Ground Mounted Solar: Single Pile vs Double Pile Selection Guide

In ground mounted solar parks, the mounting system decides three things: how fast you install, what the foundation costs and how well the system stands up to wind and snow. The fundamental choice is single pile or double pile.

In this guide we show when each system fits, with real decision criteria based on soil, wind, budget and installation speed, drawn from the dozens of MWp of installations AXINAR has built in Greece, France and Italy.

The difference, in plain terms

The single pile mount has one vertical pile per panel table. A metal structure (rail plus purlin) is bolted onto it and carries 20 to 30 panels in one or two rows.

The double pile mount has two vertical piles per table, set parallel to the direction of the tilt. The two piles are joined by a horizontal beam, and the panel structure rests on them.

In short: single pile means fewer piles, less foundation work, faster installation. Double pile means twice the piles, greater stability, greater tolerance of extreme conditions.

When the single pile mount fits

The single pile is the default choice for most projects in Greece. It fits when:

• The soil is stable: earth with CPT/SPT resistance above 10 blows, or clay at the right moisture level.
• Wind in the area is moderate: basic wind speed under EN 1991-1-4 (Eurocode 1) up to 27 m/s.
• Snow load is below 1.5 kN/m²: which holds for most of Greece apart from mountain areas.
• Installation time matters: with one pile driver, a typical crew sets 80 to 120 piles a day, that is 500 to 800 kWp a day.
• The budget is tight: foundation cost drops by 30 to 40% against a double pile.

In practice, most residential (10 to 100 kWp) and mid sized commercial (100 kWp to 5 MWp) parks in flat and rolling parts of Greece are built on single pile mounts. The AXINAR Axisol 1P1V is a single pile system galvanised with a Magnelis® ZM430 coating.

When the double pile mount fits

The double pile becomes necessary when conditions move outside the safe margins of the single pile:

• Strong wind: coastal areas, islands (Cyclades, Dodecanese, northern Crete), exposed hills with a basic wind speed above 27 m/s.
• Heavy snow: mountain installations above 800 m where the snow load exceeds 2 kN/m².
• Unstable soil: sandy or soft clay soils, geologically unstable spots, or ground with large swings in moisture.
• Longer tables in a single row: when the project calls for 40 or more panels per table, the extra stability of the second pile becomes critical.
• Steep tilt angles: installations with a tilt above 35° (close to the optimum angle for northern regions) have a longer lever arm, so they need double support.
• Agrivoltaics (agri-PV): East West agri-PV systems need extra height (2.5 to 4 m) so farm machinery can pass underneath. The taller system calls for a double pile for durability.

The AXINAR Axisol 2P2V is a double pile system with the same Magnelis® and hot dip galvanising specifications, designed for wind zone 4 under the Greek national annex to EN 1991-1-4.

Foundation, three options, three outcomes

Before you decide single or double pile, the foundation type has to be settled. The options:

1. Ram pile (driven)

The pile is driven into the ground with a hydraulic hammer. Speed: 2 to 4 minutes per pile. Ideal for earth and clay soils free of stones.

• Advantages: Speed (500 to 800 kWp a day), low cost, no concrete, easy removal later on.
• Disadvantages: Does not work in rocky ground, needs a special machine, noisy during installation.

2. Screw pile

The pile has a helix at its tip and is screwed into the ground with a special head. Speed: 5 to 8 minutes per pile. Ideal for relatively hard soils with few stones.

• Advantages: Works in harder ground than a ram pile, controlled depth, no concrete.
• Disadvantages: More expensive than a ram pile (15 to 25% more), slower to install, again not for rock.

3. Concrete foundation

A hole is dug, the pile is set and the hole is filled with concrete. Speed: very slow (it needs 7 days to cure). Ideal for rocky ground or where the other two are not feasible.

• Advantages: Works everywhere, maximum wind resistance.
• Disadvantages: Expensive (2 to 3 times a ram pile), slow, irreversible (a problem in agrivoltaics where the land has to be restored).

