Remote assets for energy operators boil down to the net revenue they are able to generate. The more energy is produced for the longest time with the least cost, the more attractive the asset. That's why inspections are so burdensome on these structures: they cost a lot since people need to be transported onto the structure and the asset can't produce energy while a climber or a helicopter is on the premises. That's why combining inspections with remote monitoring allows operators to decide on the right moment for an inspection and lower the cost of the intervention.

The cost of inspections

An inspection of a remote structure is logistically challenging. One US drone-inspection vendor can quote from USD 3,000 to 5,000 per turbine for a rope-access inspection of a wind turbine tower, with 8 to 12 hours of shutdown. A crew climbing a lattice tower could cost USD 800 to 1,500 per structure and get through one or two structures a day. Helicopter patrol of a transmission line runs USD 1,200 to 2,000 per mile, and a ground crew with bucket trucks USD 2,500 to 4,000 per mile. These figures lower the net revenue of an asset, so they are usually avoided until necessary.

The intervals written into standards and O&M plans reflect this. ANSI/TIA-222, the US reference for telecommunication and similar steel towers, recommends a condition assessment every three years for guyed masts and every five years for self-supporting structures, plus a visit after severe wind or ice. Most wind farm O&M plans call for an annual foundation crack inspection and for anchor bolt re-tensioning after the first 500 operating hours and then every five years. Transmission pylons are covered by ground patrols or flyovers at intervals of years, and a climbing inspection is scheduled only when a patrol has reported something. None of these intervals comes from how fast a foundation degrades or a bolted flange loses preload. They come from what the owner can afford to spend on access.

What happens in between can be expensive. In February 2016 a landslide in Badong, Hubei, cracked the foundation of a 500 kV transmission tower on the Yanzi slope above the Yangtze, and the line was out of service for 100 days. A study in Scientific Reports (2024) puts the cost of rebuilding and relocating the three affected towers at roughly EUR 9.4 million, with indirect losses, including a 34.5-hour closure of river navigation and the evacuation of 352 residents, higher than the direct ones. The slope was a known landslide. Monitoring of it started after the cracks were found. At a smaller scale, a maintenance crew at a wind farm in southern Europe noticed cracks wider than the 0.3 mm Eurocode 2 limit on a foundation slab during a routine visit, with water already reaching the reinforcement. The foundation was repaired with a concrete collar. Found one visit later, it would have been replaced, at several hundred thousand euros and months of lost production.

There are ways of extending the time between inspections and limiting the costs associated with pausing the operation of an asset. Remote monitoring offers a continuous stream of data that can be used to follow the state of an asset without risking its health. Any sudden damage caused by weather and any long decline in structural integrity is observable through sensors that report that damage through wireless communication.

Remote alternatives

Installing wireless monitoring sensors such as accelerometers or tiltmeters on an asset is a quick and cost-effective solution for observing it without the need of constant inspections. Sensors can provide data on general integrity, but also on weather conditions and specific parts of the structure.

The sensors themselves need no power supply. A MEMS tiltmeter or accelerometer on a LoRaWAN link transmits a few bytes per reading and runs for five years or more on a lithium cell at low sampling rates. The only element that needs continuous power is the gateway, which at a substation or a turbine base plugs into the auxiliary supply and elsewhere runs on a 50 to 100 W solar panel with a battery sized for the local winter. The GW-PRO gateway carries its own 4G/LTE modem, so the site needs cellular coverage at the gateway position and nowhere else. Sensors reach it over LoRaWAN from several hundred metres to a few kilometres away depending on terrain, which means one gateway on the tower that has a mobile signal can collect from its neighbours.

Data arrives in MyMove, where thresholds can be set on a single parameter or on combinations, for instance tilt together with temperature so that a cold snap does not trigger a visit. Battery voltage is transmitted with every reading, so a failing node is flagged months before it stops and the replacement goes on the work order of a visit that is already planned. What the sensors measure, and what the operator should look for, depends on the type of asset.

Poles and transmission towers

A lattice pylon usually fails at the foundation, which is caused by the ground moving. Slope creep, scour, frost heave, mining subsidence or a neighbouring excavation shifts one leg relative to the others, causing the structure to rack. The change takes months and is not visible from the ground until it is well advanced.

Using tiltmeters, the trend of the inclination can be measured and tracked. A pylon that has leaned 3 mrad since construction and has not moved since is in a stable condition. A pylon that has moved 1 mrad in the last six weeks needs a visit, whatever its absolute inclination. The alert should therefore be set on the rate of change over a defined window rather than on an absolute value, and, once a year of data exists, on the departure from the seasonal baseline.

