Energy-saving bulbs repay themselves in 3 months
The Sunday Nation
Nairobi,
15 September 2013
Five years ago, I
wrote a piece investigating whether it made economic sense to replace a
normal filament bulb with a fluorescent energy saving type. At the
prevailing prices of that time, the conclusion was that it does not.
In 2008, the
energy-saving bulbs were going for about Sh1,000 each while the price of
electricity was about Sh14 per unit (kilowatt-hour). The price of
ordinary bulbs at the time was only Sh35. Putting everything together,
it turned out that the savings made in power bills would be eaten away
by the purchase cost over the life of the energy saver.
But now things have
changed. Five years down the road, the price of electricity has
increased by a small margin from Sh14 to about Sh15 all adjustments
and levies included. My July bill, for example, shows that I consumed
400kWh of energy and, for that, I charged a total of Sh6,222. This works
down to Sh15.56 per unit.
Over the same period,
the prices of fluorescent energy-saving bulbs have come down from
Sh1,000 to between Sh150 and Sh300. The variation is dictated by market
forces, but we can use an average value of Sh200 in our calculation.
One of the key
features of the energy saving bulbs is that they dont get as hot as the
normal filament type. The reason for this is that fluorescent bulbs
produce light by exciting atoms directly while the ordinary type do so
through heating the filament to a very high temperature typically
about 2,500 degrees celcius.
As a result, a
filament bulb consumes about five times as much power as a fluorescent
one generating the same amount of light. For example, a 12W energy saver
is as bright as 60W normal bulb.
Now if you replace a
60W filament type with a 12W energy saver, you will reduce the
consumption by 42W. Suppose that your room if lit from 7pm to 11pm; that
is, a continuous 4 hours daily. Then each day you will save
168watt-hours of energy. In one month, this accumulates to 5,040Wh. In
other words, 5kWh or 5 units of electricity.
At the current price
of Sh15 per unit, you will make a saving of about Sh75 per month from
this one bulb alone! In three months, you will recover the full Sh200
cost of the bulb.
The remaining
question, however, is whether the bulb will still be working. Well, the
average lifetime of the energy-savers is about 6,000 hours. If you use
it for 4h daily, it will serve you for 1,500 days; that is 50 months 4
years and two months! So obviously, it lives for longer than the 3
months required to repay itself.
But apart from the
fluorescent energy-savers, there is also the new LED type. They cost
between Sh300 and Sh1,000. However, they consume about the same power as
the fluorescents. The only advantage of LEDs is that they have a very
long life-time about 25,000 hours. That is they can last for over 17
years!
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