I'm still weighing up options. It's not that unrealistic is it? 4 newish GPU's per machine, 500MH/s each GPU. You're only taling 10 or 15 machines. Plus it has the benefit of switching to LTC unlike ASIC?
Let's say you bought a bunch of 7950's. According to the
mining hardware comparison chart, high-end, you'll get 600 MH/s out of each of them. So just to get to 50 GH/s (50,000 MH/s), you need 84 of them (well... 83.3333... but let's round up). Divide by 4 per machine, that's 21 machines. But that's not even the point...
Let's say you can get a good deal on all those 7950's. $250 USD each sound fair? For 84 cards at a good price, you'll pay $21,000. Just for the cards. Now you need 21 motherboards, 21 processors, 21 sticks of ram, 21 PSU's, 21 harddrives (or USB keys, most likely). The motherboards can't be total trash, because you need at least 4 PCI-E slots.. (1x lanes are fine, but then you need PCI-E 1x to PCI-E 16x riser cables.). The real stickler will be the PSU's. 4 GPU's are going to pull ~800 watts. After the hardware cost, your major and ongoing cost will be electricity, so you'll want an efficient PSU. PSU's operate most effeciently around 50% load. Maybe you can get away with a 1200W power supply, which would be 66.67% load. The cheapest one at Newegg is $150 USD and operates at 87% efficiency. There's $20 rebate too, but I doubt they'll let you claim it 21 times. So another $3,150 on power supplies. And we'll say the CPU/MB/RAM/USB key run another $150 each, so yet another $3,150...
GPUs x 84: $21,000
PSUs x 21: $3,150
Rest of it: $3,150
Total: $27,300
Output: 50,000 MH/s
Total Wattage of GPU's: 16,800
Wattage @ 87% eff.: 19,310
Cost of electricy (guess) $0.15/kWh.
Cost to run these machines for 24Hrs: $70
Cost to run these machines for 1 year: $25,550
Cost of upgrading your electric service to supply an additional 160 Amps of service...
?
With me so far?
Cost last batch of Avalon ASICs: 75 BTC... or $8,775 at the exchange rate *right now*.
Output >65,000 MH/s *each*
Wattage: 620W
Cost to run this machine for 24Hrs: $2.25
Cost to run this machine for a year: $821.25
Soo... Does it make more sense to spend >$27K on a GPU based system, plus $25K per year in electricity? Or just $9K on a system that provides 130% of the performance and only costs $821.25 per year to operate? And remember that Bitcoin offers diminishing returns every 2 weeks. You may find that the diminishing returns far outpace your ability to recover the cost of a $27K investment.
[EDIT]
Heck, I forgot about COOLING cost. The 21 machine GPU farm equates to a 20kW furnace, running 24/7. A 20kW furnace is sufficient to heat a 1500-2000 sqft home, and they don't tend to run 24/7. Unless you live in a year-round sub-zero climate, expect your cooling costs to increase by another $25k per year also.
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