Installation speed, the real numbers

For a typical 1 MWp project on a Greek farm with earth soil:

The time difference of ~4 to 6 days per MWp turns into labour and equipment hire cost, which matters on projects running several MWp a month.

Cost per kWp

Indicative prices for Greece (2026 prices, excluding VAT):

The extra 40 to 50% cost of the double pile is justified only when the single pile does not cover the conditions. Otherwise it pulls down the project’s investment IRR.

Wind resistance, how it is calculated

The study follows Eurocode 1 (EN 1991-1-4) with the Greek national annex. The parameters that go in:

• Basic wind speed (v_b,0) per wind zone (Zone 1: 27 m/s, Zone 2: 30 m/s, Zone 3: 33 m/s, Zone 4: 33 m/s).
• Terrain category (0 to IV): flat water surface, open plain, or urban fabric.
• Panel height above ground: at 1.5 to 2 m the single pile is sufficient. Above 2.5 m a double pile is recommended.
• Tilt angle: a steeper tilt means a longer wind lever arm.
• Panel dimensions and spacing: larger panels (500 to 620 W bifacial, for example) have a larger surface, so higher loads.

AXINAR supplies a full static calculation report with every quotation, based on Eurocode 1 and on NF P 94-262 (the French standard for piles) for projects that require it. The engineering design is done in Thessaloniki.

Soil geology, the primary factor

Before you decide on a mounting system, you need a geotechnical survey (CPT or SPT tests) on every site. Without one, you are working on assumptions.

Typical results and recommendations:

Use in real AXINAR projects

AXINAR has built mounting systems for large PV projects in Greece, France and Italy. Examples of what was chosen:

• Ronchamp / Magny-Danigon, France (5 MWc): Single pile Axisol 1P1V with ram piles, on farmland with a CPT resistance of 15+ blows. Time to install the mounts: 8 weeks.
• Massarosa, Italy: Double pile Axisol 2P2V on unstable peaty ground with ram piles 3 m deep, with a reinforced anti corrosion protocol (Magnelis ZM620).
• Brou, France: East West agri-PV on a farm, mount height 2.8 m so a tractor can pass. Double pile mandatory because of the height.
• Geruge (Jura), France: Mountain area with a snow load of 2.5 kN/m². Double pile with a reinforced cross beam, screw piles because of the rocky ground.

Magnelis® or plain hot dip galvanising?

Whether you go single or double pile, the coating decides the service life.

• Magnelis® ZM120 (120 g/m²): for moderate environments, French category C3, inland Greece. Service life 25+ years.
• Magnelis® ZM430 (430 g/m²): for coastal areas up to 20 km from the sea, category C4. Service life 30+ years.
• Magnelis® ZM620 (620 g/m²): for extremely damp or salty environments, category C5-M. Service life 40+ years.
• Hot dip galvanising to EN ISO 1461: an alternative coating for particularly aggressive environments or where a coating thickness above 85 µm is required.

On PV projects meant to last 25 to 30 years, the choice of coating matters as much as the choice of mount.

The decision tree

A practical decision guide:

1. Do you have a geotechnical survey? If not, ask for one. Without it, every choice is an assumption.
2. Is the site exposed to strong wind (coastal, island, high altitude)? Yes, double pile. No, carry on.
3. Snow load above 2 kN/m²? Yes, double pile. No, carry on.
4. Is it agri-PV at a height above 2.5 m? Yes, double pile. No, carry on.
5. Is the ground unstable (loose sand, organic)? Yes, double pile. No, single pile.

Between 65 and 70% of projects in Greece end up with a single pile solution. The double pile is for special conditions, not a default choice.

Frequently asked questions

Conclusion

Choosing a single or a double pile mount is not a matter of preference, it is a matter of conditions. The parameters that count: the geotechnical survey, the wind zone of the site, the snow load, the panel height, the budget. On 65 to 70% of Greek projects, the single pile Axisol 1P1V is the right choice. For extreme conditions, the double pile Axisol 2P2V becomes mandatory. Both are manufactured in Thessaloniki with Magnelis®, with dozens of MWp installed in Greece, France and Italy.