WIND INTO THE GRID

All on small wind turbines for in-house grids and battery charging

by Günther Hacker

New wind turbines, new testings

The house we finally chose was located in the sunny part of town, with a nice office space and an easily accessible roof big enough for my solar energy-requirements. In this new and quiet residential area, we installed our old solar energy system to the roof under the neighbours’ close scrutiny. Additionally, we installed a big thermal solar unit complete with new and secure large area flat-plate collectors, that I had developed together with a manufacturer of collectors.

We replaced the old oil-fired boiler in the basement with a modern 1000 liter combined thermal/solar-storage-tank. Using the 16m^2 collector surface, we can heat the house in transition periods; supported by a modern gas-firing condensing boiler on days with low levels of sunlight. The washing machine and the dishwasher are connected to the hot water, and we use the Alfa Mix valve for the washing machine to save on electricity.

Thanks to the homepage that my sons had set up for my company, word soon spread about the fact that we had developed large area flat-plate collectors. Their specific advantage is an in-built, indirect ventilation system that keeps them from clouding and going blind, as many of the tightly glued collectors do.

More and more customers ordered our new collectors and a new combined-storage-tank-in-tank-system, and so not long after that, the cold Black Forest had its first residential and office building completely heated by 55m^2 of solar collectors and a 8000 liter combined thermal/solar-storage-tank.

But let’s get back to wind energy: on a trade fair in Freiburg where we presented our collectors, I came upon a small wind turbine mounted on a long pipe. It just stood there, with no personnel around. I was able to get the manufacturer’s address and a few days later, the AIR 303 arrived on our doorstep by mail.

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Help from Canada

Now I have to come back to Rolf Heckmann. You remember that he made the small American wind turbines AIR popular in Europe. Then he sold his company and went on the “World Wind Tour” with his wife, dog and a motor home truck.

One day Rolf called and told us that he wound up in Canada, where the locals of Val Marie gave him a small church, which he could refurbish into a house. As there was no water or electricity, the house could also serve as a pilot plant for the farmers who had energy supply problems.

For this purpose, he needed a complete thermal solar plant from me, including a solar collector made for extreme weather conditions. The solar panels, the charge controller and the battery he obtained inexpensively from the US and the two small wind turbines already worked for several months.

This got my attention: If someone could provide enough energy for a household by operating two small wind turbines in a country with temperatures as low as -40°C and storms with winds of 130 km/h lasting for weeks, they had to be perfect!

Rolf then soon sent us a WHISPER H40 and an H80 from the American company SOUTHWEST WINDPOWER (SWWP) with a specially developed generator via expensive airfreight.

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RUTLAND 910: English six-bladed, old model with robust metal housing. Approximately 80 Watt measured. Successor with many plastic parts, power limited at 70 Watt, no storm brake, originally built for ships, designed for charging a battery via a charge controller.

PACIFIC: Quiet and robust 100 Watt small wind turbine from England. Aluminum housing, plastic blades and seawater-proof ball bearings appear to be durable, which was proven right by our long-term test with 5 Pacifics. The six-bladed rotor spans 91 cm, the weight is 12.5 kg. The Pacific is only suitable for charging batteries in strong wind areas.

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3. Why does a wind turbine turn?

The flat side of the wind turbine’s blades faces the wind, while the rounded side faces away. When the wind flows around the blade, it flows faster on the front face and slower on the back. The shorter path on the front causes a pressure difference between the front and backside. This pressure difference causes a force with an uplift component (lift) and a resisting component (drag). As the blades are fixed on the middle axis, this driving force turns the blades in rotational direction.

The ratio between lift and drag, the so-called L/D ratio strongly depends on the blade profile. The profile should preferably be chosen so that the lift is much higher than the drag, as pure drag turbines (e.g. westernmill) turn much slower and generate less power. For this reason, rotors of ventilators and car coolers are not suitable for building your own wind turbine to generate electricity.

When using the word wind turbine blade, we are actually not being correct. It should be called repeller because it is the opposite of an air propeller (rounded side in the front, flat side in the back), which are used to “screw” the engine powered airplane forward.

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The density of air also affects the energy output: The denser and heavier the air, the more energy can be generated from it. Therefore, a location at sea level is ideal. As the air gets thinner in higher altitudes, a wind turbine on top of a mountain would make little sense (not only for optical reasons).

All these things mainly affect large wind turbines, which are supposed to generate as much electricity as possible. However, we can draw many conclusions for our small wind turbines:

The power of wind turbines is also affected by how equally the wind can flow against the blade’s surface from all directions. That is why large wind turbines are mounted on high masts, so that houses and trees do not cause turbulences.

http://www.youtube.com/watch?v=7qd8ulm9nec

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Part IV Technology

1. In-feeding

1.1 Function

For an in-feeding system it doesn’t matter if the generated wind energy is fed directly into the public grid or into one’s own house network. The required equipment is identical:

Wind turbine, stop switch, net inverter with internal or external surge protection, digital display for control and the power connector.

The current generated by the three-phase generator of the turbine must be rectified inside the inverter, then transformed to 230 Volt (alternating current) and synchronized with the grid before it can be fed into the network. The inverter must either be connected to the grid at all times (stand-by) or switch on instantly. The inverter consumes 8 to 20 Watt for its own operation and switches from grid supply to self-supply once the minimum voltage of the wind turbine is reached.

