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Institute of Operating Systems and Computer Networks A Feasibility Study on Energy Harvesting from Soil Temperature Differences Sven Pullwitt, Ulf Kulau, Robert Hartung, Lars Wolf, 2018-11-04 Introduction Soil Temperature Experiment Peltier

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A Feasibility Study on Energy Harvesting from Soil Temperature Differences

Sven Pullwitt, Ulf Kulau, Robert Hartung, Lars Wolf, 2018-11-04

Institute of Operating Systems and Computer Networks

SLIDE 2

Introduction Soil Temperature Experiment Peltier Experiment Simulation Conclusion

Smart Farming

2018-11-04 Sven Pullwitt, Ulf Kulau, Robert Hartung, Lars Wolf Page 2 A Feasibility Study on Energy Harvesting from Soil Temperature Differences Institute of Operating Systems and Computer Networks

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Introduction Soil Temperature Experiment Peltier Experiment Simulation Conclusion

Smart Farming: Challenges

Problem: Solar cells not possible Nodes near surface of soil Lots of dirt, no sun due to crops

2018-11-04 Sven Pullwitt, Ulf Kulau, Robert Hartung, Lars Wolf Page 3 A Feasibility Study on Energy Harvesting from Soil Temperature Differences Institute of Operating Systems and Computer Networks

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Introduction Soil Temperature Experiment Peltier Experiment Simulation Conclusion

Idea: Harvest from soil

2018-11-04 Sven Pullwitt, Ulf Kulau, Robert Hartung, Lars Wolf Page 4 A Feasibility Study on Energy Harvesting from Soil Temperature Differences Institute of Operating Systems and Computer Networks

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Introduction Soil Temperature Experiment Peltier Experiment Simulation Conclusion

Setup

ID0 ID1 ID2 ID3 ID4 ID5 ID6 ID7 ID8

Temperature sensors WSN node

Surface

2cm 8.5cm 15cm 21.5cm 28cm 34.5cm 41cm 47.5cm

ID8 ID7 ID6 ID5 ID4 ID3 ID2 ID1 ID0 INGA WSN node (IEEE 802.15.4) Deployment

duration: 1 year, sample rate 10s, data are available1

1https://www.ibr.cs.tu-bs.de/projects/reap/soil_temp.html

2018-11-04 Sven Pullwitt, Ulf Kulau, Robert Hartung, Lars Wolf Page 5 A Feasibility Study on Energy Harvesting from Soil Temperature Differences Institute of Operating Systems and Computer Networks

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Introduction Soil Temperature Experiment Peltier Experiment Simulation Conclusion

Examplary Data

1 2 3 4 5 6 7 8 9 10 11 12 2016-10-25 2016-10-25 2016-10-25 2016-10-26 2016-10-26 2016-10-26 2016-10-26 ID=0 (Surface) ID1 (2cm) ID2 (8.5cm) ID3 (15cm) ID4 (21.5cm) ID5 (28cm)

First week

2018-11-04 Sven Pullwitt, Ulf Kulau, Robert Hartung, Lars Wolf Page 6 A Feasibility Study on Energy Harvesting from Soil Temperature Differences Institute of Operating Systems and Computer Networks

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Introduction Soil Temperature Experiment Peltier Experiment Simulation Conclusion

Results

1 . 1 1 . 1 6 1 . 1 2 . 1 6 1 . 1 . 1 7 1 . 2 . 1 7 1 . 3 . 1 7 1 . 4 . 1 7 1 . 5 . 1 7 1 . 6 . 1 7 1 . 7 . 1 7 1 . 8 . 1 7 1 . 9 . 1 7 1 . 1 . 1 7 1 . 1 1 . 1 7 7.5 5.0 2.5 0.0 2.5 5.0 7.5 10.0 12.5 Average T [°C] positive T negative T

Gaps due to battery exchange

2018-11-04 Sven Pullwitt, Ulf Kulau, Robert Hartung, Lars Wolf Page 7 A Feasibility Study on Energy Harvesting from Soil Temperature Differences Institute of Operating Systems and Computer Networks

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Introduction Soil Temperature Experiment Peltier Experiment Simulation Conclusion

Temperature vs. depth

2018-11-04 Sven Pullwitt, Ulf Kulau, Robert Hartung, Lars Wolf Page 8 A Feasibility Study on Energy Harvesting from Soil Temperature Differences Institute of Operating Systems and Computer Networks

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Introduction Soil Temperature Experiment Peltier Experiment Simulation Conclusion

Conclusion

Temperature differences of several degree every day Exception: transition period (spring, autumn) Q: can we actually harvest energy?

