Replacing Kenya Power with a diesel generator? Don’t even think about it!

 By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

05 October 2014

Nine years ago wrote in this column that “contrary to popular belief, the Kenya Power and Lighting Company does NOT sell electricity; it sells it sells the energy transmitted by the electricity”. Without knowing it, John Kariuki has revisited that idea by asking: “how much diesel [do] you require to produce one kilowatt hour…?” I suspect that Kariuki is thinking of buying a diesel generator and say good bye to Kenya Power’s ‘high bills’.

Before getting into the calculation, I must note that the reason why our power bills are so high is that there are so many adjustments, levies and taxes. The highest of these is the fuel adjustment which comes as a result of Kenya Power buying electricity from diesel-based producers. So, if my suspicion is correct, should Kariuki then forget his idea completely? Let us find out.

Electricity the world over is sold in units of kilowatt-hours (kWh). 1kWh is the amount of energy consumed when a 1,000-watt device is operated for one hour. However, the kWh is NOT the international standard scientific unit for energy.

Energy is measured in joules (J) and one watt is equal to one joule per second. Therefore, 1kWh is the same as 1,000W x 3,600s = 3,600,000J. In other words, there are 3.6 mega-joules per kWh, or 3.6MJ/kWh.

Burning one litre of diesel produces about 35.8MJ of heat energy – that is, approximately 36MJ. Therefore, one litre of diesel will yield about 36MJ divided by 3.6MJ/kWh = 10kWh.

Now, I don’t know where Kariuki is based, but in Nairobi, a litre of diesel is currently going for Sh102.36. So, if he was able to convert all the energy into electricity, the cost per unit (kWh) would be Sh102.36 divided by 10kWh/L = Sh10.24.

How does that compare with electricity from Kenya Power? My September bill shows that I consumed 289kWh and for that, I was charged Sh6,509.7 (all adjustments, levies and taxes included). Dividing the two figures reveals that the average unit cost is Sh22.53 per kWh. This is more than double the cost of running a diesel generator!

Something doesn’t add up… The problem is that we have assumed that the generator can convert all the energy in a litre of diesel into electricity. This is far from the truth – very far indeed!

Looking at the technical data sheets of several generator manufacturers I found out that a 1,000-watt gen-set consumes about 0.32L of diesel per hour. At the current price of fuel (Sh102.36/L), this comes to about Sh33 per hour.

Since the generator is producing 1,000 watts (or 1kW) for one hour, it is easy to see that the cost of this electricity is Sh33 per kWh. Now this is much higher than the Sh22.53 that Kenya Power is charging me.

The bottom line is this: grid electricity from Kenya Power is very cheap. Think very carefully before attempting to replace it.