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PV System Sizing - Interactive tutorial
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Electrical Load Calculation -How Much Power Does Your
Renewable System Need?
Finding The Sun
The first thing you need to do when siting a house or solar panel, is to find the Sun. True South (not to be confused with Magnetic South) can be determined in a number of ways. (For folks down under, replace south with north.
1. The first thing I'm interested in knowing is my Latitude. A GPS receiver is a handy thing to have, but given the expense, I'll show you the frugal way. Hop on over to http://msrmaps.com/default.aspx, enter your street address, and this handy web app tells me my latitude is 44.69769, and my longitude is -74.74631. (This will come in handy later for positioning your panels and deciding roof pitch).
1.1 NASA Surface meteorology and Solar Energy Data Set -
- Average Daily Radiation on Horizontal Surface (kWh/m2/day)
- Average Temperature (° C)
- Average Relative Humidity (%)
- Average Wind Speed (m/s)
- Heating Design Temperature (° C)
- Cooling Design Temperature (° C)
- Mean Earth Temperature (° C)
- Annual Earth Temperature Amplitude (° C)
- Average Summer Daily Temperature Range (° C)
- Average Atmospheric Pressure (kPa)
- Heating degree-days below 18 ° C
- Frost Days at Site (days)
2. Now I hop on over to http://www.esrl.noaa.gov/gmd/grad/solcalc/, plug in my longitude and latitude, and it gives me my solar noon time (midday).
3. Put a stick in the ground. The shadow at solar noon is a direct line from True South to True North. This is the direction your house or fixed panels should be lined up on for maximum solar absorbence.
4. For positioning solar panels, head on over to Wattsun enter the Latitude number we discovered earlier. This will give you your tilt angle you need. Panels and roofs should be set at about latitude (from horizontal). In my example that would be 44 degrees. Steepen by up to 15 degrees for better winter collection, or -15 degrees in summer.
5. For detailed information on doing a Solar Site Survey, see Performing the Solar Site Survey
6. For sun charts, declination maps, and an inclinometer (complete kit) see http://www.jshow.com/sunkit/listings/6.html
7. Roofers refer to pitch (angle) in a phrase similar to "10.9 in 12", meaning a roof that rises 10.9 in. for every 12 in. of horizontal run. If you take a steel square, place a mark at 12" on the long side, and at 10.9" on the upright, you will find a 47.8 degree angle. See http://daveosborne.com/dave/articles/roofpitch.php for additional info.
8. PV System Sizing - Interactive tutorial
Map of average daily global solar radiation on a south-facing flat surface at latitude tilt.
See http://www1.eere.energy.gov/femp/pdfs/FTA_pv.pdf for more info.
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