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Author Archives: tyler

The Power of Donations

wishlist2In the course of our Startup Campaign, many people have asked us what we will do with the money we raise. The easy answer is, “pay the rent ($500/month)”. A similar answer is, “pay ourselves” – we’d like to start receiving a living stipend starting in the New Year. But both of these responses give an incomplete picture of the situation and to what ends the funds we raise will be used. Because we charge a fee for our services and because a substantial amount of our time and energy is spent on project work, much of our future salaries and operating expenses will be paid for by earned income. That portion of our operating expenses not paid for by earned income is covered by donations and grants – the more donations we receive the less we need to charge for our services. However, to say that donations received will simply go to pay our operating expenses is to oversimplify the value and importance that this money plays. In essence, donations are the leverage by which we increase our ability to bring life-changing products and technologies to those in need – the more donations we receive the wider the array of promising projects on which we may work. Allow me to explain:

If we were to work only on those projects that could pay for program costs and operating expenses our hands would be tied with regard to project selection. We would be unable, as an organization, to consider those promising and worthwhile projects that were not well-funded enough to pay our rates as set by our hard costs. But, with the addition of a second revenue stream, charitable donations, we have more latitude in our ability to select mission-critical project work and to increase the likelihood that promising products come to fruition.

For example, for the last few years we have been working on a small-scale, open-sourced, wind turbine with the San Francisco Professionals chapter of Engineers Without Borders – USA (EWB). The goal of the project is to develop a low-cost turbine that could be used to bring a modest, if meaningful, amount of electricity to a substantial number of the 1.6 billion people living without regular access to electricity.

Currently this project is unfunded beyond prototyping costs, which are covered by EWB. All work that happens on the turbine is performed by EWB volunteers and Catapult personnel operating at a loss. As a result, the project, though promising, moves ahead slowly and uncertainly. If Catapult were able to dedicate a full-time engineer and design fellow to the project for three months we would be able to drive the design to completion, build and test a functional prototype, and travel to Guatemala to install a turbine for field-testing. The cost of this three-month program is only $25,000 but stands to benefit tens, if not hundreds, of millions of people. If that’s not leverage, I don’t know what is.

Another potential project we could work on is also energy-focused. The client, a small renewable energy generation company that uses agricultural waste products to power generators, would like to increase their operations from the 3,000 individuals they currently serve to the 50,000 potential customers they have identified. Part of their efforts to scale-up their operation involves finding a way to monetize the waste byproducts produced in the process of generating electricity. For $12,000 Catapult could conduct the material and technology research they need to evaluate this sustainable and environmentally friendly opportunity. While our potential client is able to afford $7,500, they cannot afford the rate we must charge. With a relatively small contribution from donations, Catapult would be able to leverage the limited resources of our potential client and to help them dramatically increase the scope of their operations.

While the type of products on which we work ranges from energy generation to medical devices and water sanitation, all are focused on the effort to realize the promise and opportunity that technology offers to dramatically and positively transform lives. With the addition of money we collect from donations, such as we have been raising during our Startup Campaign, we are able to work with idea-rich but resource-poor organizations to leverage the resources they do have to do an amazingly disproportionate amount of good. So the long answer to the question of, “What does my donation buy?” is the simple response of, “leverage”.

Testing Our Turbines in the NASA-Ames/AFDD Wind Tunnel

NASA-Ames 7x10 wind tunnel

The end of September saw a major milestone completed on the wind turbine project – we finished our wind tunnel testing at the NASA-Ames research center! The experience was fantastic and so far we have been blown away by the quality and quantity of data we collected. While it is still a bit too soon to publish our complete test results here (we still have a lot of analysis to do), I nevertheless wanted to get started by explaining our test set-up and posting a few photos from the tunnel.

Test Set-up

Since the beginning of this project we have focused on two vertical-axis turbine designs: Savonius and Lenz (see photos below). The major purpose behind our wind tunnel testing was to characterize the performance of these turbines, allowing us to select the most promising design and move forward with developing the alternator that will generate the electricity. In order to characterize the turbines, we needed to collect data on how they perform in different wind speeds while under different loads.

