Jeff C, I just thot I'd add this....
I was looking at installing one of these systems until I looked at the payback period and it just does not make sense for me or my situation.......
And the average system will last for 30-40 years....... I used two different calculators and they were very close to each otehr in payback period.......
One additional thing to consider is storage battery replacement. The solar panels produce DC (Direct Current) at a low voltage. Obviously a household needs 120 volts AC (Alternating Current). The way its commonly done in these systems is the output of the panels charge fairly hefty deep-cycle storage batteries.
The battery interface is needed because the solar panel output , obviously,is not constant. Night time hours, cloudy days, precip, etc.
Still in the DC world to this point. Note: a transfromer can't be used to step up voltage with DC input. It will overheat, and prob'ly burn out.
So, to make AC from DC requires an "inverter". Back in history a DC motor driving an 120Volt AC alternator was used. Worked fine, but not energy efficient.
Now days a solid state inverter using high power handling transistors operating in an switching-oscillator at 60 Hertz (cycles) provide interrupted DC into a step-up transformer, with the secondary windings providing the desired voltage. 120 Volts AC, in this example. This current then can be utilized.
There are other electronic methods to do the "inversion", but this system is easy to understand.
So my point, again, was that deep cycle batteries will need to be replaced over time, so that would be another cost to be considered.
Interesting, I have worked on systems like this on the North Slope Alaska, between Fairbanks and Dead Horse (Prudhoe) back in '91. The solar systems were used to power radio repeater tower sites for mobile telephones used by trucks hauling supplies to the oil field. (not cellular)
OK, somebody will ask what powers the sites when it's pitch dark in winter.?
Easy. Thermoelectric generators. These produce DC as well. Consists of an array of metallic thermocouples, that are heated by a catalytic oxidizer (burner.) It uses propane as a fuel.
The same inverter is used... it doesn't care where the current comes from.
Now somebody will ask, when it's -60F how do you get the propane to flow?
Insulated tanks buried in the ground, close to the equipment shack.
How do the tanks, usually 1,000 gallons total get refuled? A helicopter flies in replacement propane about 2X per year.
There, you now have more than you wanted to know about it. I got 35mm slides from that adventure, somewhere.
Edit: one last interesting fact. Not solar, but all cell phone tower sites, and central switching offices, as well as land line copper wire phone systems run off 48 Volts DC massive battery banks. These are float-charged off the commercial power grid, or back-up Diesel Generator. The inverters in this app are "scary". 48 Volts DC, and between 600-800 Amperes. Copper buss-bar connections damn near as large as your arm!
This is why a standard "corded" phone will work even when the AC power is out to your home. Land phones are all powered from the Central Switching office. Been that way since the early 1900's, believe it or not.
Everybody should keep an old standard wired phone handy for loss of power emergencies. Unless a cordless phone base unit has some kind of battery back-up, they won't obviously work with loss of AC.
My $1.98.
