Without SmartPower installed
You have 100 computers that are on 168 hours a week. Your computers consume electricity at an average rate of 50 watts.
This means your computers are using 840 kilowatt hours per week, 3,640 kilowatt hours per month, and 43,800 kilowatt hours per year.
You pay £0.16 per kilowatt hour, giving a weekly cost of £134.40, a monthly cost of £582.40, and a yearly cost of £7,008.00.
With SmartPower installed
You will save £408.59 per month and £4,922.29 per year.
You estimated that your computers will only be on for 50 hours a week.
That will reduce their electricity usage to 250 kilowatt hours per week, 1,086 kilowatt hours per month, and 13,036 kilowatt hours per year.
Your costs will be reduced to £40.00 per week, £173.81 per month, and £2,085.71 per year.
Purchasing 100 SmartPower licenses will cost you £2,000.00 (if you are a commercial user), but you'll recover that cost in 149 days.