid Development Projects, European Network of Transmission System Operators for Electricity (ENTSO-E), Brussels.
ENTSO-E (2021). European Resource Adequacy Assessment. European Network of Transmission System Operators for Electricity (ENTSO-E), Brussels.
Poncela Blanco M; Spisto A; Fulli G; Hrelja N. Generation Adequacy Methodologies Review. EUR 27944. Luxembourg (Luxembourg): Publications Office of the European Union; 2016. JRC101590