[mythtv-users] [Slightly OT] solar power for all our gadgets

[Paul Gardiner]

Simon Hobson wrote:
> raphy wrote:
> 
>>  > That's the crux of it. If the heating is electric then there is ZERO
>>>  difference in efficiency - both the electric heating and light bulb 
>>> are 100%
>>>  efficient at turning incoming electricity into heat. For other forms of
>>>  heating there will be some saving - but I don't know what it will be 
>>> other
>>>  than "nothing like 80%".
>>>
>>
>> This is utterly wrong. I don't need to mention anything more than the
>> fact that your electric heater doesn't emit nearly as much or even the
>> same wavelengths of visible light that your light bulb does to debunk
>> that one.
> 
> Thank you for proving the point ! Lets not allow facts to get in the way 
> of prejudice.
> 
> So, I'm sat at home, and I've just pulled the curtains closed (which I 
> have actually, it's going dark). Say I have a light bulb consuming 100W 
> of electricity - and directly emitting 90W of heat. It's therefore also 
> emitting 10W as visible light.
> 
> Without ignoring the laws of physics, and in particular the law of 
> conservation of energy, could you please explain where that 10W goes to 
> if it doesn't heat up the room ?
> 
> 
> 
> OK I'll admit that after the nice warm day we've had here, the heating 
> isn't on. But it will be by the morning - a cold night is forecast. I 
> did say things are actually quite complicated.
> 
> PS - I don't actually have a 100W bulb, the lights in this room (like 
> the majority in the house) are CFL.

Simon is completely correct in what he is saying.

All devices output 100% of the energy they consume (other than ones that
involve nuclear reactions). It's a physical law: the conservation of
energy. The efficiency figures are because a light bulb is intended to
produce light, and only that fraction of the energy output is in the
form of light. The rest is mainly heat, and what ever it is it ends up
as heat, as does the light, when it has bounced around the room enough
times partly being absorbed on each bounce. So it is true that 100W bulb
puts 100W of energy out, that that energy ends up as heat, and that that 
heat almost all ends up in your house. You in effect have a 100W heater 
that lights your room as a side effect for free.

Practically, though, I think you can ignore this fact. The case where
it really doesn't matter that a light bulb is inefficient at generating
light is a rare one:

1) The whether is cold enough to have the heating on.

2) The heating is electric (and not a heat pump).

3) The heating is thermostatically controlled.

4) The bulb is in a room that is in the range of the thermostat.

Only then will the heat produced by the bulb cause the heating to cut
back by a similar 100W. If your heating is gas, it makes an enormous
difference. Using ordered energy to make heat (other than with a heat
pump) is extremely inefficient. The inefficiency is at the power station
and is an unavoidable consequence of another physical law to do with
entropy. You can't generate oredered energy (electricity) from
disordered energy (heat) without a huge proportion ending up in the
outside as heat, where it is of no use. Use of gas doesn't involve
that inefficiency (hmmm, as far as I know). So, if your bulb heats
the room a bit, and your gas central heating cuts back in response,
you are trading inefficient heating for efficient heating, which
isn't so good.

Cheers,
	Paul.