Cost of electricity | RS. 5.00 per unit (kWh) |
Total heat gain kcal/ day | System capacity x Temp. difference |
= 125 x 40 = 5000 kcal/day | |
= 5000 x 4.2 kJ/ day = 21,000 kJ/day | |
Total heat gain | = 21000/ 3600 kWh/ day |
Saving in electricity | = 5.83 kWh / day |
Saving in electricity cost | = Units saved x cost / unit |
= 5.83 x 5 | |
Saving / day | Rs. 29.15 |
Saving per year | = 29.15 x 300 |
= Rs. 8745 | |
Payback period | = Total cost/ saving per year |
= 25000/8745 | |
Payback period | = 2.85years |
Payback period with subsidy | 19000/8745 = 2.17 years |
Actual payback period becomes much shorter if the periodic rise in the cost of oil/ electricity, maintenance and handling charges for geysers or boilers and depreciation allowance available are accounted for.
With MNRE upfront subsidy under JNNSM, the cost of the system becomes Rs. 19000/- and payback period works out to 2.77 years and 2.17 years respectively.