Glossery Of Terms

Built in help text and supporting documentation supplied with the AQUARIUS software.

Interactive facilities in AQUARIUS for defining and editing model data such as hydrology, demands and plant characteristics.

Term for annotated system schematics created by Programs AQUARIUS and CAPRICORN and used to display simulation and optimisation results. Such mimic diagrams can include all types of system components and visualise data stored in the database files created during AQUARIUS simulations.

Use of AQUARIUS to optimise operating rules for reservoirs, hydropower plants and power supplies over daily or seasonal time scales.

Definition of operating zones or regimes in AQUARIUS which guide releases and generation decisions.

Use of AQUARIUS to run alternative hydrological and demand scenarios or operating rule sets for comparison.

The time stepping simulation model within AQUARIUS that mimics system behaviour under specified operating rules.

Facilities in AQUARIUS for viewing and outputting simulation results.

Length of the modelling period in AQUARIUS, for example daily, weekly or monthly time steps.

Application of AQUARIUS to estimate firm energy or water supply that can be delivered at specified reliability levels.

Typical planning studies for which CAPRICORN is used, such as national master plans, interconnection studies and tariff support.

Structured data describing candidate generation and transmission projects used by CAPRICORN when building expansion plans.

Set of physical, operational and policy constraints that CAPRICORN must respect when building expansion plans.

Use of CAPRICORN to compare the costs and benefits of alternative power system development strategies.

Different hydrological sequences or inflow scenarios used within CAPRICORN to test robustness of expansion plans.

Determination of commissioning years for new generation and transmission projects within CAPRICORN.

The optimisation module in CAPRICORN that selects preferred expansion plans and operating decisions subject to technical and economic constraints.

Tabular and graphical outputs produced by CAPRICORN summarising investments, generation, costs and reliability indices.

Complementary simulation routines in CAPRICORN that test the performance of candidate expansion plans and dispatch strategies.

Modelling of new transmission lines and interconnections within CAPRICORN expansion planning studies.

Brazilian wholesale electricity market operator supported by PWSC for validation of long- and medium-term planning tools.

Multilateral development bank for which PWSC has undertaken several hydro-thermal planning and training assignments.

Sri Lankan power utility for which PWSC has assisted with hydro-thermal expansion planning and operational optimisation.

European institution for which PWSC developed planning manuals and managed decentralised energy co-operation programmes.

Regulatory bodies in England and Wales for which PWSC developed MOSPA/MOSES tools and water resource strategy studies.

Consultancy supported by PWSC on hydropower scheme economic evaluations.

Ethiopian utility for which PWSC helped develop and apply national generation and transmission master plans.

German technical co-operation agency for which PWSC helped frame hydropower evaluation work in Sri Lanka.

Power engineering consultancy for which PWSC supplied optimisation inputs to Tanzanian planning studies.

German engineering consultancy frequently partnered with PWSC on hydro and power planning studies.

Economic consultancy for which PWSC provided modelling support for Tanzanian tariff and optimisation studies.

Intergovernmental river basin organisation for which PWSC undertook basin hydropower expansion studies.

Power engineering firm assisted by PWSC on Transkei hydroelectric simulations.

Turkish power sector institutions for which PWSC reviewed investment planning and proposed modelling frameworks.

Brazilian ministry for which PWSC advised on restructuring, modelling needs and grid procedures.

Scottish utility for which PWSC advised on marginal production cost models.

Consultancy for which PWSC reviewed optimisation studies for a major Nepalese multipurpose scheme.

Consultancy supported by PWSC on Peruvian hydroelectric optimisation.

Scottish utility advised by PWSC on optimisation of mixed hydro-thermal generation and trading.

Cameroon national utility for which PWSC developed river system management and reservoir optimisation tools.

National utility of Tanzania for which PWSC has provided long-term support on hydro-thermal operation, optimisation and dispatch.

UK aid agency for which PWSC contributed to major hydroelectric appraisal and planning studies.

Water company in North West England for which PWSC has developed and extended major water resource system models over several decades.

UK consulting engineers supported by PWSC on pumped storage scheme design studies.

