Renewable Energy and Energy Conservation
What this domain tests
You must estimate solar PV output, connect panels correctly, size a battery, and apply conservation measures such as LEDs, star-rated appliances and energy audits with payback calculations.
Core rules
- A PV panel is rated in watts peak (Wp). Daily energy = panel wattage × peak sun hours; Bengal averages about 4–4.5 peak sun hours a day.
- Panels in series add voltage; panels in parallel add current. The array voltage must match the charge controller and battery.
- Battery energy = V × Ah. Usable energy depends on depth of discharge, commonly 50 percent for lead-acid.
- An MPPT controller tracks the maximum power point and usually gives more harvest than a simple PWM controller.
- Conservation: replace incandescent lamps with LED, use 5-star appliances, avoid standby loads, and improve power factor.
Worked example
A 100 W panel works in a place with 4 peak sun hours. How much energy does it give daily, and how long will a 12 V, 100 Ah battery at 50 percent depth of discharge last? Daily energy = 100 × 4 = 400 Wh. Usable battery energy = 12 × 100 × 0.5 = 600 Wh. Days of autonomy = 600/400 = 1.5 days, and allowing for controller and wiring losses, a 100 Wp panel gives roughly 60–70 Ah of charge on a good day.
Traps that cost marks
Multiplying panel watts by 24 hours instead of peak sun hours; adding currents when panels are in series; using the full Ah rating rather than the usable depth of discharge; confusing peak sun hours with daylight hours.