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  • Writer's pictureNed Patton

A Quick Update on Renewable Energy and Composites – The interesting and the Strange

#String_and_Glue, #Renewable Energy, #Wind Turbines, #Composites in Renewable Energy

This week I want to talk about some new and – at least to me – interesting developments in renewable energy, primarily wind turbines, but there is a bit about use in solar energy installations a bit later in this newsletter. Just as a little background, the windmills that you see in places like the Coachella Valley in California are horizontal axis turbines, usually with three blades. These machines are oriented with the blades facing into the wind and develop power based on the lift force on their blades. These are the wind turbines that I have featured in pics in this newsletter many times – primarily because these machines are part of my early background as an engineer.

First, a little about aerodynamics for those that don’t already have an idea what some of these terms mean. There are two aerodynamic forces, lift and drag. Lift is what makes an airplane fly, and is also the force that powers most installed wind turbines. The little pic to the right here shows what these two forces do for an airplane wing (or a horizontal axis wind turbine blade), just so that you get an idea what they are. Most wind turbines that have been installed use the lift force from the airfoils that you see and that I have shown pics of in this newsletter in the past. What happens aerodynamically is that the air has to speed up as it goes over the top of the airfoil which makes the pressure lower on the top of the wing than on the bottom of the wing – which gives you a positive upward force – called lift. For a wind turbine blade, the angle of attack or the angle at which the turbine blade attacks the incoming air stream is always positive upward, as in the front part of the airfoil is always pointed toward the incoming air and usually to reduce drag is directly in line with the incoming air velocity vector. I’m not going to bore you with the math, but think about the turbine blade as an airplane wing in level flight. This is the most efficient direction for a lift-based wind turbine. If you look at most of the larger wind towers they have a little weather station on top of the Nacelle that senses the direction of the wind do that the axis of the wind turbine can be driven into the direction of the oncoming wind. All of this is automated in the large wind turbine farms that you see.

Drag, on the other hand comes in two different types. Most of the drag force is what is called form drag, which is the force that the wind exerts on the airfoil as you try to push it through the air. This is of course overcome by the thrust provided by the airplane’s engines, so usually minimizing drag is a very important thing to do for an airplane. It is also a very important thing to do with a lift-based wind turbine because drag takes away from the total rotational speed of the wind turbine, robbing some of the energy from the lift forces. That is why everything that can be done to reduce drag on a lift-based wind turbine is critical to overall performance.

Drag-based wind turbines on the other hand use the drag force to turn the blades and generate electricity. There are two types of these that are fairly common, the Savonius turbine or the Lenz turbine. The Lenz turbine pictured here is more efficient than the Savonius, so that is the one I am going to show as an example. The pic to the right here is an example of a simple Lenz drag-based wind turbine. These are simple to build and operate, but are much less efficient than the lift-based wind turbines that you see more of. These types of turbines are usually only installed in locations where the wind speeds are too low to install a large horizontal axis wind turbine because they are simple, inexpensive to build, and start turning at lower wind speeds than the common horizontal axis wind turbine.

So, here comes the new and the strange part, and the reason that I’m writing about this in a composite materials newsletter. There is an article in Composites World about a new design drag-based wind turbine that has been developed by a company by the name of Zenecore (New York City). This company has developed and is working on scaling up a drag-based wind turbine blade based on their experience with monocoque ribbed composites with thermoplastic microspheres to reduce weight. And this thing looks pretty strange for someone that is used to the thin blades of a typical horizontal axis wind turbine.

But the company claims to be able to harvest a couple of orders of magnitude more energy from the same diameter turbine. And this thing looks to be a variation on the theme of horizontal axis wind turbines, but using a blade configuration tailored to use the drag force of the wind crossing over the blade to generate electricity. They have a concept that has several of these things on a large structure that could be anchored either on land or offshore to generate quite a bit of power. The pic to the left here is just such a structure, and it looks pretty strange for someone used to the thin three bladed lift-based horizontal axis wind turbines.’

But, enough about windmills. What’s happening in other areas of renewable energy where composites are making inroads. Actually, composites are making fairly significant inroads into the structures and framing that holds solar panels.

Glass fiber composites are stronger than aluminum and about half the weight. And glass fiber / thermoplastic composites are quite inexpensive, easy to manufacture into fairly complex shapes, and have extremely long life expectancy. So, quite a few of the solar panel manufacturers as well as the fabricators of the framing that holds up all of these panels in the large solar panel farms are turning to glass fiber/thermoplastic composites for the bulk of their new infrastructure. The pic to the left is an example of this where the frames and the support structure are all made from molded fiberglass – specifically a product called Sheet Molding Compound or SMC.

This stuff can be cut off of a roll and formed into whatever shape you want and you can do it inexpensively and very rapidly, making this a lower cost, longer lasting alternative to metal structures. There are even concepts for building very large arrays of solar panels using nearly all molded fiberglass supporting structures. This is because these materials are very weather resistant, including UV resistant, have superior corrosion resistance to metals, and are also fire retardant because of the resin systems used. The picture here is of a rather large array of solar mirrors in Seville, Spain all pointing at these two large towers. Infrastructure as large as this installation is made possible and affordable because of the application of glass fiber composites.

As you can see, composites are making significant inroads into the renewable energy industry, and there are even some new and to my eyes a bit strange things being done that once you understand the physics make a lot of sense. Just thought I would share this with you.

That’s about it for this week. As for my book that is coming out, my publisher says August, and that it will be about two weeks after I see the proofs that the book will hit the street. So, I will keep you all updated. And as a reminder, if you want to pre-order the book, here’s the McFarland pre-sale link:

See you all next week.


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