On 25/11/2011 15:59, The Natural Philosopher wrote:

snip

This leads to a basic principle that can be expressed thus:

"Costs are proportional to the set of the worst cases. Earnings are
proportional to the average case."

This has a huge impact in terms of renewable generation from
intermittent sources. Basically the engineering has to be able to
absorb
the peak generator output (or the source must be throttled back and
the
energy discarded) BUT the income is calculated ion the average power
output - in the case of wind that's a 4:1 difference. Or more. That is
on average the size of the generator and link wires is 4 times greater
than on average, it needs to be.

Irrelevant for domestic PV installations. 4KW is well below the load
that even the meanest domestic connection will supply so no additional
infrastructure is required.

It gets worse. The backup likewise has to be as good as the worst case
wind output. One of the things that has become established over the
last
year or two is that national wind output can, on occasion, drop to as
near zero as makes no difference.

Solar PV is even worse. It's guaranteed to do this every night.

Solar PV doesn't really need any hot reserve, let alone spinning
reserve. With a multitude of very small generators over an extended
area the actual output could be predicted to very close limits merely
on the basis of cloud cover and date.


it doesn't matter.

You STILL have to ramp up gas to cope at sunset, and that gas needs to
be warmed up on the way, and while it ramps up, its wasting gas, and
when it ramps down, its losing stored heat.

Reading the above paragraph a stranger to this argument could easily
believe that a) PV goes from full output to zero in an instant and b)
that demand is at a constant level 24/7. For some of the year at least
declining output from PV would parallel declining demand lessening the
need for intervention.

It makes **** all difference if you KNOW what variation you have in
advance - you still have to DEAL with it.

Now what was that difference you were describing not so long ago - oh
yes, the difference between hot reserve and spinning reserve. Knowing
more accurately what is to come should make a difference.

Only in your mind.

Just because you are blind to the possibilities ...

You still have to put your foot on the accelerator to get up the hill
whether you know about it in advance or not.

But if you know there is no hill you don't need to plan for that
eventuality.

Solar PV may do little to help with the 5.30 pm peak but almost all of
its output (all for most of the year) will fall within the high demand
zone during the day unlike the output of windmills which is much less
predicable and close to random in distribution through 24 hours.


Wrong again, the forecasts are accurate to 70% typically.

Accuracy on which particular factors?

power output over time.

At what anticipation?

And I see that you at least think that maximum wind power at the time
of minimum demand is not a problem.

at the moment its relatively pathetic so it isn't.

You sure about that?

It is not the unpredictability of intermittency that is the problem its
the variation, and, in particular, the slew rate.

I am tempted to say what has that got to do with the price of fish.
Without cloud cover the rise of solar power from early daylight to
solar noon with be slow and smooth with the decline after noon
likewise. Cloud cover will have an effect but with the PV generation
widespread the rate of change due to changes in cloud cover will be
small.


Bull****

You have no real answer to that then.

clouds reduce power from a solar panel by 4-10 times.

Clouds are not amenable to prediction.

Cloud cover on a national scale is.

And none of it matters: all it does is reduce the amount of spinning
reserve you need. Hot standby still needs to be cued in for diurnal
valuations.

So a reduction in the need for spinning reserve is of no account then.

--
Roger Chapman