The farmer-built Savonius rotor: A low-tech approach to renewable power for farms

The farmer-built Savonius rotor: A low-tech approach to renewable power for farms

Summary

Small-farm scale alternative electricity generation is priced out-of-reach for most farmers. We propose to design and construct a prototype of a silo-mounted augmented Savonius wind turbine that could deliver substantial power output, yet is inexpensive and simple enough in its construction, installation, and electrical engineering to be easily built and maintained on a typical small farm.

Nearly all farms use electrical power for daily operations. Though the general public is aware of the need for sound renewable alternatives to our current grid-based supply, the dialog is usually framed in terms of large, highly capitalized commercial wind, solar or methane projects. For small farm operations, generation of electricity is seldom made a priority because the residential and light commercial scale options on the market all demand high up-front cost, prolonged payback periods (generally well over 10 years), complicated technical issues, possible permitting problems, and the likelihood of expensive repairs requiring specialized parts and labor. Given these high costs, the less-than-ideal regional meteorological conditions for both solar and wind provide an additional disincentive to take individual action.

An effort needs to be made to use the skills and resources of farmers to create a durable region-wide micro-generation infrastructure. The silo-mounted augmented Savonius Rotor described in this proposal is a part of such an effort. It is low-tech, inexpensive to build and maintain, and makes use of typical farm skill sets and a typical farm structure. While it does not compare to a state-of-the-art horizontal-axis wind turbine in terms of efficiency, it more than compensates with its low cost and simplicity. The resulting power can make a real difference in the economics of farm operations, whether it is used mechanically, in a stand-alone 12-volt system, or in a grid-tied net-metered system.

Our search for others involved in low-tech wind power produced scant local activity. We consulted Gary Flomenhoft, a fellow with the Gund Institute for Ecological Economics since 2002. Sustainable energy production is, for him, both a personal and professional interest. He is familiar with the Savonius rotor and has found no local or regional initiatives using vertical axis rotors. He explains, “Everything is focused on achieving commercial generating scale because of high cost of horizontal rotors.”

We have also made contact with Job Ebenezer, a mechanical engineer and former professor who now runs an Ohio-based project entitled “Technology for the Poor.” This project evaluates appropriate technologies to accomplish significant work in less-developed countries yet are easily built and maintained by local people. He built the Savonius rotor pictured in figures 1 and 2, during the 1970’s. which produced about ½ horsepower and cost $200 (at 1978 values) in materials. As energy costs dropped in the 80’s, interest in such projects has diminished and Ebenezer’s prototype has not led to widespread use of such wind collectors. Yet its simplicity and proven effectiveness suggests that such devices deserve a place in any consideration of renewable power generation.

We have been working closely with project team member Victor Gardy, a local retired engineer whose career has been devoted to turbines, chiefly those of aircraft and power plants. As a personal hobby, he has also been researching and developing versions of the Savonius rotor for 29 years, including one installation in Charlotte, Vermont in the early 90’s. Gardy also shares our view that this useful device has been almost completely overlooked by the engineering community.

Boundbrook Farm is a 110 acre farm in the town of Ferrisburgh, comprised of a small (1/2 acre) market garden, 15 acres of cropped fields, 60 acres of pasture, as well as woods and wetlands. The farm is worked primarily with draft horses, and produces grass-fed beef, pork, poultry, and grains. The grains are processed into feed or milled by Good Companion Bakery, our on-site brick oven bakery, and baked into bread or made into other goods.

The key people in the project are Erik Andrus, co-owner of the farm and bakery, Amos Baehr, resident farm employee, and engineer Victor Gardy. Prior to starting this farming operation, Erik Andrus was a freelance renovation contractor for 10 years. Amos Baehr also brings to the project many years of construction experience and a facility for data analysis. Victor lends his involvement from a personal commitment to bring about simple, effective, home-built generation devices to serve as a counter-example to the large and high-tech installations that dominate the public discourse on alternative energy.

We began farming here in 2006 with the goal of creating an integrated diversified farm with an emphasis on sustainable, horse-powered grain production and European hearth breads. A key component of the operation is the milling of our grains. We have an Austrian-made 30 cm stone mill with a sifting apparatus, which can mill all the grain we as a farm produce, and can make sifted flour of various grades.

