Hi Tim:
Thanks for catching the error in my arithmetic. You're correct, of
course, I combined two calculations (conversion of power to energy, and
application of the efficiency factor) in one line, but only applied the
10% factor. That would bump everything up by one order of magnitude,
increasing my original numbers to ~3.2 gal/year of oil and
~29.6 lb./year
of coal, which numbers are in agreement with your recalculated results.
I had never done the calculations before, so I have to admit that I was
a bit surprised at the result; I hadn't realized that it was that
gloomy a picture for photovoltaics. I'm glad to see that it's not so gloomy. However, it's
still not likely to be feasible from my perspective... it's just not
preposterously unfeasible. The numbers now make enough sense for me to
mount the doggone thing on my roof (assuming I could get a code
clearance, and that it's not prohibited by my
CC&Rs).
Of course, that means doing a structural analysis, including seismics,
etc. ...but those are just the specific difficulties of my location. If
it were generally cost-effective, such that packaged systems could be
mass-produced and sold inexpensively and it became sort of a cultural
fixture, those sorts of things would be accommodated as a matter of
course in the construction of new homes, in the same way that automatic
garage door openers, 200-amp electrical service, steel tie-downs, and
all sorts of other stuff gradually makes its way into the building
codes. Even if such systems weren't required, they'd be permitted. As
things stand now, you'd play bloody hell trying to get something like
that approved in some of the municipalities around here. I could
probably pull it off, since I live in an unincorporated area of the
county (by design).
Nevertheless, that mitigating factor of 10 isn't enough to overcome the
inherent physical limitation in the incident energy flux. For example,
I based my calculations on ideal conditions, which I don't have. A
32-year data base showing % of astronomically possible sunshine for Los
Angeles yields an annual average of 73%. Since this is "sunny"
Califo'nia, other locations are likely to be less sunny...say, oh I
dunno... Rochester, NY just to pick an eastern city at random... 51% of
possible sunshine there. But hey, it could be worse... like, Syracuse
(46%). It's still more than Juneau (30%).
The best data to use are actual measured hours of sunshine per year. I
found a weather station in Granada Hills (a sunnier location than mine)
that shows year-to-date sunshine hours totaling 2,667.3 hours (Jan. 1
thru Nov. 10 = 314 days). Normalizing that to an annual figure...
365 days/year ÷ 314 days = 1.16/year
2,667.3 hours x 1.16/year = 3,094.1 hours/year
...which probably overstates the available sunshine, because the
remaining 51 days are in the period approaching the winter solstice,
not to mention the rainy season. So the 3,094-hour figure errs on the
high side.
The rest of the limitations are in the technology itself. You're never
going to run your microwave and
your refrigerator and your
air conditioner and your TV
and your washing machine and your table saw all at the
same time off the real-time output of a photovoltaic system unless
you've got some massive collection going on. And there will be times
when collection just isn't possible (like every night), so you must run
off storage. That means you need way more collection during the day to
accumulate what you're going to use at night, and all the storage
capacity. I guess I'd have to take a look at the costs, the amount of
equipment involved, etc. I just can't imagine that there's anything
even close to a 24 to 30-month ROI, which is what most businesses would
want to see.
OK... now for some tighter calculations to see what it would take to go
completely independent, energy-wise, in real time... meaning that I
would be able to access the same amount of energy from a [photovoltaic + storage]
system that I can now access via the grid.
Note:
I won't argue over the efficiency of the system, because it's
irrelevant to the question of whether the current technology is
practical... by which I mean affordable,
part of which determination depends on its ROI -- assuming I had the
money in the first place. All I need to know is how much installed [photovoltaic + storage]
system capacity I need to deliver the same performance I get from the
grid, how much the capital cost of that system will be, and what will
be the operating costs. I really don't care about the efficiency -- it
is whatever it is, and neither I nor the vendor can change that.
First of all, the system must be able to deliver the same capacity that
I get from the grid in real time, plus it must have the additional
capacity necessary to store energy (over and above the real-time
demand) for those periods when there's no sunshine. So, I need to know
what my real-time demand is; that's easy -- it's the supply capacity of
my current system:
220 VAC x 200Amp = 44,000 Watts = 44kW
Now, to factor in the additional capacity needed to accommodate
no-sunshine periods, I need to compare hours of sunshine per unit time
(say, one year) to total hours per year:
24 hr./day x 365 days/year = 8,760 hr./year
8,760 hr./year ÷ 3,094 hr./year = 2.83
44kW x 2.83 = 124.52kW = ~125kW
To be honest, that's actually more than I would need, because I'm not
going to run the system at full capacity all the time; I mean, I don't
run at full capacity now... ever. But if we're going to be fair and
compare apples to apples, let's see how the cost of 125kW photovoltaic
system stacks up against the cost of grid-provided power, to see if
it's at least economically feasible. If those numbers look halfway
decent, then it might be worthwhile to explore it further. I'll check
it out and report back.
I want to repeat that I have absolutely nothing against the idea of
photovoltaic electrical energy solutions -- not even some perverse or
contrived "objection in principle" -- for anyone who has the space, the
tracking equipment, the $bux, and the inclination to set themselves up
in that way. I don't have any of those things, but I have no objection
to anyone else going for it if that's their desire.
In fact, nothing would please me more than saying good riddance to the
lunacy of buying electrical energy from a soulless, castrated,
state-controlled entity like Southern California Edison, which
essentially functions as a vassal of the political state. I don't know
how the economics of the hypothetical 125kW system will
turn out, but I must admit that with the absolute political travesty
that our elected criminals have created in the California electrical
energy market, ROI is probably a lot easier to recover here than
elsewhere. Such are the benefits that political stupidity (oh... I
guess that's oxymoronic, isn't it) provides to its victims
...oopth, I mean the thitithenry of the United Thtateth of 'Merica.
Peathe,
Pete
Tim Gwinn wrote:
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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