An industrial plant buys its evenings at the peak ToD rate and its middays from a roof that is already spilling. The battery moves one into the other. The model sizes it, finances it at a target equity IRR, and then asks the only question that matters commercially — whether the rental that clears the return is smaller than the saving it creates.
Battery
6.9/28
MW / MWh · 4.0 hour
Rental required
36.3
₹L/mo
Net saving
1.58
₹Cr/yr
Headroom
13.1
₹L/mo
State
MSEDCL · HT-I Industrial (Express feeder)
Consumer category
Cement plant · base ₹8.44/kWh · 9.3% duty · ₹475/kVA/month
Factory contract demand15 MW
57k m² of roof · 82% load factor, 7 days a week · Grinding, packing and utilities running flat around the clock. Dense load on a modest roof, which is why the array runs onto the ground inside the premises.
On-site solar45 MWp
7.1 MWp on the roof, 38 MWp on 150 acres of ground inside the premises
On-site solar capacity factor16.0%
3,840 kWh a day per MWp — fixed tilt on a roof or a constrained yard, not trackers on open land
Solar generation cost₹3.75/kWh
what the plant pays per delivered unit. Behind the meter this is also the landed cost — no wheeling, no surcharge, no loss between the array and the load.
Diesel generator, hours a day0 h/day
the plant never loses supply — set hours to build the diesel case
Rooftop-charged storage · Maharashtra industrial
MERC MYT Order, Case 226 of 2024 — FY 2025-26 · MSEDCL · HT-I Industrial (Express feeder)
✓Bankable and sellable. The rental that clears a 15% equity IRR is ₹36.3 L/month. The plant can bear ₹49.4 L/month before the deal stops saving it money, so there is ₹13.1 L/month of headroom to split between developer and consumer.
The rental
Rental for target IRR
36.3₹L/mo
₹5.3 L/MW/mo
Consumer can bear
49.4₹L/mo
rental at which saving hits zero
Headroom
13.1₹L/mo
margin to split
Net saving
1.58₹Cr/yr
4.9% of the peak-hour bill
How it is built
Cells · 27.6 MWh at ₹0.72 Cr/MWh₹19.87 Cr
Power block · 6.9 MW at ₹0.30 Cr/MW₹2.07 Cr
Installed cost₹21.94 Cr
Debt 70% at 9.50%, 15 yr₹15.36 Cr
Equity₹6.58 Cr
Rental that makes equity IRR 15% over 20 yr₹36.3 L/mo
₹4.35 Cr a year ÷ 8.70 MU discharged₹5.00/kWh
Per MW of power, per month₹5.3 L
Per MWh of storage, per month₹1.3 L
The rental is not assumed — it is bisected until the equity cash flow, discounted at the target return, comes to exactly zero. The per-kWh figure is that rental divided by what the battery actually delivers, so it moves with cycling when nothing about the asset has: the same ₹36.3 L/month is ₹5.00/kWh at 350 cycles a year and ₹8.76/kWh at 200.
Why this rating
Net saving against battery size. The first MWh earns the widest part of the spread and cycles every day; each one after it reaches further into hours the array cannot fill, so it cycles less often while costing exactly as much. The model stops at the top of the curve.
Landed cost of a stored unit
EVERYTHING PER kWh THE BATTERY DELIVERS
Solar you now pay for₹4.26
1.14 kWh in at ₹3.75 for each kWh out — the tariff is unchanged, 12% is lost in the round trip
Storage rental₹5.00
₹36.3 L/month ÷ 8.70 MU delivered a year
Cost of a stored kWh₹9.26
Grid peak charge it replaces₹11.07
₹10.13 tariff + 9.3% electricity duty
The plant saves+₹1.81
× 8.70 MU a year = ₹1.58 Cr
The charging side already carries the round trip: 1.14 kWh goes in for every one that comes out, and every figure above is stated per kWh out. Demand charges are untouched — this sells energy, not capacity.
