Quote from: mrjones on April 13, 2011, 08:46:31 PM

Quote from: arachn1d on April 13, 2011, 12:14:14 PM

Second question. The difilculty within a year changes how much? Will 2x 6950's generate a good amount of bitcoin for another year or do you guys have to upgrade GPU's for bitcoins every year?

The difficulty changes every 2016 blocks, which on average will be once every two weeks. It can change by up to a factor of four in either direction, but lately has been much less than that. Right now, the difficulty is 82347, and best estimates say it will increase to 93094 at the next change in 717 blocks (+13%).

Suppose you had a configuration that could produce 580 million hashes per second (roughly a pair of 6950's). That means it takes 7 days, 1 hour, 23 minutes to generate 50 bitcoins on average right now. That's just a hair under 50 bitcoins per week. Let's say 49.35, which is a number I happened to do the math with earlier today.

As a simple example, consider the case where the difficulty continued to increase by 13% every two weeks for a year. We'll assume the difficulty changes exactly every two weeks for simplicity. That means the following would happen:

Code:

Week 1 BTC 49.35
Week 2 BTC 49.35
Week 3 BTC 43.67
Week 4 BTC 43.67
Week 5 BTC 38.65
Week 6 BTC 38.65
Week 7 BTC 34.20
Week 8 BTC 34.20
Week 9 BTC 30.27
Week 10 BTC 30.27
Week 11 BTC 26.79
Week 12 BTC 26.79
Week 13 BTC 23.70
Week 14 BTC 23.70
Week 15 BTC 20.98
Week 16 BTC 20.98
Week 17 BTC 18.56
Week 18 BTC 18.56
Week 19 BTC 16.43
Week 20 BTC 16.43
Week 21 BTC 14.54
Week 22 BTC 14.54
Week 23 BTC 12.87
Week 24 BTC 12.87
Week 25 BTC 11.39
Week 26 BTC 11.39
Week 27 BTC 10.08
Week 28 BTC 10.08
Week 29 BTC 8.92
Week 30 BTC 8.92
Week 31 BTC 7.89
Week 32 BTC 7.89
Week 33 BTC 6.98
Week 34 BTC 6.98
Week 35 BTC 6.18
Week 36 BTC 6.18
Week 37 BTC 5.47
Week 38 BTC 5.47
Week 39 BTC 4.84
Week 40 BTC 4.84
Week 41 BTC 4.28
Week 42 BTC 4.28
Week 43 BTC 3.79
Week 44 BTC 3.79
Week 45 BTC 3.35
Week 46 BTC 3.35
Week 47 BTC 2.97
Week 48 BTC 2.97
Week 49 BTC 2.63
Week 50 BTC 2.63
Week 51 BTC 2.32
Week 52 BTC 2.32

The current exchange rate is USD 0.92 for one BTC. (Please note that I am not considering exchange rate fluctuations; that is a different topic, and if you want to make money on exchange rate speculation, you can simply buy the bitcoins rather than generate them.)

Each 6950 consumes 200 watts at full load, so that is 400 watts total. A high-end power supply is approximately 85% efficient, so that means they will consume 470 watts of power. Per day, that is 11.28 kilowatt hours, or 78.96 per week. According to the Department of Energy the average power cost in the US right now is 11.04 US cents per kilowatt hour, which means a cost of USD 8.71 per week.

That means that after week 30, you would actually be losing money, so you would stop then.

Up to week 30, you will have made 660 bitcoins, which at the current exchange rate is USD 607.20. Your electricity costs will have been USD 261.30. This gives you a net profit of USD 345.90.

Considering that a 6950 sells for USD 240 right now, this does not pay for the cards (let alone any associated computer) before mining with them is no longer profitable. You will need to sell the cards to see a profit. The days of making a fortune in the bitcoin market by buying hardware are likely numbered.

Wow, great math thanks. It really does seem that it's pointless to "mine" for money now. Best way to make money is typical stock market stuff, buy low, sell high.