PVs plus Timber: The Earth Centre’s Solar Canopy

Photo: Carpenter Oak and Woodland

Arrival – the Earth Centre’s entrance, with Bill Dunster Architect’s Welcome Centre in the foreground – Photo ZEDFactory

Photo – FCBStudios

Photo – Carpenter Oak & Woodland

The buildings and structures at Doncaster’s Earth Centre, which was briefly open over the millennium years, were ahead of their time. This included its incredible timber space frame, which straddled the main visitor concourse, holding up an array of Solar PVs.

If you happened to be traveling south-west of Doncaster the evening of October 12th last year, and looked up, you might well have seen a sky filled with fireworks. It may not have been, but most probably was, for the launch of the Solar Canopy, the latest of the buildings to be officially unveiled by Doncaster’s, and indeed much of the north-east’s, celebrated and indeed somewhat controversial sustainability and environment education project, the Earth Centre.

Amidst the beaming faces of proud council officials and other dignitaries, the Canopy took its place centre-stage in the Earth Centre’s assortment of buildings. In so doing it brings to a close the long drawn out journey in the development of the centre’s buildings, which have moved from wild blue-sky eco-dreamings, to the more ‘down-to-earth’ projects which made it through.

The Solar Canopy is the exception. It is the most visually exciting structure on the site, immediately demanding onlookers’ attention as soon as it is seen. By contrast, the entrance feels understated. You first pass the Welcome centre, the first of Bill Dunster’s two buildings, with its clamplike glulam timber beams, mounted at the edge of the sharp drop to the river Don. From there you cross onto the old concrete mining bridge, where the Earth Centre’s complex of main site buildings edge into view. To the right is Dunster’s conference office, and FeildenClegg’s half buried Earth Gallery, engineered by Atelier ten. To the left, FeildenClegg restaurant facilities – and there, spanning the two, like a prehistoric dinosaur bird  temporarily resting from its Jurassic flight, the solar canopy.

Once there, you turn round and look west. In front is the Dunster afterthought, the conference centre, with two conning towers bedecked with the practice’s by now trade-mark wind cowls. Inside, NHS heaters have been reused and painted a sprightly orange, whilst old telegraph poles hold up the central body of the building. Closer to, still on the left, is the gallery, burrowing into the side of the rising limestone hillground. From a certain angle, and in isolation, its limestone face could be mistaken for a vertical wall section of a motorway bridge embankment but conjoined with the solar canopy it adds to the sense of throughway and ‘centres’ the concourse. On the canopy’s opposite side is the two-tier restaurant, with its light and airy wooden chair and table area. Taken in all together these feel somewhat like a slightly random matching of four disparate building styles, supplemented in the middle distance by Conisborough castle.

Up close, it takes on shades of an elaborate and complicated piece of organic meccanno covering the central concourse, or in Southern Europeanese, the Plaza. To the restaurant side of the canopy are five supporting concrete pillars. On the Planet Earth galleries’ side, two wooden pillar structures issue out and up from the ground rest, multiplying in number and reaching upwards into a crows’ nest gantry of dark-brown larch rods, or members, joined by steel nodes. There is an elegant sculptural quality about the form, using six of these members to cross from side to side. At its peak rests a space frame, angled at a mere 5 degrees, and on that, 250 or so photo-voltaic cells. It feels singularly small when an immediate peer, the recent Hannover Expo mega-canopy or expo-deck designed by Thomas Herzog and engineered by Julius Natterer is recalled, or the massive scale of Nordic glulam projects, but in its context, the timber structure is undeniably impressive. The pencil-thin larch members supporting the space frame with its load of photovoltaics, showcases a compelling if novel environmental synergy, – combining the living quality wood brings with it, and the renewable hopes symbolised by the latest hi-tech generation of cutting-edge photovoltaics.

If the solar canopy looks like a prehistoric beast laden with a man-made load from afar, closer to the add-on above ground root-and-branch analogy takes hold, even if FeildenClegg abbreviated it to an ‘abstracted tree’ canopy. It is actually trapezoidal in form, a distorted or irregular space frame. Its irregularity adds to its beauty, a regular space frame would have been significantly less interesting, if more economic. The concept’s inspiration, according to Neil Thomas of the structural engineers, atelier one, owes much to an ex-colleague, Jane Wernick, when both were at Buro Happold. Wernick had proposed a timber space frame canopy, which she had distorted, for a project in Atlanta USA. This set Thomas thinking and the canopy, after much testing, was the result.

