This is a worked design for illustration. It describes a representative spinning mill, not an installation completed by Ray2Volt. Its loads and financial figures show a calculation method. The photographs are illustrative too.
Use your actual bills, roof survey and tariff to make a decision. Request an estimate for your facility.
Main findings in the model
- After raw cotton, electricity is a major spinning expense and represents 30% to 40% of the model's conversion cost.
- The example 25,000-spindle mill draws 1,200 kW to 1,600 kW continuously. Its 500 kWp plant is therefore modelled with 100% on-site use.
- The Tier-1 DCR array generates about 7,25,000 units a year and avoids more than ₹61.6 Lakhs in HT grid charges in this calculation.
- Lint cleaning and 11 kV integration are part of the design. The example's cash payback is about 3.4 years, within a typical business range of 3 to 5 years after a site audit.
From Guntur, Rayalaseema and Tirupati district to Coimbatore and Rajapalayam, spinning mills turn cotton into yarn through a long mechanical line. Bales are opened and blended, cleaned in blowrooms, carded into slivers, combed, drawn into roving and fed to ring frames. Thousands of spindles then run at 18,000 to 22,000 RPM. Each stage adds to the mill's electrical load.
Spinning can run 24 hours a day, 365 days a year. Stops break yarn, disrupt tension and bring a large motor-starting load when frames restart. In this example, power is the largest conversion cost after cotton and accounts for 30% to 40% of conversion spending. Using the APERC tariff order dated 25 March 2026, the model applies an effective APSPDCL HT Category III(A) Industry (General) cost of ₹8.20 to ₹9.40 per unit. A 25,000-spindle mill in the wider scenario has monthly bills of ₹25,00,000 to ₹35,00,000 or more. Check the current order and your bill.
A steady daytime load gives solar output somewhere to go without relying on export credits. The representative Andhra Pradesh 25,000-spindle mill lets us examine a 500 kWp roof layout, lint control, 11 kV connection and indicative returns. For other industrial applications, see our manufacturing solar services and factory solar guide.
Which machines use the mill's power
Start with the equipment that stays on through each shift. Its operating hours matter as much as the connected load when sizing a solar system:
- Ring frames, 60% to 65% of load: Each modern frame carries 1,200 to 1,800 spindles. IE4 motors with variable frequency drives (VFDs) keep them running on three-phase power.
- Cooling and humidification, 15% to 20%: Cotton absorbs moisture, so the model holds the spinning floor at 28°C to 30°C and 60% to 65% relative humidity to limit static and yarn breaks. Supply fans, exhaust trenches and high-pressure atomising pumps work through day and night.
- Blowroom, carding and winding, 15% to 18%: Carding machines, auto-coner winders with optical yarn clearers and waste briquetting presses add a steady base demand.
The model assumes factory demand stays above 1,200 kW even at shift change. Against that load, the 500 kWp solar array is fully used at the factory bus during daylight, giving 100% self-consumption in the calculation. Every solar unit replaces a grid unit, and the worked case assigns no export credit. Confirm this assumption against interval meter data.
At the modelled production and energy intensity, a ₹0.50 reduction in electricity cost per unit lowers the conversion cost of 40s count combed cotton yarn by about ₹1.80 to ₹2.20 per kilogram. Check that relationship against your own yarn output and bill.
The representative 25,000-spindle mill
The following plant details are inputs to the illustrative Andhra Pradesh calculation, rather than a record of a customer installation:
- Output: 25,000 ring spindles make 14 tonnes of combed cotton hosiery yarn daily, mainly 30s to 40s counts for knitwear exports.
- Motor demand: 2,100 HP (~1,566 kW) connected inductive load and a 1,350 kW running base load across three 8-hour shifts.
- Contract demand: 1,500 kVA under APSPDCL HT Category III(A) Industry (General), supplied by a dedicated 11 kV feeder.
- Use before solar: 9,20,000 to 9,80,000 kWh a month and an average monthly bill of ₹82,50,000. The blended ₹8.50 per unit includes demand and FPPCA charges.
- Backup: 2 x 1,000 kVA diesel generators reserved for grid failures.
