Is Rooftop the best way to electrify the world?Not as it is today! Take, for example, a 1,000 watt (or 1 kW) solar panel array that costs $4 per watt. This means that if you wanted this system to help provide electricity to your home, you would have to pay (at least) $4,000 from which you might get a rebate from the government of a sizable percentage. At 30%, $2,800 is invested into a system that delivers 1Kw at best for a few short hours per sunny day. This does not include all the other parts such as batteries, grid tie connection, inverter and charge controller.With feed in tariffs, the posibilities for PV is endless! Germany produces the most PV generated electricity, has the fastest growth rate and are developing automated PV factories. All this for a country that has a better wind potential than solar! Germany's example PROVES that the more sunny regions can indeed power themselves completely with PV (up to the point where utility scale electrical storage is needed). Sunlight (here on Earth) is rated at 1Kw per square meter which is about 10 and 3/4 sq ft (about 3 feet, 4 and 1/2 inches square). Any smog, dirt on panel and especially, wrong angles will reduce that intake. If your panel is facing due south and the sun is at 4:00 PM, it will recieve less light and it will also reflect more of that little bit available. That system therefore will only generate about 5 Kwh at best during an average day. Times that by 30 days and you will have collected 150 kWh, enough to power an average home for about one week. If a homeowner buys (or makes) a thousand dollars worth of panels every year... Eventually that person would be selling back to the grid if the laws allow.  The size of the red arrow represents the amount of energy the same panel recieves at different times of the day. The red in the small arrow should also be diminished somewhat due to the fact that there is more air for the sunlight to travel through (which lessens its intentity). Sun tracking panel mounts are available, but at a cost that approximates benifits, about 30% more. With these, there is also the possibilty that the moving parts may not hold up to the extreemes. Debris and ice may cause problems. The main problem with rooftop solar is the fact that not everyone is willing to dedicate their lives to utilize green energy. It has been priced out of the reach of the majority.
Photovoltaics or PV can be fun though, on a much smaller scale. You can build solar powered electronic gadgets just by searching Ebay. Also, you can make your own panels out of discounted cells, glass, flatwire, solder, silicone, and a diode (which is a one way valve for electricity) that prevents juice from draining back into the battery at night. One of my favorites is the The magic of PV is best explained by photons of light knocking electrons from their parent atom, thus creating current. Normal monocrystaline cells convert about 14% of the sunlight's energy into electricity. A polycrystaline (one that is not quite as pure) are about 12 to 13%. A 7% efficient, (but cheaper) version is the amorphus kind. They are the glass ones that do not contain individual soldered cells. A newer glass version called CiS or CiGS are 14% and promise to revolutionize the industry (after all the priporitary, 'let's keep it expensive' time frame passes). The amorphus and CiGS panels are quite literally printed on glass. There are also plastic, organic and so on. I don't believe that plastic could last long enough to justify replacing its glass counterpart. Individual cells (and the stuff between the lines on CiGS) each produce about 1/2 volt, no matter how large. A 3x6 inch monocrystaline is rated 3.6 amps, thus 24 in series would (in theory) generate 3.6 Amps at 12 volts. However, since they loose strength when heated, they drop voltage (and a 12 volt battery needs 15 volts charging current). Thus the need to string 36 together for reliable 12 volt charging. 3.6 amps x 18 volts = about a 65 watt panel in this case.
 The price of PV should have come down due to the recent building of additional PV manufacturing plants, but they are still up, probably from an increased demand for the expensive silicon ingots, and to increased demand from eco-awareness. Personally, I think the price will never come down because of priporitary issues. Unless feed in tariffs are enacted, PV will lag behind as it already has here in America. Rooftop solar power generation requires an inverter that boosts the battery bank's voltage to house voltage, requires a grid tie (if little or no batteries), a charge controller that protects the batteries from over and under charge, hardware and a trained installation professional. Residential PV is also lacking in optimum siting. This provides for the argument to make the utilies to pay the extra for largescale than to do it all by ourselves via roof tops. Also, there is not quite enough sunny rooftops to power all of the USA (but enough to bring about a PV boom necessary to further reduce the price of PV). When the price per installed watt comes down, and when batteries can be made to last the lifetime of any utility scale project, then solar PV can be a real solution past the 20% mark. If you live in the desert, you probably already have a good site, however, you would have to compromise shade trees, a must have for in keeping with another solar objective.... Passive solar.
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