Select Solar PV Panels to Meet Your Need

What is a Solar PV Energy?

     When I was in elementary school, the movie projector had a light inside. I asked what was the light for? My teacher told me the light shined through the film onto a special surface in a vacuum tube. The surface turned the light into an electric signal that produced the sound for the movie we were watching.

     Solar PV  panels work much the same way. Sunlight is transformed into electric energy. The amount of energy is determined by the intensity of the light. Sun angle, shadows, clouds, haze, and temperature all affect the energy transfer. Solar Panels are made up of solar cells in series to increase voltage and in parallel to increase current.

    When any one cell in a series group is not illuminated or faulty, then the total current of the series is zero -- no current, no power from the series.


     When any one cell in parallel group is not illuminated or faulty, then only the power from one cell is missing from the group.


     Wiring the cells in a series-parallel matrix gives you reliability but it sure makes it hard to find and replace a failed cell.

Power Requirements

     How much power would you like to generate from a Solar Panel array?


      (a) Enough to charge your battery bank to last 5 day in a row without usable sunshine?

kwh per month / days in month x 5days = energy used

energy used /days in month/ sunshine hr per day

 = additional system capacity to recharge storage in a month

     Best case

     For July       1908 kwh /31 days x 5 days = 307.74 kwh
                          307.74 kwh /31 days /6.5 hr/day = 1.53 kw system

Monthly Average

     Month avg   2359 kwh/(365 days/12 mo) x 5 days =387.8 kwh
                   387.8 kwh /(365 days/12mo) /4.5 hr /day = 2.83 kw system

Worst case

     For Dec       4136 kwh /31 days x 5 days = 667.1 kwh
                         667.1 kwh / 31 days / 2.5 hr /day = 10.25 kw system

     The above calculations show the additional system capacity necessary just to recover in a month from 5 strait days of cloud cover or grid failure.

      (b) Just to cover average monthly use?

kwh/mo /(usable sunshine hours/day x days in month) = system size kw

Best case

     For July        1908 kwh  /(6.5 hr /day x 31 days) = 9.47 kw system

Yearly Average -- Net Metered Zero Average Grid Use

     Year avg      28319 kwh /(4.5 hr/ day x 365 days) = 17.24 kw system

Worst Case

     For Dec        4136 kwh / (2.5 hr /day x 31 days) = 53.36 kw system
     The above calculations show the size of a system necessary to handle power consumption for a current life style. You can easily see that your electric utility using fossil fuels doesn't experience the extreme constraints that a pure solar PV system would have trying to keep pace with your current life style, sun cycles and the whims of weather conditions.

     Your life style would have to be modified to thrive within the capability of a reasonable and economical stand alone solar PV system. Net metering is a reasonable solution for keeping the initial cost of a solar PV system manageable and still not need to drastically change your life style. However, you would still be dependent on the utility grid.

     You will need to do your own calculations because your location and life style is probably different from mine. 

Space & Orientation Requirements

     About 70 feet from my house is a barn with unshaded roof area facing south that is 20 ft x 24 ft. If one were to choose Sun HS-195 (195 watt Solar Panels) that are approximately 3 feet wide by 5 feet long and produce about 190 real watts each. They each weigh 40 lbs and are listed at $503ea. A 4 long by 8 wide matrix will fit the roof nicely.

 That would be 40 lb x 32 = 1280 added weight to the roof.
 $503 x 32 = $16,096 plus shipping.
32 panels x 190 watts = 6080 watts or 6.08 kw

Cost Efficiency

$503 per panel x 0.7 tax credit /190 watts = $1.85+ per watt from panels

Power Factors

     I'm currently paying something like $0.09 /kwh. An installed panel remain functional for about 25 years.

If you assume 25 years x 365.25 days x 4.5 hrs x 190 x 0.9 time loss
 you get 7026.5 kwh per panel lifetime
$503x 0.7 tax credit / 7026.5 kwh = $0.0501 per kwh fixed

     And It won't be affected by any fossil fuel tax, oil prices or inflation. But it will take some up front money.

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Karl Kinkel - President
Karl Kinkel, President & Founder
Longsgap Services LLC
5262 Elk Creek Pkwy
Independence, VA  24348
(276) 773-3730
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