International development bank for which PWSC has provided expert advice and optimisation studies in several regions.

Assigned monetary value per unit of supplied energy, often based on average or marginal tariffs.

A limit on allowable carbon dioxide emissions from power generation within an optimisation study.

A penalty cost applied in models when demand cannot be fully met, used to represent the economic impact of supply shortfalls.

Rate used to convert future costs and benefits to their present value in economic assessments.

The assessment of costs and benefits associated with alternative operating policies or expansion plans.

Price assumptions for domestic sales and exports of electricity used in economic and financial evaluations.

Impacts of power system development that are not directly captured in market prices, such as environmental and social effects.

Evaluation of alternative development strategies against several economic, environmental and social criteria, rather than cost alone.

Measure of the net economic worth of a project or development plan, calculated by discounting costs and benefits to a common base year.

A structured process for assessing environmental impacts of power development plans, complementing traditional economic analysis.

Operating or allocation policies where reservoir releases are wholly or partially determined by assigned water values as a function of current reservoir contents.

Combined live storage available to regulate inflows and match hydropower generation to demand.

A series of hydropower and storage reservoirs arranged along the same river system.

The amount of hydropower generation that can be guaranteed with a specified level of reliability.

Use of reservoir storage and operating rules to reduce downstream flood peaks.

A configuration of reservoirs, waterways and power stations used to generate electricity from water stored in upstream catchments.

The minimum flow that must be released downstream of a reservoir or hydropower plant to protect river ecosystems or other uses.

A reservoir scheme designed to serve several functions such as hydropower, water supply, irrigation and flood control.

Operating hydropower units mainly during daily or weekly peak demand periods.

A hydropower scheme that pumps water back to an upper reservoir so that it can be re used for generation at times of high demand.

The volume of water in a reservoir that lies below the lowest outlet level and cannot normally be used.

The rules and practices governing how water is stored and released from reservoirs to meet power and water supply objectives.

A hydropower plant with little or no storage where output closely follows river inflow.

Model variables that represent choices to be made, such as reservoir releases, generation levels or new plant capacities.

Two broad approaches to representing uncertainty: deterministic models use single input traces, while stochastic models treat inputs as random variables.

A modelling approach in which optimisation is used to design operating rules or expansion plans and simulation is then used to test their performance.

Process of adjusting and checking a model so that it reproduces observed system behaviour with acceptable accuracy.

The quantity that an optimisation model seeks to minimise or maximise, such as total cost or net benefits.

The optimisation of day-to-day or seasonal operating policies for reservoirs, hydropower plants and power systems within specified constraints.

Checking whether preferred solutions remain acceptable when assumptions or data are varied within plausible ranges.

Evaluation of alternative future conditions or assumptions, such as inflow records, demand growth and fuel prices.

Investigation of how model results change when key input parameters are varied.

Equations and inequalities in the model that enforce physical, operational or policy limits.

Choice of the modelling period length, for example hourly, daily or monthly, when representing system behaviour.

Initial assessment of a wide range of potential projects to identify a manageable set of candidates for detailed optimisation.

Long-term planning of new generation and transmission investments to satisfy future demand and reliability targets at least cost.

Planning of new generation plant additions over the study horizon to meet projected demand and reliability targets.

A recommended sequence of projects and commissioning dates produced by expansion planning studies.

Approach to expansion planning that considers supply side options and demand side management measures on a comparable basis.

Consideration of new cross border transmission links and associated import or export opportunities in expansion studies.

Development plan that minimises discounted system costs subject to demand, reliability and policy constraints.

The percentage by which installed dependable capacity exceeds forecast peak demand in each year.

Quantitative targets such as loss of load expectation or maximum expected unserved energy that expansion plans must satisfy.

The timing and phasing of new projects over the planning horizon to match demand growth and financial constraints.

Planning of new transmission lines and substation reinforcements required to support generation development and demand growth.

Services other than energy that are required to maintain secure and reliable operation of the power system.

Allocation of generation among available units in each period to meet demand at minimum operating cost.