With tiltmeters fixed to legs close to the foundation, an operator can monitor inclination trends with sub-milliradian resolution without any physical intervention for years. On a line crossing unstable terrain, only the towers on the exposed section need instrumenting. Our tiltmeter also reports RMS and peak vibration between 0.1 and 31.25 Hz with each reading, so a tilt step that coincides with an impact or a nearby blast can be told apart from slow foundation movement. Where the concern is the slope itself rather than the tower, tiltmeters go on the slope, which is the approach used on retaining walls and embankments.

Wind turbine towers

A tubular steel tower fails at its flanges or at the foundation. Flange bolts lose preload through relaxation and thermal cycling, and a joint with reduced preload has a lower rotational stiffness. At the base, grout crushes, anchor bolts lose tension or the soil under the slab softens on one side. Each of these changes either the fundamental frequency of the tower or the tilt of its base, and both can be measured while the turbine is running.

The first fore-aft mode of a modern onshore tower is below 0.5 Hz. Xing et al. (Frontiers in Built Environment, 2026) measured 0.249 Hz on a hybrid concrete-steel tower and found that across ambient temperatures of 17 to 35.8 °C the correlation between temperature and the first three modal frequencies was between 0.03 and 0.10, while wind direction shifted them by less than 2%. A frequency change larger than that scatter, sustained over several weeks, comes from the structure. Dai, Rotea and Kehtarnavaz (Sensors, 2025) estimated the rotational stiffness of the foundation to within 7% using only acceleration and wind speed data, so the foundation's condition can be followed without excavating it.

Using accelerometers, the first natural frequency can be tracked against its own history. A DECKAXE-SHM on the platform below the nacelle, sampling at 40 Hz, resolves a 0.25 Hz mode with a wide margin, and the Modal Analysis Tool in MyMove follows the identified frequency over weeks, so a drift of 2 to 3% stands out against the day-to-day variation once rotor speed, yaw and pitch have been accounted for. A tiltmeter on the base flange covers the foundation. Two sensors per turbine is a typical first installation, and both can be mounted during a scheduled maintenance stop without adding downtime.

Plant structures in service

Pipe racks, flare stacks, cooling tower shells and equipment support frames inside an operating plant are remote in a different way. The site has power and a network, but the structure cannot be reached without a shutdown, a permit, scaffolding or all three, and a visual inspection has to be planned into a turnaround months in advance.

Using tiltmeters on the columns and accelerometers on the deck, settlement of individual footings under vibrating equipment and loss of section from corrosion, which shows up as a change in stiffness, can both be followed between turnarounds. Sensors are installed during one turnaround and report until the next. Battery-powered nodes also avoid running a cable tray through a hazardous-area classification, which on a running unit is often the slowest part of a wired installation.

When monitoring is not worth it

A structure that has an inspection regime that is being followed, shows no active deterioration, has no ground movement or construction nearby and carries no regulatory obligation to monitor gains little from a permanent installation. The same is true where the failure mode is fast. A conductor gallop event or a lightning strike is not a trend, and a tiltmeter will not predict it. Continuous monitoring does not replace the inspection either. Sensors do not see corrosion under paint or a cracked weld on the far side of a member. The visit still has to happen, but it happens when the structure shows a reason for it, and the crew arrives knowing which leg, which flange and roughly when the movement started.

Frequently Asked Questions

Can a permanent installation justify extending a regulatory inspection interval?

In some jurisdictions, yes, with documentation. ANSI/TIA-222 presents its intervals as recommendations that may be lengthened or shortened according to age, maintenance history, environment and risk category, and condition data is the natural evidence for a longer interval. Where the interval is fixed by the regulator or the insurer, monitoring does not change the paperwork, but the visit is planned around conditions that are already known.

Is a single tiltmeter per pylon enough to detect a landslide?

For the tower, yes. When a foundation displaces the tower moves as a rigid body and one tiltmeter at the base records it. For the slope, no. A slope creeping toward a tower may not have reached the foundation yet, and catching that requires tiltmeters on the slope itself.

What is the failure mode of the monitoring system itself on a remote site?

Loss of backhaul, almost always. A sensor that stops reporting looks the same as a sensor that has been destroyed, so the system has to raise an alarm on silence as well as on movement. Without that, a solar-powered gateway with an undersized battery goes dark in December, comes back in February, and the record shows two months in which nothing appears to have happened.

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