GB2446530A

GB2446530A - A predictive control apparatus for metering of renewable energy devices

Info

Publication number: GB2446530A
Application number: GB0806214A
Authority: GB
Inventors: Peter Boait
Original assignee: De Montfort University
Current assignee: De Montfort University
Priority date: 2007-02-08
Filing date: 2007-02-08
Publication date: 2008-08-13
Anticipated expiration: 2027-02-08
Also published as: GB2446418B; GB0806212D0; GB0806214D0; GB2446530B; GB2446418A; GB2446972A; GB2446972B; GB0702392D0

Abstract

A metering apparatus is used to meter at least one renewable energy device that derives energy from a renewable energy source such as a wind turbine 32 or combined heat and power (CHP) generator 34. The apparatus includes an electronic control unit 46 an energy sensor 44. The energy sensor 44 measures an energy parameter that is affected by an energy output of the renewable energy device. In the case of the embodiment shown in Figure 8 the energy sensor 44 is an electrical load sensor that measures electrical load flowing in the connection 42a between a supply busbar 36 and a distribution panel 42. The electrical load sensor provides energy data in the form of electrical load measurements to the electronic control unit 46. The electronic control unit 46 uses the energy data to derive a profile of the change in the energy parameter and correlates the derived profile with a reference profile corresponding to the particular type of renewable energy. The results of the correlation and the energy data are then used to quantify the energy output of the renewable energy device over a selected period of time.

Description

TITLE

Apparatus and methods for metering of renewable energy devices

DESCRIPTION

Technical Field

The present invention relates to household and building energy management, and in particular to apparatus and methods that can be used to meter the energy output of devices that are used to capture energy from renewable energy sources.

Background Art

In order to minimise carbon dioxide emissions, households and businesses are encouraged to install devices that capture energy from renewable energy sources such as solar radiation, air and ground heat, wind, waves and tides. These renewable energy devices can take various forms such as solar water heaters, solar photovoltaic generators, wind turbines, and wave and tide generators, for example. Households and businesses may also install a combined heat and power (CHP) generator. These take a source of chemical energy like natural gas or wood and use it to generate both heat and electricity. Electricity is only generated as a by-product when there is a need for heat to be provided by the CHP generator. This means that the amount of electricity that is generated by the CHP generator is intermittent and dependent on the weather in a similar manner to energy generated from a renewable energy source; when the weather is colder then there is more need for heat to be generated by the CHP generator and hence more electricity is generated and vice versa. For the purposes of the following description, it is therefore convenient to treat the electrical output of a CHP generator as a renewable energy source and the CHP generator as a renewable energy device.

Because such renewable energy sources tend to be intermittent, they are usually used in conjunction with one or more controllable auxiliary energy sources such as mains electricity or natural gas, for example. The operation of an auxiliary energy device such as an electric immersion heater, a gas boiler or a diesel generator, for example, is normally controlled and regulated by some sort of electronic control unit. In order to make efficient use of the renewable energy source, the electronic control unit should also be able to predict the amount of energy that will be generated from any renewable energy sources so that an auxiliary energy device can be controlled in an efficient and economic maimer. This is simply not possible with conventional electronic control units.

In the United Kingdom, part of the value of renewable energy devices that generate electricity comes from the fact that so-called Renewable Obligation Certificates may be claimed from the industry regulator for each Megawatt-hour of electricity that is produced. This is irrespective of whether the electricity is consumed locally or exported into the power grid. There is therefore also a need to provide accurate metering for the energy output of renewable energy devices and also to validate that the electricity has actually been generated from a renewable energy source.

Summary of the Invention

It is sometimes necessary to identify a particular type of renewable energy device from the properties of its energy output. For example, it can be necessary to identify a newly installed or previously unrecognised renewable energy device such as a solar water heater, a solar photovoltaic generator, a wind turbine or a combined heat and power (CHP) generator with reference to its energy output characteristics. Although not forming a part of the present invention, it may therefore be useful to provide an identification apparatus for identifying a particular type of renewable energy device that derives energy from a renewable energy source, the identification apparatus comprising an electronic control unit, and an energy sensor for measuring an energy parameter that is affected by an energy output of the renewable energy device and providing energy data indicative of the energy parameter to the electronic control unit, wherein the electronic control unit uses the energy data to derive a profile of the changes over time in the energy parameter, wherein the electronic control unit correlates the derived profile with one or more reference profiles, each reference profile corresponding to a particular renewable energy source, and uses the results of the correlation to identify the type of renewable energy device.

It may also be useful to provide a corresponding method for identifying a particular type of renewable energy device that derives energy from a renewable energy source, the method comprising the steps of measuring an energy parameter that is affected by an energy output of the renewable energy device to obtain energy data, using the energy data to derive a profile of the changes over time in the energy parameter, correlating the derived profile with one or more reference profiles, each reference profile corresponding to a particular renewable energy source, and using the results of the correlation to identify the type of renewable energy device. The energy parameter is preferably measured using an energy sensor. The steps of deriving the profile, correlating the derived profile with one or more reference profiles and using the results of the correlation to identify the type of renewable energy device are preferably carried out by an electronic control unit.