But this was already after considerable nursing. Peter Clegg, one of the earliest members of the original team who worked on the first Earth Centre masterplan, also played a central part in his practice’s involvement in the building, working on the project for what is now near-on a decade. Initially FeildenClegg envisaged the canopy as the centre piece of a grand entrance to the centre. Stage one of the plans had proposed off-site car parking, with an eco-transit system bringing passengers from the car park to this entrance, with the canopy envisaged as covering for the ticketing facilities, and a gift shop. Its use as a solar energy support system was out of the picture. Not only this, but the space frame skeleton was to have been in glass. Planning proceeded almost to ticket stalls being installed when, in 1997, the Lottery Commission revised the funding conditions. Originally a phased project with £50 million committed for both phases 1 and 2, with the solar canopy always pencilled in for phase 2, suddenly, phase 2 had dropped out of the equation.

At the same time, the centre had registered another project, a two stage EU Thermie bid for PV usage and monitoring but was proposing to use these for different buildings. This was part of the original aim, that the centre be wholly self-sufficient energy-wise. With the Lottery regulations changed, and the buildings now in the planning application queue, a decision was made to reposition the PV bid onto the space frame, so inaugurating the solar canopy concept. Linking the two projects under one roof, as it were, worked well, after certain technical problems were resolved, (for instance the covering of the roof which avoided overshadowing; or electrical systems problems, where a further detailing for housing the wiring in the aluminium space frame skeleton was needed). Thus, the space frame became a showcase for PV and the potential uses and affects the specific roof space could have in terms of renewable energy creation.

Initially, there was considerable resistance to the idea of using timber for the space frame, let alone a distorted trapezoidal space frame. Various contractors, including Bovis, argued that it was neither realistic, nor economic, and exerted considerable pressure for a steel frame. FeildenClegg, with sympathetic nods from the Earth Centre management withstood this, and eventually the timber version was approved, and the “sustainability-friendly Taylor Woodrow replaced Bovis.”  In winning this argument, FeildenClegg, and Atelier One have proved a point – that the costs of the structure were only marginally above the probable costs of a steel frame. Coming in at £225 000, this is, as atelier one’s Thomas states – cheap. This was for the canopy itself. Small additional work such as the rainwater systems, had not been accounted for in the budget, and pushed the figure slightly upward. Overall the whole structure, PVs and all, amounted to £1.2 million.

Atelier one arrived at the distorted space frame by imagining the frame as an upside-down membrane surface, with a doubly curved surface to prevent buckling. This is a combination of using membrane structure technique with compression shell surfaces. Such mixing and matching is the fruit of the enabling facilitation of computers. Where Gaudi­ toiled many hours over his membrane structures, the compressed hanging arches, and Frei Otto spent an equal amount of endless days and nights on his Mannheim Multihall Gridshell and other lightweight structures, these twentieth-century experiments in pure tension surfaces have taken a quantum leap with the coming of computerisation, and their capacity to model, analyse and simulate before the building begins. For atelier one, the Solar Canopy was also a smooth piece of computational analysis, although there were problems where wood shrinkage affected the movement of the canopy, which hadn’t been anticipated. Wood shrinkage of between one and two mm, dragged the bolting system between the larch membranes and the galvanised steel nodes, which in turn meant movement across the canopy, before it came, safely, to rest. It remains an impressive feat, each of the timber membranes have unique measurements, flying out every which way and with no repeats, in turn making production processes that much more complicated. For FeildenClegg the design process has been seen as straightforward, although repeated testing was required before a part of the building could proceed further. A point in hand is the roundwood use of pins and straps, although during this testing it became clear the most economical system was simple bolt-through – flitch-bolting – application. This achieved stronger tolerance and was easier to tighten. The actual construction eventually happened in 2000.

FeildenClegg had already looked at home-grown woodland, specifically pine and sweet-Chestnut, with the idea of reducing the transport energy costs. The carpentry company helped guide FeildenClegg towards larch, after their initial choice of spruce was rejected, for reasons of durability and longevity.