Coordinated operation of hydropower and thermal plant to make best use of water and fuel resources.

Operational scheduling of imports and exports over interconnections between power systems.

Adjustment of generation output to track gradual changes in demand over minutes to hours.

Planning of planned outages for inspection and maintenance while maintaining adequate capacity and security of supply.

Capacity that is kept available to respond to sudden changes in demand or unexpected loss of generation or transmission.

Use of certain generating units primarily during daily or seasonal peak demand periods.

Short- and medium-term scheduling of generation and transmission to meet electricity demand while respecting technical limits.

Operational limits imposed to ensure the system can continue to operate acceptably after credible contingencies.

Short-term scheduling problem that decides which generating units should be on or off in each period.

Application of simulation and optimisation models to assess the impact of climate variability and drought sequences on system performance.

Detailed assessment of a specific hydropower project to confirm its technical, economic and environmental viability.

Planning study that examines how best to develop the hydropower potential of a river basin or cascade of sites.

Analysis of new cross border transmission links and associated power trade between neighbouring systems.

Study that uses detailed simulation and optimisation to refine day to day or seasonal operating rules for existing systems.

Comprehensive long term study that defines an overall development strategy for a country or region's power system.

Study that investigates refurbishment, modernisation and uprating options for existing hydropower or thermal plants.

Study that examines how different development or operation strategies affect electricity tariffs and economic indicators.

Structured programme in which PWSC software and modelling methods are transferred to client staff through training and joint studies.

Risk that extended periods of low inflow will reduce generation or water supply below acceptable levels.

Reliability index that measures the expected volume of energy demand that cannot be supplied over a period.

Amount of generation capacity that can be relied upon to be available with a specified level of reliability.

Reliability index that measures the expected number of hours or days in a period when demand cannot be fully met.

Reliability index that measures the probability that available capacity will be insufficient to meet demand in a given period.

Assessment of reliability using probability distributions for key uncertainties rather than single deterministic cases.

Specified level of reliability, expressed using indices such as LOLE or EUE, that a system or plan must meet.

Relationship between the cost of additional investment or operating measures and the resulting improvement in reliability.

Broad concept describing the ability of a power or water system to supply customers reliably under normal conditions and credible disturbances.

A numerical measure of how consistently a system can meet demand, often expressed as the frequency or size of shortages.

Model variables that represent choices to be made by the optimisation, such as generation levels or investment decisions.

Simulation approach that uses a single specified inflow and demand trace without explicit probabilities.

Optimisation approach that breaks a multi stage problem into smaller stages linked by state variables.

Optimisation technique in which the objective function and all constraints are linear in the decision variables.

The use of linear or non-linear optimisation techniques to find the best decisions subject to constraints representing the physical system.

Use of repeated simulation runs under different assumptions or scenarios to explore uncertainty and policy choices.

A model that mimics the behaviour of a water or power system over time by stepping through inflows, demands and operating rules.

Length of each period in a simulation run, for example hourly, daily, weekly or monthly.

Variables that summarise the current condition of the system in a simulation model, such as reservoir storage or unit status.

Optimisation framework that explicitly represents uncertainty using scenarios or probability distributions.

PWSC software for integrated modelling of power and water supply system operation using simulation and optimisation.

PWSC software for planning and optimisation of power system expansion and related investment decisions.

Coordinated use of surface water and groundwater resources to improve reliability and efficiency.

Pre-agreed set of actions for managing water resources during extended dry periods.

Specification of flow patterns needed to sustain downstream ecosystems and river uses.

A water resource system where reservoirs, rivers, demands and transfers are modelled together rather than in isolation.

Scheme that transfers water from one river basin to another to relieve deficits or support hydropower generation.

Area of land supplied with irrigation water from a particular reservoir, canal or diversion.

System with several reservoirs whose storage and releases must be coordinated to meet downstream objectives.

Long-term plan for the development and operation of water infrastructure within a river basin.

System supplying treated water to towns, cities and industrial users from reservoirs, rivers and groundwater sources.

Rules that determine how available water is shared between competing sectors and regions.