The correlation is preferably performed using known mathematical techniques for correlation and pattern recognition that give a quantitative assessment (referred to in this description as the "correlation factor") of the accuracy of the match when the derived profile is compared against a reference profile. It will be readily appreciated that various mathematical and statistical processes can be used to determine if the derived profile matches a reference profile. In other words, the correlation factor is not necessarily limited to a single number that can be compared against a selected threshold, but may be a more complex expression of the probability that a match exists dependant on other variables that apply in a particular application.

The energy sensor measures an energy parameter that is affected when energy is provided by the renewable energy device. The energy parameter might be the water temperature inside a domestic hot water cylinder (which would be expected to rise if the water was being heated by solar radiation captured by a solar water heater) or the amount of electricity that is imported from, and exported to, the mains supply, for example. In the latter case, the amount of electricity that is imported from the mains supply would be expected to fall if electricity were to be supplied to a domestic supply busbar by a wind turbine, solar photovoltaic generator or CI-IP generator or the like, and in fact electricity may be exported to the mains supply if the electricity supplied by the renewable energy devices exceeds the amount of electricity that is needed locally to power the various electrical appliances and loads connected to the supply busbar.

More than one type of energy sensor can be provided depending on the circumstances.

For example, if the apparatus is to be used to identify renewable energy devices that provide energy in the form of hot water and renewable energy devices that provide energy in the form of electricity then both a temperature sensor and an electrical load sensor will be needed. It may also be desirable to have more than two energy sensors of the same type. For example, temperature sensors could be located at the top and bottom of a domestic hot water cylinder so that the difference between their respective measurements could be recorded.

The measurements of the energy parameter provided by the energy sensor or sensors may be stored and then retrieved by the electronic control unit to derive the profile.

The measurements may be stored in the form of a series of discrete time-stamped values.

The energy sensor may measure the joint effect of more than one type of renewable energy device on the energy parameter. In this case, the electronic control unit is capable of identifying the different types of renewable energy device that are present and of discriminating between them.

In general terms, the electronic control unit is able to identify a type of renewable energy device if the derived profile is considered to match one of the reference profiles with a level of accuracy that exceeds a threshold that is chosen to suit the particular application. Since each of the reference profiles corresponds to a renewable energy source, the electronic control unit can make a direct link between this renewable energy source and the type of renewable energy device. For example, if the derived profile is considered to match a reference profile that corresponds to solar radiation intensity and the energy parameter is water temperature then the electronic control unit will identify the renewable energy device as a solar water heater. On the other hand, if the energy parameter is electrical power flowing in a domestic supply busbar then the electronic control unit will identify the renewable energy device as a solar photovoltaic generator. If the derived profile is considered to match a reference profile that corresponds to wind turbine capacity factor then the electronic control unit will identify the renewable energy device as a wind turbine and so on.

If the energy parameter is affected by more than one type of renewable energy device then this will be reflected in the derived profile. A derived profile may therefore match more than one of the reference profiles. For example, in a case where two different types of renewable energy device supply electricity to a domestic supply busbar then the derived profile indicative of changes in the electrical power flowing in the supply busbar may be matched to two different reference profiles.

The correlation between the derived profile and the one or more reference profiles can be carried out in the time domain. Alternatively, the correlation may be carried out in the frequency domain between a Fourier transformed version of the derived profile and a Fourier transformed version of the one or more reference profiles. Where additional accuracy or speed of recognition is required then correlation may be performed in both the time and frequency domains.

The matching of the derived profile with the one or more reference profiles can be based on a correlation factor in one or both of the time and frequency domains. For example, the derived profile can be correlated against a reference profile that corresponds to a particular type of renewable energy source and if the resulting correlation factor is greater than a predetermined threshold then there is considered to be a match. If the correlation factor is less than the predetermined threshold then there is no match and the derived profile can be correlated against a reference profile that corresponds to a different type of renewable energy source. This correlation process can be continued until the correlation factor is greater than the predetermined threshold for one of the reference profiles (i.e. there is a match) or until the derived profile has been correlated against all of the reference profiles without a match. In the latter case, a failure to find a match may be because the total amount of energy data that is used to derive the profile is insufficient. The electronic control unit may therefore continue to store energy data to increase the total amount of energy data before deriving a new profile and repeating the correlation process at selected intervals.

Alternatively, the electronic control unit may store only a certain amount of energy data (such as the energy data for any selected time period such as days, weeks or months, for example). Therefore, once the storage limit of energy data is reached, the electronic control unit will store the new energy data that it receives from the energy sensor and discard the oldest energy data. The electronic control may derive a new profile using the stored energy data and repeat the correlation process at selected intervals.

Each reference profile preferably describes the dependency of a particular renewable energy source on the time of the day and the date (i.e. the season of the year) and may be stored internally or provided from an external source. The electronic control unit may therefore further include an internal clock and a calendar.

