Clamping a Mirror Onto a Steel Pipe Why a Solar Thermal Company Patented a Bracket

This application covers the fitting that joins a sun tracking mirror to the steel post driven into the ground beneath it. Claim 1 is a heliostat securing assembly: an insert that drops into the open top of a tubular foundation post, a wedge shaped clamp that rides against it, and bolts that pull the two together so that axial movement is converted into sideways movement and the whole thing jams itself between the mirror’s support shaft and the inside wall of the post. It was filed by Vast Solar Pty Ltd, the Australian concentrated solar thermal company, and names Bruce Alexander Leslie and Benjamin Charles Plant as inventors. The application is a divisional of Australian application 2020251711.

The Problem

A heliostat is a flat mirror on a two axis drive. Its job is to track the sun across the sky and keep the reflected beam pointed at a fixed target, usually a receiver at the top of a tower. A concentrated solar power plant is a field of these mirrors, all aiming at the same target, concentrating enough sunlight on it to heat a fluid to a temperature useful for generating steam and therefore electricity. The field is the plant. Everything else is a boiler and a turbine.

The important consequence, and the one this patent is about, is arithmetic. A commercial solar power tower plant needs thousands of heliostats, and each one is an identical small structure that has to be built, transported, stood up, levelled and secured in an empty paddock. The mirror and the drive are factory items whose cost falls with volume. The installation labour does not. Any minutes saved on installing one heliostat get multiplied by the number of units in the field, which is why a company that builds solar fields ends up patenting a bracket.

The background section of this specification puts it in one line: in a tower based CSP installation, many heliostats are required, and they need to be installed as cheaply, quickly and accurately as possible. Each mirror has to be supported around its centre of gravity, which means a foundation post holding it above the ground, cantilevered. The specification says the simplest post that gives adequate bending and torsional support is a hollow steel section, circular or rectangular, put into the ground.

It then lists the ways that post can be installed: vertical hammering, posts with auger flutes rotated into the ground, pre augered holes with the post concreted in and the surrounding ground compacted, or concrete plinths. And it observes that whichever method is used, you still have the same problem at the top of the post, which is getting a heliostat onto it quickly, securely and reliably.

The specification then sets out four things it wants from that attachment, and those four wishes are effectively the design brief for the claims. It should tolerate burring or unevenness on the top edge of the post, because hammering a steel post into the ground damages the rim. It should seal the hollow post against rain. It should be able to be fixed to the rest of the heliostat in a single piece, so that installation in the field is just installing posts and then lowering otherwise complete heliostats onto them. And it should be reliably actuated by non specialist staff.

What This Invention Does

Claim 1 has three components and one functional requirement.

The three components are an insert that sits inside the upper opening of the foundation post and defines an aperture that receives the heliostat’s support shaft, a clamp arrangement that locates the insert in that opening and carries at least one inner or outer bearing surface bearing against a corresponding surface on the insert, and one or more urging connectors that join the insert to the clamp and can pull one toward the other along the axis of the post.

The functional requirement is where the invention actually lives. At least one of those bearing surfaces has to be configured to transform part of the relative axial movement between insert and clamp into relative transverse movement. So when the assembly is in the post and you operate the connectors, the clamp is driven sideways, outward, and the assembly wedges itself between the support shaft and the post wall. Claim 2 spells out the ordinary way of achieving that, which is to incline the bearing surfaces relative to the axial direction. This is a wedge, and functionally the insert plus clamp behaves like an oversized collet.

Two embodiments are described. In the first, the insert is a collet sleeve with an integral annular cover portion and an insert portion carrying a single continuous frusto conical outer bearing surface. Three arcuate clamping wedges sit around it, each with a matching inclined inner face and an outer clamping face. Three equally spaced bolts, with drive heads accessible from above, pull the wedges up the cone, so they climb axially and spread radially until their outer faces friction fit against the inside of the post.