Savonius & Lenz Turbines

The end result of this testing will be a series of power curves (see chart below) describing the mechanical energy generated by the turbine as a function of wind speed and turbine speed (rpm). We also explored three different angles of attack for the turbine blades on both turbine designs to see how they impacted turbine performance.

Lenz Power Curve

The theory behind our turbine test is this simple equation:

Power = Torque x Rotational Speed

When the wind blows it hits the turbine, causing it to spin. In spinning, the turbine converts the energy contained in the wind into mechanical power. In order for us to figure out just how much wind energy is converted into mechanical power we needed to place the turbine in a flow of wind with a known speed and then apply a known torque load to the turbine while measuring the effect of the load on the turbine’s rotational speed. Referring to the equation above, we would supply a known torque and measure the rotational speed, thereby allowing us to calculate power.

The way we mechanically applied the torque load was relatively straightforward. We coupled a DC motor to the bottom of the turbine shaft and tried to turn the motor opposite the direction of the turbine rotation (see image below). Since the torque produced by a DC motor is a function of current, we could apply a known load to the turbine by applying a known current to the motor.

Wind Turbine Test Set-up

This test set-up, while elegant, nevertheless proved problematic as the motor we sized proved unable to resist the amount of torque the turbine was generating and we quickly overheated the motor. Another way of applying torque to the turbine was needed, fast. Thankfully, the NASA-Ames facility is full of advanced testing labs, many of them working on rotating equipment. The day after we identified our problem we had a torque cell in-hand and connected to the turbine shaft (see image below).

Torque Cell

This torque cell contained a strain gage mounted on a shaft that output a voltage based on how much stress was applied to the shaft. One end of the shaft was attached to the turbine and the other end had a mountain bike disc brake attached to it that could apply a drag load that would slow the turbine and provide the strain that the gage would measure. This set-up allowed us to apply our known torque load as desired and the testing went on as planned. The only downside was that we were unable to maintain a steady torque and were forced to take our readings dynamically as the torque applied and turbine speed varied. This scenario was less than ideal, but we still managed to collect a copious amount of data that should allow us to compensate for any dynamic and inertial effects.

Ultimately we collected all the data we wanted and, at first blush, the results look great! My next blog post will focus on that data and our resulting analysis. Many thanks to Malcolm Knapp, Jeremy Kimmel, Sarah Felix, and Charlie Sellers who all devoted many days to the wind tunnel testing. Other Engineers Without Borders volunteers that played an important role are Jerry Pugh, Matt McLean, and Ann Torres. Finally, none of this would have happened without the help of Jose Navarette, Nili Gold, and Farid (all of whom work at the NASA-Ames facility), the technicians running the tunnel, and the generous donation of the facility by the US Army Aeroflightdynamics Directorate (which leases the tunnel from NASA).

To see more images of our wind tunnel tests, check out our Wind Tunnel album and watch the video below:

Wind Tunnel Preparations

US Army Aeroflightdynamic Directorate

Since our last post the wind turbine team has been single-mindedly focused on our wind tunnel tests at the NASA-Ames research center. This testing opportunity will be a godsend for us as we will finally be able to get some clean, quality data concerning the performance of the two turbine styles we are evaluating: Savonius and Lenz. Good bye chasing wind around San Francisco!

What we are most excited about is the controllable nature of the wind tunnel and the ability we will have to set our test parameters. As a result of this unprecedented level of control, we will finally be able to apply a degree of rigor to our tests that has previously been unattainable. This more scientific approach will allow us to accurately predict not only the performance characteristics of the turbines, but also determine the appropriate alternator specifications for maximum power extraction from the system.

