Illustrative hospital, not a customer installation. This 100-bed facility is a representative model. Its loads, cost and payback figures show how an engineer might assess a project; they are not measurements from a Ray2Volt site. The photographs are illustrative too.
Your bill, roof and essential-load list will change the design. Ask for a site-specific estimate.
Key points
- ICU, NICU and operating-theatre circuits need a tested transfer path and clean supply at all hours.
- For the example, the effective commercial tariff is ₹10.20 per unit and generator power costs more; confirm your APSPDCL category and current order.
- An 80 kWp array with a 60 kWh LiFePO4 bank models ₹11,83,200 less grid expenditure and ₹4,11,600 less diesel cost each year.
- The model payback is 3.22 years before tax and 2.90 years after its assumed section 33 effect; a site audit is needed for your hospital.
For a hospital, a short voltage dip matters as much as a long outage. Operating theatres, NICUs, ICUs, recovery wards, CSSD equipment, medical gas plants, MRI and CT systems, and blood-bank fridges all need stable supply. A five-second gap while a generator starts could restart monitors or interrupt sensitive instruments. The electrical design therefore begins with a schedule of critical loads and the transfer time each one can tolerate.
The same site pays for electricity around the clock. Chillers, positive-pressure ventilation, imaging equipment and autoclaves run alongside patient care. This example assumes the applicable APSPDCL commercial HT or LT category and an effective ₹9.80 to ₹11.20 per unit, based on the APERC FY 2026-27 order dated 25 March 2026. Check the latest tariff order. When a 125 kVA to 250 kVA DG set is needed, its modelled generation cost reaches ₹26+ per unit, making backup operation a separate cost to measure.
The proposed answer is an 80 kWp solar array with lithium iron phosphate (LiFePO4) storage and hybrid inverters. Solar reduces purchased daytime units, while the battery supports the selected critical-care bus during a short transfer or outage. This worked example covers electrical layout, safety, diesel displacement and payback for a Tirupati multi-speciality hospital. See our healthcare solar service and business solar options for project scope.
Plan the hospital power transfer
Most hospitals already have three power layers: utility supply, an automatic transfer switch (ATS) linked to a diesel generator, and a battery UPS for sensitive circuits. The weak point is the period between losing the grid and accepting stable generator output. Map which circuits remain on the UPS, test battery condition, and confirm the switch sequence before connecting a solar hybrid system.
The generator start interval
In this example the generator needs 8 to 15 seconds to start, stabilise at 415 V and close the ATS breaker. The UPS must carry surgical and monitoring equipment throughout that interval. Ageing lead-acid cells can shorten the expected hold time, so a load test is more useful than relying on the battery label or maintenance log alone.
The running cost of diesel backup
Short feeder trips can put a hospital generator to work for hours even when grid supply soon returns. The model 125 kVA set uses 22 to 28 litres of diesel an hour over two to three hours of daily use. At an assumed ₹98 per litre, the estimated electricity cost is ₹25 to ₹29 per kWh. Compare logged litres and run-hours with metered generator output before counting fuel savings.
Noise and exhaust near care areas
Noise, vibration and exhaust are also difficult to manage near patient areas. Solar produces no on-site combustion while it runs, and a battery can reduce generator starts for short interruptions. Neither removes the need for the hospital backup plan; critical circuits must remain supported when solar output is low or equipment is under service.
The example hospital has demand all day and night. Its 100% modelled daytime solar self-consumption means the generated units are used inside the premises, with no export assumed. Verify that result against interval readings, especially on low-occupancy days.
The representative 100-bed Tirupati hospital
Use the following 100-bed Tirupati hospital as the basis for the worked calculations. Its equipment list and bills are representative assumptions, not the operating records of a named hospital.
- Clinical capacity: 100 beds, 3 modular operating theatres, a 16-bed adult and neonatal ICU, pathology laboratory and digital CT facility.
- Cooling plant: Two 40 TR screw chillers serve a central chilled-water system for surgical temperature and humidity control; patient rooms also have inverter split units.
- Approved supply: 150 kVA contract demand in the applicable APSPDCL HT commercial category.
- Monthly grid use before solar: 26,000 to 30,000 kWh, with a model bill of ₹2,85,000 and ₹10.20 per kWh blended cost including demand charges and duty.
