Harvester - Building the Energy Forest

An Open Source project to build cheap linear generators to harvest the wind energy which moves trees in a forest (or waves in the sea)

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Harvester is an ongoing Open Source project. The goal is to build a platform which is able to harvest the energy inside oscillations of trees which are swinging in the wind. This eliminates the need to build big, ugly wind turbines and and lets the landscape unchanged. Switching to another object the system is mounted on, also other sources of energy, eg. waves, could be harvested.

The Problem

Fighting global warming is one of the biggest challenge for humankind. Therefore most of the industrialized nations try to increase their output of renewable energy. In Germany in particular this means despite other approaches to build wind turbines. A majority of people is in favor of wind energy, but in many places building a huge wind turbine is not possible because of the opposition of the residents, which usually don't like the look, sound or shadow of these turbines, or because of environmental reasons (e.g. nearby endangered birds).

The Solution

The solution for this problem is to use trees as a energy source. To be more precise: This project tries to generate electricity by using the bowing motion of trees which are exposed to wind.

From the technical standpoint the most likely solution will be to make a link between two trees at a certain height and use a linear generator to generate the electricity, which is then collected via cables at a central point. This linear generator can of course also be used as a single unit at one tree to power a garden light or to charge up a mobile phone.  Also the generator can be mounted at a buoy and generate electricity out of the movement of the waves.

Since the only mechanical interface to the outer world are two mounting points it is very easy to use this linear power generation unit in other projects where linear motion/oscillation should be harvested!

Current Status

To find the best solution, more research has to be done, which goes into three main directions:

► Energy: How much energy is trapped inside a swinging tree and how much can be recovered?

► Configuration: Where should the harvester be mounted? Between two or more trees or with connection to the ground? Directly at the ground or at the top? Shall the harvester be usable only with one tree (aka in a garden)?

► Engineering: How can the linear movement be converted into electrical power? Use of an hydraulic/pneumatic system, simple ropes or linear generators for direct electrical power generation?


First CAD Sketch
First data from the field

  • Harvester is going into the woods!

    Tobiwan8 hours ago 0 comments

    Yesterday I had a talk with a friend of mine who owns a small forest here in Bavaria, Germany. He got excited about my idea and offered that I can mount data collection systems and prototypes at his trees. Its a working forest with mainly spruces and it is situated at a hillside, which is very good for wind energy harvesting :) As soon one of my prototypes is ready I will bring it there and test it. If I can get some funding I also plan to test a small (<10 units) batch of the most promising prototype, but more about my future plans in one of the next project logs.

  • Research: First data from the tree

    Tobiwan3 days ago 0 comments

    Yesterday I took the phone back off the tree (see yesterdays project log entry) and today I look for the first time into the data. The graph shows the acceleration values parallel to the ground over time:

    First obvious statement: We had some wind in the evening and during the next day, but the night was very calm. By the way: This is not the raw data, I used the calm period at night to get rid of the baseline (which is caused by gravitation, which is a constant acceleration), so the whole graph is shifted to zero (the unit to the top are m/s2 by the way, to the left there is the number of 500ms timesteps, which means 2*3600=7200 is one hour) . Besides that there seems to be some osscilations so lets look closer at the red rectangle:

    There are smaller oscillations, but not around zero, interesting... I think the bow of the stem brought back the constant influence of gravity (perhaps we can use that to run a running average and then have an idea to which angle the stem bowed?). Nevertheless, the oscillations we can see here are in the order of minutes, which is not what I expected from just watching the trees swing in the wind (there I estimated swing periods below 30s). My first guess is that the wind is changing in this time period, but so regulary? Second guess would be that the swing period of trees is indeed in the minutes, I have to do more research about that :) We also have to keep in mind that this is just the x-direction, so if the wind direction changes, this can also have a influence on the data, since this is only the projection of the movement on the x-axis.

    All this questions the method to use a phone as a monitoring device for low frequency oscillations, so either I use a more sensitive accelerometer/more sophisticated data analysis in the future or I try to measure the amplitude, which means the distance from the place where the stems is without wind. More about that coming soon!

    If one of you guys wants to look into the raw data, you can find it on Github. A second opinion/approach about analyzing the data would be much appreciated!

  • First 3D Sketch

    Tobiwan4 days ago 0 comments

    Today put a little bit more thought into solution 1 (see last project log entry, the one with rack and pinion). I think I will go with a rack, which slides in a tube and rotates a small gear. Connected to this gear is the rotor of an axial flux generator. This type of generator are well suited for low RPMs, you can see the principle at the end of this project log post.

    In the following you can see an overview of the design I came up with. Point A and B are connected to the trees and the linear power generation unit is in its fully compressed state:

    A more detailed view into the core. Please ignore the design of the housing :-). On the left is the tube where the rack sits in during full compression, in front you can see the pinion which is connected to the (transparent) rotor with 16 permanent magnets. Behind that is a red stator which holds 8 coils. The size and number of magnets and coils is not defined yet, this is just for illustration.

    Last but not least the difference between radial and axal flux in generators:

  • Brainstorming

    Tobiwan4 days ago 0 comments

      Today I made some sketches brainstorming different configurations and technical solutions:

      The main technical challenge is to use the motion of the tree, which is most of the time very powerful, but also very slow and with low amplitude. Therefore a mechanism has to be found, which can convert this motion into electricity.

