I'm not sure if your unit is correct... I am quite sure that you meant £1 per kWh (Kilo Watt Hour) per year.
£1 per Watt for one year. Rough estimate, but it's in the right ballpark. I pay 12p/kWh. That's £0.00012 for 1W for one hour. For one day, it costs £0.00288. For 365 days, it costs £1.0512, so an estimate of £1/Wyear is only 5% off. The unit of kWh per year wouldn't make sense: Watts are a unit of power (energy per unit time). 1kWh is one kW (1000W) for one hour. i.e. my price of £0.12/kWh means that it costs £0.12 to have something that draws 1kW on for one hour (or to have something that draws 100W on for ten hours, and so on). I probably should have written £1/Wyear for consistency with kWh or £1/(W/year), but I assumed that readers could figure it out and was lazy.
A 6 wH router would require 52.56 kW to operate in a year (24/7 and 365 days a year)... So, I don't get the part where you are talking about saving.
What is a 6wH router? Even if you mean 6Wh, that doesn't make sense: how long does it take to consume 1Wh (a unit of energy, not of power)? If you mean a 6W router, then will consume 52.56Wh in one year (not 52.56kW, because that's a unit of power and when you divide by time [i.e. over a year] then you get energy, not power). In contrast, a 60W old PC will consume 525.6kWh. At £0.12/kWh, that works out at £6.3072 to operate the small router or £63.072 to operate the old PC for one year. These numbers are very close to my back-of-an-envelope estimate of £6 vs £60, but more accurately the saving is £56.7648/year, or £113.5296 over two years. If you spend £100 on a low-power embedded router board to replace a 60W old PC that you got for free then you will be £13.5296 better off after two years (assuming electricity prices don't go up and you're on the same-priced tariff as me). After four years, you'll be over £100 better off. The one that I bought lasted 5 years before it was too slow for the network, so that's a saving of £283.824 of electricity. The new version of the same board (three gigE ethernet adaptors and enough CPU power to happily handle line rate on all of them) costs £125, probably around £160 by the time that you've added a case and some flash storage. So over the lifetime of the device (assuming it only lasts five years - I'd actually be quite surprised if GigE is not fast enough in 5 years for most home users), the saving is around £120, more if electricity prices go up. The break-even point is just over two years. As an added bonus, you get a small form-factor device that's silent, so can be hidden in a corner in a room that you actually use, or stored in an under-stairs cupboard without overheating.
Using an old PC for this is likely to be a waste of money and be inconvenient. If you can get £20 for the old PC from someone who actually needs a machine capable of running a GUI, then you're even better off!
Raven, read the post by PhunkySchtuff again. There is no mention of 87600 anywhere.
You might want to try again. He says:
At an optimistic 100W, that's 87600 kWh/year
Looks like it contains the number 87600 to me...
Right now this is attractive because it gives you a potential path to work at big names like Google and facebook.
Which is fairly depressing: come and do CS, you can use your experience to increase the efficiency of advertisements by 0.01%!
What is mind? No matter. What is matter? Never mind. -- Thomas Hewitt Key, 1799-1875