Dynamic Glass and Building-Integrated Photovoltaics
The moment a pane has a cable, the facade stops being an envelope and becomes a building service. Everything changes: who installs it, who commissions it, who repairs it — and above all, a pane can no longer be replaced without an electrician.
Overview
TAV. 00Electrochromic glass and building-integrated photovoltaics answer two opposite questions about the same facade: the first decides how much light and heat to let in, the second turns radiation into energy. Technically they are close relatives — both are laminated panes with an active layer and an electrical connection leaving the edge — and they bring the same three consequences, which are design consequences before they are technological ones. First: the cable has to leave the glass and cross the frame, so the window detail must be drawn with that route inside it, not adapted afterwards. Second: the pane is no longer an interchangeable part, and maintenance requires genuine access to the connections. Third, and most underestimated: the control electronics have a far shorter service life than the glass, and must be designed to be replaceable without dismantling the facade.
The site score
TAV. HThe detail of the craftwhere the cable exits
The frame and the cable route
Fitting the frame with the cable route already provided and the junction box positioned so it is accessible from inside.
The cable does not run in the gasket rebate. Water runs there: give the cable its own place, in the design.site notebook — editorial synthesis
click a beat · arrow keys ← → walk the site · dashed pauses are the chemistry at work
The constraint that changes the design
Glass with a cable is no longer glass
This is the conceptual step that supports everything else. A conventional pane is a passive, interchangeable component: it breaks, you order one, you replace it in half a day. A dynamic or photovoltaic pane has a conductor leaving its edge, a connection in a box, a controller upstream and a precise position in a schematic: replacing it needs an electrician, access to the connections and reconfiguration of the system. Designing these panes means designing that maintenance chain, not just the facade.
This is why on these systems the most important specification clause is not about the glass but about accessibility: where the electronics are, how you reach them, who replaces them and with what documentation.
Where it is worth putting it
Photovoltaics pay off on the parapet, not on the vision glass
Putting the cells where you cannot see out seems counter-intuitive, and is in fact the most efficient choice. In the vision band photovoltaics compete with the view and with daylight, get shaded by internal furniture and by projections, and every shaded cell limits the whole string. In the opaque band — parapet, spandrel, floor-edge strip — there is nothing to sacrifice: that surface already existed, it is continuous, it is controllable, and there the cells work at their best. In most multi-storey buildings it is also the larger area.
Actual yield depends on orientation, inclination, shading and operating temperature, and must be calculated case by case: a vertical south facade produces appreciably less than a pitched roof at the same latitude.
How it ages (and what betrays it)
TAV. PQuestions from the site
TAV. QHow long does electrochromic glass last?
The glass lasts like glass; two other things expire sooner. The first is the number of switching cycles declared by the manufacturer, which in a building switching a few times a day covers decades. The second, far more critical, is the control electronics: drivers and controllers have a service life of the order of ten to fifteen years and must be treated as replaceable parts, like the motors of a powered blind. The real risk on these systems is not the glass stopping: it is a discontinued controller in a building where nobody has the schematic.
Is dynamic glass better than external shading?
On energy balance alone, external movable shading remains very effective, because it stops the radiation before it touches the glass, and it costs less. Dynamic glass wins on other fronts: it adds no elements on the facade to maintain and replace, it has no moving parts exposed to wind, it keeps the view open even in the dark state and it needs no space in front of the window. It becomes the sensible choice where external shading is impractical — constraints on appearance, wind exposure, great heights, listed buildings — and where the periodic maintenance of blinds and brise-soleil is precisely the problem you want to avoid.
Is BIPV worth it on a vertical facade?
It depends what you are comparing it with. Against a pitched roof at the same latitude, a vertical facade produces appreciably less, and if the aim is only to maximise kilowatt-hours the roof comes first. But the right comparison is a different one: against an opaque band in sheet metal or stone, which produces nothing, BIPV uses a surface that already existed and consumes neither land nor roof. In tall buildings, where the ratio of facade area to roof area is skewed, it is often the only surface available in quantity. And in winter, with a low sun, a south-facing vertical performs better than people expect.
What does anyone working on this facade need to know?
That part of the installation can be live even with the breaker open, as long as there is daylight. It is the most important safety point and must be communicated explicitly: signage on the board and along the cable routes, an as-built schematic handed over and retained, a clear indication of where to isolate. It matters for maintenance staff, but above all for firefighters, who need to know within seconds that this facade is a source. It is also why disconnection systems close to the modules are not an accessory: they lower the voltage along the cable routes, which is exactly the information whoever enters needs.