Need advice on Polystyrene VAWT Blades

ConceptXConceptX Registered Users Posts: 3
Hi everyone, I am currently working on a project to develop a wind turbine. My design is of Straight Bladed Darrieus Wind Turbine (or Giromill). The blades I'm using is of the shape of NACA 0012 with EPS material for my prototype. I have done some reading and most people said I should coat my EPS blade with Fibreglass + epoxy resin. However, if I do not have the budget, can I just leave my wind turbine with a naked EPS blades? What are the effects on this? I need some advice. Thank you

Comments

  • JoshKJoshK ✭✭ Solar Expert Posts: 232 ✭✭
    For the type of blades that scoop wind the extra friction would be good on one side. But the side that makes the return trip should be smooth so they glide with less effort. If the blades are the airplane wind style then they should be smooth on all sides to create the desired forces. Otherwise I imagine you are missing out on some of the efficiency.
  • BB.BB. admin Super Moderators, Administrators Posts: 29,634 admin
    aYou need to coat them with something to protect them against UV--I believe that EPS is susceptible to Ultraviolet degradation. Whether or not you need epoxy+fiberglass or not -- I do not know EPS material strength to understand if it has enough to withstand the forces and leading edge damage from dust/insects/bird strikes/etc.

    Why a Darrieus wind turbine? In general, for optimum operation you really want to harvest your wind at, at least, 60 feet (~20 meters) minimum above the ground to avoid turbulence. I have not seen very many large format vertical axis wind turbines that are mounted on towers that tall.

    Running a turbine in turbulence and the Darrieus type with "naturally" pulsing output (maximum torque when blades are up wind/down wind, and having to pass through turbulence of upwind blade motion and support column), makes it very hard on the turbine/blade structure and alternator+drive train hardware.

    Here are some of the problems found when testing a Mariah brand VAWT (2009):

    http://www.nrel.gov/wind/smallwind/pdfs/mariah_report.pdf

    Because these types of "lift based airfoil" turbines (Darrieus and standard horizontal axis wind turbines) can "spin faster than the wind"--You need some sort of method to control maximum RPM. With larger HAWT designs. Brakes, shorting the alternator, and such are standard. But so is altering the blade pitch/feathering blades--Which you cannot do with a typical Darrieus machine. I am a believer that you need at least 2-3 methods to control turbine RPM/shut them down safely/reliably. And have read about more than a few HAWT units that have overheated the alternator when shorting the windings in high winds.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ConceptXConceptX Registered Users Posts: 3
    Thank you so much for your response, Josh K and BB. My full scale product will be using aluminium for the blades, but fabricating airfoil shape with aluminium will be very expensive. Hence for my prototype, I'm using only EPS, which is to show others that the wind turbine works. The efficiency of the prototype does not matter much compared to staying in budget (I'm doing a project for my university, budget is very tight).

    So, can my wind turbine still works fine if I use just the EPS? It's quite hard to find epoxy resin and hardener + fibreglass around my area. Probably I'm just going to stick perspex at the flat section of airblade just to make sure it's not that fragile. I'm worried will it affect the efficiency so much that the wind turbine will not work. Guys, please do advise. Thanks
  • JoshKJoshK ✭✭ Solar Expert Posts: 232 ✭✭
    For keeping costs low consider 3D printing moulds at 3Dhubs.com and getting your coatings at smooth-on.com The trial sizes are only $30 and depending on the size of your turbine it might be all you need.
  • BB.BB. admin Super Moderators, Administrators Posts: 29,634 admin
    I believe ConceptX is out of Malaysia... So any sources towards that end of the world may be helpful.

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ConceptXConceptX Registered Users Posts: 3
    Thanks for the websites, JoshK. But what if I am to stick to EPS? Can the wind turbine work with a naked EPS? It's not meant for long term, once I have presented the prototype, it will be probably kept in a closet. So what I want is just a working prototype.
  • JoshKJoshK ✭✭ Solar Expert Posts: 232 ✭✭
    I don't have any experience with EPS. Another thought... maybe you could just build a model and drive it with a motor for showing it off indoors?
  • ramlouiramloui ✭✭ Solar Expert Posts: 103 ✭✭
    Hello ConceptX,
    In the past, I have worked at polystyrene manufacturing facilities and, for that application, I believe that the mill made of EPS is going to come apart quickly because of the high centrifugal force if it picks up ant speed. That is why it needs to be reinforced. The EPS provides a lightweight form to build from. But it has no structural strength.

    Polystyrene comes in many different forms: EPS (expanded polystyrene) is made up of beads that swell and stick together when heated in a mould like a coffe cup. Similarly, XPS (extruded polystyrene) like insulation panels, has more stregth than EPS, but only marginally for such an application. On the other end of the spectrum, there is solid polystyrene which is much more resistant. That material also divides in 2 categories: crystal PS (CD boxes, plastic wine glasses which will shatter in a million sharp pieces) and impact PS (beer cup at the stadium, small milk container at the restaurant) which has rubber in it providing for some flexibility. This last one is what I would use if I chose to build a mill out of PS.

    Good luck!
    Off-grid cabin in northern Quebec: 6 x 250 W Conergy panels, FM80, 4 x 6V CR430 in series (24V nominal), Magnum MS4024-PAE
  • mike95490mike95490 ✭✭✭✭✭ Solar Expert Posts: 8,417 ✭✭✭✭✭
    Yellow paint seems to provide reasonable UV protection when I was researching painting exposed PVC pipes. It does not absorb as much heat as Black paint does, and so causes less thermal stress.
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