2018-11-04 Sven Pullwitt, Ulf Kulau, Robert Hartung, Lars Wolf Page 9 A Feasibility Study on Energy Harvesting from Soil Temperature Differences Institute of Operating Systems and Computer Networks

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Introduction Soil Temperature Experiment Peltier Experiment Simulation Conclusion

General Idea

P(∆T)[W] Simulation Temperature Data Feasability

2018-11-04 Sven Pullwitt, Ulf Kulau, Robert Hartung, Lars Wolf Page 10 A Feasibility Study on Energy Harvesting from Soil Temperature Differences Institute of Operating Systems and Computer Networks

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Introduction Soil Temperature Experiment Peltier Experiment Simulation Conclusion

Setup

TEG Chamber left Chamber right Metal Metal Fan Fan Load

How much energy can we produce? Electronic load to simulate harvester+microcontroller

2018-11-04 Sven Pullwitt, Ulf Kulau, Robert Hartung, Lars Wolf Page 11 A Feasibility Study on Energy Harvesting from Soil Temperature Differences Institute of Operating Systems and Computer Networks

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Introduction Soil Temperature Experiment Peltier Experiment Simulation Conclusion

Setup

Fixed value for load, cycle through temperatures (10-50 ◦C) Constantly measure temperature

In chamber (TC) Near element (TE) But: |TC − TE| ≫ 0

Result: |TC − TE| → E

TEG Chamber left Chamber right Metal Metal Fan Fan Load

2018-11-04 Sven Pullwitt, Ulf Kulau, Robert Hartung, Lars Wolf Page 11 A Feasibility Study on Energy Harvesting from Soil Temperature Differences Institute of Operating Systems and Computer Networks

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Introduction Soil Temperature Experiment Peltier Experiment Simulation Conclusion

Results

2nd Experiment: Fixed temperature, cycle through resistance (MPPT)

2018-11-04 Sven Pullwitt, Ulf Kulau, Robert Hartung, Lars Wolf Page 12 A Feasibility Study on Energy Harvesting from Soil Temperature Differences Institute of Operating Systems and Computer Networks

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Introduction Soil Temperature Experiment Peltier Experiment Simulation Conclusion

Harvesting Model

Temperature gradient in chamber differs from the one at TEG ⇒ factor h is introduced P(∆T, h) = h · (a · ∆T2 + b · ∆T + c) [W] with TEG specific a,b and c Store harvested energy Estimate the energy collected by a simulated harvester

2018-11-04 Sven Pullwitt, Ulf Kulau, Robert Hartung, Lars Wolf Page 13 A Feasibility Study on Energy Harvesting from Soil Temperature Differences Institute of Operating Systems and Computer Networks

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Introduction Soil Temperature Experiment Peltier Experiment Simulation Conclusion

Harvestable energy with different efficiency η

Soil temperature experiment → harvested energy per month

Okt 16 Nov 16 Dez 16 Jan 17 Feb 17 Mär 17 Apr 17 Mai 17 Jun 17 Jul 17 Aug 17 Sep 17 Okt 17 Nov 17 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Total energy [Wh] Best case Average case Worst case Positive Polarity Negative Polarity

Best Case η = 99%, h = 99% Average Case η = 60%, h = 41% Worst Case η = 20%, h = 20%

2018-11-04 Sven Pullwitt, Ulf Kulau, Robert Hartung, Lars Wolf Page 14 A Feasibility Study on Energy Harvesting from Soil Temperature Differences Institute of Operating Systems and Computer Networks

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Introduction Soil Temperature Experiment Peltier Experiment Simulation Conclusion

Sample Application

Harvester MCU Energy Store Radio

Observe Control

Simulate a virtual node Slots in simulation, where:

Energy is harvested data is sensed, and (MCU active) transmitted if possible (Radio active)

Additionally, MCU can sleep (MCU alive)

2018-11-04 Sven Pullwitt, Ulf Kulau, Robert Hartung, Lars Wolf Page 15 A Feasibility Study on Energy Harvesting from Soil Temperature Differences Institute of Operating Systems and Computer Networks

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Introduction Soil Temperature Experiment Peltier Experiment Simulation Conclusion

Slot Example

MCU alive MCU active Radio active

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Introduction Soil Temperature Experiment Peltier Experiment Simulation Conclusion

Active states

10.04.17 12.04.17 14.04.17 16.04.17 20 40 60 80 100 Usable slots [%]

Slots MCU alive Slots MCU active Slots Radio active

State is entered, if there is enough energy

2018-11-04 Sven Pullwitt, Ulf Kulau, Robert Hartung, Lars Wolf Page 17 A Feasibility Study on Energy Harvesting from Soil Temperature Differences Institute of Operating Systems and Computer Networks

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Introduction Soil Temperature Experiment Peltier Experiment Simulation Conclusion

Transmitted frames

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Introduction Soil Temperature Experiment Peltier Experiment Simulation Conclusion

Conclusion

Long-term experiment with soil temperatures from 8 depths Temperature-controlled chambers with TEG to model harvestable energy from ∆T Simulated WSN Application:

7.5 packets per hour in winter, 40 in summer

Next step: deploy an actual system!

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