The latest Guide from Excel Energy's certified ground mount commercial solar panels installer

Ground mount commercial solar panels apply a bespoke approach to system design and efficiency, with factors such as climate, soil composition, and regional regulations all playing critical roles.

A primary technical consideration is the optimal routing of underground cabling, particularly for extended AC cable runs.

Quick Overview!

For the most efficient and reliable ground mount solar installations, always assess your site’s soil thermal conductivity and use high-conductivity bedding materials like Cable Sands or Cement Bound Sands (CBS) for underground AC cable runs. This approach prevents cable overheating, extends system lifespan, and ensures compliance with industry standards, delivering safer, more cost-effective ground mount commercial solar panels regardless of location.

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It’s important to remember that regional standards matter; for example, BS7671 isn’t just relevant to the UK, but also for many of the 230V parts of the Middle East, Malta and probably a few other hot, dry places too. In the UK soil, wet clay soils are much better conductors of heat than the dry, dusty soils found in some other regions, a difference clearly reflected in BICC figures and acknowledged by BS7671, which, while generally cautious in its default values, does allow for local adjustment using rating factors.

UK Distribution Network Operators (DNOs) and other providers have detailed knowledge of local soil characteristics and usually apply less conservative design margins than those prescribed by BS7671. In practice, these operators report minimal operational issues, demonstrating the effectiveness of site-specific assessment over default standard assumptions.

SOIL THERMAL CONDUCTIVITY VARIATIONS

For context, typical soil thermal conductivity values present the importance of accurate site assessment – conductivity in W/(m.K)

Here is a table comparing the different variations of soil thermal conductivity:

DRY SAND

Typically presents a conductivity of approximately 0.5 W/(m·K), corresponding to a thermal resistivity of 2.0 K·m/W.

SATURATED SAND

When saturated, sand conductivity increases to around 2 W/(m·K), or 0.5 K·m/W.

CLAY SOILS

Clay soils generally maintain more consistent thermal properties, although freezing conditions can significantly enhance their cooling capacity.

These variations underscore the necessity of factoring local soil conditions into underground cable design.

THERMAL CONDUCTIVITY (OR RESISTIVITY) OF DIFFERENT SOIL TYPES

The table below presents the thermal conductivity values for a range of soil types typically found on ground mount commercial solar panels.

These values are a key consideration when designing underground cable routes, as soil thermal properties directly affect cable heat dissipation, operational efficiency, and long-term reliability:

MATERIAL	MIN	MEAN	MAX
Peat (Dry)		0.17
Peat (Wet)		0.54
Peat (Icy)		1.89
Sand Soil (Dry)	0.43	0.56	0.69
Sand Soil (moist)	0.87	0.955	1.04
Sand soil (soaked)	1.9	2.16	2.42
Clay Soil (Dry)	0.35	0.435	0.52
Clay Soil (moist)	0.69	0.78	0.87
Clay Soil (Wet)	1.04	1.3	1.56
Clay Soil (Frozen)		2.51
Gravel	0.9	1.075	1.25
Gravel (sandy)		2.51
Limestone		1.3
Sandstone	1.63	1.885	2.08

This level of assessment may not be justified, provided there is a thorough understanding of how thermal performance will fluctuate with seasonal changes.

HOW DOES SOIL RESISTIVITY AFFECT CABLES?

Soil resistivity affects underground cables by determining how efficiently they can dissipate heat into the surrounding ground, which in turn impacts cable performance and lifespan.

System design and efficiency for ground mount commercial solar panels can vary significantly based on your location; factors such as climate, soil composition, and local regulations all play a role. One important aspect to consider is the method for running cables underground, especially when dealing with long AC cable runs.

In typical environmental conditions, the current-carrying capacity (CCC) of the cables is reduced as water migration occurs, and a fully loaded cable creates a dry zone in its surrounding area due to the higher temperature. The thermal resistivity of the soil decreases when the temperature rises, while the resistivity of cooler soil rises with the same water content.

As a result, dry soil that has high thermal resistivity will trap heat around the cables, quickly increasing the local temperature.

HOW DOES TEMPERATURE AFFECT CABLES?

Cables reaching high temperatures cause water migration, resulting in the real thermal resistivity of the soil consistently becoming much higher than assumed in the project design.

Project designers can maintain favourable conditions for the transfer of heat from cable to soil by blocking the migration of water through the soil via backfilling with excavated material that has lower thermal resistivity.

When thermal resistivity in the soil is relatively high, e.g. 2.5 (K.m)/W, there should be a stabilised backfill of low thermal resistivity (1.0 (K. m)/W or less) surrounding the cables. A larger backfill area improves the thermal conditions for heat transfer, increasing cable capacity.

Cable capacity also depends on the position in which they are buried. Potential exposure to external heat sources should also be taken into account when selecting cables, as it has a direct impact on the reliability of supply.

Many countries have set recommended standards for soil thermal resistivity for the purpose of cable sizing. Standards like IEC 60287 specify the maximum current a cable can carry in certain environmental conditions and installations without the temperature exceeding the rating of the insulation material.

