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Actually, after
reviewing the numbers, I think I do see one error in the following
calculation:
0.7 kW/m^2 x 10 hr/day x 10% =
0.07 kW-hours/m^2/day
The
correct answer should be: 0.7 kW-hours/m^2/day (the 10
hrs/day and the 10% basically cancel each other)
This
changes the later calculations as follows:
0.7
kW-hours/m^2/day x 365 days/year =
255.5 kWh/m^2/year
Cut in half (for less than ideal weather
conditions) is ~ 128
kWh/m^2/year
This
means the fuel oil calculation is:
128 kWh/year x 3,414 BTU/kWh = 436,992
BTU/year
436,992 BTU/year ÷ 139,000 BTU/gal. =
3.14 gal/year
And the coal calculation is:
436,992 BTU/year ÷ 15,000 BTU/lb. = 29.1
lb./year
Even
though the corrected numbers are generally increased by a factor of 10, the
results are still pretty low. If we go one more step and are pretty optimistic,
and allow a conversion efficiency of 35% instead of
10%, the numbers change as follows:
2.45 kW-hours/m^2/day
~ 447kWh/m^2/year (less than ideal weather)
1,526,058 BTU/yr
10.9
gal/yr of oil
101.7 lb/yr of
coal
And,
if we are looking at ultimate theoretical limits of
photovoltaics, and allow a conversion efficiency of 85% instead
of 10%, the numbers change as follows:
5.95
kW-hours/m^2/day
~ 1086 kWh/m^2/year (less than ideal weather)
3,707,604 BTU/yr
26.7 gal/yr of
oil
247.2
lb/yr of coal
The most
severe limit to all these calculations is imposed by the weak amount of
energy per sq-meter of sunlight hitting the earth, as Pete pointed out.
I've seen numbers of 0.9 - 1.3 kW/m^2 maximum, so 1 kW/m^2 seems a reasonable
value to begin with. Everything else seems to follow from that limit pretty
straightforwardly.
I want to
reiterate that this does not mean that photovoltaic systems
are useless. It can act as a supplemental power source to a grid.
But as a real-time technology to
reliably replace connectivity to the grid for any significant length of
time is pretty costly.
Besides an
active tracking system for a large solar array (otherwise the conversion
efficiency really suffers), the real difficulty, though, is how to reliably handle
several snowy days in a row. I can't even imagine how many batteries would be
required. I'll have to try to find some kWh numbers for storage
batteries.
Regards,
Tim
Judith,
What are the
specific errors and misconceptions you saw?
Tim
Sorry Pete and Tim, but you are both wrong. Each of your
posts were riddled with errors and misconceptions (possibly assumptions
of your own?), but you plugged them in to your analyses and came out with an
answer that you based your conclusions on. I have to admit, I'm surprised.
Such resistance to new ideas, when you have both embraced my father's work
and spoken out harshly against the resistance he faced?
I don't expect you to simply "take my word for it". Therefore,
I have taken the liberty of forwarding on the two posts to an expert in
alternative energy that I happen to know and, rest assured, I will post
the results of her investigations.
Judith
Sent: Saturday, November 08, 2003
8:30 AM
Subject: [ROSEN] FW: Tholar Energy
Mythth
Forwarded on
behalf of Pete Giansante.
(The server
had rejected it:
The enclosed message, found in the
ROSEN mailbox and shown under the spool ID
6473672 in the system log, has been identified as a possible
delivery error
notice for the following reason: "Sender:", "From:" or "Reply-To:"
field
pointing to the list has been found in mail body.
I think it
was because there was a hyperlinked "mailto" in one of the
included headers.)
Tim
-----Original
Message-----
From: Pete Giansante
[mailto:***
Sent: Saturday, November 08, 2003 6:25
AM
To: ***
Subject: Tholar
Energy Mythth
(...Yeth, thatth the plural of
"myth" with a lithp.)
Judith is correct in her preference for using
renewable resources like solar energy wherever they are appropriate. Tim
is correct in his assertion that intensive, reliable, on-demand power
generation is not one of those applications.
NOTE:
"Intensive" means that the backup
power generation technology is capable of completely replacing
centralized grid-supplied power (by which I mean your electrical utility
company) for any period of time that might be required to provide an
uninterrupted electrical energy supply. [ energy = power x time,
usually expressed in kilowatt-hours (kWh)]
"Reliable" means that the backup power
supply can operate as long as needed. If you want a number, call it "a
minimum of 95% operation/a maximum of 5% downtime for
maintenance".
"On-demand" means that the backup
power supply is available whenever you need it.
The
economics of installing engine-driven generators must indeed be balanced
by the ROI such an investment would make. In addition to the capital cost
of the power generating, distribution, & switching equipment, and the
facilities to house it, there's the expense of storing and recycling fuel
(usually Diesel No. 2) -- with all its associated regulatory hassles. Add
to that the personnel cost of maintenance & operations, and you have
to have a very compelling reason to load that kind of cost into the
goods/services you offer your customers. In fact, if your competitors
decide against going that route and the market prefers the resulting lower
prices of their goods/services, you won't have any customers. Gas turbine
technology has improved, but it's more costly in capital &
maintenance. Regardless, if you want reliable backup and your market
provides the economics to support it, you're going to be going with some
form of combustion engine-driven generating plant.