- Generator record assumed: One 125 kVA set runs 40 to 50 hours monthly in summer, using around 1,100 litres and ₹1,07,800 in fuel and oil per month.
- Roof available: 8,200 sq ft of concrete roof on the clinical block and diagnostics annex.
How the hybrid supply is arranged
A conventional on-grid inverter shuts down when the utility fails. For the selected hospital circuits, the example instead uses a hybrid architecture with a defined critical-care bus, battery and generator input. The single-line diagram must show isolation, bypass and protection clearly. A transfer-time claim only counts after testing it with the actual connected loads.
Two parallel hybrid string inverters
Two 40 kW Deye three-phase hybrid inverters operate in parallel in this example. Each combines an inverter/charger with a static transfer switch. While APSPDCL supply is healthy, the inverters synchronise to the grid and feed solar energy into the main LT distribution bus. Their output and battery controls must be matched to the hospital earthing and protection scheme.
Transfer to the battery-backed bus
When the grid trips, the proposed inverters isolate the critical bus from the street transformer in less than 10 milliseconds and use the battery and available solar power. That is shorter than the stated 20 ms hold-up of the model power supplies, but actual ventilators, monitors and surgical lights must be tested. Retain the dedicated UPS where clinical equipment specifications require it.
Generator start during a long cut
If an overcast outage continues until battery state of charge reaches 20%, the inverter sends a start request to the 125 kVA DG set. The generator then takes the remaining load and recharges storage within its approved operating range. Commission the controls so the engine does not run at a damaging light load, and test the handover with the hospital facilities team.
80 kWp sizing and example cash flow
The model uses 80 kWp DC from 138 DCR-compliant 580 Wp N-type TOPCon bifacial modules. Elevated steel frames provide 8.5 ft clearance around terrace chillers and oxygen manifolds. A 60 kWh high-voltage LiFePO4 rack provides the storage allowance. The structural survey must confirm that both the array and its maintenance routes fit the available 8,200 sq ft.
| Operating measure | Before the array | With the model hybrid plant | Yearly change in the model |
|---|---|---|---|
| Grid units bought per year | 3,36,000 kWh | 2,20,000 kWh | 34.5% fewer grid units |
| Solar units made per year | 0 kWh | 1,16,000 kWh | Yield of 1,450 kWh/kWp a year |
| Solar used at the hospital | N/A | 100% (no curtailment assumed) | All modelled units used on site |
| Yearly utility bill | ₹34,27,200 | ₹22,44,000 | Grid cost lower by ₹11,83,200 |
| Generator fuel used yearly | ~13,200 Litres | ~9,000 Litres | 4,200 litres less (31.8%) |
| Fuel saving using ₹98 per litre | ₹0 | ₹4,11,600 | Fuel and DG service cost avoided |
| Combined yearly operating saving | Not applicable | Not applicable | ₹15,94,800 for the year |
For this illustrative 80 kWp package, the capital allowance is ₹49,50,000. It includes DCR modules, two 40 kW hybrid inverters, 60 kWh of LiFePO4 storage, raised galvanised steelwork and DG controls. Since the June 2026 ALMM List-II shift, we quote DCR modules for new commercial work unless a verified exemption applies; the assumed premium is ₹9 to ₹12 per Wp. This example cost is not a site quote.
| Cash-flow measure | Before the assumed tax effect | After assumed 40% depreciation |
|---|---|---|
| Capital for array and battery | ₹49,50,000 | ₹49,50,000 |
| Year 1 tax effect: 40% AD at 25% tax | ₹0 | ₹4,95,000 |
| Capital after model tax effect | ₹49,50,000 | ₹44,55,000 |
| Yearly saving after O&M | ₹15,34,800 | ₹15,34,800 |
| Calculated simple payback | 3.22 Years | 2.90 Years |
| Model internal rate of return | 28.4% | 33.1% |
| Model net profit over 25 years | ₹3.42 Crores | ₹3.47 Crores |
The cash-flow table calculates 3.22 years before the model tax effect and 2.90 years after it. Those figures rely on the stated grid and diesel savings, including fewer short generator runs. For a business, typical payback is 3 to 5 years after a site audit. No transfer performance or payback should be promised without reviewing circuits, bill data and the generator log.
