TECHNICAL FIELD

The present system relates to corrosion protection systems for foundations that support single-axis solar trackers thereon.

BACKGROUND

Solar energy harnesses the essentially limitless supply of energy emanating from the sun. A solar cell is a sandwich of positive and negatively doped layers of silicon on either side of an absorber layer. When photons strike the surface of the cell, they cause electrons in the absorber layer to go from a lower energy ground state to a higher energy excited state. The P-N junction induces an electric field around the absorber layer that allows current to flow in a controlled manner. This direct current is converted to alternating in an inverter and fed into the grid or consumed onsite.

Distributed solar is typically configured as small grid-connected rooftop arrays on homes and businesses. So-called utility scale solar systems are ground-based and usually configured as fixed-tilt arrays or single-axis trackers. Fixed-tilt arrays are oriented along East-West rows and inclined at an angle with respect to the ground that is dictated by the latitude of the array site. Single-axis trackers are oriented along North-South rows and use a torque tube that rotates slowly throughout the day to allow the solar panels to remain orthogonal to the sun as its position moves from East to West each day.

All ground-mounted solar arrays must contend with the problem of corrosion. Corrosion is the gradual destruction of materials via chemical or electrochemical reaction with their environment. Non-stainless steel that is exposed to outdoor conditions will inevitably undergo corrosion, even if only exposed to air. Foundation components that penetrate the ground are exposed to harsher corrosive environments because they are in contact with reactive soils and sometimes water, both of which will expedite corrosion over above-ground atmospheric conditions. The industry standard calls for using galvanized steel in to protect these components from corrosion.

In the context of single-axis solar trackers, the monopiles that are currently used to support them are cannot be optimized to their environment because that are one-piece components. This is a consequence of their design. Relatively speaking, monopiles are not good at resisting bending forces. Therefore, to deal with this, much larger piles are used than that necessary to support the weight of the array alone. Also, because of corrosion, it is assumed that percentage of the pile's thickness will disappear each year. Therefore, if the system is expected to perform for 30 years than there must be enough uncorroded material left at year 30 to withstand the worst cases forces. As a result, in the system must be over spec-ed so that it continues to be perform to minimums levels over its entire financed life. The monopile paradigm mandates this.

What is instead desired is a system that customizes each component to the specific corrosive environment it will be exposed to. Ideally, such a system will conserve the amount of material used in the components that form the foundation. In addition, such a system will be strong enough be able to resist the forces that a single-axis tracker must resist.

SUMMARY

In preferred aspects, the present system provides a corrosion resistance system for use in general with foundations that extend below and above ground. In exemplary aspects, the present system is ideally suited for use with foundations used for creating structures that support single-axis solar trackers thereon but is not so limited.

In one preferred aspect, the present system provides a truss leg comprising: a first elongated member having an open hollow shaft; a second elongated member having an open hollow shaft; and a connecting portion for joining second elongated member to the first elongated member, wherein the first and second elongated members each have a first corrosion protection layer formed on inner and outer surfaces thereof, and the first member has a second corrosion protection layer formed over the first protection layer on the outer surface only.

In another preferred aspect, the present system provides A truss foundation system comprising: a pair screw anchors, each screw anchor comprising an elongated body with a circular cross section that is open at both ends; and a pair of upper legs, wherein the screw anchors and upper legs have a first corrosion resistance layer formed on inner and outer surfaces thereof, and the screw anchors have a second corrosion resistance layer formed over the first layer on the outer surface only.

A truss component installed by a method that reduces a rate of internal corrosion comprising: driving an open screw anchor into supporting medium with a rotary driver, the screw anchor having a first corrosion resistance layer on inner and outer surfaces thereof and a second corrosion resistance layer over the first corrosion resistance layer on the outer surface only; passing a mandrel through the screw anchor into the supporting medium while driving; and releasing pressurized air proximate to a tip of the mandrel within the screw anchor to blow the medium out of the top end so that the open screw anchor is substantially devoid of the medium after driving.

As such, the present foundation system for single-axis trackers preferably utilizes truss foundation rather than monopiles. A-frame-shaped trusses have the advantage of translating lateral loads into axial forces of tension and compression rather than bending. Moreover, because columns are relatively good at resisting axial loads, the legs of an A-frame can be much smaller than an equivalent monopile supporting the same sized tracker (thus conserving material).

Another advantage of trusses stems from their modularity. H-piles are unitary in nature and are manufactured with uniform thickness and to a uniform finish. That means that even though only a portion of the H-pile is below ground, the entire pile is made to deal with the worst-case under-ground corrosion conditions. The two-sided geometry of the H-pile means that the flanges and web are corroding from two-sides at once, requiring the flanges to be doubly thick. In contrast, the embodiments of the present system disclosed herein take advantage of a truss's potential modularity to customize each component to perform to its specific corrosive environment and to provide installation methods and machines that reduce the rate of corrosion for underground components.

It is to be understood that although the present system is ideally suited for use with single-axis trackers, the present system is not so limited. In fact, it can be used to support other solar systems and also, to provide foundations outside of the solar tracker field.

