Joel: The PV system in Long Beach was built within a stone's throw of a twin smoke stack for a big furnace devoted to a "Trash to Energy" project. It burns garbage to produce energy.... and LA has plenty of trash. Combine that with all of the diesel soot being generated by ocean long haulers which bring cars, refrigerators and yes, PV modules into the busiest port and rail hub on the left coast for our consumption. The modules, and everything else in the port, are just plain dirty. We install mostly in southern LA County. Our systems are always above predicted outputs by PV Watts 2 & the CSI EPBB. The degradation over the years seems not be have been as severe as predicted, except for some of the PhotoWatt units we installed for a brief while. I think that the lower degradation may be due to our mild climate? Since we are coastal, we really stress tilting the mods at least 10 degrees to help them weep from the almost daily condensation, which also has the effect of cleaning the panels. Then the soot-laden sludge at the lower edge accumulates to the point that we recommend annual scrubbing. Simple Green has been suggested as a good product for cleaning the modules and that is what we tell our customers (but is it really 'bio-degradable'?) Patrick A. Redgate Ameco Solar, Inc. 7623 Somerset Blvd Paramount, CA 90723 888-595-9570 In a message dated 6/10/2010 4:19:23 P.M. Pacific Daylight Time, joel.david...@sbcglobal.net writes:
PVWatts is a good general estimator when you fine-tune the derate factor. For single crystal and multicrystalline arrays, I generally use 0.65 for battery-based PV and inverter systems and 0.82 for batteryless inverter systems. PVWatts annual results are l5% low for Unisolar arrays because PVWatts uses the crystalline silicon temperature coefficient. Even though PVWatts2 may seem more accurate, it does not factor in unique local climate conditions like California coastal morning and afternoon fog or inland persistent winter Tule fog. However, NREL's climate data does include LA's "June gloom" see _http://en.wikipedia.org/wiki/June_Gloom_ (http://en.wikipedia.org/wiki/June_Gloom) For flat roofs in snowy climates like the Unisolar project in Rochester NY, I deduct 30% from PVWatt's November through March estimates for a fairly accurate annual estimate. Powerlight (now SunPower) also uses an additional 30% monthly derating for flat roofs in snowy locations. PVWatts does not account for really dusty and dirty air locations. Bill Brooks worked at PVUSA and is very knowledgeable about power loss from soiling from agricultural dust in central California. Bill also measured 35% power loss at the Long Beach CA harbor waste-to-energy powerplant PV systems. That location and most LA county freeways experience particulate pollution that not only reduces PV production but causes permanent respiratory damage to children and shorten the lives of elderly people, sort of like the canary in the mine. Joel Davidson ----- Original Message ----- From: _Kelly Keilwitz, Whidbey Sun & Wind_ (mailto:ke...@whidbeysunwind.com) To: _RE-wrenches_ (mailto:re-wrenches@lists.re-wrenches.org) Sent: Thursday, June 10, 2010 7:57 AM Subject: Re: [RE-wrenches] Real world PV production Thanks, Don, 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. 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. 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. Thanks, -Kelly Kelly Keilwitz, P.E. Whidbey Sun & Wind Renewable Energy Systems _ke...@whidbeysunwind.com_ (mailto:ke...@whidbeysunwind.com) 360-678-7131 On Jun 9, 2010, at 8:59 AM, i2p wrote: On Jun 9, 2010, at 8:22:12 AM, "Kelly Keilwitz, Whidbey Sun & Wind" <_ke...@whidbeysunwind.com_ (mailto:ke...@whidbeysunwind.com) > wrote: Thanks, Joel How about PV systems away from the coast, in a hotter, dustier location, like Bakersfield, Fresno, Sacramento, Palm Springs, etc........? 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. Don Loweburg
_______________________________________________ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org