Illustrative calculation for a representative site. The agro cold store in this article is a model, not a Ray2Volt installation. We use sector assumptions to demonstrate sizing, bill savings and payback. The photographs also illustrate the type of facility; they do not document a customer project.
Your result will change with your roof, demand pattern and tariff. Request a site-specific estimate.
Key points
- In the model cold store, electricity can account for 60% to 70% of recurring operating cost, mainly because the ammonia and freon chillers run through the day.
- The hottest hours raise compressor work and also bring the strongest rooftop solar output.
- The illustrative 150 kWp DCR array makes about 2,16,000 units a year, with ₹19,20,000 in grid-bill savings and ₹1,80,320 in avoided diesel cost.
- The cash-flow table calculates 3.33 years simple payback or 2.86 years with its assumed section 33 tax shield; your result needs a site audit.
For a cold store in Chittoor, Tirupati or the wider Rayalaseema produce belt, the refrigeration plant cannot simply pause when electricity becomes costly. Fresh produce chambers in this example hold -2°C to 4°C, while frozen goods require -18°C to -25°C. The compressors must keep running through hot afternoons and overnight, unlike equipment that a factory can reschedule.
That steady demand makes the power bill a major operating cost. For the model 5,000 MT site, we assume APSPDCL Category III(A) Industry (General), with HT or LT supply and an effective ₹8.50 to ₹10.50 per unit after demand charges, time-of-day charges and fuel adjustments. These are illustrative figures based on the APERC FY 2026-27 tariff order dated 25 March 2026; check the current order. Harvest-season bills of ₹3,00,000 to ₹3,50,000 a month can represent up to 70% of operating expenditure.
The useful question is how much of that daytime demand a roof-mounted plant can cover. This worked 150 kWp example walks through compressor load, roof fixing, generator coordination and cash flow. For project options, see our cold storage solar service and business solar overview.
What daytime cooling demand means for solar
Refrigeration has to move heat from the chamber evaporator to an outdoor condenser. On a 42°C May afternoon in Rayalaseema, the larger temperature difference raises condensing pressure. In this example, the compressors may need up to 35% more kilowatt-hours for each tonne of refrigeration (TR) than they do at night. That is exactly when cooling capacity is most valuable.
The model facility draws heavily from 10:30 AM to 4:30 PM, which overlaps with its strongest solar production. A warehouse with a different work pattern may export more energy, so compare interval meter data with the proposed generation curve. Here, the near-continuous cooling load makes daytime consumption likely.
With compressor demand above most of the array output, the model uses more than 95% of its solar energy on site. DC power passes through protection equipment and string inverters before reaching the main LT panel. Each unit used there reduces grid purchase behind the meter; a battery is not needed for that daytime bill saving.
The chambers can also hold some cooling for later. If produce specifications allow, lowering the set point by 1°C around noon can shift some compressor work away from the evening peak tariff. Confirm the permitted temperature band and product quality requirements before changing controls.
The 5,000 MT Renigunta cold store example
Use this representative multi-commodity warehouse in the Renigunta industrial corridor near Tirupati to follow the calculations. The following loads and bills are assumptions for the example, not measurements from a named customer site.
- Storage capacity: 5,000 metric tonnes in 4 separate chambers for table mangoes, sweet oranges and seasonal dry chillies.
- Cooling equipment: Two 75 HP semi-hermetic screw compressors and one 40 HP standby reciprocating unit, using an ammonia/glycol secondary loop and evaporative condensers.
- Approved demand: 200 kVA under APSPDCL HT Category III(A) Industry (General).
- Grid use before solar: 34,000 to 38,000 kWh monthly during the March to July harvest peak, falling to 22,000 kWh in the winter maintenance period.
- Monthly bill assumption: ₹3,15,000 on average, using a ₹9.10/kWh blended grid rate that includes energy, demand and electricity duty.
- Backup generator: One 160 kVA DG set runs about 25 to 35 hours a month during daytime feeder work and summer cuts. It uses around 28 litres an hour at ₹98 per litre.
