GB2481048A

GB2481048A - Thermal storage device controller

Info

Publication number: GB2481048A
Application number: GB1009698.0A
Authority: GB
Inventors: Alan William Mcdonald
Original assignee: Basic Holdings
Current assignee: Basic Holdings
Priority date: 2010-06-10
Filing date: 2010-06-10
Publication date: 2011-12-14
Anticipated expiration: 2030-06-10
Also published as: GB2481048B; GB201009698D0

Abstract

AÂ controller 120 provides selective activation of thermal storage devices, such as electrical storage heaters 130 or water cylinders 140, within a network to balance requirements of a user to manage their heating and the network operator 110 to balance the load available with the load on the network 100, some of which may be generated by renewable sources. The controller includes an interface for receiving a signal from a network operator regarding the availability of power within the supply network and a processor that determines whether to activate a heating element of a thermal storage device upon receipt of the signal. The controller can monitor the status of the devices and may consider historical data when determining operation times or may be able to change the thermal storage capacity of the devices. An electrical grid management tool may comprise a plurality of these controllers with a network of storage devices.

Description

Thermal storage device controller

Field of the Invention

The present invention relates to electrical grids and load management within same. The invention more particularly relates to thermal storage devices provided within an electrical network and in particular to controllers for same.

Within the context of the present teaching the term thermal storage device includes electrical storage heaters which provide space heating and water cylinders which are heated using an electrical element. The invention also relates to the control of the operation of such thermal storage devices in response to variances in expected load within an electrical grid.

Background

With the developments of green technologies and the use of renewable resources such as wind and wave energy for provision of mains electricity more and more electrical network utilities are considering the use of such resources in the make-up of their electrical supply.

While these renewable resources have many advantages including their sustainability they suffer in their lack of consistent contribution to the overall make up of the network supply. For example wind generators can only provide energy when the wind is blowing and wave energy convertors require a wave pattern to provide power. Both of these have weather and climatic considerations which do not necessarily match the load requirements of the network.

As a result of the fluctuation in supply from these renewable energy resources the network operators typically also provide traditional sources of power when defining the overall make-up of the origination of the power.

However these "carbon-based" power sources cannot typically be activated immediately and require time to come on-line to ensure the grid does not suffer from brown-outs or more critically complete lack of power. To ensure that there is sufficient power for the load at any one time, the predictable power supplies are typically always operated with the transient power that is available during the day from the renewable resources being used as available and as required.

However where the available power from such resources exceeds the load on the network the network utility operator will typically discard that energy by deactivating the wind turbine or the like in preference to stopping the predictable power supply. This load management dilemma results in not all available power from the renewable resource being utilised.

Different solutions have been considered for such problems including those generally considered as grid energy storage where electrical energy is stored during times when production (from power plants) exceeds consumption and the stores are utilized at times when consumption exceeds production.

Considered solutions contemplate powering batteries for electrical vehicles, compressing air and use of flywheels. All of these while useful in addressing the variances in the load thereby improving efficiency and decreasing energy losses require a conversion to a energy storing mains electricity grid which represents a very costly solution.

There is therefore a problem in management of such network loads to ensure that the use of renewable resources within a network grid can be optim ised.

Sum mary These and other problems are addressed by a thermal storage device controller in accordance with the teaching of the present invention. Such a controller provides for selective activation of thermal storage devices that are distributed within an electrical network so as to correlate their operation with available power from renewable resources.

Accordingly the invention provides a thermal storage device controller according to claim 1. Advantageous embodiments are provided in the dependent claims.

These and other features of the present invention will be better understood with reference to the following drawings.

Brief Description Of The Drawings

The present invention will now be described with reference to the accompanying drawings in which: Figure 1 shows in schematic form portion of an electrical grid network in accordance with the present teaching.

Figure 2 shows a controller in accordance with the present teaching.

Figure 3 shows in graphical form the effect of raising the point within a water heater on the available energy take-up.

Figure 4 shows in graphical form an exemplary form of a delay time calculation in accordance with the present teaching.

Detailed Description Of The Drawings

Exemplary arrangements provided in accordance with the teaching of the present invention will be described hereinafter to assist with an understanding of the benefits of the present invention. Such arrangements will be understood as being exemplary of the type of controllers that could be provided and is not intended to limit the present invention to any one specific arrangement as modifications could be made to that described herein without departing from the scope of the invention.

In addressing the problems associated with load management within a network electrical grid the present inventors have realised that within the network thermal storage devices such as electrical storage heaters and water cylinders could be selectively powered to match the available power within the grid.

