This is an illustrative calculation. The mill is a representative facility, not a completed Ray2Volt installation. The figures demonstrate one way to assess plant size, bill reduction and payback. The photographs also illustrate the sector rather than this specific site.
Your actual result will depend on your electricity bill, roof and tariff. You can request a site-specific estimate.
What the example shows
- After paddy purchases, electricity is a major mill expense because three-phase motors run for most of the shift.
- The representative 60-tonne-per-day (TPD) mill uses 30,000 to 45,000 units a month under the APSPDCL HT Category III(A) Industry (General) tariff.
- Its modelled 200 kWp array generates about 2,84,000 units a year and avoids more than ₹24.8 Lakhs in grid energy cost. A small share is exported.
- A 14-degree module tilt and scheduled washing help manage husk and bran dust. Cleaning performance still needs checking on site.
Rice mills across Nellore, Srikalahasti, Tirupati and East Godavari work with narrow margins. In this example, the margin on raw or parboiled rice is ₹1.50 to ₹3.00 per kilogram. Paddy prices move with agricultural market committee (APMC) and open-market conditions, so the mill has more control over its processing costs. Electricity is one of the largest.
Polished rice passes through several powered stages. Bucket elevators feed pre-cleaners and vibrating destoners. Rubber-roll de-huskers, paddy separators, emery whiteners, mist polishers and optical colour sorters follow, while aeration blowers keep material moving. A 60 TPD mill can have 250 kW to 350 kW of connected motor load. Under high tension (HT) industrial billing, the monthly DISCOM bill in this scenario is ₹3,50,000 to ₹4,50,000.
The example mill works from 7:30 AM to 6:00 PM. Much of its demand therefore occurs while panels are producing power. We use a 200 kWp design for a representative Srikalahasti parboiled rice mill to examine the electrical layout, motor starts, cleaning plan and indicative returns. For related applications, see our manufacturing solar systems and guide to factory solar.
How electricity affects milling costs
Many parboiled mills burn paddy husk in fluidised bed combustion (FBC) boilers to make steam for parboiling and drying. This uses a processing by-product, although the steam system still has operating costs. Motors and other electrical equipment draw purchased power from APSPDCL at HT rates. If your facility also chills grain or paddy, our cold storage and food processing solar page covers that additional load.
The APERC retail supply tariff order dated 25 March 2026 is the basis for this APSPDCL HT Category III(A) Industry (General) example. It uses an energy charge of ₹6.75 to ₹7.50 per unit, with time-of-day (TOD) charges where applicable. The example also allows for monthly Fuel and Power Purchase Cost Adjustment (FPPCA) of ₹0.80 to ₹1.40 per unit, electricity duty of ₹0.06 to ₹1.00 per unit and demand charges of ₹475 to ₹550 per kVA of sanctioned contract demand. Together, these illustrative bill items can take the effective cost above ₹8.80 per kWh. Check the current tariff order and your own bill before using that figure.
For the modelled plant processing 1,500 tonnes of paddy a month, electricity use averages 25 to 30 kWh per tonne of milled rice. At ₹8.80 per unit, that is about ₹220 to ₹265 of electrical cost per tonne processed. The example assumes a levelised solar energy cost below ₹2.40 per unit over a 30-year module life. On those assumptions, behind-the-meter solar reduces the electrical processing cost by more than 65%. Actual cost and savings depend on the final quotation, generation and maintenance.
A parboiled rice mill that runs for 10 to 11 months can use solar output through much more of the year than a seasonal operation such as a sugar mill running for four months. Compare monthly consumption with expected generation before setting the array size.
The representative 60 TPD mill
The worked facility is a 60 TPD parboiled rice mill in the Srikalahasti industrial corridor. These inputs describe the illustrative plant used for the calculations:
- Daily throughput: 60 tonnes of paddy in a 10-hour shift, yielding about 40 tonnes of sortex-cleaned parboiled rice.
- Motor equipment: 365 HP (~272 kW) of connected inductive load. It includes two 50 HP de-husking lines, four 25 HP emery whiteners, three 15 HP polishers, multi-tier bucket elevators, aspirators and a 5-chute optical colour sorter.