Each reference profile is preferably a daily profile and represents the amount of energy that a particular renewable energy device could extract from the appropriate renewable energy source at any time over the course of a 24 hour period. A series of reference profiles for each renewable energy source can be stored so that the daily reference profile for any given date can be retrieved. Alternatively, a daily reference profile for each renewable energy source can be generated for a particular date using stored information.

In the case of solar radiation, the daily reference profile may represent the average solar radiation intensity for the United Kingdom (or a particular locality within the United Kingdom) versus time, for example. In the case of wind speed, it is more conventional to look at capacity factor where the average output power of a wind turbine at a specific time of day is averaged for all occurrences of that time of day over a month (or other suitable period) and expressed as a proportion of the average peak output power that the wind turbine would provide when operating at its physical limit. The daily reference profile may therefore represent the wind turbine average capacity factor for the United Kingdom (or a particular locality within the United Kingdom) versus time, for example. In the case of the electrical output power provided by a combined heat and power (CHP) generator then it is once again more conventional to look at capacity factor where the average output power of a CHP generator over the course of a 24 hour period is expressed as a proportion of the average peak output power that the CHP generator would provide when operating at its physical limit. The daily reference profile may therefore represent the CHP generator average capacity factor versus time, for example.

The capacity factors for the wind turbine and the CHP generator can be averaged over any selected time period such as days, weeks or months.

The electronic control unit may store the energy data over any selected time period such as days, weeks or months. The derived profile will therefore represent the change in the energy parameter over this selected time period. However, the energy data is preferably used to form a derived daily profile of the change in the energy parameter over the course of a 24 hour period. In many cases, the derived daily profile will therefore comprise a set of average values taken at convenient time intervals (5 or 10 minutes, for example), each value comprising the average of all instances of the energy parameter value at that specific time of day during the selected time period.

All of the stored energy data may be used to derive the daily profile. Alternatively, just a selected part of the stored energy data may be used. This is described in more detail below.

When the apparatus is first operated or a new renewable energy device is connected to it, the electronic control unit may store the measurements of the energy parameter provided by the energy sensor for a selected period of time before trying to identify the type of each renewable energy device. The stored energy data can be divided into consecutive 24 hour periods and then averaged together to form a single derived daily profile. The derived daily profile can then be correlated with the one or more daily reference profiles, each one corresponding to a particular type of renewable energy source and labelled as such. The daily reference profiles will preferably relate to a date that lies within the selected period of time for which energy data has been stored.

If the correlation process does not result in a match, the electronic control unit may store the measurements provided by the energy sensor for a further selected period of time before trying to identify the type of each renewable energy device. The derived daily profile will therefore be an average of the energy data stored over a longer period of time and should be a more accurate representation of the change in the energy parameter.

When the electronic control unit has been operating for some time, it may not be practical or necessary for the daily profile to be derived from all of the stored energy data. In this case, the stored energy data for a selected preceding period of time only may be used. The derived daily profile will therefore be an average of the energy data stored over the selected preceding period of time and in practice can be considered to represent a "rolling average" of the change in the energy parameter. As a practical matter, the electronic control unit may also have limits to the amount of energy data it can store. The oldest energy data may therefore be discarded in favour of new energy data once the storage limit is reached. In this case, the daily profile may be derived from all of the stored energy data but can still be considered to represent a "rolling average" of the change in the energy parameter.

The apparatus may also receive weather related information and use this to adjust each reference profile to take account of weather conditions. The weather information may be weather forecast data that can be provided remotely using a known method such as text messaging or radio-frequency broadcast, for example.

The weather information may also be provided from a weather sensor that can provide measurements such as the external air temperature, wind speed or barometric pressure.

It will often also be desirable to have a simple way of accurate metering for the output of renewable energy devices that is also suitable for validation purposes.

The present invention therefore provides a metering apparatus for use with at least one renewable energy device that derives energy from a renewable energy source, the apparatus comprising an electronic control unit, and an energy sensor for measuring an energy parameter that is affected by an energy output of the at least one renewable energy device and providing energy data to the electronic control unit, wherein the electronic control unit uses the energy data to derive a profile of the change in the energy parameter, correlates the derived profile with a reference profile corresponding to the at least one renewable energy device, and uses the results of the correlation and the energy data to quantify the energy output of the at least one renewable energy device over a selected period of time.

The present invention also provides a method for metering at least one renewable energy device that derives energy from a renewable energy source, the method comprising the steps of measuring an energy parameter that is affected by an energy output of the at least one renewable energy device to obtain energy data, using the energy data to derive a profile of the change in the energy parameter, correlating the derived profile with a reference profile corresponding to the at least one renewable energy device, and using the results of the correlation and the energy data to quantify the energy output of the at least one renewable energy device over a selected period of time. The energy parameter is preferably measured using an energy sensor. The steps of deriving the profile, correlating the derived profile with one or more reference profiles and using the results of the correlation to quantify the energy output of the at least one renewable energy device are preferably carried out by an electronic control unit.

