WO2016135508A1

WO2016135508A1 - Solar home system

Info

Publication number: WO2016135508A1
Application number: PCT/GB2016/050509
Authority: WO
Inventors: Simon BRANSFIELD-GARTH; Michael James SALES; Nigel PRESTON; Duncan Barclay
Original assignee: Azuri Technologies Limited
Priority date: 2015-02-27
Filing date: 2016-02-26
Publication date: 2016-09-01
Also published as: GB2551287B; GB201712861D0; CN107258044A; GB2551287A; GB201503332D0

Abstract

A Solar Home System comprises photovoltaic panels (1), rechargeable batteries (2), a system controller (3) and one or more loads and provides an intelligent and adaptive operation. This operation optimises the solar charging and then adjusts the output for each device on the system to match predicted usage patterns that are developed by tracking typical usage.

Description

SOLAR HOME SYSTEM

FIELD OF THE INVENTION

The present invention relates to solar powered home energy systems that provide lighting and power for consumers. In particular the systems are designed for consumers in areas where there is no, or intermittent, access to a national grid electricity supply.

BACKGROUND OF THE INVENTION

It is estimated that over 1.6 billion people do not have access to electricity and in such circumstances the lack of lighting has a huge impact on the quality of life. For the majority of the developing world the only source of light is from burning wood, dung, candles or kerosene and this is both harmful and unsustainable. To overcome this problem many off-grid rural areas now have access to solar home systems (SHS). A typical SHS consists of photovoltaic (PV) panels, a battery, a charge controller, and several loads (appliances). The battery stores energy collected by the panels, the charge controller prevents the battery from being overcharged, and the loads (typically some combination of one or more lamps, mobile phone charging capability and other consumer electronic devices such as a small radio, TV, Tablet, Laptop or similar) draw power from the system. Such systems are described for example in SIMbaLink: Towards a Sustainable and Feasible Solar Rural Electrification System; Nahana Schelling, et al; Proceedings of the International Conference on Communication Technologies and Development (ICTD); London, UK, December 2010.

Many SHS installations are provided on a pay-as-you-go (PAYG) or progressive purchase basis because the consumers are unable to purchase the devices outright and instead pay a nominal sum for the unit and then pay for their use of the unit in small increments typically at half the cost of their equivalent purchase of kerosene. Various mechanisms for collecting payment are available such as via mobile phones as described in US2013212005. PROBLEM TO BE SOLVED BY THE INVENTION

One of the main problems with SHS is that the available power is not always sufficient to provide full use of all the appliances on the system. This may be because over time the battery loses its capacity, the PAYG credits may be about to run out, or because some days are cloudy and the solar panels are not able to fully charge the battery in preparation for the night time. In these situations typically a SHS will operate until the battery is discharged and then turn off. However, from the perspective of the end user, not all devices are created equal. For example, access to a small amount of light may be more important than an extra few minutes of phone charging. It is therefore highly desirable to have some form of power management to predict the typical lighting and power needs and to allocate the energy resource so that the appliances can operate over their required period of use. However, to optimise both the way a battery is charged and the way energy is consumed, it is desirable to adjust both the charging and discharging strategies based on an estimate of historical charging and usage patterns.

SUMMARY OF THE INVENTION

The inventors have developed a system which uses the components of a SHS to monitor the customer usage patterns over time and match this to one or more characteristic patterns, which may be expressed in the form of templates or other means. The SHS infers information from the parameters available to it such as panel voltage, panel current, battery charging current, battery voltage and the discharge current of various outputs. This information is used to estimate time of day, weather conditions, time of year and historical available sunshine levels in order to dynamically estimate the likely quantity and pattern of charging current available to the system. This information is then used to modify the charging regime to the battery. For example, in conditions where extended sunshine can be expected, the charging rate is reduced in order to maximise battery life. However, where it is expected that sunshine will be available in short bursts, which would ordinarily result in the battery receiving inadequate charge, the charging rate is increased in order to maximise the stored energy. Similarly, the historical current drain on the outputs is monitored and the system uses this information to estimate the likely use - distinguishing between a main light (typically on for an extended period in the evening and again in the morning), a bedroom (typically on for a short time evening and morning) and an outside light (typically on all night). This information, coupled with the quantity of usage is used to provide a performance target for the system i.e. the idealised typical usage.

