Subject: Re: Solar Energy

From: [email-masked] (Nick Pine)
Date: 20 Sep 1995 13:49:12 -0400

Stephen Lajoie <[email-masked]> intended to write:

>Your position is that because there is no solar technology that can provide 

			 ***electrical***

>power at reasonable cost (true cost, including reliability...) but its 
>just might be possible in the future...

Nick

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From: [email-masked] (Nick Pine)
Date: 21 Sep 1995 10:37:45 -0400

Stephen Lajoie <[email-masked]> again overgeneralizes: 
 
>I gave solar the benefit of every doubt, and it still comes up as 
>impractical on any kind of meaningful scale. 

Solar what?

>>An active solar system is competitive with fossil fuel heating systems.
 
>GEEZE. You don't get it, do you? You have to collect that energy and put 
>it in some sort of usable form, and to do that takes equipment, and 
>equipment has a lifetime and a cost. It is *not* free, and to say so is 
>deceptive. 

Did someone say the equipment was free? I do get 40 plastic 55 gallon drums
a month free, from a local food processing plant. I could buy them elsewhere
for about $15 each. Even the metal ones should last 20 years. I just bought
a nice 560 cfm fan for $60, 36 watts, max, with a temperature rating of 149 F.
Grainger part number 4C688. They also sell $10 thermostats. Replex, GE and
Dynaglas sell long-life thin polycarbonate plastic glazing for about $1/ft^2,
and Home Depot sells automatic foundation vents for $12 each, 1 x 3s for 84
cents each and 1/4" Aspenite and 6" fiberglass insulation for 25 cents/ft^2.
It seems to me that a simple house heating system built out of things like
this can be competitive with a fossil fuel heating system.

Heating a house this way seems so simple to me, almost anywhere in the
country, that I wonder if we shouldn't change the building code to forbid
all use of fossil fuels for house heating. 

Nick

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From: [email-masked] (Nick Pine)
Date: 21 Sep 1995 11:34:00 -0400

Stephen Lajoie <[email-masked]> once more vaguely overgeneralizes:

>In short, Solar is a crack pot idea if proposed for large scale 
>applications. 

Perhaps once could construe this as "solar electricity is expensive,
compared to grid power, if that is available, and solar thermal power
is difficult to transport."

Large buildings are easy to heat with the sun. It is harder to heat small
buildings, but that doesn't matter, considering how large people are:
it is very hard to make a 2' cubical house that is 100% solar heated.
A 4' cube is easier, an 8' cube, easier still, and a 16' cube is a piece
of cake. This has to do with time constants and surface to volume ratios,
as well as the fact that taller passive solar collectors work better. 

Nick

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From: [email-masked] (Nick Pine)
Date: 21 Sep 1995 11:46:23 -0400

Stephen Lajoie <[email-masked]> implacably waxes:

>...giving solar every benefit of a doubt...

Solar what?

Nick

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From: [email-masked] (Nick Pine)
Date: 21 Sep 1995 13:02:12 -0400

Stephen Lajoie <[email-masked]> wrote:

>How do you propose to save energy over a six month period?

How about a 16' solar closet? Some 55 gallon drums full of water inside
a cube, surrounded by 2' of insulation. The insulation would cost about
$1/ft^2 and the drums are free, sometimes, sometimes $15 each. The box
itself might cost 50 cents/ft^2 of all-around surface.

A cubical solar closet, L feet on a side, has a time constant of about
L^2 days. A 16' solar closet would take about 288 days to cool to 70 F,
if it sat outside at a constant temperature of 32 F, with no sun.

A 3' cube full of water surrounded by 6" of insulation has an RC time
constant of 432 hours, or 18 days. So if it starts out at, say 117 F,
and sits outside at 32 F, it will cool to 70 F according to the equation
70 = 32 + (117-32) exp(-t/18), where t turns out to be 14.5 days. 

An 8' solar closet with 18 55 gallon drums full of water, and 1' of
insulation, would cool from 145 F to 70 F in 46 days, sitting outside
in the same cold, cloudy weather.

>How do you plan to move all this energy about?

Moving heat is difficult. One can move air efficiently through large
ducts over short distances, say 20', and hot water over longer distances,
using air-water heat exchangers, but that is more expensive.

>For the UMPTEENTH time... There was NO allowances for reliability...

I wonder, when you say "reliability," Steve, are you talking about
the fact that some days are cloudy, or that solar equipment breaks? 

>There was NO allowance for clouds, fog, dust...

Clouds and fog are covered in NREL's solar data book, which gives averages
and extremes for amounts of sun and outdoor temperatures. Cloudy days
reduce solar input by about 50% where I live. This is fairly predictable,
over long times. I've read that dust on glass, even very dusty looking
glass, reduces the sun's intensity by at most 6%.

>I mention the need for storage, and someone says that they can save 90% of the
>energy put into a battery. Yeah, sure.

