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AreWeDrunkYet posted:Once again, you are completely failing to discount the costs involved. What's the point of tossing around a bunch of nominal dollar figures? Kaal posted:I don't quite follow you. Could you please generate an example of the correct accounting of the figures? I think he's talking about discounted cash flow, which is a way of accounting for the fact that, thanks to the wonders of economics,  today is worth more than in a year's time. A sum of money in the future has a net present value, which is basically how much that sum of money at that point in time would be worth in today's money. So, for example, if the annual rate of inflation was 5%, then this time next year would be worth 10/1.05 = $9.52 today.If you are talking about discounted cash flow, AreWeDrunkYet, I'm not sure I get your point. Assuming electricity costs remaining constant at 12.12c/kWh, and the prices, lifetimes and usage specified by Install Gentoo, LED bulbs come out cheaper than CFL at interest rates below 20%. Given that energy prices are trending upwards and according to Wikipedia, at least, inflation in the US has only reached that level very occasionally and briefly, LED bulbs are looking pretty good. Calculations: Assuming 8 hours of use per day, 365.25 days per year, that's 2922 hours per year. At a 11W power draw for the CFL that's ~32.1 kWh, costing $3.89 at 12.12 c/kWh. At a 6W power draw for the LED that's 17.5 kWh, costing $2.12. That's the yearly electricity cost, so using an inflation rate of 5% which I pulled straight out of my backside, and assuming that all power bills are paid at year's end, the net present value of 17 years' worth of electricity can be approximated by [Annual cost * (1 - 1/{1 + annual inflation rate}^no. of years)/annual inflation rate] - giving a NPV of $43.92 for the electricity used by the CFL bulbs, and $23.96 for the LED. Cost of the bulbs is simpler. With unit costs of $7 for a CFL and $23 for a LED, and the CFL needing replacement every 10,000 hours (1250 days or 3.42 years), the net present values are [Unit cost/(1 + annual inflation rate)^no. of years] - giving NPVs of $7, $5.92, $5.01, $4.24 and $3.59 for the CFL bulbs and $23 for the single LED. Totalling all that gives a net present value of $69.69 for the cost of five CFL bulbs and the electricity to run them for eight hours per day over the course of 17 years, and $46.96 for one LED bulb used for the same time. Advantage: LED. The advantage stays with LED until the annual inflation rate hits ~20%, at which point the NPV for CFL is $33.01 and that for LED is $33.14. Of course, this is neglecting the month and a bit left over (50,000 hours comes to 17.11 years) but gently caress it, this is close enough. Especially given it ignores much more significant things like changes in costs, inflation and real wages. EDIT: That'll teach me to hit 'preview' more often. Friend Commuter fucked around with this message at 18:41 on Sep 13, 2012 |
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Sep 13, 2012 18:38
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double nine posted:So is nuclear/fossil/solar/hydro/wind/geothermal the energy mix that we're stuck with, or are there still sci-fi level energy sources that could plausibly be the saviour of our energy concerns? Fusion's the only sci-fi energy source anybody vaguely credible has been talking about, and it's been 20+ years away since the first H-bomb was detonated and the price tag on test reactors is stratospheric and rising, so I reckon we're poo poo out of luck on sci-fi power plants.
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Oct 11, 2014 12:39
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