The system uses the estimate of the available charging energy and the idealised typical usage to make decisions regarding the system's operation. In cases where the available charge is less than that required for idealised operation, the system uses its knowledge of the typical demand profile to choose where to allocate power. For example, if the lighting is used for typically 6 hours per day, the system will choose to adjust the light intensity to preserve this duration rather than to provide full power lighting for a shorter time. Similarly, the system will make choices about the routing of power for example to accessory devices or phone charging versus power for lighting.

In a similar way, if the system is a pay as you go SHS that charges depending on energy usage, the system may adjust the power output of the system when the available energy credit is less than that required to power all the outputs for a given period, in order to prioritise essential services such as lighting over more discretionary services such as TV. It will be appreciated that reference to "charge" above in the context of a pay as you go SHS, refers to a monetary charge. Reference to an "available energy credit" refers to user's monetary balance that is associated with the SHS.

According to one aspect of the present invention there is provided a solar home system comprising a photovoltaic (PV) panel array, a rechargeable battery pack, a system controller and one or more connected appliances (a) having a tracking means for monitoring an output from the PV panel array and a usage pattern for each connected appliance to establish an operation profile over a period of one or more days, and (b) periodically adapting the operation profile according to use of the system over a time period.

The system controller may use the operation profile to select a match from a plurality of built in templates to represent the typical climate conditions and appliance usage patterns for the system. The system controller may be configured to allocate power to the one or more connected appliances according to the operating profile.

The system controller may use an algorithm for matching an operation profile of the PV panel to one of a set of typical climatic conditions.

The system controller may use an algorithm for matching typical climatic conditions to an adaptive battery charging strategy and to an expected resulting charge in the battery.

The system controller may use an algorithm to match a usage pattern for each appliance to one of a set of typical usage profile templates.

The system controller may adapt the adaptive battery charging strategy in order to achieve a desired charge in the battery.

The system controller may use an algorithm to create an idealised customer demand target for each appliance based on the usage pattern of the respective appliance.

The system controller may adjust the output to each appliance based on the available power and information from the usage profile and the customer demand target.

The system controller may communicate with a remote device for aggregation of data from one or more units operating within a region.

One or more of the connected appliances may be light sources. In this embodiment, the system controller may adjust the output by pulse width modulation to increase or decrease the light output.

One or more of the connected appliances may be mobile phones or other similar computing devices.

One or more of the connected appliances may be television or radio or other similar communication devices.

The system controller may adjust a period and duration during which one or more of the appliances can operate.

The operation profile may be adapted periodically according to the daily use of the system. The system controller may adjust power to one or more appliances to prioritise daytime battery charging.

The system may adjust power to one or more appliances when an anticipated battery charge is less than that required for overnight operation. The system controller may select an operating profile from a plurality of templates that represent typical climate conditions and appliance usage patterns.

The system controller may use an algorithm to match an operating profile of the photovoltaic array to one of a set of typical climatic conditions.

The system controller may use an algorithm to match typical climatic conditions to an adaptive battery charging strategy and to an expected resultant charge in the battery.

The system controller may use an algorithm to match the usage pattern for each appliance to one of a set of typical usage profile templates.

The system controller may use an algorithm to create a target customer usage profile for each appliance on the solar home system based on the measured usage pattern of the appliance. The system controller may allocate power to each appliance based on an anticipated battery charge and information from the target customer usage profile.

According to another aspect of the present disclosure there is provided a solar home system comprising a photovoltaic panel array, a rechargeable battery pack, one or more connected appliances, and a system controller configured to: monitor at least one output from the photovoltaic panel array, at least one output from the rechargeable battery pack, and a demand current of each connected appliance; use the at least one output from the photovoltaic panel array and the demand current of each connected appliance to establish an operating profile over a time period; infer information from the at least one output from the rechargeable battery pack; and allocate power to the one or more connected appliances based on the operating profile, the inferred information and an estimated time of day.

The system controller may monitor a voltage of the photovoltaic panel array and/or a current of the photovoltaic panel array. The system controller may estimate the time of day from the at least one output from the photovoltaic panel array.

The solar home system may further comprise a light sensitive device, and the system controller estimates the time of day from at least one output from the light sensitive device.

