Hi,
TheHermit <carlw@hermit.net> writes:
<<
And given the energy cost in producing it, all current plant energy
carriers are energy negative
>>
Be that as it may, I think we can get around it by reengineering the plants to be easy to service. In fact, I said as much in my description of them. If done correctly, the requirements for those forests of "natural gas" trees would be virtually nil, in terms of human labour and chemical supplements, although they might have a significant start-up capital cost (to grow and connect each tree to a proper distribution grid).
<<
Most uses of the nature you propose suffer from thermal inefficiencies
(Carnot Cycle)
>>
Do we care? If the fuel is plentiful and renewable, inefficiencies are not nearly as important. But all that aside, I didn't talk so much about energy use as about energy *creation*.
<<
and produce CO2 - which contributes to Greenhousing.
>>
I think you've missed the large picture here. If the fuel is *grown*, then the carbon contained in the fuel was *taken out of the air* -- and so re-releasing it is hardly a crime! It would become just another aspect of the large carbon cycle that life already drives here on earth.
<<
We have nuclear power, we should be using it much more than we do. It
is one of the smallest polluters on the planet.
>>
Ha! Maybe in quantity it is the smallest polluter. In terms of *quality* of pollution -- the danger it poses, and the length of time it lasts -- nuclear power (fission, not fusion) is the most polluting of all fuels! I feel that using nuclear power is criminal until we can find a cost effective and safe system of long term storage. (and this is not a mere acedemic debate -- I live not 200 km from a very large nuclear installation, and it's been a local issue for years and years. Frankly, everybody here thinks the nuclear station was a mistake.)
<<
I would in any case be worried about increasing the amount of
low-level (i.e. unusable) heat energy on earth if we discover a cheap
new source of energy without discovering a way to get some of it away
from our spaceship (earth).
>>
What you have again missed is that my analysis does not bring more heat to Earth. All of the solar energy I used already strikes earth and turns into heat. All I'm doing is proposing that we use a staged approach to that energy conversion. Not the current
sunlight --> heat
but rather
sunlight --> plants --> fuel --> work --> heat
Which is far more beneficial to us humans!
<<
If you want to see renewable energy, then (as you hinted) a vast space
based biological or microstructure collector beaming power back to
earth as laser or microwave energy is the way to go.
>>
On the other hand, the system you just described *would* bring more heat to the Earth. You'd have to do it on a *really* big scale for me to start worrying about heat pollution, however... (like, on the order of one percent of the total solar energy striking Earth, which I show to be 1.73 *billion* MW, or about 35 times the entire current world energy usage... If we ever reach that level of use, I think we will have bigger problems than extra heat!)
<<
In the biological system, the organisms used might produce electricity
directly, or would produce Hydrogen which would be used in a fuel cell
before being re-electrolysed by the organisms (closed system). In a
microstructure each microstructure would act as an antenna to tune
into light and like a crystal radio produce power at its terminals. It
is only in space that the efficiencies of this system would make it
cost competitive with current power costs.
>>
That's an interesting system as well -- but I think it ignores the much easier (and more useful) system of chemical energy (based on carbon) that plants on earth are already adapted to. In my opinion, we will be able to make my "natural gas" trees in twenty or thirty years. Your electrolyzing algae (as that would be the easiest plant to adapt, I think) will probably take another twenty years after that, not to mention the fact that it will be harder to implement, what with it's increased water requirements and the more difficult storage problems of hydrogen.
<<
The number you quoted is very theoretical. In (not sunny) Iowa for
example 600W.m^-2 would be considered high. In sunny Arizona the peak
available power is 1200W.m^-2. At 20,000 ft we get 1.72x the energy we
see at the surface. So the efficiencies you quoted are way too high.
Even under optimum conditions.
>>
Clouds! I knew I was forgetting something. What sort of a factor do I need? A tenth? A fifth? Half?
As to sunny Arizona at 1200 w/m^2, if you calc your latitude above the equator and multiply 1350 by the cosine of that angle, I think you'll find I've got it right. (that's why that cos(20) factor was there in my analysis -- should it be more than 20 degrees?)
<<
Sorry to be pouring cold water on a "nice" idea
>>
On the contrary, I think the idea stood up rather well. You'll have to do better.
ERiC