Re: Simple Math (Score: 1) by mlmitton on Monday, November 10, 2003 @ 22:09:43 EST (User Info  Send a Message)  Has the GWE page changed since you had this exchange about their numbers? Because it seems everybody commenting here is screwing up these numbers.
There are two costs hereThe fixed cost of purchasing the device, and the operational cost. The fixed cost is $112.50 'per KwH of daily capacity.' The operational cost is 1.9 cents per KwH. So, if you have a unit producing 26.6 KwH per day, the daily operational cost will be slightly over 50 cents (26.6 * .019). So the monthly operational cost will be about 15 dollars (30 * .50). This is very simple, so please tell me the page has been cleaned up.
The associated question is this: Give these costs, does it make financial sense to purchase the Edison Device? Or to phrase it another way, how much would electricity need to cost from my utility company so that I would be indifferent between buying an Edison device and staying with the power company.
To do this, you need to calculate the present discounted value of the Edison Device over the next 20 years, the expected life of the device.
Using their numbers, the $2992.50 is a cost incurred today, and the $15 cost will be incurred monthly for the next 20 years. Using the formula for an annuity, the PDV of $15 per month for 20 years, assuming a 6% annual interest rate is about $2094. So, the present discounted value of all costs for the Edison device, over the life of the device, is $5086 (2094 + 2992).
Now, how much would you have to pay in electricity to your utility company each month, for the next 20 years, for the PDV of those payments to equal $5086. You use the same annuity formula, but solve for the monthly payment. I get about $36.50.
So, if your average electric bill is $36.50, then you will be exactly indifferent (monetarily) between staying with the utility company and purchasing an Edison device. If your bill is more than that, then you would be better off with an Edison. If your bill is less, then you would be better off staying with your electrical company.
Are we clear on these numbers now?
Postscript for the interested. The discounting formula for an annuity is:
PDV = N * D * [(1D^n)/(1D)]
where,
D = 1/ 1+i
N = The amount paid in each period
n = The number of periods
i = The appropriate interest rate. Note that if you're using monthly periods, you need to convert an annual interest rate into a monthly interest rate. A 6% annual rate is a .5% monthly rate (6%/12) 
 Parent Simple Math by chipotle_pickle on Tuesday, November 11, 2003 @ 01:57:36 EST
 "Operational cost" by chipotle_pickle on Tuesday, November 11, 2003 @ 12:16:24 EST
 Re: by mlmitton on Tuesday, November 11, 2003 @ 14:11:39 EST
 Re: by Anonymous on Tuesday, November 11, 2003 @ 14:38:32 EST
 Re: by Anonymous on Wednesday, November 12, 2003 @ 10:02:54 EST
 Mixing means and extremes by chipotle_pickle on Friday, November 14, 2003 @ 09:47:46 EST
 Re: Mixing means and extremes by mlmitton on Friday, November 14, 2003 @ 11:00:24 EST
 Still mixing means and extremes by chipotle_pickle on Friday, November 14, 2003 @ 11:26:21 EST
 Re: Still mixing means and extremes by mlmitton on Friday, November 14, 2003 @ 12:10:57 EST
 Mixing means and extremes by chipotle_pickle on Friday, November 14, 2003 @ 12:52:22 EST
 average=max by chipotle_pickle on Friday, November 14, 2003 @ 14:14:05 EST
 this dialog? by Anonymous on Friday, November 14, 2003 @ 14:22:03 EST
 Sorry by chipotle_pickle on Friday, November 14, 2003 @ 15:35:30 EST
 Re: ?? by Anonymous on Friday, November 14, 2003 @ 17:44:06 EST
 Anthony by chipotle_pickle on Friday, November 14, 2003 @ 18:08:13 EST
 Re: Anthony by Anonymous on Friday, November 14, 2003 @ 18:57:57 EST
 Re:follow up question by Anonymous on Friday, November 14, 2003 @ 19:07:24 EST
 good questions by chipotle_pickle on Saturday, November 15, 2003 @ 06:51:59 EST
 Re: next by Anonymous on Saturday, November 15, 2003 @ 16:48:30 EST
 Tougher question by chipotle_pickle on Sunday, November 16, 2003 @ 09:46:06 EST
 Re: Tougher question by Anonymous on Sunday, November 16, 2003 @ 10:34:59 EST
 Re: Follow up by Anonymous on Sunday, November 16, 2003 @ 17:47:45 EST
 Easier said than done by chipotle_pickle on Monday, November 17, 2003 @ 07:08:33 EST
 Re: silence by Anonymous on Tuesday, November 18, 2003 @ 17:36:51 EST
 Re: silence by Anonymous on Wednesday, November 19, 2003 @ 06:08:34 EST
 Re: silence by Anonymous on Thursday, November 20, 2003 @ 09:27:54 EST
 Re: silence by Anonymous on Thursday, November 20, 2003 @ 11:38:15 EST
 Re: silence by Anonymous on Friday, November 21, 2003 @ 10:27:28 EST
 Re: silence by baldy on Friday, November 21, 2003 @ 11:22:37 EST
 Re: Pickle? by Anonymous on Friday, November 21, 2003 @ 20:12:06 EST
 Re: silence by Anonymous on Tuesday, November 25, 2003 @ 14:55:00 EST
 Re: silence by baldy on Tuesday, November 25, 2003 @ 15:28:29 EST

