Access to affordable electricity is written into the constitution, as is housing, so authorities are forced to comply and provide services to all, even though they may not recoup the cost of doing so anytime soon in the poorer areas. But to charge wealthy people more for the same service is not a solution, but just a shifting of responsibility that will create other problems downstream.

Far better to establish a cost + small % rate, limited to say R200 and give that free to every household  (no matter what your income or area), and increase it exponentially according to usage. Rich households will obviously spend more, and poor households will try and stay within the minimum. The City did this with water, and it worked rather well. 

To base it on the value of your property is just plain lazy, because you are not taking all factors into consideration.