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Optimisation of Power & Water Supply System Operation

Optimisation of Power & Water Supply System Operation
AQUARIUS Demonstration System Model - Daily Simulation

The Challenge

Rising demands and energy prices, and the threat of increased flow variability due to climate change, will continue to heighten appreciation of water as a scarce and valuable resource. It is thus vital that water resource systems be operated as efficiently as possible.

Benefits from the conjunctive use of water sources and different forms of electricity generation have led to the development of many computer programs for simulating and optimising system operation over both long and short time scales.

In the past, computational constraints have often dictated that significant simplifications be made when simulating and optimising long and short term operating policies. However, continuing advances in computer technology now make it possible to create a new generation of software which eliminates the need for many such simplifications, whilst providing greater transparency of the decision making processes involved.

Program Scope

Drawing on experience in modelling water supply and hydro-thermal power systems throughout the world, AQUARIUS has been developed to provide a powerful, yet user friendly, software package for simulating and optimising the operation of water resource systems of virtually any size and complexity.

In addition to component operating costs and physical constraints on their usage, detailed account can be taken of statutory and environmental constraints, and the imposition of demand management measures. Modelling of multiple demand areas and transmission systems enables consideration of losses, and the determination of marginal supply costs.

AQUARIUS uses Linear Programming to minimise costs of system operation within each time step, according to specified operating policies, and stochastic Dynamic Programming for deriving long-term policies which satisfy prescribed supply reliability criteria.

Simulation Module

This module simulates system performance over a sequence of inflows when operated according to specified rules. The module is automatically employed as part of the long-term operating policy optimisation and 'yield determination' facilities, to evaluate costs and supply reliability.


A menu driven Graphical User Interface is employed for defining the components and configuration of the system to be modelled, and the input or modification of associated data via on-screen templates.


Whilst most simulation programs employ a 'step-by-step' approach for allocating resources to demands in each time step, in accordance with defined operating rules and 'priorities', AQUARIUS uses Linear Programming (LP).

The LP problem is automatically formulated from the system configuration and associated data, and guarantees that the least cost solution is obtained which satisfies the constraints imposed. A further advantage is the identification of marginal supply costs at all demand centres and transmission system nodes.

Modelling Features

AQUARIUS can model a wide range of water and power system components in considerable detail. For example: evaporation and seepage losses, maximum release rates and hydro-plant efficiencies as a function of reservoir level; 'times-of-travel', and transmission system losses. Detailed consideration can also be given to the definition and imposition of Demand Management measures and rationing.

Facilities are included for short-term flow and wind speed forecasting based on historic records or specified probability function parameters.

AQUARIUS allows modelling of conventional control rules for individual reservoir operation, release balancing and pumping, as well as 'multiple regime' and Stored Water Value system based policies.

Direct comparisons can thus be made between alternative approaches employed for system operation.

Up to 24 load blocks can be defined for modelling daily electricity demand variations and optimising the outputs from hydro-electric, thermal and wind power plants, and transmission line flows in each block. 'Take or Pay' supply contracts can be modelled as well as capacity and availability charges and emissions constraints.

Simulations can be undertaken using daily, weekly or monthly time steps, over historic or generated flow sequences, or for 7 day periods based on current starting conditions and forecast inflows and demands.

Dimension limits can be set by the user to match those of the system to be modelled, enabling the analysis of systems of virtually any size and complexity, while minimising computer memory needs.


As a simulation proceeds, AQUARIUS can display screen graphs to show the behaviour of up to 15 user selected system components or groups of similar components. A separate 'window' gives the simulation results 'to date', including operating costs and penalties.

Outline Description of Program AQUARIUS

Detailed simulation outputs are automatically stored in a Microsoft ACCESS© format database, providing full modelling transparency.

Utilities are included for direct inspection of all database contents, thus facilitating internal and regulatory audits.

AQUARIUS includes comprehensive screen and printed graphical output facilities, enabling the user to plot any combination of values stored in the database as time series, or as accumulations over weekly, calendar monthly, annual or simulation period time periods.

Outline Description of Program AQUARIUS

Time series can also be viewed in tabulated form, or output as a 'Comma Separated Values' files for direct input to spreadsheet programs.

Values for a particular time steps, or averages over the simulated period, can also be displayed on 'mimic' diagrams. Multiple mimic diagrams can be built thus enabling, for complex systems, the display of results for different parts of the system in varying levels of detail.

Outline Description of Program AQUARIUS

For power system components it is possible to display energy based quantities over the time step, or power based quantities in each load block.

A facility is also provided to automatically step through the simulated period, and such displays enable the user to rapidly analyse system behaviour, and can be printed with high definition for inclusion in reports.

Operating Policy Optimisation

AQUARIUS enables the optimisation of long-term operating policies with the objective of minimising average operating costs while satisfying given supply reliability criteria. The latter may be defined by the consecutive or total incidence of demand management measures, supply deficits or minimum reservoir levels.

AQUARIUS permits the optimisation of control rules for individual reservoir operation, release balancing and pumping, as well as 'multiple regime' and Stored Water Value based policies. Direct comparisons can thus be made between alternative approaches employed for system operation.

To optimise such policies, AQUARIUS employs PWSC's Stochastic Dynamic Programming algorithm to determine the optimal operating 'regime' to be adopted as a function of the time of year and the water held in reservoir storage. Such regimes can be defined in terms of target reservoir release rates, river and groundwater abstractions, thermal power plant outputs or stored water values. An example optimised policy is shown below.

Outline Description of Program AQUARIUS

Experience shows that application of this fully integrated simulation/optimisation technique results in practical operating policies, and can yield significant savings when compared with more conventional methods of operation.

Stored Water Value rules can be particularly effective for balancing releases in multiple reservoir systems, and provide information often required for short-term optimisation models.

The optional short-term optimisation module is capable of optimising system operation for up to 7 days ahead, based on forecast inflows, wind speeds, component availabilities and demands. For power system applications up hourly generation plant schedules can be produced.

Yield Determination

Planners and regulators frequently require an assessment of the maximum water or electricity supplies that can be met by a system, based on given flow sequences and supply reliability criteria. For water resource/supply systems such estimates are sometimes referred to as 'firm yields' or 'deployable outputs'. For hydro-thermal power generation systems they are analogous to 'firm energy' assessment if a single load block is employed in the simulation.

AQUARIUS incorporates a search procedure for identifying the demand multiplier consistent with satisfying such criteria, and also permits the user to select the individual water and electricity demands to be subjected to the multiplier. A key attribute of the approach is that the assessment takes into account the constraints on system operation incorporated within the AQUARIUS simulation model.

Programming Details

Program AQUARIUS is written in Microsoft Visual Basic© (Version 6), and will run under Microsoft Windows 95, 98, NT4, 2000, XP and 7 operating systems. All code, including that associated with the proprietary Linear and Dynamic Programming algorithms, has been written by PWSC, thereby eliminating reliance on any third-party suppliers.

Applications and Availability

In addition to long and short-term operations planning, potential applications of AQUARIUS include tariff setting, supply contract evaluation, water and energy trading, and the evaluation of proposed development projects for expansion planning purposes.

It is available for purchase by utilities, consultants and lending agencies, subject to standard software protection measures being installed.


While other software packages are available for modelling water resource, water supply and hydro-thermal power systems, AQUARIUS has a unique combination of attributes, including:
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Water Resource & Hydro-Thermal Power Systems Modelling - Optimization of Large-Scale Hydropower System Operations - Power Generation Optimisation