Re: Oil replacement
Robert wrote:
> "Duane C. Johnson" <redrok@xxxxxxxxxx> wrote:
> > Robert wrote:
> Even more reason to have polar axis tracking...but
> the engineering problems and capital outlay will be
> enormous.
> If these are in a desert, they could easily
> be covered with sand during one severe storm.
This is a problem. However, it is lessened when using
a tracker because parts of the day the panels are
vertical dumping some of the dust. There will still
be some dust that will still stick due to static
charges though. One can't totally eliminate cleaning.
> > Do you have any examples of this high cost of
> > tracking arrays?
> > Please don't use the cost bloated government
> > financed stuff. These were never powered by the
> > sun, they were powered by government dollars.
> Well, you could estimate that at least about 1/4 ton
> of metal would be needed to track each 100m^2 panel.
I would think a panel that size would weigh much more
than that.
I use a rule of thumb for home sized systems:
The total weight of a standard "Sun Flower" mount
including the PV panels is about
Panel Watts * .5 = pounds
So, a 1000W tracked PV panel weighs:
1000W * .5 = 500 lb.
In your case of a 100m^2 panel.
At 15% efficiency and a standard solar insolation
of 1000W/m^2:
100m^2 * 1000W/m^2 * 15% = 15KW
15KW * .5 = 7500 lb or almost 4 tons.
There is another factor I rarely see.
Many think that scaling factors are an advantage in
solar power plants. I don't think this works well in
solar power plants as opposed to conventional power
plants.
The main structural design factor is wind. I usually
use the National building code recommendation of a
horizontal wind load of 10 lb/ft^2. The structural
stress goes up linearly with height and to the square
of the linear dimension of the panel. Prudent design
would increase the structural member size which
decreases the scaling weight in half.
So the total weight increase in dimension is more
like X^3 / 2 (if I have done this correctly).
Since I know the weight of the smaller panel using
the square law the 100m^2 system would weigh:
The linear dimension increase over the smaller panel
is about:
(15KW/1KW)^(1/2) = X = 3.87/1
3.87^3 / 2 = 29/1
500 lb * 29 = 14500 lb = about 8 tons
Condensing the above equations:
(15KW/1KW)^(3/2) / 2 = 14500 lb = about 8 tons
This is about 1 lb / W
If we make 15 of the smaller panels we should
have produce the same power but weigh less:
( 1000W * .5) * 15 = 7500 lb = about 4 tons
This is about .5 lb / W
So the large tracked panels are about double the
weight suggested by the other linear scaling factor.
The effect is that more smaller units tend to be
lower in cost than less larger units for the
I wish I had better actual data.
Does anyone have the weight data so I can do
a more accurate estimate?
Don't forget the fixed panels.
They have a weight advantage of about
80% per unit.
However they produce less energy per day.
I estimate this to be 60% or so.
Lets use the same 1000W panel with these factors
and the weights calculated for the trackers:
1000W
500 lb * 80% / 60% = 667 lb
667 lb / 1000W = .667 lb/W
15000 100m^2 panel
14500 lb * 80% / 60% = 19400 lb
19400 lb / 15000W = 1.29 lb/W
In summary
1. Small tracker .5 lb/W
2. Small fixed .67 lb/W
3. Large Tracker 1.0 lb/W
4. Large Fixed 1.29 lb/W
> How much energy does it take to make and
> set up that much steel or aluminum?
> Quite a lot I should think.
Sure. But I don't really need to know the fully
accounted manufacturing energy costs. What is
important is the comparison of the materials
weights with the different mount types.
> > Duane
Duane
--
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