Wind turbine comparisons. 6

[waross]

I have a customer who operates a small electric utility on an island. Their peak load is about a megawatt. With the high cost of fuel the retail price of energy is about $0.42 US.
They are considering a wind turbine. They are considering installing a vertical turbine on top of a range of hills. I have been asked to comment. I'm heading out to the island next week. tmawind.com is the proposed supplier.
Any comments or information is welcome. Comments on the feasibility of using used wind turbines are also welcome. I don't even know what web sites to check. I'll be happy to receive relevant URLs.
Thanks in advance.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[davidbeach]

Think of the wind turbine as a block of negative load. Can the present system deal with block loading and unloading with a step size that large? One nasty, nasty, feature of wind is the plot of the output vs. wind speed curve; output goes up nicely with speed until the point that speed exceeds a maximum value and the output drops to zero. When the wind source instantly disappears the rest of your generation has to respond instantaneously.

How will the turbine supplier meet their VAr requirements for excitation? Hopefully with local capacitors and not by pulling the VArs from the "system" meaning your existing generation.

 

[waross]

Hi David Beach.
Thank you for the reply. I will be watching the VAR issue. I will add capacitors if needed. I have discussed with the manager the issues with the diesel engine governor. I pointed out that as the wind varied, the generator throttle would be hunting back and forth and that the generator will have to be capable of taking the whole load almost instantly.
I have read quite a bit about conventional turbines, but I have not seen anything about vertical turbines. I'm wondering how they compare with prop type turbines. There is not much info on the web site, but they claim to be able to sustain much greater over speed winds than prop types.
Thanks again.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[eyec]

check out

http://www.massmegawatts.com

they have a multi-axis vertical arrangement

Steven C
Senior Member
ThirdPartyInspections.com

 

[dalcazar]

how much wind do they actually get? the main problem people have with installing a turbine is that they bite the bullet and spend the money and then find out they don't have enough wind to make it worthwhile.

Vertical axis turbines have a few notable problems, some don't apply to a savonius rotor like that, but at least one that does is that when you have to do any major repairs to the generator or the main bearings, it can mean removing the entire turbine to gain access to it, if the generator is connected directly to the turbine then this particular model will have that issue. they may have a belt or shaft drive to the generator which eliminates that problem, but you´ll still have the issue with the main bearings. This particular model won't be as suceptible to them as a darreius rotor.

They can also be tricky to assemble depending on the configuration, most need a crane to be brought up for installation and service, and crane rentals aren't cheap. the rotor for the TMA turbine looks like it's built on the spot in pieces and looks like you wouldn't need a crane, but make sure to ask.

A vertical rotor also doesn't have the height to capture the highest speed winds which are usually at least 50 ft above ground level.

Smaller horizontal axis turbines can be hoisted up by hand by a crew of people using a pulley system. Larger ones usually have to have their rotor blades shipped in one piece and that can get very expensive.

Logistics may well be the limiting factor in turbine size and type depending on what kind of access there is to the island.

Some people have had great success buying used wind turbines, provided that the turbines are in good shape. If I remember correctly, someone in colorado bought one of nasa's very large experimental wind turbines for around $100,000 and it churned out a very profitable amount of megawatts before one of the blades struck the tower in a big storm and it destroyed itself. I forget the reference and the exact numbers on this.

All in all the TMA turbine looks like a decent bet provided their product is as efficient at they say it is, because from reading their page they talk about being 45% efficient in a wind tunnel, but not in practice.

 

[waross]

Thank you, dalcazar;
I assume that there is enough wind. they bare on an island off the coast of Honduras. The proposed location is atop the highest range of hills on the island.
So far I had a luncheon meeting with the general manager of the utility, and we had more to discuss than wind turbines.
I will have more information next week.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[metengr]

Installation of a wind turbine farm (one or more machines) requires several commissioned studies that should be performed by a 3rd party.

First, is a commissioned wind study of the site. Once this is completed, the results of this study would be part of a request for proposal (RFP) regarding wind turbine OEM's. Once you get back bids, now you perform a net present value analysis to determine if the wind farm is a good business decision. There may be political forces at work to drive toward using wind, but lets fact it you should be in the business to make money and provide a reliable product.

What I listed above is a short cut of a very lengthy process from start to finish for a wind turbine farm. Now, for the various wind turbine OEM's based on current availability and O&M (best to worst);

GE
Siemens
Vestas
Mitsubishi
Clipper
and last, is Suzlon.

I would not by used equipment unless you have access to a detailed maintenance history and understand the design of a wind turbine. The two main sources of industry problems with wind turbines has been gear box reliability, main shaft and generator bearing issues and blade cracking.

