1. Introduction to Energy Harvesting
EE174 – SJSU
Tan Nguyen

2. OUTLINE Introduction to Energy Harvesting (EH)
Identify key trends and market forces driving the need for Energy Harvesting-based power
The economics behind Energy Harvesting
How does EH work?
Sources of Energy
Energy conversions
EH Components
EH system and EH Circuit
Energy storage is a Must
Application
Future Research Issues

3. Introduction Energy Harvesting (EH)
Energy Harvesting (EH); also known as Power Harvesting or Energy Scavenging, is the process in which energy is captured from a variety of ambient energy sources and converted into usable electric power.
Energy harvesters provide a very small amount of power for low-energy electronics.
EH allows electronics to operate where there's no conventional power source, eliminating the need for wires or replacement of batteries.
EH systems generally includes circuitry to charge an energy storage cell, and manage the power, providing regulation and protection.
EH-powered systems need reliable energy generation, storage and delivery:
Must have energy storage as EH transducer energy source is not always available (solar at night, motor vibration at rest, air-flow, etc.)
EH can provide “endless energy” for the electronics lifespan. In many cases, energy harvesting can eliminate batteries from wireless devices.
Ideal for substituting for batteries that are impractical, costly, or dangerous to replace.
System’s environment = ambient energy
Ambient energy is energy that is natural, non-electrical in nature, and is self-regenerating or renewable
Small power in term of uA, mV range, not enough to replace household enegy
Over 1 billion people without electric and this is really good application

4. Why Energy Harvesting (EH)?
1) Transducers Are Getting More Advanced
Transducers are the devices that turn one form of energy into another. Steady advances in transducer technology, especially recent breakthroughs in materials and semiconductors, have made new types available and increased the efficiency of all of them.
2) Low-Power Circuitry Uses Even Less Power
Just as the power available from transducers has been increasing, the power needed to run electronic circuits has been decreasing.
Power improvements do not totally depend on semiconductor advances. Power consumption has become a major concern with larger chips this motivated circuit designers to develop low-power designs for digital and analog circuits. The improvements made for large chips are being carried over to smaller circuits, resulting in devices that can be powered entirely from harvested energy.
3) The IoT Is Driving Devices Closer to the Edge
The Internet of Things (IoT) is here and expanding rapidly. Depending on which analyst you refer to, predictions of connected “things” range from 20 billion to 50 billion in three years. Our computers, smartphones, and web servers are already connected, so the next connectivity wave will focus on devices.
As connected devices get smaller and further out on the edge, powering them with batteries becomes more of a problem. The prospect of replacing batteries, even as infrequently as every five to 10 years, is simply a non-starter. Consider sensors embedded within structural members or walls. Battery replacement is simply not an option in such locations.

5. Why Energy Harvesting (EH)
4) Electronic Costs Are Coming Down Faster than Battery Costs
The price of the electronics is so low, if a battery is needed, it can represent a major fraction of the cost of the device cost. This is a major reason behind the move to devices relying on energy harvesting for power.
Battery technology has not kept pace, so modules that require batteries may not satisfy design requirements because modules would be too large.
One possibility for addressing the reliability, management, and size issues associated with batteries is to remove them all together. Energy harvesting is making this possibility a reality.
5) Devices Are Only as Reliable as their Power Sources
As wireless devices are deployed in larger numbers, end users are discovering that battery reliability is not usually up to the task. A typical goal for the low-power networking protocols described above is often a 10-year battery life on a single coin cell. Several approaches are claiming success. These estimates often rely on simple calculations that compare steady-state power consumption to battery capacity specifications. Real-world deployments, however, often show unacceptable failure rates.
The problem is that battery lifetime is a multi-dimensional problem. Battery reliability begins with the manufacturing process. Unlike electronic components that have easy-to-predict lifetimes, batteries are based on chemical processes that have many different failure modes. Even manufacturers who weed out infant mortalities still have field failures, and the unavailability of data makes it impossible to include those failures in models and calculations.