That was me, altho you are misparaphrasing. Having studied batteries and
patented one battery system, I recall that lead-acid battery charging is
about 90% efficient, ie if you do it right, you have to put 10% more energy
into a battery than what you can extract. That's for the battery itself.
That doesn't include the efficiency of the charging circuit.

>Over a period of three months?

Who said anything about 3 months? Of course batteries discharge over time,
altho not much if they are kept cold. But if they are cold, they have
limited capacity, until they are warmed up to room temperature, at which
point their capacity returns. Cold batteries are also difficult to charge,
and they last a lot longer than warm ones.

>Just the temperature difference between 80 F and 0 F (summer to winter) will
>reduce that down to 40%,

I wonder where you got that number? I wasn't aware that just temperature
cycling had any effect on battery capacity or state of charge, in itself.
Warm batteries do self-discharge more rapidly, but you seem to be saying 
something about temperature cycling...

>I think that most people that don't live in third world countries will 
>not accept the poor reliability that such small scale solar systems would 
>provide.

Again it seem strange to talk about the sun as being "unreliable." It is,
of course, in the short term, but over longer periods of time, measured
in weeks, it is very reliable. So if a solar system doesn't depend on
getting sun every day, like clockwork, eg if it stores heat for a few weeks
or months, it too can be very predictable and reliable. And if it runs out
of heat once in a while, that is not a disaster. That event may be part of
a design that makes sense, economically.

>...your numbers about the 
>cost of solar power are highly deceptive. Hidden is the cost of reliability.

Where is it then, exactly? What is the cost for a given level of reliability,
and what are the consequences of a "failure"? Buying some power from someone
else? Using up some reserve? Missing 8 hours of work? An airplane crash?

>I think it is important for people to know that solar power is not the 
>answer that some people make it out to be.

I think it's important for people to realize that there is more than
one form of solar power, when they read sentences like the one above.
Or perhaps the sentence might be phrased less misleadingly.

>In the small scale, yes, you can cheat out of paying your fair share of
>the power grid cost...

My electric company, which is not known for its benevolence, charges about
$8 per month to be connected to the grid, even if I consume no electricity.
Is this too little? Perhaps they should raise the minimum rate...

Nick

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From: [email-masked] (Nick Pine)
Date: 26 Sep 1995 09:19:02 -0400

Barry Smith  <[email-masked]> wrote:
>[email-masked] (Stephen Lajoie) wrote:
>>Nick Pine <[email-masked]> wrote:

>> Solar anything. I figured the area, then applied a thermodynamic 
>> efficiency to get the total area in shadow. It doesn't matter at all how 
>> you convert it. Someone threw out a 30% efficiency for PVs. Okay, so I 
>> used PVs. With an assumption of PVs, I showed that the cost would be 
>> far more than the country could spend.

In talking about costs, the efficiency and the technology do matter.
 
>By your statement, Edmund's price is $9375 per square meter, which most
>folks in the business would say is a bit high.  Your mark down brings
>that down to $4687.50, and your miracle factor of ten reduces that to
>$468.75 per square meter.

Which is about $40 per square foot. Polycarbonate glazing costs about
$1 per square foot in small quantities. You don't need much more than
that to collect solar hot air. In fact, you can do a good job collecting
solar hot air with some curved steel pipes, say 20' long, on 4' centers,
such as the ones used in commercial greenhouses, leaning against the south
wall of a two-story house, covered with a large piece of 5 cent/ft^2
polyethylene film, which is guaranteed for 3 years, with a large piece
of 15 cent/ft^2 greenhouse shadecloth inside the greenhouse. 

For $600 you can buy all the material for a 600 ft^2 sunspace from a
commercial greenhouse supplier like Stuppy: some curved steel pipes and poly
film that you can turn into a sunspace in a day or so. Three people can
put up a 3000 ft^2 commercial greenhouse in less than a day... This sort
of arched lean-to structure is nicely described on pages 34-36 of William
Shurcliff's 1978 Brick House book, _New Inventions in Low-Cost Solar Heating--
100 Daring Schemes Tried and Untried_. 

Dr. Shurcliff says "Here we discuss a scheme that may be ideally suited to
retrofit application to existing houses the south vertical faces of which
receive much solar radiation even in winter. The scheme is much like that
pioneered by S. R. Kenin and others of Solar Room Co./Box 1377/Taos, NM 87571.
There are already several buildings that use his scheme, or schemes reasonably
similar to it. An example is Egri House in Taos, NM. This house is described
in detail in my book _Solar Heated Homes of North America: 120 Outstanding
Examples_... ***It is hard to think of any other system that supplies so much
heat (to an existing house) at such a low cost***." He goes on to explain how
to make this a low-thermal-mass sunspace, eg by hanging a piece of greenhouse
shadecloth inside, which costs about 15 cents per square foot and comes in
rolls up to 30' wide and 300' long. (It comes in green too.)

