Solar Water Heater Calculator

LPD = Liters Per Day. It's the standard sizing metric — 100 LPD means the system heats 100 L of water from ambient to ~55-60°C daily. A family of 4 typically needs 150-200 LPD. Our calculator derives LPD from family size × usage per person.

FPC (Flat Plate Collector): durable, hail-resistant, works well in north India, 50 L/m² capacity. ETC (Evacuated Tube Collector): 60 L/m² (20% more efficient), better in cold/cloudy weather, cheaper by 10-15%. For most Indian homes, ETC offers better value. FPC is preferred in hailstone-prone and hard-water areas.

FPC: ₹280/LPD. ETC: ₹250/LPD. A 200 LPD ETC system costs ₹50,000 before subsidy. MNRE provides ₹1,360/m² (FPC) or ₹1,700/m² (ETC) subsidy — reducing cost by ~20%. Net cost for 200 LPD ETC: ~₹40,000.

Heating 1 L from 20°C to 60°C needs 0.046 kWh. A 200 LPD system saves ~9 kWh/day = ~3,350 kWh/year. At ₹7/unit, that's ₹23,500/year saved vs electric geyser. Payback is typically 2-3 years.

All standard solar water heaters include an electric backup heater (1-3 kW) that kicks in automatically when tank temperature drops below a threshold. On cloudy days, solar still provides 40-60% of heating; backup covers the rest. On rainy days, backup runs fully — but only for 1-2 hours.

Yes. ETC collectors work well even at 5-10°C because the vacuum insulation retains heat. You may see slightly lower output in December-January (4-5 hrs of good sun vs 6-7 in summer), but solar still covers 60-75% of hot water needs year-round.

On the roof, south-facing, at roughly 25-30° tilt for India. The collector needs direct sunlight from 10am-3pm. The insulated storage tank sits behind or above the collectors. Cold water input and hot water output pipes run down to your bathroom/kitchen plumbing.

FPC collector: 15-20 years. ETC tubes: 12-15 years (individual tubes can be replaced if damaged). Tank: 10-15 years (check for hard water scale). Pumps/valves: 5-10 years. Overall system life: 15-20 years with light maintenance (₹1,500-3,000/year).