9. Portable Electric Energy Sources Available
Batteries
– Wide spread availability, high reliability
– Low-cost, mature technologies
– Replacement/recharging is an issue
• Too numerous in the future
• Location is unreachable
– Sensor size limited by battery size
- Relative Improvement in
Laptop Technology 􀂃
Battery energy is the slowest trend

11. EH Market Forcasts

13. EH vs. Battery Business Case Realities
Small device designs that do not have a charging source –either AC/DC, Energy Harvesting or Wireless Power –use a primary battery
Primary batteries have reached commodity status with billions/yr shipped
Example using 3Volt batteries:
CR2032 coin + holder: $1.00/250mAh = $0.0040/mAh
Tadiran coin: $4.82/1000mAh = $0.0048/mAh
2 Lithium AAA + holder: $6.00/1000mAh = $0.0060/mAh
Energy Harvesters can be designed as cost effectively as Primary Batteries
Example: Simple Solar Energy Harvester at 200Lux with 24/7 operation. Use Sanyo AM V solar cell $4.39 (1K pcs) output is 147uW + electronic components for $ Total cost: $5.64
Calculation: 3.3V x Current = 147uW  Current = 44.7μA output
Total capacity over 10 year 24/7 life = 10 x 365 x 24 x 44.7μA = 3,916mAh
 $/mAh for Solar EH = $5.64/3,916mAh = $0.0014/mAh.
Lower than AAA and Coin cell costs

14. How Energy Harvesting works?
An energy harvester comprises one or more transducers, power conditioning, and energy storage. These technologies work together to collect energy and deliver power to the device. On the other hand, the device which uses the energy needs to be designed to work with energy harvesting as the power source.
Light RF/Electromagnetic Vibration Thermal
Processor Sensor Wireless Link Device

15. How Energy Harvesting works?
The transducer: converts energy from one energy type to a another energy type, usually electricity.
Power conditioning: is necessary because the natural output of the transducer can be intermittent, and at the wrong frequency, voltage and current to directly drive the device. A specialised DC-DC converter microchip takes in power from the transducer and convert to voltages which can then be stored or used.
Energy storage: is needed to balance the energy supply and energy demand. For applications where energy is used as soon it is collected (e.g. RFID and wireless light switches), no storage is needed. Usually however a rechargeable battery, capacitor, or supercapacitor is used. Batteries degrade over time, and so the lifetime of the storage device can often be the limiting factor in the overall lifetime of the harvester.

16. Sources of Energy
Energy harvesting uses unconventional sources to power circuitry:
Light (captured by photovoltaic cells)
Vibration or pressure (captured by a piezoelectric element)
Temperature differentials (captured by a thermo-electric generator)
Electromagnetic and Radio Frequency (3k-300GHz, captured by an antenna, λ=c/f)

18. General Overview of Ambient Energy Sources
Light Energy: This source can be divided into two categories of energy: indoor room light and outdoor sunlight energy. Light energy can be captured via photo sensors, photo diodes, and solar photovoltaic (PV) panels.
Mechanical Energy: Vibrations from machines, mechanical stress, strain from high-pressure motors, manufacturing machines, and waste rotations can be captured and used as ambient mechanical energy sources;
Thermal Energy: Waste heat energy variations from furnaces, heaters, and friction sources.
Electromagnetic Energy: Inductors, coils, and transformers can be considered as ambient energy sources, depending on how much energy is needed for the application.
Human Body: Mechanical and thermal (heat variations) energy can be generated from a human or animal body by actions such as walking and running;
Natural Energy: Wind, water flow, ocean waves, and solar energy can provide limitless energy availability from the environment;
Additionally, chemical and biological sources and radiation can be considered ambient energy sources

19. Block Diagram of General Ambient EH systems.
The first row shows the energy-harvesting sources.
The second row shows actual implementation and tools are employed to harvest the energy from the source are illustrated.
The third row shows the energy-harvesting techniques from each source.

29. Energy Harvesting Block Diagram

30. Energy Harvesting (EH)
EH uses of ambient energy to provide electrical power for small electronic and electrical devices.
An Energy Harvesting System consists of an Energy Harvester Module and a processor/transmitter block.
Energy Harvesting Module  captures milli-watts of energy from light, vibration, thermal or biological sources. A possible source of energy also comes from RF such as emitted from cell phone towers.
The power is then conditioned and stored within a battery, an efficient quick charging capacitor or one of the newly developed thin film batteries.
The system is then triggered at the required intervals to take a sensor reading, through a low power system. This data is then processed and transmitted to the base station.
This kind of EH System eliminates the dependency of the system on battery power and reduces the need to service the system..