- Roof: 65,000 sq ft on three linked pre-engineered sheds clad in standing-seam Zincalume.
Protect equipment from cotton lint
Cotton lint, fine fibres and fly can reach the roof through humidification exhaust and waste suction vents. Inspect likely deposition areas before locating modules and inverters. The issue is more than lost generation: dry fibres near electrical equipment also need careful fire protection.
Dew can bind lint into a mat on panel glass. Heat then makes it harder to remove, shading cells and increasing the risk of local hot spots. This example uses three measures to limit build-up. Their effectiveness should be checked through inspection and generation monitoring:
1. Specify coated module glass
The example specifies Tier-1 modules with a fluoropolymer anti-soiling coating. Its hydrophobic surface has a water contact angle above 110 degrees and is intended to reduce adhesion from cotton oils and moisture. Check the coating's warranty and cleaning instructions with the selected module maker.
2. Raise the module tilt to 12 degrees
The shed roof slopes at 5 degrees in this comparison. Adapter brackets would face modules south at 12 degrees so loose lint can move down the glass more readily. Morning moisture may help light deposits shift, but roof structure and wind uplift must be checked before adopting the steeper mounting.
3. Use a scheduled washing manifold
The worked design runs CPVC/GI piping along each row, fed by a 10 HP multi-stage booster pump and a timer. Calibrated 180-degree nozzles rinse the 500 kWp array with demineralised water for 14 minutes at 5:00 AM each Sunday. Inspect the modules after washing; the real cleaning frequency should follow local lint build-up and the manufacturer's instructions.
Specify IP66 protection for the model's outdoor inverters, junction boxes and cable glands. Cotton lint can burn, so poorly sealed electrical joints increase fire risk. Include enclosure checks and lint removal in maintenance.
Connect the array to the 11 kV system
A 500 kWp plant must be coordinated with the mill's medium-voltage network and protection scheme. The illustrative single-line design contains these parts:
- Inverters: Five 100 kW Sungrow three-phase string units sit in a ventilated electrical room beside the shed. The specified units have multiple MPPTs, I-V curve scanning and Type-II AC and DC surge arrestors.
- Step-up transformer: A low-tension synchronising panel collects 415V AC output and feeds a dedicated 630 kVA, 0.415 kV / 11 kV dry-type transformer. It matches the mill's 11 kV ring main.
- Feeder protection: A motor-operated vacuum circuit breaker (VCB) connects the solar feeder to the primary HT switchboard. Numerical directional overcurrent, earth fault and reverse power relays require CEIG approval.
- Power factor correction: Solar reduces grid kW imports while motor kVAR demand remains. Fast-switching thyristor banks in the APFC panel are modelled to hold grid PF above 0.99 lag. Meter readings and the current tariff determine any rebate.
The 500 kWp energy and cost calculation
The illustrative DC array uses 862 Tier-1 DCR-compliant 580 Wp N-type TOPCon monocrystalline bifacial modules to reach 500 kWp. For southern Andhra Pradesh, the model gives 7,25,000 units each year, or about 1,450 kWh per kWp. Confirm that forecast with roof orientation, shade, soiling and an equipment-specific design.
| Measure | Grid-only case | 500 kWp solar case | Effect in the model |
|---|---|---|---|
| Grid electricity bought each year | 1,14,00,000 kWh | 1,06,75,000 kWh | 7,25,000 kWh replaced directly |
| Solar electricity produced each year | 0 kWh | 7,25,000 kWh | 1,450 kWh/kWp yearly yield |
| Solar used behind the meter | N/A | 100% (~7,25,000 kWh) | 100% used at the mill; none exported |
| Average monthly power bill | ₹82,50,000 | ₹77,35,000 | ₹5,15,000 less per month |
| Annual grid bill | ₹9,90,00,000 | ₹9,28,37,500 | ₹61,62,500 annual bill reduction |
| Power factor rebate above 0.99 lag | ₹0 | ₹96,000 | Assumed DISCOM PF credit |
| Yearly O&M, water and cleaning cost | ₹0 | ₹1,80,000 | Washing and electrical checks |
| Net saving each year | Not applicable | Not applicable | ₹60,78,500 per year |
We prepare new commercial and industrial quotes with DCR panels after the June 2026 ALMM List-II change, unless a verified exemption applies. The model includes a ₹9 to ₹12 per Wp DCR premium. Its ₹2,10,00,000 turnkey cost (₹42,000 per kWp) covers Tier-1 modules, five 100 kW inverters, a 630 kVA 11 kV step-up transformer, an 11 kV VCB panel, seam clamps, jet washing and CEIG approvals. A real price requires the final design and vendor quotation.
