ECONOMICS OF USING SOLAR POWER----Carl Schwab

Recently the writer published a BLOG concerning the increasing interest in using solar power to supplement electrical power on a home residence. It doesn’t address casual use of solar powering sites such a remote campsites. This BLOG will address some of the issues that should be considered in contemplating use of solar power. Figuring out whether you save, and if so how much, depends on lots of factors---especially where you live. The big question for any homeowner considering installing solar power is a simple one: How quickly will the system pay for itself? Well it depends where you live. That doesn’t just mean how sunny it is, though weather obviously matters. Just as important are subsidies, such as tax credits and rebates, which differ from state to state and between cities. Another BIG local factor: how much you currently pay for electricity—because it determines what you can expect to save each month once you start producing power.

PRACTICAL CONSIDERATIONS-----Materials presently used for photovoltaic solar cells include monocrystalline silicon, polycrystalline silicon, amorphous silicon, cadmium telluride, and copper indium selenide/sulfide. For the present time the silicon based PV are the most practical and actually mostly concentrated on polycrystalline silicon. Presently these are made into 3” x 6” cells and then series/parallel connected into panels of larger dimension that are frequently referred to by voltage i.e. 12 or 24 or 36 volt and wattage. A typical 3” x 6” cell in full zenith sunlight will produce approximately 0.5 volts at 3.5 amps or 1.75 watts. Some arithmetic computes that a square foot of area, at zenith, would produce 14 watts. Assembled panel sizes range up to 4’ x 8’ which yields 4 x 8 x 14 = 448 watts per panel at zenith. 10 of these panels would produce 4480 watts with the sun at zenith. So to achieve 5000 watts at zenith we need 5000/14=358 ft^2 or less than 20 x 20. BUT reality sets in---as the sun goes off zenith the amplitude drops as the cosine of both the horizontal and vertical angles and of course the sun is NOT present most of the 24 hours of the day. As the wheeze goes,”—you have to make hay while the sun shines”. So while the solar panel is producing power we need to convert it into AC power in such a manner that it affects the wattmeter reading. That is where the Grid Tie Inverter comes into play. The function of the GT Inverter is to take the DC from the panel and convert into properly phased AC for your house so that the house wattmeter recognizes it as negative power thus giving you credit. Grid Tie Inverters are made in a wide range of sizes from 1 to several 100 kilowatts.

MOUNTING---Most people think mounting on a second story (height) roof that faces south and is sloped up at 30 degrees is “perfect”—certainly on LI. Well it IS a good start; however precautions still have to taken to prevent shadowing. BUT there is more to it than simply putting the solar panels up there.

A Quick story:  This happened in Minnesota when a person found an available 2-story house that faced south and had a south facing half-roof at about 30 degrees. After mounting the panels and checking operation, a few days later, after high north winds, he was shocked to find his solar panels on the ground south of the house and severely damaged. What happened? Analysis showed that the upper edge of the panels was about 4 inches above the roof and that the high wind speed “rammed” pressure below the panels which combined with the “airfoil effect” above the panel simply ripped the panels off. Also he had not sealed the lead edge to prevent wind UNDER the solar panel edge. Further the panel supplier stated the owner had used insufficient mount points per panel by nearly 3 to 1. That probably was the largest error. An EXPENSIVE lesson.

Designing the roof (or even off-roof) mounting requires professional thought and experience. Such obvious problems as high wind speeds (hurricanes and cyclones) and hail storm damage must be considered. Also ice loads which can easily exceed the panel weight itself. As an owner you have to know how your Home Owner insurance will treat damage and an additional cost may be for a “rider” to cover such damage. An article in the WSJ, September 17, 2012 compared the economics of solar panels at 5 different locales in the US. They considered a 5000 watt DC system in Brooklyn, NY, Denver, CO, Los Angeles, CALIF, Minneapolis MN and a 3000 watt DC system Portland,OR and tabulated cost/rebates etc. The system costs were $27,500 except for Portland which was $16,500 because it was only 3000 watt DC. A useful measure was the payback period. Surprisingly Brooklyn was the shortest at 5 years and Portland the longest at 15 years. The shortest payback period was due to the MOST expensive electric cost per Kwh! No mention was made in the article about insurance costs. Each location was roughly the same size unit, placed on a south-facing roof tilted at 30 degrees. Each home was assumed to consume 11,500 Kwh per year. BTW this 11,500 Kwh/year is the average in US according to the Energy Information Administration for 2010. The article DOES STRESS using licensed professionals to design and install.

INTERESTING-----

Comments

[Neal Yanoff]

http://www.raiservices.com/

Is a professional Solar Panel Installer and electrical contractor.

[solar panels calculator]

Green energy is where we need to commit our attention and resources...this post is an awesome write up.Lot of information is there.Keep posting!

[Solar Panels]

You have provided excellent information about solar power system. This post is very useful for those who want to use solar power system. They can choose solar power by reading your narrative post.

[Sean Carter]

good overview of the costs and the process of solar power. I have been using solar companies in the bay area for a few years now and it has been great. Setting it up was not much of a hassle and it has been running smooth ever since