 

[FreddyNurk]

I agree with metengr, there are a number of areas that need to be assessed in terms of wind resources and suitable locations, certainly before the turbine is installed. I also note that Enercon is not on the list given, though I'm not sure where it would rate in metengr's list.

Another factor that needs to be taken into account, certainly if they're looking at more than about 20% wind penetration, is the issue of whether the wind turbine is capable of being given a set point for power output, and what the likelyhood of the generational plant being pushed backwards is.

I'm assuming at this point that waross is most likely aware of these issues, or the size of the wind turbine is nowhere near the rest of the generational capacity. A company I used to work for had much success in integration of wind turbines with diesel generation plant, along with appropriate measures for counteracting the possibility of reverse power on the diesel gensets in wind gust situations.

The Enercon turbine is quite good at being able to be regulated, other brands not so much. Worth noting too, is that the Enercon units don't suffer from the same gearbox issues, but do have more maintenance (as far as I'm aware) in the power processing gear.

 

[waross]

Thanks for the responces. I am aware of most of the points mentioned.
A couple of points that hit the mark:
Wind velocity;
The customer has wind recording instruments that have not yet been installed on site.
Percentage of wind energy of the system total energy. Not a problem with the first turbine. May be an issue if more than one turbine are eventually installed, but the vendor claims that the turbine may safely free wheel in high wind/ over driving conditions.
An interesting feature of the site is that the geographic features may lend themselves to pumped storage. (Subject to enviromental safegaurds. We don't want to polute the ground water with sea water.)
A combination of wind energy and pumped storage may allow almost 100% wind derived energy to supply the community. If anyone is looking for a research site.....
Back to the immediate issues;
The wind tunnel test reports and computer simulations paint a glowing picture of performance. However, this is a fixed stator machine which cannot turn into the wind. There is one sentence buried in a brochure that mentions that off axis winds may decrease production by 5% to 8%. I am nervous that such an important issue seems relatively unimportant to the designer/builders.
Any comments on this issue friends??

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[FreddyNurk]

I would have thought, and admittedly this is just educated speculation on my part, that since the majors (Vestas, Enercon etc) are all capable of pointing the turbine into the wind, then there would be benefit in doing so.

Such systems make the turbine more costly, in terms of systems to detect the wind direction, the mechanics of rotating the nacelle as well as from a reliability point of view (I believe that its possible to shear the cables in an Enercon turbine, but there are plenty of prevention mechanisms to stop this). As such, I'd be very sceptical of manufacturer's claims that this isn't necessary.

Having said that, it should be taken into account during the wind assessment stage to see if the return (and noting that the figures quoted are best case) will be good enough to allow use of such a turbine.

As for the freewheel out of the wind issue, I've noted that other turbine manufacturers equipment can also do this, the main issue with doing this on a weak grid where the wind penetration is high, is that during the time that it takes for the turbine to 'feather' the blades out of the wind, output greater than the setpoint often occurs. It is during these periods that the risk of loss of primary generation plant is greatest due to the prior mentioned reverse power issue.

Note too that this is different to solar power, whereby the primary plant must be able to handle large block loading, but the solar output cannot exceed the installed (solar) plant capability, and thus the issue of reverse power is nowhere near a problem, particularly if you scale the solar to be less than 100% of generational capacity.

Again, its not such an issue when the output of the turbine is nowhere near the spinning capacity of the plant, and the plant is capable of quick loading changes, but since your suggested project is an isolated grid, with transport difficulties for fuel, I'd imagine that they would be pushing for as much renewable sources as possible.

 

[waross]

Hello FreddyNurk;
Thanks for your reply. This is a verticle turbine. See the brochure at tmawind.com
The customer is just exploring options at this point. The ability to erect this type of turbine with much smaller cranes and maintain without crane services is a plus on a small island.
I was pretty negative at first but the possible advantages grow on you.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[dalcazar]

I have to agree waross, that the more I look at the turbine, the more it seems like a very good match for the location.

Is the island on the atlantic or pacific side? if they're on the atlantic side then you'll have to factor in the effect of hurricanes.

The buried sentence makes complete sense and isn't something I would worry about either, it's just a feature of the design that you have to live with, the 3 vertical columns for the machine help it to funnel air into the rotor, but if you get a wind coming from the exact direction as one of the colums then they're going to interfere in wind flow and decrease your power output and there is no getting around that fact. They have probably designed those columns to keep losses to a minimum while still maintaining enough structural integrity.

Given that the turbine will be on an island probably makes that particular issue of very little importance. They are going to be harnessing the power of prevailing oceanic winds which will change very little in direction thruout the year. A year's worth of wind data should prove that to be true (and the turbine should not be installed before the data is in really), so if the turbine is correctly installed and oriented it should almost never enter the decreased efficiency state.