[SPAM] - RE: Rain-X on module glass? [RE-wrenches] - Email found in

[Joel Davidson]

Chris,

Good points. One side does not fit all. Load, climate, array configuration,
batteries, line-tie, etc. require the designer to specify each system.

Black framed, black Tedlar modules look better than round-cell polka dot
solar arrays, but all-black modules 53 watt Hoxan modules produced 15% less
power at 25 degrees C. I think other crystalline cell modules perform
approximately the same. The lower voltage may not be a problem if you only
need 14.8 volts for battery charging.

In the late 1980s in Tokyo a PV system line-tie inverter was not turning on
due to low voltage. The PV array was made of black framed, black Tedlar
solar module that were flashed in with no ventilation to give the appearance
of a building integrated PV array. Cell temperature in September was 83
degrees C.

>From a 1993 paper titled "Characteristics of PV cell temperature on
stand-off type PV array" presented at the Japan Solar Energy Society:
Measurements and analyses have been made on simulated houses to identify
output variations in photovoltaic cells installed on roofs due to
temperature rise. Measurements of the photovoltaic cell temperatures were
made on stand-off type photovoltaic arrays installed on roofs made of
Japanese roof tiles, roofing slates, and metal plates. A time band windless
with long and strong insolation in summer was selected to identify the
highest values. As a result, it was found that the slate roof had the
largest temperature rise, and the Japanese tile roof had the smallest. As a
result of analyzing the data, it was inferred that temperatures of the PV
cells in an atmospheric temperature of 40 degrees C and an insolation
strength of 1 kW/m2 were from 72 C to 81 C and the output voltage would drop
down to 155 V to 162 V against the standard 200 V. With regard to air
cooling effect, a breeze with an average velocity of even as gentle as 1 to
2 m/s can reduce the temperature by 10 C or more as compared to
windlessness. Very little difference was found in cooling effect between the
kinds of roofing materials.

>From PowerLight's booklet Understanding your PowerLight Solar System "In
general, PowerLight assumes a minimum of 8% performance degradation (for
early spring and late fall months) to a maximum of 30% (for mid-winter
months) for systems in regions that experience significant snow in winter."

Best regards,
Joel Davidson

----- Original Message ----- 
From: "Christopher Freitas --- OutBack Power" <cfreitas at outbackpower.com>
To: <RE-wrenches at topica.com>
Sent: Thursday, January 08, 2004 5:30 PM
Subject: RE: [SPAM] - RE: Rain-X on module glass? [RE-wrenches] - Email
found in


> Jason Fisher wrote:
> > Not to be too much of a smart-a** but aren't we concerned about how
> > modules will do in the sun?
>
> Boy - these grid-tie guys think all that matters with PV is the peak
> summer output...
>
> In off-grid systems the performance in the winter is more important - so
> the module shedding snow sooner means more charge in the battery. The
> slight temp increase does not affect the winter performance
> significantly.  In the summer the batteries would be full by noon
> typically so it doesn't matter if they are much hotter.
>
> Don't forget to mount the modules side-by-side in a "vertical" position
> (per module) instead of the "horizontal" way with one above another. The
> snow will slide off much better when arranged one way versus the other.
>
> Arthur Rudin of Sharp had mentioned that the Japanese have been trying
> out melting the snow on PV arrays by back-feeding current into the
> modules.  Seems like a crazy idea to me...
>
> Christopher Freitas
> OutBack Power Systems, Inc.
> cfreitas @ outbackpower.com
> www.outbackpower.com
> Arlington WA USA
> Tel 360 435 6030

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