Battery selection and service life
Battery chemistry is one part of patient safety. Traditional tubular lead-acid and VRLA banks need suitable ventilation and handling because charging can produce hydrogen and corrosive exposure. A hospital also has to consider floor area, fire separation, monitoring and access for maintenance. The battery room design should follow the selected equipment instructions and local approvals.
This example specifies a 60 kWh high-voltage LiFePO4 battery rack. The chemistry is generally more thermally stable than common alternatives, but the rack still needs a battery management system, suitable enclosure, temperature control and fire review. The design assumptions below should be confirmed against the supplier data sheet.
- Stability: The model cites a LiFePO4 thermal runaway threshold above 270°C. Verify the complete rack and fire design; cell chemistry alone cannot remove fire risk.
- Gas and ventilation: Sealed LiFePO4 cells avoid routine acid fumes and hydrogen release, but the room must still meet the supplier’s ventilation and safety instructions.
- Cycle allowance: More than 6,000 cycles at 80% depth of discharge is assumed, giving a 12 to 15 year design estimate versus 3 to 4 years for lead-acid. The quoted battery product warranty is 10 years.
- Power response: A stated 1C continuous discharge can meet short, high draws from equipment such as MRI chillers or suction pumps, subject to inverter and battery ratings.
For more detail on cycling, backup duration and cost, see our battery storage assessment and comparison of on-grid, off-grid and hybrid systems.
Roof access, fire review and approvals
A hospital roof has to remain accessible to the fire service, maintenance teams and medical plant operators. The example layout is checked with the local authority, fire department and Chief Electrical Inspectorate to Government (CEIG). Treat the clearances below as design assumptions to verify against the current site approval, structural drawings and equipment positions.
- Fire access: The model uses a 1.2-metre roof-edge setback and 1.0-metre paths between panel tables for stairwells, vents and hose reels. Confirm NBC Part IV and local requirements.
- DC isolation: Specify IP65-rated rooftop combiners and switches away from biomedical waste exhaust and medical gas cylinder areas; the electrical design must be approved.
- Earthing and lightning: The example uses separate copper earthing pits with resistance below 1.0 ohm, coordinated with biomedical equipment earthing to limit interference.
All financial figures here are indicative; tariffs and schemes can change. A trust, society and company may have different tax treatment. Section 33 of the Income-tax Act, 2025 provides 40% written-down-value depreciation where eligible, but ask your chartered accountant to confirm the current rate and the hospital entity’s eligibility. Ray2Volt does not give tax or investment advice.
Frequently asked questions
Can the hybrid system carry ICU and theatre loads through a grid cut?
The proposed hybrid inverters isolate the critical bus and transfer it to battery and available solar in under 10 ms. That may bridge the model 20 ms supply hold-up, but it is not a blanket guarantee for ICU or operating-theatre equipment. Keep the required UPS and test each critical circuit, alarms and bypass procedure with the clinical engineering team.
Why choose LiFePO4 instead of lead-acid storage?
LiFePO4 cells avoid the routine acid and hydrogen issues associated with lead-acid charging and can support deeper cycling. This model uses a 6,000+ cycle assumption and compares it with 1,200 cycles for industrial lead-acid banks. Actual service life depends on temperature, depth of discharge and controls; Ray2Volt quotes a 10-year lithium-ion battery product warranty.
Where do the model diesel savings come from?
During a daytime feeder cut, solar and the 60 kWh battery can carry selected loads before the 125 kVA generator starts. The example models 4,200 litres of diesel displaced each year, including avoided short runs. Check generator logs, battery capacity and essential-load demand to estimate your own result; a 70% reduction is not assured.
What approvals and fire access does a hospital roof need?
Yes, an installation needs roof, electrical and fire review. The example provides a 1.2-metre perimeter, 1.0-metre access walkways, IP65 DC isolation and CEIG approval. Confirm the applicable NBC Part IV interpretation and site-specific fire access with the authority before treating those dimensions as final.
What payback does the 80 kWp hospital example calculate?
The model table gives 3.22 years simple payback, or 2.90 years after its assumed depreciation tax effect. It uses illustrative ₹9.50 to ₹10.80 per unit HT tariffs and the stated diesel savings. A business should assess a typical 3 to 5 year range after an audit, with the actual tariff and section 33 treatment confirmed for its own entity.
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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Send your electricity bills, single-line diagram and list of critical circuits. We will assess solar capacity, battery duration and generator handover for your site before preparing a proposal.
