Re: Sahar solar farm project to power Europe?

mike weber <fairportfan@xxxxxxxxx> wrote:
But then they started talking about a new transcontinental power
grid to deliver the juice northward ... and they said it would be
DC, because AC transmission involves too much loss.

Huh?

Has anybody else heard anything else about this?

I haven't heard about that particular project, but it makes perfect
sense to me.

The power capacity of a line is the product of the RMS voltage and the
RMS current. The allowable peak voltage depends on the size of the
insulators. The allowable RMS current depends on the thickness of
the conductor and on what it's made of. And of course you want to
maximize the power capacity (since power is what customers pay you
for) while minimizing the size of the insulators and the thickness
of the conductors (since those cost you money).

All this is true for both AC and DC. But with AC the peak voltage is
sqrt(2) (about 1.414) times higher than the RMS voltage. With DC the
peak voltage is the same as the RMS voltage. So the same line can
carry sqrt(2) times more power.

It costs something to convert current from AC to DC and back again.
But this cost doesn't depend on the length of the line. Since the
cost of thicker conductors and larger insulators increases linearly
with the length of the line, it's obvious that there's a length above
which it makes sense to use DC, and below which it doesn't.

(This is the sort of economic reasoning that's conspicuously absent
from arguments that since everyone uses roads to some extent, directly
or indirectly, everyone should pay equally for them. If everyone was
taxed equally to provide electric power, no matter how or where it
was produced, transmitted, and consumed, we'd probably still be using
Edison's original inefficient system, as there would be no incentive
to improve it.)
--
Keith F. Lynch - http://keithlynch.net/
Please see http://keithlynch.net/email.html before emailing me.
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