TECHNICAL FIIO:Lil
The present invention relates 10 oontrollin; and metering of energ) consumption, and more
specifically to a prepaid metering system for a micro grid.
BACKGROUND OF TilE DISCLOSURE
Typically, prepaid systems include energy meters Y.hich are based on advanced communication
technologies such as GSM and Zigbee. Howe,er, such solutions are very expensive, given their
high maintenance and operation cosL Also, such solutions do not fit into business models for
off-grid projects designed to deliver energy services to under-served communities at the bottom
of the pyramid. Most conventional prepaid systems are unable to fully address technical and
operational challenges of ofT-grid projects, and are also not compatible for 24x7 democratic
energy accesses for off-grid communities without limiting their energy consumption.
U.S. Patent Number 4,73 1,575 ('575 patent) discloses a prepayment utility metering method
and apparatus which uses encoded mag-stripe cards to transfer purchase information from the
utility bill ing office to the customer's premises. The mag-stripe cards are read at the customer's
premises by a microprocessor-controlled utility metering and control device which meters the
utilities according to the amount purchased at the utility billing office. The value information
encoded on the mag-stripe cards is comprised of the amount of the purchase coded in terms of
number of shaft revolutions of the metering disk, a rate schedule for metering the value of the
utilities consumed, and a special sequential password containing an encrypted combination of
the consumer's account number, the consumer's site identification, and the sequence number of
the current purchase. This encoding scheme for prepayment of utilities provides an effective
and economical method of distributing utilities that prevents fraud and tampering. The present
invention also includes a method and apparatus for providing an emergency credit to utility
consumers when the prepurchased amount is exhausted. An emergency mag-stripe card is used
to credit the user's account with a purchased amount of utilities adequate to tide the consumer
over until the bill ing office opens on the next business day. The emergency mag-stripe card
cannot be used more than once, and the credit amount in the meter must be replenished by a
new purchase of utilities before the emergency card can be used again.
SUMMARY OF THJ<: DISCLOSURE:
In one embodiment of the present invention, a prepaid metering system for a micro-grid is
2
provided. The prepaid metering S) stem ioc!udes a sman conuoller located in a central charging
station. Further. the smart controller is a 1"\ ,_,based chat£e conuoUer which has functionalities
of a high voltage solar charge conuoller, a Global System for Mobile Communications (GSM)
module, an external antenna for boosting signal, control panel with a display and keypad, a
recharge port, memory for data storage and DC and AC Miniature Circuit Breakers (!vi CBs) for
system protection. The smart controller is configured to store energy credits. The smart
controller is configured to establish communication with a remote server via a module. The
smart controller is configured to enable remote monitoring and managemenL The smart
controller is configured to perfonn energy credit transaction to the portable charging device
(from herein referred to as energy stick) and also capture user data from the energy stick.
Further, the smart controller is configured to log technical complaints. The smart controller is
configured for input voltage range between 70Vdc and 170Vdc with a maximum allowable
charging current of 1 OA. The smart controller also has capability to disconnect from the battery
bank in case battery voltage reduces below 86.4Vdc. The smart controller is configured for
protection against input surge current/voltage, load short circu it current and against battery
reverse current connection.
In another embodiment of the present innovation, the smart controller also uses an inbuilt
functionality of the GSM Module to assign the date and time Stamp for all the values that have
been sensed and stored by the smart controller at a frequency of I second in the memory chip
(256 kB). This data is in tum sent to the central server at a frequency of one hour. The timer
intervals for data storage and transmission to server has been kept Oexible to change as per need.
The smart controller is also capable of continuously storing the data in the memory chip without
any loss of data in case the GPRS signal is absent for any reason. When the signal is restored the
smart controller can automatical ly detect the signal and transfer all the stored data into the
central server. The smart controller houses the memory chip which can store the data for a
period of 15 days continuously in the absence of signal.
In another embodiment of the present innovation, the central station uses a quad band GPRS
module for enhanced connectivity. The central station is also provided with an external 'high
gain' antenna which will amplify the signal strength further.
In another embodiment of the innovation, an LCD display is incorporated in the central station
wherein the current details/status of the charg.ing and discharging parameters are displayed,
either for viewing or diagnostic purpose. In another embodiment of the innovation, the keypad
for the central station is a 16 keys membrane keypad which is used for system operation.