Storage heaters are well known and generally comprise a core consisting of a heat storage medium ("bricks") in an insulated casing. Heating elements are disposed in the midst of the bricks to heat the bricks. Generally the storage heaters are locally controlled so that the heating elements are switched on during a time when the supply of electricity is cheaper (the"off-peak"time), which is usually overnight. This conventionally has been programmed at installation of the heaters, the time of activation of the heating elements being coincident with an advertised time provided by the network operator.

From some electricity suppliers, one or more off-peak periods may be defined during the day, so that, for example the day includes two or more relatively shorter peak periods with off-peak periods in between. During the off-peak period the bricks are heated by the heating elements, typically to a temperature of about 650 C so that heat is stored in the bricks. The insulation ensures that the rate off heat loss from the bricks is reduced to a desired level.

During the day, when electricity is more expensive, the heating elements are turned off and heat from the heat storage bricks is radiated into the room to heat the room. The amount of insulation affects the rate of heat loss from the core into the room. This method of heating is advantageous in that it is relatively simple and inexpensive to install, clean in use and relatively cheap to run.

However, there are a number of disadvantages.

For example, because heat is stored in the bricks during the off-peak (overnight) period, the core reaches its highest temperature in the early morning, normally at about 7.OOam. Consequently, the heat output from the storage heater is greatest at this time. This is not ideal since most people are more active in the early morning (preparing to go out to work or school etc) and so less heat is required. After reaching its maximum temperature in the morning, heat is lost from the core during the day. The heat output decays approximately exponentially so that by the evening-before the core is recharged with heat-the heat output can be quite low.

In an analogous fashion it is known to heat water within a domestic hot water cylinder using an immersion heating element. Such heating of the water is desirably to a set-point, typically about 60°C to address potential issues regarding contamination by legionella bacteria. Domestic water cylinders are typically about l5Olitres capacity and being well insulated can be heated at any time during the day in the anticipation that unless water is drawn from the cylinder such heat will remain in the cylinder until required. Availing of off-peak demand it is known to provide such heating through activation of the electrical coil that forms part of the immersion heater during the off-peak periods.

The present inventors have realised that rather than powering the devices at set pre-determined periods during the day, that by selectively powering them during periods of high power supply from renewable resources such as wind generators that it is possible to maxirnise the take-up of the renewably sourced electricity within the network. Typical heat values associated with storage heaters are 1 8kW hours per day. Taking into account that there are approximately 8 million storage heaters in the United Kingdom, this represents an available load to the grid of 100MW hours within any 24 hour period.

In order to provide this selective powering of the devices, the present invention provides a controller which is configured to be interfaced between the mains electricity supply and heating elements of the thermal storage devices, the controller defining the supply of electricity to the heating elements and as a result the load taken by the thermal storage devices at any period within the day. In this way the controller acts as a switch or valve between the mains electricity power and the heating elements. The controller is responsive to a signal received from the network operator to availability of excess power within the network and on receipt of the signal is configured to activate the heating elements to absorb some of that excess load.

It will be appreciated that this load take-up function of the thermal storage device represents a secondary function of the device. In the exemplary context that the thermal storage device is a storage heater or a water cylinder, the primary function is to provide to the user of the device respectively space heating or hot water as desired. To this end, while it is useful that the take-up of available energy from the network can be based on signals received from the network operator, the present inventors have realised that it is important that the dictation of when to receive power and effect a heating of the thermal storage device does not result in a situation where the thermal storage device has not received appropriate energy to allow it to meet its expected demand. To that end the controller is desirably configured to monitor the available capacity of the thermal storage device to meet expected demands over a future time period to ensure that the capacity at least meets that demand. Where it is determined that the capacity does not meet the expected demand, the controller may be configured to selectively activate the powering of the heating element(s), overriding any signals received from the network operator to ensure that the primary function of the thermal storage device is met. This override function may be configured to ascertain future periods of high expected load within the network and ensure that the powering of the heating elements is not coincident with those high loads within the network.

The controller may be further configured to select predetermined time periods within any time cycle, for example a 24-hour duration, as periods of low load within the network and selectively activate the heating elements for times within these predetermined load periods irrespective of receipt of signals from the network. For example, it is known to conventionally power these thermal storage devices during the hours of 0000 to 0700 where the network load is conventionally low. A controller within the context of the present teaching could also be configured to select time periods within this predetermined periods to selectively activate the heating elements such that within any time cycle-for example 24 hours-the heating elements will be activated for a minimum period to ensure that the thermal storage device is never depleted to completely low levels.