| Financial measure | Without tax effect | With 40% accelerated depreciation |
|---|---|---|
| Installed project cost | ₹2,10,00,000 | ₹2,10,00,000 |
| Year 1 tax saving (40% AD at 25% tax) | ₹0 | ₹21,00,000 |
| Capital after modelled tax saving | ₹2,10,00,000 | ₹1,89,00,000 |
| Annual cash benefit | ₹60,78,500 | ₹60,78,500 |
| Calculated simple payback | 3.45 Years | 3.10 Years |
| Modelled internal rate of return (IRR) | 26.9% | 31.5% |
| Modelled net profit over 25 years | ₹13.48 Crores | ₹13.69 Crores |
Using solar data in buyer reporting
Lower grid use can also help a mill document its electricity-related emissions. Buyers such as H&M, Inditex/Zara, Nike and Marks & Spencer may ask suppliers for energy and carbon records. Keep meter data and the method used to calculate any reduction so the figures can be checked.
The European Union's Carbon Border Adjustment Mechanism (CBAM) is one policy buyers may discuss when reviewing embedded emissions; confirm whether it applies to the goods you supply. At 7,25,000 kWh of annual output, this example estimates 594 metric tonnes of CO2 avoided each year. A mill can use verified International Renewable Energy Certificates (I-RECs), where eligible, and Scope 2 reporting to document renewable electricity. Certificate issuance and buyer acceptance require their own checks.
The table models 3.45 years of cash payback and more than ₹13.4 Crores in net profit over 25 years. These are illustrative results, not a guarantee of financial return or compliance with a buyer's requirements. Businesses typically plan for 3 to 5 years after a site audit.
Frequently asked questions
What does cotton lint do to rooftop solar modules?
Fine fibres and oil vapour can adhere to glass. The example allows for an 8% to 15% loss of light transmission if deposits remain. It specifies anti-soiling coated glass, a 12-degree tilt and a timed washing manifold. Inspect output and glass condition to set the actual cleaning interval.
How does the 500 kWp plant connect to the mill's 11 kV bus?
Five inverters supply 415V AC to a low-tension synchronising panel. A dedicated 630 kVA dry-type or oil-cooled step-up transformer raises it to 11 kV for the main VCB bus. Directional and reverse-power protection must be coordinated with the site's switchgear and approvals.
Will this mill need to export solar electricity?
The example assumes no export. Its 25,000-spindle plant draws 1,200 kW to 1,600 kW continuously, above the 500 kWp array's peak rating. That gives 100% on-site use in the model. Verify the lowest daytime demand from interval data before relying on it.
What solar records might an export buyer request?
Buyers may ask for metered renewable generation, Scope 2 calculations and verified certificate records. The rounded FAQ estimate uses over 7,20,000 units and about 590 metric tonnes of CO2 avoided; the main calculation uses 7,25,000 units and 594 tonnes. Check the reporting standard, certificate eligibility and whether CBAM applies to your product before making a claim.
What payback range should a spinning mill plan around?
A typical business planning range is 3 to 5 years after a site audit. The table calculates 3.45 years without tax effects and 3.10 years in its tax scenario. It uses an illustrative ₹8.20 to ₹9.20 per unit. Section 33 of the Income-tax Act, 2025 provides 40% accelerated depreciation on written down value where eligible. Confirm your tariff, current tax rate and eligibility with your chartered accountant. Figures are indicative, schemes change, and Ray2Volt gives no tax or investment advice.
Ray2Volt Solar Private Limited
We design, install, and service rooftop solar for homes and businesses across Tirupati district and Andhra Pradesh, from PM Surya Ghar residential systems to commercial and industrial plants. Every enquiry starts with a free power audit.
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