The Naked Scientists

The Naked Scientists Forum

Author Topic: Solar energy  (Read 3717 times)

Offline realmswalker

  • Sr. Member
  • ****
  • Posts: 205
    • View Profile
Solar energy
« on: 04/06/2006 03:54:56 »
Can you guys answer a few questiosn i have? Or provide useful links or information?
I look but cant find any that are particuarly useful...
Im looking for things like how mcuh energy per square foot falls on the earth from the sun. What is the current highest efficiency of solar panels(how much of the sunlight that hits them is converted to energy). What is the cost per foot of solar panel?
How do solar panels work?
I know solar panels need to be directly facing the sun for full efficiency, but i had an idea. Would it be possible to use prisms to bend light so that it didnt matter as much if the solar panel was not directly facing the sun?
How does the intensity of the light on the solar panel affect it?
Does color(or wavelength) matter at all?
Why is silicon used in solar cells?
Why not carbon or germanium?
On a related topic, is it possible to, without using energy, convert a wavelength of light to a different one?
Alot of questions i know, but im just curious.


 

another_someone

  • Guest
Re: Solar energy
« Reply #1 on: 04/06/2006 10:30:50 »
 

Offline Hadrian

  • Neilep Level Member
  • ******
  • Posts: 2175
  • Scallywag
    • View Profile
Re: Solar energy
« Reply #2 on: 04/06/2006 11:57:20 »
Thanks for putting light on that for me!

:D:):D:D

What you do speaks so loudly that I cannot hear what you say.
 

another_someone

  • Guest
Re: Solar energy
« Reply #3 on: 04/06/2006 12:38:06 »
quote:
Originally posted by realmswalker

Can you guys answer a few questiosn i have? Or provide useful links or information?
I look but cant find any that are particuarly useful...
Im looking for things like how mcuh energy per square foot falls on the earth from the sun. What is the current highest efficiency of solar panels(how much of the sunlight that hits them is converted to energy). What is the cost per foot of solar panel?
How do solar panels work?
I know solar panels need to be directly facing the sun for full efficiency, but i had an idea. Would it be possible to use prisms to bend light so that it didnt matter as much if the solar panel was not directly facing the sun?
How does the intensity of the light on the solar panel affect it?
Does color(or wavelength) matter at all?
Why is silicon used in solar cells?
Why not carbon or germanium?
On a related topic, is it possible to, without using energy, convert a wavelength of light to a different one?
Alot of questions i know, but im just curious.



Cost will depend on many factors, the more efficient crystalline solar cells are going to be more expensive than the less efficient amorphous ones, and in between one has polycrystalline.

One example of retail cost, in small quantities, for very small solar panels, is:

http://www.bullnet.co.uk/shops/test/solar.htm
quote:

Code: [Select]

Model    Maximum   Maximum     Maximum     Short      Open      Wt      frame        Price
         Power     Operating   Operating   Circuit    Circuit           L x W x D
                   Current     Voltage     Current
         Pm(W)     Ipm (A)     Vpm (V)     Isc(A)     Voc(V)            (mm)
SP9WC          9        0.55        17         0.57      21.6  1.5kg    346x286x25     59
SP15WC        15        0.83        17         0.88      21.6  2.2kg    436x286x25     85
                                                                        416x306x25
SP22WC        22        1.25        17         1.5       20.2  2.8kg    616x286x25    129
                                                                        426x416x25
SP60WC        60        3.31        17         4.0       20.7  6.2kg    976x446x38    259



No doubt that wholesale prices for massive solar arrays would be very much different to that.

Since one can judge how much electricity is required to power a light bulb, and how much light one obtains from starlight, it is clear that even if one could obtain 100% efficiency of conversion, one could not extract more energy out of starlight than would be available to power a light bulb that would have the same intensity of light as that observed under starlight.