3
The central station also uses UART based ptOIOCOls for communication between central station,
energy meter and the energy sticl. .. In anocber embodiment of the innovation, the central station
and energy meters are also enabled for shutdown from lhe remote location/server in case there
are natural calamities or unexpected disturbances \\hich would damage the microgrid.
In another embodiment of the present invention, the smart controller is also enabled to establish
voice communication, send and receive text messages and establish communication with remote
devices over the G SM connection.
The prepaid metering system also includes an energy meter located in each household, and in
communication with the smart controller. The energy meter is configured to convert high voltage
DC to low voltage DC. In an embodiment of the invention, each energy meter bas a unique
energy stick which uses UART communication protocol based dongles. The energy stick is
configured to establish communication between the energy meter and the smart controller. The
energy stick is configured to transfer energy credits from the smart controller to the energy
meter. Further, the energy stick is configured to store data pertaining to energy consumption
from the energy meter.
In another embodiment of the innovation, the energy meters (20W and 60W capacities) have
been designed using flyback topology with negative control. Further, the meters have the
required protections for input reverse connection, output short circuit and output overload
condition.
In another embodiment of the present innovation, the meter is also enabled to automatically shut
down if overload is sensed for more than 5 seconds. The meter will remain shut down for a
minute and recheck if the overlond still exists. If the overload is removed, the meter shall
function normally. In case the overload conditions still persists, the meter shuts down and keeps
iterating the process.
In another embodiment of the energy meter, an LED provided on the meter switches 'ON' to
indicate the low recharge levels and the user's energy credits are about to finish.
The prepaid energy meter combined with the energy stick, a server and a smart controller
located in the central charging station form the complete smart metering solution for the
microgrids.
The energy meter and central charging station is configured to manage dynamic pricing based on
the battery bank voltage and also based on amount of power being drawn by the household.
Another innovation in t.he energy meter is the dynamic pricing which is managed by detecting a
voltage of the battery bank via Zero Current Conductor. Different per unit pricing can be set
4
corresponding to difTerem baUer) bam. \'Olta;e Similart}. different per unit pricing levels can be
set based on amount of po-.er drawn. Diiferential pricing is implemented to encourage low
consumption of energy in case batter) is about to be cut ofT the system due to low voltage.
Differential pricing is also implemented to incentivize higher usage of the system among the
user.
The dynamic pricing is implemented through two pricing levels in the 20W meter and through 4
pricing levels in the 60W energy meter.
In another embodiment of the present invention, the energy stick can be embodied as one of the
Universal Serial Bus (USB) sticks, USB cards, Bluetooth tags, Radio-Frequency Identification
(RFID) tags and also a Mobile Application.
In one embodiment of the present invention a method for charging an energy meter with energy
credits is provided. The method includes receiving energy credits from a remote server into the
sman controller. Funher, the method includes transferring energy credits from the sman
controller to energy meter located in a household via the energy stick. The method also includes
storing data penaining to energy consumption from the energy meter.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure I illustrates a prepaid metering system for a micro-grid, according to an embodiment of
the present invention;
Figure 2 illustrates a perspective view of a central charging station having a sman controller,
according to an embodiment of the present invention;
Figure Ja-3b illustrates perspective views of energy meters of the prcpoid metering system for
the micro-grid, according to an embodiment of the present invention;
Figure 4 illustrates a perspective view of the energy stick of the prepaid metering system for the
micro-grid, accord ing to an embodiment ofthc present invention;
FigureS is a Oowchan of a method for charging an energy meter with energy credits, according
to an embodiment of the present invention; and
DETAILED DESCRIPTION
Figure I illustrates a prepaid metering system for a micro-grid according to the embodiment of
the present invention. As shown in FIG 1, the prepaid metering system for a micro-grid includes
multiple components that, when combined together, deliver innovative and frugal prepaid, pay
per unit metering solution with dynamic pricing and remote monitoring. It should be noted that
5
the dynamic pricing will be d~nDcd la:cr in the present disclosure. The basic scheme of a
microgrid can be broken into 3 pans; the centnll charging station, transmission and distribution
part and the internal household wiring section.
