Tuesday, 8 May 2018

BIPV


What is BIPV and what are the advantages of this approach to using solar on our buildings?




Building Integrated Photovoltaics (BIPV) are photovoltaic materials that are used to replace conventional materials to form part of a building envelope.  Buildings come in all sorts of shapes and sizes from the smallest homes to huge tower blocks, but photovoltaics is such a versatile technology that as we'll see the potential applications for BIPV are very wide.

Roofing


The most obvious location to put BIPV is the places that get the most sunshine.  This is normally high up the building (to avoid shade) and (in the northern hemisphere) tilted towards the south.  Roofing, roof windows and sloping patent glazing are ideal parts of building envelopes where photovoltaic materials can be used.

As part of a refurbishment of Kings Cross railway station, London, the historic barrel-vaulted roofing was renewed in 2014.  The patent glazing at the top of each arch was fitted with 1,400 glass-glass BIPV laminates by Sundog Energy (now part of Photon Energy).  In glass-glass laminates the silicon solar cells are encapsulated in clear plastic and sandwiched between two clear sheets of glass.  The gaps between cells allow light transmission into the building through the BIPV laminates.  Both sides of the apex were treated in this way, facing east and west.

Kings Cross Station 
240kWp BIPV patent glazing, generating 175,000kWh/year ( 730kWh/kWp)


At the Ziekenhuis (hospital) in Aalst, Belgium, an eye-shaped atrium is formed from sloping curtain walling system with glass-glass BIPV laminates supplied by SAPA building systems forming the entire cladding.  Cells are spaced further apart than in a standard PV panel to create the desired light transmission into the atrium behind, resulting in a beautiful dappled light in the enclosed space.




Ziekenhuis, Aalst, Belgium 
46kWp sloping curtain walling, generating 31,000kWh/year (675 kWh/kWp)


It's not only new build projects that can benefit from BIPV.  The renovation of the Appleton Tower at Edinburgh University included 80 solar PV modules attached to the building with the Schletter Efa facade mounting system by installers Absolute Solar and Wind.

Appleton Tower, Edinburgh University
26kWp facade cladding, generating 19,000kWh/year (703 kWh/kWp)

At a more modest scale, buildings such as homes and offices often have a sloping roof covered with tiles or slate.  Here, more standardised BIPV products are available that replace the tiles and slates.

This house in Cambridgeshire has a patch of BIPV solar interlocking tiles, each tile replacing a row of standard concrete tiles.

Tile format BIPV integrated in concrete interlocking tiles


This roof is on the set of "Desperate Housewives" where Elon Musk launched his BIPV glass slates and tiles.  Details of these products are still emerging as (aside from those of Tesla executives), only one or two homes have been completed with this product.  Early indications are that this is a premium product with a very high price - one of the first customers said the product was "not for financially sensitive people", describing an installation process that took 10-15 people 2 weeks and cost him $100,000.

Tesla glass slates for launch event, Desperate Housewives set, California


A more cost effective approach is to take advantage of the huge economies of scale in solar PV panels that are mass produced in standard formats and figure out a clever way to make them part of the roof covering.  This house near York has Clearline fusion roof integrated solar panels covering the whole roof.  The installer, The Phoenix Works were involved in the design of the new build eco home from an early stage so could work closely with the architect, with stunning results.

Whole roof BIPV roof on a new eco home
6kWp Clearline Fusion roof integrated solar from Viridian Solar


Walls and Facades


Of course as building become taller, the available roof area becomes ever smaller in proportion to the building size.  However, an unshaded south facing vertical wall will still get 70% as much incident light each year as an unshaded south facing pitched roof at optimum angle, and a much larger available surface area on the walls can easily makes up for any shortfall

The very first large scale BIPV project in the UK was a facade system on the Northumberland Building at the University of Northumbria in Newcastle upon Tyne.  BIPV solar was installed to a south facing wall as part of a building renovation in 1994.   The 85Wp BP Solar modules were mounted on frames on a south facing facade, tilted to catch more light and to partially shade the windows below from the high summer sun, so helping the building avoid over-heating in summer.

Northumberland Building, University of Northumbria, Newcastle upon Tyne
40kWp facade and solar shade, generating 25,000kWh/year (625 kWp/kWh)


Fast forward to the present day and the 230m high Heron Tower in London, completed in 2011 has 153kWp of glass-glass laminates built into the south elevation of curtain walling in two great stripes running from street level to the top of the tower in front of the two lift shafts.

Heron Tower, London
153kWp BIPV curtain walling  generating 92,000kWh/year (620kWh/kWp)

As well as being a stunning example of what is possible with BIPV, Heron Tower is, unfortunately something of a cautionary tale too.  For across the road  from the south facing elevation at [[110]]] Broadgate, another tower that will top out at 181m is rising from the ground.  When complete this tower will obscure the entire south elevation from direct sunlight for large parts of the day (see image).




Windows


We've already seen how BIPV curtain walling and patent glazing can be configured to allow light through, but from time to time reports come out of new materials that will enable the creation of BIPV windows that you can see through but which generate electricity too.  It's normally accompanied by a picture of a hand holding a clear piece of glass.  Sometimes the hand has a latex glove on it.  Most of these remain lab curiosities for the present, however thin film solar panels are already available that are partially transparent.  They tend to finish up with a finish that is either orange in colour or smoked.

Bus station at Bournemouth University has two power generating BIPV canopies
20% transparent CdTe thin film modules from Polysolar




Advantages of BIPV


The principal advantage of BIPV is an aesthetic one.  At its best, BIPV alooks like a considered part of the building, rather than a bolt-on.

New home in Sussex with Clearline fusion roof integrated solar replacing slates


BIPV also produces offset costs - the cost of the materials that you would have used if the BIPV was not there plus the cost of fitting it. Sometimes these costs can be substantial, for example in this project where Welsh slate was substituted for integrated solar PV and the saved costs for slate were equivalent to the cost of the PV roofing.


There are also advantages in the ease of ongoing maintenance compared to bolt-on PV. For example access to tiles on roofs. If a tile fails and needs replacement, the task of doing so is made very much more complex and costly if it is behind an above-roof solar PV system. The system must be decommissioned, removed and the tile replaced before the system is reassembled and recommissioned. A job that could have been completed from a ladder now involves scaffolding and electrical works.


It is becoming evident that birds nesting behind bolt-on solar is an issue, especially for domestic installations where the noise nuisance is disturbing. A mini-industry has sprung up to bird proof above-roof solar by fitting wire mesh around the system.

Conclusion


When you take the time to include solar as part of your design for a new building or refurbishment, BIPV means that your solar can be beautiful as well as functional.

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