The results of the correlation will include a quantitative expression of the relationship between time, probability and the level of energy output from each renewable energy device present. When more than one renewable energy device is present then these -10-probabilities can be used to determine the most likely proportion at any given time of the measured total energy attributable to each renewable energy device.

The at least one renewable energy device may first be identified by using the identification apparatus/method described above. In this case, it may be possible to quantify the energy output of the at least one renewable energy device retrospectively from the energy data provided to the electronic control unit before the at least one renewable energy device was identified.

Once the at least one renewable energy device has been identified, the correlation with the corresponding reference profile and computation of the quantity of energy produced will preferably be carried out on a regular basis, for example, hourly, daily, weekly, monthly or quarterly depending on the particular circumstances. The correlation will be as described above with reference to the identification apparatus/method.

Once the energy output of the at least one renewable energy device has been, quantified, this information may be presented as visual information on a display screen or provided as an output signal for the purpose of reporting the performance of the at least one renewable energy device or as metering information for commercial purposes such as the award of Renewable Obligation Certificates. The metering apparatus/method helps to prevent Renewable Obligation Certificates being awarded in cases where the energy output has not been derived from a renewable energy source. This is because the electronic control unit will only quantify the energy output of a device that affects the energy parameter in such a way that the derived profile matches a reference profile corresponding to a known renewable energy device. In other words, if the energy parameter were only to be affected by the energy output of an auxiliary energy device (i.e. there are no renewable energy devices present) then the derived profile will not match a reference profile corresponding to a known renewable energy source and the energy output will not be quantified or validated.

Where two or more renewable energy devices are present then the electronic control unit can be configured to quantify their energy outputs separately over a selected period of time. This may be useful for reporting or monitoring the performance of each individual renewable energy device, or if different awards of Renewable Obligation Certificates are applicable, for example. In other cases, the electronic control unit can simply aggregate the energy output of some or all of the renewable energy devices and report accordingly.

It will often be desirable to predict the energy output of a renewable energy device over some future time period so that the operation of one or more auxiliary energy devices such as an electric immersion heater, a gas boiler or a diesel generator, for example, can be controlled and regulated in an efficient manner. Although not forming a part of the present invention, it may therefore be useful to provide a predictive control apparatus for use with at least one renewable energy device that derives energy from a renewable energy source and at least one of an auxiliary energy device that derives energy from an auxiliary energy source and an electrical appliance, the predictive control apparatus comprising an electronic control unit, and an energy sensor for measuring an energy parameter that is affected by an energy output of the at least one renewable energy device and providing energy data to the electronic control unit, wherein the electronic control unit uses the energy data to derive a profile of the changes over time in the energy parameter, wherein the electronic control unit correlates the derived profile with a reference profile corresponding to a particular renewable energy source and uses the results of the correlation to determine a quantitative relationship between the reference profile and the energy output of the at least one renewable energy device at an instant in time, wherein the electronic control unit uses the quantitative relationship and the reference profile to predict the energy output of the at least one renewable energy device at a future instant in time, and wherein the electronic control unit uses the predicted energy output of the at least one renewable energy device to control the operation of the at least one of an auxiliary energy device and an electrical appliance in accordance with the predicted energy output.

It may also be useful to provide a corresponding method for predicting the energy output of at least one renewable energy device that derives energy from a renewable energy source and controlling at least one of an auxiliary energy device that derives energy from an auxiliary energy source and an electrical appliance, the method comprising the steps of measuring an energy parameter that is affected by an energy output of the at least one renewable energy device to obtain energy data, using the energy data to derive a profile of the changes over time in the energy parameter, correlating the derived profile with a reference profile corresponding to a particular renewable energy source, using the results of the correlation to determine a quantitative relationship between the reference profile and the energy output of the at least one renewable energy device at an instant in time, using the quantitative relationship and the reference profile to predict the energy output of the at least one renewable energy device at a future instant in time, and using the predicted energy output of the at least one renewable energy device to control the operation of the at least one of an auxiliary energy device and an electrical appliance in accordance with the predicted energy output. The energy parameter is preferably measured using an energy sensor. The steps of deriving the profile, using the energy data to predict the energy output of the at least one renewable energy device and controlling the operation of the at least one of an auxiliary energy device and an electrical appliance are preferably carried out by an electronic control unit.

The energy parameter measured by the energy sensor may also be affected by an energy output of the at least one auxiliary energy device.

The correlation between the derived profile and the reference profile will be as described above with reference to the identification apparatus/method.

Once the required level of correlation for identification is achieved, a mathematical model of the identified renewable energy source for any given time interval can be constructed from stored energy data in the form: 0 f(P) -13-where 0 is the observed energy output of the renewable energy source, f is a modelling function which could be as simple as multiplication by a constant, and P is the reference profile for the time interval. Once the modelling function f is determined then a predicted energy output 0 can be calculated from the value of P at the future time of interest. If weather information or weather forecast data is available then the value of P at the future time of interest can be modified accordingly. The measured energy output of the renewable energy device may itself provide weather information that can be used for this purpose. For example, if the level of solar radiation is high at a given instant then it is likely to be sustained over subsequent minutes or hours depending on the time of day and the time of year.

