I am a fan of renewable energies. Wind turbines make a lot of sense to me. Besides, they are not particularly beautiful. I was shocked to learn that large turbines contain up to 30 tonnes of copper! And all the steel, the concrete, the plastic for the rotors … wow, what a consumption of materials!

There are quite a few energy harvesting projects on the internet. Also here on Instructables you can find many contributions. Solar cells, wind and water wheels seem to be environmentally friendly. I like small and discreet projects, like the energy harvesting in the sole of a shoe.

I've tried this, and it works well. But it's not always easy: the piezos slip easily, either the shoe gets too heavy with the battery, or the cable gets in the way of the pant leg.

So I want to make an uncomplicated and low-maintenance piezo power plant for home. And I want to find out whether something like that can be economical.

What is the science of this project?

Using the piezos in this way is quite unusual. The diagrams are intended to show that the battery can recharge itself despite consumption by the Wemos D1.

Supplies

[Prices per piece]

Energy harvesting:

2 piezo sensors ............... [0.45€]

2 rectifiers / 8 diodes ...... [0.60€]

LiPo battery + holder ...... [7.00€ + 0.75€]

Charging unit TP4056 ..... [1.80€]

Capacitor 100uF...............[0.25€]

Spring steel (25 cm)....... [ ~5.00 €]

Screws, adhesive tape, heat shrink tubing

Wood for the wind blade

Research: (Not necessary)

Wemos D1 mini ..... [5.70€]

INA219 ................. [5.50€]

Waterproof case

Account at thingspeak.com (for free)

Step 1: The Idea

On my property there is almost always a bit of wind, at least a very light breeze. Wind turbines are quite ugly, to be honest. All right, they can achieve considerable power, but they are also resource-intensive: in a large commercial wind turbine, up to 30 tonnes of copper are built into the generator and rare earths in the magnets. Then there is the reinforced concrete for the base and tower, with very energy-intensive cement and steel production; the rotor blades are largely made of plastic and glass fibre. This is not really environmentally friendly.

Leaves of grass, on the other hand, are beautiful and the whole meadow often move in the light wind. I do something like that too.

The idea: wind makes a wooden kind of "blade of grass" and some spring steel vibrate, which generates electricity by applying pressure to a piezo component.

Environmentally friendly, resource-saving, bird-friendly, discrete, cheap, aesthetic.

Step 2: The Research Electronics

For research I first built a shoe sole energy harvester. The energy from the piezos is polarized by two rectifier elements. (You can also use two rectifier circuits consisting of four diodes each). A charging board controls the charging of the battery (18620). This in turn runs a "Wemos D1 mini, this is an Arduino microcontroller with wifi capability. The INA219 sensor makes it possible to collect data about the state of charge. The Wemos D1 sends the data every 3 minutes via my home wifi to my Thingspeak* account, where I can access the data in form of a graph at any time.

* Register for free, then you will receive an access key with which you can upload or query your data. You must enter the key later in PiezoEnergyPlant.ino.

Please note the green jumper on Wemos between Reset and D0. It is necessary so that Wemos can wake itself up from a deep sleep. Do not solder it: for programming the connection must be removed! You can choose a sleeping time from 1ms to ~70 min.

I chose the 3 minutes (and added a LED) to simulate more energy consumption.

A steady decrease in energy can be seen in the curve at Step 8.

You can find different projects:

https://www.instructables.com/Generate-Electricity-Using-Footwear-Charge-Your-Mo/

https://www.instructables.com/Piezoelectric-Shoes-Charge-Your-Mobile-Device-by-W/

https://www.instructables.com/Electricity-Generating-Footwear/

These project use only one rectifier for all (parallel-connected) piezos. But I give each piezo element its own rectifier because it is not only a producer but also a consumer at the same time: a piezo generates energy that causes the neighbouring element to vibrate. The energy is then lost for storage.

Attention: Operation does not start by itself, even with a fully charged battery. You first have to wake up the charging unit by a short power supply via the USB connection.

CONCLUSION of the circuit:

The kinetic energy of the blade should be enough to power a sensor, a weather station, a small webcam or an LED lamp. And to do so quite discretely, maybe without letting the technology be visible.

