… народные ветряки! Rotating Header Image

homemade wind generator

Perfect wind turbine criteria

Янв 26th, 2010
by Slawa Gorobets.
No comments yet

Thus, the task of building a good wind turbine is transformed into a task to build the right kind of a wind turbine for a certain place and a certain consumer. Here it would be useful to do a research of the existing market and to define the goods and the bads of the designs available.

Now it’s necessary to set up some characteristics (preferably digital ones) and apply them to the regions of operation. The key characteristic of the operation area is its “productivity”, i.e. the quantity of energy which the wind potentially has.  This “productivity” is rather good characterized by the wind speed in annual figures, for example. The CIS regions could be divided in three regions according to the annual average wind speed:
– lower than 3m/s
– from 3 to 5 m/s
– more than 5 m/s

At the same time one should keep in mind that the wind speed does not have an equal time distribution. For the CIS territory there is a general characteristic with light winds comprising 70-80% of the time, moderate winds – 15-20%, high winds – 5-7%, fresh gales – 2-3%, storms – 1%. As you can see the average wind speed is about 1-3 m/s. Storms are very rare. It stands to reason to keep in mind the light winds even if you have to stall or fold down your wind turbine when there is a high wind or a storm. The system of folding down a wind turbine when there’s a high wind complicates its design but it is the other side of the question.

Now it’s time to have a look at the offer. The great number of the models offered is two-, three- or four -bladed horizontal axis turbines of different sizes and power output. Multi-bladed turbines are less common. Companies offer various sets: from separate units to the full package including assembling and checkout on the customer’s site. Few models of the own made, many offers of imported machines – from Chinese to well-known European makers.

If we look at the digital characteristic, it appears that the customer contract demand is gotten out at a speed of 8-15 m/s; at the same time the lowest wind speed (so called pull away speed) is 2.5-4 m/s. A bit different characteristics you can expect from multi-bladed and jib wind turbines. The lowest wind speed is 0.5-1.5 m/s. The peak power is at the speed of 6-20 m/s. The limit operating speed is 15-30 m/s. The difference between characteristics is mainly defined by “the filled-up” of the periphery spun by blades. When the blades rotate fast enough, the entire periphery is used rather efficiently and does not depend entirely on the quantity and surface of the blades. But in light winds multi-bladed and sail turbines have an obvious advantage. They have it all to catch the wind and are able to convert very low airflows into the useful yield. With the wind intensification they lose that advantage and with gales they’re outdone by the “bladers”. The friction loss grows along with the speed.

Now let’s try to anchor wind turbine characteristics to the territory. It is clear that in the major part of the CIS territory “bladers” stand or work in half-force. And costal districts would make an exception. Just the same thing we can see in the consumers’ report. The wind machines fall short on expectations. The power output is not enough taking in account long periods of time.
There’s less experience gained with multi-bladed and wind sail machines but performance expectations and the experience at the disposal indicates it to be more effective over the major part of the CIS territory.

Maintenance issues and solutions

If we generalize the maintenance issues of the wind turbines, it makes only two – light winds and gales. Consumers get irritated watching the high-priced equipment stand idle because of the feeble wind of after it was damaged by the storm. Besides it is important to do the aftermath. Engineers underestimate the consequences of the dead time caused by the windcalm and overestimate consequences of the storm wind. As a matter of fact, any dead time means negative profit. Several weeks of windcalm could do much harm than a unit change within a few days after the turbine was damaged by a storm.

An increase of power limit is not an answer as well. If you buy a wind generator of the maximum capacity of 10kWt to let it generate only 2kWt, it would be a pricy buy to say the least. In the long run all the extra costs will be applied to the energy price.
On the other hand the potential to resist storm winds will also increase the cost as the design gets weighty. Maybe there is no need to resist a storm?  The grass doesn’t fight it! It just falls on the ground just to rise when it’s all over. And a palm tree could give away its leaves but saves the trunk. The leaves will grow back again really quick.

We could try to describe a perfect wind turbine:
– simple generator head of a given power capable to work at a low speed;
– light blades of large surface area to harvest energy from the lowest wind;
– a system of folding down the blades in case of the wind intensification;
– a footing which allows to lower the generator with the blades in case the wind intensifies;
– an ability to increase/reduce to some extent the wind turbine power output without redesigning it.

The generator design for the wind turbine should meet several basic requirements:
– generator should be a low-speed one; no scrub or sliding contacts;
– a possibility to switch the winding to keep the voltage within certain limits;
– simplicity;
– fabricability;
– servicability.

