How this calculation works
Separate the electricity you use immediately from electricity sent to the grid: they need not have the same value. Multiply a site-specific generation estimate by those two rates, subtract upkeep, and follow the remaining cash flows until they cover the installation cost. The annual table makes output degradation visible instead of applying the first year’s savings unchanged to the entire project.
Worked example
This example uses illustrative inputs. Your current result is shown above.
For an illustrative ₹1,80,000 quote, no subsidy, 3 kWp and yield of 1,500 kWh/kWp/year, first-year generation is 4,500 kWh. With 70% self-consumption, ₹8/kWh avoided imports and ₹3/kWh exports, value is ₹25,200 + ₹4,050. After ₹2,000 maintenance the first-year saving is ₹27,250. At 0.5% degradation, year 2 generates 4,477.5 kWh and saves ₹27,103.75 after maintenance; cumulative net saving after two years is −₹1,25,646.25.
Assumptions and limits
- Inputs are manually supplied assumptions, not a site survey, a live tariff lookup or a guaranteed installation quote. This calculator does not call a solar-generation API.
- Expected yield is usable AC generation after losses. Capacity is DC panel nameplate capacity. Annual generation reduces geometrically after the first year; weather variation is not simulated.
- A fixed share of each year’s generation displaces imports on site; all remaining output is exported. Choose this share from the household load profile: self-used energy cannot exceed actual simultaneous demand and bill savings cannot exceed displaced import charges. Storage, curtailment, export limits and detailed hourly matching are excluded.
- Import and export rates stay fixed and are applied separately. The model is not a complete net-metering bill: slabs, fixed charges, credit expiry, settlement caps and later policy changes must be checked with the DISCOM.
- Subsidy reduces investment at time zero for this simple comparison. Actual PM Surya Ghar eligibility, approved equipment/vendor conditions, inspection and payment timing require confirmation; an entered subsidy is not an entitlement.
- Maintenance remains fixed. Loan interest, discounting, tax benefits, tariff escalation, replacements, battery storage and residual asset value are excluded.
- Payback is the first recovery of net investment, with annual savings treated as accruing evenly. Later declining generation and maintenance can reverse that recovery. A fully funded installation has zero upfront payback but can still have negative ongoing savings.
Questions people ask
Will this calculate my PM Surya Ghar subsidy?
No. The subsidy starts at zero and accepts only an amount you have independently confirmed. Check the official scheme, qualifying installation and vendor requirements, application status and DISCOM process. A quote or a value entered here does not establish eligibility or guarantee payment.
Is exported electricity worth my normal retail tariff?
Not necessarily. The applicable metering arrangement and settlement rules determine how exports are valued. Use your approved effective credit, including any practical limits. Set export value to zero if it will not be credited. This simplified annual model does not reproduce every electricity bill.
Where should I get the expected annual yield?
Ask the installer for an AC generation estimate that accounts for location, roof direction, shading and system losses. A tool such as PVWatts can provide a separate performance estimate. Enter annual AC kWh divided by installed DC kWp; this page itself does not model weather or your roof.
Does 70% self-consumption mean a 70% lower electricity bill?
No. It means 70% of the generated solar kWh are used on site while produced. Your bill reduction also depends on total consumption, when appliances run, tariffs and fixed charges. The example percentage is not measured from your home.
Can a zero-cost installation or an early payback still lose money?
Yes. Maintenance may exceed the value of generation, especially as output declines. Zero net investment means there is nothing upfront to recover, not that electricity has no ongoing cost. The table and total net saving show whether costs later outweigh the benefits.