On 10/10/16 08:16, Brian Gaff wrote:
The problem seems to be that no matter what you try to generate power from
any naturally occurring force like wind or tides or even the sun, you
actually are taking power from the earth and if you do enough of it, you
alter the environment in some way, often a way which was unexpected.

That is ONE problem Brian.
Environmental impact. Essentially 'renewable energy' comes in low power
density, so that automatically and irrevocably means, with no
possibility of technological development changing it, that the devices
used to capture it will be *LARGE*.

Let me repeat that for the avoidance of doubt. Low power density means
that all renewable power generation will be *LARGE*. And hence of high
environmental impact.

And potentially expensive.

Let me stress again that this is simply unavoidable. Anything big enough
to get the very low grade energy out of the environment will have to be
big enough to make a significant impact on the environment. There simply
is no answer to that.


The second problem is intermittency. Not unpredictability, but the sheer
fact that the power is not coming from an energy store, but has to be
generated and used when the energy source is available. Again no amount
of clever technology cam make the wind always blow steadily or the sun
always shine, at least on the earth's surface.

And if attempts are made to store the intermittent energy, you run into
two further problems.

Firstly it's very costly to store large amounts of electrical energy.
and secondly is very dangerous. Depending on the energy density it may
also be quite big, and therefore exact a further environmental penalty.

Then intermittency adds another problem. If the store and the source are
not co-located, a further problem arises with intermittency, and that is
the connectivity. High peak to mean power flows generate cables more
costly than the mean flow would dictate. And these larger cables too,
have more environmental impact.

Finally, if the dispatch side of the generation needs are not handled by
(rechargeable) stored energy, they have to be handled by some other
access to stored energy - typically fossil or nuclear. This means
complete duplication of capital equipment, since all renewable sources
are capable of simultaneously dropping to zero output over very large
geographic regions, and if not co-operated with conventional power, they
must incorporate very long, expensive and vulnerable inter-connectors.

Yet more cost, yet more environmental impact.

What needs to be stressed is that all these drawbacks are not something
that can be 'developed out' of renewable energy. *THEY ARE INHERENT TO
THE VERY NATURE OF IT*.

Renewable energy will always be large, and will never be more than a
partial solution. Simply because the power density is low, and the
source is inconstant.

You may ask 'why then are we bothering with it?'

Why indeed?


--
The theory of Communism may be summed up in one sentence: Abolish all
private property.

Karl Marx