Hi all,
I've been mining bitcoins for about about a month now. I have 5 5870 on 3 different computers and have pulled in close to 1500 BTC. Rough calculations indicate I'll have paid for my hardware investment in another month and a half. (WOOT!)
1) This first line did more damage than good if you are trying to advocate lower power consumption for others. Now, many people will run out and buy hardware and start mining based upon this projection.
The quick return on investments is just about up. About every 2 weeks the difficulty increases about 20%, meaning, the average BTC mined decreases by about 20%. Unless the price of BTC jumps sharply again in the next few months, the ROI will decrease to a year or more. There is also a potential for the price of BTC to run the other direction which could push the ROI further than 2 years out. Here are the difficulties I recorded. (Note that I started recording them on 1/26.)
1/26 - 18437.64 ( I don't know how long it was at this difficulty.)
1/27 - 22012.49 ~ 20%
2/8 - 25997.87 ~ 20%
2/18 - 36459.88 (40% increase in difficulty.)
I spent around $2700 for hardware, and I'm guessing the next increase will be sometime around 3/4 or 3/5. At the current rate of difficulty, I average around 44 BTC per day, so I figure:
2/26 to 3/4 - 44*7 = 308
3/5 to 3/18 - (35.3*14) = 492.8 (2.7+ months to recover 2.7k assuming no change in difficulty and $1 BTC)
3/19 to 4/1 - (28.16*14) = 394.24 (3+ months to recover 2.7k assuming no change in difficulty and $1 BTC)
4/2 to 4/15 - (22.52*14) = 315.39 (4+ months to recover 2.7k assuming no change in difficulty and $1 BTC)
4/16 to 4/29 - (18.02*14) = 252.31 (5+ months to recover 2.7k assuming no change in difficulty and $1 BTC) (my ROI)
4/30 to 5/13 - (14.41*14) = 201.82 (6+ months to recover 2.7k assuming no change in difficulty and $1 BTC)
5/14 to 5/27 - (11.53*14) = 161.42 (8+ months to recover 2.7k assuming no change in difficulty and $1 BTC)
... etc...
So a straight line of 161.42 per month assuming $1 per BTC, it would take 8+ months to pay for my hardware again (not including electric costs). If you take that one more month out, you are looking at 12+ months to pay for hardware again (not including electric costs).
If I were to do it all over and buy the hardware now, I would not break even until sometime in September (7 months away). If I were to bet on the price of BTC going up, then it may be sooner. However, if I think the price will go up again, I would not invest in hardware again, I would purchase BTC's outright. In fact,
had I purchased BTC's instead of $2.7k of hardware, I would have been ahead by about $1k of my current position. (But building those systems was fun!)
2) Respectfully, the projection may be incorrect. I have 4 5970's myself so I've done all the math. Difficulty has shot way up recently with no corresponding increase in bitcoin price. In fact, price has gone down. The market is volitile enough that if you are holding bitcoins you cannot be sure what they will net you until you sell them. If bitcoins stay at a dollar and difficulty stays the same you'd be right on. However, I'd be interested in a calculation where someone accurately projects out the recent exponential increase in difficulty for a month and a half. But even with you calcs at present difficulty and 5870's being a minimum of $200 (more like $250 w/ tax & shipping but we'll stick w/ $200), how are you building computers for under $290 each considering mobo, adequate power supply, cpu, memory all of that?
Note that I spent around $2700 for the 5 graphic cards and two extra computers. One 5870 for my existing rig, and 4 5870's on two new systems. I was not aiming to optimize for khash per $ investment. I was aiming to create reasonably buildable systems that would not crash. I also have not over clocked, but I may switch to Ubuntu for added performance.