Re: ENERGY: State of the Art in Photovoltaics?

From: Michael S. Lorrey (retroman@turbont.net)
Date: Wed Sep 06 2000 - 15:08:26 MDT


Eugene Leitl wrote:
>
> Michael S. Lorrey writes:
> >
> > Actually, for thin film amorphous, 10% is about exactly what the conversion
> > efficiency is. I was wondering where you get your 'insolation' figure from. The
>
> True, but you can get 20% panels, too, and more, if price is
> irrelevant (~32% is about the best we can get iirc with multilayer
> GaAs). With 10% I'm operating on the low end of the efficiency
> spectrum, not coincidentially the best efficiency in wattage/$
> produced.

Yes, that is my experience. The higher you go in efficiency, the cost rises
faster, so its actually the least efficient technology that is most affordable
and cost effective.

>
> > atmosphere cuts solar flux from just over 1.4 kw/m^2 down to just over 1 kw/m^2.
>
> The insolation figure is totally ad hoc, since I don't have access to
> my library, and a websearch via dialup in Krautland is a bear. I just
> thought that 0.5 kW/m^2 on the average over a 10 h period in
> California-type area is the about the right ballpark figure, if the
> solar flux constant is 1.3 kW/m^2. I would of course welcome seeing
> real numbers.
>

You only get the 10 hour period if your panels are consistently reoriented to
face the sun directly. Static panels will have a sine wave of intensity as the
sun moves into and out of direct opposition (which in reality only occurs twice
a year at most), in addition you have the sine wave of intensity imposed by the
variance in the amount of atmosphere the sunlight travels through during the day
causing variance in the insolation on site.

> > > 2) solar cells do not require direct sunlight to generate
> > > juice. diffuse daylight does nicely, especially when we're talking
> > > about amorphous cells.
> >
> > Sure, but their efficiency decreases as flux decreases, and total flux does
> > decrease with diffusion, as visible is converted to IR. If your flux drops by
>
> I thought thin-film amorphous did at least NIR rather well.

Its works well as a sensor, but not really for power except at higher
intensities, which are high enough that actually a thermal fluid system would be
more effective.

>
> > half due to diffusion by cloud cover, and the efficiency drops as well as flux
> > drops, your output decreases markedly.
>
> I did not know the average number of cloudy days in California, and
> just took 365, assuming the few 10 days would not make a difference,
> as other parameters have been chosen rather conservatively, and this
> is a back of the envelope estimate.

Death Valley is one thing. LA is another completely, where smog cuts several
hours off of morning and evening sunlight. Don't know the exact number of sunny
days, but its not quite as much as residents would like us to beleive, but
definitely a significant number.

> Nitpicker!

Ayuh!



This archive was generated by hypermail 2b29 : Mon Oct 02 2000 - 17:37:22 MDT