Your payback slide shows one number a year. Bengaluru's monsoon doesn't work that way.

Most quotes average your generation across 12 months. Bengaluru's June to September doesn't average anything.

Every solar proposal you've seen quotes one number — units per year, or units per kWp per year — and builds the whole payback story on it. That number is real, but it's an average, and Bengaluru's generation curve isn't flat enough for an average to tell you much about any given month. Four months a year, cloud cover from the southwest monsoon cuts your output well below what the annual figure implies. If your installer hasn't shown you the month-by-month breakdown, you've only seen half the picture — the half that makes the payback period look shorter than it usually runs.

What the month-by-month curve actually looks like here.

Bengaluru's clear, low-humidity months — roughly December through March — typically deliver 140-155 kWh/kWp, among the best generation of any Indian metro thanks to the altitude and dry air. April and May hold up reasonably well despite pre-monsoon haze. Then June through September drops to roughly 95-115 kWh/kWp — a 25-30% dip driven by sustained cloud cover, not just occasional rain days. October and November recover as the northeast monsoon tapers off. Add it up and the annual average looks healthy. Live through August with a system that's producing a quarter less than what you budgeted for, and the annual average stops feeling relevant to that month's bill.

Why this matters for your BESCOM bill, not just your generation graph.

Net metering banks your surplus units and nets them against consumption — so a strong February can carry a weaker July, as long as the banking cycle lines up. The catch is the annual settlement date. If your connection's settlement point falls right after the monsoon rather than after your strongest months, you're heading into settlement with a thinner credit buffer than a system sized purely on the yearly average would suggest — and, as we've covered before, unused credits at settlement get valued at a fraction of retail, not carried forward indefinitely. A monsoon dip you didn't plan for and a settlement date you didn't check can compound into a payback period that runs longer than the slide promised.

The number your installer's payback slide almost never shows you.

Ask for the monthly generation estimate, not just the annual figure and the average monthly savings derived from it. A system that "saves ₹4,200 a month on average" might genuinely save ₹5,500 in March and closer to ₹2,800 in August — and if your household's consumption also rises in some of those same months (school holidays, more time at home, more AC use), the gap between what you expected and what you get during monsoon can be sharper than the brochure implies. Homeowners who've only seen the annual number are the ones most likely to call their installer in August asking why the bill looks off — when the system is performing exactly as a Bengaluru system should during monsoon.

What it means for sizing your system, not just for setting expectations.

Sizing purely off your average monthly bill and an annual generation number tends to undershoot slightly, because it implicitly assumes the year is flatter than it is. If your heaviest consumption months overlap with the monsoon dip — which is common, since June-September in Bengaluru is also when many households run more indoor appliances — it's worth sizing with a small margin above the bare average-case number, rather than exactly to it. It's a modest difference in panel count, not a dramatically bigger system, but it's the difference between a payback estimate that holds up in year three and one that quietly slips by a season.

Three questions worth asking before you sign.

• Ask for a monthly generation table, not just an annual kWh/kWp figure. Any installer using real local irradiance data can produce one; a generic annual number usually means they haven't.
• Ask when your connection's net metering settlement date falls, and whether it lands before or after the monsoon dip for your specific sanctioned load and billing cycle.
• Ask what your break-even assumption looks like in the worst month, not the best one. A payback period that only survives on peak-month numbers isn't a payback period you can rely on.