Roof fixing, modules and inverter layout
Start with the roof. Many cold stores use pre-engineered building frames and polyurethane foam (PUF) insulated sandwich panels. A fixing that punctures the outer sheet can admit water to the insulation, reduce its thermal performance and create condensation or corrosion. The attachment design therefore needs the exact roof profile and structural drawings.
Standing-seam clamps and mini-rails
On a standing-seam PUF roof, aluminium clamps can grip the raised seams without drilling through the weather skin. For trapezoidal sheets, anodised aluminium mini-rails attach at the raised crowns with self-drilling screws and EPDM washers. Keep fasteners out of the drainage valleys, check pull-out resistance and agree the waterproofing detail with the roof supplier.
DCR bifacial modules on a light roof
For the example₹258 DCR-compliant 580 Wp N-type TOPCon bifacial modules make up the proposed array. The white PUF roof has an assumed reflectance of 28% to 35%, giving the module rear face some additional light. The model allows 6% to 8% extra yield in clear midday conditions. Since the June 2026 ALMM List-II shift, we quote new commercial projects with DCR panels unless a verified exemption applies.
Three string inverters with separate MPPTs
Three 50 kW three-phase string inverters, such as suitable Sungrow or Deye models, divide the plant into sections. Each proposed unit has four MPPT inputs and a 200 V to 1,000 V DC operating range. Separate trackers limit the effect of dust or local shade on other strings. If one inverter stops, the other two can still serve roughly 67% of the plant while the fault is addressed.
Match 150 kWp output to compressor demand
For southern Andhra Pradesh, allow roughly 4.0 to 4.5 units per kWp per day on an annual-average basis, or 1,400 to 1,600 units per kWp a year. This model uses 150 kWp and about 13,500 to 14,500 sq ft of shade-free roof. A 5,000 MT shed may have 20,000+ sq ft overall, but ducts, access paths and shade still have to be deducted during the survey.
| Measure | Before solar: grid supply | After adding 150 kWp | Change in the model |
|---|---|---|---|
| Grid energy bought each year | ~3,80,000 kWh | ~1,72,000 kWh | 54.7% fewer grid units |
| Solar units produced yearly | 0 kWh | 2,16,000 kWh | Yield of 1,440 kWh/kWp a year |
| Solar used on site | N/A | 96% (~2,07,360 kWh) | Used at the facility as generated |
| Solar export credited by the meter | 0 kWh | 4% (~8,640 kWh) | Annual APSPDCL settlement assumed |
| Typical monthly grid bill | ₹3,15,000 | ₹1,55,000 | Monthly Savings: ~₹1,60,000 |
| Grid bill over a year | ₹37,80,000 | ₹18,60,000 | ₹19,20,000 Direct Bill Saving |
| Daytime generator fuel in a year | ~9,600 Litres/Year | ~7,760 Litres/Year | ~1,840 Litres Saved (₹1,80,320) |
| Combined yearly operating saving | Not applicable | Not applicable | ₹21,00,320 per year |
The costliest grid units in this example occur when heat pushes compressor demand up. Solar used at the same hour reduces those purchased units. Check the actual time-of-day tariff and interval load profile before assigning a value to each solar unit.
Keep solar working with the DG set
Outages remain part of the design brief for a cold store on an 11 kV or 33 kV feeder. Feeder work, wind and pre-monsoon storms can put the 160 kVA DG set to work during the day. At the example fuel assumptions, its power costs about ₹24 to ₹28 per kWh, compared with the stated grid tariff. Your generator consumption should be measured rather than inferred from its nameplate.
An ordinary on-grid inverter disconnects when the utility supply fails. To use solar alongside the running generator, the example adds a DG-solar controller with reverse-power protection. It reads generator conditions through Modbus RS485 and limits inverter output as the facility load changes. The generator and protection scheme must be checked together during commissioning.
The controller uses the generator frequency as its operating reference and holds a minimum 25% to 30% engine load. That helps avoid wet-stacking and reverse power into the alternator. Under the example daytime loads, solar can supply up to 70% of instantaneous demand and the model displaces more than 1,800 litres of diesel a year. Actual fuel savings depend on outage hours, load and controller settings.
