Protostar Fusion · Capture. Store. Share.

Solar for the whole building. Backup for every home in it.

Protostar Fusion puts shared solar and a shared battery on the one roof you all own. Your AC, fridge, geyser and Wi-Fi run on sunshine through the day, on stored sunshine into the night, and stay on through every power cut. A patented SPDU for every flat and office makes it work.

  • 300 flats powered
  • 3 patents on SPDU technology
  • Payback in about 5 years, without subsidy
  • Harvard Business Publishing case study
Rooftop solar installation at Scorpio, Fortune Estates in Pune, distributing power to all 24 flats

Whole-home backup

through every power cut

~5 year payback

without any subsidy

One Day With Fusion

From sunrise to sunrise, without a flicker

Morning

The sun runs every home

Panels across the shared roof power each flat through its own SPDU, and the surplus quietly fills one big shared battery.

Evening

Stored sunshine takes over

The sun sets and your building switches to the battery. Dinner, TV, AC. Nobody notices a thing.

The power cut

The street goes dark. You don't.

Lights, fans, fridge and Wi-Fi carry on through the outage. No inverter, no diesel generator, no candles.

Late night

A seamless hand-over

Once a flat's solar share is used up, its own SPDU slides it onto its own grid connection until sunrise. No flicker.

Scroll to live one day with Fusion ↓
The Problem

Rising bills. Power cuts. And solar that switches off with the grid.

Every building lives with all three. Protostar Fusion was engineered to end them together, with one system on the roof you already own.

Bills that only go up

Electricity tariffs rise year after year while the sunniest real estate you own, your own roof, sits idle. Common-area solar barely dents what each family actually pays.

Backup that barely backs up

The typical home inverter runs a few lights and fans on lead-acid batteries that die every 3 to 5 years. The AC, geyser and fridge all go quiet the moment the power does.

Even solar stops in a power cut

Here is the part nobody tells you: an ordinary grid-tied solar system must switch itself off during an outage. Panels on the roof, and still no power in your home.

How Fusion Works

Capture. Store. Share.

One engineered system does what a solar plant, an inverter in every flat and a diesel generator used to do, together, and does it better.

Step 01

Capture

Solar panels cover the one roof you all share, on a raised structure that keeps the terrace usable and the top floors cooler.

Step 02

Store

One central lithium battery bank stores the day's surplus. It is built for 20 years, unlike the lead-acid inverter batteries homes replace every few years.

Step 03

Share

Every flat and office gets its own patented SPDU in the meter room, metering its share of the power, from the sun by day and the battery by night. No wiring changes inside your home.

Step 04

Seamless hand-over

Only when your share is fully used does the SPDU slide your home onto its own grid connection, without a flicker, until the next sunrise tops everything up again.

Protostar Smart Power Distribution Unit (SPDU), the device that shares rooftop solar and battery power between flats

The SPDU makes Fusion possible

One smart IoT device for each flat and office, installed together in the meter room. 3 patents. Fitted in weeks.

Engineered Value

The numbers work on the system, not on any subsidy

Fusion pays for itself through the bills it erases and the UPS, batteries and diesel it retires. Everything after payback is simply free power.

~5 yrs

payback for homes, without any subsidy

~3 yrs

payback for commercial establishments

30 yrs

performance warranty on the panels

20 yrs

service life of the lithium battery bank

Stronger together

The more flats and offices that join, the larger the shared array and battery bank, and the lower the cost for each one. One roof, one system, one maintenance contract, instead of dozens of small ones.

Costs about the same as solar plus a UPS

A family that buys individual solar and a basic UPS spends nearly the same as it would on Fusion, and gets partial backup on lead-acid batteries that need replacing every 3 to 5 years. Fusion backs up the whole home on a battery built for 20.

What You Get

More than a smaller bill

One Fusion system quietly upgrades the whole building, for every family and business in it.

Backup for the entire home

Not a few lights and fans. The AC, geyser, fridge, Wi-Fi and pumps all stay on through a power cut, running on the shared battery bank.

