Take the total installed system cost and calculate annual savings using conservative generation and your real electricity tariff. Then calculate the payback without subsidy. If the project is still reasonable, the subsidy improves a sound investment. If the project works only because a vendor assumes immediate subsidy, reconsider the quote.
Also model lower generation caused by shade, downtime or equipment performance. A system that is oversized relative to daytime consumption may export more energy at a value different from retail electricity saved. Use the current DISCOM rules for your area rather than a national average.
Monitor the first year
Save monthly generation and electricity bills. Compare actual output with the proposal after accounting for season. Large unexplained underperformance should be raised during warranty while evidence is fresh.
The scheme can reduce upfront cost, but long-term value comes from a safe system that generates as expected for years. Design quality, equipment support and monitoring matter after the subsidy has been paid.