[mythtv-users] valuing electricity savings (was: transcoding HD stuff)

[Gavin Peters]

On Thu, Sep 24, 2009 at 06:50:19PM -0500, Christopher Meredith wrote:
> >
> > FWIW, I would bet that the additional cost of the power used in
> > transcoding all your recordings to a 1/4-sized or 1/9-sized MPEG-2 for
> > playback with your PVR-350 plus the lack of good power-saving features
> > in the old system that's running the PVR-350 would pay for a nice Core 2

(more elided text)

> I seriously doubt that.

It's hard to say without working numbers, and we don't have enough
information to do that.  I'm going to help the situation by making
numbers up.

Where I live, in New England, the marginal cost of electricity to me
is about US$0.20/kwh.  Saving one watt of base load works out to about
0.73kwh/month, $0.15/mo or $1.80/yr.

That's an ongoing expense, so we should find a way to convert that to
capital.  I see two ways; as a perpetuity (assume you saved that money
_forever_), or over the life of a computer, say five years.  Let's
talk about the second.

Depending on the discount rate you put on future cash flows, the
present value of five years of saving $0.15/mo is $8.14 at 4%, and
$7.76 at 6%.

So, if you can save 30W of base load, you're saving between $244.20
and $232.80 over five years.  How much would the old computer sell
for?  How much does the new one cost?

- Gavin