The Central Charging System includes a smart controller, a banery bank for energy storage and
an array of solar modules. The smart controller is in communication with a remote server for
monitoring various parameters of the central charging system. The proposed prepaid metering
system can used for both DC and AC micro-grids, but same is theft-proof in case of lligh
Voltage (greater than 30Vdc) DC micro-grids.
The Sman Controller enables 2-way communication between the system and server using
GPRS technology. The smart controller also serves as customized high voltage charge
controller. providing necessary protection to the central charging station
As mentioned earlier, the prepaid metering system for a micro-grid includes multiple
components to deliver innovative and frugal prepaid. pay per unit metering solution with
dynamic pricing. Dynamic pricing is implemented via the energy meters, wherein they detect
the voltage of the storage battery bank via 'Zero Current Conductor' which is another key
innovation in the system. This means that the dynamic pricing is implemented without the use
of any communication technology between the central power generation and storage system and
the energy meters. Implementing dynamic pricing using 'zero current conductor' is another key
innovation. High voltage DC micro-grids enabling a theft proof prepaid metering technology is
a path breaking innovation designed to reduce operational costs in remote off-grids systems.
The Dynamic Pricing is a unique proposition integrated into the prepaid metering system. The
final pricing is defmed by 2 input parameters, resulting in a 2x2 pricing matrix. More
specifically, the final pricing is defined by a first parameter and a second parameter. The first
parameter indicates the voltage of the bauery bank of the energy meter. Adverse weather
conditions like cloudy days and fogs will result in rapidly depleting storage capacity. In an
effort to encourage users to limit their consumption when supply is limited, the pricing is
increased when the voltage of the battery bank goes below a certain defined level (for example
below 50"/o Depth of Discharge). The pricing returns to normal level once the voltage of the
battery bank rises above the defined level. The voltage of the bauery bank is detected by the
energy meter using a 'zero current and the pricing decision is made by the energy meter
accordingly.
The second parameter indicates an amount of power being drawn by an individual user. This
allows the project developer to charge different unit prices for loads below or above a certain
6
rated power. For example, in ca:oe of DC micro-gri account all lighting (LED) loads and
mobile charging. For loads rated abo\e 15\\ans. such as fans and television, the pricing can be
different. The final pricing is based on the combination of the first parameter and the second
parameter. The figure explains the energy meter recharge process and the flow of economy and
energy credits. By integrating various payment mechanisms available with the micro-grid web
platfom1, the financial dexterity of the system can be improved allowing user friendly payment
mechanisms between the company and the owner/ manager of a micro-grid. Further, the data
sourced from micro-grids is compiled, processed and analyzed by a custom-made web
platform. The interface allows for energy credit transactions, remote monitoring, data analysis
and reporting.
Figure. 2 illustrates a perspective view of the central charging station having the smart
controller, according to the present invention. Referring to FIG.2, the smart controller includes a
solar charge controller, a Global System for Mobile Communications (GSM) module, an
antenna, a smart controller and a DC Miniature Circuit Breaker (MCB) for Photovoltaic Array
(PV) array. The smart controller is a customized high voltage solar charge controller integrated
with GSM module to enable remote monitoring and data connectivity. The sman controller is
configured for input voltage range between 70Vdc and 170Vdc with a maximum allowable
charging current of lOA. The smart controller also has capability to disconnect from the battery
bank in case battery voltage reduces below 86.4Vdc. The smart controller verifies the battery
voltage level at a frequency of I second and latches on when battery bank voltage reaches
100.8Vdc. The sman controller is configured for protection against input surge current/voltage,
load short circuit current and against battery reverse current connection.
The smart controller is also used to store energy credits which can be further transferred to the
energy meters via the energy sticks. Further, the smart controller is configured to storing energy
credits purchased by a Grid Manager, and recharging the energy sticks. Furthermore, the smart
controller is configured enable 2-way communication between servers and the system. The
smart controller is configured to establish communication between the charging station and a
remote sef\er via GSM module, enabling remote monitoring and management
More specifically, the central station uses a quad band GSM module for enhanced connectivity.
lltc central station is also provided with an external 'high gain' antenna which will an1plify the
signal strength further. The smart controller also uses UART based protocols for
communication between smart controller, energy meter and the energy stick.
