How Much Can a Mumbai Factory Save with Rooftop Solar? A Real Numbers Breakdown

Walk into most mid-sized factories in Mumbai’s industrial belt — Thane, Bhiwandi, Navi Mumbai, Ambernath — and you’ll find the same story repeated on every P&L sheet. Electricity is one of the top three operating costs, often crossing ₹5–15 lakh a month, sometimes much more. The tariff slab keeps climbing. The DG set runs during load-shedding. And somewhere between chasing production targets and managing raw material costs, the electricity bill just gets paid — reluctantly, every month, without question.

Here’s what most factory owners don’t realise: that bill is negotiable. Not with the utility provider, but with the sun.

Rooftop solar for industries isn’t a new concept anymore. But what’s still surprisingly murky is the actual numbers — what a factory in Mumbai can realistically save, what it costs to get there, and how long before the investment pays for itself. Let’s break it down honestly.

First, Understanding Mumbai’s Industrial Electricity Reality

Maharashtra’s industrial electricity tariff for HT (High Tension) consumers typically ranges between ₹7.50 to ₹10+ per unit, depending on load category and time of use. For LT commercial and industrial consumers, you’re looking at ₹9–12 per unit once you factor in fixed charges, fuel adjustment charges, and other levies that quietly inflate the actual per-unit cost.

A factory running two shifts and consuming 1,00,000 units per month is spending anywhere from ₹75 lakh to ₹1.2 crore annually — just on electricity. That’s not an extraordinary number for a mid-sized manufacturing unit. For larger plants, it’s a fraction of what the real figure looks like.

This is precisely why rooftop solar delivers such a compelling case for Mumbai’s industrial sector. The higher your tariff, the faster your return.

The Real Numbers: What a 200 kW Rooftop Solar System Delivers

Let’s take a concrete example. A factory in Thane with a sanctioned load of 300 kVA and monthly consumption of around 40,000–50,000 units installs a 200 kW rooftop solar power plant.

System Size: 200 kW (approximately 450–500 sq. metres of usable rooftop area required)

Average Daily Generation in Mumbai: Mumbai receives roughly 4.5–5.5 peak sun hours per day. A 200 kW system generates approximately 800–950 units per day.

Monthly Solar Generation: ~24,000 – 28,500 units/month

Grid Tariff Offset: At ₹9/unit (blended rate including all charges), monthly savings work out to approximately:

• Conservative estimate: 24,000 × ₹9 = ₹2,16,000/month
• Optimistic estimate: 28,500 × ₹9 = ₹2,56,500/month

Annual Savings: ₹26 lakh – ₹31 lakh

Now let’s look at what this system costs.

What Does a 200 kW Rooftop Solar Installation Actually Cost?

Industrial-grade rooftop solar installations in Mumbai — using Tier-1 panels, string inverters, and proper mounting structures — currently range between ₹40 to ₹55 per Watt, all inclusive.

Total Project Cost for 200 kW: ₹80 lakh – ₹1.1 crore

This includes panels, inverters, mounting structure, civil work, net metering application, commissioning, and a monitoring system. Variations depend on roof type (RCC vs. metal sheet), structural requirements, and cable run lengths.

The Payback Period Nobody Talks About Honestly

This is where things get interesting — and where most generic solar content glosses over the details.

Simple Payback Calculation:

• System cost: ₹90 lakh (midpoint estimate)
• Annual savings: ₹28 lakh (midpoint estimate)
• Simple payback: ~3.2 years

Add accelerated depreciation under Section 32 of the Income Tax Act — industrial and commercial solar installations are eligible for 40% accelerated depreciation in the first year — and the effective post-tax cost drops substantially. For a company in the 25–30% tax bracket, the net system cost after Year 1 tax benefit can come down by ₹9–12 lakh or more, effectively pushing the payback period closer to 2.5 to 3 years.

After that? The solar plant runs largely maintenance-free for 25+ years. Eighteen to twenty-two years of near-free electricity generation from an asset that sits on your own roof.

Scaling Up: What a 500 kW System Looks Like

For larger factories — steel fabricators, food processing units, pharmaceutical manufacturers, cold storage operators — the numbers scale proportionally, with some advantages.

System Size: 500 kW

Estimated Monthly Generation: 60,000 – 70,000 units/month

Monthly Savings at ₹9/unit: ₹5.4 lakh – ₹6.3 lakh

Annual Savings: ₹65 lakh – ₹75 lakh

System Cost: ₹2 crore – ₹2.5 crore

Payback Period (post tax benefits): 3 – 4 years

And here’s a detail worth noting: larger systems often achieve a slightly better cost-per-watt due to economies of scale in procurement and installation. The per-unit savings also tend to be higher because larger factories typically fall under higher HT tariff slabs where the grid cost per unit is steeper.