Milling is, for us, the most energy-intensive part of our grain-to-bread process. Doing all of our own flour milling in a given year (about 10 tons per annum at the bakery’s current rate of sales) would require between 3200 and 6400 kilowatt hours, costing between $500 and $1000 in electricity annually (at 15 cents per kilowatt hour). Based on his previous projects and estimated wind available at our site, Victor Gardy estimates the planned augmented Savonius rotor will generate about 17,000 kWh per annum, more than enough power to offset this economic cost to the operation as well as the environmental costs associated with the consumption of this quantity of grid-based electricity. This hands-on approach to reducing costs and environmental impact is a good fit for our farm and its mission.

Objectives/Performance Targets

We have already obtained analysis of the wind properties at our farmstead. Our average wind speed is 10.9 mph, just below the threshold at which conventional investments in wind power are considered in the least way viable. But given than the Savonius functions well at lower wind speeds, we have determined that our farm will make a good test site.

The first stage is design. The prototype rotor is an innovative application of a proven concept (first developed by the Finnish engineer Sigurd Savonius in 1922), and makes use of cheap, readily available building materials. Per Gardy’s suggestion, this prototype features features stators, or fixed panels, to reduce drag on the rotor cups as they return into the wind. Gardy’s previous research suggests a marked increase of nearly 100% in efficiency with the use of stators. We have good reason to believe that the proposed device will perform within the desired output parameters. The builders (E. Andrus and A. Baehr) worked with Victor Gardy to complete a comprehensive design for both the rotor and the structural frame that houses it, as well to specify appropriate generators and metering devices. A basic design was created in April 2010 and modified slightly as the project progressed.

The second phase involved construction of the array, which was completed in January 2011. Using the working design, an array of augmented Savonius rotors comprised of two rotors, each 12 feet in height, was assembled and placed into a bracing structure. All of this work took place at ground level in or adjacent to the farm workshop. The finished prototype is a complete structural unit, which can be moved by crane to the nearby installation site, or dragged to various test locations on skids.

The third phase is testing. The rotor is now complete and ready to evaluate under a variety of conditions. The goal remains to collect at least 3 months of continuous production data. Construction delays prevented us from adhering to the late summer/early fall test period originally outlined. More recently, severe winter weather has limited our ability to test and monitor the rotor during the winter. However we are ready to resume testing as soon as snow conditions make movement of the rotor to the test sites possible.

The final phase is evaluation. We will complete at least 3 months of data collection by July 2011. The collected data can be exported to our farm computer and then analyzed and graphed. Since our goal is to develop a low-tech, cost effective generator, the production of power must be weighed against the cost of the power through both conventional grid-based sources and competing renewable/alternative power sources.

The usefulness of the prototype is easy to assess once the output is known. The most useful measure is “payback time,” which is the cost of the turbine divided by its annual production of kilowatt hours at the going rate. We will also compare its payback time to various commercially available generation options on the market. At this point we estimate the array will be able to produce about 660 watts per hour under average winds, and should therefore yield an estimated 17000 kWh over the course of a year. At such a rate, given the $2450.00 projected cost of materials and components for the rotor itself, the project could pay for its own materials in savings in less than two years. The labor and other costs could be paid for in another three or four years, for a total projected payback period of five or six years.
In addition we will also evaluate and graph variation in the prototype’s production of electricity, make note of the revolutions per minute of the rotors at various wind speeds, describe any noise or vibration associated with the unit, and evaluate its performance at very low wind speeds and its durability in high winds. If the test period proves to be more or less windy (based on airport reports) then we will adjust projections accordingly.

A failed result might involve extremely low output, serious structural failure of the rotors, their bracing system, or structural damage to the silo base. Even such results could be instructive as they might point the way to improvements in design or installation.

If the prototype performs within anticipated parameters, it would serve as a model for farm-based wind power that could be replicated on a very large number of Northeastern farms. While most commercial wind technology is only economically justifiable if one has an excellent wind site, the production cost and complexity of this prototype are so low that even farms such as ours with marginal wind availability may profit from installing one.