The system controller may use estimates of the time of day and the demand current of each connected appliance to determine a usage pattern for each connected appliance over the time period.

The system controller may use the at least one output from the photovoltaic panel array and the usage pattern for each connected appliance to establish the operating profile.

The system controller may monitor (i) a charging current of the rechargeable battery pack and a discharging current of the rechargeable battery pack; and/or (ii) a voltage of the rechargeable battery pack.

The system controller may infer a level of battery charge from the at least one output from the rechargeable battery pack.

The system controller may use the monitored at least one output from the photovoltaic panel array to estimate one or more of a time of year and weather conditions. The system controller may instruct a charge controller associated with the rechargeable battery pack to modify a charging regime of the rechargeable battery pack.

The system controller may adjust power to one or more appliances to prioritise daytime battery charging. The system controller may adjust power to one or more appliances when an anticipated battery charge is less than that required for overnight operation.

The system controller may select an operating profile from a plurality of templates that represent typical climate conditions and appliance usage patterns. The system controller may use an algorithm to match an operating profile of the photovoltaic array to one of a set of typical climatic conditions.

The system controller may use an algorithm to create a target customer usage profile for each appliance on the solar home system based on a measured usage pattern of the appliance.

The system controller may allocate power to each appliance based on the anticipated battery charge and information from the target customer usage profile. The system controller may communicate with a remote device for aggregation of data from one or more units operating within a region.

The one or more of the connected appliances may comprise at least one light source. In this embodiment, the system controller may control the at least one light source by pulse width modulation to increase or decrease the light output. The system controller may adjust a period and duration during which one or more of the connected appliances can operate.

The one or more of the connected appliances may comprise one or any combination of: at least one mobile phone; at least one television; at least one radio; and at least one fan. The system controller may prioritise power to essential appliances when an available energy credit is less than that required to power all of the one or more connected appliances for a given period.

In another aspect of the present invention there is provided a solar home system comprising a photovoltaic panel array, a rechargeable battery pack, a system controller and one or more connected appliances characterized by (a) having a tracking means for monitoring the current from the PV panel and the usage pattern for each connected appliance to establish an operation profile over a period of one or more days, (b) using the operation profile to select a match from a plurality of built in templates to represent the typical climate conditions and appliance usage patterns for the system, and (c) periodically adapting the operation profile according to the daily use of the system.

In another aspect of the present invention there is provided a solar home system comprising a photovoltaic panel array, a rechargeable battery pack with an associated charge controller, and one or more connected appliances, characterized by having a power management controller for: (a) monitoring and inferring information from the photovoltaic panel, battery and the demand current of each connected appliance to establish a target operating profile over a period of one or more days; and (b) allocating power to the outputs of the solar home system according to the target operating profile.

ADVANTAGEOUS EFFECT OF THE INVENTION

The use of energy management to adjust light output is well known for solar powered lights so that outdoor lighting can be maintained throughout the night for typical applications such as street lighting or illuminated signs. An example of such methods is described in US2012091901. This invention describes a further improvement in which the solar charging of the PV panels and the usage patterns of one or more lights and other devices on a SHS are monitored to provide an intelligent and adaptive operation that optimises the solar charging and then adjusts the output for each device on the system to match the predicted usage pattern and avoid premature loss of function during each period of use. The inventors have developed a set of mechanisms including but not limited to templates which uniquely characterise each usage so that it is possible to predict the on-times and intensity of any lights to meet the purpose for which they are being used. Similarly the typical periods during which mobile phones are charged or radios or other appliances are operated can be predicted and the system adjusted accordingly.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 : A schematic representation of a Solar Home System

Figure 2: A schematic representation of a system controller of the Solar Home System

DETAILED DESCRIPTION OF THE INVENTION

The invention uses adaptive techniques to optimise the charging and discharging of a solar home system. A typical configuration for a SHS is shown in Figure 1. The SHS can be built using known technology, for example, the solar panel (1) can be built from any known photovoltaic technology (e.g. mono/multi crystalline silicon, III-V, amorphous Si, thin film (CdTe, CIGS, dye sensitised, organic, nanoparticle)). Equally, the solar panel can be one that is developed in the future. The rechargeable battery unit (2) can be selected from any existing or future battery type such as sealed lead acid, Ni-metal hydride etc. and is preferably of the lithium iron phosphate variety. The system typically provides DC power from a few watts to several hundred watts but is preferably in the range 2.5W to 200W or more preferably 2.5W to 50W. The system controller (3) can be built using components known to anyone skilled in the art of circuit design. It would typically use a

microcontroller and could be built in any number of configurations to achieve the desired functionality as described below.

