[RE-wrenches] Real world PV production

[SOLARPRO at aol.com]

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.davidson at 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:kelly at whidbeysunwind.com)  
To: _RE-wrenches_ (mailto:re-wrenches at 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
_kelly at whidbeysunwind.com_ (mailto:kelly at 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" 
<_kelly at whidbeysunwind.com_ (mailto:kelly at 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










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