Example cash flow and depreciation
The example assigns ₹67,50,000 to a turnkey 150 kWp plant, including DCR bifacial modules, string inverters, aluminium mounting, DCDB and ACDB protection, HT CT/PT metering and CEIG approvals. That is ₹45,000 per kWp within this worked calculation, not a Ray2Volt price quote. The assumed DCR premium is ₹9 to ₹12 per Wp, depending on brand and the final bill of materials.
| Cash-flow measure | Before depreciation benefit | After assumed depreciation benefit |
|---|---|---|
| Installed capital for 150 kWp | ₹67,50,000 | ₹67,50,000 |
| Year 1 tax effect: 40% AD at 25% tax | ₹0 | ₹6,75,000 |
| Capital after the model tax effect | ₹67,50,000 | ₹60,75,000 |
| Operating savings in Year 1 | ₹21,00,320 | ₹21,00,320 |
| Yearly cleaning and O&M allowance | ₹75,000 | ₹75,000 |
| Yearly cash benefit after O&M | ₹20,25,320 | ₹20,25,320 |
| Calculated simple payback | 3.33 Years | 2.86 Years |
| Model internal rate of return | 26.4% | 31.2% |
| Model net profit over 25 years | ₹4.48 Crores | ₹4.55 Crores |
On the table assumptions, the model shows ₹20,25,320 a year after cleaning and O&M, with 3.33 years simple payback or 2.86 years after its assumed tax shield. Those values describe this example only. Businesses typically assess 3 to 5 years after a site audit, and the outcome can move with tariff, self-consumption, outages and capital cost. Panel cover is a 12-year product warranty and 30-year performance warranty; it is not a promise of free electricity. Read our solar depreciation guide and CAPEX and OPEX comparison before choosing an ownership route.
The financial and tax figures are indicative, and schemes and tariffs can change. Section 33 of the Income-tax Act₹2025 allows a 40% written-down-value depreciation rate where eligible; the model assumes a 25% tax rate. Ask your chartered accountant to confirm the current rate, timing and your eligibility. Ray2Volt does not give tax or investment advice.
Frequently asked questions
What happens to the compressors when clouds reduce solar output?
The solar inverters run alongside the utility grid while it is available. If cloud reduces output, grid supply makes up the difference at the distribution panel. Compressor continuity still depends on the quality of the grid and the site protection design; solar alone cannot prevent a grid outage.
How can panels be fixed to a PUF roof without leaks?
It can be done with a roof-specific fixing design. Standing-seam PUF panels can take seam clamps without piercing the outer sheet. Trapezoidal profiles may need mini-rails fixed to raised crowns with EPDM-sealed screws, leaving drainage valleys clear. Check loading, pull-out strength and the roof warranty with the panel supplier before installation.
Can the array produce power while the diesel generator runs?
The example uses a DG-solar controller with reverse-power protection. It trims inverter output against the live facility load and keeps the generator at a 25% to 30% minimum load. The fuel reduction depends on outage duration and compressor demand; the model should not be treated as a guaranteed 60% cut.
Does PM Surya Ghar cover a commercial cold store?
No. PM Surya Ghar assistance applies to eligible residential rooftops, not commercial cold stores. A business may examine net-metering treatment, GST input credit and 40% written-down-value depreciation under section 33 of the Income-tax Act, 2025. Confirm each item with the DISCOM and your chartered accountant.
What payback does the 150 kWp example show?
In this 150 kWp illustration, the table gives 3.33 years simple payback and 2.86 years after the model tax shield. It assumes ₹8.50 to ₹10.50 per unit and the stated generation and diesel savings. A business should usually plan around a site-audited 3 to 5 year range, with no guaranteed result. Confirm the live tariff and tax treatment for your facility.
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.
Check the solar potential of your cold store
Send us a recent power bill and roof dimensions. We will review compressor demand, usable roof area and generator operation, then prepare a site-specific proposal with stated generation assumptions.
