Invisible Energy: Active Building Skins and Solar Glass for Sustainable Real Estate- By Arindam Bose
INVISIBLE ENERGY — HOW BUILDING SKINS LEARN TO GENERATE POWER
By Arindam Bose
Every Tuesday, when it’s time to write about technology in real estate, the same lie shows up on the blank page:
“This week, Arindam… pick something simple. One system. One idea. One clean line.”
And every Tuesday, that promise dies.
Because construction is no longer an industry.
It is a collision zone.
Where façades are no longer just weather skins — they are circuits.
Where glass doesn’t just transmit light — it harvests it.
Where paint doesn’t just colour walls — it turns them into solar arrays.
Last week, it was mycelium — a material that shouldn’t grow, but does.
This week, it’s something even stranger:
a building envelope that stops being passive and starts behaving like hardware.
This is the story of invisible energy — of walls, windows, and paints that quietly turn buildings into power plants.
THE COLLISION ZONE: PASSIVE VS ACTIVE SKINS
For most of construction history, a building envelope was passive.
You designed the thickness, orientation, shading, and insulation. You let physics do the work.
Sun, wind, mass, and geometry.
A passive envelope:
- Uses sunlight, shading, cross‑ventilation, and thermal mass to regulate comfort.
- Has no moving parts, no wiring, no firmware updates.
- Works by not doing anything except being well designed.
An active envelope is different.
It measures, responds, and generates.
An active skin:
- Carries photovoltaics in the glass and paint.
- Uses smart windows that darken, clear, or frost with a tiny electric pulse or a temperature change.
- Talks to control systems, HVAC, and sometimes to the grid.
If passive buildings are like lungs that evolved to breathe naturally,
active buildings are lungs stitched to sensors, algorithms, and solar cells.
Same body. Different nervous system.
THE CORE MATERIALS: WHEN GLASS AND PAINT START MAKING POWER
At the heart of this shift is a deceptively simple idea:
stop treating the façade as dead surface area.
The new active envelope is built around three material families:
- Solar paint
- Smart windows
- Energy‑harvesting glass
The Big Three: solar paint, smart windows, and energy‑harvesting glass.
Each one takes a familiar element of a building — paint, glazing, curtain wall — and quietly wires it into the energy system.
SOLAR PAINT — WHEN PEROVSKITES BECOME INK
Perovskite is not a brand.
It’s a crystal structure — a family of materials that, arranged in a certain pattern, behave like brutally efficient light sponges.
Perovskite solar cells:
Use an crystal structure to absorb light in very thin films.
Are solution‑processed — think inks and coatings, not wafers and furnaces.
Have raced from 3% efficiency in 2009 to around 27% lab efficiency today in single‑junction cells.
What matters for construction is not just the efficiency number.
It’s the manufacturing grammar.
Silicon says:
Give me high‑temperature furnaces, cleanrooms, and rigid wafers.
Perovskite says:
Give me a roll‑to‑roll coater. A spray head. A printing line.
Because perovskites can be deposited as ultra‑thin, low‑temperature coatings on glass, metal, or flexible films, they unlock exactly the things buildings need:
Thin‑film, flexible PV layers on curved façades, roofs, shading fins.
Solar “paint” that can, in theory, be sprayed or printed onto panels, cladding, and even retrofitted surfaces.
Lightweight modules that don’t demand heavy sub‑structures.
Perovskite’s main edge over silicon is simple:
High‑efficiency PV that is printable, coatable, and bendable.
That’s the difference between bolting panels onto buildings…
and growing power inside the skin.
SMART WINDOWS — GLASS THAT THINKS IN SHADOW
Look up at most glass towers and you see two old technologies:
clear panes, and blinds struggling to undo the mistake.
Smart windows flip that script. The glass itself becomes dynamic.
Electrochromic — tint on command
Electrochromic glass sandwiches thin layers of materials like tungsten oxide between transparent electrodes.
Apply a tiny voltage: ions drift, the material changes oxidation state, and the glass darkens.
Reverse the voltage: ions move back, the glass clears.
No moving blinds. No glare battles at 3 PM.
Just a façade that quietly tunes its own transparency to the sun and the sky.
Done right, this saves up to double‑digit percentages of cooling energy, cuts peak loads, and gives occupants something they rarely get in glass offices: view and comfort.
Thermochromic, thermotropic, photochromic — passive cousins
Beyond the wired, app‑controlled glass, a quieter tribe of smart windows is emerging:
Trigger: temperature.
