h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

a solar panel is a device that is used to move polution from one place to another.

Why do you say that?

I've heard that one before..

It certainly used to be true, that the amount of energy used in mining, processing the materials and manufacturing a solar panel was greater than the total energy output of a panel during it's usable lifetime.

So in effect all you had done was to move the pollution from the site you installed the panel to the mines and factories.

It's been a while (years) since I last looked up the figures so improvements in the design and manufacture of panels will have improved the ratio since, but I doubt if they will be in overall energy "profit" yet

I takes five years for a solar panel to give back the energy that was used to produce it, and its life expectancy is 20 years.

sorry but that just is not true, solar cells loose efficency very fast in the sun.

It is possible to make a solar/steam generator that can last long enough to get a pay back, but even that is borderline.

Photovoltaic cells just are not yet efficient enough. Though I am sure that one day they will be.

You say you get a 400% return on investment (5yrs pay back and 20 yrs life). believe me if there was that much profit in solar cells, we would be using them and someone would be getting rich.

The world record of efficiency is 25% for crystalline cells, and 11% for amorphous cells. The life expectancy of crystalline cells is 20 years, I don't know how much they degrade though, but after 5 years the production enery has returned. Amorphous cells work for approximately 15 years and work with positive balance after 3 years. Their degradation (due to the Staebler-Wronski effect) is more or less 3%. Crystalline cells degrade less.

The *real* problems of solar cells are that they are expensive, you need a large area, and energy is produced when not so much enery is actually needed (namely during daylight).

I knew that there were two different types of solar panel, is one better than the other? I used to 'debate' with Ashley about this, because he said they weren't much good either. I did a bit of research (toyed with the idea of writing an entry) and it did seem as if one type was much better than the other. I'll have to see if I can find out again.

For ordinary use crystalline cells are much better, and I think that typically you can only by cells of that type. I gave the figures: 25% versus 11%. This is the part of sunlight that is actually transformed to electrical energy.

The ones I was looking at were for heating and water only - I tried to become a 'showhouse' for those (cheaper!), as I have a south facing garden that gets loads of sunlight. They suddenly decided that 'they had enough showhomes in my area thanks' when they found I worked for the BBC. I assume they thought I was from Rogue Traders and had something to hide. So a lucky escape I guess.

Okay, but that seems to be something totally completely utterly different. I was talking about photovoltaics, but your devices apparently are mere solar heaters. That's like comparing cars and bikes.

Solar heaters are viable in areas that have a large number of sun days. Simply because they last a long time.

Photovoltaic cells that hit 25% use a lot of energy to make, so they can not pay for them selves.

It is so simple, if solar cells produced more energy that it took to make them, then we would have people getting rich by selling us free energy.

SOLAR CELLS DO NOT HELP THE ENVIRONMENT!

Si I should be thinking of solar heaters, not trying to power my entire house with solar panels?

> It is so simple, if solar cells
> produced more energy that it
> took to make them, then we
> would have people getting rich
> by selling us free energy.

I don't see the logic in this. Again: The primary problem is that they are expensive in terms of *money* in comparison with other sources of energy. Of course fossile resources are much cheaper, but we hadn't had to create the forrests that turned into oil a couple of million years ago, had we?

To Mina: That is a question that cannot be answered this way. You have to ask a local expert I'm afraid.

what hasmoney" got to do with it. you need electrical energy to create the cells. This energy is more than you will get back. Money is just a measure of energy in.

> You need electrical energy to create the cells.
> This energy is more than you will get back.

Do you have Internet references for this?

A late addition to the thread
Work on improving the efficiency of solar cells continues.

http://slashdot.org/articles/04/05/09/1454252.shtml?tid=134