I've done the calculations in terms of cost per unit of energy.
The calorific content of LPG is 46.1MJ/kg, or 415MJ in a 9kg bottle. That's about 115Kwh. So compare the cost of 115kwh of electricity to the cost of a 9kg refill.
115kwh costs just over R200, and a bottle of LPG is around R220 right now, so it costs about the same per unit of energy.
So it comes down to the efficiency of heating. An electrical element inside a volume of water is darn near 100% efficient. The same cannot be said for gas. So electricity has to win this one, though I cannot say by how much.
Since a heat pump typically has a COP of as much as 3, that means a heat pump remains by far the most efficient, with the possible exception of a solar geyser in the right climate.
In terms of cooking on a stove, a suitable utensil that makes proper contact with the heating plate can be around 70% efficient (>80% for induction), gas is about half that.
I think the only place where gas wins is space heating.
That doesn't mean gas doesn't have a place in your energy plan. Just don't expect to save money.
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