- Sanctioned demand: 250 kVA on APSPDCL HT Category III(A) Industry (General).
- Monthly use before solar: 36,000 to 42,000 kWh in the October to June peak milling season and 18,000 kWh during off-season paddy drying.
- Annual bill before solar: ₹39,60,000, equivalent to a ₹3,30,000 monthly average.
- Roof available: 22,000 sq ft on two pre-engineered metal sheds for raw paddy storage and finished rice bagging.
What happens when large motors start
A 50 HP de-husker or blower motor can draw 5 to 7 times its normal full-load current for a few electrical cycles when started across the line without a variable frequency drive (VFD). That short surge may also cause a voltage dip. The solar design must account for the mill's starting sequence and existing switchgear.
The proposed grid-tied plant operates alongside the mill's 11 kV supply. During a motor start, the utility transformer provides the voltage reference and most of the brief reactive inrush. The string inverters remain synchronised to the grid and supply active power to the facility bus, lowering active power purchased from APSPDCL. Inverter settings and protection coordination still need to be checked against the actual motor starts.
The worked layout specifies two 100 kW three-phase commercial string inverters, with Sungrow or Polycab industrial models as examples. Their active power controls should follow changes in mill demand. Before installation, we would review inverter response, harmonic levels and motor control centre (MCC) protection with the equipment actually selected.
Keeping husk dust off the modules
Paddy intake, cleaning and husk aspiration release fine dust that contains silica and grain oils. It can stick to module glass and form a hard layer. The example allows for generation loss of up to 20% within three weeks if that layer is left in place. Your cleaning interval should follow measured soiling at your mill.
The worked design addresses that dust in two ways:
1. Set a suitable south-facing tilt
Industrial shed arrays in Andhra Pradesh often follow a low 5° to 8° roof angle to limit wind uplift. Here, the proposed module tilt is 12° to 15° to help loose husk chaff move off the glass. Morning dew may shift light dust down the panel, but it does not replace cleaning. A structural and wind check must confirm the higher angle is suitable.
2. Schedule water cleaning
Cleaning a large roof by hand takes time, and walking on modules risks damage. The illustrative layout includes a permanent CPVC/GI pipe network with calibrated 180-degree nozzles above each row. A 5 HP booster pump and timer rinse the 200 kWp array for 8 minutes at 5:30 AM every ten days. The operator should inspect the glass and adjust this schedule if dust remains or water use is excessive.
Clean panels early in the morning. Spraying cold water onto glass that has reached 60°C at midday can cause thermal stress and may damage the glass or cells.
The 200 kWp energy and cost model
The proposed 200 kWp DC plant is intended to meet about 65% to 70% of the mill's daytime energy requirement. It uses 345 Tier-1 DCR-compliant 580 Wp TOPCon monocrystalline bifacial modules. For this southern Andhra Pradesh example, annual output is estimated at 2,84,000 units, or about 1,420 units per kWp after allowing for dust maintenance. The model expects more than 95% direct use; the table applies 97.5%. An audit must establish the actual roof capacity and generation forecast.
| Measure | Grid-only case | 200 kWp solar case | Annual effect |
|---|---|---|---|
| Grid electricity bought each year | 4,20,000 kWh | 1,42,000 kWh | 66.2% fewer grid units |
| Solar electricity generated each year | 0 kWh | 2,84,000 kWh | 1,420 kWh/kWp yearly yield |
| Solar used at the mill | N/A | 97.5% (~2,76,900 kWh) | Used by milling motors |
| Solar exported for net-metering credit | 0 kWh | 2.5% (~7,100 kWh) | Export occurs on non-milling days |
| Average monthly power bill | ₹3,30,000 | ₹1,23,000 | ₹2,07,000 saved per month |
| Annual grid bill | ₹39,60,000 | ₹14,76,000 | ₹24,84,000 in avoided grid cost |
| Power factor rebate with APFC | ₹0 | ₹42,000 | DISCOM rebate at PF above 0.985 |
| Total operating benefit each year | Not applicable | Not applicable | ₹25,26,000 per year |
Since the June 2026 ALMM List-II compliance change, we prepare new commercial quotations with DCR modules unless a verified exemption applies. The assumed premium is ₹9 to ₹12 per Wp, depending on the brand. This worked 200 kWp package includes Tier-1 DCR modules, two 100 kW Sungrow string inverters, hot-dip galvanised structures, raised walkways, sprinkler piping and HT net-metering synchronisation. Its illustrative capital cost is ₹88,00,000 (₹44,000 per kWp), not a site quotation.
