Renewable Energy and Energy Conservation
Renewable Energy and Energy Conservation
This domain covers solar PV, wind, small hydro, biomass, storage, net metering and energy auditing. Numerical questions focus on energy yield, capacity factor and payback.
Core rules
- Solar PV energy ≈ kWp × peak sun hours × performance ratio. Irradiance is measured in W/m²; 1 kW/m² is standard test condition irradiance.
- MPPT adjusts the operating point to extract maximum power from the PV array as irradiance and temperature change.
- Wind power in the swept area is P = 0.5ρAv³. Betz limit is 16/27, about 59.3%, the maximum theoretical extraction.
- Capacity factor = actual energy generated/(rated power × time). It is not the same as efficiency.
- Hydro power ≈ ρgQHη.
- Net metering credits exported solar energy against import. Storage improves self-consumption.
- Energy conservation includes energy audits, waste-heat recovery, efficient motors, power-factor correction and avoiding standby losses.
- Simple payback = capital cost/annual savings.
Worked example
A 5 kWp rooftop system receives 4.5 kWh/m²/day and has a performance ratio of 0.8. Daily energy = 5 × 4.5 × 0.8 = 18 kWh. Annual energy ≈ 18 × 365 = 6570 kWh. At ₹7/kWh the saving is ₹45,990 per year. If the installed cost is ₹3,00,000, payback ≈ 6.5 years.
Traps
Do not confuse kWp with kWh. Do not call capacity factor efficiency. Do not claim Betz limit as actual turbine efficiency. Do not ignore temperature derating and inverter losses.