The OPEX Option: Zero Investment, Immediate Savings

For factory owners who don’t want to deploy capital upfront — or where the promoter prefers to keep balance sheet clean — there’s the OPEX model, also known as a Power Purchase Agreement (PPA) or third-party ownership model.

Under this arrangement, a developer installs and owns the solar plant on your rooftop at zero cost to you. You simply agree to buy the solar power generated at a fixed per-unit rate — typically ₹4 to ₹6 per unit — for a contracted period of 10–25 years.

The savings are lower compared to the CAPEX model since you don’t own the asset, but the cash flow benefit is immediate. A factory currently paying ₹9/unit from the grid and buying solar at ₹5/unit under OPEX is saving ₹4 per unit from Day One — without spending a rupee.

For a factory consuming 40,000 solar units/month, that’s ₹1.6 lakh saved every month, or ₹19.2 lakh annually — at zero investment.

What About Net Metering? Does It Apply to Industries?

Yes, and it’s a significant advantage. Maharashtra’s net metering policy allows grid-connected rooftop solar systems to export surplus power back to MSEDCL or BEST and receive credit against future bills.

For factories that run one shift or have weekend shutdowns, this matters. Solar panels generate power whether your machines are running or not. Under net metering, units exported during low-demand hours are credited against units drawn during peak production hours. Effectively, your roof becomes a power bank.

The banking of units is typically allowed on a monthly basis, with annual settlement. This ensures you don’t lose the value of any generation — even on days when consumption is lower than solar output.

Hidden Benefits That Don’t Show Up in the Savings Calculation

In our experience working with industrial clients, the conversation often starts with the electricity bill and ends with a much bigger realisation.

Demand charge reduction: Many factories pay significant fixed charges based on contracted demand (kVA/kW). Solar generation during peak hours can reduce maximum demand drawn from the grid, lowering these fixed charges as well.

DG set dependency reduction: Factories running diesel generators as backup spend ₹18–25 per unit on DG-generated power. Pairing rooftop solar with a battery system — or even using solar to displace some DG hours — can meaningfully cut fuel costs.

ESG and sustainability credentials: This one is increasingly commercial, not just ethical. Buyers, exporters, and large corporate procurement teams are now asking suppliers about their carbon footprint. A rooftop solar installation is documented, verifiable proof of clean energy use — and it strengthens your position in tender evaluations and export compliance.

Property and asset value: A solar plant is a fixed asset on your books. It adds to your facility’s valuation and signals operational maturity to investors and lenders.

What to Check Before Signing Anything

Not every factory roof is equally suited for rooftop solar without some groundwork. Before committing to any system size, these are the checks that matter:

Roof structural load capacity: Solar mounting structures add 15–25 kg/sq. metre. Older industrial sheds may need structural reinforcement.

Roof orientation and shading: South-facing, unshaded roof area generates the most. Water tanks, AC units, chimneys, and adjacent structures create shading that reduces output. A proper shadow analysis is non-negotiable.

Sanctioned load and net metering eligibility: The system size eligible for net metering is typically capped relative to your sanctioned load. Understanding this ceiling upfront prevents over-investment.

Consumption pattern: A factory that shuts down for 15 days a month generates solar power it can’t consume. The system should be sized to actual consumption patterns, not peak load.

A professional site feasibility study — which Visol India offers at no cost — addresses all of these and gives you a clear, site-specific picture before any investment decision is made.

The Bottom Line

Mumbai factory owners are sitting on underutilised rooftops while paying some of Maharashtra’s steepest industrial electricity tariffs. That combination makes rooftop solar one of the few capital investments with a genuinely predictable, measurable return — typically paying back in 2.5 to 5 years, then generating free electricity for the next two decades.

The numbers above aren’t theoretical projections. They reflect real system performance in Mumbai’s climate and real tariff structures in Maharashtra’s industrial segment. The variance in savings comes down to your specific consumption, roof conditions, and the financing model you choose.

If you’re a factory owner who’s been curious but hasn’t yet run the actual numbers for your facility, that’s the logical next step. Visol India’s team specialises in exactly this — customised solar assessments for industrial and commercial clients across Mumbai and Maharashtra, with end-to-end support from design to commissioning to long-term O&M.

Your roof is already paying rent to the sun every single day. The only question is whether you’re collecting it.