Vadim Belyaev, “Vetronet”,
Design Manager

Wind sail turbine – another step to the personal energy security

Янв 25th, 2010
by Slawa Gorobets.
No comments yet

Man always has been using wind energy. Cave ventilation or grain aeration for glumes removal all these are examples of the wind usage. For any savage crossing a lake was yet another experience of wind being helpful or hindering. So it is clear why boats have been rigged with sails since the beginning of time. Then came the turn of “land-based windjammers” – wind turbines.

Wind turbines are rather ancient device as they had been used for water elevating, sawing up logs, grinding flour – that is, in modern terms, to obtain mechanical energy. Owing to wind turbines the civilization received an evolution impulse. Then the decline came on. Windjammers don’t range the seas and oceans and wind turbines hardly can find its place in the energetics. Why did it happen?

There are definitely more powerful and handy energy sources. The demands for the quality of energy have definitely been stepped up as the lack of voltage or even voltage drops irritate consumers.
But material and device technology is not at a stop! Nowadays it should come as no surprise that there are composites and energy converters. Automatic machines and robots are doing hard and dangerous work for humans.

So why modern wind turbines are so expensive?

Why an owner of a Jeep that has a few hundreds of HPs under the hood can’t afford having a wind turbine and his grandfather could build a windmill to grind flour for the whole community.  Windmills had been standing at almost every village for tens or even hundreds of years. There are lots of reasons for that but I think the main ones are wrongly interpreted or being hushed up.

The modern energetics inclines to big stuff. The most powerful reactor or the most powerful turbine is a matter of the country’s international image! There is the same approach for wind turbines: the biggest wind turbine or the most powerful wind power generator is the pride and envy. One of the indicators of wealth and success of a country is quantity of energy per capita – the more, the better!

On the other hand centralized networks are just another way to control population or even the whole world. A law abiding citizen consumes energy working to pay the energy bills and keep his head down.  If something goes wrong, the master switch goes down! Nowadays the one who has energy, rules the world.

But it’s not the case with the environmentally safe, alternative, green energetics. On one hand the energy is everywhere – sun, wind, waves are all around us. On the other hand the thickness is not that high and to harvest it energy receivers of large area are needed. Two approaches are possible here. A “sky-high” generator could be constructed which is oversized and very expensive (that’s the common thing with them) or to make hundreds of little ones scattered over a vast territory literally in every backyard.

But only the oversized giant fits into the total control centralized system and the hundreds of little ones could cause losing of the control and in the long run, the loss of the power itself. Sure enough no one is willing to give up on power! This is the reason for the evident and concealed opposition to the “small energetics”.  No one has a stake in research and development of compact moderate-priced devices. Some models are developed and produced by efforts of few enthusiasts. But these models usually are copycats of the commercial giants just on a considerable scale.

There is the following issue behind it – integrity of the design characteristics. Actually design calculations recently become more available and the necessity of experimental verification was pushed to the sideliners.  If you look through any of the online forums focused on engineering, you may notice that a great deal of trained (and not) users lock horns with each other on theoretical topics and no one sets about having a field test made. Those who actually make it to the metal are being watchful of as well as their practical results. The rule of good theory being tested by practice is somehow forgotten. As a result clueless schemes emerge just to discredit smart ideas.

If you put the abovementioned in wind energetics terms, you could see that the vast dry land territories are not perspective for setting up wind turbines as the wind intensity is insufficient. I beg you pardon! If this approach had been used by shipping companies, no one would have designed off-roaders as the railway is more advantageous for shipping the goods. But there is an approach for every task. If the wind was not sufficient for flour grinding, our ancestors used to spread sails between the blades and carried on. But modern “connoisseurs” can’t stand a wind sail turbine just because it doesn’t look too much of a propeller and they go on with shooting the bull! The airplane propeller theory is really well developed but why to apply it to an almost static mechanism? For different areas with different wind intensity different designs of wind turbines should be applied! A Formula 1 car cannot do the same thing a heavy-duty dump truck does!

Thus, the task of building a good wind turbine is transformed into a task to build the right kind of a wind turbine for a certain place and a certain consumer. Here it would be useful to do a research of the existing market and to define the goods and the bads of the designs available.

To be continued in “Perfect wind turbine criteria”…

Vadim Belyaev, “Vetronet”,
Design Manager