Becomes darker as it heats up, then clears as it cools.
Great for cutting solar gain in hot hours without any wiring.
Trigger: temperature, but instead of tinting, a layer goes milky / diffuse.
Think frosted skylights that scatter harsh sun into soft light.
Gives both solar control and privacy.
Trigger: light intensity (especially UV).
Darkens in bright sun, clears in low light — like transition lenses.
Naturally follows the sky’s brightness, ideal where glare is the main enemy.
Electrochromic glass is actively controlled.
Thermochromic, thermotropic, and photochromic systems are passively triggered.
Different mechanisms, same idea:
let the window become a thermostat for light and heat.
TRANSPARENT PV — WHEN WINDOWS SECRETLY BECOME PANELS
The sexiest phrase in this space might be the simplest:
“solar windows.”
Transparent photovoltaics (T‑PV) and luminescent solar concentrators (LSC) do something that sounds impossible:
they let you look through the glass while silently harvesting part of the light.
The core trick
Two main approaches dominate:
Selective absorbers (Transparent PV)
Special semiconductors absorb UV and infrared, but let most visible light pass.
The glass still looks like normal or lightly tinted glazing.
The PV layer creates current from the invisible wavelengths.
Luminescent Solar Concentrators (LSC)
Dyes or quantum dots in the glass absorb some light and re‑emit it at a different wavelength.
The re‑emitted light gets trapped inside the pane by total internal reflection and travels to the edges.
Conventional PV cells on the edges convert that guided light to electricity.
In both cases, the main surface reads as window.
The edges and coatings read as solar farm.
Transparency vs. efficiency
There is a trade‑off:
Commercial and near‑commercial T‑PV products today:
3–10% power conversion efficiency typical.
Visible light transmittance ~40–70% — from strong solar‑control tint to office‑like glazing.
Push VLT above 70–80% and efficiency usually falls into low single digits.
A realistic spec for façade design today:
3–10% efficiency at 40–70% VLT — enough to matter at scale, especially on glass‑heavy buildings.
WHERE THE WALLS ARE ALREADY WORKING
This is not theory. There are buildings whose skins are already alive with electrons.
Electrochromic at scale — The Rio Business Park, Bangalore
At Rio Business Park in Bengaluru, the façade doesn’t just shine — it thinks.
Bagmane Developers and Glass Wall Systems executed what is billed as the world’s largest electrochromic glass project, using SageGlass across the curtain wall.
All day, the glass automatically tints and clears:
Cutting glare without blinds.
Shaving cooling loads.
Turning a standard glass box into a responsive optical device.
Luxury, here, is not a chandelier.
It is visual comfort and stable indoor climate baked into the glass.
Perovskite on a façade — Spark, Warsaw
In Warsaw, Skanska’s Spark office building hosts a quiet revolution:
a pilot perovskite solar façade supplied by Saule Technologies.
Semi‑transparent perovskite films laminated into part of the glazing:
Generate enough electricity to cover at least a workspace’s lighting.
Test how printable perovskite modules behave on a real façade: wind, moisture, maintenance.
It is one of the first real‑world BIPV deployments using perovskite, and a preview of what “solar paint on glass” looks like in the wild.
BIPV as architecture — Copenhagen International School
Then there is the Copenhagen International School (Nordhavn Campus) in Denmark.
About 12,000 custom BIPV panels.
Roughly 6,000 m² of façade that is both cladding and solar farm.
A shimmering pixelated skin created by coloured Kromatix glass.
The result: a building that doesn’t hide its energy system on the roof.
It wears its power plant as its face.
THE ECONOMICS: WHY THIS STARTS ON PREMIUM PROJECTS
Right now, active envelopes are not cheap experiments for budget box buildings.
BIPV façades often fall around 200–625 €/m², with glass‑glass PV modules 120–250 €/m².
Conventional façades in glass, metal, stone, fibre‑cement: anywhere from ~100 to 900 €/m², and high‑spec curtain walls often 520–1,120 €/m².
Transparent PV glass can be 20% to 2×+ more expensive than basic cladding or glazing, but is competitive with premium curtain wall once you realise:
it replaces the cladding and produces power for 25–30 years.
That’s why the first wave is showing up in:
High‑performance campuses.
Flagship offices.
Iconic schools and research buildings.
Where the conversation is not “What’s the cheapest façade?”
but “What is the smartest skin we can afford over 30 years?”
