The cost of capital is inversely proportional to the NPV.
As capital costs increase (i.e. the interest rate increases), NPV decreases.
As capital costs decrease (i.e. the interest rate decreases), NPV increases.
You can see the relationship in the following equation:
NPV = a * ((1+r)^y - 1)/(r * (1+r)^y)
Where:
NPV = Net Present Value (The present value of a future amount, before interest earnings/charges)
a = Amount received per year
y = Number of years
r = Present rate of return