Why the numbers change
The subsidy shown combines the central PM Surya Ghar amount with the Bihar Govt. top-up, and applies to residential connections only. Commercial and industrial consumers instead claim 40% accelerated depreciation, which is not shown here.
Roughly ₹0 a year, from a 0 kW system
These are indicative figures based on 132 units per kW per month for Bihar and current market prices. The subsidy shown assumes both the central and the Bihar Govt. amounts are available for your connection. Your exact numbers depend on roof orientation, shading, brand choice and your DISCOM tariff — we confirm them in writing after a free site survey.
Get an exact quote for my roofWhat sits behind the maths
The assumptions, stated openly
So you can judge the estimate rather than just trust it.
132 units per kW per month
A realistic year-round average for Bihar, allowing for the monsoon and for ordinary dust on the panels. Peak months run higher, July and August lower.
₹48,000–₹62,000 per kW
Current market pricing for a quality on-grid system with a galvanised structure, tapering as the plant gets larger. Hybrid systems with batteries cost more.
Central + Bihar slabs
₹40,000 at 1 kW, ₹80,000 at 2 kW and ₹98,000 at 3 kW and above — applied only to residential property types.
12% lifetime degradation
The 25-year figure assumes panels gradually lose output, as all panels do. It does not assume 25 years at day-one performance.
0.82 kg CO₂ per unit
The standard grid emission factor for India, used to estimate the carbon your plant avoids each year.
What it leaves out
Maintenance, one inverter replacement in the plant's life, and any future tariff increase — which in practice makes the real saving larger, not smaller.
About these numbers
Calculator questions
It is a good first estimate, not a quotation. It assumes 132 units per kW per month, which is a fair average for Bihar, and current market prices for good-quality equipment. Your real figures depend on roof orientation, shading, the brands you choose and your DISCOM tariff — which is why we survey before quoting.
The calculator sizes the plant to cover your consumption. A higher bill means more units consumed, which means more kilowatts needed. It rounds to the nearest half kilowatt, the way a real system would be configured.
PM Surya Ghar is a residential scheme. Commercial, industrial and institutional consumers instead claim 40% accelerated depreciation in the first year plus GST input credit — a benefit this calculator does not attempt to model, because it depends on your tax position.
Divide your bill amount by the units consumed on the same bill. For most Bihar domestic connections it works out between ₹6 and ₹8 per unit; commercial connections run higher.
It does not. Budget a modest annual maintenance contract and one inverter replacement somewhere between year ten and fifteen. Even with both, a well-built plant comfortably pays for itself several times over across its life.
From estimate to quotation
The only number that matters is the one for your roof.
A calculator cannot see that your water tank shades the south-west corner from two o'clock, or that your sanctioned load will not support the system you were hoping for. A survey can.
Book one and we will give you the same figures you see here — system size, cost, subsidy, payback, lifetime saving — measured for your building and put in writing.
Turn this estimate into a quote
Send your details and we will survey your roof free of cost, then confirm these numbers in writing.