Just think how long it will take for FPGA miners buying new kit to pay that stuff off assuming

the price stays under 6-7 for the next year!

ouch.

In the next year? They *WON'T* pay it off! You would have to be extremely bullish -- or just plain foolish -- to think a $500 FPGA mining card is a good investment right now. Let's just assume they're so power efficient that there's no "cost" to run them. And let's assume that you've got a really good model like the X6500 that can do 400 MHash/s. Even skipping the halving of the BTC reward, right now at the current difficulty (and again, let's assume that it

*doesn't* increase, just for our estimate), your current reward will be around 0.23BTC per day, or 6.9BTC per month, or 84BTC per year. If the (current) $5.6 per BTC price, and the difficulty, and reward all stayed constant, you would pay off the $560 FPGA in just over 14 months.

But let's be more accurate. Technically, that FPGA will use 16.5W, and the system it's in will likely use at least 35W, so really you're looking at 50W or 1.2 kWh per day, or 438 kWh per year. That works out to a cost in power of $44 per year if we go with the typical "$0.10 per kWh" figure many use. For six months, assuming difficulty stays constant, you will spend $3.60 per month on power, and you will mine $38.60 in BTC, giving you a net profit of $35 per month. After six months, the reduced reward goes into effect, and if difficulty, price, and everything else stays constant you will suddenly drop to earning 3.45 BTC per month, or $19.32, for a net profit of only $15.72. At that rate, it would take nearly three years to pay for the cost of the FPGA.

Hell, let's be really generous. Let's say you run six FPGA miners off of one system so that you maximize efficiency. Now, the miners all use 16.5W each, and realistically your system will probably be using more power as the CPU will have to do more work. But if you can run everything off of a

45W i7-3770T, and your mobo and RAM and storage all use 15W, you're now drawing 160W from the PSU, so with an 85% efficient PSU you're using 188W. Per year, if you live in a place where you pay $0.07 per kWh, you will spend $115 on power, or if you pay a more likely $0.10 per kWh you spend $165 on power. With the six FPGAs now active, you're mining 1.37 BTC per day for six months (250BTC), and then the block reward halves and you get 125BTC for the next six months. If we just round off and say BTC prices average $7.00 over the course of the year, you make $2625 from selling BTC. Your hardware costs for just the FPGA mining equipment is $3360. You'll still take nearly eighteen months to pay off just the FPGA hardware. Whew!