Case study: Madurai 150-bed hospital 100 kW hybrid solar — 22-month payback

**Client profile:** 150-bed multi-specialty private hospital, Madurai city outskirts. Established 2011. Departments: 3 OTs, 15-bed ICU + 10-bed NICU, MRI + CT scan, dialysis unit (8 machines), pathology lab, general wards, OP, pharmacy, 2 elevators, HVAC (12 tons split + 2 central VRV).

**Pre-solar power profile:** connected load 285 kVA (HT-IIA tariff). Monthly consumption 42,000-48,000 units. TNEB bill ₹3.6-3.9 lakhs. Diesel genset (250 kVA Kirloskar) backup for outages — monthly diesel ₹55k-75k depending on outage frequency. Combined power cost ₹4.2-4.6L/month.

**Pain points:** (1) TNEB power cuts 8-12 events/month, avg 45 min each — critical during OT scheduling. (2) Diesel genset noise complaint from residential neighborhood. (3) Board meeting pushed for NABH accreditation — sustainability + reliability KPI. (4) HVAC + MRI cooling account for 40% total consumption, growing.

**Roof survey:** 3-floor building, terrace area 1,240 sq m. South + south-west orientation ideal. Water tank tower + AHU units occupy 180 sq m. Usable rooftop 1,020 sq m — supports ~120 kW panels with 20% walkway spacing.

**System design decision — hybrid over pure grid-tied:** hospital criticality (OT, ICU cannot tolerate 5-second grid drop during genset switchover) mandated seamless backup. Grid-tied solar shuts down during outage (anti-islanding). Solution — hybrid solar with battery + AATS (Automatic Transfer Switch) sub-second changeover.

**Final BOM:** 100 kWp Waaree Aditya 580W TOPCon bifacial panels (172 units) + Sungrow SG100CX-P2 100 kW three-phase grid-tied inverter + 3 × Sungrow SBR192 64 kWh LFP battery banks = 192 kWh total + AATS panel + monitoring SCADA + ground earthing 4 pits + lightning arrestor + galvanized mounting.

**Load segregation strategy:** critical bus (OT + ICU + NICU + MRI cooling + server room) 45 kVA — 100% solar+battery backup, zero outage. Non-critical bus (wards + lighting + admin) 240 kVA — solar-first grid-supplement, no battery backup. Segregation via dedicated MCC panel + interlocking.

**Cost breakdown:** panels ₹22.5L (172 × ₹13,100) + inverter ₹5.8L + battery bank ₹42L (3 × ₹14L) + mounting + civil ₹6.5L + AATS + electrical panel ₹4.2L + wiring + protection ₹3.2L + install labour ₹3.5L + monitoring + commissioning ₹2.8L = ₹90.5L final (initial estimate ₹78L, upgrade during install added ₹12.5L).

**Tax + subsidy benefits:** MSME accelerated depreciation not applicable (hospital private ltd). Standard depreciation 15% × ₹90.5L = ₹13.6L year 1 → 30% tax bracket saves ₹4.08L. Zero central/state subsidy for private hospitals in TN 2026.

**Effective investment:** ₹90.5L cost − ₹4.08L tax saving = ₹86.4L net cash outflow.

**Install timeline (phased, no hospital shutdown):** feasibility + design 12 days. Panel + inverter procurement 22 days. Mounting structure erection 8 days (night shifts). Panel install 6 days (2 sections/day). Inverter + battery bank install 4 days. AATS + electrical panel integration 3 days (weekend shutdown windows). Commissioning + testing 3 days. Total 58 days from PO to power-on.

**Post-install operational data (12 months):** solar generation 12,600 units/month avg (140 units/kWp/month). Battery cycles 320/year (0.88/day, mostly outage backup). Grid consumption 8,400 units/month (from 45,000 pre-solar). Monthly EB bill ₹85,000 (from ₹3.8L). Diesel usage ₹12,000/month (from ₹65k) — genset used only for full-battery-drain scenarios.

**Financial result:** monthly savings ₹3.5L (EB + diesel combined). Annual ₹42L. Payback = ₹86.4L / ₹42L = 2.06 years = 24 months. Actual achieved 22 months (bonus from higher-than-modeled generation).

**25-year cumulative saving projection:** average tariff escalation 6%/year → 25-year savings ₹15.8 crore against ₹86.4L investment. NPV @ 10% discount ₹6.2 crore.

**NABH accreditation bonus:** sustainability + power reliability KPIs scored 96/100 in NABH review (previously 78). Directly aided accreditation grant. Marketing team leveraged 'green hospital' angle — 12% increase in outpatient consultations year 1 (attributed partially to green certification media coverage).

**Lessons for other hospitals:** (1) Battery investment justified — OT downtime cost + reputational risk exceeds any battery payback math. (2) Load segregation essential — 100% coverage over-sizes battery, 0% coverage defeats purpose. (3) Phased install mandatory — 24×7 operation cannot tolerate blackout. (4) Genset stays as tertiary backup even after solar+battery — insurance for extended monsoon overcast weeks.

**SVN hospital solar portfolio:** 8 hospitals installed 2022-2026 across TN — Madurai, Trichy, Salem, Erode, Coimbatore, Chennai. Reference site visits arrangeable pre-booking. Design + install + 10-year AMC available as one contract.