31. Portable Electric Energy Sources Available
Solar Cells
Commercial-off-the-shelf (COTS) energy harvesting
1cm x 1cm; 0.14 mW (much less inside)
Recent research trend to improve the efficiency, robustness, costdown, etc.
Often limited by the availability of direct sunlight and size.

32. Energy Harvesting (EH) Equivalent Circuits

33. Biochemical Energy Production
Catabolism: metabolic reactions in which large molecules are broken down into smaller molecules – Usually produce energy (but not always)
Anabolism: metabolic reactions in which smaller molecules are joined to form larger molecules – Usually consume energy
Metabolism

34. Energy Storage is a Must
Almost all energy-harvesting scenarios require some sort of energy storage element or buffer. Even if the voltage and current requirements of an embedded application were so low as to be run directly on power captured or scavenged from the environment, such power would not flow in a constant way.
Storage elements or buffers are implemented in the form of a capacitor, standard rechargeable lithium battery, or a new technology like thin-film batteries. What kind of energy storage is needed depends greatly on the application.
Some applications require power for only a very short period of time, as short as the RC time constant discharge rate of a capacitor. Other applications require relatively large amounts of power for an extended duration, which dictates the use of a traditional AA or a rechargeable lithium battery

35. Li-Ion Battery
Thin Film Battery
Super Cap
Recharge cycles
Hundreds
Thousands
Millions
Self-discharge
Moderate
Negligible
High
Charge Time
Hours
Minutes
Sec-minutes
Physical Size
Large
Small
Medium
Capacity
mAHr
μAHr
μAHr
Environmental Impact
Minimal

36. Industry Applications
Remote patient monitoring
Efficient office energy control
Surveillance and security
Agricultural management
Home automation
Long range asset tracking
Implantable sensors
Structural monitoring
Machinery/equipment monitoring

38. Solar cell 
A solar cell is an electrical device that converts the energy of light directly into electricity by the photovoltaic effect.
The solar cells that you see on calculators and satellites are also called photovoltaic (PV) cells, which as the name implies (photo meaning "light" and voltaic meaning "electricity"), convert sunlight directly into electricity.

39. Solar Cells: Converting Photons to Electrons
Solar cells are made of the same kinds of semiconductor materials, such as silicon, used in the microelectronics industry. For solar cells, a thin semiconductor wafer is specially treated to form an electric field, positive on one side and negative on the other. When light energy strikes the solar cell, electrons are knocked loose from the atoms in the semiconductor material.
If electrical conductors are attached to the positive and negative sides, forming an electrical circuit, the electrons can be captured in the form of an electric current -- that is, electricity. This electricity can then be used to power a load, such as a light or a tool.

40. Solar Cells: Converting Photons to Electrons
A module is a group of cells connected electrically and packaged into a frame known as a solar panel.
Modules are designed to supply electricity at a certain voltage, such as a common 12 volts system. The current produced is directly dependent on how much light strikes the module.
Multiple modules can be wired together to form an array.
Solar panels or array can be connected in both series and parallel electrical arrangements to produce any required voltage and current combination.

41. Typical Solar Power Setup
A solar system consists of: Solar Panels, a Charger Controller, a Power Inverter, and
Batteries.
Solar Panels: supply the electricity and charge the batteries. A very small system could get away with a couple 240 watt panels but figure at least 4 to 8 for a small to medium system.
Charge Controller: is needed to prevent overcharging or draining too much of the batteries. Proper charging will prevent damage and increase the life and performance of the batteries.
Power Inverter: is the heart of the system. It makes 120 volts AC from the 12 volts DC stored in the batteries. It can also charge the batteries if connected to a generator or the AC line.
Batteries: store the electrical power in the form of a chemical reaction. Without storage you would only have power when the sun was shining or the generator was running.

