South or West for TOU (quantified) [RE-wrenches]

Tue Jun 15 22:57:48 PDT 2004

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Hi y'All
My analysis is not very scientific but here it is.
Best total energy is the sun perpendicular to the module at noon a month 
and a half before and after the summer solstice.
The sun moves 15 degrees an hour
You want good power to start at noon
The modules make good power for about 5 1/2 hours a day.
That is 2 1/4 hours in the morning, or 32 1/2 degrees.
Daylight savings time shifts an hour of morning into afternoon.
Rotate the modules 15 to the west
The sum of daylight savings and rotation is 30 degrees, leave 1/4 hour 
in the morning just to keep it simple.
In PG&E land the peak rate is ~.32 and off peak ~.09.
So if you rotate 15 degrees west, the benefit is one peak hour ~.23 
Wkday x 5 days or 1.15/ week x 26 weeks or about $30 / year x 30 year 
life of system or $900 lifetime benefit. Other effects like shading and 
good voltage cuurrent match with the inverter will make more difference 
than that. As you rotate more than 15 degrees, total energy suffers and 
the benefit erodes quickly.
Just pick a roof that is south or somewhat west of south, mount plane of 
the roof, don't explain too much, and set expectations low, and your 
customers will be satisfied.

cul deant

Matt Tritt wrote:

> 
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>When using TOU metering and a ground mount, we always try for SSW @ 35
>degrees. We find that this makes a big difference in net energy savings for
>our Ag. Customers when we can convince them to do irrigation at night or
>early morning.
>
>On another note, we just got an article from a German energy on-line
>magazine describing China's implementation of the German model for solar and
>wind energy policy. WOW! My first reaction was to imagine that every solar
>chip in creation would go to China (those that haven't gone to Germany,
>Spain and Italy, that is); but after calming down a bit I believe that this
>might actually spur the Chinese to produce highly efficient modules of their
>own, which in turn may eventually find their way to this market and possibly
>bring the cost of solar down a bit. Hope springs eternal.
>
>
>
>Matt T
>
>-----Original Message-----
>From: Antony Tersol [mailto:tony at appliedsolarenergy.com] 
>Sent: Tuesday, June 15, 2004 8:09 AM
>To: RE-wrenches at topica.com
>Subject: RE: South or West for TOU (quantified) [RE-wrenches]
>
>
> 
>
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>Short answer: South at 35 deg tilt is better than West at it's best tilt of
>15 
>for San Francisco weather.  Even at 15 deg tilt, South is better.  But 
>south-southwest is best.
>
>Long answer: For San Francisco, using real weather data, running a
>simulation 
>that calculates performance over a 365 day year, every hour, for each
>azimuth, 
>tilt combination (for each azimuth below, the simulation was done for 19 
>different tilts (every 5 degrees) x 365 days x 24 hours).
>
>btw, this is weather dependent.  For example, for Fresno, straight south is 
>optimum for total production, as opposed to SF, which favors SSW.
>
>  Site Latitude	(lat)	36.6   degrees
>
>The following chart shows percentage of optimum at each azim/tilt combo. For
>example, for west, a tilt of 15 degrees, produces 87.1% of optimum. For
>south, a tilt of 35 degrees, produces 99.3% of optimum. The optimum is at
>azimuth of 15 or 20 degrees west of south, at 35 deg tilt.
>
>Sorry if the formatting is hard to read.  Anyone wishing a nicer format
>email 
>me, and I'll send you a .pdf file.
>
>
>I ran simulation with TOU value for each of the optimums, based on an array
>of 
>18 sharp 165, sb2500 inverter.
>
>
>azim \ tilt	0	5	10	15	20	25	30	35
>40	45	50	55	60	65	70	75	80	85
>90
>
>ARRAY PERFORMANCE (%)
>
>West
>	-90deg	85.6	86.5	87.0	87.1	86.9	86.2	85.2	83.9
>82.3	80.5	78.5	76.3	74.1 
>71.7	69.3	66.7	63.8	61.0	58.2
>
>Optimum tilt
>
>Total annual  energy / TOU value at 15 tilt (18 sharp 165, sb2500)
>4040kwh $773.08	
>
>Southwest
>	-20deg	85.6	89.3	92.5	95.1	97.1	98.6	99.6
>100.0	99.7	98.9	97.5	95.4	93.0 
>90.0	86.6	82.7	78.4	73.6	68.7
>	-15deg	85.6	89.3	92.5	95.2	97.2	98.7	99.6
>100.0	99.8	99.0	97.6	95.6	93.1 
>90.0	86.5	82.5	78.0	73.2	68.1
>Total annual  energy / TOU value at 35 tilt (18 sharp 165, 
>sb2500)  		4618 kwh $856.49	
>
>South
>	0deg	85.6	89.2	92.3	94.9	96.8	98.3	99.1	99.3
>98.9	97.9	96.3	94.2	91.6	88.5 
>84.9	80.8	76.3	71.4	66.1
>Total annual energy / TOU value	at 35 tilt (18 sharp 165, sb2500)
>4588 kwh $837.23
>
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