PV panels on the Heron Tower in London represent a long-standing technology
As the heron tower on London’s Bishopsgate is wrapped in glass curtain walling by cladding contractor Scheldebouw, the south facade is emerging as a 40-storey advertising poster for building-intergrated photovoltaics (BIPV). The glazing panels here feature around 3,000m2of PV cells, which will both reduce solar gain to the interiors and generate an estimated 92,000kWh of electricity a year.
The PV cells, supplied by Q Cells of Germany, are laminated between glass panels by sub-contractor Scheuten Glass.
The power they generate will be enough to meet 2.5% of the building’s electricity demand, reducing its carbon emissions by 850,000kg a year.
But while the Heron Tower’s PV panels are visibly flying a green flag, they represent technology that has been available for around a decade – in which time the PV sector has failed to keep pace with advances in other sustainable products. Reasons include worldwide shortages of silicon keeping prices high, the failure of many “thin-film” installations, and the lack of integration between PV manufacturers and building product companies.
But now it looks like BIPV could be about to enter a new era, stimulated by the financial incentive of feed-in tariffs (FITs). “It used to be that the PV industry didn’t really speak to the building industry. But now product manufacturers like Kingspan and Corus are talking to the specialist solar companies and developing new products,” says Ray Noble from the Renewable Energy Association.
Under the government-backed FIT system, due to take effect on 1 April, utility companies will be taxed on the energy they sell, with the income pooled into a fund administered by Ofgem. The money will then be redistributed to owners of micro-generation facilities.
While the government has not yet announced the final price per kilowatt, it is thought unlikely to fall below the 36.5p set in last autumn’s consultation document. With a tariff at this level, Noble calculates that a facade with integrated PV could pay for itself in 15-20 years.
“And for the rest of the building’s lifetime, you’re getting free electricity,” he adds.
To be eligible for the scheme, specifiers will have to select products and systems certified under the forthcoming Department of Energy and Climate Change-sponsored micro Generation Certification Scheme. The first products that make the grade – likely to be those that already have a track record in UK installations – will be announced in February, while the criteria new products must reach will be announced later.
One company anxious to comply will be cladding and roofing manufacturer Corus Colours, which is pursuing two sectors of the BIPV market. First, it is talking to specialist PV supplier Unisolar about integrating its products into various Corus brands, including Kalzip roofing. Second, it is investing in Australian dye-sensitised, solar cell PV technology, which generates electricity by mimicking photosynthesis.
Currently at prototype testing stage, products using the technology could be in commercial production by 2012. Rodney Rice, PV business development manager at Corus Colours, concedes that metal Dyesol panels only offer half the output of silicon-based arrays when tested in “full sun” conditions, but says they come into their own in the changeable British climate. “Because it’s copying photosynthesis, it’s able to extract benefit from lower light levels,” says Rice. “When you factor in less than perfect conditions – such as low light levels, cloud cover and shading – it will close the gap.”
Meanwhile, Kingspan, the largest supplier of insulated cladding panels to the UK market and a major player in the health and education sectors, is developing a range of panels with integrated PV arrays.
Its ambition is an envelope that reduces energy consumption by 90% and produces enough electricity to fill the gap – creating a zero-carbon envelope. The REA’s Noble concedes that BIPV will have to overcome cultural resistance in the building sector, but believes it will soon be on an upward curve. “As the regulations get tighter, uptake will be higher. The first step will always be reducing energy consumption, but once you’ve done that PV will be more affordable and more attractive.”
The Snowdonia National Park Authority wanted to replace its former summit building. Built in the 1930s, after unsympathetic alteration in the 1960s and a long-term lack of maintenance it was infamously called “the highest slum in Wales” by Prince Charles.
The new £8.3m visitor centre sits on the old building’s footprint, is radial in shape and includes a cafe, visitors’ facilities and a railway terminus. The west elevation incorporates a bank of large picture windows from Technal’s FXi65 range, which are set into deep reveals in the granite cladding, allowing cafe visitors to take in impressive views of Wales. To exploit the views we needed the slimmest frame and the largest glazed area possible. However, the precarious location meant the size and weight of glass had to be minimised to ease replacement. Each pane is 2.5m high and 2m wide and the windows are angled to reduce solar heat gain, which also helped appease locals living at the base of the mountain who were worried about glare.
Window profi les are fi nished in lowmaintenance anodised aluminium to blend with natural materials used elsewhere on the scheme and the glass is etched with lines of poetry by Gwyn Thomas, the former national poet of Wales.
Building on the top of a mountain in freezing temperatures, battered by winds of up to 150mph, is not ideal, especially when materials can only be delivered to site via a narrow-gauge railway used by tourists. We wanted to use a helicopter, but it was considered too dangerous.
Despite studying meteorological data from previous years, the weather was hugely chaotic and changeable, and even in the middle of summer we needed thick jackets and gloves.
Technal’s solution met all our criteria and gave us the confi dence to incorporate a glazing system that finally does justice to the incredible view.
Kawneer has upgraded the thermal performance of its AA600 window range to comply with the update of Part L of the Building Regulations. The company’s AA602 pivot and AA603 tilt-turn and fi xed-light windows now have convection fi ns that allow more air to circulate. The units also feature a closed-cell solid polyethylene rod fitted between the outer edge of the glass and the window frame, which creates an extra thermal break. U-values for the AA603TE window have been cut to 1.5W/m2K, below the Part L 2010 target of 1.7W/m2K. www.kawneer.com
AccentHansen has introduced two new products combining aesthetics and high technical performance. Available in single, double and tiltslide variations, AlGlaze is a glass door with extremely thin aluminium profi les. It is suitable for both residential and commercial buildings. Clearglaze is a frameless double-glazed door, sealed with double nitrile swipes around the perimeter to provide a completely fl ush front facade. The glass can incorporate any coating from any leading glass manufacturers. www.accenthansen.co.uk
The Glass and Glazing Federation has set up a petition urging the government to endorse a window scrappage scheme that would provide cash grants to householders and landlords who swap old, poorly insulated windows for energy efficient ones. The GGF claims the scheme would help dramatically improve the effi ciency of existing buildings, while cutting carbon emissions and reducing household energy bills. The petition has been set up on the PM’s website: http://petitions.number10.gov.uk/windowscrappage
The main practical consideration for installers is ‘buildability’. Will the size of the panel pass through the scaffolding? Would another access method be more preferable? An architect may envisage a monolithic panel, but can they be handled safely and without damage on site? Panels may need to be resized to assist with the installation and maintain the programme.
Behind every facade is a support system which has to be engineered to work with the chosen cladding. The manufacturers of these systems take many factors into consideration, including the orientation, thickness and weight of the intended cladding. Make use of their expertise.
Combinations of cladding genres and brands are commonplace on the modern facade. This creates challenges when designing the support structure. The interface and aligning of materials will be critical to the delivery of a successful scheme. Use a systems company that can offer support for all types of cladding.
Be conscious of directionality of finish on materials. This can have a big impact on material optimisation and a single panel installed against the grain will be immediately noticeable on a finished facade.
Andrew Schutt, Eurofox Engineering