June 13, 2013 | Engineering + Technology, Wind Resource Assessment


What happens to your NRG Systems tower after its first measurement campaign? If you’re like many of our customers, it goes into storage, but it doesn’t have to stay there. Reusing met towers can be an economical, green practice—as long as safety is taken into account.

I asked Michael Fisher, our resource assessment product manager, to answer some common questions about reusing tilt-up towers.

What’s the typical life of an NRG Systems tower?

It depends on where it was previously installed. All NRG Systems tubular tower components are hot-dipped galvanized steel, and under normal conditions, they will survive many years. In dry climates like deserts, they can last up to 10. But, unsurprisingly, lifespans are shorter in harsh, damp, or icy environments.

Check for these signs of wear on your tower:

    • Rust: If rust is exhibited through any of the tubes, that particular tube must be replaced. In contrast, surface rust won’t compromise the integrity of the structure. But since surface rust is a sign of age or a corrosive environment, it warrants a closer inspection of all components.
    • Dented Tubes: A minor ding on a tower tube has little effect on its structural strength, but severely dented tubes can be dangerous, especially if the damaged tube is located in a section of tower that experiences high compressive forces during the tower lift (mid-level sections). If there is any doubt about a tube’s integrity, discard it and contact us for replacement.

Michael Fisher, RNRG product manager

Does it matter if my used tower is painted or unpainted?

Yes. Certain locations require the top section—or even the entire tower—to be painted per FAA guidelines. If the used tower doesn’t have a painted top section or if it’s not clear that the paint is FAA-regulated, we suggest purchasing a painted top.

Painted towers are also preferable in corrosive environments, including those with high concentrations of agricultural fertilizer. We use a high quality, two-part epoxy industrial painting process that significantly improves corrosion resistance.

Finally, before reinstalling a used tower, always be sure to check with local authorities for the latest marking requirements. With many regulations being added in the last five years, it’s possible that the same area where the tower was originally installed now requires marking. Installation service provider Harness Energy maintains a database of met marking requirements for the U.S.

Are there any tower components that I should not reuse?

We strongly recommend that you do not reuse guy wires. As the most wearable parts of a tower, guy wires are composed of multiple strands of high-strength steel wire. When turned sharply (e.g. to secure wire rope clips) or stretched in severe wind events, they become more brittle. This can be a serious safety concern.

Can I reuse sensors?

To ensure data accuracy, you should replace used anemometers when starting a new measurement campaign. As for sensor booms, the current NRG Systems version—which is IEC 61400-12 compliant—is 95” (241.3 cm). If you have legacy booms that are shorter, you might want to replace them to comply with more recent regulations.

In addition, the exterior sensor wire sheath ages over time with exposure to the climate and the sun’s UV rays. Consider replacing for optimal reliability.

Does NRG Systems offer any replacement kits?

NRG Systems has several  tower upgrade kits available: NOW System Sensor + Wire Replacement Kits.

Are there any other considerations when deciding between installing a used tower or a new tower?

In addition to the safety considerations mentioned, it’s important to factor in the total cost of the used tower. While some are available for a relatively low price, the administrative and logistical expenses involved with verifying a complete component inventory, repackaging, and shipping used towers to a new site can add up quickly. In addition, used towers lack the manufacturer warranties that back new ones. For the most accurate assessment, compare the price of a new tower with free shipping to the cost of acquiring and shipping a used tower.

To learn more about NRG Systems tower retrofit kits, contact the sales team at sales@nrgsystems.com or +1-802-482-2255.