Figure 1 shows an exemplary network arrangement 100 in accordance with the present teaching. A network utility provider 110 which is symbolizing the mains electricity grid is configured to provide power to one or more users within the grid as required. In the schematic of Figure 1, a single user 115 is shown, but it will be appreciated that this user is representative of a plurality of users of electricity within the grid structure. The user 115 comprises in this exemplary arrangement first 130 and second 140 thermal storage devices. In this exemplary schematic the first 130 and second 140 are provided as a storage heater and a water cylinder respectively but it will be appreciated that certain users will have multiples of each of these devices and certain users will have none of one particular type. A controller 120 is provided in the power path between the devices 130, 140 to control the provision of power to heating elements within each of the two devices. While this embodiment shows a single controller that is controlling each of the two devices, it will be appreciated that each device may have its own dedicated controller.

Figure 2 shows in more detail components of the controller 120. The controller has an input interface 200 for receiving a signal from the network operator regarding availability of power for take up by the thermal storage devices. This signal may be provided in one of a number of different signal types. For example the signal could be provided in a wired or wireless communication protocol. Examples of wired signals include using the mains power lines to transmit a signal or incorporating a dedicated pilot wire.

Examples of wireless signals include those used for mobile telecommunication networks, radio frequency signals, WiMax or the like. It will be appreciated that one or more of these signals types could be used and it is not intended to limit the present teaching to any one specific example of signal transmission type.

Signals could be provided in any one of a number of different fashions.

For example a digital signal comprising a plurality of bits could be used to transmit commands from the network operator to the controller. The controller may be configured to recognise a specific signal as being appropriate to that controller or that controller type. Such an arrangement could be most usefully employed where a plurality of controllers are simultaneously in receipt of signals from the network operator but the operator wishes to selectively activate individual ones of the controllers. By initially configuring the controllers to recognise and act on specific signals then a plurality of signals could be transmitted concurrently but each of the controllers would act as appropriately to the signal intended for that controller. In this way the plurality of controllers could be grouped into similar groups or subsets, and each subset would react differently to the signal transmitted from the network. In this way, the load taken from the network could be selectively controlled by timed activation of the specific subsets of thermal storage devices.

On receipt of a signal confirming that it is desired that the thermal storage device being activated thereby taking available power from the network, the controller is configured to, as appropriate and as will be discussed further below, activate to one or more of the storage devices that is coupled to that controller. This activation is desirably through a switch mechanism 210 that selectively couples heating elements of the coupled thermal storage devices to the available power for energising same.

In a first configuration, the energisation of the heating elements is effected immediately on receipt of a command signal from the network operator.

However a second configuration provides for selective energisation dependent on the current status of the thermal storage device. As was discussed above each thermal storage device typically has a set point defining the capacity of that device. Heating over this set point may cause damage to the device through overheating. For example in a thermal storage heater, it typically requires the heating element to be activated for a seven hour period in any 24 hour period to provide the necessary heating in the other times. If the storage device is heated constantly the temperatures of the storage bricks may exceed their rated value.

In a water cylinder, once the water temperature has reached 60 degrees (or some other preset value) the heater will typically not activate to ensure that the water does not heat excessively. In a water heating environment where the water is to be used in a domestic water supply it is also important to ensure that the user cannot get scalded through provision of water that is too hot.

Mindful of both these potential dangers the controller is desirably configured to monitor, on receipt of a signal from the network operator, whether any additional heating is required to meet the preset set point. If no heating is required-for example where 7 hours continual heating has already been provided or the device is at its maximum temperature, the controller may elect not to activate the heating elements irrespective of the command received. This capacity of the controller to override instructions received remotely ensures the safe operation of the device. The controller includes a processor 220 that is configured to monitor the powering of the thermal storage devices over a predetermined period. This monitoring may be one or both of recording the timed operation of the heating elements over a historical time period or ascertaining the current operating parameters of the thermal storage devices to ascertain whether additional heating is required to meet the set-point conditions or not. This latter arrangement may require interrogation of the actual devices by the controller through two way signals at the time of decision as to whether to send power to the heating elements or not. In another arrangement a sensor co-located with the individual thermal storage devices may periodically transmit the status of the device to the controller. This status -for example a temperature-may be stored locally at the controller in one or more buffers 225.

