I don't think you know how this works.

The solar system is grid tied meaning you are connected to TNB. Under the old system, you will have 2 meters. One for how much you use which you pay as usual and another for how much you generate which you sell to TNB for a pre agreed rate for 20 years. So if you ROI in 5 years, you untung for 15.

Under the new system, the meter is 2 way. Whatever you generate you consume. What ever you don't consume is sold back to the grid so your meter will effectively gostan. So end of the month, your electric bill is kWh consumed- kWh generated and then the standard blocking applies.

So why is it worth it if your bill is high? You reduce the number of units in the higher blocks.