In the summer, you might hang the greenhouse shadecloth over the poly film,
on the outside. This would prevent overheating and provide shade and make
the poly film last longer.

Dr. Shurcliff talks about using a thin layer of insulation on the north wall,
and says "Then, practically no heat is delivered to the massive components
of floor or wall; practically all of the heat is promptly transferred to
the air. And since the thermal capacity of the 100-200 lb. of air in the room 
is equal to that of one fourth as great a mass of water (about 25 to 50 lb.
of water), the air will heat up very rapidly. I estimate that its temperature
will rise about 40 F degrees in about two minutes, after the sun comes out
from behind a heavy cloud cover [unlike most solar collectors,] At the end
of the day, little heat will be "left on base" in the collector floor or
north wall and accordingly, the enclosure will cool off very rapidly [and
very little of that captured solar heat will be lost at night, unlike, say,
a Trombe wall.] 

This is more like a transparent tent than a structure, but the galvanized
steel pipes last at least 40 years, I'm told. You could also grow grapes on
them. Sounds great (or grape :-), doesn't it? Whatever happened to this idea?
Why aren't more people using it? Why isn't real Goods selling it, somehow?

I'm not a passive purist: I would probably put a $12 20" box fan in a second
floor window looking out into that sunspace, with a thermostat, and a plastic
film damper of course. This would make it work better, and it would be
cost-effective. (Fans move more air per watt than blowers, and larger fans
are more efficient than smaller ones. Norman Saunders says that the
efficiency of a fan is about the same as the blade diameter in inches.)

Why doesn't someone make some sort of modular solar air heating kit? A
well-thought-out, lightweight, large, inexpensive version that could be
shipped UPS? Plastic film, shadecloth, etc. No blower. I just got a 10 pound
UPS package with an 16' x 32' piece of 80% black shadecloth, with hems and
grommets on all four edges, a part of a 500 square foot solar air heater,
(that's about 50 kW, for all you PV people) from PAK Unlimited in Norcross,
Georgia at (404) 448-1917. The cost was $71.25, including shipping. 

Low-thermal-mass sunspaces seem like a good way to heat houses, perhaps
with the warmstores of Norman Saunders or my solar closets, ie insulated
boxes with containers of water inside them, heated by sun-warmed air.
With a fin tube just under the closet ceiling and a natural warm water
convection loop to a water heater upstairs that provides close to 100%
of the hot water for the house, even after a week or two of cloudy days,
while the solar closet provides 100% of the space heating...

Nick

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From: [email-masked] (Nick Pine)
Date: 29 Sep 1995 05:37:13 -0400

Gary Coffman <[email-masked]> wrote:
>[email-masked] (Nick Pine) writes:
>[snip]

I think you snipped the wrong part. Saving energy for six months requires
something more like a 16' solar closet, with its storage time of 288 days.
 
>Putting that in perspective, you're talking about 594,000 BTU, about
>the amount of heat my furnace puts out in two hours.

Gee, your furnace is five times bigger than mine, and you live in a
warmer climate...

>What do you suggest for the other 2158 hours I need heat each season?

This is way out of context... Unless you live at the North Pole, I suggest
you build a low-thermal-mass sunspace sized to provide all the hot air
you need to keep your house warm on an average day in December. Then build
your solar closet into the north wall of that sunspace, (or the south wall,
if you are Orstralian), an 4' x 8' x 8' insulated closet with another 8' x 8'
layer of glazing inside the sunspace glazing, so the lost heat from the closet
ends up in the house, via the sunspace air, and the warm sunspace environment
when the sun is shining makes the closet run hotter inside... 

So this closet would have a separately-glazed passive solar air heater attached
to its insulated south wall, and it would be filled with some containers of
water, and on an average December day, the solar hot air would just keep
the closet warm, like a stagnant solar collector. The closet would be just
coasting, lurking, without providing ANY heat to the house on an average
December day, with some sun, except what leaks through the insulated walls
between the closet and the house. THEN when the sun goes in for a week or so,
you let some heat out of the closet to keep the house warm. Simple, no?

Nick

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From: [email-masked] (Nick Pine)
Date: 3 Oct 1995 15:02:58 -0400

In article <[email-masked]>, Stephen Lajoie <[email-masked]> wrote:
 
>The point Gary was trying to make was that the 16 foot (cube?) water box 
>didn't hold as much energy after a certain time period as his furnace 
>could put out in 2 hours. 

So what? The box ONLY supplies heat to the house when the sun is not shining.
And a 16' cube is overkill. At 130 F, it would store over 5 million Btu
of useful heat, enough to keep a well-insulated house warm for 2 months,
in my 5500 degree day Philadelphia climate.

>His post does not say that his furnace was on for 2160 hours, just that 
>he needed heat for that long. The furnace may or may not be on. But the 
>heat in the water box was expended in the first two hours, and he had the 
>rest of the winter to go.

I don't recall that he lived at the North Pole :-)

Nick