A new renewable energy generation system has a life-time of 10 years. It is assumed that the salvage value of the system at the end of the 10 years' life-time is negligible. The initial (Present time) investment of the system costs $50,000. The manufacturer agrees to maintain the system every year over the 10 years' life-time with a uniform annual maintenance fee of $1000/year. At the end of the 5th year, a key component should be replaced, which will cost $10,000. Each year, this renewable energy system will generate 5,000 kWh electricity. It is assumed that the electricity price in the first year is $1/kWh, with an annual escalation rate of 3%. The interest rate is 5%.

Please investigate that how the "interest rate" and its variation will affect the results of

(1) The present value of the total maintenance fee over 10 years' life-time.

(2) The present value of the total saved electricity cost over 10 years' life-time.

(3) The net present value of this system, by considering all the cash flows mentioned in the question statement.

(4) The deposited money per year if the replacement cost $10,000 of the key component at the end of the 5th year is accumulated by depositing a fixed amount of money per year in the first 5 years.

and discuss and comment on their sensitivity. For example, the "interest rate" varies +/- 0~0.03 based on the original 0.05 (i.e. the interest rate varies in the range between 2%~8%).