7x10 FT WIND TUNNEL

The tunnel in which we will perform the tests is a 7’x10’ wind tunnel owned by NASA, but leased to, and operated by, the US Army – specifically the Aeroflightdynamics Directorate (AFDD). We are extremely grateful to both the US Army and the folks at the test facility for their generosity and assistance. Without this unique opportunity, we would be hard pressed to continue making substantive progress with our turbine design.

Over the past handful of weeks Jeremy Kimmel, our wind turbine intern, and Malcolm Knapp, an EWB/Catapult volunteer, have been diligently working out the bugs in our set-up. Malcolm has spent countless hours programming the Data Acquisition System (DAQ) and they have both made a number of trips down to the test facility in order to ensure that we’ll be ready once the wind tunnel is ready for our appearance. Speaking of which, we’ve been told that we will finally get into the tunnel on August 17th! There have been a number of delays, but it is finally going to happen.

Below is a photo from our data collection training session just prior to shipping the turbine down to the NASA-Ames facility. We are fortunate enough to have an entire two weeks of dedicated wind tunnel time! During that period, Jeremy, Sarah, and Charlie will be leading our testing efforts and maintaining a constant presence at the tunnel. A number of other volunteers will cycle through to lend a hand and participate in this major testing milestone. Stay tuned for a post about our wind tunnel experience…

Left to right: Sarah Felix, Malcolm Knapp, Charlie Sellers, and Jeremy Kimmel

Left to right: Sarah Felix, Malcolm Knapp, Charlie Sellers, and Jeremy Kimmel

What is electricity worth?

The “holy grail” as it were of developing world solar power proponents is $1/watt. This is often seen as the point at which local electricity generation becomes affordable for the majority of the world’s population that do not currently have regular, reliable access to a regional electrical grid. This then begs the question, “Should $1/watt be the target of any new, small-scale renewable energy project?” Furthermore, if that price point appears unattainable is it foolhardy to chase after a technology that is otherwise very appealing? The only way we can know for certain is by dealing directly with our end-user to establish what they can afford and how much they will be willing to pay.

wind_solar1That said, it is still informative to thoroughly evaluate a technology to see how it fits into the panoply of options. This is exactly what we are attempting to do with our wind turbine and the testing we intend to conduct at the NASA-Ames research center. Our goal is to establish just how much mechanical power one can reasonably attempt to collect from the wind with a small, family-sized, vertical-axis wind turbine using the most promising blade designs we’ve encountered. Using the data we collect we should be able to estimate just how much it will cost per watt to simply capture the energy before turning it into electricity (this is based on the costs associated with building the turbine: blades, bearing, shaft, etc.). From there we will be able to predict just how much money we can afford to spend on the generator and circuitry and still achieve the price point our partner, AIDG, will help us establish (is is truly $1/watt or a more achievable $10/watt?). The amount of money available for the generator and circuitry based upon this price point will directly inform just how feasible this product may be for rural Guatemalan villages.

It could well be that the raw materials alone for the alternator simply price the whole concept above our acceptable price target; it is, after all, notoriously difficult to scale wind generation down and keep it cost-effective. As a rule of thumb, the larger a turbine is the less the electricity it generates costs per watt. We hope our tests prove that small, vertical-axis turbines are a promising avenue for additional design research (we’re fans of wind energy, after all), but the numbers won’t lie and should allow us to provide AIDG with a realistic evaluation as to how good an investment their continued development appears to be.

Prepare for lift-off

It’s looking more and more like our proposed NASA testing will indeed happen. In fact, the testing schedule has been accelerated and we’ve been told to be ready to go by the end of April! Thankfully we’ve already been hard at work getting our new Lenz blades built and sprucing up our old Savonius blades for prime time. In the below photo you can see Charlie assembling the “spines” of the Lenz blades over which well will affix some light plastic sheet. These blades reportedly have some very exciting performance characteristics and we’re looking forward to seeing how they perform in the tunnel.

windIn addition to making certain the turbine is mechanically ready for the wind tunnel we have also been busy jumping through the hoops that NASA and the Army (which manages the the 7′x10′ wind tunnel we’ll be using) sets up for all prospective wind tunnel users. One of those hoops is a “failure analysis” of the turbine and its component parts to ensure that the turbine won’t fail during testing and harm the tunnel or its operators.