The buffers may also provide a data store for look-up tables or the like where a relationship between percentage charge of the device and temperature are defined. In this way the controller may process the actual temperature relative to the capacity or set point of the device and define the level of charge necessary to have the device at full capacity. Core

% charge temperature (°C) 0 100 250 300 350 400 450 500 550 600 650 700 Table 1: Exemplary relationship between the % charge and the core temperature of a storage heater Water % charge temperature (°C) 0 20 25 30 35 40 45 50 55 60 65 70 Table 2: Exemplary arrangement between % charge and water temperature of a water heater In a modification to the arrangement just described the controller may be configured to shift the set-point of the thermal storage device to allow the device to receive additional heating above what is required for the normal usage of the device. An example of such an arrangement is where a water boiler has a first set point of 60 degrees centigrade and the water within the cylinder is at 60 degrees. The controller may be configured to temporarily provide a second set point above the first set point, for example 80 degrees, and allow a heating of the water within the cylinder to that temperature to increase the load within the network to compensate for the available power from the renewable resources. It will be appreciated that such arrangements may be effected upon receipt of specific signals from the network. Figure 3 shows an example of such an arrangement whereby by raising the water temperature set point by 20 degC an additional 3.5 kWh additional energy may be stored per day in a typical 150 litre cylinder.

Another example is in the context of a storage heater where the set-point is 7 hours heating within a prescribed 24 hour period but the usage of the device-for example during the winter-allows for the activation of the heating elements for additional time periods as the heat stored is being distributed actively during the day. The controller in this configuration is optirnised to monitor the actual temperature of the storage device and allow for additional heating times until a set point temperature as opposed to time is reached.

The controller is desirably also configured to ensure that the primary function of the thermal storage devices is always met. It will be recalled that these primary functions are the provision of space heating and domestic hot water as appropriate. Using the example of space heating, in order to provide heat during the day it is important that the storage device has been previously heated. In the scenario where the heating of the elements is predicated solely on provision of a signal from the network operator, it is possible in times of low wind or the like that the capacity of the network is not such as to require activation of the thermal storage devices. In such a scenario the time period between activation of the thermal storage devices could exceed that required for the storage device to maintain sufficient heat for distribution as a space heater. To ensure that this does not happen the controller may be configured to monitor the current capacity of the thermal storage device to provide energy and the expected requirement for heat over a future time period. When the expected requirement exceeds the capacity the controller may be configured to activate the heating elements irrespective of the fact that a signal has not been received from the network requiring activation.

It will be appreciated that such expected load may overlap with periods of traditional high load within the network. For example the periods of 1700-1900 are typically high load times within an electrical network where multiple cooking devices are simultaneously activated. This also is a time where heating is required. To ensure that the thermal storage device is appropriately charged to provide the necessary heating the controller may be configured to monitor future load and capacity and effect a heating of the heating elements based on this forecasting. This forecasting can ensure that heating of the thermal storage device to meet the primary function does not overlap with periods of already high load within the network, thereby assisting in network load management.

It will be appreciated that on receipt of a signal to activate heating elements in a plurality of thermal storage devices that simultaneous activation of these plurality of devices may cause a temporary spike in the network frequency. To ameliorate this, each of the controllers may be configured to activate their respective heating elements after expiry of a delay period to ensure that concurrent activation is not provided. This may be computed on the basis of a random variable, a fixed time or the like. Such shifting of the start time of a plurality of devices may assist in load management at a network level.

Heretofore, the activation of the heating elements has been described with reference to receipt of a start signal received from the network at the controller.

On receipt of such a signal, the controller is configured to allow for heating until one or more of receipt of a subsequent stop signal from the network, the reaching of a set point representing capacity of the device, or for example in the context of a space heater where the room temperature has reached a desired level. In a modification to that described heretofore the activation signal may include a start and stop time for the controller or a start time with a request that heating of the device is continued until a prescribed level of storage is achieved.

Figure 4 shows such an exemplary arrangement whereby the controller receives a signal @16:00 representing a request for the controller to provide the thermal storage device at a 65% charge over a 4 hours operation (charge time).

The controller interrogates the device and determines that its current charge as a percentage of the overall charge in the heater core @16:00 is 55% The charge controller will then calculate a delay start time based on a lookup table (as tabulated from for example Table 1 above). In this instance the difference in charge level is 10% (65%-55%) so this equates to a delay time of 1 Omins. The controller will then start a countdown timer ((CT) in this case 4 hours). The heater will not charge until the delay time (lOmins) has elapsed. At the end of the 10 minutes the charge controller will compare the room temperature versus the room temperature setpoint. As this is day period 2, the room temperature setpoint is the setpoint on the user interface + 2°C (this is to allow boost in the afternoon period). If the room temperature is <0.2°C below the set temperature then the heater will charge. The heater will stop charging if any of the following conditions are true: -the room temperature equals the set temperature.

