Question

A 15W compact fluorescent lamp (CFL) provides the same light as a 60W incandescent lamp. Electricity costs the end user 10 cents per kW-hr.

a. If an incandescent lamp costs 60 cents and the CFL costs $2, what is the "payback" period?

b. Over the 9000-hr lifetime, what would be saved in carbon emissions? (280 g carbon emitted per kW-hr)

c. At a (proposed) carbon tax of $50/tonne, what is the equivalent dollars saved as carbon emissions? (1 tonne = 1000 kg)

Answer 1

(a) Energy consumed by incandescent lamp in 1 hr = 60 X 1 = 60 Whr = 0.06KWhr

cost of the energy = cost of one unit X no. of units = 10 X 0.06 = 0.6 cents

0.6 cents is the cost for one hr,

Energy consumed by CFL in 1 hr = 15 X 1 = 15Whr = 0.015KWhr

cost = 0.015 X 10 = 0.15 cent

Hence CFL saves 0.6 - 0.15 = 0.45 cents in 1 hr

1 cent will be saved in 1 / 0.45 = 2.22hr

200 cents 0r $ 2dollars will be saved in 200 X 2.22 = 444hr

200 cents or # 2 dollars will be saved in

200 cents will be consumed in = (1/0.15) X 200 = 1333.33hr

(b)Energy consumed by CFL in 9000-hr = 15 X 9000 = 135000Wh = 135.00KWh

Carbon emittd = 280 X 135.0 = 37.8kg

Energy consumed by incandescent lamp in 9000-hr = 60 X 9000 = 540000Wh = 540.0KWh

Carbon emittd = 280 X 540.0 = 151.2kg

Sving in carbon emissions = 151.2 - 37.8 = 113.4kg

(c) tax on 1000kg = $50

tax on 1kg = 50/1000 = $0.05

hence tax saved 113.4kg = (50 / 1000) X 113.4 = $5.67