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Mobile driving energy efficiency in Managing Power in off-grid homes
Ashok Jhunjhunwala, Prabhjot Kaur, Anusha Ramachandran, Sai Ram Mannar, Mrinalini Ramakrishnan, Sree Hari Nagarajan
IIT Madras
Power for Indian Homes: A dilemma
• 50 million homes not connected to grid
• About 100 million homes have load-shedding between 4 hours a day to 16 hours a day
• 50% of Indian homes can not afford power even at subsidizedrate of ₹5 per unit
– At this tariff all DISCOMS lose money
ITS Cambridge 2
$1 = ₹66
September, 2016
Power of 125W Solar Panel
In first week of December 2015• When whole of IITM had no power for 75 hours
– Even 1 MW solar plant at IITM failed to provide any power
– one home which continued to have two tube-lights+ a bulb and a fan + laptop charged / discharged fully 15 times + cell phone charging• 125W solar panel + 0.5 kWh effective battery
– Solar DC Inverterless• Full DC wiring, all Loads DC, solar and battery connected on DC
line, input grid power converted to DC • Avoided 45% losses due to three converters
– Also, DC-powered DC loads save power• LED lights, fans with BLDC motors
TVs and all electronics arepreferably powered on DC line
ITS Cambridge 3September, 2016
AC Load
DC-AC
Battery
AC-DC DC-AC
Grid
Solar DC
Fans AC fan BLDC fan
At full Speed 72W 30W
At speed 1 60W 9W
Lighting CFL Tube light LED tube
At Max. Intensity 36W 15W
At Lowest Intensity NA 4W
Smart Homes should have Solar-DC
• DC Micro-grid connecting– Solar Panel
– Battery
– DC Appliances
• Highly efficient usage of Power– Low-power from grid alone converted from AC-DC
(Designed to have minimal losses)
• 48V DC chosen due to – Safety considerations
– Lower cable losses compared to 12V/24V DC systems
• But design non-trivial– Solar MPPT voltage varies
– Battery needs independent charge voltage
– Load is at some fixed voltage
– DC-DC converters will add similar losses
ITS Cambridge 4September, 2016
AC-DC
battery
Loadgrid
Solar
48VDC
48VDC
48VDC
IITM designed Solar-DC Inverterless
5
125W to 500W 48V DC (and possibly 150W uninterrupted AC) Power with BLE prepaid recharge
125W panels• Upto 500W possible
230V AC
Special 1 kWh VRLA battery with 1600 cycles for 50% DoD• Up to 5 kWh possible
ITS Cambridge
Designed as an expandable product, still keeping losses low
Monitored using Bluetooth
September, 2016
And worked with start-ups to build Appliances
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LED Bulb• 5W instead of 30W bulb
BLDC Fan• 30W instead of 72W AC fan• 9W at lowest speed Remote Control for Fan &
Tube light• ON/OFF and for dimming
Cell phone Charger/Socket• DC charger with USB port
LED Tube light• 15W - dimmable to 4W, instead of 36W
fluorescent tube
Cost: ₹20000 for 125W SP + 1 kWh Battery+ appliances
$1 = ₹66
Energy-efficient DC appliances being expanded
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DC-powered 19/24” Colour TV• Consumes 30W along
with set-top box at 48V DC
DC Desert Cooler• Consumes 80W
instead of 180W AC cooler
Refrigerator and Stove• Still experimental
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DC Mixer• Consumes 150W,
whereas AC Mixers consume 350W
September, 2016
Deployment of Inverterless DC Solution in off-grid rural homes
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Rajasthan: 4000 Homes
Jodhpur District
Jaisalmer District
Other States: 1000 Homes
4000 scattered Homes provide excellent field conditions
• The system design was new and complex with each sub-system beingjust optimal in terms of size and costs
• The stated aim to reduce cost and size by reducing losses
• Question: Is this reduction in losses realised in practice (it did in labprototypes) in different field conditions
• Is system functioning well at these remote location?• are sub-systems behaving right?• Is solar power getting wasted?• Is battery remaining healthy?• Can performance be further improved?
– Cost / performance needs to be examined
September, 2016ITS Cambridge 10
Need to monitor each system
• For the purpose of diagnostics and performance evaluation– Measure solar-power, battery (in / out)
power and Load power every few minutes
– Building such diagnostics in Inverterless was trivial
• But requires connectivity to the cloud
• Needs to be Low-cost as compared to Inverterless– Operations costs needs to be low
• Inverterless costs ₹3000; wireless modem will cost similar + monthly cost of usage– Need a different approach
• Most homes have a phone• Use Blue-tooth to connect
– Use phone to relay to cloud
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Over Internet
$1 = ₹66
Connectivity for Power Management
• Connectivity can do more, not just Monitoring
• Management
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Remote Monitoring helps
• Faults example– Certain repeated short-circuit
behaviour
• Design deficiency examples– Battery may be charging / discharging
faster• Solar pattern variance
• Usage pattern variance
• Blackout period pattern, if grid-connected
– Battery switching from normal to boost
– End of Life (for battery behaviour
• Some can be corrected by software/ algorithm upgrades– Some other would require hardware
changes
• A major design aspect that emerged– Provision of an emergency line kept
ON when SoC of battery goes low
ITS Cambridge 13September, 2016
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Measurements from a home in Bhom Ji ka Gaon, Jodhpur from 9am to 5pm
• Understanding use of solar Power and losses: performance evaluation• Is customer using more than what solar power provides?
