Background
This case study follows a household in Beltola, Guwahati — a family of four in a two-storey RCC home with fans, a refrigerator, a washing machine, two ACs used mainly in summer evenings, and typical daytime appliance use. Their average monthly APDCL bill before solar was around ₹2,400, occasionally higher in peak summer months when AC usage rose. They installed a 3kW on-grid rooftop system with APDCL net metering in early 2025 and agreed to share their generation and billing data for this write-up, with figures rounded and anonymised for privacy.
Why They Chose 3kW
Based on their electricity bill history and roof survey, a 3kW system was recommended as the best fit — large enough to meaningfully cut their bill, but sized appropriately for their available east-facing roof area of roughly 300 sq ft without shading from neighbouring buildings. A larger 5kW system was considered but not chosen, since their consumption pattern didn't justify the extra upfront cost at the time.
Month-by-Month Bill Comparison
| Month | Bill before solar (approx.) | Bill after solar (approx.) |
|---|---|---|
| March | ₹2,200 | ₹650 |
| April | ₹2,600 | ₹800 |
| May | ₹3,100 (AC season) | ₹1,450 |
| June (monsoon onset) | ₹2,800 | ₹1,700 |
| July (peak monsoon) | ₹2,500 | ₹1,850 |
| October (post-monsoon) | ₹2,300 | ₹900 |
The pattern that stands out most clearly is the monsoon dip — generation and bill savings both narrowed noticeably in June and July, when cloud cover cut daily output by roughly a third compared to the clearer pre- and post-monsoon months. This matched what we'd projected during the site survey, but it was still the part that most surprised the family, who had expected savings to stay flat year-round.
What Surprised Them
- The monsoon dip was real but manageable. Even at its weakest point in July, the system still cut their bill by roughly 25-30%, which they hadn't expected given how overcast the weeks felt.
- Net metering credit rolled over usefully. On unusually sunny days when the family was away and using less power, excess export credited against later usage, smoothing out some of the monsoon-month bills.
- The inverter app made troubleshooting easy. When one panel's output dipped due to a loose connector after a storm, the daily generation graph flagged the drop clearly enough that the family called for a check-up before it became a bigger issue.
Approximate First-Year Numbers
Averaged across the full first year including the monsoon dip, the family's bill fell from roughly ₹2,500/month to roughly ₹1,100/month — a reduction of around 55% on average, higher in dry months and lower during peak monsoon. Based on this pattern, their simple payback period against the after-subsidy system cost works out to a little over 4 years, after which the system is effectively generating free electricity for the remainder of its expected 25-year life, subject to normal maintenance.
What We'd Tell a Similar Household
Don't judge system performance from a single month — look at the pattern across a full year, including monsoon. A well-installed 3kW system in Guwahati with reasonable roof exposure should comfortably cut a ₹2,000-3,000 monthly bill by roughly half on average, even accounting for four weaker monsoon months.
FAQs
Are these numbers guaranteed for every home?
No — this is one real household's experience shared for illustration. Actual savings depend on your roof direction, shading, consumption pattern, and system size. See our Disclaimer for more on how we present estimates.
Did the family use any battery backup?
No, this was a standard on-grid system without battery backup, which is why the system shuts off during grid power cuts as explained in our power cut explainer.
How long did installation take?
Physical installation was completed in under two days; the APDCL net-meter commissioning took a few additional weeks after that.