At the suggestion of the extremely helpful tunnel technicians we’ve been working with we decided to forgo the analytical approach to failure analysis and instead go with real-world “proof” testing. This involves showing the turbine can withstand substantially larger loads than it is expected to see in the tunnel by calculating the maximum load it is should see in the tunnel, multiplying that of a factor (say four), and then subjecting the turbine to that load outside the tunnel. If it survives it should pose no threat to the tunnel at the loads it will see.

In this photo we are applying a 40 lb load horizontal to the middle of the turbine to simulate approximately four times the 11 lb force the turbine is expected to see if we test it to our proposed maximum speed of 25mph. I think it’s going to be ok.

The Whim of the Wind

As we have said a number of times, the vagaries of the wind are proving to be quite the hurdle. The forecast called for wind this last Saturday, so we prepared in advance and I had a number of people “on call” to help set up the test turbine and take some data when the wind arrived. However, the wind didn’t get here until Sunday and everyone was busy after having cleared their Saturday schedules. End result: no testing. This is why we desperately need a wind tunnel, so we are no longer at the mercy of the wind.

nasa-possibility

The good news is that we are in ongoing talks with the folks at NASA’s Ames Research Center at Moffett Field near Mountain View. They have a number of wind tunnels of varying size (up to 80’x120’) and have expressed interest in allowing us to test our turbine in their tunnels. This is a fantastic development and we are currently in the process of writing our formal test proposal. Hopefully they agree to help us out! The only downside to the testing option at NASA is that we won’t have access, if we are granted access, until June. That means we have to either spend the next three months continuing to chase the wind or commit to building our own “rough-and-ready” wind tunnel for some preliminary tests.

The turbine, in its current form, is a test prototype. We have attached a variety of digital meters to the turbine to allow us to calculate how much wind energy the turbine is capturing and converting into rotational mechanical energy (this information will be used to help design the generator which will produce the electricity). The equation for power in a rotating system is very simple: Power = Torque x Speed.

1) Friction Collar; 2) Optical Tachometer; 3) Torque Arm; 4) Force Gauge

1) Friction Collar; 2) Optical Tachometer; 3) Torque Arm; 4) Force Gauge

The photo above shows our test set-up. To measure speed (in rpm) we use an optical tachometer (2). To measure torque we machined a plastic collar (1) that fits around the end of the turbine shaft and is attached to a long aluminum bar (3). At a specific distance down the length of the bar we have attached a force gauge (4). The collar can be loosened and tightened to decrease or increase the amount of drag (in the form of friction) caused by the collar on the turbine. This resistive force is transferred along the aluminum bar to the force gauge. The resulting arrangement is that the forge gauge measures how much resistance (torque) the turbine is overcoming to spin. We also have a hot-wire anemometer included in the set-up (not shown) that measures the velocity of the wind. As a result of measuring torque, speed, and wind velocity, we can now calculate how much power is generated by the turbine at a specific wind speed. All of these devices are connected to a Data Acquisition System (DAQ) written in LabView and running on a laptop computer.

Cracking open the mold

Resin-cast stator based on 200W design by Hugh Piggott.

Resin-cast stator based on 200W design by Hugh Piggott.

This last Sunday we cracked open the mold for our new stator based on a 200W design by Hugh Piggott, and this is what we found.  The eight coils seen inside were cast in resin and fiberglass the week before (the colors are from crayon we used to coat the inside of the mold). While we hope to generate only 10% of what this stator was designed for, we decided that building a small alternator on an existing design would not only prove to be educational from a fabrication standpoint, but would also give us a well-understood baseline from which to proceed.  At some point I hope to slap this baby on the bottom of our turbine just to see what it will do.  After all, a direct drive alternator would be superior to a smaller, chain driven alternator for a whole host of reasons…