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Chennai Solar Calculator (TNPDCL)

Rooftop solar payback for Chennai and Tamil Nadu on TNPDCL's bi-monthly slabs, with the state's free units taken into account.

Updated · By Niraj Kumar · 1 source

Your home

Solar forSolar for
From your bill, enterFrom your bill, enter
₹
₹100₹50K

About 359 units a month on the TNPDCL tariff. TNPDCL bills every two months: enter a month's share.

Roof typeRoof type

Fine-tune

kW

Sized to cover a year of your consumption, at 5.4 peak sun hours a day in Tamil Nadu.

sq ft

About 100 sq ft per kW. Leave at 0 for no limit.

₹

Typical for an on-grid system from an empanelled vendor. Replace it with your quote.

%
0%15%

Indian residential tariffs have historically risen 4-7% a year.

%
0%2%

Monocrystalline panels typically lose about 0.5% a year.

How you payHow you pay
Pays for itself in2.7 yearsthen ₹15.67 L ahead after 25 years

A 3 kW system makes about 379 units a month, 100% of your use. Your bill drops from ₹3,000 to about ₹0 in year one.

Installed cost
₹1,80,000
PM Surya Ghar subsidy
− ₹78,000
Net cost to you
₹1,02,000
Saving in year one
₹36,710
Return (IRR)
40.4% a year
over 25 years, before tax
CO₂ avoided
77 tonnes
over 25 years
Subsidy43%
  • You pay57%
  • Central subsidy43%
Your money over 25 yearsStill to recoverAhead
₹-5 L₹0₹5 L₹10 L₹15 L₹20 LPayback, year 2.704812162025
Year-by-year cash flowShow
YearUnits madeBills without solarBills with solarUpkeep and EMIsRunning total
14,553₹36,097₹0₹0-₹65,290
24,530₹37,902₹0₹0-₹26,833
34,508₹39,797₹0₹0₹13,464
44,485₹41,787₹0₹0₹55,693
54,463₹43,876₹0₹0₹99,956
64,440₹46,070₹0₹1,800₹1,44,557
74,418₹48,374₹0₹1,800₹1,91,406
84,396₹50,792₹0₹1,800₹2,40,619
94,374₹53,332₹0₹1,800₹2,92,316
104,352₹55,999₹0₹1,800₹3,46,625
114,330₹58,799₹0₹1,800₹4,03,679
124,309₹61,738₹0₹22,800₹4,42,620
134,287₹64,825₹0₹1,800₹5,05,645
144,266₹68,067₹0₹1,800₹5,71,912
154,244₹71,470₹0₹1,800₹6,41,582
164,223₹75,043₹0₹1,800₹7,14,825
174,202₹78,796₹0₹1,800₹7,91,821
184,181₹82,735₹0₹1,800₹8,72,756
194,160₹86,872₹0₹1,800₹9,57,829
204,139₹91,216₹0₹1,800₹10,47,244
214,119₹95,777₹0₹1,800₹11,41,221
224,098₹1,00,565₹0₹1,800₹12,39,986
234,078₹1,05,594₹0₹1,800₹13,43,780
244,057₹1,10,873₹0₹1,800₹14,52,854
254,037₹1,16,417₹0₹1,800₹15,67,471

How the Chennai Solar Calculator (TNPDCL) works

Saving₍y₎ = [Bill(U) − Bill(U − G₍y₎/12)] × 12 × (1 + e)^(y−1), G₍y₎ = kW × H × 365 × PR × (1 − d)^(y−1)

This page uses the same method as the Solar ROI Calculator India, which explains each term and assumption in full.

Worked example

A Chennai home on TNPDCL with a ₹3,000 monthly bill and a flat RCC roof, assuming prices rise 5% a year.

  1. 1Working the bill back through the TNPDCL slabs, charges and duty gives about 359 units a month
  2. 2At 5.4 peak sun hours, 3 kW makes about 379 units a month, 100% of that use
  3. 33 kW at ₹60,000 per kW costs ₹1,80,000; PM Surya Ghar pays ₹78,000, leaving ₹1,02,000
  4. 4The first year saves ₹36,710, and the saving grows as tariffs rise

The system pays for itself in about 2.7 years and leaves the household about ₹15,67,471 ahead over 25 years.

Frequently asked questions

How do Tamil Nadu's free units affect solar savings?

Homes get the first 200 units of each two-month bill free if they stay within 500 units, and 100 otherwise. Solar that brings a home under that line recovers the extra free units, which the calculator includes. Since those free units cost nothing already, solar mainly saves on the upper slabs, which reach ₹12.15 a unit.

Why does the calculator show monthly slabs when TNPDCL bills every two months?

To keep one monthly bill field for every state. TNPDCL's two-month bands are halved to monthly equivalents, which gives the same result for a steady household. Enter half of your bi-monthly bill.

How does net metering settle on TNPDCL?

Net metering for domestic consumers, billed every two months, with surplus settled yearly at the TNERC rate.

Sources

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