Renewable energy has been on an upswing in construction across the US. A record 31 GW of solar energy was installed in 2023, which is a 55% increase from 2022. Wind energy installations added about 8 GW in 2023, and another 17 GW is planned for 2024. This means that total renewables installed generation represented about 25% of electricity generated in the US in the first half of 2023. Studies predict that over a five year period between 2023 and 2028, the US solar industry is expected to nearly triple in size. The lion’s share of this growth will be concentrated on utility-scale renewable sites, with most of the new renewable generation coming from solar.
Motivation for Spacer Cable at Renewable Energy Sites
Renewable energy installations for wind and solar are quite different. The wind farms utilizing Spacer Cable are usually “ridgeline” windfarms, with turbines located on mountain tops and along mountain ridges. This creates challenges for designers in that the collection systems which must travel back down the mountainside to the gen-tie substation are often confronted with steep inclines, rocks, and high winds. This is very different than the average solar energy site, which is normally flat, hot, dry, and extremely space constrained.
The benefits of using Spacer Cable at renewable sites can be summarized as follows:
- Conductor Clashing – This phenomenon of conductors swinging in high winds to the point of coming into contact with one another is present at solar sites, but is more pronounced risk at wind energy sites, which are by definition located in high wind areas. With Spacer Cable, the conductors are held in place and unable to touch one another. Should an extremely violent wind gust occur which forces the conductors to come into contact with one another, there will be no flashover, no outage, and no conductor damage. The polyethylene covering protects the cable.
- Improved Voltage Regulation - An indirect benefit of Spacer Cable is its intrinsic ability to improve voltage regulation. While spacing between phase conductors of a bare wire system might be six or eight feet, the phase to phase spacing of Spacer Cable phase conductors is closer to one foot. As the phase conductors come closer together, the mutual inductance of the system is vastly reduced, with the result that the total system impedance is 15% or so lower (than an equivalent bare wire configuration). This means there will be a better end-of-line voltage, or that a line 15% longer can be built utilizing the same size conductor. Alternatively, depending on losses, a smaller conductor size may be selected for the collection circuit, effectively saving significantly on aluminum conductor purchases for the facility. The farther the wind turbines or solar blocks are from the substation, the greater this benefit is in terms of cost savings for materials.
- Underground (UG) Conductor De-rating Issues – While a possible consideration for wind energy sites, UG cable ampacity de-rating is a significant concern for solar farms, which are often located in hot desert climates. The first challenge is high soil resistivity. The dry soil has a high thermal resistivity, which traps heat and reduces the cable’s current carrying capacity. The second challenge is the high ambient temperature. Design criteria usually consider a fifty-year high ambient temperature. For example, if the ambient temperature is very high (e.g., 125°F), the UG cable’s ampacity is significantly reduced.
In such conditions, an UG cable rated at 1,000 A can be de-rated to less than half, requiring parallel phase conductors to achieve sufficient ampacity. For instance, a Spacer Cable system with 1033 kcmil, 34.5 kV covered conductors transitioning to UG at a riser needs two 1000 MCM UG cables per phase to match the ampacity of a single aerial Spacer Cable. This is shown in the photo below. The cost difference between these options is substantial.
- Multiple Circuit Construction - Utility-scale renewable energy sites, are, by definition, multiple circuit facilities. Building collection circuits with bare wire limits the number of circuits per pole to two. Some sites use three bare wire circuits per pole, but it is cumbersome and requires more work and caution for maintenance. With Spacer Cable, there are no such restrictions. Systems have been built with as many as nine circuits per pole line. While this increases financial outlays for poles, the overall savings is significant. The photo below shows six 34.5 kV circuits, built with 1272 kcmil AAC Spacer Cable, carrying one hundred percent of the solar farm’s generation on a single pole line.
- OPMW – Optical Messenger Wire - Fiber optics monitor and control turbines and solar panels, including automated fail-safes to prevent issues. Spacer Cable integrates fibers into the messenger, eliminating the need for taller poles. This reduces costs and minimizes tower shading, which can affect solar panel efficiency.
- Collection System Substation Entrance - A common method to bring powerlines into a substation involves terminating the aerial cable on a pole outside the fence, transitioning to an underground cable, and connecting to the substation bus. This method is costly and cumbersome. Using spacer cable allows for a simpler connection by running a slack span from the last pole directly to the substation bus, thereby providing significant savings in cables, trenching, and labor.
Summary
Incorporating Spacer Cable Systems into renewable energy sites has significantly reduced construction costs, enhanced reliability and safety, and improved economic viability by avoiding shutdowns. Additionally, these systems protect wildlife by covering energized parts, thus protecting birds and climbing animals. As we move towards a greener future, Spacer Cable Systems will remain essential for achieving cost-effective, reliable, and sustainable designs.
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