| Financial measure | Without tax effect | With 40% accelerated depreciation |
|---|---|---|
| Installed project cost | ₹88,00,000 | ₹88,00,000 |
| Year 1 tax saving (40% AD at 25% tax) | ₹0 | ₹8,80,000 |
| Capital outlay after modelled tax saving | ₹88,00,000 | ₹79,20,000 |
| Annual cash benefit after O&M | ₹24,26,000 | ₹24,26,000 |
| Calculated simple payback | 3.62 Years | 3.26 Years |
| Modelled internal rate of return (IRR) | 25.8% | 29.7% |
| Modelled net profit over 25 years | ₹5.62 Crores | ₹5.71 Crores |
Check power factor when adding solar
Power factor (PF) can affect an industrial bill as well as energy use. The illustrative tariff applies a 2% to 10% surcharge when monthly PF falls below 0.90 lag and a 0.5% to 2.0% rebate above 0.95 lag. Confirm the thresholds and charges in the current APSPDCL tariff order before putting either item into a savings estimate.
Solar supplies active power (kW), reducing active grid imports. Motors may still draw reactive power (kVAR), so the grid-measured PF, expressed as kW divided by kVA, can fall. We would review the existing capacitor bank and inverter settings, then include the following controls where the electrical study calls for them:
- Reactive power settings: Suitable commercial inverters can supply leading or lagging reactive power to the AC bus. The setting must be coordinated with the utility connection.
- Automatic power factor correction (APFC): Retuned capacitor banks with stepped thyristor switching can respond to changing motor loads. The model aims for PF above 0.985; actual performance needs metering and commissioning checks.
The example assigns ₹42,000 a year to an APSPDCL rebate at PF above 0.985. Include that benefit in your own model only after checking your tariff and measured PF.
Frequently asked questions
How should a rice mill manage husk dust on solar panels?
Husk and bran dust can stick to module glass and, in this example, could reduce output by 15% to 25% if ignored. A 12° to 15° tilt helps loose dust move down the glass. The proposed pipe manifold and sprinklers wash the rows every 10 to 14 days, with the interval adjusted after inspecting actual soiling.
Can starting a large mill motor trip the solar inverters?
Across-the-line starts can draw 5 to 7 times full-load current for a few cycles. In the proposed grid-tied design, the utility transformer supports that brief reactive surge while the inverters supply active power. Protection settings and the mill's starting sequence must still be checked during design.
Why might the mill's power factor change after solar is installed?
Solar reduces active grid imports in kW, while motors can continue drawing reactive power in kVAR. That can lower the PF measured at the meter. APFC capacitor banks and inverter reactive power controls can be set to target PF above 0.985, subject to commissioning results and the current DISCOM rules.
What happens to solar output when the mill is closed?
The worked design assumes that permitted excess power on Sundays or maintenance days passes through a bidirectional meter to APSPDCL. The utility then applies export credit under the applicable HT or LT net-metering arrangement. Confirm eligibility and settlement terms for your connection.
What payback should a rice mill use for planning?
Businesses typically plan around 3 to 5 years, depending on a site audit. This table's 3.62-year cash calculation and 3.26-year tax scenario are illustrative. They assume the modelled load and tariff; ₹8.00 to ₹9.50 per unit is only a planning range. Section 33 of the Income-tax Act, 2025 permits 40% accelerated depreciation on written down value where applicable. Confirm the current rate and your eligibility with your chartered accountant. Figures are indicative, schemes change, and Ray2Volt does not give 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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Share a recent APSPDCL bill and drawings of your sheds. We can review motor demand, roof condition and daytime use, then prepare a site-specific solar layout and payback estimate.