The electronic control unit will preferably predict the energy output of the at least one renewable energy device over a selected period of time such as hours or days. This will depend mainly on the desired accuracy of the predicted energy output and the purposes for which the prediction is required. For example, a more accurate prediction can normally be made over a shorter selected period of time.

The electronic control unit may also use the energy data to derive information about the energy output of the at least one auxiliary energy device. This can assist the electronic control unit to control the operation of the at least one auxiliary energy device once it has made aprediction about the energy output of the at least one renewable energy device. For example, if the auxiliary energy device is an electric immersion heater that is used to heat the water in a hot water cylinder under the control of the electronic control unit then the electronic control unit can use measurements of the temperature of the water to determine the energy output of the immersion heater when it is switched on. Once the energy output is known, the electronic control unit can determine the rate at which the immersion heater will heat the water in the hot water cylinder when it is switched on. Thus, if the electronic control unit predicts that a solar water heater will stop providing hot water in the evening when solar radiation falls below a usable level then the immersion heater can be switched on at the appropriate time so that the desired temperature of the hot water is maintained over a period of time when the electronic control unit knows that hot water is required. In the case of a CHP generator that is operating under the control of the electronic control unit as a source of heat, the electronic control unit can use energy sensor measurements of the electrical power flowing in a supply busbar to which the CHP generator is connected to determine the energy output of electricity from the CHP generator as a function of the output of heat, and hence predict the amount of electricity that will be generated from a known future requirement for heat.

The relationship between the electrical output and the heat output of a typical CHP generator is shown in Figure 12.

Examples of electrical appliances that are particularly suitable for use with the predictive control apparatus/method are those that can be switched on at a time that makes the most efficient use of the available energy i.e. those that do not have to operate continuously or at fixed times. A typical example of electrical appliances that are particularly suitable would include washing machines, tumble driers and dishwashers. The electrical appliance may be automatically switched on by the electronic control unit using some sort of remote switching device, for example.

The electronic control unit essentially builds a mathematical model of the performance of each renewable energy device (and where appropriate each auxiliary energy device) under different weather conditions and at different times of the year.

It can then use the mathematical model to predict the energy output for hours or days ahead. Each auxiliary energy device or electrical appliance can then be controlled and regulated by the electronic control unit to make the most efficient use of the predicted energy output of each renewable energy device.

The metering apparatus may be combined together with one or both of the identification apparatus and the predictive control apparatus in a single commercial unit for convenient installation. The metering method may be combined with one or both of the identification method and the predictive control method as appropriate. -15-

Drawings Figure 1 is a schematic diagram showing how a first apparatus can be used to control the heating of a domestic hot water cylinder; Figure 2 is a schematic diagram of an electronic control unit that forms part of the first apparatus of Figure 1; Figure 3 is energy data indicative of the energy output of a solar water heater; Figure 4 is a daily profile derived from the energy data of Figure 3; Figure 5 shows a daily pattern of solar radiation in the United Kingdom; Figure 6 shows an average wind intensity in the United Kingdom expressed as the proportion of peak output produced by a wind turbine; Figure 7 shows a typical proportion of peak output produced by a domestic combined heat and power (CHP) generator; Figure 8 is a schematic diagram showing how a second apparatus can be used to control and meter a photovoltaic panel, wind turbine and CI-IP generator; Figure 9 shows a daily pattern of the aggregate electrical power generated by the photovoltaic panel, wind turbine and CHP generator shown in Figure 8; Figure 10 is a schematic diagram of an electronic control unit that forms part of the second apparatus of Figure 8; Figure 11 shows an average wind intensity in the United Kingdom expressed as the proportion of peak output produced by a wind turbine that has been modified by weather forecast data; Figure 12 shows the relationship between the heat output of the CHP generator of Figure 8 and the electrical output; and Figure 13 is a schematic diagram showing how the second apparatus can be used to control and schedule the operation of an electrical appliance such as a washing machine.

A first apparatus that represents technical background and which does not form part of the present invention will now be explained with reference to Figures 1 to 5.

The first apparatus is used to control the heating of the water inside a domestic hot water cylinder 2. A solar water heater includes a solar panel 4 that is located, for example, on the roof of a building. Cold water is supplied to the bottom of the hot water cylinder 2 from a mains water supply as shown. A pump 6 circulates cold water from the bottom of the domestic hot water cylinder 2 through the solar panel 4 where it is heated by solar radiation captured by the solar panel. The heated water is then returned back to the hot water cylinder 2 from where it can be withdrawn by the occupants of the house by turning on a hot water tap, for example. The hot water cylinder 2 is also fitted with an electric immersion heater 8 that is switched on and off by an electronic control unit 10.

in a conventional arrangement, the immersion heater 8 would be controlled by a timer unit that can be manually set by a user to determine certain times of the day and night when the water in the hot water cylinder 2 needs to be heated. A thermostat control would then be used to switch the immersion heater 8 on when the temperature of the water in the hot water cylinder 2 falls below a certain threshold level. The electronic control unit 10 is therefore used in combination with a timer control 12 and a thermostat control 14.

