Jacob Maroga CEO Eskom and Water Heating
Jacob Maroga who is the CEO of Eskom believes that switching off a geyser in the afternoon saves electricity and has started a debate with two sides, one agreeing with Jacob Maroga and the other disagreeing.
In my view Jacob Maroga is wrong. Here’s why.
When a geyser is switched off the water in the geyser starts to cool due to heat losses from the sides of the geyser … these losses are reduced to some extent by a well insulated geyser but nevertheless heat (ie energy) is lost. The amount of heat loss is easily calculated since it is based upon the weight of water in the geyser multiplied by the temperature drop.
When the geyser is switched back on the water is then reheated back to the original temperature. The amount of energy required to achieve this is more or less equal to that lost during cooling. Therefore no energy (electricity) is saved.
What is an advantage of shutting off a geyser is that it reduces the electrical load at a specific point in time. If the shutting down of millions of geysers could be coincided with the daily peak demand across all uses of electricity then no overloading of the power generation capacity would be experienced at peak times. However no energy consumption would be saved for that day.
The only way to save electricity costs at the geyser is to reduce the thermostat setting AND at the same time by using less water than normal through the geyser.
For example if you take a hot bath using 400 litres of water at 38 degrees C you can achieve this in two ways:
If geyser is set at say 60 degrees then a certain amount of cold water will have to be mixed to get to 400 litres at 38 degrees. The amount of cold water entering the geyser to replace the hot water is then heated to 60 degrees.
If the geyser temperature is dropped to 55 degrees then less cold water will be need to be mixed in the bath with the hot water at 55 degrees to reach 400 litres of bathwater at 38 degrees … this means MORE water must come out of the geyser and then be replaced with cold water even though the thermostat has been reduced. In turn this extra amount of cold water entering the geyser has to be reheated to 55 degrees.
In summary if you want to save money at the geyser use less hot water and improve the insulation of the geyser. Messing around with the thermostat will not really help. Neither will switching off the geyser for short periods. Of course shutting the geyser down while away on holiday does save energy.
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