Solar Savings Calculator for Indian Factories 2025

Key Takeaways

• A factory consuming 1 lakh units per month can save ₹40–80 lakhs annually by installing solar, depending on grid tariff and system sizing.
• The solar savings formula is straightforward: Annual Savings = Solar Generation × (Grid Tariff − Solar LCOE), with LCOE of just ₹2.5–3.5/kWh for owned systems.
• Use the 80% rule: Size your solar system to offset 80% of daytime consumption for optimal self-consumption and maximum ROI.
• RESCO/PPA savings are simpler to calculate: Savings = Solar Units × (Grid Tariff − PPA Rate).
• Sun Wave Technologies provides a detailed financial model with your site assessment — request a free solar savings analysis for your factory.

Step-by-Step Solar Savings Calculation

Step 1: Gather Your Electricity Data

From your last 12 months of electricity bills, extract:

Important: Use the effective tariff (total bill ÷ total units), not just the energy charge. Include demand charges, fuel surcharge, and other levies divided across your consumption.

Step 2: Determine Your Solar System Size

The 80% daytime rule:

1. Calculate daytime consumption (8 AM–5 PM) — typically 60–75% of total for factories
2. Size the solar system to offset 80% of this daytime consumption
3. This maximizes self-consumption and minimizes low-value grid export

Formula: Solar Size (kW) = Target Monthly Generation ÷ (Monthly CUF Hours)

Where Monthly CUF Hours in India = 120–140 hours (depending on location and season).

Step 3: Estimate Annual Solar Generation

Step 4: Calculate Annual Savings (CAPEX Model)

Formula: Annual Savings = Annual Generation × Grid Tariff − Annual O&M Cost

Example: 500 kW system in Faridabad, Haryana

Step 5: Calculate Payback Period

Simple payback = Total EPC Cost ÷ Annual Net Savings

For our 500 kW example:

• EPC cost: ₹2.1 Crore
• Annual savings: ₹68.75 lakhs
• Payback: 3.05 years

Payback with accelerated depreciation:

• Year 1 tax savings from AD: ₹2.1 Cr × 40% × 25% tax rate = ₹21 lakhs
• Effective cost: ₹2.1 Cr − ₹21 lakhs = ₹1.89 Crore
• Payback with AD: 2.75 years

Step 6: Calculate 25-Year Total Savings

Account for:

• Grid tariff escalation: 5% per year
• Solar degradation: 0.5% per year
• O&M cost escalation: 5% per year
• Inverter replacement at year 12: ₹10 lakhs for 500 kW

25-year cumulative savings: ₹28+ Crore on a ₹2.1 Crore investment — an ROI of over 1,200%. The bottom line: solar is the most profitable capital investment available to Indian factory owners today. This means your ₹2.1 Crore investment generates ₹28 Crore in returns — the best risk-adjusted return in industrial finance.

Step 7: Calculate Savings for RESCO/PPA Model

For RESCO, the calculation is simpler — no investment, just the tariff difference:

Formula: Annual Savings = Solar Units Consumed × (Grid Tariff − PPA Rate)

Example: Same 500 kW system, RESCO at ₹4.50/kWh

Quick Reference: Savings by State and System Size

100 kW System Savings

500 kW System Savings

1 MW System Savings

Factors That Increase Your Savings

1. Higher Self-Consumption Ratio

Every unit consumed on-site saves the full grid tariff (₹8–13/kWh). Exported units via net metering may be settled at a lower APPC rate at year-end. Optimize for 80–90% self-consumption.

2. Accelerated Depreciation

40% AD in year 1 reduces effective cost by 25–30%, cutting 6–8 months off the payback period.

3. DG Replacement

If your factory currently uses a diesel generator for backup, solar displaces ₹18–28/kWh diesel power instead of ₹8–13/kWh grid power, nearly doubling the savings per unit.

4. Time-of-Day Tariffs

Some states charge higher tariffs during peak hours (10 AM–6 PM) — exactly when solar generates most. Under ToD tariffs, solar savings can be 10–15% higher than the average tariff calculation suggests.

5. Combining Rooftop + Open Access

Maximize rooftop solar (cheapest per unit), then add group captive open access for additional demand — achieving 50–80% total solar offset.

Factors That Reduce Your Savings

1. Oversized System

A system larger than your daytime consumption leads to excess export settled at APPC rate (₹3–4/kWh), not grid tariff (₹8–13/kWh). Right-sizing is critical.

2. Poor Maintenance

Skipping panel cleaning and O&M reduces generation by 15–25%, eroding savings by ₹15–35 lakhs per MW per year.

3. Low-Quality Equipment

Cheap modules degrade 1.5–2% per year vs. 0.5–0.7% for Tier-1 brands. Over 25 years, this compounds to 15–25% less generation.

4. Weekend/Holiday Shutdowns

Factories that don't operate on weekends lose 28% of potential self-consumption (2 out of 7 days). Net metering helps recover some value, but at a lower rate.

In short, the key to maximizing savings is right-sizing your system and maintaining it well.

Frequently Asked Questions

How much can a factory save with solar per month?

Monthly solar savings depend on system size, grid tariff, and self-consumption ratio. A 100 kW system in Haryana saves approximately ₹1.0–1.3 lakhs per month. A 500 kW system saves ₹5–6 lakhs per month. A 1 MW system saves ₹10–12 lakhs per month. These are CAPEX figures; RESCO savings are approximately half these amounts but require zero upfront investment.

What is the formula for calculating solar electricity savings?

For CAPEX: Annual Savings = Annual Solar Generation (kWh) × Grid Tariff (₹/kWh) − Annual O&M Cost. For RESCO/PPA: Annual Savings = Annual Solar Generation (kWh) × (Grid Tariff − PPA Rate). To calculate 25-year savings, apply 5% annual grid tariff escalation, 0.5% annual solar degradation, and 5% annual O&M cost escalation. Include inverter replacement cost at year 12–15.

How do I calculate the right solar system size for my factory?

Start with your monthly electricity consumption. Calculate your daytime consumption (typically 60–75% of total for day-shift factories). Size the solar system to offset 80% of daytime consumption. The formula: Solar Size (kW) = Target Monthly Generation ÷ 130 (average monthly generation hours in India). For a factory consuming 1 lakh units per month, the recommended solar size is approximately 400 kW.

Is the solar savings calculation different for RESCO vs CAPEX?

Yes. In CAPEX, you save the full grid tariff value for every solar unit consumed (minus O&M costs), and you need to account for the upfront investment and payback period. In RESCO, you save the difference between grid tariff and PPA rate — there's no upfront cost and no O&M expense to deduct. CAPEX delivers 2–3x higher total 25-year savings, but RESCO has zero investment risk.

How much does grid tariff escalation affect long-term solar savings?

Grid tariff escalation is the biggest multiplier for long-term solar savings. At 5% annual escalation, a ₹9.50/kWh tariff today becomes ₹15.50 in 10 years and ₹25.20 in 20 years. Since your solar generation cost (LCOE of ₹2.5–3.5/kWh) is fixed, the savings per unit increase every year. A system saving ₹68 lakhs in year 1 will save ₹1.94 Crore in year 25. This compounding effect is why the 25-year savings (₹28+ Crore for 500 kW) are so much larger than 25× the year-1 savings.

Can I get a customized solar savings calculation for my factory?

Yes. Sun Wave Technologies provides a free, detailed solar savings analysis as part of every site assessment. We analyze your actual electricity bills, load profile, roof area, and local conditions to create a customized financial model showing monthly and annual savings, payback period, IRR, and 25-year savings projection. Contact us for a site visit at your factory in Delhi-NCR or Haryana.