The second embodiment reduces the same idea to one wedge and one bolt. Here the insert has a pair of inclined track portions with tongues on one side, and the wedge has matching channels that slide on them. Because there is only one wedge, the reaction has to come from somewhere else, so the insert carries stationary reaction members on the opposite side, each with a pair of axially spaced contact projections that press against the inner wall. The specification puts these at about plus or minus 60 degrees from a transverse axis through the centreline of the wedge, with a stated workable range of plus or minus 30 to plus or minus 80 degrees, and notes that with the wedge included the three contact points end up equi angularly spaced at 120 degrees. Claim 15 records the consequence: in this version the shaft aperture and the post opening are deliberately not concentric when clamped.

The specification is candid that the second embodiment exists to save money. It says the insert portion has been optimised by removing as much mass as practicable, which can lead to a reduction in overall manufacturing and material costs, and that the sleeve may be cast, machined or both. Materials given for the sleeve are a hardened plastics material such as polycarbonate or glass reinforced plastic, or a metal such as aluminium or an alloy such as brass.

Several details map directly onto the four wishes in the background. The cover portion is a locating flange that fits over the upper rim of the post, so the assembly hangs at the right height without anyone holding it, and its lower face has an annular recess to accommodate that rim. The specification says this covers burring and unevenness from installation and creates a weatherproof seal, which is the rain wish and the burring wish answered by one part. The bolts are pre installed and loosely engaged with their nuts, with a lower ring washer holding the wedges together, so the entire securing assembly travels attached to the heliostat and goes into the post as a single unit, which is the single piece wish. An upper ring washer gives the bolt heads a bearing surface and doubles as a percussive surface so the assembly can be hammered down into the post. And the actual field operation reduces to lowering the heliostat and tightening bolts from above, which is the non specialist staff wish.

Claim 26 is the corresponding method, and claim 28 covers the whole heliostat arrangement: the tubular post, the securing assembly, and a heliostat whose drive assembly support shaft is received in it. One neat secondary use appears in the detailed description. The support shaft is a hollow cylinder containing a torsional spring that tensions the drive around the azimuth axis, and the cap end base of the collet sleeve retains and encloses that spring, protecting it from the weather.

Key Features

• Axial pull converted to radial grip. The defining limitation of claim 1 is a bearing surface geometry that turns the axial travel produced by tightening a bolt into transverse movement of the clamp, so tightening from above generates the sideways force that locks the assembly in the post.
• A cover flange that locates, seals and hides damage. The annular cover sits over the rim of the post with a recess in its underside. It sets the assembly’s height without measurement, keeps rain out of the hollow post, and covers burring left by hammering the post into the ground.
• Shipped as one piece with the heliostat. The bolts are pre installed and loosely engaged, and a lower ring washer holds the wedges together, so the complete securing assembly arrives attached to the mirror and is inserted as a single unit rather than assembled in the field.
• A percussive top washer. The upper annular ring washer provides a bearing surface for the bolt heads and a surface that can be struck, so the assembly can be hammered into position in the post when the fit is tight.
• Two clamps for two cost points. The first embodiment uses three arcuate wedges and three bolts around a continuous frusto conical surface. The second uses a single wedge, a single bolt, and stationary reaction members on the opposite side, with the insert lightened to cut material and machining cost.
• Reaction members at a stated angle. In the single wedge version the reaction members sit about plus or minus 60 degrees from the transverse axis through the wedge centreline, within a stated range of plus or minus 30 to plus or minus 80 degrees, giving three contact points spaced 120 degrees apart.
• Tolerant of the post it is given. Claim 9 covers a circular hollow section, and the description adds rectangular, elliptical and square posts, plus an inverted arrangement where the wedges sit inside the insert and grip the shaft rather than the post.