-the core temperature is above the target temperature -the charge time has elapsed.

It will be appreciated that a controller in accordance with the present teaching allows for a flexible interface between the requirements of the network operator to balance the load available with the load on the network by selectively activating thermal storage devices within the network and the requirements of the user to manage their heating (be that space or domestic water supply). Conventionally this relationship was defined by static definitions of when the heating elements could be activated-typically in low network usage times such as between 0000 and 0700. In accordance with the present teaching the controller allows for additional balancing during periods of the day when the network has additional capacity due to bringing on of renewal energy source based on favourable weather conditions. As the thermal storage device can be rapidly brought on-line to compensate for the additional capacity-for example within about 10 seconds, this represents a rapid resource of large capacity to counter the increased available power within the network. To ensure that the selective activation of the heating elements does not result in deterioration in the primary function of these devices, the controller is provided with an override function to ensure that the thermal storage devices are adequately powered at any one period to meet their future heating requirements. This could also be done in combination with fixed charging times. For example if the network utility provides a minimum of 4 hours between 0.00 to 7.00 and up to a further 6 hours between 9.00 and 24.00 (avoiding 17.00 to 19.00) the controller can optimise the use of that energy up to a set point of 7 hours charging to ensure comfort during the main heating periods.

The words comprises/comprising when used in this specification are to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

While the present invention has been described with reference to some exemplary arrangements it will be understood that it is not intended to limit the teaching of the present invention to such arrangements as modifications can be made without departing from the spirit and scope of the present invention. In this way it will be understood that the invention is to be limited only insofar as is deemed necessary in the light of the appended claims.

