Physics
Physics
Problem
An electricity board follows a two-part tariff: Rs 5.0 per kWh of energy plus a fixed demand charge of Rs 250 per kW of recorded peak demand in the month. A small bakery uses the appliances listed in Table 3 every working day. Table 3 Appliance Power Normal daily schedule Oven 4 kW 06 00 h – 08 00 h Dough kneader 1 kW 07 30 h – 08 30 h Refrigerator 0.4 kW Runs continuously Lighting load 0.6 kW 05 30 h – 09 30 h (i) Assuming the above schedule is followed for 26 days in a month and no load is used at other times, calculate (a) the peak demand recorded and (b) the total energy consumed in the month. (ii) Determine the monthly bill under the existing schedule. (iii) The owner is advised to shift the dough kneader operation to 08 30 h – 09 30 h with no other change. Re-calculate the peak demand and the new monthly bill. (iv) By how much (in rupees and in percentage) does the bill reduce because of the rescheduling? Comment briefly on why this change is effective.Intuitive explanation
The key to this problem is understanding that peak demand is the maximum power drawn at any single moment, not the total energy used—and the demand charge penalizes you for that instantaneous maximum, regardless of how briefly it occurs. By identifying when appliances overlap and then strategically shifting one to reduce that overlap, you can lower the peak without using less total energy, saving money on the fixed demand charge. The energy charge stays the same, but the demand charge drops significantly.
Intuitive explanation
The key to this problem is understanding that peak demand is the maximum power drawn at any single moment, not the total energy used—and the demand charge penalizes you for that instantaneous maximum, regardless of how briefly it occurs. By identifying when appliances overlap and then strategically shifting one to reduce that overlap, you can lower the peak without using less total energy, saving money on the fixed demand charge. The energy charge stays the same, but the demand charge drops significantly.