Renewable Energy Power Generation, Storage and Management System

Field of the invention

The present invention relates to a renewable energy power generation, storage and management system. In preferred embodiments of the invention, the system is configured for powering industrial equipment at remote sites. The system may be stand alone or connected to an existing electrical grid.

Background

Electrical networks at remote industrial sites require a reliable power supply, particularly for important equipment such as well pumps for example. Diesel, gas or hybrid power generators are commonly used for such applications, however, they require a physical fuel supply that must be transported to the remote site, which can be expensive and unsafe under certain conditions. It is also desirable to reduce use of fossil fuels. Furthermore, diesel generators lack load control management systems and tend to operate in an oversupply state so that system efficiency is reduced.

Furthermore, for redundancy multiple generators are provided in a remote power supply network, further increasing capital costs to install such systems.

There is a need to address the above, and/or at least provide a useful alternative.

According to one aspect of the invention there is provided a renewable energy power generation, storage and management system, comprising a power generation system harnessing renewable energy, an energy storage device, and a control system, each in communication with each other, wherein the control system includes: a load prediction module configured to predict a required power supply for a load connected to the system; and a weather prediction module configured to predict the energy output of the power generation system, wherein the control system is configured to: monitor the level of the energy storage device, the output of the power generation system and the power requirements of the load, and based on an expected power supply for the load predict the level of the energy storage device, and reduce the supply of electrical energy to the load when the level of the energy storage device is predicted to fall below a predetermined level.

According to a preferred embodiment of the invention, the power generation system includes a plurality of photovoltaic cells or wind turbines.

Preferably, the power generation system includes a plurality of photovoltaic (PV) cells grouped into at least one array, the or each array being in communication with a respective battery house including a plurality of battery cells for storing electrical energy from the PV cells. Preferably, the or each array includes at least one inverter to convert the power generated to AC power.

In preferred embodiments, each battery house has an inverter-charger to convert incoming power from AC to DC and convert outgoing power from DC to AC, and a DC-DC converter between the inverter charger and the batteries, to modify the voltage of the incoming power to a level sufficient for charging the batteries.

Preferably, the inverter-charger has a short time surge rating. The control system may be formed of a plurality of like control modules each of which being disposed in a respective battery house. Preferably, the control system includes a predictive controller which comprises a first programmable logic controller (PLC) and an electrical controller which comprises a second PLC.

Preferably, the electrical controller includes a software sequence to manage the start-up of the inverter-charger, the sequence allowing for a slow ramping up of voltage and frequency of the inverter-charger to provide a soft start for high inductive load equipment.

The predictive controller may be configured to isolate the batteries to prevent over charging. Preferably, the predictive controller receives historical weather data from a remote computer terminal via a modem and antenna. The predictive controller may receive control instructions from a remote control computer terminal.

Brief description of the drawings

In order that the invention may be more easily understood, an embodiment will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic drawing of a renewable energy power generation, storage and management system according to a preferred embodiment of the invention;

Figure 2 is a perspective view of a preferred embodiment of the system;

Figure 3 side view of a solar array on the system, the PV panels of the array being in a stacked arrangement;

Figure 4 is a plan view of the solar array of Figure 3, the PV panels being in an expanded arrangement;

Figure 5 is a side view of the solar array in a first condition of use;

Figure 6 is a side view of the solar array in another condition of use;

Figure 7 is a perspective view of a battery house of the system;

Figure 8 is a system diagram of an electrical system for use in the system;

Figure 9 is a graphical view of a load management system; and

Figure 10 is another view of the load management system.

Detailed

A renewable energy power generation, storage and management system 100 is shown in Figure 1. The system 100 is configured to supply electrical power to an industrial site at a remote location. In preferred embodiments, the system 100 includes industrial grade equipment suitable for harsh remote environments and which can tolerate high temperatures.

The system 100 comprises a power generation system 110 harnessing renewable energy, an energy storage device 120, and a control system 130, each in communication with each other.

