Re: Research: Wind power pricier, emits more CO2 than thought

On Jul 19, 2:27 pm, disgoftunwells <disgoftunwe...@xxxxxxxxxxx> wrote:
On 19 Jul, 19:48, "rlbell.ns...@xxxxxxxxx" <rlbell.ns...@xxxxxxxxx>
wrote:

On Jul 18, 12:36 pm, disgoftunwells <disgoftunwe...@xxxxxxxxxxx>
wrote:

On 18 Jul, 17:01, "rlbell.ns...@xxxxxxxxx" <rlbell.ns...@xxxxxxxxx>
wrote:

- Nuclear - if you look at the cost models, the overriding cost driver
is cost of capital. The French Government had a low cost of capital is
therefore able to supply very cheap electricity. The next biggest
variable is uncertainty over construction costs. I would expect
nuclear to be cheaper than the current cost of wind power. However,
Britain is not going to build more that a dozen nukes, which could
provide a maximum of 40% of the electricity supply.

Did they pass laws banning the construction of more than dozen?

For better or for worse, in effect and by default, yes. (Except on the
other side of the channel).

So, in truth, the UK has not irreversibly banned further construction.

- Gas: Cheap to build, but very expensive to operate. Given current
gas prices, on shore wind is cheaper. In future, gas should be used
for peaking units (or for home power generation - where its efficiency
can approach 100%).

When you talk about CHP and electricity production, at the same time,
you must sperate the heating efficiency from the conversion
efficiency. You must also seperate the electrical output from the
heat output. As a heat source, they are expensive, but thermally
competitive, however, their heating efficiency goes down when they are
also producing electricity (but it does produce electricity). As a
generator, they are comparable in output to a portable gasoline
powered generator, except that they are less efficient and more costly
(way, way too much waste heat). Their only excuse for existing is
producing heat and power at the same time. Getting electricity out of
them when they are not producing heat is really expensive.

I was looking for a cost competitive successor to the whispergen. That
could be a fuel cell or a small gas turbine, producing about 25%
electricity, 70% usable heat, and perhaps 5% waste (which is more than
a condensing boiler).

Going by the spec/info (and interpreting them as optimistically as
possible), the whispergen has an electrical conversion efficiency of
(1kw electric and 7.5 kw heat) 12%-- with a Sterling cycle! Sterlings
are actually a really good choice, as a well designed installation,
with appropriate duct work, can supply heat and electricity, draw
power and pull heat in from outside, or draw power and pump heat out
of the house. Another interpretation of the specs puts the efficiency
up to ~18% (0W electricity and 7.5kW heat to 1kW electricity and
12.3kW of heat). While not as good as a Carnot engine, the Sterling
is as good an engine as can be built (unless you care about size--
they are very large for their output).

The words 'small', 'gas turbine' and '25% efficiency' do not go
together. Much of the losses in a gas turbine arise from air slipping
past the blade tips. Large gas turbines get around this by having a
tiny clearance, relative to their blade length, but the smallest
possible clearance gap is not that different for a two foot blade, as
a two inch blade (once both units are at speed and up to normal
operating temperature). Another loss is heat passing through the wall
of the combustor, and out of the engine, before the working fluid gets
to the turbine, which also unfairly penalises small units.

I would like to be wrong, but does anybody make a gas turbine CHP unit
under 50kW?

Not sure. I've seen quite a few whispergen type units at about 10KWe -
good for blocks of flats and small factories.

I went to Whispergen's website-> Homes -> on-grid and all they
mentioned was the 1000 We unit.

You mentioned earlier you expected a hydrogen economy. A better goal
might be domestic fuel cells. These can convert gas to electricity at
about 40%. Capturing the vast majority of heat should be trivial.

The only problem with the domestic fuel cells that you suggest is that
they are dependant on a fossil fuel, natural gas, for their fuel
supply.



Two and a half times the cost of a nuclear generated kWhr is still
less than the cost of a peaking unit kWhr.

Gas would have to go up a lot more for that.

I said peaking power, not gas-fired combined cycle plants which are
almost as bad at load following as nuclear plants. Generators that
you can afford to switch on at a moments notice and turn off again
after less than an hour are expensive per kilowatt and per
kilowatt*hour

And for storing energy a VRB unit will be much more cost effective
than hydrogen.

If there is a market for hydrogen, the back-to-back conversion
efficiency is less of a problem, as peaking power comes from
temprorarily halting hydrogen production.



There are schemes like this though:http://www.vrbpower.com/technology/ess-specifications.html

It would be interesting see what the cost is per GWhr of storage. If
you were designing a HVDC grid (as a CEGB / French Government might,
rather than having economics dictate it), it might make sense to have
a few GWHr storage plants at the ends of the HVDC net.

Storage of real energy is less important for HVDC systems than a solid
source of reactive power. Once you get past driving large motors, you
really do not want to use inverters-- they are too inefficient, so the
receiving end of the HVDC link has to have enough reactive power to
excite the rectifier bridge. HVDC links cannot transfer reactive
power and both ends of the link are heavy reactive loads. Also, there
is no coupling between the ends of the HVDC link, so weakness at one
end cannot be assisted by stiffness at the other and the large
inductance of the HVDC line will prevent fast power responses.

So if I was designing an HVDC grid, there would be large synchronous
reactances to provide reactive power, and their rotational inertia
would stiffen the grid long enough to adjust power distribution
(alternatively, a diesel engine helps keep the system frequency from
falling).

As I understand HVDC beats AC for lengths of more than a few hundred
kilometres, or under water.

There are even special situations where it beats out AC for lengths of
approximately zero km-- connecting 50Hz regions of Japan to the 60Hz
regions (previously done by motor-generator sets that run at the same
mechanical speed for the different electrical frequencies).

The transfer of power is controlled by computer, rather than
reactively following loads.

Not even a computer. There is effectively a knob that adjusts the
trigger pulse for the thyristors. For steady state operation, the
knobs at each end have to be at equal and opposite positions (after
accounting for losses at the driving end). Not following loads is a
feature when you want to avoid power wheeling, but a bug when trying
to dynamically maintain system stability during an event.

Any distribution system is limited in the power it can transport, so a
storage system at either end can be useful.

Storage is usually some combination of limited availability (pumped
storage), low efficiency, or high cost. For stability purposes,
spinning reserve is good, sheddable loads are better, but fast
responding peaking units will do

.

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