In a house at location A, an On-Grid Solar Power

In a house at location A, an On-Grid Solar Power Generation system has been built. Based on the technical analysis carried out, the components needed have been selected and an investment cost of Rp. 88,500,000 has been incurred. The house has an average electrical energy requirement of 31,250 Wh per day. After using the Solar Power Plant, the house can save 1/2 of the electricity cost per month from the initial condition before the Solar Power Plant was used.

a) What do you know about the payback period?

b) If the current Basic Electricity Tariff is IDR 1,049/kWh, how long is the payback period of the above Solar Power Generation system? (Assuming the Basic Electricity Tariff is constant / not increasing)