• Is she using less? Is power being wasted?• In Grid-connected system (no reverse feeding for small system), grid-usage can be optimized
to use all of solar power
Solar
Battery
Load
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-75
-55
-35
-15
5
25
45
65
85
105
125
Jul-
01
00:
00
1:5
5
3:5
0
5:4
5
7:4
0
9:3
5
11:3
0
13:2
5
15:2
0
17:1
5
19:1
0
21:0
5
23:0
0
Jul-
02
00:
55
2:5
0
4:4
5
6:4
0
8:3
5
10:3
0
12:2
5
14:2
0
16:1
5
18:1
0
20:0
5
22:0
0
23:5
5
Day and Time
Battery power (W) Load power (W) Solar power (W)
September, 2016
Remote Monitoring monitors Usage
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Solar Power not fully Captured, as load is less and Battery is full
September, 2016
Lower Usage may waste Solar Power
Customer Monitoring
• Using Mobile App on customer phone
– Tracks power usage throughout day
– Tracks power generated and stored
– Tracks State of Charge (SoC) of battery
• For grid connected system
– Power availability
– Help her plan conserve if required• Dim lights / fans
– Helps user alter usage to avoid waste
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Management using connectivity
• Manage at what SoC battery should switch to emergency load andto cut-off– Depends on solar power availability at a location and load usage patterns
• Manage (using user mobile or from cloud) order of priority inutilising solar power, grid power and battery to drive load– makes the Inverterless system highly adaptable
• Configuring parameters like voltage thresholds and power-availability for battery to go in Boost Charging mode
September, 2016ITS Cambridge 17
Management using connectivity
• Four home cluster system allows homes to share the fixed costs, includingsolar panels and battery pack
– Homes unlikely to use peak load simultaneously: enables system design for averageloads
– mobile application helps monitor usage patterns, implement usage limits and billing forindividual homes
• ‘Pay as you go’ models for Inverterless administered using Bluetoothapplication
– packages can be designed for users to purchase credit for power only when they require
– can discontinue and resume usage
September, 2016ITS Cambridge 18
Learnings from monitored deployment
• When will Micro-grid help? Can wastage of Solar Power be avoided
• How will use of Li-Ion battery and reduction of losses to 5% help and at what cost-point?
• Capital and Operation Costs of grid Vs off-grid solar
• How much will on-grid Inverterless help?
ITS CambridgeSeptember, 2016
Ashok Jhunjhunwala, Aditya Lolla, Prabhjot Kaur, “Solar-DC Microgrid for Indian Homes: Transforming Power
Scenario”, IEEE Electrification Magazine, Vol 4, Issue 2, pp: 10-19. June 2016
Jhunjhunwala, Current Science, Vol. 111, No 4, August 2016 http://www.currentscience.ac.in/Volumes/111/04/0599.pdf
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Small Home AC Home DC Home
Energy/ day kWh
Cost per day ₹
Energy / day kWh
Cost per day ₹
AC Grid + 0 LS 3.27 16.3 1.29 6.45off-grid + Battery + Solar 4.9 50.6 1.33 12.6AC +Battery + Solar + 4h LS 3.75 28.9 1.35 7.3
And finally the economics
Device Numbersdeployed
Operationhrs/ day
Tubelights 2 6
Fans 2 12
Bulbs 2 10
Phones 1 4
TV 1 10
Cost / day includes depreciation and interest for solar panel and battery assuming grid costs of ₹5 per unit
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Off-grid home power-costs with solar-DC (₹12.6 per day) less than the cost of on-grid AC homes with no power-cuts (₹16.3 per day) $1 = ₹66
September, 2016
To Sum Up
• 500W solar power (50 sq ft) with DC appliances can take care ofmost essential loads in middle class homes– 240M homes with 500W solar panel produces close to total domestic
consumption in India in a year• 240M x 0.5 kW x 1550 solar hours a year = 190,000 GWh per year
• Innovative systems like solar-DC needed to provide power to lower sections of people in India
• Monitoring and Managing Power for such small systems is a true example of power of IoT
September, 2016ITS Cambridge 21