The electronic control unit 10 of the first apparatus receives energy data in the form of continuous temperature measurements from a pair of sensors 16 ahd 18 located at upper and lower regions of the hot water cylinder 2, respectively.

The internal functions of the electronic control unit 10 are shown schematically in Figure 2. The electronic control unit 10 includes a database 20 for storing energy data and a fixed read-only database 22 of energy source reference profiles. The temperature measurements from the sensors 16 and 18 are stored in the database 20 in the form of discrete time stamped values captured at suitable time intervals. The electronic control unit 1 0 also has access to basic information such as the time, date and the day of the week as represented by process block 24.

The electronic control unit 10 is able to detect the energy output of the solar water heater from a rising difference between the temperature of the water inside the hot water cylinder 2 as measured by the sensors 16 and 18. The temperature -17-measurements from the sensors 16 and 18 are stored in the database 20 over a period of time as energy data. A graph of the energy data (i.e. a representation of the energy output of the solar water heater as detected as a changing temperature by the sensors 16 and 18) versus time is shown in Figure 3 for the case where the energy data is stored for seven days. The electronic control unit 10 will use the stored energy data to derive a daily profile. This is carried out by dividing the whole of the stored energy data into consecutive 24 hour periods and then averaging these together to form a single derived daily profile. An example of a daily profile averaged from the seven days' worth of stored energy data is shown in Figure 4.

The fixed read-only database 22 contains a series of 365 individual daily reference profiles (i.e. one for each day of the year) for a solar radiation source. Figure 5 is an example of two daily reference profiles for solar radiation and shows average solar radiation intensity for a location in the United Kingdom versus time. The first profile labelled S is for a day in July and the second profile labelled W is for a day in January.

Instead of the fixed read-only database 22 containing a large number of daily reference profiles, a daily reference profile for any particular date may be calculated on demand using a mathematical formula in combination with a smaller number of reference profiles where necessary. In practical terms this would be useful if storage capacity was limited.

The electronic control unit 10 knows the period of time over which the energy data has been stored, or alternatively the period of time over the part of the energy data that has been used to derive the daily profile has been stored, and selects or calculates a daily reference profile for each type of renewable energy source for a date that falls within the period of time under consideration. For example, if the energy data shown in Figure 3 was collected over the first seven days of July then the electronic control unit 10 may select or calculate a daily reference profile for any date between the 1St and 7th of July.

A mathematical correlation function is then used to compare the derived daily profile shown in Figure 4 against the reference daily profiles. If the correlation function determines that the derived daily profile matches the reference daily profile (for example, if it returns a correlation factor that is greater than a selected threshold) then the electronic control unit 10 can use this determination and any other known information to confirm that a renewable energy device is present. For the particular arrangement shown in Figure 2, the correlation function will match the daily derived profile of Figure 4 with the reference profile S for solar radiation shown in Figure 5.

Once the renewable energy source has been identified as solar radiation, the electronic control unit 10 can identify the previously unknown source of heat as a solar water heater.

The process of correlating the derived daily profile with the daily reference profiles to determine a match is represented in Figure 2 by the process block 26. The output of the process block 26 is therefore a recognition of the presence of a renewable energy device that is to be taken into account in the decisions of the electronic control unit 10.

By storing energy data over time, the electronic control unit 10 can determine the relative efficiency with which the solar panel 4 converts the captured solar radiation into heat energy at different times of the day and times of the year. The energy data can therefore be used to predict the amount of heat energy that the solar panel 4 will capture over the next 24 hours (or any other time period as required for the particular application).

In addition, the electronic control unit 10 can determine the performance of the immersion heater 8 by working out the rate at which the temperature of the water in the hot water cylinder 2 increases when the immersion heater is switched on. It can therefore predict when the immersion heater 8 should be switched on for the temperature of the water in the hot water cylinder 2 to reach a desired level at a certain time. The prediction modelling is represented in Figure 2 by the process block 28. The output of the process block 28 is a command to control the on/off operation of the immersion heater 8.

As part of the prediction modelling, the times when the water in the hot water cylinder 2 needs to be heated can be determined from the manual settings of the timer control 12 or automatically using a known technique such as that described in JP 2005- 351547. The electronic control unit 10 can then allow the solar panel 4 to heat the water in the hot water cylinder 6 whenever possible and switch on the immersion heater 8 to the minimum extent necessary to achieve the desired heating. More particularly, the immersion heater 8 is only switched on by the electronic control unit when the heated water provided by the solar panel 2 of the solar water heater will be insufficient to meet an expected future demand for heated water.

If the desired temperature of the water in the hot water cylinder 2 is set by the thermostat control 14 to be less than 60 C for normal purposes then the electronic control unit 10 may also determine the most efficient time to raise the temperature to 60 C for routine sterilisation.