The control system 130 includes a load prediction module in the form of electrical controller 134 which is configured to predict a required power supply for a load 140 connected to the system 100 and a weather prediction module 132 configured to predict the availability of solar energy and the energy output of the power generation system 110.

The control system 130 is configured to monitor the level of the energy storage device 120, the output of the power generation system 110 and the power requirements of the load 140, and based on an expected power supply for the load 140, predict the level of the energy storage device 120, and reduce the supply of electrical energy to the load 140 when the level of the energy storage device 120 is predicted to fall below a predetermined level.

Power Generation System and Energy Storage Device

In the illustrated embodiments, the power generation system 110 is a solar power installation and includes three separate solar arrays 110a, 110b, 110c of photovoltaic (PV) cells. It will be appreciated that the power generation system 110 may similarly be configured to harness power from wind or tidal energy sources. It will also be appreciated that the number of solar arrays 110 may be varied according to the power demands of industrial site and may include one or more arrays.

Figure 2 illustrates an actual physical embodiment of the system 100. It can be seen that each PV array 110 includes a plurality of solar panels 112, which are described in further detail below with reference to Figures 3 to 6. In this embodiment, two energy storage devices 120 are illustrated, with inverters 113 being disposed between the power solar arrays 110 and the energy storage devices 120, which are referred to herein as battery houses.

Each battery house 120 includes a plurality of battery cells which may be of any commercially available type, such as lithium ion, lead acid etc. Although two battery houses are shown, systems having more than two are possible.

As illustrated in Figure 5, the solar panels 112 within each array 110a, 110b, 110c are coupled together in a hinged or concertina arrangement so as to be generally folded against each other in a packed configuration (Figure 3) and then expanded to the deployed configuration shown in Figures 4 and 5 and secured to a ground surface. A ground mount solar solution is utilised so as to be safer, more cost effective and faster to deploy than traditional single axis solar trackers or comparable solar tracking solutions.

Advantageously, each solar array can be installed quickly with minimal infrastructure being required. Also, as shown in Figure 6, each array 110 can accommodate for variances in terrain level up to 350mm or a plus/minus panel angle variation of 5 degrees, thereby reducing the need for extensive site preparation prior to installation of system 100.

A particular commercial embodiment is illustrated in Figure 2, corresponding to a remote location in Queensland Australia. In this embodiment, the array 110 includes up to 90 solar panels mounted on racks and optimised for 540-550W module class of the utility scale solar industry.

In the embodiment of Figure 2, the modelling and report data shows that the load varies throughout the year between 8.6kW and 36.1 kW. To satisfy energy demand, the following solar plant components have been selected - 540 solar panels of 540 watts each with the total capacity of 292 kW. These solar panels will be arranged in 6 groups, each group consisting of 90 x 540W panels. Each group has six strings of 15 x 540W panels and each group feeds one 50kW PV inverter 113 which has 6 x MPP trackers incorporated (one per string).

The site layout is preferably optimised to minimise AC cabling and cable tray requirements. The DC connection points from the groups will be in the centre of the set of arrays and feed the PV inverters 113 which will be arranged at the south of the arrays.

The system 100 has two interconnected energy storage devices 120a 120b, otherwise known as battery houses. Each battery house 120a, 120b incorporates a battery section and an electrical / control section as identical as possible but there will be a lead and slave battery house in effect. Each battery house will have 2 control systems: a Hybrid Controller and a Load Management and Weather Forecasting Controller.

Each battery house 120 is a modular unit and multiple battery houses can be connected in parallel for larger power requirements and redundancy. The modular system design allows the system described herein to be rapidly mobilised and demobilised on a customer site.

In the embodiment described herein, there are 2 battery banks 120 arranged and interconnected. Each has 192 x 2V x 2000Ah cells which total 768kWh each (Total 384 batteries for 1536kWh). Each battery bank will be charged by 6 PV inverters which feed onto a common bus and the battery banks are charged from this common bus.