Claims

Claims 1. A controller for managing the activation of at least one heating element within a thermal storage device, the controller comprising: a. A first interface for receiving a signal from a remote network operator regarding availability of power within a electricity grid for take up by the thermal storage device; b. A processor configured on receipt of the signal to determine whether to switch the heating element to take up available power and to provide an activation signal in positive response of said determination; c. A switch in communication with the processor and configured on receipt of the activation signal to energise the heating element.
2. The controller of claim 1 configured to selectively energise the heating element dependent on the current status of the thermal storage device.
3. The controller of claim 2 wherein the processor is configured to monitor, on receipt of the signal from the network operator, whether activation of the heating element is required to meet a preset set-point of the thermal storage device.
4. The controller of claim 3 wherein on determination that no heating is required, the controller is configured to elect not to activate the heating element irrespective of the signal received.
5. The controller of claim 3 or 4 wherein the controller is configured to record the timed operation of the heating element over a historical time period to determine whether additional heating is required.
6. The controller of claim 3 or 4 wherein the controller is configured to interrogate current operating parameters of the thermal storage device to ascertain whether additional heating is required to meet the set-point 7. The controller of claim 6 wherein the controller is configured to interact in a two-way signal interaction with the thermal storage device at the time of decision as to whether to energise the heating element.8. The controller of claim 6 or 7 wherein the controller is configured to receive a periodic signal from a sensor co-located with the thermal storage device regarding a status of the device, the controller being further configured to use this periodic signal at the time of decision as to whether to energise the heating element.9. The controller of claim 7 or 8 comprising at least one data store providing a defined relationship between a percentage charge of the thermal storage device and temperature.10. The controller of claim 9 configured to process a sensed actual temperature relative to the capacity or set point of the device and define the level of charge necessary to have the device at full capacity.11. The controller of claim 3 configured to shift the set-point of the thermal storage device to allow the device to receive additional heating above what is required for the normal usage of the device.12.The controller of any preceding claim configured to monitor the current capacity of the thermal storage device to provide energy and the expected requirement on the device to provide heat over a future time period.13. The controller of claim 12 configured such that when the expected requirement exceeds the capacity the controller activates the heating elements irrespective of the fact that a signal has not been received from the network requiring activation.14.The controller of claim 12 or 13 configured to forecast future load on the network and to effect an energising of the heating element based on this forecasting to ensure heating of the thermal storage device does not overlap with periods of already high load within the network, thereby assisting in network load management.15.The controller of any preceding claim configured to generate a delay in providing the activation signal in positive response of said determination to switch the heating element to take up available power.16.The controller of any preceding claim wherein the received signal from the network includes an indicated start and stop time for the controller or a start time with a request that heating of the device is continued until a prescribed level of storage is achieved, the controller being configured to interrogate the signal and determine an appropriate action.17.The controller of any preceding claim wherein the received signal comprises a plurality of signals for different controllers, the controller being configured to determine a correct signal for that controller.18.The controller as claimed in any preceding claim configured to effect activation of the at least one heating element at predetermined times.19.The controller of any preceding claim coupled to and controlling a plurality of thermal storage devices.20. The controller of any one of claims 1 to 18 co-located with the thermal storage device which it controls.21. A electrical grid load management tool comprising a plurality of controllers as claimed in any preceding claim, the controllers allowing for selective activation of a network of thermal storage devices to absorb excess capacity within the grid.22.The tool of claim 21 wherein the controllers are grouped into sets, the tool being configured to selectively activate individual sets of thermal storage devices.Amendment to the claims have been filed as follows Claims 1. A controller for managing the activation of at least one heating element within a thermal storage device, the controller comprising: a. A first interlace for receiving a signal from a remote network operator regarding availability of power within a electricity grid for take up by the thermal storage device; b. A processor configured on receipt of the signal to determine whether to switch the heating element to take up available power and to provide an activation signal in positive response of said determination; c. A switch in communication with the processor and configured on receipt of the activation signal to energise the heating element, wherein the controller is configured to adjust a preset set-point of the thermal storage device thereby allowing the thermal storage device to operate outside the limits of the preset set-point.2. The controller of claim 1 configured to selectively energise the heating element dependent on the current status of the thermal storage device.3. The controller of claim 2 wherein the processor is configured to monitor, on receipt of the signal from the network operator, whether activation of the heating element is required to meet the preset set-point of the thermal storage device.4. The controller of claim 3 wherein on determination that no heating is required, the controller is configured to elect not to activate the heating element irrespective of the signal received.5. The controller of claim 3 or 4 wherein the controller is configured to record the timed operation of the heating element over a historical time period to determine whether additional heating is required.6. The controller of claim 3 or 4 wherein the controller is configured to interrogate current operating parameters of the thermal storage device to ascertain whether additional heating is required to meet the set-point.
7. The controller of claim 6 wherein the controller is configured to interact in a two-way signal interaction with the thermal storage device at the time of decision as to whether to energise the heating element.
8. The controller of claim 6 or 7 wherein the controller is configured to receive a periodic signal from a sensor co-located with the thermal storage device regarding a status of the device, the controller being further configured to use this periodic signal at the time of decision as to whether to energise the heating element.
9. The controller of claim 7 or 8 comprising at least one data store providing a defined relationship between a percentage charge of the thermal storage device and temperature.
10. The controller of claim 9 configured to process a sensed actual temperature relative to the capacity or set point of the device and define the level of charge necessary to have the device at full capacity.
11.The controller of claim 3 wherein the adjusted set-point of the thermal storage device allows the device to receive additional heating above what is required for the normal usage of the device.
12.The controller of any preceding claim configured to monitor the current capacity of the thermal storage device to provide energy and the expected requirement on the device to provide heat over a future time period.
13.The controller of claim 12 configured such that when the expected requirement exceeds the capacity the controller activates the heating elements irrespective of the fact that a signal has not been received from the network requiring activation.
14.The controller of claim 12 or 13 configured to forecast future load on the network and to effect an energising of the heating element based on this forecasting to ensure heating of the thermal storage device does not overlap with periods of already high load within the network, thereby assisting in network load management.
15.The controller of any preceding claim configured to generate a delay in providing the activation signal in positive response of said determination to switch the heating element to take up available power.
16.The controller of any preceding claim wherein the received signal from the network includes an indicated start and stop time for the controller or a start time with a request that heating of the device is continued until a prescribed level of storage is achieved, the controller being configured to interrogate the signal and determine an appropriate action.
17.The controller of any preceding claim wherein the received signal comprises a plurality of signals for different controllers, the controller being configured to determine a correct signal for that controller.
18.The controller as claimed in any preceding claim configured to effect activation of the at least one heating element at predetermined times.
19.The controller of any preceding claim coupled to and controlling a plurality of thermal storage devices.
20.The controller of any one of claims 1 to 18 co-located with the thermal storage device which it controls.
21. A electrical grid load management tool comprising a plurality of controllers as claimed in any preceding claim, the controllers allowing for selective activation of a network of thermal storage devices to absorb excess capacity within the grid.
22.The tool of claim 21 wherein the controllers are grouped into sets, the tool being configured to selectively activate individual sets of thermal storage devices.