A second apparatus that forms part of the present invention will now be explained with reference to Figures 6 to 11.

The second apparatus is used to meter the electricity supplied by a number of renewable energy devices. Figure 8 shows a house that is equipped with a roof-mounted photovoltaic panel 30, a wind turbine 32 and a CHP generator 34. Each of these renewable energy devices is connected to a domestic electricity supply busbar 36 through appropriate power conditioning and safety protection devices 38. The supply busbar 36 feeds a typical assortment of lighting and power circuits 40 through a conventional distribution panel 42 with a fuse or circuit breaker for each circuit.

The electrical load flowing in the connection 42a between the supply busbar 36 and the distribution panel 42 is continuously measured by an electrical load sensor 44.

The electrical load sensor 44 may be an induction sensor clamped around the connection 42a, for example.

-20 -The supply busbar 36 is connected to the mains supply through an electronic control unit 46. The electronic control unit 46 is powered directly from the mains supply (typically it would be integrated with the normal electricity meter if dedicated to a metering application) and the energy data from the electrical load sensor 44 can be transmitted to the electronic control unit 46 using an electrical cable as shown.

The electronic control unit 46 quantifies and records the amount of electricity that is imported from, and exported to, the mains supply. This importlexport measurement is used with the measurement provided by the electrical load sensor 44 to calculate the energy parameter whose daily profile, as shown for the example in Figure 9, will represent the total amount of electricity supply to the supply busbar 36 by the photovoltaic panel 30, the wind turbine 32 and the CHP generator 34.

The energy parameter is therefore calculated as follows. The instantaneous amount of electricity that is imported from, or exported to, the mains supply has a value A (kW) and the instantaneous amount of electricity flowing in the connection 42a between the supply busbar 36 and the distribution panel 42 has a value B (kW). The total amount of electrical power C (kW) generated at any moment by the photovoltaic panel 30, the wind turbine 32 and the CHP generator 34 is therefore given by: C=B-A where A takes a positive value for electricity imported from the mains supply and a negative value for electricity exported to the mains supply. The value of A is measured by the normal electricity meter, which in this case is integrated with the electronic control unit 46. The value of C is computed by the electronic control unit 46 and stored as energy data.

The internal functions of the electronic control unit 46 are shown schematically in Figure 10. The electronic control unit 46 is similar to the electronic control unit 10 for the first apparatus and like components have been given the same reference numerals.

One difference is that weather related information can be provided from a local sensor 48 such as a wind speed sensor or external air temperature sensor, for example. The measurements provided by the local sensor are stored in the database 20 together with the measurements provided by the electrical load sensor 44. Alternatively, weather forecast data is supplied from an external provider represented in Figure 10 by the process block 50.

The weather information provided by the local sensor 48, or alternatively the weather forecast data, is used by the electronic control unit to modify or adjust the daily reference profiles to take account of the local weather conditions. For example, if the measurements provided by the local sensor 48 suggest that it is particularly windy then the daily reference profile for a wind source can be adjusted accordingly. Figure 11 shows how the first reference profile labelled S in Figure 6 can be modified to reflect the expected intensity in the next 24 hours when a weather front is predicted to pass through the locality in the morning.

When the electronic control unit 46 is operated for the first time, or a renewable energy device is connected to the electronic control unit for the first time, it must perform an energy source recognition process to determine the type of renewable energy device that it has to meter. The process of correlating a derived daily profile with the daily reference profiles to determine a match is represented in Figure 10 by the process block 52 and is the similar to the process described above for the first apparatus. In this case the fixed read only database 22 contains a series of 365 individual daily reference profiles (i.e. one for each day of the year) for a variety of different types of renewable energy source. For example, the database 22 may contain 365 daily reference profiles for a solar radiation source, 365 daily reference profiles for a wind source and 365 daily reference profiles for combined heat and power (CHP) generator. As mentioned above, Figure 5 is an example of two daily reference profiles for solar radiation and shows average solar radiation intensity for a -22 -locating in the United Kingdom versus time. Figure 6 is an example of two daily reference profiles for wind and shows wind turbine average capacity factor for a location in the United Kingdom versus time. Figure 7 is an example of two daily reference profiles for a CHP generator and shows CHP generator average capacity factor versus time. In all three examples, the first profile labelled S is for a day in July and the second profile labelled W is for a day in January. Alternatively, instead of the fixed read-only database 22 containing a large number of individual daily reference profiles, a daily reference profile for any particular date may be calculated on demand using a mathematical formula in combination with a smaller number of reference profiles.

The daily reference profiles may be modified by the weather related information provided by the local sensor 48 or by the weather forecast data supplied by the external provider 50. In the example of Figure 9, the derived daily profile will give a correlation factor above the required threshold when correlated against daily reference profiles for solar radiation, wind and CHP generator capacity factor. The output of the process block 52 is therefore a recognition of the type of renewable energy device that is connected to the supply busbar 36 and the electronic control unit 46 knows that it has to meter electricity supplied by a photovoltaic panel, a wind turbine and a CHP generator.