43. Types of Solar Panels
Monocrystalline solar panels : The most efficient (15 – 20%) and expensive solar panels are made with Monocrystalline cells. These solar cells use very pure silicon and involve a complicated crystal growth process. Long silicon rods are produced which are cut into slices of .2 to .4 mm thick discs or wafers which are then processed into individual cells that are wired together in the solar panel.
Polycrystalline solar panels : Often called Multi-crystalline, solar panels made with Polycrystalline cells are a little less expensive & slightly less efficient than Monocrystalline cells because the cells are not grown in single crystals but in a large block of many crystals. This is what gives them that striking shattered glass appearance. Like Monocrystalline cells, they are also then sliced into wafers to produce 12 the individual cells that make up the solar panel.
Amorphous solar panels : These are not really crystals, but a thin layer of silicon deposited on a base material such as metal or glass to create the solar panel. These Amorphous solar panels are much cheaper, but their energy efficiency is also much less so more square footage is required to produce the same amount of power as the Monocrystalline or Polycrystalline type of solar panel. Amorphous solar panels can even be made into long sheets of roofing material to cover large areas of a south facing roof surface.

44. How long do solar panels last?
Solar photovoltaics slowly lose their generating capacity. Although some solar panels are still working satisfactorily 40 years after installation, the conventional view is that most will dip below 80% of their rated capacity within about 20 years. This will vary slightly between manufacturers and between different types of silicon.

45. Solar Photovoltaic Panel
An individual photovoltaic cell produces an “Open Circuit Voltage” ( VOC ) of about 0.5 to 0.6 volts at 25oC (typically around 0.58V). When connected to an external load, such as a light, the output voltage of the individual cell drops to about 0.46 volts or 460 mV as the electrical current begins to flow, and will remain around this voltage level regardless on the sun’s intensity.
Example:
Connect 10 x 0.46 volt PV cells in series  V = 0.46 x 10 = 4.6 3A
or P = V x I = 4.6 x 3 = 13.8W peak power.
A typical 12 volt photovoltaic solar panel contains PV cells produce 18.5 to 20.8 volts peak output (assuming 0.58V cell voltage).
If 24 volt panel is required then individual cells within one single solar panel.
To increase the current use parallel connected photovoltaic solar cells to boost current output.
For an output of two 64 PV cells panel to be connected in parallel.

46. Steps To Calculate How Many Solar Panels Do You Need?
Inputs:
Average kWh (kilo-watts-hour) per month.
Average sun hours per day at location to install solar panels.
Power range of solar panel that to be used.
Derate factor (DC to AC efficiency, typical range 0.8 – 0.85)
Range of Power Output of Solar Panel Manufacturers: 220W – 350+W
Calculations:
AC rating = Average kWh per month / 30 days / average sun hours per day
DC rating = AC rating / derate factor
Number of panels = DC rating / Panel Rating
Example:
For an average monthly usage of 900 kWH per month. The location has average of 6 sun hours a day. Find the total of the panel require.
Solution:
AC rating = 900 kWh per month / 30 days / 6 hours = 5 kW AC
DC rating = 5 kW AC/0.8 = 6.25 kW DC (use 0.8 for conservative when derate factor is not given)
Number of panels = 6.25 kW/ 250 W = 25 Solar Panel with 250 W Or
Number of panels = 6.25 kW/ 300 W = or 21 Solar Panel with 300 W

47. CPC1822 - 4V Output Solar Cell
Description
Features
The CPC1822 is a monolithic photovoltaic string of solar cells with switching circuitry. When operating in sunlight or a bright artificial light environment the optical energy will activate the cell array and generate
a voltage at the output. The solar cells are capable of generating a floating source voltage and current sufficient to drive and power CMOS ICs, logic gates and/or provide “trickle charge” for battery applications.
• 4V Output
• Triggers with Natural Sunlight
• Provides True Wireless Power
• No EMI/RFI Generation
• Wave Solderable
• Replacement of Discrete Components
• Solid State Reliability
• Small 8-Pin Surface Mount SOIC

48. CPC1822 - 4V Output Solar Cell
Pin Configuration
Applications
• Portable Electronics
• Solar Battery Chargers
• Battery Operated Equipment
• Consumer Electronics
• Off-Grid Installation
• Wireless Sensors and Detection
• Flame Detection
• Self Powered Sunlight/ Light Detection
• Self Powered Products
• Remote Installation

50. References:
file:///C:/Users/test1/Downloads/Energy%20harvesting%20(1).pdf
Energy Harvesting with Functional Materials and Microsystems Edited by Madhu Bhaskaran • Sharath Sriram Krzysztof Iniewski