7
In another embodiment of the present inno\ation. the smart controller also uses an inbuilt
functionality of GSM module is to assign the date and time stamp for all the values that have
been sensed and stored by the smart controller. The smart controller senses and stores the data
frequency of I second in the memory chip {256 kB). This data is in turn sent to the central
server at a frequency of one hour. The smart controller is also capable of continuously storing
the data in the memory chip without any loss of data in case the GPRS signal is absent for any
reason. When the signal is restored the smart controller can automatically detect the signal and
transfer all the stored data into the central server. The smart controller houses the memory chip
which can store the data for a period of 15 days continuously in the absence of signal.
In another embodiment of the central station it is capable of recording following parameters
every second for efficient system operation.
• Address of Central Charging Station
• Time&Date
• Solar Charging Voltage
• Solar Charging Current
• Battery Voltage
• Battery Current
• Load Current
• Total Energy Consumed in Watt hours
• Grid Status
• Complaints
In another embodiment of the innovation, an LCD display is incorporated in the smart controller
wherein the current details/status of the charging parameters is displayed, either for viewing or
diagnostic purpose. In another embodiment of innovation, the keypad for the smart controller is
a 16 keys membrane keypad which is used for system operation.
In another embodiment of the innovation, the smart controller and energy meters arc also
enabled for shutdown from the remote location/server in case there are natural calamities or
unexpected disturbances which would damage the microgrid.
The smart controller also has protection against reverse connection,output short circuit current
and overload protection. The energy stick needs to be plugged into the meter in order for the
meter to function. This also enables transfer of energy credits from the energy stick to the
8
energy meter and logging of consumption d;,.ta. The prepaid metering system maybe used for
prepaid payment mechanisms for SCI' ices other than energy services.
The proposed prepaid metering system iJ> the most frugal and cost effective solution while
delivering similar functionality as metering solutions based on advanced and expensive
communication technologies. Dynamic pricing is a very unique feature of the proposed
metering solution.As explained earlier, enabling the energy meters to make the pricing decision
based on an input from the 'zero current conductor' is a fine technical innovation, effectively
dismissing the requirement for advanced communication technologies. The smart controller is
also configured to log technical complaints, if any.
Brief Specification for CeJ~tral Cha rging Statio"
rPV Charging Data
Jlnput Voltage Range
Chargong Current (maximum)
~fliclency of Charging
Load Data t Maximum No of Connections
M8X1mum Wattage of the Microgrid
[self Consumption/ No Load ConsumpUon -
Load Orsconnect from Battery Bank
I Load Reconnect to Battery bank
Fuse Rating
[
Miscellaneous Data
Cooling
~Storage Temperature
Operating Temperature
Protection Against TransienVSurge at Input
Protection Against Load Short Circuit
l rotection Against Battery Reverse Connection
] 7oVdc to 170Vdc
10A
1>90%
10 Meters ( 20W Meters· 35Nos & 60W Meters •
5Nos)
i1ooowatts
-~6 Watts (144 Watt Hours a Day)
9
186.4 Vdc
tO.BVdc
I10Amps
Natvr81Nr
~20 to 80 deg C
·10 to 65 deg C
Yes ( Rated MOVs have been provided )
Yes
Yes
I
1
I l
J
Sensors
[ Maximum Sensing Voltage
Maximum Sensing Current
Data Logger & RTC
lData Sensing Frequency
Data Transmitting Frequency (To Server)
!Data Receiving Frequency (From Server)
Internal Memory
Time Format
Date Format
Parameters Recorded
GSM Module with Antenna
l8ands
Sim Slot t GPRS Connectivity Requited
Antema
1 LCD with Keypad Interface
rLCD
10
180Vdc
20Amps
1 Second
