About electricity tariffs
The Electricity Tariff component in InfoWorks WS Pro allows you to take into account the cost of various control strategies when working out the optimum control strategy for a system.
With the Electricity Tariff editor, tariffs can be created that represent the charging structure of electricity suppliers.
This page contains the following sections:
Tariff types
Prior to privatisation of the UK electricity industry, each electricity board issued a choice of tariffs to the water companies for running the pumping plant in their areas. The tariffs, which are still published for each electricity supplier, are complex but followed similar principles across the UK. For the larger sites (that is, those for which the tariff modelling module in InfoWorks WS Pro is appropriate), the tariffs fell into three main categories:
- Demand: This tariff had no restrictions or penalties and electricity was supplied effectively on demand to the consumer.
- Night/Day: This tariff offered incentives for night time use and has always been more attractive financially in the water industry where night time pumping may be possible by using reservoir storage.
- Seasonal Time of Day (SToD): This relatively recent form of tariff offered higher savings if certain peak periods could be avoided generally at winter peak hourly demands.
Following the privatisation of the electricity industry, however, major consumers are now able to negotiate contracts with a variety of electricity suppliers and this has made cost modelling very much more difficult. For this reason the InfoWorks WS Pro module has not been updated and further enhancements will depend upon feedback from users and the feasibility of providing a reliable energy cost modelling package under the conditions which now prevail in the UK.
Currently it appears that all the suppliers tend to follow broadly the same tariff structure, though the unit charge per kWh varies between supplier. For this reason the existing module in InfoWorks WS Pro can still be used as a good relative guide to the tariff that is most appropriate for pumping stations in the network.
Some of the common elements of electricity tariffs (UK tariffs) are listed below.
Standing charge
A fixed charge that covers provision of metering, meter reading, billing, and other fixed costs.
Availability charge
This charge is also known as the capacity charge. The electricity company undertakes to provide a supply to a site up to a defined limit (usually equal to total installed power). The availability charge is a unit rate of charge per kVA (or kWh) of demand available to the customer whether it is used or not, and is therefore independent of consumption.
Maximum demand charge
Maximum demand is measured as twice the highest number of electricity units (kiloWatt hours) supplied to the site over any half hour of a given time period (typically one month).
The maximum demand charge is a unit charge multiplied by the recorded maximum demand in peak demand periods.
Maximum demand charges are generally applied during winter months when electricity is in greater demand and therefore more difficult to supply. The higher price encourages users to reduce peak demands during these periods.
Unit charges
Unit charges are the charges for the total energy used by the customer and are charged per kWh.
The rate varies between day and night periods and may also vary with season. Rates are lower during the night and higher during the day to encourage users to take supply at off peak times.
Seasonal Time of Day (SToD)
Multi-rate tariffs are typically known as Seasonal Time Of Day (SToD) tariffs. This is a supply tariff where the unit rates charged vary between day and night periods and also with season. Rates are lower during the night and higher during the day to encourage users to take supply at off peak times. They may also vary between weekdays and weekends. Rates are highest in the winter months at peak demand when the electric system is under severe loading.
Reactive charge
The reactive charge is a charge related to the efficiency of equipment being supplied.
Electrical equipment like transformers and motors require an electro-magnetic field to work. The power required to generate this field is called the reactive power and is measured in kilovolt-amperes-reactive (kVAr). This power does not produce any useful work.
The power used to operate the equipment is known as the working power, measured in kW.
The sum of the working power and reactive power makes up the apparent power (kVA) - the power supplied to the load.
The power factor is a measure of efficiency and is the ratio of working power to apparent power. Reactive charges are sometimes levied when power factors fall below 0.9.
Climate change levy
The climate change levy was introduced in the UK on 1 April 2001.
The levy was established as part of the UK's commitment to reducing greenhouse gas emissions as agreed under the 1997 Kyoto Protocol on Climate Change.
The levy is charged at a flat rate on each kWh of energy consumed and is applicable to certain forms of fuel (electricity, natural gas, coal, and LPG). The intention is to increase energy efficiency by reducing consumption of traditional forms of energy and promote use of renewable forms of energy.
Modelling of electricity tariffs
InfoWorks WS Pro incorporates a tariff modelling component that enables you to compute energy costs for different operating strategies at the same time as modelling the effects of the strategy on flow, level, and pressure. Risk management assessments are therefore possible in terms of cost saving, storage levels, and pressures in the system.
This is particularly important with the move towards Seasonal Time of Day tariffs (SToD) in the UK. There are generally significant savings to be made with such tariffs with the appropriate pump control devices.
Cost modelling can be complex, with tariffs being made up of many elements. The InfoWorks WS Pro module takes into account the most common UK electricity tariff elements, which make up the bulk of the costs.
Due to the wide variation of charging schemes, further enhancements of the module will depend upon feedback from users.
Tariff charges
Rates can be defined for HIGH (>1000 volts) and LOW voltage electric systems.
The following items are taken into account in the model:
- Standing charge - fixed charge per month
- Availability charge - unit charge per kVA per month
- Maximum demand charge -unit charge per kVA of maximum demand
- Unit charges: day/night - unit charge per kWh
- Seasonal demand charges - unit charge per kVA
There are other items which are not included:
- Excess demand charges - vary wildly from one supplier to another
- Unit charges: 24 hour kWh rates - not used very much by water companies
- Reactive charges - usually a very small amount
- Purchase cost adjustment - arranged on individual basis
As the top five items make up the bulk of costs, the computed costs will be very close to the real ones, permitting you to evaluate the relative merits of different tariffs.
Cost calculations
A simulation run by InfoWorks WS Pro will yield for each PST:
Power (kW):
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Electric power (kW) is calculated as:
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where: REMP is the ratio between electric and mechanical power PHyd (t) is the Mechanical Power at timestep t |
Cost of energy consumption (due to daily rates charges):
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where: UNCH = Daily Rates Unit Charge Dt = Timestep interval (mins) / 60 mins |
Cost of availability:
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where: PMAXLicenced = Licenced Maximum Power Demand of Pump Station Availability Rate of Power = cost defined on Application Dates & Fixed Rates page of Electricity Tariff |
Monthly charge for maximum power used:
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where: PMAX= the Maximum Averaged Electric Power (averaged over kVA Time Interval specified on the Max Power Demand Rates 1 page of the Electricity Tariff) PF = Power factor defined on the Pumping Station Parameters Page of the Pump Station Property Sheet Max Power Demand Rate = cost defined on Max Power Demand Rates 1 page of Electricity Tariff |
Editing electricity tariffs in InfoWorks WS Pro
An electricity tariff component contains one or more tariffs that describe the charging schemes for supply of electricity to a site, including fixed charges, 24 hour charging profiles, and changes in charging profiles over the year.
An electricity tariff component is defined and edited using the Electricity Tariff editor.
Electricity tariffs can be assigned to pumping stations. For more detailed information on assigning electricity tariffs and editing the associated data fields for cost calculations, see the Assigning electricity tariffs to pumping stations topic.
Every simulation can include an electricity tariff component. An electricity tariff component is included by adding it to the Schedule Hydraulic Run view. See Simulations for more details.
