Geysers are often the single biggest consumer of electricity in the home, making up as much as 40% of the total bill. Naturally this does depend on how much hot water you consume. If you set your thermostat to heat the water to 60 degrees and you want to heat up 150L from a starting temperature of 15 degrees.
150L x 4.16 (specific heat capacity of water) x 45degrees = 28, 080 Kilo joules of energy required
We are used to Kilo-watt hour, not kilo-joules so we need to divide by 3, 600 (number of seconds in an hour) to convert kilo-joule to kilo-watt.
28080/3600 = 7.8 kilo-watt hours to heat a geyser. At 2.45 per unit this geyser is costing around R19 per day to heat up.
Then we have to add the standing losses of 1.1kWh for a B rated 150L geyser.
In total we are using 8.9kWh which costs around R21.80 rand per day, or R654 per month. In some cases you will not be heating water up from 15oC so this cost may be less, however, it is still a significant part of your monthly bill.
As the element ages, performance also drops and the monthly cost of running the geyser increases. With XTEND elements we save money in many ways, our element is 25% more efficient at heating water than conventional elements and our standing losses are reduced as we keep the element away from the base plate. Finally, XTEND elements are built to last with minimal drop in performance over time as our element is protected from scaling with a marine grade stainless steel outer casing.
Source Article: https://blog.homebug.co.za/?p=34