The plant's bill, year 1
Without storage₹87.16 Cr
With storage, before rental₹81.23 Cr
Gross benefit₹5.93 Cr
Storage rental−₹4.35 Cr
Net saving₹1.58 Cr
Levelised over the term₹13.4 Cr NPV at 10%
Representative working day
ToD slot
Hours
Adj
₹/kWh
Normal
0000–0600
—
8.44
Normal
0600–0900
—
8.44
Solar
0900–1700
−15%
7.17
Peak
1700–2400
+20%
10.13
Energy balance, year 1
Plant consumption107.7 MU
Grid import, without storage61.2 MU
Grid import, with storage52.5 MU
Renewable generation63.1 MU
Surplus before storage16.5 MU
Clipped and never delivered6.6 MU · 10%
Charged from surplus9.89 MU
Charged by diverting self-use0.00 MU
Charged from RE contracted for it0.00 MU
Charged from the grid0.00 MU
Round-trip loss, paid for but never delivered1.19 MU
Discharged into the peak8.70 MU
Equivalent full cycles350/yr
Container used, over its 4-hour window100%
Battery & finance assumptions
One 1 MW / 4 MWh container
Installed cost₹3.18 Cr
₹7,950 per kWh · ₹2.88 Cr cells + ₹0.30 Cr power block
Rental at 15% IRR₹5.3 L/mo
₹5.00/kWh if it cycles 350 times a year
Cell cost, per MWh₹0.72 Cr/MWh
₹7,200 per kWh of storage installed
Power block, per MW₹0.30 Cr/MW
inverters, transformer and switchgear · whole project ₹21.9 Cr for 6.9 MW / 28 MWh
Contract term20 years
contract term binds at 20 yr · 15-year debt · augmentation ₹7.4 Cr over the term
Target equity IRR15.0%
70:30 debt:equity at 9.50%
Cycle life8,000 cycles
22.8 yr at 350 cycles/yr · contract term binds at 20 yr
Nominal duration4 hours
how long the battery can hold its rated output
Round-trip efficiency88.0%
AC to AC, auxiliaries included. 1.14 kWh has to go in for each kWh out, so a ₹3.75 unit costs ₹4.26 once stored.
Depth of discharge90%
24.8 MWh usable per cycle
Annual degradation5.00%/yr
held at nameplate by ₹7.4 Cr of augmentation
Developer's case
Installed cost₹21.94 Cr
Debt 70% at 9.50%₹15.36 Cr
Equity₹6.58 Cr
Equity IRR15.00%
Minimum DSCR1.59
Term20 yr · contract term binds
Renewable contract
The generator bills only the units the plant actually takes, so surplus is simply lost at the inverter. Storing a surplus unit therefore costs the full generation tariff, because it becomes a billable unit. This is a behind-the-meter arrangement — an open-access seller schedules and injects, and expects to be paid for it.
Cash flow to equity
Yr
Revenue
EBITDA
Interest
Tax
FCFE
1
4.35
3.94
1.46
0.24
0.68
2
4.35
3.93
1.36
0.25
0.77
3
4.35
3.91
1.26
0.27
0.85
4
4.35
3.89
1.17
0.28
0.94
5
4.35
3.87
1.07
0.29
1.02
6
4.35
3.85
0.97
0.31
1.11
7
4.35
3.83
0.88
0.32
1.19
8
4.35
3.81
0.78
0.33
1.27
9
4.35
3.79
0.68
0.74
0.94
10
4.35
3.76
0.58
0.78
1.00
11
4.35
3.74
0.49
0.80
1.06
12
4.35
3.71
0.39
0.83
1.12
13
4.35
3.68
0.29
0.85
1.18
14
4.35
3.65
0.19
0.87
1.25
15
4.35
3.62
0.10
0.89
1.31
16
4.35
3.59
0.00
0.90
2.39
17
4.35
3.56
0.00
0.89
2.38
18
4.35
3.52
0.00
0.89
2.36
19
4.35
3.48
0.00
0.88
2.34
20
4.35
3.44
0.00
0.87
2.58
₹ crore. Equity of ₹6.58 Cr at year 0. Tax is the higher of 25.168% on profit after 40% WDV depreciation and 17.16% MAT on book profit.
This model needs a presentation-sized window — at least 1100 × 620. The stage, the controls and the economics column have to be visible together for any of it to mean anything.