# Hi and Help

Tevion
Im trying to get to grips with factors? and want to check my methodology, so:

It all about solar panels..I've calculated how much power the cell will produced @ AM1.5 this is 73 mW cm-2 .

Now my question is, i have to calculate the short fall by a factor of 1000 due when its used indoors for example. So am i right saying:

73 mW cm^-2
/ 1000

= 7.3^-3 mW cm^-2

- 73 mW cm^-2

= 65.7 mW cm^-2 (is this the shortfall answer)

Any help would be appreciated. and if you have any subsequent Q's, il try and answer them

Tevion
i can't believe nobody can help!

Homework Helper
Welcome to PF!

Hi Tevion! Welcome to PF!

If by shortfall you mean a decrease of 1/10, or 0.1, it's probably easier, instead of multiplying by that factor and then subtracting, to multiply by (1 - the factor), in this case (1 - 0.1), = 0.9.

So, having worked out the factor, just say:

73 mW cm-2 x 0.9 = 65.7 mW cm-2.​

Or if you mean a decrease of 1/1000, or .001, it's

73 mW cm-2 x 0.999 = 72.927 mW cm-2.

Tevion
So can you clarify how to deduce

7.3^-3 mW cm^-2

by a factor of 1000.

Thanks Tim

Homework Helper
Hi Tevion!

I'm honestly not sure what you mean.

Do you mean reducing it by one part in 1000, or to one part in 1000?

You were orignally talking about the efficicency of solar panels indoors, and a reduction of 1/1000 seems far too small, while a reduction to 1/1000 seems far too large.

Anyway, starting with 7.3, a reduction by 1/1000 would be 7.2927 (or 7.29 approx), while a reduction to 1/1000 would be .0073.

What is it about factors that's worrying you?

Homework Helper
Hi Tevion!

Thanks for the PM.
Tevion said:
"When used indoors, the avaiable power (73 mW cm-2 .) from a solarcell maybe reduced by a factor of 1000. Calculate the shortfall in power generation needed for the calculator if the power output of the solar panel is reduced by this amount."

What do you make of that?

Well, it seems a slightly strange way of putting it (I would say "a factor of 1/1000", not "a factor of 1000" ) … but I'd say they mean 0.999 x 73.

Tevion
I still don't quite understand it, how did you arrive @ the 0.999?

Im about to send you a PM :)