Start with a load list
| Load | Qty | Watts each | Total |
|---|---|---|---|
| BLDC fan | 2 | 36W | 72W |
| LED light | 4 | 12W | 48W |
| Laptop | 1 | 65W | 65W |
| Total running load | — | — | 185W |
Load energy (Wh) = Running watts × Backup hoursA 185W load for three hours requires 555Wh ideally. Conversion losses, usable capacity, ageing and reserve can require a larger nominal battery.
Running load
Add normal wattage of devices that run together.
Starting/surge load
Motors and compressors can need more startup power; check manufacturer specifications.
Usable battery energy
Not all nominal Wh may be usable depending on chemistry, BMS and depth-of-discharge limits.
Real-world losses
Conversion, wiring, temperature and battery age can reduce backup time.
Basic logic for estimating solar
Daily solar energy ≈ Panel kW × Effective sun hours × System efficiencyRoof orientation, shading, weather, inverter clipping, cable loss and location affect actual generation.
Under SREDA Net Metering Guidelines 2025, eligible grid-connected consumers can use renewable electricity generated on their premises and receive credit for surplus exports. Net-metering eligibility should therefore be a separate step in an on-grid rooftop-solar estimate.
Sources & references
- SREDA — Net Metering Guidelines 2025Official guideline covering net metering and system requirements.
- SREDA National Solar Help DeskSolar and net-metering resources and notices.