Stirling Engine

Solar Low Temperature Stirling Engine

A very interesting project to build in the student of grade 7/8 a Stirling engine for watering your school garden.
All this is supported with many images, PDF files and an easily understandable theory.
An ideal project for more school gardens and a nice resource for personal knowledge base.

… 12 students of the Montessori High School have done something very special. They want to water their school garden with innovative technology. In cooperation with the Stirling Institute of Technology a non-profit company from Potsdam will to be built a solar low temperature Stirling engine. The invention is based on the patent of the Institute with the no. 100 16 707.

selfmade Wooden Generator 1 – Experiment 2 with rectifier

Wooden Generator 1 with rectifier

Based on Wooden Generator Experiment 1, the circuit was now extended by a bridge rectifier.

For this I used BAT48 Schottky diodes because they consume only 0.2 volts.
A 1000 μF electrolytic capacitor is used as a stabilizing element.
The capacitor buffers the whole a little and the LED should light up longer and more stable.
With a small LED as a consumer, I get a current of approx. 5 mA and a voltage of approx. 1.7 V with fast speeds.
The result is a proud performance of 8.5 milliwatts.
So there is still much room for improvement :-)

Wooden Generator Schaltplan Experiment 2 Wooden Generator Versuchsaufbau Exeperiment 2

The following video gives a brief impression of the rather poor yield.

(Deutsch) Wooden Generator 1 – Experiment 1

Sorry, this entry is only available in German.

Dimensioning – own construction VAWT vertical axis wind turbine

From the beginning I wanted to build a vertically running wind turbine since it does not have to be oriented towards the wind. A vertical turbine usually starts at low wind speeds and withstand strong winds.

For vertical turbines there are several popular approaches, such as the Darrieus rotor, the Savonius rotor and various modifications.
Since I do not have the tools and possibilities of a production company as a private person, the rotor should be as simple as possible from the structure, so that I am able to implement it from home.
After much research on the net, I found an Excel list for dimensioning a Lenz2 rotor.

According to the inventor of the wing profile, it has a quite high efficiency, with manageable construction complexity.

Now, where it was clarified, what kind of rotor it should become, the dimensions had to be determined.
As can be inferred from this study, the average wind speed in Saxony is 10 meters above the ground at approx. 5 m / s.
My windmill is about 4 – 5 meters above the ground and at a distance of about 10 meters there are a few bushes, which surmount the wind wheel.
So the 5 m / s average wind speed is not achievable.
My assumption is an average wind speed of 3m / s, which would be immediately the end for a location for a productive plant.
But unfortunately I don’t have a beach property with 10 meters high mast available.

The wind turbine is supposed to feed a significant output of more than 10 KW / h per year into the battery. This is much more than I could generate in 2012 with my small solar cells.
I’ve played a little with the Excel list for the dimensioning of Lenz2 rotors around and I decided at the end for 70cm diameter and 70cm height with 3 wings.
This corresponds to almost half a square meter area where air flows through.
If I assume the 2.65 watts, which can be generated with the 70/70 rotor at average 3m / s within a year, I come to 23.2 KWh per year. This is equivalent to 3.5 times my electricity generation from 2012.

Calculated output (according to Lenz)
Wind speed km/h Wind speed m/s Speed loaded rpm Speed idle rpm Electrical power in W
4 1 22 44 0,10
7 2 44 87 0,79
11 3 65 131 2,65
14 4 87 175 6,29
18 5 109 218 12,28
22 6 131 262 21,22
25 7 153 306 33,70
29 8 175 349 50,30
32 9 196 393 71,62
36 10 218 437 98,25
40 11 240 480 130,77
43 12 262 524 169,78
47 13 284 567 215,86
50 14 306 611 269,60
54 15 327 655 331,59
58 16 349 698 402,43
61 17 371 742 482,70
65 18 393 786 573,00
68 19 415 829 673,90
72 20 437 873 786,00
76 21 458 917 909,90
79 22 480 960 1.046,17
83 23 502 1004 1.195,41
86 24 524 1048 1.358,21
90 25 546 1091 1.535,16
94 26 567 1135 1.726,85
97 27 589 1179 1.933,86
101 28 611 1222 2.156,79
104 29 633 1266 2.396,22
108 30 655 1310 2.652,76
112 31 677 1353 2.926,97
115 32 698 1397 3.219,46
119 33 720 1441 3.530,82
122 34 742 1484 3.861,63
126 35 764 1528 4.212,48
130 36 786 1572 4.583,96
133 37 808 1615 4.976,67
137 38 829 1659 5.391,19
140 39 851 1702 5.828,11
144 40 873 1746 6.288,01
Rotor diameter: 0,7 m
Rotor height: 0,7 m
Number of blades: 3 pcs
Efficiency according to Lenz: 41 %
Efficiency generator: 80 %

The 2.65 watts are, however, also the lower end of the scale as far as power generation is concerned.
The generator should perform well in the speed range 60 – 500 rpm.
Typically, the power that can be delivered should increase as described in the table.

Radius of the slats: 66 mm
Length entire blade: 280 mm

A look at the back of the table, but also shows what can work beyond the 15m / s for forces.
On one site, the wind turbine does not provide much more than 20 KW / h per year, but the design must be stable enough to withstand several thousand watts of wind power.
The lighter the construction is, the better.
It is relatively easy to see that such a project has a certain claim.