To optimise the charging, the system measures the light intensity, typically by periodically short circuiting the solar panel to measure the short circuit current. By correlating the current to an internal timer, over a period of several days, the system is able with some certainty to determine the durations of night and day. From this, it is able to estimate both real time and also the season. Within a day, a number of solar patterns are characteristic e.g. bright sunshine, overcast, intermittent sunshine. At certain times of year, these patterns are characteristic e.g. sunny in the morning and thunderstorms in the afternoon. By comparing the light pattern to stored templates, the system estimates the likely weather pattern. This comparison provides an estimate of the expected light that will be available in the day. The expected light is compared to the required light for charging and the rate of charge to the battery adjusted to optimise the probability that the battery will charge while minimising the instantaneous current into the battery, in order to maximise battery life.

The computations above may be carried out locally on the device or communicated back to a remote server or computing device where both the calculations are performed and the data from a number of devices in a region may be compared to further improve the estimate of climatic conditions for transmission back to the device or for refining the templates.

The operation of the discharge circuitry is similar. The system measures the current discharge from the battery and the current drain profile of each of the attached devices over a period of several days. From this a usage pattern emerges. The system will characterise the outputs to estimate which is for example a room light (used for extended periods night and morning), bedroom light (used for short periods night and morning) and an outside light (left on all night).

Similarly the system measures the total load current typically taken by the customer on a daily basis. This information is used to create a target load. By measuring the solar panel current, it is possible to estimate dusk with some accuracy.

This is likely to correspond to the point of maximum charge of the battery. The system compares the available charge to the target charge and if the available charge is less than the target charge, will reduce the light intensity of the lights using for example pulse width modulation so that the light duration target is satisfied, albeit at a lower brightness. The system adapts based on the recorded performance. If the target charge is not met despite the scaling of the light output, the target charge is increased incrementally so that in future days the percentage light output is further reduced. Similarly, if the battery has residual charge remaining when the sun begins to recharge the battery, the target charge is reduced. In this way, the system adaptively adjusts to try to meet the lighting duration target set by the customer's usage, irrespective of the quantity of sunshine in the charging period. This process may operate over a period of one day or be aggregated over a period of several days. The option to override the adaptive behaviour can also be provided if the customer requires periods of unrestricted power.

As before, the computations above may be carried out locally on the device or communicated back to a remote location where both the calculations are performed and the data from a number of devices in a region may be compared to further improve the estimate of target current and light scaling strategies.

Whilst it has been described above that the system measures the light intensity by measuring the panel current of the solar panel. In other embodiments, the system measures the light intensity by measuring a current of the solar panel (e.g. short circuit current or an operating current measured when load devices are connected to the system) and/or a voltage of the solar panel (e.g. an open circuit voltage or an operating voltage measured when load devices are connected to the system). In particular, the system controller may measure the light intensity by periodically measuring the open circuit voltage of the solar panel by electrically isolating it from the battery and appliances. By correlating the current or voltage measurements to an internal timer, over a period of several days, the system controller is able with some certainty to determine the durations of night and day and the solar midpoint of the day. From this, it is also able to estimate the time of dawn and dusk, the local time of day and also the season.

The system controller uses information gathered from the demand current of each connected appliance and its knowledge of the time of day or night to determine a likely daily use profile (otherwise referred to herein as a usage pattern or usage profile) for each appliance. For example a usage profile for an appliance may comprise a set of data collected over a 24 hour period (or other time period) which includes the current drawn by the appliance at intervals (e.g. every 5 mins) during the time period. In the context of the load of the SHS comprising one or more lamps, the system controller is at least able to identify the demand current for the lamps, the typical amount of time the lamps are used during the daytime and the typical duration the lamps are used overnight.

The system controller uses (i) a charging current of the rechargeable battery and a discharging current of the rechargeable battery (also referred to herein as the total load current); and/or (ii) a voltage of the rechargeable battery, to estimate the level of available battery charge.