60 Minutes
10 Minutes
256 KB (can store data of 15 Days)
24 Hours
Address of Central Charging Station
Time & Date
Solar Charging Voltage
Solar Charging Current
Battery Voltage
Battery Current
Load Current
Total Energy Consumed In Watt hours
Grid Status
Complaints
Grid Status
!Quad Band
1 No (Regular Size)
2G/3GI4G
High Gain External Antenna
I_-
16 x 4 Uquid Crystal Display
Signal Strength
Date & Time
Currency Balance of Entrepreneur
Battery Voltage
Battery Current
I Keypad
Functionality of Keypad
~echarge Module
ommunication Type with Dongle
LED Indication Data I system ON
System Alive
Solar Charging
Batlel'f Low
Currency Low
Dongle OK
Signal OK
Solar Voltage
Solar Current
Load Current
Price Levels
Central Station Address I Grid Status
16 keys Membrane Keypad
Recharge the Energy Stick
Manual Activation/Deactivatlon
Log/Close Complaints
IUART
Green LEO
Green LED
Yellow LED
Red LEO
Blue LED
Green LED
Yellow LED
Figure: 3 illustrate the energy meters situated in each household which are customized for
different load limits. Energy meters with 2 load variations have been designed, i.e. 20W and
60W model. The energy meters are configured to convert the high voltage DC input electricity
into usable 12Vdc electricity. The energy meters come with uniquely mapped UART
communication technology based dongles. Enabling prepaid recharging energy sticks is central
to the innovation. This enables data communication, remote monitoring and pre- paid metering
wbile using only a singular GSM module at the Smart Controller.
The energy meters arc prepaid, pay per unit meters, which also steps down high voltage DC to
12Vdc for end user consumption. In another embodiment of the innovation, the energy meters
(20W and 60W capacities) have been designed using llyback topology with negative control.
Purthcr, the meters have required protections for input reverse connection, output short circuit
and output overload condition.
II
In another embodiment of the present inno\1Uion. the meter is also enabled to automatically shut
down if over load is sensed for more than 5 seronds. The meter will remain shut down for a
minute and recheck again. If the over load is remo,ed, the meter shall function normally. In case
the overload conditions still persists, the meter shuts down and keeps iterating the process. In
another embodiment of the energy meter, an LED provided on the meter switches 'ON' to
indicate the low recharge levels and the user's energy credits are about to finish.
The prepaid energy meter c0111bined with the energy stick, a server and a sman controller
loeated in the central charging station fonn the complete sman metering solution for the
microgrids.
The energy meter and central charging station is configured to manage dynamic pricing based
on the battery bank voltage and also based on amount of power being drawn by the household.
Another innovation in the energy meter is the dynamic pricing which is managed by detecting a
voltage of the battery bank via Zero Current Conductor. Different per unit pricing ean be set
corresponding to different battery bank voltage. Similarly, different per unit pricing levels ean
be set based on amount of power drawn. Differential pricing is implemented to encourage low
consumption of energy in case battery is about to be cut off the system due to low voltage.
Differential pricing is also implemented to inccntiviz.e higher usage of the system among the
user.
The dynamic pricing is implemented through two pricing levels in the 20W meter and through 4
pricing levels in the 60W energy meter. The energy meters have dynamic pricing as a key
functionality. The pricing varies based oo parameters defined for amount of power being drawn
and status of storage battery bank. The energy is used to transfer energy credits from the sman
controller to user, and it also stores usage data from the energy meters. The data is transferred
to smart controller during the recharge process and from there to the pre-defined servers.