To reduce cable size without losing power-carrying capacity (ampacity), you must backfill your trench with a material that is less thermally resistive. Lower thermal resistivity (measured in K ⋅ m/W) allows heat to escape the cable efficiently.

ESSENTIAL REQUIREMENTS TO GUARANTEE LONG-TERM RELIABILITY

To guarantee the long-term reliability of the electrical grid, backfill materials must meet precise specifications:

LOW THERMAL RESISTIVITY

For optimal system performance, it is essential that the backfill material maintains a thermal resistivity below 1.2 K·m/W, with a preferred target of less than 1.0 K·m/W, even under dry conditions. This ensures efficient heat dissipation from the cable, minimising the risk of overheating and supporting long-term operational reliability.

MOISTURE MIGRATION RESISTANCE

Premium backfill materials are engineered to retain moisture effectively, which is critical in preventing thermal runaway. By maintaining consistent moisture levels, the backfill helps to stabilise the soil’s thermal properties, guaranteeing that heat generated by the cable does not drive water away from the installation and increase thermal resistance.

MECHANICAL PROTECTION

The backfill must deliver a stable and uniform bedding that safeguards the cables' health against potential damage from sharp stones or soil movement. High structural integrity is required to withstand compressive forces, ensuring the cable remains protected throughout its operational lifespan and reducing the risk of mechanical failure.

OVERVIEW OF UNDERGROUND THERMAL BACKFILLS

OPTIMISING UNDERGROUND AC CABLE RUNS FOR GROUND MOUNT SOLAR

Ground mount commercial solar panels frequently demand extended underground AC cable runs. If improperly managed, these long runs can create resistance, voltage drop, and unwanted power losses, ultimately raising installation and operational costs.

To minimise cable size and keep systems efficient, it’s vital to focus on material choices and installation practices that improve heat dissipation and maintain cable integrity. By using high-conductivity bedding like Cable Sands, robust Cement Bound Sands (CBS), and advanced engineered backfills, solar installers can ensure reliable, cost-effective underground cable routes that comply with ENA TS 97-1 standards while reducing the demand for oversized cables.

BEDDING AND BACKFILL SOLUTIONS FOR UNDERGROUND CABLE INSTALLATIONS

Selecting the right bedding and backfill materials is a critical step in any underground cable project. These materials not only anchor and protect cables but also help regulate temperature, prevent mechanical damage, and extend the service life of the entire installation.

Effective bedding and backfill solutions are essential for safe, efficient, and long-lasting infrastructure, whether for solar farms, utilities, or transport networks.

Here are the smart energy solutions that can help you achieve reliable underground cable performance:

Cable sands are manufactured to strict ENA TS 97-1 specifications, assuring optimal thermal conductivity for underground cable installations. They are an excellent choice for solar sites, railways, and energy infrastructure, offering:

✅ Consistent particle distribution for dependable bedding

✅ Superior heat dissipation reduces the chances of cable overheating

✅ Robust compaction for lasting ground stability

✅ Reliable operation and safety for low, high, and ultra-high voltage cables

CABLE SANDS: RELIABLE SUPPORT FOR UNDERGROUND POWER AND DATA

CBS products are pre-mixed, semi-dry blends designed for reinstating trenches, bedding ducts, and filling voids. With adjustable mix ratios ranging from 1:3 to 1:20, CBS solutions provide:

✅ Prolonged workability, accommodating installations that require extra time

✅ Low thermal resistance (≤1.2 Km/W) to help maintain optimal cable temperatures

✅ High strength to support significant surface loads

✅ Full adherence to ENA TS 97-1 and NGTS 3.05.07 quality standards

CEMENT BOUND SANDS (CBS): DURABLE AND ADAPTABLE FILL

Our specialised backfill options are bespoke for durability and ongoing protection in a variety of civil, utility, and renewable energy applications. Key advantages include:

✅ Dense compaction to minimise the risk of future ground settling

✅ Resistance to moisture for stable, long-term performance

✅ Maintains the right thermal environment for buried cables and pipes

✅ Helps reduce future maintenance and repairs

BACKFILL SOLUTIONS:D LASTING PROTECTION AND PERFORMANCE

WHAT’S NEXT FOR YOUR SOLAR PROJECT?

Optimising for ground mount commercial solar panels is about understanding soil conditions, using thermally efficient backfill materials, and designing with longevity and performance in mind.

By focusing on careful planning and proven bedding and backfill solutions, ground mount commercial solar panels not only reduce the size and cost of long AC cable runs but also provides the reliability and efficiency of your solar project for years to come.

If you are planning or undertaking a cable installation project, please provide the following technical details so that our team can recommend the most suitable solution for your requirements:

✅ What is the operating voltage of the cable system (for example, 33kV, 132kV, or 400kV)?

✅ Will the cable be installed as a direct burial or routed within a duct?

✅ What are the ambient soil characteristics and prevailing ground conditions at the installation site?

If you have this information available, contact our team of renewable energy specialists today to discuss how we can deliver a bespoke cable solution that meets your project’s technical and operational requirements.