Every C&I facility in India running a diesel generator believes it knows what backup power costs. It is the monthly fuel bill — typically ₹25–28 per kWh of backup power generated, depending on diesel prices and generator vintage.

That number is wrong. Or rather, it is incomplete in ways that matter enormously to a CFO trying to understand the real operating cost of keeping the lights on during grid failures.

The Three Costs Your DG Bill Doesn't Show

1. Maintenance, AMC and Operator Cost

A diesel generator requires oil changes every 250 hours, injector servicing, load bank testing, coolant maintenance and periodic filter replacements. On top of the equipment AMC, most facilities carry a dedicated DG operator or an outsourced AMC contract. For a 500 kVA generator, this amounts to approximately ₹1 lakh per year — a figure that is typically budgeted under "facility maintenance" and never appears in the backup power cost calculation.

2. Thermal Efficiency Losses

A diesel generator at 60% loading — typical for most C&I backup scenarios — operates at roughly 28–32% thermal efficiency. The remaining 70% of the fuel's energy is lost as heat. This is why the effective cost per kWh of backup power is substantially higher than the diesel price per litre implies. At ₹90/litre and 0.35 litres per kWh, you are paying approximately ₹31.50 per kWh of actual backup power delivered — before maintenance is counted.

₹31–35 True all-in cost per kWh of diesel backup power at ₹90/litre diesel price, including fuel losses and maintenance. Grid-charged BESS delivers the same kWh at ₹7–9.

3. The Switchover Gap — the Invisible P&L Leak

This is the most significant cost, and the one almost never captured in any facility's backup power budget.

A diesel generator takes 10–30 seconds to reach stable operating voltage after a grid failure. During those 10–30 seconds, PLCs reset to their last saved state (losing in-process data), CNC machines fault and require manual restart, cold room controllers trigger temperature alarms and compressors cycle inappropriately, and injection moulding machines lose the current shot — wasting material already in the barrel.

For a mid-sized manufacturing facility running 200+ outage events per year — common in states like Haryana, UP, Rajasthan and Maharashtra — this switchover gap translates to ₹6–15 lakh in annual production loss, raw material wastage and machine restart labour, depending on the process and shift pattern.

Why this never appears in P&L: The production losses from switchover events are typically absorbed into "production variance," "machine downtime" or "material wastage" — budget lines managed by operations, not facilities. The DG appears to be working correctly because it starts and takes load. The cost of the gap it cannot bridge is invisible to the facilities manager — but very visible to the plant manager and CFO.

The Full P&L Comparison: 500 kVA Facility, 200 Outage Hours/Year

Cost Line 🔴 Diesel Generator 🟢 PWRNXT BESS
Energy cost (fuel / grid charging) ₹21.6L ₹8.3L
Maintenance, AMC & operator ₹1.0L ₹0 (included in lease)
Equipment lease / depreciation ₹3.5L (depreciation equiv.) ₹7.2L (OpEx lease)
Unrecovered production margin — switchover gap ₹7.2L ₹0 (<10ms — zero gap)
Total annual operating cost ₹33.3L ₹15.5L

Assumptions: 500 kVA facility, 60% load factor, 40 outage hours/month, ₹90/litre diesel, ₹7.5/kWh off-peak grid tariff. BESS lease based on 60-month PMT at 14% p.a. with levelized AMC. Production loss: ₹2,500/event × 480 events/year.

Net operating margin improvement: ₹17.8L per year — a 53% reduction in total backup power operating cost. This figure flows directly to EBITDA improvement, not just cash saving, because the BESS lease is a fixed OpEx line replacing a variable one.

Why the Lease Structure Changes the Finance Equation

The comparison above uses an operating lease cost for BESS — not a capital purchase. This is important for two reasons that matter specifically to Indian C&I finance teams.

Balance sheet treatment: Under Indian GAAP and Ind AS 116, an operating lease for equipment where the lessor retains ownership and risk can be treated as off-balance-sheet OpEx rather than a capitalised asset. PWRNXT owns the BESS asset throughout the lease term. This means no CapEx approval, no depreciation schedule, no technology risk on your books.

Tax deductibility: The full quarterly lease payment is 100% tax-deductible as a business operating expense in the year it is incurred — exactly like your current diesel AMC contract or any other facility maintenance spend. There is no depreciation timing difference to manage.

The Break-Even Question

The question most operations and finance heads ask is: at what diesel price does the switch to BESS make commercial sense?

The answer, based on current BESS lease rates and Indian grid tariffs, is: any facility paying above ₹75/litre for diesel with 150+ annual outage hours will see a positive cash flow from switching to BESS on operating lease — before counting production loss recovery. With current diesel prices at ₹88–102/litre across most Indian states, virtually every C&I facility with a 125 kW+ DG set is in positive cash flow territory from month one.

Month 1 Most clients achieve positive cash flow from the first month of BESS operation — the quarterly lease payment is structured at or below the quarterly diesel spend it replaces.

What This Means for Your Facility

If your facility runs a diesel generator of 125 kVA or above and experiences 100+ outage hours per year, the economics of switching to BESS on operating lease are almost certainly positive. The variables that matter most to your specific case are:

  • Your actual diesel price (varies significantly by state and procurement route)
  • Your outage frequency and duration profile (DISCOM data + your DG run log)
  • Your process sensitivity to the switchover gap (high for manufacturing, cold chain, healthcare — low for simple lighting and HVAC)
  • Your local DISCOM off-peak tariff (determines BESS charging cost)

PWRNXT provides a free, data-backed feasibility study that quantifies all four variables for your specific facility — typically returned within 5 business days of receiving your DG capacity and monthly diesel consumption data.