How new cable geometry impacts utility-scale solar tasks

By Scott Rand June 1, 2023

For these of us within the renewables business, utility-scale solar tasks have a selected feel and look. Row upon row of solar modules, PV stretching so far as the attention can see, maybe drone seize from above that exhibits acres of gleaming panels. What you don’t see are the underpinnings — aka steadiness of system (BOS) elements — which can be essential to the event, energization and long-term energy yield of all solar power vegetation.

While it’s not the flashiest matter within the solar business, cable administration is a essential element. These bundles of cables beneath and subsequent to the PV modules additionally characterize hidden challenges that mission engineers face each day. And it seems that “cable geometry” or “cable math” is a misunderstood — however extraordinarily vital — side of this business.

To perceive this, let’s take a look at the solar business’s historical past.

Traditionally, engineers have relied on generalized tables offered by the National Electric Code (NEC) to find out cable ampacity, or how a lot power a cable can safely conduct over lengthy durations of time. However, these tables don’t account for the complexities of recent solar installations, notably with revolutionary cable hangers and preparations. As a consequence, engineers typically make assumptions about cable capacities, resulting in less-than-optimal cable ampacity choice.

One of the challenges that engineers face in figuring out cable ampacity is cable geometry, or orientation. In the previous, engineers would set up cables into groupings referred to as bundles, which have been presumed to simplify design and cut back prices. However, bundling cables creates an issue that has been missed prior to now: extreme warmth.

The wires at utility-scale solar tasks carry large quantities of power — wherever from a number of hundred kilowatts to some megawatts — and due to this fact generate fairly a bit of warmth. By grouping wires collectively, the airflow is restricted round every cable, which prevents pure warmth dissipation. This will increase the temperature within the cables and may speed up the degradation of the insulation across the power cables, which may result in decreased energy yield, untimely wire burnout and different electrical failures.

To work round this drawback, engineers low cost the whole power working by every cable based mostly on suggestions from the NEC 310.15 desk used as we speak. It considers elements together with cable sort, ambient temperatures and bundle dimension to find out what quantity of power a wire can deal with safely.

The consequence of the mathematics is straightforward: The greater the bundle, the decrease the airflow, the much less energy allowed by a given cable. Often this leads to a developer paying greater prices for bigger cables to make sure the system will nonetheless have the ability to deal with the power load as soon as the cables have been bundled collectively.

The catch is that the NEC tables that engineers at present use to find out how a lot power to low cost will not be tailor-made to cable geometries which can be incessantly utilized in renewable energy. Without solar-specific tables, mission engineers are left to approximate which pre-existing desk is the most effective match for a given state of affairs. The key info lacking from the present code is a transparent definition of what constitutes a cable bundle with extra advanced geometries.

NEC 310.15 doesn’t precisely characterize trendy hanger design. In truth, present NEC tables power engineers to imagine nearly all preparations represent a bundle, even people who permit considerably extra cooling.

cable math ampacity guidance

Up till now, builders have had no choices for cable administration methods that might improve energy yield and final by the lifetime of the power plant. New evaluation from the Affordable Wire Management (AWM), NEI and Autodesk groups present a greater choice is on the horizon.

Enter cable geometry

Cable geometry, or sensible “cable math,” is a brand new idea in cable administration engineering that’s a game-changer.

The cable geometry idea is to design an optimum association of wires that will increase the whole ampacity, or most present that may be run by a wire constantly with out threat of degradation or failure. Cable geometry is difficult math that requires engineering experience and a deep understanding of how convection and warmth dissipation will have an effect on close by cables in numerous spacing patterns, and beneath totally different circumstances.

This is the place CFD (Computational Fluid Dynamic) evaluation turns out to be useful. CFD evaluation is a complicated modeling science that helps engineers perceive how fluid actions, like convection cooling, operate beneath totally different circumstances. It has been extensively utilized by engineers in aviation and different industries for years.

Today, the AWM crew makes use of Autodesk’s CFD software program to unravel the “hot” solar cable administration drawback. Let’s take a look at the evaluation tables under:

The visible output of the evaluation, as proven above within the left diagram, illustrates the hotspots that happen in cable bundling. All the wires within the bundle are scorching, and some are close to the utmost temperature indicated by crimson.

You may assume that spacing these cables out in nearly any means would assist, however the diagram exhibits this isn’t the case. When these cables are organized into parallel rows of 4, proven on the underside left, comparable warmth concentrations happen regardless of the obvious spacing. In this association, a number of cables nonetheless attain harmful temperatures. The proper facet diagrams present that should you re-engineer the design fastidiously and provides these cables extra room to breathe, these hotspots disappear.

By combining Autodesk’s computing experience with AWM’s examine on cable ampacity willpower utilizing CFD simulations, engineers can discover the results of higher airflow between cables, resulting in improved system effectivity. Leveraging the power of CFD lets engineers simulate and analyze the warmth switch and airflow round cables in numerous hanger configurations, leading to a extra correct evaluation of cable ampacity. This revolutionary method highlights the significance of contemplating the complexity and variability of cable preparations in trendy solar power vegetation.

AWM has discovered that CFD simulations can present engineers with vital steerage. For occasion, Autodesk’s software program has helped AWM optimize the Arden Series hanger design, our most up-to-date hanger launched, which in flip reduces prices for our clients. The CFD evaluation supplies the reply to that lingering query left by the present NEC tables: “What do we need to consider a bundle of cable?”

cable math ampacity analysis

This is an providing that actually solves real-world engineering challenges within the solar cable wire administration sector.

The proof is obvious. Not all cable geometries are created equal, and now we’ve the instruments to point out why. With greater confidence within the cooling capabilities of a design, engineers can then downsize the cable dimension. This is important, as smaller cables equal substantial value financial savings – typically within the thousands and thousands of {dollars} for utility–scale solar tasks — whereas growing the operational security and lifetime of the cables.

In the long run, the creation of specialised NEC ampacity tables would permit for a widespread adoption of extra environment friendly cable administration options. We actually hope that it turns into a actuality within the close to time period.

For now, Autodesk’s CFD software program evaluation has began to fill within the info hole. Using this technique, engineers and procurement groups can extra precisely assess which cable administration merchandise might be most useful to their tasks.

In truth, the applying of the CFD evaluation is beginning to spark a change in how engineers take into consideration and method cable administration altogether. Solar energy stakeholders can save on their backside line, improve the lifespan of cables, and supply utility-scale asset homeowners with extra certainty round ongoing mission efficiency. All these elements may also help carry the price of solar down and pace the proliferation of fresh power technology sources, which is significant to the way forward for our business and planet.

Now, doesn’t that sound like an equation everybody can agree on? We suppose so.

Scott Rand is CEO and a founding member of Affordable Wire Management (AWM). AWM’s product line consists of Arden Messenger Cable Hangers, Bonsai Module Hangers and the Solar LOTO lock-out providing. AWM’s solar cable administration options are the popular alternative for top-ranked EPCs in North America. For extra info, please e-mail us at gross, or go to us on the net at:

Special due to Carson Bates of NEI for serving to AWM refine the mannequin and authoring our ampacity report.

Autodesk® CFD software program creates computational fluid dynamics simulations that engineers and analysts use to intelligently predict how liquids and gases will carry out. For extra info, go to us on the net at:

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Tags: Affordable Wire Management, BOS, utility-scale

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