Quote from: RHA on October 19, 2012, 08:31:00 PM

Let's assume bASIC 57GH/s uses 180 W.
[...]

Uhh. If you want to do conservative figures which you ought to if you're trying to convince other people since non-conservative figures will be ignored you should be using about 3-4x that power consumption. I'd potentially be willing to entertain bets that no 54GH/s device is ever going to exist on 130nm at that level of power consumption, but regardless, it's certainly not a conservative number.

Though the below analysis shows that even using 150w it's not super attractive.

Quote from: Syke on October 19, 2012, 09:14:13 PM

All the people claiming power matters aren't showing the math. Power only matters at end-of-life. GPUs are still profitable today. Initial cost and starting date are the biggest factors.

Uh. GPUs are power substantially power cost dominated now.

Lets go through the math:

The equilibrium for mining profits is

Code:

(17179869184*diff*kwh)/(719989013671875*exc*mhj)=1

exc = BTC/$ exchange rate, we'll use 11
mhj = MH/joule, lets use 2 (which is conservative as hell: it's the best gpu figure, and ignores cooling costs)
diff = difficulty, currently 3072321.73202076
kwh = $/KWH

So right now, that means that breakeven is at $.30/KWH. Anyone paying that much or more for power is losing money on GPU mining thats most (all?) of germany, brazil, most of california (the initial rate is lower, but the marginal rate is higher) and some other places. The US average is $0.12/KWH. At that price power consumption is _40%_ of your mining income.

Thats where GPUs are today and I believe that the deployment of hashrate is somewhat retarded by expectations around asics: People would buy _more_ GPUs and FPGAs and mining would be even less profitable but they're waiting on ASIC products and they're anticipating the halving. I don't see any reason to assume the stable point for difficulty vs power to be more profitable in the future than it is now.

Regardless.... It's better if we compare these things without caring with the difficulty will do, since future difficulty just adds a lot more debate to the question.

But how do we compare an operating cost with one-time cost? Trying to figure in lifetime costs creates confusion because we don't know what the devices lifetime is: we don't know how long it will last, how long until 13nm ASICs, when really clever SHA256 optimizations make it obsolete, or what its resale value would be. So instead lets use the opportunity cost. Opportunity cost is especially useful when the good in question is durable and can be resold at any time at the same price, so every day you're effectively making the same decision to keep the device or not, which may not apply here but it frees us from having to pick a bunch of debatable parameters.

Lets say you have a stack of cash. You could buy a miner ASIC or you could put it in another investment, so one way to look at the price of a miner is the forgone income which you could have received by doing something else with it. 8%/yr is a commonly used figure for very long term average stock market returns, so lets use that.

8% per year is 0.6434% per month.

For the BFL:
$1300 costs you $8.36/month in forgone investment income. At 60 watts it takes 43.83 KWH/month, or $5.26 at .12/KWH to power.

For the btcfpga:
$1070 costs you $6.88/month in forgone investment income. It's also only advertised as having 9/10th the performance.

So for the btcfpga device to match the BFL operating cost (($8.36 + $5.26) * 9/10 =$12.258) under this model it must use less than 12.258-6.88 = $5.378 in power or 61.35 watts. This isn't going to happen. (And I'm a little shocked by how low BFL's claimed power is...).

This tradeoff depends on power costs, So the formula under this model is:

Code:

((1300*.006434)+(730.5*60/1000*kwh))*(54/60)=(1070*.006434)+(730.5*cpwatts/1000*kwh)
which we can rearrange to:
kwh = 6434 / (7305 * cpwatts - 394470)

So at 300w your power must cost only $.00358/kwh for them to match, or $.009/kwh for 150 watts.

So I suppose it could be a good deal for people who wouldn't pay for a few hundred watts of additional power (e.g. flat rate rent), or for people who could otherwise make use of the waste heat and only have electrical heating available. Of course, for those people it really is only about the initial cost... at least up to the power consumption level that they can get for 'free'.

We could instead solve for the initial price needed to make it match:

Code:

price=-(365250*kwh*cpwatts - 19723500*kwh - 3763890)/3217

At $0.12/kwh the btcfpga would need to draw no more than 139.87 watts (which isn't going to happen) or the price would have to be _negative_ to make it more attractive than a $1300/60w/60GH device. At $0.04/kwh (about as low as it goes in the US), it could use as much as 311 watts before you should ask to be paid to run one instead of a BFL. At $0.04/kwh and 150 watts the price would need to be $734 or less to make it more attractive.

Of course, all of this analysis can be largely mooted by a small difference in shipping times, failures of BFL to live up to their specs, or CP's device beating its specs.

I'm personally pre-ordered for the btcfpga devices (as well as avalon, which I expect to have similar economics) but I expect to lose money on them, and I wanted to support secondary players. If they arrive early enough then even if the BFL's use a lot less power a faster arriving alternative still may have turned out to be a better buy. I expect major price wars in the future, and getting on a backlog list now sounds really unwise to me even ignoring BFL's long history of schedule slips (even on this product now). (I don't begrudge them for this: doing this kind of small scale high tech stuff is hard... but it is what it is)

Plug in your own discounting rate for the costs of assets, but you'll reach the same conclusion for any reasonable value.

It was an analysis like this that convinced me to not produce a ASIC miner myself on 130nm over a year ago. It would have been a bit win IF I was one of only a few to do it. I estimated the odds of someone doing a miner on better process (which was a bit too costly and risky for me to undertake personally) as too great to justify because once they were available they'd be much more competitive than 130nm. I still have a hard time really believing that BFL's products are going to be real and meet their claims, but assuming that they are Inaba is right about his power arguments but at the moment it's all about shipping times. Six months from now this market may be radically different.