In embodiments, the system controller uses the measured light intensity and the usage profiles of each appliance to establish an operating profile over a time period (e.g. a period of one or more days). The operating profile includes data of the measured light intensity over the time period (providing an indication of an available sunshine level) and the sets of data of demand current of each connected appliance over the time period (provides an indication of how a user is using the SHS). It will be appreciated that the system controller adapts the operation profile according to the daily use of the SHS. That is, the operation profile will change in dependence on changes in the current/voltage of the solar panel and the demand current of each connected appliance.

In embodiments, the system controller uses the operating profile, estimated time of day, and the estimated level of battery charge to make decisions regarding the SHS operation. In particular, the system controller uses the operating profile, estimated time of day, and the estimated level of battery charge to allocate power to the connected appliances.

Figure 2 illustrates a schematic representation of the system controller 3. As shown in Figure 2, the system controller 3 comprises a tracking means 4 for monitoring outputs from the PV panel array and a usage pattern 10 for each connected appliance to establish an operation profile 6 over a time period (e.g. one or more days). The system controller further comprises one or more algorithm 7 that is referred to above. Some or all of the individual functions performed by the system controller can be performed by separate units some or all of which may be remotely connected to the SHS by a communications networking system such as the Internet or a cellular telephone network. For example, whilst Figure 2 shows the system controller 3 comprising the templates 8 that are referred to herein, it will be appreciated that these templates may be stored in a memory coupled to the system controller 3. The memory may be local to the system controller (e.g. mounted on the same PCB or housed in the same unit as the system controller) or remote to the system controller (e.g. cloud storage).

The SHS may further comprise a charge controller that prevents the battery from being overcharged. The charge controller uses information gathered from monitoring either the photovoltaic panel array (e.g. open circuit) voltage or the photovoltaic panel array (e.g. short circuit) current or the battery charging current (i.e. the charging current and discharging current of the battery) or the battery voltage or some combination of all of these quantities to modify a charging regime of the battery. For example, many battery chemistries require that the battery is charged at a constant current until the battery voltage rises to a predetermined voltage after which the battery should be charged with a constant voltage, typically the same as the predetermined voltage, or in conditions with high levels of sunshine, the battery charging rate may be reduced in order to maximise battery life. In addition to the above effect, the system controller is able to instruct the charge controller to stop charging the battery or to increase the charging rate of the battery or to decrease the charging rate of the battery. Whilst the charge controller may be separate to the system controller, it will be appreciated to persons skilled in the art that functionality of the charge controller can alternatively be performed by the system controller.

As explained above, the system controller may uses information gathered from monitoring either the photovoltaic panel array voltage (e.g. open circuit voltage) or the photovoltaic panel array current (e.g. short circuit current) or some combination of both quantities to distinguish between day time and night time and may also be used to estimate weather conditions, time of year and historical available sunshine levels in order to dynamically estimate the likely quantity and pattern of charging current available to the SHS over a desirable period of time such as a day or a week. This information can then be used to modify the charging regime of the battery. For example, in conditions where extended sunshine can be expected, the charging rate is reduced in order to maximise battery life. However, where it is expected that sunshine will be available in short bursts, for example during a rainy season, which would ordinarily result in the battery receiving inadequate charge, the charging rate is increased in order to maximise the stored energy.

It will be appreciated the SHS may comprise other elements not shown in the Figures such as a user interface and/or an inverter.

Whilst example loads (otherwise referred to herein as connected appliances) of the SHS have been referred to above such as one or more lamps, one or more mobile phones (or other similar computing device such as laptop, tablet etc.), one or more radio, and one or more TV, it will be appreciated that embodiments extend to other load devices such as one or more fan, one or more hair clipper, one or more razor, one or more sewing machine or other appliances not explicitly mentioned herein. It will be appreciated from the above, that the inventors have developed a set of mechanisms including but not limited to algorithms and templates that uniquely characterise each usage pattern so that it is possible to adjust the on-times and intensity of any lamps to meet the purpose for which they are being used. Similarly the typical periods during which mobile phones are charged or radios or other appliances are operated can be predicted and the SHS operation adjusted accordingly. Similarly, the inventors have developed mechanisms including but not limited to algorithms and templates for identifying different daily weather patterns, seasonal patterns of sunshine duration and climatic patterns that make it possible to predict the potential levels of sunshine available to power the SHS during that day to further optimise the battery charging profile.

It is preferable for the system controller predicts the time of day based on historical information from the photovoltaic array rather than instantaneous information from the photovoltaic array to overcome false predictions of night time due to short term cloud cover. In addition it is preferable for the day and night time predictions to be based on measurements rather than an embedded real time clock to reduce system cost and to avoid erroneous actions due to the clock being set incorrectly. It will be appreciated from the above that the system controller may prioritise allocation of power to appliances providing essential services such as lighting (e.g. essential appliances). The system controller may determine that one or more appliance is an essential appliance based on preconfigured priority information, user-configured priority information or determine this dynamically through a user's use of the SHS (e.g. determining that a particular appliance is used every day during one or more time intervals).

Whilst embodiments have been described above in which information such as time of day, weather conditions, time of year and historical available sunshine levels are estimated using a voltage and/or current of the photovoltaic panel array. Alternatively or additionally, the system may comprise a further light sensitive device, and the system controller may estimate this information using the output from the further light sensitive device. The further light sensitive device may be a photovoltaic (PV) panel array, light dependent resistor, photodiode, phototransistor, charge coupled device etc. Other examples of further light sensitive devices that may be used will be apparent to persons skilled in the art.

The examples and descriptions given are illustrative of the spirit and scope of the invention and are not intended to be limiting.

Claims

CLAIMS:

1. A solar home system comprising a photovoltaic (PV) panel array, a rechargeable battery pack, a system controller and one or more connected appliances

(a) having a tracking means for monitoring an output from the PV panel array and a usage

pattern for each connected appliance to establish an operation profile over a period of one or more days,

and

(b) periodically adapting the operation profile according to use of the system over a time period.

2. A system according to claim 1, further comprising using the operation profile to select a match from a plurality of built in templates to represent the typical climate conditions and appliance usage patterns for the system.

3. A system according to claim 1 or 2, wherein the system controller is configured to allocate power to the one or more connected appliances according to the operating profile.

4. A system according to any preceding claim in which the system controller uses an algorithm for matching an operation profile of the PV panel to one of a set of typical climatic conditions.

5. A system according to any preceding claim in which the system controller uses an algorithm for matching typical climatic conditions to an adaptive battery charging strategy and to an expected resulting charge in the battery.

6. A system according to any preceding claim in which the system controller uses an algorithm to match a usage pattern for each appliance to one of a set of typical usage profile templates.

7. A system according to claim 5 in which the system controller adapts the adaptive battery charging strategy in order to achieve a desired charge in the battery.

8. A system according to claim 6 in which the system controller uses an algorithm to create an idealised customer demand target for each appliance based on the usage pattern of the respective appliance.

9. A system according to claim 8 in which the system controller adjusts the output to each appliance based on the available power and information from the usage profile and the customer demand target.

10. A system according to any of the preceding claims in which the system controller communicates with a remote device for aggregation of data from one or more units operating within a region.

11. A system according to any of the preceding claims in which one or more of the connected appliances are light sources.

12. A system according to any of the preceding claims in which one or more of the connected appliances are mobile phones or other similar computing devices.

13. A system according to any of the preceding claims in which one or more of the connected appliances are a television or radio or other similar communication devices.

14. A system according to claim 11 in which the system controller adjusts the output by pulse width modulation to increase or decrease the light output.

15. A system according to any of the previous claims in which the system controller adjusts a period and duration during which one or more of the appliances can operate.

16. A system according to any of the preceding claims, wherein the operation profile is adapted periodically according to the daily use of the system.

17. A system according to any of the preceding claims in which the system controller adjusts power to one or more appliances to prioritise daytime battery charging.

18. A system according to any of the preceding claims in which the system adjusts power to one or more appliances when an anticipated battery charge is less than that required for overnight operation.

19. A system according to any of the preceding claims in which the system controller selects an operating profile from a plurality of templates that represent typical climate conditions and appliance usage patterns.

20. A system according to any of the preceding claims in which the system controller uses an algorithm to match an operating profile of the photovoltaic array to one of a set of typical climatic conditions.

21. A system according to any of the preceding claims in which the system controller uses an algorithm to match typical climatic conditions to an adaptive battery charging strategy and to an expected resultant charge in the battery.

