Aside from what other readers have noted (that getting a 5% return is very optimitics right now), you are not counting long term savings.
That is to say, today we have 1st generation power units which cost 3,500,000$ and save 100,000$ a year. Investing that money in the bank will return you 175,000$, all right, 75,000$ more than buying the machines.
But if you buy the power units, you are investing in power unit technology. So if they get a lot of customers, assume in 5 years time the units will cost 1.000.000$ and save you 300.000$ a year, a 30% ROI, no bank can compete with this. This is what happened with computer hardware, just look 20 years ago!