<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div>Thanks, Don,</div><div>Performance predictions such as from PV Watts VASTLY underestimate PV production in our area. For example, PV Watts estimates 940 kWh/kW for a 4:12 pitch at 180˚, whereas such systems are actually producing up to 1300 kWh/kW (as measured by a renenue-grade production meter). We have to set the derating factor to nearly 100% in order for the predictions to match.</div><div><br></div><div>I assume that is partly due to coarse irradiance data (not accounting for higher irradiance for our location in the rain shadow of the Olympic Mountains), but also due to our clear, cool, windy summers, good natural washing, and (perhaps) dispersed distribution of irradiance.</div><div><br></div><div>I want to know if the opposite is true: Do performance predictions OVERESTIMATE PV production in areas with historically high irradiance, but significant soiling and temperature issues.</div><div><br></div><div>Thanks,</div><div>-Kelly</div><br><div apple-content-edited="true"> <span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: medium; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><div>Kelly Keilwitz, P.E.</div><div>Whidbey Sun & Wind</div><div>Renewable Energy Systems</div><div><a href="mailto:kelly@whidbeysunwind.com">kelly@whidbeysunwind.com</a></div><div>360-678-7131</div><div><br></div></div></div></span></div><div><div>On Jun 9, 2010, at 8:59 AM, i2p wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div name="Mail Message Editor"><div><span class="Apple-style-span"><br></span></div><div id="replyPrefaceElement">On Jun 9, 2010, at 8:22:12 AM, "Kelly Keilwitz, Whidbey Sun & Wind" <<a href="mailto:kelly@whidbeysunwind.com">kelly@whidbeysunwind.com</a>> wrote:</div><br><blockquote style="padding-left: 5px; margin-left: 5px; border-left-width: 2px; border-left-style: solid; border-left-color: blue; color: blue; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: medium; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><span class="Apple-style-span" style="font-f amily: monospace; font-size: 11px; ">Thanks, Joel<br>How about PV systems away from the coast, in a hotter, dustier<span class="Apple-converted-space"> </span><br>location, like Bakersfield, Fresno, Sacramento, Palm Springs,<span class="Apple-converted-space"> </span><br>etc........?<br><br></span></span></blockquote><div><span class="Apple-style-span">In central CA we do a little better. I casually monitor several systems in this area and expect around 1500-1600 kwh/kw. per year.<div><span class="Apple-style-span" style=""><br></span></div><div><span class="Apple-style-span" style="">Don Loweburg</span></div></span></div><div class="aol_ad_footer" id="u9CD372ACEC35420CBD4E99C9A7DEA98B"></div></div><br></blockquote></div><br></body></html>