The electronic control unit 46 uses the stored energy data to derive a daily profile that represents the energy output of the renewable energy devices. The derived daily profile is correlated on a daily basis with daily reference profiles to quantify the energy output of each renewable energy device as a fraction of each stored value of C. For example, in a domestic situation, if the value of C at a particular instant in time is 2 kW then the electronic control unit 46 can determine that the solar photovoltaic panel 30 was providing 200 W, the wind turbine 32 was providing 750 W and the ClIP generator 34 was providing the remaining 1050 W. By integrating each fraction of C over time the electronic control unit 46 can determine the number of kW-hour units output by each renewable energy device. The peak output of each renewable energy device can also be determined. This metering process is represented in Figure 10 by the process block 54.

The electronic control unit 46 can report the number of kW-hour units output by each renewable energy device and the number of kW-hour units imported from, or exported to, the mains supply as required. For example, it can report hourly, daily, weekly, monthly or quarterly and in any convenient manner such as through a visual display on the electronic control unit itself or by transmitting the report to a remote site that will use the report for billing, validation and payment. This removes the need for a separate metering unit to be attached to each renewable energy device. The use of the electronic control unit 46 also simplifies the process of installing a renewable energy device since the electricity it supplies will be metered automatically as soon as it is connected to the supply busbar 36. Metering information can be provided for commercial purposes such as the award of Renewable Obligation Certificates.

If the number of kW-hour units from any of the renewable energy devices falls below expected levels then this can be used to prompt maintenance or repair if necessary.

As well as metering the electrical output of the photovoltaic panel 30, wind turbine 32 and CHP generator 34, the electronic control unit 46 can be used to control the operation of any auxiliary energy devices connected to the supply busbar 36 as described above.

The electronic control unit 46 may also be used to control and schedule the operation of any electrical appliances or loads connected to the supply busbar 36. Figure 13 shows an example that is similar to that shown in Figure 8 and like components have been given the same reference numerals. A roof-mounted photovoltaic panel 30 and a wind turbine 32 are connected to a domestic electricity supply busbar 36 through appropriate power conditioning and safety protection devices 38. A washing machine 56 is connected to the supply busbar 36 through a conventional distribution panel 42 and a remote switching unit 58.

-24 -The electronic control unit 46 can predict the amount of electricity that the solar photovoltaic panel 30 and the wind turbine 32 will provide over the next 24 hours (or any other time period as required for the particular application). The electronic control unit 46 can then control the operation of those appliances that do not have to run continuously so that they operate when a surplus of electricity is predicted. In other words, the electronic control 46 may control the remote switching unit 58 to switch on the washing machine 56 when it believes that the solar photovoltaic panel and the wind turbine 32 will be supplying electricity to the supply busbar 36. The electricity supplied by the renewable energy devices may therefore be used in a more efficient manner. Any commands sent from the electronic control unit 46 to the remote switching unit 58 may be transmitted using a known means such an electrical cable or the LON WORKS power line transmission technology.

Claims

1. A metering apparatus for use with at least one renewable energy device that derives energy from a renewable energy source, the apparatus comprising: an electronic control unit; and an energy sensor for measuring an energy parameter that is affected by an energy output of the at Least one renewable energy device and providing energy data to the electronic control unit; wherein the electronic control unit uses the energy data to derive a profile of the change in the energy parameter, correlates the derived profile with an reference profile corresponding to the at least one renewable energy, and uses the results of the correlation and the energy data to quantify the energy output of the at least one renewable energy device over a selected period of time.

2. A metering apparatus according to claim 1, wherein information relating to the energy output of the at least one renewable energy device over the selected period of time is presented as visual information on a display screen.

3. A metering apparatus according to claim 1, wherein information relating to the energy output of the at least one renewable energy device over the selected period of time is provided as an output signal.

4. A metering apparatus according to any preceding claim, wherein the electronic control unit receives weather data and is adapted to use the weather data to adjust each reference profile.

5. A metering apparatus according to claim 4, wherein the, weather data is weather forecast data.

6. A metering apparatus according to claim 4, wherein the weather data is provided from a weather sensor.

-26 -

7. A method for metering at least one renewable energy device that derives energy from a renewable energy source, the method comprising the steps of: measuring an energy parameter that is affected by an energy output of the at least one renewable energy device to obtain energy data; using the energy data to derive a profile of the change in the energy parameter; correlating the derived profile with a reference profile corresponding to the at least one renewable energy device; and using the results of the correlation and the energy data to quantify the energy output of the at least one renewable energy device over a selected period of time.

8. A method according to claim 7, further comprising the step of presenting information relating to the energy output of the at least one renewable energy device over the selected period of time as visual information on a display screen.

9. A method according to claim 7, further comprising the step of providing information relating to the energy output of the at least one renewable energy device over the selected period of time as an output signal.

10. A method according to any of claims 7 to 9, further comprising the step of using weather data to adjust each reference profile.