Further, this project makes use of typical farm infrastructure. A barn or silo can make a good platform for installing this kind of array. Initially we favored installation on a flat platform on a steel farm silo, but in the end we chose instead to integrate a support tower into our gambrel-roofed dairy barn. We anticpate moving the rotor to the barn roof loaction before the conclusion of the project.

It should also be noted that this design does not need a prime wind site (or a silo) to perform. Low towers, platforms, or barn-roof installations and the placement of mobile rotors in open spaces such as pastures (generated power can be delivered to the farm by a reeled-out cable) are additional placement options that may work for other farms.

The short payback time expected from this project means that farmers may see quick returns on their installation investment and dramatically reduce their utility costs. This can be true whether the resulting power is used mechanically, in a stand-alone 12-volt system, or in a 110/220 volt net-metered system where surplus electricity is sold back to the local electric utility. In our case we are pursuing both net-metering and the powering of some processing operations through a 12-volt system, notably flour milling.

For farms that must have a backup to the grid, this design may offer a cost-effective alternative source of power for essential devices during blackouts. It also does not entail the noise, pollution, and fuel cost associated with gas generators.

The prototype features a simple design; farmers will find it easy to construct using basic carpentry, mechanical and electrical skills and common building materials. This design therefore presents an opportunity for farmers to use their skills and talents to reduce their overhead, make a positive contribution to our regional energy economy, and become more self-reliant in a universally needed commodity.

This project will deliver information on the augmented Savonius wind turbine through a variety of educational and outreach techniques to other farmers throughout the Northeast. We have already had some media exposure and will continue to publicize the project through local (i.e. Agriview) and regional venues (Country Folks) at the conclusion of the three month trial period in October 2010 to share our results.

We are consulting with NOFA VT to hold a field day on the farm as part of the Summer Workshop Series in 2011. This field day will feature a demonstration of the small scale wind-turbine. During the workshop, we will talk about designing and building the turbine as well as performance and practical applications for various farm settings.

After the 3-month trial has been completed and data compiled, will produce a 10-page construction manual featuring complete plans, photos and diagrams, available for free download from the Northern Grain Growers Association (NGGA) website, or from the farm website, or upon request, by mail for a nominal $5.00 fee to cover printing and postage. We also will print 200 copies of this manual to distribute free of charge at the above-mentioned farm field day and at conferences at which we will present the project. We have submitted proposals to present the work at the NOFA summer conference in Amherst and at Solarfest 2011.

In addition, an article on the project results will also be included in the NGGA quarterly newsletter (distribution to over 200 farmers). An Extension leaflet will be published and made available through the UVM Extension Publications Center and on the Extension website.

Lastly, presentation of our results will be delivered at the 2011 NGGA annual conference and the 2012 NOFA-VT winter conference. These annual conferences will distribute project information to more than 500 farmers.

Accomplishments/Milestones

Most significantly, the first and second phases of the project (design and construction) have already been completed. In particular, construction is a significant milestone as it accounts for a large portion of total project labor and supplies. For these two phases, total material expenditures were within our original budgeted projections and less labor was required than anticipated. This suggests that building a similar unit is a feasible and affordable proposition for a typical small farmer, just as we had hoped.
While we have made some initial observations on performance, we have yet to record a significant volume of data. However easy the unit may be to build, we cannot draw conclusions about its economic utility until we have ample performance data. For this reason the project requires more time to properly complete.
In addition, we have completed some of the outreach activities initially proposed. The project has already received some media exposure through an interview on Vermont Public Radio’s program, Vermont Edition (July 19th 2010) and a print article in the Addison Independent (“Ferrisburgh Baker Builds Low-Cost Windmill, May 10th, 2010). The project has also been publicized on our farm and bakery website (www.goodcompanionbakery.com) which we will continue to update as the project continues.

Impacts and Contributions/Outcomes

The project has resulted in a sound design of protoype rotor that is now available for testing. Refinements in design and construction have been made along the way, and this will surely benefit others interested in similar devices.
The true outcome of the project cannot be assessed without performance data, however. For this reason it is still too early to draw conclusions about the economic viability of the prototype.

Collaborators: