Introduction: How to Test a Wind Turbine - an Instructable in Progress
Testing wind turbines isn't as easy as it may sound. Energy in the wind varies widely, changing with temperature, altitude and of course, with location, time of day, and time of year. Understanding what's going on with a turbine requires measuring at least 3 things, at the same time, ideally many times per second, for long periods of time. I'm going to show you how I've done it, and discuss other possibilities for how it can be done.
I've been working in this field for quite a while, and to start this instructable process, I've made the youtube video attached and am making this instructable to help people understand some of the complexity of this kind of testing, and why I'm excited to be testing my new design.
I'll be adding more to this instructable as I complete this round of testing. Both the turbine, and the instructable are works in progress.
Wind is a tricky resource to capture most especially on a small scale. In the past decade or two most north american small wind turbine manufacturers have gone out of business, and few new ones have popped up to replace them.
The industry was full of manufacturers making extraordinary claims for both their HAWT and VAWT products, but after the green energy research boom that went along with the fear of fossil fuel shortages in 2007-8, a lot has changed.
A big change was driven by the unlikely claims of industry, and the Small Wind Certification Council was founded with the mandate to encourage manufacturers to have their turbines 3rd party tested and the results certified so that consumers would have a reliable supply of performance information. This process and other testing showed that most small turbines are poor performers, and may not even return the energy it cost to manufacture them, when installed in most sites. Good information drove a lot of manufactures to abandon products or go out of business (like UGE, turby, SouthWestWindpower,).
One of the largest realizations that testing and evaluation brought forward was that few people live in windy enough environments for a small wind turbine to function usefully. It takes a lot more wind than most people expect for a site to produce useful power.
With Solar power it's fairly simple to assess a site, basically most sites that aren't shaded, are likely OK, one might be 2x as good as another, but it's unlikely that one site will be 10X as good as another. Wind is different, sites will commonly have average wind speed differences of 10X, and because wind energy is cubic to wind speed, a very windy site may collect 10,000 x the energy that a low wind site may have.
So with all that said, why jump into testing turbines that may not even be useful?
For me it's because I saw a historical technology, the Savonius VAWT, as misunderstood by most researchers who characterized it as a simple "drag" based turbine and therefore unlikely to ever reach a high enough level of efficiency to be useful. I started research to see if I could see any radically inexpensive way of building them was possible, hoping to make them so inexpensive that it wouldn't matter if they were not as efficient. I had the good fortune of the budding internet as a resource, and a wide skillset. In diving a bit deeper into the understanding of Savonius turbines I found a sea of controversy. In the 1970's what was hoped to be a thorough evaluation of the Savonius type of turbine was done by a USA federal gov institution (the Blackwell report). It relied entirely on wind tunnel tests, and it found that the Savonius, even when optimized as a two bucket rotor about 2x as tall as wide, and with a small amount of overlap (not joined) was a little more than 1/2 the effectiveness as a HAWT of the same size range, and the HAWT could be made with less than 1/2 the material.
On top of the apparent low efficiency and higher cost to construct, researchers testing in the real world, not the wind tunnel, found that they couldn't achieve the energy collection efficiency from the Blackwell report.
Little research was done after this, though there were a few outliers, including in my own back yard, at the University of British Columbia. Researchers Modi, Fernando, and Benesh questioned the idea that a Savonius had a single mechanism of action, Drag, and postulated that a portion of the energy collected by the turbine was from lift, and that might be able to be optimized to improve functioning. They tested an improved rotor vs the historical design optimized by Blackwell in a wind tunnel, and found a large increase in energy collected. Then when they tested it in the real world, it didn't live up to the expectations built on wind tunnel data. This took place in the 80's when green energy and sustainability weren't the concern they are now.
In the 90's and early 2000's some independent researchers were attempting to optimize the Savonius type of turbine, and were confounded by the difference between wind tunnel and real world results. Finally a masters student Ian Ross took on the investigation, and in 2010 published a paper "wind tunnel blockage correction factors in high solidity VAWT's". He found that wind tunnel investigations of VAWT turbines was much more complex than had been expected, and that in cases where the turbine was greater than 5% of the swept area of the wind tunnel, results would be deceptive, especially in cases where standard blockage correction factors were applied. This investigation also found that they historical Savonius was likely much less than 20% efficient, and closer to 5%!
Had I known that in 2005, when I started down this path, I may have changed direction earlier, and never developed the turbine I patented in 2007, with 3rd party testing in 2012 that revealed an efficiency of between 29 and 31%! As good or better than the best small HAWT systems of a similar size!