Fluent Pillar, heritage setting


Fluent Pillar, oak poles


Fluent Pillar, Mediterranean heritage town


Fluent Pillar, Les orgues, montagne


Fluent Pillar, Hotel pool heating


Fluent Pillar, park seating


Fluid Pillar, Montpellier proposal


Fluent Pillar, prototype


Fluid Pillar, prototype flush


Fluent Pillar, Isographic drawing



The Fluent Pillar is a solar thermal collector that offers an independent vertical form, in order to overcome many of the siting limitations that are associated with panels The vertical form extends solar system siting potential in general. The vertical form gives extra versatility for physical and visual integration. It’s versatile sculptural form offers both a dramatic architectural statements and sensitive integration.

Fluent Pillars have an omni-directional, volumetric absorber element. This method of absorption means that the collector’s orientation is not critical to its output, meaning that it can be mounted in a number of different ways. e.g. On a roof, or on plinths near to the host building, or it can be mounted on posts high above the ground.

The Fluent Pillar is ideally suited to low temperature high thermal mass applications such as domestic water/space heating, pool heating, and under floor heating.

The working principles are simple, Fluent Pillars comprise two glass containers, mounted concentrically into a base, which, in turn, can be mounted onto a plinth or a pole. The chamber formed between the two glass components and the base, is evacuated to form a partial vacuum, this acts as insulation.

The inner glass chamber contains a fluid, which acts concurrently as the absorbing element and heat transfer medium; this is plumbed through a heat exchange system in a closed loop. Circulation is achieved by PV powered pumps which provide variable flow.

The fluid can be pigmented with a variety of colours and optionally with micaceous powder, which creates a billowing effect. This acts as a visual indicator of the amount of energy being absorbed by the collector. Giving the appearance of a calm billowing effect at low energy levels and a vigorous flaming effect at high energy levels.

The design also gives many opportunities for multi-purpose uses. The omni-directional energy pick-up opens the potential for using landscape features such as hard groundworks and structures to act as light concentrators, The output of the collectors can be boosted by over 200% in this way. This aspect of the Fluent Pillar allows new creative applications for designers and architects. For example use of large sweeping parabolic structures, or the potential for seating that also acts as a light concentrator; Or even placement amidst a water feature. The possibilities are endless.

Each collector can be altered in the vertical dimension giving further versatility. The output capacity and the visual character can be finely adjusted by altering the height, proportions and quantity.

The Fluent Pillar of particular value to people who live in conservation areas and to those who live in buildings of historical interest and/or architectural significance. It is also ideal for use in dual function scenarios where it can be combined with outdoor lighting. Another major usage will be heating swimming pools where concern for aesthetics and the desire to maximise ground space are high priorities.


The Fluent Pillar was the first Solar Power generating sculpture developed by Dan Hughes-McGrail. One of the motives to start the Fluent Pillar’s development was a lack of alternatives for people who want solar power in heritage buildings.

Traditional product development cycles lead to designs that are concentrated on quantifiable physics and mass manufacturability. Aesthetic quality is considered incidental throughout the development process. The result is a lot of products that are not appropriate for items in the built environment where people must live with them.

A friend of Dan’s, the owner of a beautiful old vicarage in rural England wanted to install solar power. He searched but could not find anything on the market that he could bear to see on his lovely old building.

He approached Dan and so began an investigation into developing a sculptural solution that maintained the character of the building whilst harvesting solar energy.

The research Dan undertook revealed that this was not an isolated matter of one man’s personal taste. Beauty and versatility in design are needed not only for commercial, practical and regulatory reasons but for cultural sustainability reasons



A prototype was tested to a limited degree. In a non-optimised configuration with very simple reflector/concentrator in Gloucestershire, UK, the temperature log data shows that the overall average usable output about is approx. 1.4 KW/day/m2 of exposed surface. Peak daily average in summer is 2.3 KW/day/m2 and the low in midwinter is 0.53 KW/day/m2. To translate to an installed system, 1m2 is equivalent to 2×1.5m tall Fluent Pillar collector units. In a 7KW average output rated installation an array of 10-12 collector elements is appropriate.

An optimised set up can expect up to 400-500% increases in output

The data also showed that Fluent Pillar’s are particularly effective at ambient light conversion. The Fluent Pillar has a relatively high thermal mass. So temperature response to input is highly damped. If needed, responsiveness can be adjusted by reducing the fluid volume with the inclusion of volume reducing baffles within the collector chamber.

The upright orientation naturally protects the collectors from the temperature spiking in the middle of the day, by shadowing itself, but is more sensitive in the early and late parts of the day.

Running temperatures are proportional to flow and overall fluid volume. The running temperature adjusted with flow rates and the inclusion of baffles. For longevity, running temperatures of about 75ºC or below are recommended.

Generally speaking the Fluent Pillar is best suited for high thermal mass applications like domestic water/space heating, pool heating, under floor heating, etc.

The main tubes are optionally variable in the vertical dimension between 1200 mm and 1700 mm. The diameter of the base is 295 mm or 210 mm. The outer glass diameter is 150 mm.
The fluids should contain an anti-freeze, a surfactant and an anti caking agent to prevent the particles forming plaques.


The mileage in the supply chain is kept to a minimum. The laser cut components, seals and base are produced in the UK. The glass parts are made in Germany.
The Fluent Pillar system is designed to be assembled and installed by general trades with minimal instruction and oversight. The Fluent Pillar can be assembled on site or in any clean bench scenario using only an Allen key, a vacuum pump and some careful handling. The other components of installations – materials like stone, ceramics and wood may be sourced local to the site, as you would with any small construction project.