Saturday, July 12, 2008

Why Philippe Starck's Wind Turbine Probably Won't Work

Some wind turbines on the market today will generate more disappointment than electricity and that poses a major threat to the eventual acceptance of small wind systems for alternative home and business power. Wind power properly designed and installed works, but you get what you pay for. Wind power that looks too good to be true, probably will provide a great conversation piece, but not much electricity.

Philippe Starck's mysterious wind machine

The difference between a wind turbine that works and one that doesn't has to do with lift verses drag and also with the relationship between wind speed and turbine power. Some wind turbines being hyped now appear to violate those laws. The most unlikely candidate for successful wind power comes from French designer Philippe Starck. His "Democratic Ecology" wind machine, as described at Inhabitat, looks like a drag-effect machine.

If you have seen a cup anemometer that measures wind speed, you have seen a drag-effect device. It can move no faster than the speed of the wind it is being pushed by and because of it's own drag, it can't even achieve that speed. It can't go faster than it is being pushed. Another example would be a sailboat sailing with the wind directly behind it. Put out every sail you have and you will still be sailing slower than the wind speed and not generating nearly as much power as you would if you were sailing a "reach" perpendicular to the wind and using the gift of lift. Drag is the aerodynamic force parallel to the flow. Lift is the aerodynamic force perpendicular to the flow and it is much more useful. As a student pilot I was terrified by the difference between flying fast enough for the wings to have lift and flying too slow where lift suddenly disappeared or stalled. 

When a wing or a sail or a turbine blade does not have enough airspeed, it loses lift and has only drag, which is a real drag when you are falling out of the sky like a rock or watching a very expensive wind turbine just sitting there motionless. So when you are shopping for wind power, remember that lift is uplifting, drag is a drag.

The other key piece of physics to know as it relates to wind power is that the relationship of wind speed to wind power is not a linear one. The power of a wind turbine is proportional to the cubed velocity of the wind. In other words, a little difference in wind speed, means a huge difference in power output. The power output quoted on some wind power devices is with a constant twenty-miles-per-hour wind, which might be useful if you lived on an mountain ridge, but not if you live in a typical neighborhood in say, Indiana. You need to know your local average wind speed resource at the height you intend to mount the device. That is accomplished by mounting an anemometer on a tower at the proposed height or several heights to see what would be most productive. You would also want to determine your total electrical load and how much of that you want to produce by wind power. One good resource to start with to go through that exercise would be Small Wind Electric Systems: A Consumer's Guide. You will learn that tower height is critically important to get up out of ground turbulence into clear air with a more constant wind resource to produce much more power. Remember power relates to wind speed cubed, so a seemingly small difference in wind speed gained makes a huge difference in power output.

I used to be enamored by building-integrated wind power. Now I think that strategy in its current form may be detrimental to the wide acceptance of distributed wind power. Wind power integrated with a building is likely to be a drag-effect device and thus not produce much power in relation to the wind resource. That wind resource will likely be mounted within the turbulence zone that surrounds structures and trees. If it is mounted on the building it will introduce another couple of challenges. A turbine generating a significant amount of power will be subject to a significant amount of lateral force, which will have to be accounted for in the design of the supporting structural system. If the structural system has to be reinforced, the cost/benefit ratio may be significantly impacted. Even if you account for the structural load, there will be the vibration associated with a spinning machine. Can that vibration be isolated such that noise and discomforting vibration are not transmitted through the structure? Why not just invest the extra money in a a quiet building-integrated solar photovoltaic system with no moving parts?

Like many of the new building-integrated wind turbines, the Philippe Starck model is preceded by promises of amazing performance. What remains to be communicated are the numbers for power output at various wind speeds, mounting details and system costs (the turbine itself is supposed to sell in the $600 range). How long is it guaranteed to last and what kind of maintenance is required? As a general rule, the smaller the turbine, the faster it spins and the shorter its life. Big turbines spin relatively slowly, last longer and produce more power with less noise and vibration. 

"I was a producer of materiality and I am ashamed of this fact," Starck told Die Zeit weekly newspaper. "Everything I designed was unnecessary. " 

Maybe he is not yet over that stage in his career development. Show me the numbers on your new eggbeater, Phil. 


Larry Dudley said...

I am thinking over your definition of lift vs. drag. Could the problem be made cleared (perhaps only to me!) by saying that with an wind cup device you have an advancing and a receding element, with the receding element being responsible for the drag and the advancing one being responsible for the lift? And that this does not occur with turbines because they face into the wind, and therefore both blades are perpendicular?

In other words, with Starck's device, one blade is going with the wind, but the other in coming back around is fighting it by turning into it?

I would note that Starck's designs are often spectacular, but unusable -- check out his famous barstool, for example. You would have to be a circus acrobat to sit on it!

joe shoemaker said...

But it's so sexy... I very much want it to work...


prairie zen said...

Does anyone know what happened to the "Democratic Ecology" wind turbine, designed by Philippe Starck? I can't find it for sale anywhere...

tharrison said...

Thanks for posting the only technically useful bit of information on this design. Nine months later and it doesn't look like they actually exist (yet).

It is sexy though... :-)

Anonymous said...

I think you might find that this is not a 'drag' based design, that the verticals are aerofoil shaped, and therefore based on lift principals. otherwise as you say the returns would be really minimal. see Turby and Vertical Wind Energy for other lift based vawts.