Lower electricity bills

Every unit gets its own metered share of solar. Sunshine powers your meter first, so the bill shrinks from the very first month.

Retire the UPS for good

No more inverter trolley in the passage, no lead-acid batteries to replace every 3 to 5 years. For offices, the diesel generator finally stays off.

Cooler top floors

Panels shade the entire terrace, so the roof stops soaking up heat all day. Top-floor homes stay cooler and spend less on air conditioning.

A rooftop you can actually use

One elevated structure is planned around a clear terrace deck, so the roof stays open for walks, gatherings and celebrations.

See it all on your phone

The Nova app shows each home its solar share, battery status and savings in real time. Full transparency, no arguments, no guesswork.

Choose Your System

Two ways to put your roof to work

Most buildings choose Fusion for the independence and the backup. If your society only wants savings, the simpler system is yours too.

Our flagship

Protostar Fusion

Solar and storage engineered as one system. Energy independence for every flat and office, day and night.

  • Shared solar + shared lithium battery on one roof
  • Whole-home backup through every power cut
  • Runs on sunshine by day, stored sunshine by night
  • Payback in about 5 years for homes, 3 for offices
Explore Fusion
Without batteries

Shared grid-tied solar

The same shared roof and the same fair SPDU sharing, connected to the grid without storage. Savings first, simplicity first.

  • Shared solar with SPDU allocation, no batteries
  • Lower upfront cost, solar savings on every bill
  • For residential societies in Maharashtra, under the Grid Connected Micro-Grid framework
  • Like all grid-tied solar, it pauses during a power cut
See how the sharing works
From Our Rooftops

Real installations, not renders

Every photo here is a roof we have built on. Yours could be next.

Drone view of Scorpio, Fortune Estates in Pune with its full rooftop covered in solar panels

Full rooftop coverage on a residential society

Shaded rooftop deck with seating underneath raised solar panels

The shaded deck residents gain under the panels

Bank of SPDU meters in a building meter room distributing solar to each flat

SPDUs in the meter room, one share per home

Cars parked under a solar carport structure

Solar carport with EV-ready parking

Rooftop solar panels at sunset with the Pune skyline behind

Golden hour on a society rooftop

Proof, Not Promises

It already works. Families live with it every day.

Scorpio, Fortune Estates in Pune became India's first net energy positive affordable housing building. The SPDU was invented there.

300

flats already powered

100

free units per flat per month at Scorpio

₹0

green premium charged to homebuyers

3

patents on SPDU technology

The Protostar team receiving a national award for the Scorpio project

Taught at business schools

Our first building, Scorpio, is a Harvard Business Publishing case study authored by IIM Bangalore: India's first net energy positive affordable housing project.

Awarded and certified

IGBC Platinum rating, Bharat Leadership Award from the Governor of Maharashtra, and selection among India's top 11 green housing projects by CRISIL under the EU-backed SUNREF programme.

See It in Action

Watch how one roof powers every home

Two minutes that show exactly how Protostar brings rooftop solar into individual apartments.

Residents Speak

Hear it from the families themselves

Real residents, real bills, real savings. In their own words.

"Having solar in my flat has significantly slashed my bills. While neighbors from my previous building face soaring electricity costs, I've remained in the lowest tariff slab thanks to the 100 units from solar."

Yogita

Resident, Scorpio - Fortune Estates, Pune

"Living in Scorpio has been a step up for my family because we have experienced a lifestyle upgrade without even trying. Having 24x7 hot water feels like a luxury I didn't know I needed."

Swapnil

Resident, Scorpio - Fortune Estates, Pune

How much can your building save?

Tell us how many flats you have and your average electricity bill. Get an instant estimate of your society's solar savings.

Try the Savings Calculator
Who It's For

One roof, many meters? Fusion was built for you.

If multiple homes or businesses share a single rooftop, the SPDU can share its sunshine and its stored power.

Raised solar structure covering the rooftop of a residential society building

Housing Societies

Retrofit your existing building with Fusion. Panels on the shared roof, battery bank below, SPDU in the meter room. Every flat gets lower bills and whole-home backup, with no wiring changes inside homes.

