Re: Are Solar cells are designed to last only 25 years ?

  Solar cells do not last only 25 years.  In fact, if you had one 
operating in an environment totally protected from particles striking it, 
it would last forever (well, not FOREVER, but that's a whole other bucket 
of beans).  Let me give you an overview of how solar energy works to 
clarify.
  The part of solar panels that collect the energy, are called solar photo 
volatic cells.  This means that they are voliatile (unstable, easily 
agitated) to the sun's (solar) light energy (photo). When photons strike a 
solar cell, they are almost all absorbed, partially because the cells are 
colored dark purple (dark purple is the most photo-absorbant color).  The 
stuff that the cells are made of react to the sunlight's energy and turn 
it into a flow of electrons.  Specifically, open spaces where electrons 
could be are filled by electrons, which come from the converted photons. 
This creates an electric circuit.  Energy.
  So, it flows and flows, until theres no light, and then it just sits 
there.  There's nothing to wear out, or run out.  Nothing is depleted or 
used up.  So, why don't they really last forever?
  They can wear out from being bombarded by small, dense, and very quick 
particles.  We don't have a lot of them here on our green Earth, but up in 
space they're all over.  So if you have a big panel sitting in space, it's 
going to get hit now and then.  Now, how likely are those particles to 
damage a solar panel?  Not very.  When they say "25 years," they really 
mean that by that time it will have been hit by something(s) big and fast 
and dense enough to destroy it.  Of course, that isn't true.  A well 
protected panel can last for much longer than that in space.
  So, you want to know what will happen to our space ordinance?  Well, the 
ones in space have to be maintained.  We have to keep repairing not just 
the solar panels, but all the other parts too. All things on the outside 
of space ships and such get hit by particles in space.  As for the landers 
on Mars, they don't have to worry about that, but they are no longer 
functional anyway.  Right now, solar energy is not enough to power them, 
it can only be used as a supplement.  Usually they have a radioactive 
power source like plutonium.

(NOTE: The "whole other bucket of beans,"  if you're interested, is 
radioactive decay.  All things are slowly being broken down by what is 
known as the weak force.  Things that are known as radioactive are more 
easily broken down and release high amounts of radioactive energy.  
However, all things are being broken down at some speed, even the atoms in 
you and me.  That's why there is a small amount of normal radiation all 
over the world.  So, eventually, all atoms will be broken down into their 
components.  But this takes many many billions and trillions of years, so 
I wouldn't worry about your solar panels in that respect.)