As illustrated in Figure 1, the system is AC coupled and incorporates inverter chargers 121 and DC-DC converters 123 to manage the battery charging and the system voltages. The DC system voltages are nominally 384V at the battery banks and nominally 600V at the DC links in the inverter/charger system. Using inverter chargers and DC-DC converters, the system can accommodate different battery arrangements, allowing for the stacking and unstacking of batteries in the battery house 120, as well as individual battery cell failure. Battery bank voltage may be in the range of 30v to 800v.

To allow the system 100 to be used with industrial equipment having high inductive loads, for example a large transformer or industrial equipment such as large pumps or crushers, the inverter-charger has a short time surge rating and during the startup operates with a slow ramping up of voltage and frequency, as will be described below in further detail.

An example battery house 120 is illustrated in Figure 7. The battery house 120 has a frame 122, doors 124 with ventilation sections, maintenance hatch 126 and heat extractors 128 in the form of turbine vents. Space 129, shown with door removed, is reserved for control system hardware.

Electrical System Overview

A schematic diagram of the electrical system 150 for the system 100 is shown in Figure 8. In this embodiment, two power generation systems 110a, 110b are shown and two energy storage devices 120a, 120b.

Each power generation system 110 has three PV sub systems 112 in accordance with those described above. Each energy storage device 120 has an inverter 121 and a battery subsystem 125 and a DC-DC converter 123 (not shown) as described above. The energy storage devices 120a, 120b are connected with a microgrid subsystem 136. The power generation systems 110, 110b are connected with a switchgear subsystem 138. The switchgear subsystem 138 is connected to the distribution subsystem 139 which connects system 100 with load 140.

The control system 130 may be a separate part or integrally formed within a battery house 120. A separate control system may be provided for each battery house 120, or a single control system may control all battery houses. In preferred embodiments, each battery house 120 may have a separate control system 130 for redundancy, though it will be appreciated that a single battery house 120 may contain the control system 130 and act as a master controller.

The control system 130 will monitor and regulate the PV harvesting from the power generation systems 110 as well as the battery charging process and synchronise the two battery houses 120 with each other. The load that is in demand will be fed by the system to charge the batteries. In off-grid applications the controller will define system set points and operate in voltage source mode with droop control.

The control system 130 includes a predictive controller 132 which comprises a first programmable logic controller (PLC) and an electrical controller 134 which comprises a second PLC. It will be appreciated that the controllers may be separate units or part of a single unit.

The predictive controller 132 receives weather data and uses this data to predict the availability of solar energy and therefore the energy output of the power generation system. This data is received from a modem and antenna 135. The predictive controller 132 can be configured to prevent over charging when periods of energy output exceeding demand are expected. This is done by changing the charging voltage. Depending on the state of charge, the Electrical Controller follows a predetermined battery charging curve/regime.

Additionally, operational instructions may be received from a remote terminal when it is desired to override programmed system operation. In preferred embodiments, system 100 can be integrated into a user's remote monitoring system, such as a supervisory, control and data acquisition (SCADA) system, to allow for control and monitoring from a remote location.

The control system 130 provides for black start operation and includes a software sequence to manage the start-up of the inverter-charger 121, the sequence allowing for a slow ramping up of voltage and frequency of the inverter-charger 121 to provide a soft start for high inductive load equipment. This allows for energising of the magnetic field of a transformer, thereby providing the ability for the system to drive a transformer. Previous inverters of the type used with solar/battery installations have not been able to energise transformers as they detect a high load and consider this to be a short circuit, thereby disabling operation. By being able to energise a transformer, the system 100 can transform the standard output of 400v to a voltage in the range of 11 to 33kv. It will be appreciated that system 100 may power a single transformer or multiple transformers, thereby allowing for switching of output power and the operation of multiple different machines.

Energy Management System

Prior art energy management systems used with solar/battery installations have experienced difficulty in powering industrial equipment not connected to an electricity grid due to difficulty in obtaining a stable reference. Connecting to a larger grid can solve such a problem though this is not possible for remote locations. The present system can solve this issue as control system 130, particularly inverters 121/113, monitors the load and acts as a grid forming inverter that sets the frequency of the network.

As described above, the control system 130 will predict the charge level of the battery house 120. This is done via calculation of the instantaneous battery energy in kWh from the electrical controller 134, the weather data, system battery capacity and the load on the system, as monitored from the electrical controller 134.

In the illustrated embodiment, the electrical load 140 includes a plurality of pumps, each of which can be assigned a priority value depending on the criticality of its operation. In use, the control system 130, in particular the electrical controller 134 will provide load management functionality by transitioning pumps with a lower priority operation into low power mode to preserve the energy stored in batteries if required. This might happen if the state of battery charge drops below a predetermined threshold, and is not expected to replenish soon. For example, if during a dark period of the day when there is no power generation, the electrical controller 134 detects a low state of charge (SOC) and dynamically indicates that by the time when generation is expected the SOC would drop below a critical level (to be determined during commissioning), the controller 134 will send a command to a PLC controlling the pumps (not shown) to change its mode of operation to manual with the low speed setpoint. This will also happen if the SOC drops below critical level during any period regardless of energy generation. When the forecasted SOC drops below a given DOD (depth of discharge) Setpoint, a DOD alarm will be set. The amount of forecast energy below the DOD setpoint (Deficit) is calculated.

The load schedule provides the system with the data that the load-shed system needs to schedule the reduction of pump speed requests. The data is stored and displayed as a table of load information such as the priority, enabled flag and what its low power load is. The load-shed module will calculate the energy deficit and how much time before the deficit is reached to create an estimated energy reduction by adding the load reduction to each forecast time slot.

Figure 9 illustrates graphically seven day forecast data and how an estimated battery energy (SOC) 160 may vary, with a variable estimated solar power 162, an estimated battery energy with load shed 164 and a minimum battery level 166.

Figure 10 illustrates a closer look of forecast data, showing an energy deficit 168, based on a time from start to reaching low SOC/DOD 170 and a point at which the energy meets the low limit 172.

Load reduction is carried out by lowering the power of each load (pump) and the load reduction is calculated for each load. The load priority can be set from an interface on the electrical controller 134 or can be overwritten via an external computer terminal or network. A display on the controller 134 may notify the user that the Load Schedule priority is controlled remotely.

When the load-shed software sees an energy deficit, it calculates, and subtracts the load reduction of the lowest priority load, i.e. the lowest priority pump, from the deficit and tests again. If there is still a deficit, the program continues till there is no deficit or the end of the schedule is reached. If the end is reached with a remaining deficit, an alarm will be raised. As the program is constantly being evaluated, pumps will be brought back to full speed as the load-shed program sees a higher projected battery energy. Pumps be commanded from higher to lower priority.

Several instruments and status signals will be hardwired directly to the control system 130 to provide monitoring of battery enclosures and equipment status. Average temperature and voltage will be calculated for each battery house 120 and a high alarm will be generated when any of the battery temperatures are outside desired setpoints. High and low alarms will be generated if any of the battery voltages are outside the desired setpoint. This functionality is required for battery performance monitoring and will be a trigger for additional historic recordation. A transmitter fault alarm will be generated if either PLC detects a signal status outside normal operating parameters e.g. outside 0- 10V/4-20mA or broken wire

System 100 also includes a revenue-grade power meter to accurately measure the renewable energy used by the load at the site, thereby allowing a user to claim carbon credits. Such a system may also allow an owner operator of system 100 to charge a user for the energy provided.

In configuring system 100 for a particular site, a design tool is used to establish the required size and/or number of the power generation system and energy storage device(s). The design tool does this by analysing historical weather data over a predetermined period, such as 20 years for example. Based on the historical weather data, predictions can be made as to the availability of renewable energy such a wind or solar power, and this informs the sizing of the generation system. Load predictions can also be made based on historical load data.

Taking into consideration the weather and load data, particularly taking into account magnitude, timing and reliability, the required size of the energy storage system can be determined to ensure that a predetermined system availability can be met with a predetermined degree of confidence.

Battery Management System

The Control system 130 features a versatile battery management system capable of accommodating various battery solutions, such as Lead Acid and Lithium Ion. The battery management system oversees the charging process and prioritises the optimisation of battery health for long-term performance. The battery management system is flexible and can be adapted to new battery technologies as required.

The battery management system acts to maintain the energy storage device 120 within its functional range to ensure power availability to the load 140 for system stability. Where a state of charge is greater than 100% an alarm is raised. Where state of charge is below 100%, charging of the energy storage device 120 is possible from the power generation system if available. There state of charge is below 40% another alarm is raised, with the system shutting down is state of charge is below 35%. It will be appreciated that were multiple energy storage devices 120 are used, each may be separately controllable.

A four-stage charging process may be adopted, including the following stages, bulk mode, absorption mode, float mode, and equalisation mode. These modes have been designed and optimised for the basis of recharging a battery bank to a high state of charge, based on parameters such as charge efficiency, the difficulty of implementation and the effect on the state-of-health (SOH), essentially a quantitative representation of the battery lifetime. For a lead-acid battery, the process is as follows.

In the bulk mode, the battery is charged at the maximum charge current by incrementally increasing the charge voltage until the maximum charge current is reached. The objective of this mode is to effectively charge the battery at its nominal charge current, however, it should not be charged at this high current for extended periods as it can lead to gassing and the corrosion of the lead plates.

Once the float voltage has been reached by the charge voltage, then the mode changes to absorption mode where the charge voltage is held constant, and the charge current is tapered to minimise the effects of gassing and lead plate corrosion. After a certain amount of time has passed or the tapered current charge has fallen below a threshold, the next mode will occur. When utilising a 4-stage charging algorithm, the next mode will differ depending on whether an equalise charge is required or not.

When equalise charge is not required, at the completion of absorption charging the system switches to float mode charging, where the charge voltage will be maintained at the float voltage continuously (trickle charging). Therefore, in this mode, battery state of charge stays consistent throughout float charging, this is important for lead acid batteries as they cannot be left discharged for a long period and can be used to top-up the energy storage device 120 after a long period of inactivity.

When equalise charge is required, at the completion of absorption charging the system switches to equalise mode charging. Equalisation charging sets the charge voltage at a step above float voltage to overcharge it for a short duration, during which the gassing produced is sufficient to break loose the sulphation that has settled onto the lead-acid plates which have reduced the storage efficiency. This also enables all individual cells to be fully charged, ensuring all cells are kept within voltage balance tolerances.

Equalisation mode is not necessary for every charging cycle but is still an important function required for lead acid batteries. The system will determine when equalise mode is required based on the following permissives:

Previous equalise was conducted >28 days ago and

Available solar for current day is expected to be sufficient to complete an equalise charge

When the logical AND of both of these conditions become TRUE, an equalise required flag will be set. Based on these conditions the system will determine if an equalise charge can be conducted based on the meteorological forecasts provided. If sufficient solar insolation is predicted for the current day, the system will begin an equalisation charge after the Absorption charging stage has completed.

If insufficient solar insolation is predicted, a sufficient solar availability tag will not be raised and equalisation mode will be delayed by 24 hours and rechecked the following day. If an equalise charge does not complete in a single day, it will be continued on each subsequent day until a total of eight hours of equalisation has been completed. After the eight hours of equalisation has been completed, the equalise completed tag will be raised and the equalise counter will be reset to 28 days.

Many modifications of the above embodiments will be apparent to those skilled in the art without departing from the scope of the present invention. For example, although system 100 has been described as an off-grid application, it may also be connected to an existing electricity grid.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.