Book a free rooftop survey
Large commercial rooftop covered with solar panels

Commercial Buildings

The DG set stays off. Offices, shops and clinics use solar exactly when the sun makes it, offset expensive evening power with the battery, and keep workstations and servers running through cuts. Payback in about 3 years.

Discuss your building
Walkway between rows of rooftop solar panels in golden evening light

Developers & Builders

Plan SPDU into a new project and sell homes with free solar units built in. A genuine differentiator that helped our pilot earn IGBC Platinum and sell at market price with zero green premium.

Partner with us
Common Questions

Everything your society committee will ask

The questions we hear in every general body meeting, answered straight.

Fusion is one engineered system for the whole building: shared solar panels on the roof, one shared lithium battery bank, and a patented SPDU for each flat and office that gives it its own metered share. Your home runs on sunshine through the day, on stored sunshine into the night, and stays on through power cuts. Only when your share is used up does the SPDU move you to your own grid connection, seamlessly, until the next day.

With Fusion, your whole home keeps running on the shared battery bank: lights, fans, fridge, Wi-Fi, even the AC and geyser, sized to your building's actual loads. There is no changeover delay and no flicker. This is the big difference from ordinary grid-tied solar, which must switch off during an outage, and from a home UPS, which backs up only a few circuits.

Every flat and office has its own SPDU in the meter room, and each unit's fixed share, decided together with the society at design time, is enforced by that unit's own hardware. Every share is separately metered, and you can see your balance and usage live on the Nova app. No neighbour can use your share.

Cost depends on your roof, your loads and how many units participate, so we start with a free rooftop feasibility survey and give a detailed proposal. As a rule of thumb, Fusion pays for itself in about 5 years for homes and about 3 years for commercial establishments, without any subsidy, and the panels keep producing for decades after that. Financing is available through our lending partners with zero processing fees.

We use lithium iron phosphate (LFP) batteries, the same safe, stable chemistry used in electric buses and grid storage. The bank carries a 10-year warranty and a 20-year rated service life, and it lives in a ventilated battery room, professionally installed and monitored. Compare that with the lead-acid inverter batteries most homes replace every 3 to 5 years.

Yes. For residential societies in Maharashtra we also offer shared grid-tied solar under the state's Grid Connected Micro-Grid framework: the same shared roof and the same fair SPDU sharing, without storage. It costs less and still cuts every bill, but like all grid-tied solar it pauses during a power cut. Most societies compare both and choose Fusion for the backup.

Subsidies like PM Surya Ghar apply to individual net-metered connections, not to a shared hybrid system like Fusion. We deliberately engineered Fusion so the numbers work without any subsidy: the shared battery bank, one hybrid inverter and one roof used as one plant is what makes it pay back in about 5 years on its own. Where a subsidy does apply, such as individual grid-tied systems, we will show you that option honestly in the proposal.

Participation in Fusion is flat by flat: each participating home contracts and pays for its own share, and the society contracts the common-area system. Rooftop use is a society decision, usually passed in a general body meeting per your byelaws. We support the committee with presentations, workings and documentation, and handle DISCOM paperwork after that.

We do. One annual maintenance contract for the whole building covers panel cleaning, battery health, performance monitoring and prompt issue resolution, instead of every flat chasing its own UPS vendor. Dust alone can cut generation by up to 25 percent, so maintenance is what protects your savings.

No. All work happens on the rooftop, in the battery room and in the building's meter room. Nobody enters your home, and a typical retrofit is completed in about 3 months including approvals.

Yes. Commercial establishments see the fastest economics, with payback in about 3 years. Daytime businesses use solar exactly when it is generated, the battery offsets expensive evening power, and the diesel generator stays off during cuts while workstations and servers keep running.

Be ready before the next summer. Backed up before the next monsoon.

A free rooftop feasibility survey tells your building exactly how much solar and storage your roof can hold, and what every flat and office would save. No commitment, no charge.

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