22. A system according to any of the preceding claims in which the system controller uses an algorithm to match the usage pattern for each appliance to one of a set of typical usage profile templates.

23. A system according to any of the preceding claims in which the system controller uses an algorithm to create a target customer usage profile for each appliance on the solar home system based on the measured usage pattern of the appliance.

24. A system according to claim 23 in which the system controller allocates power to each appliance based on an anticipated battery charge and information from the target customer usage profile.

25. A solar home system comprising a photovoltaic panel array, a rechargeable battery pack, one or more connected appliances, and a system controller configured to: monitor at least one output from the photovoltaic panel array, at least one output from the rechargeable battery pack, and a demand current of each connected appliance; use the at least one output from the photovoltaic panel array and the demand current of each connected appliance to establish an operating profile over a time period; infer information from the at least one output from the rechargeable battery pack; and allocate power to the one or more connected appliances based on the operating profile, the inferred information and an estimated time of day.

26. A system according to claim 25, in which the system controller monitors a voltage of the photovoltaic panel array and/or a current of the photovoltaic panel array.

27. A system according to claim 25 or 26, in which the system controller estimates the time of day from the at least one output from the photovoltaic panel array.

28. A system according to claim 25 or 26, in which the solar home system further comprises a light sensitive device, and the system controller estimates the time of day from at least one output from the light sensitive device.

29. A system according to claim 27 or 28, in which the system controller uses estimates of the time of day and the demand current of each connected appliance to determine a usage pattern for each connected appliance over the time period.

30. A system according to claim 29, in which the system controller uses the at least one output from the photovoltaic panel array and the usage pattern for each connected appliance to establish the operating profile.

31. A system according to any of claims 25 to 30, in which the system controller monitors (i) a charging current of the rechargeable battery pack and a discharging current of the rechargeable battery pack; and/or (ii) a voltage of the rechargeable battery pack.

32. A system according to any of claims 25 to 31, in which the system controller infers a level of battery charge from the at least one output from the rechargeable battery pack.

33. A system according to any of claims 25 to 32, in which the system controller uses the monitored at least one output from the photovoltaic panel array to estimate one or more of: a time of year and weather conditions.

34. A system according to any of claims 25 to 33, in which the system controller instructs a charge controller associated with the rechargeable battery pack to modify a charging regime of the rechargeable battery pack.

35. A system according to any of claims 25 to 34, in which the system controller adjusts power to one or more appliances to prioritise daytime battery charging.

36. A system according to any of claims 25 to 35, in which the system controller adjusts power to one or more appliances when an anticipated battery charge is less than that required for overnight operation.

37. A system according to any of claims 25 to 36, in which the system controller selects an operating profile from a plurality of templates that represent typical climate conditions and appliance usage patterns.

38. A system according to any of claims 25 to 37 in which the system controller uses an algorithm to match an operating profile of the photovoltaic array to one of a set of typical climatic conditions.

39. A system according to any of claims 25 to 38, in which the system controller uses an algorithm to match typical climatic conditions to an adaptive battery charging strategy and to an expected resultant charge in the battery.

40. A system according to any of claims 25 to 39, in which the system controller uses an algorithm to match a usage pattern for each appliance to one of a set of typical usage profile templates.

41. A system according to any of claims 25 to 40, in which the system controller uses an algorithm to create a target customer usage profile for each appliance on the solar home system based on a measured usage pattern of the appliance.

42. A system according to claim 41 in which the system controller allocates power to each appliance based on the anticipated battery charge and information from the target customer usage profile.

43. A system according to any of claims 25 to 42, in which the system controller communicates with a remote device for aggregation of data from one or more units operating within a region.

44. A system according to any of claims 25 to 43, in which the one or more of the connected appliances comprise at least one light source.

45. A system according to any of claims 25 to 44, in which the system controller adjusts a period and duration during which one or more of the connected appliances can operate.

46. A system according to claim 44 in which the system controller controls the at least one light source by pulse width modulation to increase or decrease the light output.

47. A system according to any of claims 25 to 46, in which the one or more of the connected appliances comprise one or any combination of: at least one mobile phone; at least one television; at least one radio; and at least one fan.

48. A system according to any of claims 25 to 47 in which the system controller prioritises power to essential appliances when an available energy credit is less than that required to power all of the one or more connected appliances for a given period.