The cost factor - W/H/D

The W/H/D or watt/hour/dollar is used as a common measurement that can be compared with solar systems, power plants wind generator, etc.. The cost of a solar systems is one of the more important question that is asked. What is more important is how much power that you get against the money that you spent. If you find this page a littele dry, skip to Summation at the bottom of this page. The standard formula used here is, “Power per dollar for a year” or watts/hour/dollar. Power is a measurement in watts used in one hour. More over it is the number of watt/hours per dollar of your investment over a period one year. To figure the watts/hour/dollar, total the watts output of your solar panel(s) for a year then divide it by the investment for the year.
Details:
The first step is the to get total solar panel watts/hours for the year. The solar system does not produce any power at night and a lower power in the morning and evening. So I selected 5.5 hour/day as an average. Now you have 30 days in a month and 12 month in a year . So the basic formula is kilowatts from panel(s) X 5.5 X 30 X 12 = kilowatts/hours for the year.  The final step is to divide  kilowatts/hours by the dollars spent in that year. This gives you watts/hours/dollar for that year. To simplifying the formula do this “panel watts” X 1980/ dollars per year = watts/hour/dollar. Watts/hour/dollar can be shorten to watt/dollar or W/D or W$

Sample 1:
I found a 5,000 watt DIY kit on the internet for $22,000.  I will not include the labor to install this system, because most everything on this site is calculated as a kit. So it is only fare that I make the comparison with other solar system kits. You can add in the labor if want to compare other solar systems with labor.  So the formula is
5K X 1980 = 9900 kilowatts/hour for the year. The final step is the watt/dollar. Covert to kilowatts/hour to watts/hour.
9900,000/$22,000= 450 watts/hour for ever dollar that you spent. In 10 years you will get 4500 watt/hour/dollar. This is assuming that you don’t spend any money for maintenance.

Sample 2.
let us look at a very simple “single solar cell setup inverter” that is found on this site at a cost of $20.00. It takes a single solar cell at 0.5 volts at 1.5 amps and converts it to 2 volts at .675 amps for charging D-cell flash batteries.
lets assume that you rotate full charge D-cell with another D-cell battery that needs charging for the 5.5 hour day. Accounting for some battery loss we multiply volts x amps to get watt/hour. 1.5 X.450 = .675 watt/hour. Now to our formula
.675 X 1980 =1336.5 watts for the year.
The cost for parts is about $20.00. So 1336.5/20.00= 66.825  watt/hour for ever dollar that you spent.  In 10 years you get 660 watt/hour/dollar. The $20.00 looked  like a great deal but the $22,000 give almost 7 time the watts for your dollar.

The electric company that I use charges their fee on a sliding scale. They start at .11 cents kilowatt/hour and goes up to about .41 cents kilowatt/hour. Doing the math for the .11 cents pre kilowatt/hour. That means the you get about 9.09 kilowatt/hour for a dollar. Translated to our formula is
9,090 watt/hour/dollar or 9090watt/dollar. you can call your electric company  to verify this number. You will hard press to beat this number.

In sample 1 above Doing the math for 10 years. Will yell 4500 watt/hour/dollar. This assume that you have zero maintenance or expense in that 10 year. Bottom line is that you get about two times more power from the electric company.  But this is not the end of the story. After using a few kilowatt/hour usage the price go up up up. level 2, level 3, level 4, level 5.....

Let us do  the math for level 5 the .41 cent kilowatt/hour. That means the you get  about 2.43 kilowatt/hour for a dollar. Translated to our formula is
2,430 watt/hour/dollar now you will find that in sample 1 is the winner by two times more power.

Summation:
sample 1:
year 1  450 watt/dollar
year 10  4,500 watt/dollar

sample 2:
year   1   66.825 watt/dollar
year 10  660 watt/dollar

electric company at .11 cents per kilowatt/hour. :
year   1   9,090 watt/dollar.
year 10  9,090 watt/dollar.

electric company at .41 cents per kilowatt/hour. :
year   1   2,430 watt/dollar.
year 10  2,430  watt/dollar.
The only one that save you money on is “sample 1” over 10 years There is no hard and fast number, but the rule of thumb 500- 1000W/D for under $100.00 investment. 2000-3000 W/D for under $1000.00. 3000-6000 for $10,000 W/D investment.