It is certainly possible to use prisms or lenses (or even mirrors) to bend light towards a solar panel, but is it just as easy to torn the solar panel towards the Sun (the solar panel being no heavier than the prism is likely to be).

The wavelength of light matters in two ways.  In general, the shorter the wavelength, the more energy exists in the wave.  Beyond that, any photoelectric effect tends to be optimised for a particular wavelength of light, depending on the particular band gap energies of the semiconductor junction.

I have not yet heard of any success in creating semiconductors using carbon (although ofcourse nature does use carbon chemistry in photosynthesis, so the possibility clearly exists for us to use it).

Germanium has been used, but silicon is a widely available substance with which we have enormous experience in the manufacture and use of, and thus its use allows us to leverage existing manufacturing technology (as well as having a very widely available raw resource).

Even selenium has been used in the past, but is not particularly efficient (even by comparison to the relative inefficiency of the other technologies currently available).

Converting light from one wavelength to another is what fluorescence and phosphorescence are.   Fluorescence will only down convert the frequency, but  phosphorescence can up convert as well as down convert.



George
« Last Edit: 04/06/2006 13:17:55 by another_someone »
 

another_someone

  • Guest
Re: Solar energy
« Reply #4 on: 04/06/2006 12:44:48 »
http://en.wikipedia.org/wiki/Solar_panels#Solar_photovoltaic_panels
quote:

Solar photovoltaic panels contain arrays of solar cells that convert light into electricity. Solar cells, or PV cells, rely on the photovoltaic effect, which describes how certain materials can convert sunlight into electricity to absorb the energy of the sun and cause current to flow between two oppositely charged layers. Individual solar cells provide a relatively small amount of power, but electrical output is significant when connected together as an array making up a panel.

On a bright day, the sun delivers about 1 kW/m to the Earth's surface. Typical solar panels have an average efficiency of 12%, with the best commercially available panels at 20%, and recent prototype panels at around 30%. This would result in 200 W/m. However, not all days have bright sunlight, and therefore not enough solar energy can be captured.

At middle northern latitudes, taking the daylight cycle and weather conditions into account, on average 100 W/m in winter and 250 W/m in summer reach the ground. With a conversion efficiency of about 20%, one can expect to obtain between 20 and 50 watts per square meter of solar cell. The Sahara desert, with less cloud cover and better solar angle, one can obtain closer to 83 W/m. The area of unpopulated Sahara desert is over 9 million km, which if covered with solar panels would provide 750 terawatts total. The Earth's total energy is around 14 TW at any given moment (including oil, gas, coal, nuclear, and hydroelectric power



http://en.wikipedia.org/wiki/Solar_panels#Theory_and_construction
quote:

Solar photovoltaic panels


Crystalline silicon and gallium arsenide are typical choices of materials for solar cells. Gallium arsenide crystals are grown especially for photovoltaic use, while silicon crystals are available in less-expensive standard ingots. These ingots are produced mainly for consumption in the microelectronics industry. Polycrystalline silicon has lower conversion efficiency but also lower cost.

Crystalline ingots are sliced into wafer-thin disks, polished to remove slicing damage, dopants are introduced into the wafers, and metallic conductors are deposited onto each surface: a thin grid on the sun-facing side and usually a flat sheet on the other.[2] Solar panels are constructed of these cells cut into appropriate shapes, protected from radiation and handling damage on the front surface by bonding on a cover glass, and cemented onto a substrate (either a rigid panel or a flexible blanket). Electrical connections are made in series or in parallel to determine total output voltage. The cement and the substrate must be thermally conductive, because the cells heat up from absorbing infrared energy that is not converted to electricity. Since cell heating reduces the operating efficiency it is desirable to minimize the heating. The resulting assemblies are called solar panels or solar arrays.n





George
« Last Edit: 04/06/2006 12:48:36 by another_someone »
 

The Naked Scientists Forum

Re: Solar energy
« Reply #4 on: 04/06/2006 12:44:48 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums