Dust down those orbital power plans

The Australian Government has, for reasons that have much to do with
politics, and little to do with the environment, decided to throw $Au 10
billion into the bottomless pit that is renewable energy.

Lest it all get turned into yet more solar panels and windfarms, I
invite all comers to submit their plans for orbital power satellites. At
least then we might get some technological advance for our money, even
though I doubt we'd actually see any orbital power.

Sylvia.

On Jul 12, 4:17 am, Sylvia Else wrote:
The Australian Government has, for reasons that have much to do with
politics, and little to do with the environment, decided to throw $Au 10
billion into the bottomless pit that is renewable energy.

Lest it all get turned into yet more solar panels and windfarms, I
invite all comers to submit their plans for orbital power satellites. At
least then we might get some technological advance for our money, even
though I doubt we'd actually see any orbital power.

Sylvia.

Please let me know more, especially who to talk to. I am hkhenson on
Skype or hkeithhenson at gmail dot com

Keith

On 14/07/2011 10:14 AM, Keith Henson wrote:
On Jul 12, 4:17 am, Sylvia wrote:
The Australian Government has, for reasons that have much to do with
politics, and little to do with the environment, decided to throw $Au 10
billion into the bottomless pit that is renewable energy.

Lest it all get turned into yet more solar panels and windfarms, I
invite all comers to submit their plans for orbital power satellites. At
least then we might get some technological advance for our money, even
though I doubt we'd actually see any orbital power.

Sylvia.

Please let me know more, especially who to talk to. I am hkhenson on
Skype or hkeithhenson at gmail dot com

Keith


It'll be a while. The government has made the announcement, and
supposedly has the numbers in parliament, but the legislation won't be
passed until later this year. A single by-election in the meantime could
yet lead to the whole thing unravelling.

Sylvia.

On 12/07/2011 9:17 PM, Sylvia Else wrote:
The Australian Government has, for reasons that have much to do with
politics, and little to do with the environment, decided to throw $Au 10
billion into the bottomless pit that is renewable energy.

Lest it all get turned into yet more solar panels and windfarms, I
invite all comers to submit their plans for orbital power satellites. At
least then we might get some technological advance for our money, even
though I doubt we'd actually see any orbital power.

Sylvia.


Didn't we go through this a couple of days ago?

On Jul 12, 9:17 pm, Sylvia Else wrote:
The Australian Government has, for reasons that have much to do with
politics, and little to do with the environment, decided to throw $Au 10
billion into the bottomless pit that is renewable energy.

Lest it all get turned into yet more solar panels and windfarms, I
invite all comers to submit their plans for orbital power satellites. At
least then we might get some technological advance for our money, even
though I doubt we'd actually see any orbital power.

Sylvia.

You could make a **** load of parabolic reflectors aimed at the hot
part of a Stirling engine, these things are about 6m wide and produce
about 10Kw
A Spanish comp[any makes them. The main problem is the colour, all
shiny and not a bit og brown or green on them :-)
\
Julian

Bohica Bohica wrote:
On Jul 12, 9:17 pm, Sylvia Else wrote:
The Australian Government has, for reasons that have much to do with
politics, and little to do with the environment, decided to throw $Au 10
billion into the bottomless pit that is renewable energy.

Lest it all get turned into yet more solar panels and windfarms, I
invite all comers to submit their plans for orbital power satellites. At
least then we might get some technological advance for our money, even
though I doubt we'd actually see any orbital power.

Sylvia.

You could make a **** load of parabolic reflectors aimed at the hot
part of a Stirling engine, these things are about 6m wide and produce
about 10Kw
A Spanish comp[any makes them. The main problem is the colour, all
shiny and not a bit og brown or green on them :-)

That's actually close to what the generating part of an orbital power
sat should be - lots of mirrors feeding sunlight to a Brayton cycle gas
turbine. Forget acres of solar cells, they are too heavy and too
expensive and too fragile.

A Brayton cycle engine in that size range is lighter than a Stirling
engine, no regenerator needed. Not as efficient, but cheaper and lighter
to launch.


-- Peter Fairbrother

On Jul 19, 5:48 am, Peter Fairbrother wrote:
Bohica Bohica wrote:
On Jul 12, 9:17 pm, Sylvia Else wrote:
The Australian Government has, for reasons that have much to do with
politics, and little to do with the environment, decided to throw $Au
10
billion into the bottomless pit that is renewable energy.