Solar energy
works pretty well in a thermal application -- that is, for heating water
and living space. Electrical power generation from solar energy is an
entirely different matter. It can be used to generate
electrical energy via photovoltaic conversion, as long as one is willing
to accept conversion losses on the order of 90%. Even if such losses are
acceptable, you still can only collect and store enough energy to operate
things like radios, stereos, and high-efficiency lighting (e.g.,
fluorescent or metal halide vapor lamps; forget about incandescent --
thermal losses are too high). But if you want to do a lot of intensive
usage (e.g., air conditioning, electrical appliances, power tools), you're
not going to be able to run that kind of stuff using photovoltaic
conversion without prohibitive equipment & maintenance costs. The cost
in lead-acid storage batteries alone would eat you alive -- assuming you
even wanted to have that much hazardous stuff lying around.
I
sympathize with the hopes of solar energy enthusiasts, but they would
perhaps be better served by a somewhat more realistic appraisal of the
ability of solar-powered infrastructure. As a source of large-scale,
intensive, reliable power generation, solar/photovoltaic conversion is
more mythology than technology.
Consider the physical constraints.
The maximum terrestrial incident power flux of solar radiation is ~1 kW
per square meter when the sun is directly overhead and is unobstructed.
The sun's output imposes that physical limitation, given the radius of
Earth's orbit, and there isn't much we can (or should) do about
it.
Perhaps some concrete examples will help to illustrate how that
limitation affects our ability to use the sun as a practical source of
electrical energy. To convert the incident solar power to energy, multiply
by the amount of time that the 1 kWh/m^2 condition is in effect. First,
you must account for the seasons. The maximum solar collection time that
you can squeeze out is 12 hours per day, twice per year... if your latitude is somewhere between
the two tropics. The rest of the year you have considerably less daylight,
and more atmospheric interference as the sun's path drops to the horizon
seasonally, so on average you have maybe 10 hours of usable sunlight per
day, under ideal conditions. If your location is between one of the
tropics and the nearest pole, it goes downhill from there.
Now you
must also account for the daily rotation of the Earth. Even under the best
of conditions (desert, during the summer, with no cloud cover), you have
that condition for maybe one hour before plus one hour after the sun is at
zenith. Of course, the sun isn't directly overhead for the other 22 hours
in the day, but let's say that you can devise some complicated tracking
mechanism to keep the perpendicular axis of your solar collector(s) always
pointed directly at the sun.
However, the average incident power
won't be the full 1 kW/m^2 for the entire 10 hours. Call it 0.70 -- again
being generous. That gives you ~0.7 kW/m^2 x 10 hr/day = 0.7
kW-hours/m^2/day of incident solar energy. Assume that you fill the entire
1-meter area with photovoltaic cells and capture all the incident energy.
With a conversion efficiency of ~10% (that's typical of current
technology), here's your maximum electrical generating capacity, under
ideal conditions:
0.7 kW/m^2 x 10 hr/day x 10% = 0.07
kW-hours/m^2/day Now, since we've already
accounted for the seasons in our average daily capacity, we can annualize
that capacity:
0.07 kW-hours/m^2/day x 365 days/year = 25.55
kWh/m^2/year
That's under ideal conditions... meaning an arid
climate with zero cloud cover. For the average location in the U.S., cut
that number in half... so that's ~13
kWh/m^2/year
Now, compare that capacity to the
energy-intensive sources that we typically find in fossil-powered
electrical generating technology. That's how Southern California Edison
generates most of its power... by burning fuel oil or coal, so for
comparison, the same capacity can be converted to the equivalent amount of
fuel oil or coal:
Fuel Oil:
13 kWh/year x 3,414 BTU/kWh = 44,382 BTU/year
44,382
BTU/year ÷ 139,000 BTU/gal. = 0.32
gal/year
Anthracite Coal:
44,382 BTU/year ÷ 15,000 BTU/lb. = 2.96
lb./year My average annual usage over
the last 36-month period is 20,385 kWh. Allowing for peak usage months,
and based on my existing 0.25-acre lot size, I
could replace the energy I'm currently getting from the grid if I were to
cover 98% of my property with photovoltaic cells... if I had ideal conditions,
and the money to spend on such things, and the
desire to live amidst that sort of ugly junk, and the
inclination to spend my time or my money servicing/maintaining such a
preposterous facility. I don't. Most people don't.
More to the
point, neither do the most vocally active "public figures" who advocate
the mythology of "soft energy" technology, and mislead others to believe
that such technologies are feasible.
I find the idea of energy
self-sufficiency attractive as a means of sustaining oneself when living
in a remote location, but even then, I would require a small generating
plant if I wanted to maintain the quality of life that I currently enjoy.
The maximum conversion efficiency attainable with current non-nuclear
technology is approximately 50%, provided by high-speed gas-fired
turbines. I suppose that when they can be made reliable enough and can be
mass-produced cheaply enough, it would be feasible for individuals to own
them.
Nevertheless, such a decentralized system would sacrifice
the economies provided by large-scale, centralized power generation and
distribution. As long as we rely on combustion-based technologies, we
might as well minimize the combustion by-products via economies of scale.
I should think that would be an article of faith among anyone who is
concerned with global warming (I'm not).
Of course, the longer-term
solution is to drop our reliance on combustion-based technologies
altogether. We have the capability to do that safely right now, but (sigh)
I'm not inclined to pursue such a controversial subject in this forum...
and besides, the content of this post has probably wandered too far
off-topic for this list as it
is...
PVG
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