In questions of energy efficiency, I wrote to several piezo manufacturers and asked about the amount of energy used in production. Unfortunately, I did not receive any answers.

PiezoEnergyPlant.ino
Download

Step 3: Research and Genesis

I thought a lot about how to move the piezo elements. There was everything from a cardan joint to a trampoline spring. Attaching the elements directly to a spring blade turned out to be the best idea.

Ring-like arrangement of the piezo elements. Without steel spring, alignment only with gravity through cardan joint.

Ring-like arrangement of the piezo elements with steel spring from an old trampoline.

Only two piezo elements with steel spring from an old trampoline.

Two piezo elements with edge steel of a snow shovel and simple plywood wind catcher (see step 4).

2-4 piezo elements with edge steel of a snow shovel wind catcher from old christmas tree.

Improved wind blade with fan.

Improved wind blade with braided materials.

Step 4: Windcatchers

We have to catch wind to make the steel spring vibrate. To do this, we need a surface that

- is as large as possible

- is as light as possible

- is made of natural material

- looks nice and natural

In the pictures you can see the development of the wind catchers with the surface area in cm2

1. hazel wood and plywood

2. an old Christmas tree made into a blade (~ 170 cm)

3. a board cut into strips and made into a fan. (v-shape or x-shape)

4. braided surface, v-shape

5. braided surface, leaf shape (~ 75 cm)

(I cut the thin wooden strips for the braiding from larch wood on a circular saw.)

Alternative materials: Wood and leather, wood and wool/jute/cloth (but too heavy in the rain). No plastic please!

Reed? Feathers?

Important:

In order to make the spring vibrate, the wind blade must not be mounted at right angles to the direction of vibration, but at a 45 degree angle to it (see pictures above). Only in this way a vibration can be stimulated from almost any wind direction and be translated to the two directions of the swinging steel. The angle is also important so that the blade can swing back even in relatively constant wind.

I insert the spring steel through a slot in the wood and fasten it with screws.

Step 5: The Piezo Unit

As I mentioned in step 2, each piezo element gets its own rectifier, both fit on a small circuit board, wrapped in heat shrink tubing.

The two piezo elements are each attached to one side of the steel spring. The middle of the spring is insulated with tape. On top of this there are the piezos, which are again fastened with tape and insulated. The cables come out at the sides. In addition, the plates are fixed at the top and bottom with screws and washers.

When the wind catcher and spring are moved, the piezos are slightly bent and generate energy that is poled by the rectifiers and temporarily stored in the capacitor.

Step 6: Pure Charging Circuit

If you are only interested in charging a battery and not in research, you can also use this simpler circuit.

Step 7: Socket and Test Operation

I used a screw clamp to fix the spring steel with the wind catcher to a large paving stone. Just align it a little - that's it.

I just added a plastic cup to protect it from getting wet.

Step 8: Charging

The blue curve is typical for the discharge of a lipo battery. The 1st red curve proves a delay in discharge of about 17 hours on a day with approx. 10km/h wind (according to the weather report).

The 2nd red curve clearly shows the charging by the piezo elements over several days.

Step 9: Interim Results

I need some time for each test run. Although the Wemos becomes active every 3 minutes, it still runs for 7 days without charging until the 2000mAh battery is empty.

In the latest test, the battery lasted 9 days. In the picture you can clearly see the daily charging processes - at night it was windless.

2000mAh : 7 days = 286 mAh /1 day that means: 571 mAh for two extra days that were added with the charging process.

Not bad for the fact that there was almost no wind during the measurement period. The weather forecast indicated air movements of 5-10 km/h.

Step 10: Conclusion

Considering that I live at 360 m above sea level, I can be quite satisfied with the energy harvest:

Without a solar cell or wind turbine, a sensor unit can be operated in the open field, without a solar cell, without maintenance. I could even charge my mobile phone with the batteries.

Summary:

Little material consumption - no copper, no plastic, little steel, only local wood

friendly to birds

low maintenance

cheap

aesthetic

Possible application: Cave research

In a cave without light but some breeze a sensor can be operated for a long time.

This P.E.P will not solve the world's energy problems. But a field or a garage roof full of pretty little energy leaves can help a little to provide electricity in areas with little sun, less wind and few resources.