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2. Battery charging

2.1. Set-up

If no public grid is available, wind turbines can be used to charge batteries for energy supply. This is called isolated application.

For this, you need a charge controller, batteries and a sine-wave inverter that transforms the voltage of the battery into 230 Volt (alternating current). If the module is big enough, you can power all normal household appliances.

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2. Wind measurement

Why does the turbine not start? How much stormy wind can it withstand? What is the annual average wind intensity?

Those are the questions that not only interest the planners of large wind turbines when looking for an ideal location. Owners of small wind turbines also want to know how good the planned location is. In many cases, one can find the reason for a noisy operation or a reduced power output through measurements.

Some wind turbine enthusiasts buy expensive weather stations with radio wind gauges to find the ideal location. They would have to measure for months and still only get the average value and the peaks. They would not know how squally and turbulent the wind at this location is. A few meters to the side and the values could be better or worse.

In order to find the best location on a plot of land, no elaborate wind measurement is needed. It is enough to set up sticks with wind vanes. Barrier tape has proven itself for this purpose. A band of 1.5 m (without the knot) is fixed on the top of the sticks. Wherever the tape vanes fly highest and steadiest is the best location for the mast. We tried it: If the band is horizontal, the wind has around 3 m/s. That is when you can start generating power. If the band winds itself around the stick, then the turbine would often swivel out of the wind.

But, tell your neighbor beforehand what you are doing. Otherwise, he will think you discovered a new festive tradition or you put up Tibetan prayer flags.

Whoever is interested in precise measurements has to buy a measuring device.

The most precise ones are the shell anemometers: Hemispherical shells rotate around an axis and emit electric impulses, which are transferred via cable or radio to the displaying device. The data is processed by a microprocessor so that one can extract different information: average, maximum, annual, monthly, weekly and daily values and the frequency of specific wind intensities.

There are handheld devices and installed measuring devices. You should make sure that the integrated memory is enough to hold the data of at least one week, after which the data can be read. Electronics shops mostly offer handheld devices for surfers and hang-gliders, which only show the current wind speed of few days.

www.windmaster2.de

Windmaster 2 (Flash-Animation)

Better, more expensive measuring devices store the data of up to some months and allow a detailed assessment of one location. With such devices, one cannot only measure the wind speed, but also the annual distribution of wind intensity, the so-called Weibull value k.

Electronics shops offer modern weather stations with wireless transmission and computer connection. Pay attention: Due to the transmission, the measurement points are 15 to 45 seconds apart, which is not precise enough for our measurements. The wireless transmission is also limited to a certain distance. A mast at a larger distance therefore requires a measurement device that can be mounted at the foot of the mast. These devices store the collected data on memory cards, which can be read once a month via a computer. Unfortunately, they are rather expensive and only worthwhile for location measurements of larger wind turbines.

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5.7. Safety

You should always keep in mind that the wind turbine is exposed to enormous pressure during a storm, even if it mechanically evades the strong squalls. You should regularly check the fixation of the mast, as well as the screws of the blades and the wind vane. Otherwise, parts can get lose through vibrations.

Before predicted storm squalls, you should short-circuit the wind turbine. In doing so, you elongate the lifespan of your wind turbine and minimize the risk of a collapsing mast or bursting blades. Large wind turbines are also stopped during storms!

Make sure to extend your liability and building insurances after mounting the wind turbine. Most of the time, a written notice or a telephone call is enough.

Imprint

Author: Günther Hacker

D-78112 St. Georgen / Germany

Tel. 0049 (0)7724 / 7377

info@wind-mobil.de

E-Book 2014

Website Solar-Wind-Team: Peter Hacker www.fatrat.de

Cover + 3D graphics: Steffen Hacker www.alexandsteffen.com

Photos: Günther Hacker, Gabriele Jerke, Steffen Hacker, Peter Hacker, Michael Heyde, Marcel Hendrickx, Christof Stalder, Thomas Fischer, Thomas Schmidt, Johannes Heger, Tjeerd van der Bij, Rolf Heckmann, Hans Sonne, Matthias Sodeik, Lutz Miesel, Henk Penning, Holger Becker, Wolfgang Zwick, Sven Grothe, Alfons Rogg, Klaus Krieger, Daniel Beer, Dr. Horst Brunck, Karl Müller, Florian Lachinger, Bauer Energietechnik, Christoph Blattert-Blüm, Hummelmasten, Bornay

Videos: Johannes Heger, Starboard Sun, David Adamko, Southwest Windpower, Bornay, Otto Heinz, Poindexter Smith, Solar-Wind-Team, MrBangthamai, NMSU Professor Thomas Jenkins, Percul9or

Collaboration: Monika Hacker, Gabriele Jerke, Steffen Hacker, Peter Hacker, Andrea Fritz

Translation: lengoo UG www.lengoo.de info@lengoo.de

E-Book creation and E-Book website: Andrea Fritz www.ebooktreibhaus.de

Published by: epubli GmbH www.epubli.de

ISBN 978-3-8442-8773-8

All rights reserved. Copying and reprinting, in whole or part, is forbidden without authorization of the author.