Lest it all get turned into yet more solar panels and windfarms, I
invite all comers to submit their plans for orbital power satellites.
At
least then we might get some technological advance for our money, even
though I doubt we'd actually see any orbital power.

Sylvia.

You could make a **** load of parabolic reflectors aimed at the hot
part of a Stirling engine, these things are about 6m wide and produce
about 10Kw
A Spanish comp[any makes them. The main problem is the colour, all
shiny and not a bit og brown or green on them :-)

That's actually close to what the generating part of an orbital power
sat should be - lots of mirrors feeding sunlight to a Brayton cycle gas
turbine. Forget acres of solar cells, they are too heavy and too
expensive and too fragile.

And it would be hard to scale up to the number needed for 100 GW/year
of new construction.

A Brayton cycle engine in that size range is lighter than a Stirling
engine, no regenerator needed. Not as efficient, but cheaper and lighter
to launch.

The turbines themselves are around 1/10th of a kg/kW. The
concentrating reflectors, radiators and heat absorbers seem to make up
the bulk of the satellite.

I have offered a spreadsheet before to anyone interested.

It's partly a refutation of an influential paper published
in 1962 and never revisited as far as I can tell.

What I did was very simple. In the radiation spread sheet, the first
column is absolute temperature, column B is deg C. Col C is
radiation per square meter at 0.95, D is at 0.1. E is how many square
meters per kW based on C (both sides radiate). D isn't further used.
Column E is the area to radiate on kW. F is the Carnot efficiency
from 1400 K down to the radiation temperature, G is the 75% of F based
on the typical real turbines. H is the square meters required to
collect one kW out at 100% of Carnot efficiency based on
1.366kW/meter^2. I is how much area it would take to collect sunlight
based on .75 of Carnot efficiency. I is the area it would take to
radiate heat from ideal Carnot, K is the area for real (.75) of
Carnot. L sums the areas for ideal Carnot cycle, M sums the radiator
area plus collector area at the temperature required to get rid of the
heat rejected by a real (75%) Carnot cycle.

This doesn't take into account the reflector (concentrator) loss or
the re-radiation loss from the working fluid heater, but I have
reasons to think both will be small.

Of course I could have expressed area as a function of the sum of the
two areas computed from radiation and Carnot efficiency as a function
of T and solved it analytically by setting the derivative to zero. I
find spreadsheets give me more insight though.

Assuming the radiator and collector mass per square meter is about the
same, then you can see from the graph that the minimum occurs a bit
above 100 deg C, which is far below the 370-650 deg C quoted in an old
paper he

http://contrails.iit.edu/DigitalColl...2article42.pdf

I can't say for sure what the mass per unit area of radiation or
collection are. I need to analyze a canvas tube (like an air
mattress) radiator filled with low pressure gas and air float
charcoal, Buckey balls or BeO. Assuming they are both around a
kg/m^2, a kW should come in around 3.2 kg. Turbines and generators
are around 0.1 kg/kW based on Boeing 777 engines. Transmitters have
been analyzed at less than a kg/kW. So giving room for such parts as
power conductors and the joint to the transmitter, it *might* come in
at 5kg/kW.

If anyone has some spare web space to hang a small xls file, I can
send it to you.

Keith

-- Peter Fairbrother

Keith Henson wrote:
[...]

Assuming the radiator and collector mass per square meter is about the
same, then you can see from the graph that the minimum occurs a bit
above 100 deg C, which is far below the 370-650 deg C quoted in an old
paper he

http://contrails.iit.edu/DigitalColl...2article42.pdf


I'd use something like 1,000 K as Tl. High efficiency and high rate heat
radiation in space is problematic unless the temp is high. Radiative
heat dispersal is about 100 kW/m^2 for the low temp radiator.

Incident radiation on the collector is 1.1 MW/m^2, the mirror (which
weighs 0.005 kg/m^2 excluding support) concentrates sunlight from 1.33
kW/m^2 to 1.1 MW/m^2, approximately 820 times at 80% efficiency.


Th is 1800 K, Carnot efficiency is 44%, assumed overall efficiency to
local electricity is 29%.


I can't say for sure what the mass per unit area of radiation or
collection are. I need to analyze a canvas tube (like an air
mattress) radiator filled with low pressure gas and air float
charcoal, Buckey balls or BeO. Assuming they are both around a
kg/m^2, a kW should come in around 3.2 kg.