The structure is comprised of 3.5 tonnes of regular roundwood, or 47.3 cubic metres, in all, 800 timbers of between 125mm to 250mm in diameter needed to make 221 nodes. The wood was grown in Scotland and cut and prepared by Carpenter Oak & Woodland at their yard at Kirriemuir, near Dundee, before being transported down, home-grown, and as, many a green architect would argue, from a relatively close supply source. If not in genuinely close proximity to the Earth Centre, then say within Bioregional’s 35 mile circumference limit. Without roundwoods regularity of form, the raw logs were first sent to a mill in Scotland to be ‘regularised’, made perfectly round and without taper from end to end, avoiding the lumpier detailing which comes with natural tree poles where one end is much bulkier than the other. The fabrication of each nodal member was done on jigs – because of the very high accuracy needed for the canopy’s triangulation to work. A high degree of three-dimensional tolerance was required for all the members to measure up together – 20mm over entire structure – and since the wood still has its living individuality; its knots and curves, very accurate drilling was needed. A tolerance of 2 mm over individual connections was aimed at. To this end, two special ‘crazy’ machines were built – the jigs – in effect a large I-beam, to process the poles to be dropped in and worked level on a line, and as each piece of timber was completely individual, allowed the necessary customised carpentry to be carried out, from end cutting to slotting. High-grade specialist German power equipment and portable drills (from Maffel, at a cool £10 000), ensured cutting and drilling to the finely honed accuracy. The logistics were tricky, since all the pieces needed tracking for the whole structure to work. This achieved, it provided the company, as part of a diverse team, with coming up with innovative solutions, making for a rewarding experience. Carpenter Oak & Woodland have since used this project to put together a specialist team of carpenters for hi-tech projects, matching the carpenters’ interests, and as an attempt to avoid dumbing down the craft.

Photos: FCB Studios

The space frame under construction
– Photo: Carpenter Oak and Woodland

That said, once it came to the assembling, some of the fascination diminished. The nodes were placed into position whilst suspended in mid-air, with the carpenters hanging from ropes in mid-air. For master carpenters, used to working on the fine detailing of timber-frame buildings, this was reportedly mundane and tedious work.

The architects had envisaged the Solar Canopy going up on 5 trusses. The carpenters came up with a solution which involved three much larger sections resting on a scaffold cradle, which were then lifted by two large cranes. Such rationalising of solutions cut this section of the work schedule by half, to one month, whilst the total erection took six weeks. This intricate piece of work involved two large sections, each covering a third of the ground space, and each being raised one by one. The concrete supports went in first, in a sea of scaffolding, although the wooden supports had already been raised. The flanges were cut out of the steel, using a similar quality control system, which Carpenter Oak and Woodland used to track each piece of timber.

It was early on in this part of the construction that the project was forced to a halt as the steel nodes were found to be faulty. Taylor Woodrow had subcontracted the steel connector nodes, and apparently reputable and certificated steel was ordered from Eastern Europe. Halfway through erecting the Canopy, defects in the steel were noticed. People went back to the paperwork and it was established the certificate was a forgery, bringing on the crushing halt. Whilst liability was sorted out, half the Canopy stood in limbo in the air, incomplete, whilst the other half remained sitting on the ground.

As to the parallel, but separate, space-frame Canopy, the aluminuum photovoltaic framework was developed in conjunction with partners, Belgian PV specialists, Ecofys; BP Solar; and Pilkington Solar International, for the fixing of the PV modules. Research was conducted on the design of the modules, the original scheme was to use ac modules (requiring different installation methods to the normal dc modules), but this proved too complex, needing a large integrated building solution. The AC modules were by and large dropped, although 22 were retained and adapted to work alongside the conventional DC modules, albeit with different inverters, for control trials. As a result, the end canopy was slightly smaller in design. The aluminium was put in place by specialist photovoltaic installers, Active Cladding Systems, from Romsey, Hants. The near side horizontal array of panels are spaced 4mm apart from each other – displaying the latest stage in the emerging art and technology of Bioclimatics. The roof has a 5% pitch leaning towards its south facing aspect. As mentioned, it is part of a European Thermie project trying to figure out the effectiveness of solar panelling at such a slight vertical pitch, and at the latitude of 52 degrees. The research is seeking answers to the question this pitch proposes, that is, what level of solar energy generation can be derived at this latitude, when usually optimal solar gain is at 45 degrees? It depends of course on the path of the sun, and its given height in the sky, high at midsummer and winter, shallower in spring and autumn. The best solution would be a form of sun tracking, to maximise solar gain, but this is not feasible.

Overall the effect is to reinforce the tree and forest symbolism. To the extent that Peter Clegg has written that the spacing of the PV cells will shower a dappled light onto the concourse providing “welcome shading in midsummer…the semi-transparency, combined with the complex geometry of the timber structure, creating an abstract representation of a living forest:  processed timber forms the trunks and branches of the “trees” with photovoltaic cells capturing and transforming sunlight as do the leaves of a tree.”

The estimates are that between 70 and 80 000 kilowatts, at a 107kW peak, can be generated from the solar array per year. This will provide 20-30% of electricity for the conference centre, galleries and restaurant. Ecofys are monitoring the solar input, with computers tallying a spectrum of information – including the amounts being generated from the different sorts of array, the few AC modules alongside the main DCs.

