Electricity bill have to be paid for the energy you have utilized in the form of electricity. Electricity company bill you for your energy consumption in kwh. A kwh energy is said to be consumed, if a 1kw consuming device or appratus is stayed turned ON for one hour. This is the simplest definition you can find at various other website too. But there is a something you have to bother about. The electricity bill, for instance a 1HP(745W) motor, can be higher than what the device is consuming. The reason is that often devices or apparatus, like motor, have capacitance and inductance associated with them. Because of these, inductance and capacitance, the power factor is less than one. which results in extra loads to the transmission system and hence, electricity company charges for these unnecessary load. Don't worry if you so not understand power factor at this point of time.In very simple form, remember, the more the power factor, lower will be the reactive power consumtion(A power which is not really consumed but puts an extra pressure to the transmission system) and vice versa. A point worth i forgot in the discussion is that power factor value is always less than or is equal to one. Hence the near the power factor to one, the more efficient is the electrical device. A device which have lower power factor can be corrected to higher power factor(which may be still less than one) by using suitable capacitors. Hence you would have seen capacitors in the control panel of the motor. They are not just to provide the necessary torque, but are also there to correct the power factor. As this post is about calculating electricity consumption by electric heaters, we will limit our discussion to heaters only.
In the previous paragraph, we discussed about power factor. It would be wise to make you aware that your electric heater power factor is always one(as voltage and current are always in phase with each other) and hence, calculation for what you will be paying for is straight forward with simple calculation. So to make you understand, how much power, your heater will consume, we will be discussing it with some examples:
Case1: An electric water heater rated 1.5kw@230v is used to heat water for 15 minutes daily. Assuming that electricity bill for each kwh is Rs2 and there is no other device which consumes electricity, calculate the electricity bill that have to be paid monthly.
Solution: As the heater is turned on for 15 min daily, the time for which the heater is turned on for a month will be: 15 x 30 = 450 min = 450/60 = 7.5 hrs/month (as 60min = 1 hour). Now per kwh, the company charges Rs2. Therefore for a 1.5kw heater that is turned on for one hour will consume, 1.5kwh of electricity or 2 x 1.5 = 3 Rs per hour. Now in a month we are utilizing 7.5 hrs. hence Electricity bill would be 7.5 x 3 = 22.5 Rs