I do not understand that. Ignoring the mirror, which I think - actually,
I don't know what you are doing -

In my example design the single sided collector has a mass of 5 kg/m^2,
the double sided radiator 1 kg/m^2.

The gas contact areas are 15 times the collecting or radiating areas.
The coefficients of convective heat transfer are 800 and 80 W/m^2 K (the
gas in the high temperature one is at twelve times the pressure of the
low temperature one). The temperature difference across each is 100 K -
the collector surface is at 1900K, the radiator surface at 900 K.

One m^2 of collector produces 400 kWe at the station, and needs 8 or 10
square meters of radiator, so 15 kg of collectors and radiators are
needed to produce 400 kWe, or 0.0375 kg/kW.

My numbers might be a little hard to achieve, though they are meant to
be only medium-tech at best, so let's be very generous and say 150 grams
per kW. That's still 20 times less.


Turbines and generators
are around 0.1 kg/kW based on Boeing 777 engines. Transmitters have
been analyzed at less than a kg/kW. So giving room for such parts as
power conductors and the joint to the transmitter, it *might* come in
at 5kg/kW.

If anyone has some spare web space to hang a small xls file, I can
send it to you.


Yes please. I seem to be missing something in your argument. Will put it
up too.

-- Peter Fairbrother



Keith

-- Peter Fairbrother

On Jul 21, 10:47 am, Peter Fairbrother wrote:
Keith Henson wrote:

[...]

Assuming the radiator and collector mass per square meter is about the
same, then you can see from the graph that the minimum occurs a bit
above 100 deg C, which is far below the 370-650 deg C quoted in an old
paper he

http://contrails.iit.edu/DigitalColl...2article42.pdf

I'd use something like 1,000 K as Tl. High efficiency and high rate heat
radiation in space is problematic unless the temp is high. Radiative
heat dispersal is about 100 kW/m^2 for the low temp radiator.

That's not what the minimum mass calculation show, at least for the
assumption that collector surface and radiator surface have about the
same mass per unit area. I am assuming about a kg/m^2 for both,
taking into account the supporting structure.

What you want is for the sum of mass for the collector and radiator
per kW, and taking into consideration the Carnot efficiency to be at a
minimum.

Here is the graph. http://www.htyp.org/Space_radiator

The minimum came out 130 C with not much penalty between 75 C and 200
C.

Of course, there could be an error in the spread sheet. If you can
find one, please let me know.

Keith

Incident radiation on the collector is 1.1 MW/m^2, the mirror (which
weighs 0.005 kg/m^2 excluding support) concentrates sunlight from 1.33
kW/m^2 to 1.1 MW/m^2, approximately 820 times at 80% efficiency.

Th is 1800 K, Carnot efficiency is 44%, assumed overall efficiency to
local electricity is 29%.

I can't say for sure what the mass per unit area of radiation or
collection are. I need to analyze a canvas tube (like an air
mattress) radiator filled with low pressure gas and air float
charcoal, Buckey balls or BeO. Assuming they are both around a
kg/m^2, a kW should come in around 3.2 kg.

I do not understand that. Ignoring the mirror, which I think - actually,
I don't know what you are doing -

In my example design the single sided collector has a mass of 5 kg/m^2,
the double sided radiator 1 kg/m^2.

The gas contact areas are 15 times the collecting or radiating areas.
The coefficients of convective heat transfer are 800 and 80 W/m^2 K (the
gas in the high temperature one is at twelve times the pressure of the
low temperature one). The temperature difference across each is 100 K -
the collector surface is at 1900K, the radiator surface at 900 K.

One m^2 of collector produces 400 kWe at the station, and needs 8 or 10
square meters of radiator, so 15 kg of collectors and radiators are
needed to produce 400 kWe, or 0.0375 kg/kW.

My numbers might be a little hard to achieve, though they are meant to
be only medium-tech at best, so let's be very generous and say 150 grams
per kW. That's still 20 times less.

Turbines and generators

are around 0.1 kg/kW based on Boeing 777 engines. Transmitters have
been analyzed at less than a kg/kW. So giving room for such parts as
power conductors and the joint to the transmitter, it *might* come in
at 5kg/kW.

If anyone has some spare web space to hang a small xls file, I can
send it to you.

Yes please. I seem to be missing something in your argument. Will put it
up too.

-- Peter Fairbrother



Keith

-- Peter Fairbrother