cost per kWh [RE-wrenches]

[Bill Brooks]

Ray,

The use the of the term "fill factor" in the PV world relates to the I-V
curve not the physical coverage of active material in a module. The
definition of fill factor is (Vpmax x Ipmax)/(Voc x Isc). Some crystalline
modules will have a fill factor of 75% at operating temperatures, and an
array fill factor of 70-72%. My AstroPower crystalline modules are using
recycled cells from the computer industry and the fill factors tend to be
about 68% on the module level at operating temperature and 60-62% on the
array level.

Amorphous Silicon arrays tend to have even lower fill factors of 52-60%.

Low fill factor means that the operating voltage is well below the open
circuit voltage. High fill factor means that the operating voltage is closer
to open circuit voltage. A battery-based system will operate closer to the
maximum power point with a low fill-factor array because of this operating
voltage difference. Ultimately it all depends on the application the module
was designed for. Since many 36-cell PV modules are designed to work in the
hottest climates in the world, their operating voltage may be above what is
absolutely necessary in more mild parts of North America.

Moral of the story is use lower fill factor modules on fixed voltage
systems. This is one of the reasons why UniSolar makes claims that they
produce more energy per rated watt. Since a-Si has a low fill factor, it
better matches the max power voltage than say, a BP 585 module (high fill
factor).

Let me know if this makes any sense.

Bill.


-----Original Message-----
From: Jay Peltz, Peltz Power [mailto:jay at asis.com]
Sent: Saturday, May 31, 2003 7:06 AM
To: RE-wrenches at topica.com
Subject: Re: RE: cost per kWh [RE-wrenches]


Hi Bill,

I don't see how fill factor is related to max power, unless you are using
the term in a different way than I do.

I use fill factor as a relationship between the amount of area the cells
cover vs the total area of the panel.

You are using fill factor as a relationship between battery voltage and max
power volts?

thanks,

jay

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