INDIA’S INVISIBLE ROOFS — THE FAÇADE AS A SOLAR ASSET
India has set itself a brutal number:
300 GW of solar by 2030 within a 500 GW non‑fossil target.
Just over 100 GW of solar is installed as of 2025.
If we try to hit 300 GW with ground‑mount alone:
Land conflicts intensify.
Transmission corridors get messy.
Per‑watt system costs rise as the easy sites get used up.
Meanwhile, our skylines are quietly filling with glass and concrete that do nothing all day.
Studies on Indian and global cities show:
Only a single‑digit percent of façade area is technically usable for BIPV.
Even that small slice translates to tens to hundreds of square kilometres nationally.
One Mumbai high‑rise study found that active façade area can be 7–8× the usable roof area.
A simple line captures the opportunity:
India’s ambitious 300 GW solar target by 2030 cannot be met by ground‑mount alone; BIPV offers a way to tap tens to hundreds of square kilometres of urban façade area that currently sits idle.
When every tall building becomes a vertical solar farm,
“land constraint” stops being an excuse.
POLICY BACKBONE: WHY THIS FITS INDIA’S PLI MOMENT
The good news: New Delhi is not asleep.
PLI for high‑efficiency PV
The Production Linked Incentive (PLI) scheme for High‑Efficiency Solar PV Modules carries about ₹24,000 crore in support.
It is technology‑agnostic but performance‑linked — the higher your module efficiency and integration, the better your upside.
That opens the door for:
TOPCon, HJT, and other advanced silicon.
Perovskite‑silicon tandems.
BIPV‑ready modules and glass.
By mid‑2025, the PLI had already pulled in over ₹48,000 crore in investment and tens of thousands of jobs in advanced solar manufacturing.
R&D for tandems and beyond
MNRE is also funding:
Perovskite–silicon tandem projects (e.g., IIT Bombay’s NCPRE and startups like ART‑PV India).
Pilot lines for 29–30% tandem cells.
Broader reliability, encapsulation, and building‑integration research.
Layer on top of this:
The National Green Hydrogen Mission (₹19,744 crore).
Push for battery energy storage and pumped storage.
The message is clear:
India doesn’t just want more solar. It wants smarter solar — higher efficiency, integrated, and manufacturing‑led.
Active envelopes — perovskite films on glass, BIPV façades, smart glazing with embedded PV — sit perfectly inside that ambition.
THE MATERIALS THAT TURN CITYSCAPES INTO CIRCUIT BOARDS
We are used to thinking of building skins as cost centres:
glass, paint, cladding, insulation — line items to be minimised.
Active envelopes flip that accounting.
Solar paint asks:
“If you’re going to paint 10,000 m² of façade anyway, why shouldn’t it make power?”Smart windows ask:
“If you’re going to spend on blinds, films, and oversized chillers, why not let the glass control the sun?”Energy‑harvesting glass asks:
“If your skyline is 70% curtain wall, why is your solar capacity stuck on the roof?”
The building stops acting like a dumb load on the grid
and starts behaving like a node in a distributed energy network.
A CHALLENGE — WHAT MUST CHANGE FIRST?
If mycelium is the material that grows itself,
active envelopes are the skins that pay their own rent.
The physics is ready.
The pilots exist.
The policy scaffolding in India is forming.
So the real question is not “Is the technology ready?”
It’s “What has to move first for our buildings to start wearing power?”
A national active envelope mission that treats façades as energy infrastructure?
A PLI 2.0 focused on BIPV glass and perovskite‑integrated products?
A real estate giant willing to turn one flagship campus into a fully active skin demonstrator?
A state building code that rewards dynamic glazing and BIPV in EPI and compliance?
Or simply one startup that cracks cost‑competitive, Indian‑made solar glass for mass‑market offices?
Comment your answer.
Because the next decade of Indian skylines will be shaped by one decision:
Do we keep wrapping our buildings in dead surfaces?
Or do we finally let the walls join the grid?
This was my Technology Tuesday rabbit hole.
Next week?
I’ll make myself the same promise:
“Keep it simple, Arindam.”
And once again,
I know I’ll fail.
Beautifully.
— Arindam Bose
If building skins can now generate power, what happens when the walls can grow themselves? → Read the mycelium story next.- Mycelium in Construction: The Future of Sustainable, Living Materials - By Arindam Bose
Comments
Post a Comment