      1. The most likely solution, a connection between two trees where a rack and pineon transform the linear movement into a rotational one, which then through some gear drive powers a generator.
      2. There is a central post between several trees, where some weights or springs pull at ropes which are connected to the trees. The ropes have a chain element which drives a gear which then drives the generator.
      3. There are two chambers mouted to the tree. When the tree bends, one chamber is compressed, the other is stretched. The compressed chamber pushes a liquid through a one-way valve into a central high pressure tank from which the fluid goes through a turbine into a low pressure tank. When the tree bends to the other side, the compressed chamber streches and gets new fluid through a one-way valve and a seperate connection from the low pressure tank. The previously stretched chamber gets compressed at the same time and the cycle continues.
      4. Same as the principle above, but instead of a compressable chamber there is a piston which generates the pressure (also two one-way walves and to connections to the high and low pressure tank).
      5. This is just another configuration, it would work with a linear generator as in Type 1 or with a piston as in Type 4. The difference to all other concept is, that it uses a connection not between two trees, but between the tree and ground.

  • Research: Data is coming!

    Tobiwan5 days ago 0 comments

    I managed to put the phone up to our big birch and enjoyed the awesome view meanwhile. It sits now at 10m height and collects accelerometer data from all three axis. It is a waterproof phone, but just in case I put a protective plastic bag around it. Better safe than sorry! I will put the phone down again in 24 hours and make a preliminary analysis then.

  • Research: Prepare for climbing!

    Tobiwan5 days ago 0 comments

    Ok, the phone mount is ready. I made a quick test on another tree at ground level:

    As you can see the phone is held by a bungee strap, which holds the device firmly against the wood. When you look closer, you can see that at the edges there is a groove of about 2cm between the two bumbers, so the phone is also not able to slide down. The app I am using has the name "Accelerometer Analyzer" and is able to log the values to a CSV file on the SD card :) Now I have to wait only until the phone is fully charged and the data collection can begin!

  • Research: Shall I tie an Arduino to a tree?

    Tobiwan5 days ago 0 comments

    The first thing I want to find out: How are the swinging characteristics of trees? I'm mainly looking into frequency and amplitude. The goal is to use this data together with knowledge about size and weight of the tree to find out how many energy is in the swinging motion. In parallel I'm doing some research in the scientific literature, but there is no alternative to get some hard, reallife data! The first idea here was to put a logging device onto the tree which can log the acceleration and after some calculation I would have the position over time and with that the data I'm looking for.

    So the question is, how to get the data the easiest way. Since I have done a lot with Arduinos, this was my first thought, so I put together a logging platform in my mind: An Arduino Uno with a SD card shield, a accelerometer, a battery  and some lines of code and, voila, the logging device is ready. But then I came to my mind, that basically the same components are inside a modern mobile phone. Luckily I had one in my "old electronics devices, which I don't use anymore, but could be come handy sometime" bin, so basically what was left to do is just downloading an app (offcourse there was an app for that!). And it is a  IP67 rated one, which means it is water proof, perfect!

    Today I will put the phone on the tree and hope for a small storm coming to get some data the next days. Stay tuned for more!


    PS: The phone by the way is a SPT-900 from Simvalley and runs Android 4.2. The built in accelerometer should be according to one of the apps a MMA8452Q from NXP and therefore sufficient for this purpose.

  • How I came up with the idea

    Tobiwan07/05/2018 at 07:41 0 comments

    I had this idea about a year or two ago. I read an article about wind turbines in Bavaria, Germany (Germany tries to increase the generation of renewable energy). There was an interview with the major of a small town about a wind turbine which was planned to be built next to the town. The major said he is in favor of wind energy, but the people in his town don't want the wind turbine next to the town, so he tried to stop the project. And that is what you hear by most of the people: Wind energy yes, but not in our neighbourhood! That was the moment when I first thought: Hey, If the wind turbines would not be visible, nobody would have a problem. How about blending them into the landscape? How about let them look like trees? ... Or... how about using the trees itself? And bammm, the idea was born :)

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Tobiwan wrote 3 days ago point

Good idea with the cables and the the winch! Perhaps one could use a second rope running from the other side of the tree to the generator to use the second stroke also. I already thought about the problem of two trees running syncronous, but I think it will be very unlikely that two trees have exactly the same natural frequency. But their are coupled then, which could cause syncronous swinging. I think I have to try that out.

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Florian Festi wrote 3 days ago point

Not sure if this is feasible at all. But if it is I would suggest the following setup:

Use a generator on or near the ground that is powered by a winch that is hooked up to the top of a tree with a cable or rope. The winch would need a return spring and a ratchet towards the generator to allow pulling the cable back in.

Yes, this wastes the power of the return stroke. But as the tree is a spring to some extend you may get some of that energy back on the next stroke.

Using a cable avoids using push rods which are very difficult to get stiff enough to transmit the relatively high forces over the long distances.

This setup is also much easier to maintain as everything but the rope is on ground level. It also avoids the issue of both trees doing the same movement and keeping the push rod at the same length.

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AndreasW wrote 3 days ago point

Great idea, want to see more!

  Are you sure? yes | no

Tobiwan wrote 4 days ago point

Hehe, you got me, Im building this just to phone home ;)

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