Re: Solar Cell Efficiency

From: Bill Kaszeta / Photovoltaic Resources (bill_at_pvri_remove_.biz)
Date: 03/23/05 

Date: Wed, 23 Mar 2005 03:22:04 GMT

On 22 Mar 2005 10:00:46 -0800, the1stlight@hotmail.com wrote:

>Before I get started, I'd just like everyone to know that I am not a
>scientist or professor or whatnot. I am a 17-year old high school
>student with an interest in physics and engineering, so if i say
>something that doesn't make scientific sense, then don't attack me for
>it. The reason that I ask is because i don't know to begin with.
>
>Is there any real feisible way to increase the efficiency of a solar
>panel? Because of the nature of solar energy, with the photons adding
>energy to the electrons of a photoconductor to knock them out, isn't
>the probability of a collison from a photon to an electron extremely
>low? Is there any way to possibly contain the electrons within a region
>that we can blast with light? Someone get back to me on this.
>
Efforts to increase solar cell efficiency include:

1. Multi-junction cells. The energy carried by a photon varies with
   wavelength and any energy above the bandgap of a junction
   is essentially lost as heat resulting in lower efficiency. Multi-
   junction solar cells are designed such at higher energy photons
   are absorbed in the first junction that has a higher bandgap while
   lower energy photons pass through to a lower bandgap junction.
   Problem is that the current through these now series connected
   layers is limited by the layer with the lowest current generation.
   The proportion of photon energies varies with time of day and
   season, making for complications.

2. Defects within solar cells (crystal dislocations, etc.) absorb
   electrons. High purity is better, but cost more.

3. There are tradeoffs between the doping of the semiconductor
   and the conductivity.

4. Then there is the problem of the front contact that has to allow
   light into the solar cell while making a low resistance connection.
   The lower percentage of grid covering (more light), the higher
   the losses due to series resistance.

There are both efficiency and cost tradeoffs. A simple one is
gold vs copper for grids. Concentrating the sunlight increases
the output per solar cell but adds the need for the lenes, etc.
and to aim the lens at the sun.

Hope this helps.
Bill Kaszeta
Photovoltaic Resources Int'l
Tempe Arizona USA
bill@pvri-removethis.biz

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