A Successful Project, Step-by-Step
1. Assumptions
- You wish to install a wind turbine.
- You have legal access to the proposed site.
- You have chosen to install a freestanding tower.
- You have given some consideration to the wind conditions.
- You have consulted with local planning and building authorities to understand their requirements.
2. Evaluate the Site Conditions
- Is the site accessible for construction?
- Are there obstructions between the proposed site and the direction of the prevailing winds? If so, you may wish to address site suitability with the wind turbine manufacturer or some other knowledgeable source, such as the American Wind Energy Association (www.awea.org).
- Are there any unusual conditions, such as severe slopes, high water table, expansive or collapsible soils, shallow bedrock, frozen soils, marshland or previous fill? If so, you may wish to discuss site suitability with a qualified geotechnical or structural engineer.
3. Obtain a Geotechnical Review and a Soils Report
- There are many situations in which permits will be required to comply with zoning and building regulations. In these cases, building officials may require construction drawings showing the foundation is appropriate for its intended purpose. Sometimes they require the drawings be reviewed and certified by a professional engineer licensed to practice in the local area. As a prelude to such certification, the professional engineer may wish to see a soils report for the site where the turbine is to be installed. Even in cases where certified drawings are not required, it is prudent to obtain a soils report and to employ good design and construction techniques. Check to see if a soils report already exists for your site. For example, one may have been prepared in connection with the construction of your home.
- There are two common methods for obtaining soils data. Soil Boring involves the drilling of core samples for subsequent laboratory testing and classification. Excavation Observation involves the visual inspection of the excavation and/or laboratory tests of soils taken from the excavation. In either case, the geotechnical engineer provides a written report of observations and recommendations. You may view sample soils reports here
(Sample Soils Report: Soil Boring and Sample Soils Report: Excavation Observation). - If you obtain a soils report by the excavation observation approach, you will need to protect the excavation for safety during the time between excavation and construction. Water and debris must also be removed before construction, and the excavation should be prevented from freezing prior to pouring concrete.
- In our recent experience, the typical cost for soil boring is about $800 to $1200 and the typical cost for excavation observation was about $250 to $350. In most cases, excavation observation is sufficient to determine the suitability of the SMarT Foundation for your site. Assuming there are no unusual site conditions, the only number required is the allowable vertical soil bearing pressure, a familiar term to your engineer.
- Once you have obtained a soils report and understand the nature of your site, a choice must be made about the type of foundation to construct.
4. Select the Foundation Type
- The SMarT Foundation is a special type of “mat” foundation – a giant slab of reinforced concrete that resists overturning forces. In some conditions, such as expansive clays or marshland, a “pier” foundation is required – a reinforced concrete column supported by the surrounding soils and possibly embedded in bedrock. In almost all cases, the SMarT Foundation is simpler to construct and less costly than a pier foundation. But if a pier foundation is needed in your situation, contact the turbine manufacturer to see if they have already designed a suitable foundation for your wind turbine.
- Based on the site conditions and soils report, your geotechnical engineer can recommend a foundation type. If your local building authorities require certified (stamped) engineered drawings, the soils report should be supplied to the structural engineer that will stamp the drawings. In some cases, but not always, the geotechnical engineer is also the structural engineer. We have made arrangements with TEP (Tower Engineering Professionals) to stamp SMarT Foundation drawings for you.
- In most cases, the SMarT Foundation is the most economical choice for your wind turbine foundation. You’ll see why in step 5.
5. Consider the SMarT Foundation
- As far as we know, The SMarT Foundation is the simplest and least expensive alternative for a small wind turbine on a free-standing tower. It can even be installed where heavy equipment is not available and the excavation must be dug by hand.
- Supplies are delivered to your door – no travel is required to procure them.
- Materials cost, including concrete, is less than other methods.
- Construction labor hours are less than other methods.
- Elapsed time is less than other methods.
- The table below will help you estimate your costs. It is based on our experience with several Southwest Windpower Skystream 3.7 wind turbines on 33 ft. (10 m) monopole towers. Naturally, costs will vary with site conditions, turbine size, tower height and labor costs.
- Additional information in the FAQs and Photo Gallery. Sample drawings/instructions and purchasing information is on the SMarT Foundation page.
Materials Cost Estimate
Estimates from 2010.
| Item | Our Experience | Your Estimate |
|---|---|---|
| Soils Report | $350 | |
| Engineering Stamp | $350 | |
| Excavator or Backhoe Rental | $250 | |
| SMarT Foundation Kit | See SMarT Foundation Page | |
| Concrete | $600 | |
| Labor Hours | 12 | |
| Labor Cost and Contractor Fees | Varies | |
| Permits | Varies |
6. Coordinate the Project
- A little planning goes a long way, especially when concrete is involved. Here are a few things you can do to ensure that your project is successful.
- Make sure the engineer of record – the one signing the drawings – sees the soils report and has the opportunity to discuss it with the geotechnical engineer.
- Coordinate with planning and building authorities to obtain the necessary building permits.
- This is a team effort involving owner, engineer, contractor, workers and suppliers. Introduce team members and identify a single point of contact for construction responsibility.
- Familiarize team members with the SMarT Foundation. Browse this web site.
- Ensure that team members review the drawings and instructions.
- Check the contents of the SMarT Foundation kit packages. Consider having a pre-assembly meeting.
- Coordinate excavation, assembly and concrete work. Make sure all tools and supplies are ready.
- Follow up with building authorities, if required, after construction is complete.
