Jim, Obviously, your latitude will make a big difference. The further north you go the wider the summer to winter sun angle. Also, I'd want to know if that data was taken using just I/V curves or through a controller which had MPPT capabilities. In a real world situation with MPPT, I'm guessing that matching the array tilt to the sun angle would make more than a 6% difference at 40°+ latitudes. Besides, what's wrong with an extra 6%?? Cheers, bob-O
On Feb 19, 2011, at 8:03 PM, North Texas Renewable Energy Inc wrote: At least that's the conclusion of Gottfried Wilhelm Leibniz. "The largest difference of the [PV] plant yield was less than 6% for tilt angles between 0° and 70°." This begs the question, where did the notion that tilt to latitude is critical come from. Surely NREL or someone else has tested this concept before. Anyway if N-S angle energy production loss is only 6% to +/-35° then E-W should be too, right? But it's not. Here's why. If you measured irradiance at 10°-70° only at noon over 12 months, the air mass would at its minimum during the entire test and so irradiance deviation would be too. AM would not be constant at +/- 35° E-W which has been verified by NREL and others for a long time, AM increases the further from solar noon the sun gets. But if the Earths tilt is 23.5 degrees and Gottfried measured to 35 degrees, the difference is 11.5 degrees at summer and winter solstice. And if your array angle is +/- 11.5 deg from true south, rule of thumb is that irradiance losses are minimal. Maybe only 6% or so. This puts the significance of array tilt in a whole new light. Pun intended... Of course there is a fee to download the entire document but the abstract is here http://tinyurl.com/4zf2syk http://www.scopus.com/record/display.url?eid=2-s2.0-78951495350&origin=inward&txGid=kX6CkwoH_w_VL01NbmaciIC%3a2 Jim Duncan North Texas Renewable Energy
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