The solar canopy is a testbed, first to provide a shelter, and second, as a structure to support photovoltaics. On both of these the canopy demonstrates to a regional and indeed national audience what can be done. Although there are a very few similar Bioclimatic projects – (two flats in Rotterdam at 7 degrees have been equipped with 25-35 roof panels, and some smallish road canopies which cars drive under) – there is no canopy structure in Europe which compares with the Earth Centre’s. Even if PVs are becoming part of a standardised range of products on the continent, with their application lagging in Britain, this integration of a range of environmental synergies, lightweight timber and canopy design, and the exploration of PV Bioclimatics is a first.

Although there are no further projects which have issued from the Earth Centre’s template this far, the project appears to have demonstrated that space frames topped with PVs, are a prospective realistic option. There are any number of contexts they might be applied to. Clegg thinks that possibly more orthogonally conventional4 canopy structures could provide the basis for PV installations – especially if PVs become cost-effective – without the PVs needing to be integrated into the building skin. He goes on to envisage their application across a variety of contexts; sports stadia, transport interchanges, malls, and sheltered streets, both against rain, and in hot climates in moderating the sun’s heat, and providing a mediated microclimate. The last example is a technological use so far untried but which, Clegg believes, could bear fruitful results in terms of future urban design. The Earth Centre Canopy is unambiguously a showcase, and novel building type, but in pursuing the environmental synergy of PVs plus timber it has stirred the imagination of architects, if not a conservative construction industry.

Photo Carpenter Oak & Woodland

Deneby Main past and present – Photos Conisbrough & Denaby
Main Heritage Group
and right Google Earth

So far there’s been considerable interest in the timber space frame, from British, continental, and particularly though surprisingly, the U.S. The Canopy is turning into a magnetic draw for British students far and near. Historically there are roundwood structures in Germany, which use adhesive strapping systems. This is a lower-tech approach deriving from the farm building tradition. It also updates the radical lightweight structures developed on the continent through the seventies, even if these were mostly gridshells and tents. The tradition harks back to the ground-breaking work of Frei Otto, and a host of other engineers, mainly German, some of whom helped build Buro Happold into the engineering powerhouse it is, others connected to Otto’s Stuttgart Institute of Lightweight Structures (ILS). There is also the clear nod to Buckminster Fuller, and other contemporary engineers such as the Bavarian massive structures proponent, Julius Natterer. For Atelier One’s Neil Thomas it is a design first, stating he knows of no other structure in Europe like it. Thomas is confident that further structures like the Solar Canopy are inevitable if people are exposed to it, and given the cost, which at £225 000 or £140 a sq metre, “is nothing”. FeildenClegg’s Mike Keys is more circumspect, stating that the production and processes pushed a few boundaries, but that it wasn’t doing anything which hasn’t been done before. He also wasn’t sure whether timber could make the translation into mainstream building practice, given British culture which generally doesn’t connect so immediately to the language of wood, in contrast to its more common cultural currency throughout Northern Europe: Germany and the Nordic countries.

And what of the Solar Canopy’s value to the Earth Centre’s surrounding community? Situated on the grounds of Deneby Main Colliery casualty to the mid-eighties mine wars, with Doncaster, a city of 200,000 population, ten minutes train journey up the line. The Earth Centre is explicit as an attempt to introduce new economic options to the immediate area, as well as bring home the environmental message that times have changed and relying on heavy manufacturing industries is a thing of the past. At its worst during the last twenty years, unemployment reached 25% in the immediate area. Those planning for revitalising the industrial sector of the region saw the opportunity and jumped at the offer of the Earth Centre project. Today, industry has gone pretty much – Doncaster was a railway centre, and a nexus for heavy ship rope manufacture. Only a few miles out though, beyond the parish boundaries of the three ex-mining villages – Deneby Main, Conisborough, and Mexborough, encircling the Earth Centre’s site, remains a rural landscape. The press officer reminds me that Doncaster too was a market town. Over the hills and ridges lie fields being worked. It may be only wishful thinking, but it would be nice to envision the transferability of some, if not all, of the technological wizardry found at the centre, as the base for new local post-industrial enterprises; a local seeding of the knowledge base which has for the most part been imported from the south. This might include the development of Solar Canopy space-frame construction. It could begin with Doncaster station, its dishevelled husk in need of a makeover. With funding apparently streaming into the railway infrastructure, how long before the launch of photo-voltaic space frames at stations, be it Doncaster or elsewhere? With or without the fireworks.

A version of this piece was originally published in Building for A Future, volume 11, no 2 Spring 2002