Who Is Behind It

Vast Solar Pty Ltd is the Australian operating company of Vast, a concentrated solar thermal developer founded in 2009. Its technology uses a modular arrangement of many small towers rather than one central tower, with liquid sodium as the heat transfer fluid, which is unusual in an industry that mostly uses molten salt. The company’s flagship project is VS1, a 30 MW plant with 288 MWh of thermal storage at Port Augusta in South Australia, described on the company’s current projects page alongside a co located green methanol demonstration plant and a planned 150 MW expansion.

The corporate position needs care, because it has changed. The group listed in the United States as Vast Renewables Limited in December 2023 through a business combination with Nabors Energy Transition Corp, trading on Nasdaq under the ticker VSTE. In May 2025 it announced a voluntary delisting, filed to deregister with the Securities and Exchange Commission, and moved its shares to the over the counter market, giving simplification of corporate structure and reduced regulatory cost as the reasons. So the company is Australian headquartered, formerly Nasdaq listed, and currently not. The patent applicant is still the Australian entity, Vast Solar Pty Ltd.

On lineage, the specification is careful about what it does and does not claim. It contains a cross reference paragraph stating only that the application is related to International Application PCT/AU2020/050333, published as WO 2020/198803 and filed 3 April 2020, whose contents are incorporated by reference. It does not state a priority or convention claim anywhere in the body, and the only other relationship established by the document itself is the title page entry recording it as a divisional of Australian application 2020251711. From the published family record, rather than from this specification, that PCT application claims priority from Australian provisional application 2019901160 filed 4 April 2019, and the corresponding granted United States patent is US 11,927,367. That makes the priority country Australia.

Why It Matters

The cost problem in concentrated solar thermal is not the physics. Reflecting sunlight at a target is well understood. The problem is that a plant is a very large number of small identical structures spread over a large area of ground, and the capital cost is dominated by the solar field. Industry roadmaps have targeted the installed cost of the heliostat field for years, and the components people usually point at are the mirror, the drive and the control electronics. Installation labour is the part that does not fall automatically with manufacturing volume, because somebody still has to stand in a paddock and attach thousands of mirrors to thousands of posts.

That is the calculation behind this application. If attaching a heliostat currently means shimming, levelling, welding or bolting a flange plate, and the alternative is lowering a pre assembled unit into the post and tightening bolts from above, the saving is small per unit and large per plant. The specification’s own wish list gives the game away: it wants the assembly to arrive in one piece, to hang itself at the right height, and to be actuated reliably by non specialist staff. Those are labour cost requirements written as engineering requirements.

The wedge mechanism also solves a tolerance problem that is easy to miss. A steel post hammered into soil does not end up perfectly plumb or perfectly round at the rim, and its internal diameter varies within manufacturing tolerance. A rigid bolted flange would need the post to be accurate. A wedge does not, because it simply expands until it meets whatever is there and then grips by friction. The second embodiment goes further and accepts that the shaft will not be concentric with the post, which is an explicit decision to trade geometric precision for tolerance of a rough site.

One caution for readers. What is published here is an application, not a granted right. It is a divisional filed in March 2026 from a 2020 parent, and the claims as filed are broad, covering any bearing surface geometry that converts axial to transverse movement rather than only the inclined surfaces the drawings show. Whether that breadth survives examination is a separate question from whether the bracket works.

Related Concepts

• Heliostat – the sun tracking mirror this assembly attaches to its foundation.
• Solar power tower – the plant architecture that requires thousands of heliostats and makes per unit installation labour the dominant cost.
• Solar tracker – the drive mechanism on top of the support shaft that keeps the mirror aimed at the receiver.
• Collet – the workholding device whose expanding sleeve and taper this securing assembly closely resembles.
• Piling – the driven post foundation methods the background lists, and the source of the rim damage the cover flange is designed to hide.

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AU 2026202183 was published in the Australian Official Journal of Patents on 9 April 2026 and is open for public inspection. Patent applications represent inventions that are sought to be protected and do not necessarily reflect commercially available products.