I have decided to use aluminum for the construction of the rotor, since this on the one hand it is a lightweight material and on the other has not to be protected against corrosion.
Aluminum is available anodised. I chose brown colored metal sheets, because it dark colors are reflecting very little sunlight from my point of view.
Naked aluminum looks like a mirror and I do not want to risk that the neighbors will be disturbed by sunshine reflections.
Except for the mast, I trust glue and screw connections.
The wing profiles are glued with UHU Endfest 300 (300 Kg / cm² adhesive force).
The connections up to the hub are screwed so that there is the possibility to align the rotor, since at relatively high revolutions a unbalance would lead to problems.
The structure in detail I will explain in the following pages (see page navigation – top right of the page).

And finally the drawing of the profile started with the project 2011:

Zeichnung Fluegelprofil

(Deutsch) Kreissägeblatt – Generator – Experiment 1

Sorry, this entry is only available in German.

selfmade disc generator on circular saw blade – electric power generation

Sorry, this entry is only available in German.

(Deutsch) Eigenbau Wooden Generator 1

Sorry, this entry is only available in German.

construction of the blades for the selfmade VAWT

blades VAWT Visually :-)

The pictures show the construction of the wings quite well.
It is best to click on the first one to enlarge it and then use the arrow to the right to view one image at a time.

Under each picture there is a brief explanation.

Preview Profile sheet metal wing 3Preview Blade 4Preview Blade 5

Material selection and fitting

I have decided for aluminum because it is light, weather resistant and easy to process. For the wings, aluminum was used, as is also seen on many roofs. I chose a dark (brown) color because I would not want to someone is being blinded with the windmill. If the sun is unfavorably reflected, that is not good.
The connection between wing plate and profile plates was glued with UHU Endfest 300.
(After half a year of continuous operation and a survived winter, I must say that the glue is not suitable!)
I have concentrated too much on the fact that the windmill can withstand strong wind and I was mainly concerned to use an adhesive with an extremely high bond force.
But UHU Endfest is rigid. A flexible adhesive is more suitable. I will bond the profiles again with a good silicone and test the next winter.
!—The profiles hold with Endfest of UHU, but I see smaller cracks after half a year—!

Größe und Maße

Zeichnung FluegelprofilThe size of the wing profiles is derived from the preliminary considerations of the page Dimensioning – own construction VAWT vertical axis wind turbine.
I have transferred the enclosed drawing to 3mm thick aluminum sheet and sawn using a decuping saw with sawblades for soft metal.
With a little patience, this goes quite well.
2 profiles per wing, were still provided with 2 holes (9mm diameter) to allow connection to the bracket at the hub.
Another 2 profiles per wing each received a 9mm hole in the center of the circle arc to reinforce the profiles on the top and bottom of the wing.

selfmade VAWT vertical axis windmill – lenz 2 turbine

selfmade VAWT

On these pages, I am about to document the construction of a vertical axis wind turbine.

So far here I have always logged my activities, when I have worked on it.

more detailed information you can find on this pages:

As a first impression here times a video, which shows the wind wheel in operation.

It is a vertical – axis wind turbine based on the model of a Lenz2.

Electricity generation with a bicycle and a car alternator

Experience report Electricity generation by bicycle and a car alternator

Since I had planned to generate 10 KWh of electricity in 2012 and had reached just 6 KWh as of 31.10.2012, a plan B had to be realized.
Unfortunately the provisional generator for the self-construction vertical axis wind turbine proved to be not helpful.

The required wind strength to get to charging voltage is simply too high.
So if the sun does not shine and the wind does not blow, only muscle strength still helps.
A person can produce between 100 and 200 watts for a relatively long time.

Examples from the Internet

The energy generation by means of muscle strength is nothing unusual, can be read on the pages of Buch der Synergie.

There are professionally built generators for the montage at the bike, but they cost a little.
Then I looked at Youtube and am found there something helpful.

Some time ago I had found a discarded car alternator and dragged them on suspicion times home.
A little bit in the net searched and a nice description to the three-phase alternator found.
I bought a corresponding V-belt at Ebay.


On 1.11.2012, a frame was then provisionally made, in which the bicycle can be clamped and the V-belt drives the alternator.
After about 5 hours of tinkering, it was possible to step into the pedals and the alternator spinned.

In order to test whether the alternator works at all, I have a 4.5 volt plug-in power supply (was available) closed to the excitation winding and connected to the output side a 6V 21 Watt bulb.
What was immediately noticeable was, that it was hard to step into the pedals. The 21 watt lamp started to light, burned brighter and burned right through.
What a success.

I have as in the video above to see also a switch to turn on the excitation winding attached and the whole test arrangement in the garage next to the 12V battery built up.
When the excitation current was switched on, an extreme resistance was noticeably.
One minute stepping into the pedals and the battery’s charge voltage rose from 12.95V to 13.2V.
But after a minute, my personal performance was at an end.

Ich gehe davon aus, dass ein permanenter (starker) Erregerstrom nicht optimal ist.
Pulse width modulation may be an approach.
I have an ATMega8 microcontroller already in use, to let generated energy consume and to measure how much was consumed.
The ATMega8 microcontroller has 3 PWM outputs, so it can take over this task immediately.

The circuit diagram of the exciter circle is somewhat more complex.
There the current flows with up to 2 amps at max. 14.4 volts. With the ATmega8 with 5V and max. 40mA per output pin this requirement can’t be realized.
On the following circuit diagram for the control and another I oriented myself and finally I purchased at Pollin the SUD45N05-20L.
Tailored to my needs, the schematic should look like this.

[will be continued]