Brief Specification of20W Energy Meter
Input Data
Input Voltage Range
Output Data
Output VoCtage
Maximum Output Power
70 Vdc to 170 Vdc
12Vdc
20Watts
12
Efficiency Data
Efl"tciency at Full Load
EffiCiency at Half Load I Self Consumption Power
Features
Protection from Input Reverae COMection
Protection from Ou1put Short C"trcuh
Protection from Overload
Cooling
Storage Temperature
Operating Temperature
LEO Indications Data
Price Level Indication
Dongle Disconnected Indication
Currency Low Indication
Parameters Displayed In LCD
Price Levels
Level A
LevelS
Set Voltage (Vs)
Brief Speci fication of 60W Energy M eter
-
put Data
ut Voltage Range
85.00%
92.00%
< 1Watt (20 Watt Hours a Day)
+ Yes
!Yes
Yes
Natural Air
·20 to 80 deg C
-10 to 65 deg C
Blue LEO
Yellow LED
Red LED
Input Voltage, Output Voltage, Output Current, Power In
Watt Hours, Currency Balance in Rupees, Price of
Levels, Total Power Consumed in all the Price Levels
Blue LED Blinks ( level A "ts active when Battery Voltage l
1 >Set Voltage (Vs))
I Blue LEO glows Continuously ( Level B is active when I
I Battery Voltage< Set Voltage (Vs))
92 Vdc PreseL 1 Volt hysteresis is provkled to this value. "I
Battery Voltage is >92.5 Vdc, Pnce Level A Is Activated If I Battery Voltage Is < 91.5 Vdc, Price Level B Is ActJvated
13
Output Data
Output Voltage I Max1mum Output Power
Efficiency Data
Etr10ency at Full Load
EfficiencyatHaffLoad
Self Consumpbon Power
Features
Protection from Input Reverse Connection
Protection from Output Short Circuit
Protection from Overload
Cooling
Storage Temperature
Operating Temperature
LED Indications Data
12Vdc
60Watts
87.00%
94.00% I < 1 Watt (20 Watt Hours a Day)
Yes
Yes
Yes
Natural Air
-20 to 80 deg C
·10 to 65 deg C
Price LevellncllcaUon for Level A and Level B Blue LED
Price Level Indication for Level C and Level D Blue LED
Dongle Disoonnectecllndication
Currency low Indication
Parameters Displayed In LCD
Price Levels
Level A
level B
Level C
level D
IYeDow LED
Red LEO
Input Voltage, Output Voltage, Output Current, Power In I
Watt Hours, Currency Balance in Rupees, Pnce of
Levels, Total Power Consumed in all the Price levels j
- I r Blue LEO Blinks ( Level A is active when Battery Voltage I
> Set Voltage {Vs) and < Set Load (Ls)) I
Blue LED glows Continuously ( Level B is active when r
Battery Voltage > Set Voltage {Vs) and > Set Loacl (Ls))
Blue LEO Blinks ( level A is active when Battery Voltage
< Set Voltage (Vs) and < Set load (Ls))
Blue LEO glows Continuously ( Level B Is active when
14
l
I
I
Set Voltage (Vs)
Set Load (Ls)
Battery Vohage Set Load (La)) I
S2 Vde P'"eL 1 Volt hysteresis is provided to this value.
If Battery Vohage is >92.5 Vdc < 16W, Prloe Level A is I
Activated. If Battery Vohage Is> 92 5 Vclc > 16W, Pnee
Level B is Activated. If Battery Vohage is <91.5 Vdc 16W, Price Level D ~Activated.
16 Watts This value has no hysteresis
Figure. 4 illustrate a perspective view of the energy stick of the prepaid metering system for the
micro-grid, according to an embodiment of the present invention. Referring to FIGS 3a, 3b and
4, the energy meter is provided with uniquely mapped energy stick, installed at point of
connection for each household. The energy meters are configured to store energy credits
purchased by individuals and delivers energy through prepaid, pay per unit metering or other
payment structures as programmed. The energy stick stores energy consumption data and
enables transfer of energy credits from the Smart Controller to the Energy Meter. In another
embodiment, the energy stick may be embodied as one of the Universal Serial Bus (USB)
sticks, US13 cards, Bluetooth tags, Radio-Frequency Identification (RFID) tags. The prepaid
energy meter combined with the energy stick, a server and a smart controller located in the
central charging station form the complete smart metering solution for the microgrids.
Figure. 5 illustrates Oowchart of a method for charging the eoergy meter with the energy credits,
according to an embodiment of the present invention. Referring to FIG. 5, the method includes
receiving energy credits from a remote location to the central charge station via Global System
for Mobile Communications (GSM). In one embodiment, the remote location may be Boond's
remote server. The method also includes transferring energy credits from the central charge
station to the energy meter located in the household via the energy stick. The method includes
storing data pertaining to energy consumption from the energy meter. Further, the method
includes managing dynamic pricing based on the battery bank of the energy meter and the
amount of power being drawn by the household.
The invention is designed specifically to address technical and operational challenges of off-grid
projects, espcciatly micro-grids. The invention allows for 24x7 democratic energy access for offgrid
communities without limiting their energy consumption, which in tum is mostly selfregulated.
The invention enables data driven understanding of energy consumption patterns of
15
communities, assisting in optimi.t.ation of system design, enable zero cash transactions for the
project developer, and remote monitoring. All th~ functionalities are delivered using frugal
and innovative mechanisms, significantly impacting the financial sustainability of ofT-grid
projects. Energy meters using advanced communication technologies such as GSM and Zigbee
are common. But such solutions are not only very expensive, given their high maintenance and
operation cost, such solutions do not fit into business models for ofT-grid projects designed to
deliver energy services to under-served communities at the bottom of the pyramid.
The present invention is used to provide energy access to ofT-grid communities, via micro-grids,
especially solar micro-grids. The invention is designed witb the purpose to reduce transactional
and operational costs for project developers, prevent theft of electricity, and eliminate risk of
defaulting on dues by the end user. The invention also enables democratic 24x7 energy access
since the consumers pay only for what they consume and their consumption is mostly selfregulated
or self-limited. The preferred form of tbe invention is as prepaid metering system for
High Voltage (Solar) DC micro-grids. The present invention is designed specifically to address
technical and operational challenges of off- grid projects, especially micro-grids.

WE CLAIM:
I. A prepaid metering system for a micro-grid, the prepaid metering system comprising a
smart controller which is a high voltage PWM charge controller, a Global System for
Mobile Communications (GSM) module, the smart controller has been configured to:
• store energy credits;
• establish communication between the solar charge controller and a remote
location via GSM module;
• enable remote monitoring and management; and
• log technical complaints;
• establish voice communication, send/receive text messages and establish
communication with remote devices using GSM technology
• with input voltage range between 70Vdc and 170Vdc
• a maximum allowable charging current of I OA
• capability to disconnect from the battery bank in case battery voltage reduces
below 86.4Vdc
• has protection against input surge current/voltage, load short circuit current and
against battery reverse current connection
An energy meter located in a household, and in communication with the smart
controller:
• Designed flyback topology with negative control
• protections for input reverse connection, output short circuit and output overload.
• meter is also enabled to automatically shut down if over load is sensed for more
than S seconds
• convert high voltage DC to low voltage DC; and
• manage dynamic pricing based on a battery bank of the energy meter and on
amount of power being drawn by the household,
• 20W energy meters have 2 levels of pricing defined while 60W meters have 4
dynamic pricing levels
• LED provided on the meter switches 'ON' to indicate low recharge levels
• An energy stick associated with the energy meter, the portable charging device
configured to:
17
• establish communication bet\\-een the energy meter and the smart controller;
• transfer energy credits from the smart controller to the energy meter; and
• store data pertaining to energy consumption from the energy meter.
a remote server capturing dnta from each micro-grid, enabling remote monitoring
and management.
2. The prepaid metering system as claimed in claim I, wherein the smart controller includes a
General Packet Radio Service (GPRS) module, an antenna for boosting signal, control
panel with display and keypad, a recharge port, and AC and DC Miniature Circuit Breakers
(MCBs) for system protection and data storage
3. The prepaid metering system as claimed in claim I, wherein the portable charging device is
embodied as a UART communication technology based dongle.
4. The prepaid metering system as claimed in claim I, wherein the portable charging device
is embodied one of the Universal Serial Bus (USB) sticks, USB cards, Bluetooth tags,
Radio-Frequency Identification (RFID) tags.
5. The prepaid metering system as claimed in claim I, wherein the dynamic pricing is
managed by detecting a voltage of the battery bank via Zero Current Conductor.
6. The prepaid metering system as claimed in claim I, the prepaid metering system is provided
for J ligh Voltage (Solar) DC Micro-grids.
7. A method for charging an energy meter with energy credits, the method comprising:
• receiving energy credits from a remote location to a central charge station, Global
System for Mobile Communications (GSM);
• transferring energy credits from the central charge station to an energy meter located in
a household via a portable charging device; and
• storing data pertaining to energy consumption from the energy meter; and managing
dynamic pricing based on a battery bank of the energy meter and n amount of power
being drawn by the household.