Hi J.S.;

"J.S.Blackburn" wrote:

mike wrote:
Anybody got any real data on this stuff.

There's no shortage of information about this. Useful
keywords are "insolation" and "solar insolation" (the word
"solar" is slightly redundant but it's commonly included).
In summer, you can expect a maximum of 1 kWatt per square
metre to reach the surface of the earth.

This is miss leading.
While there are places, nearer to the equator, that
can have 1KW/m^2 at noon this is not the norm.

The rule of thumb is 1KW/m^2 normal to the sun
not flat on the ground.
Or about 100W/ft^2.
This is a tilted surface directly facing the sun.

The units most commonly used are
kW-Hour per square metre per day -
I'll call them Units here.

Insolation tables for the USA can be seen at:
http://www.suntrekenergy.com/sunhours.htm
These figures are somewhat suspect - the difference between
"high" and "low" seems too small (a maximum of 6 Units is
rather low), especially when compared with the following,
which contains some good maps:

http://www.wattsun.com/resources/ins...map_index.html

On this page, click on Flat Plate Collector, Single Axis
Tracker and Double Axis Tracker. The latter can produce up
to 14 Units in summer. The improvement when tracking the
sun's angle is very large. It pays to live in California.

I have seen a similar table somewhere for the UK, showing
that 5 Units is the best that can be expected, and maybe
less than 1 Unit in winter.

Bear in mind that the efficiency of Solar Cells is less than
20% in the very latest state-of-the-art devices, typically
10%, and maybe as low as 5% in reject/hobbyist cells.
Generating hot water directly from flat solar collectors is
probably more efficient, and certainly cheaper, but not much
use if it's electricity you want.

If, on a bad day, the cell voltage is less than the battery
voltage, you can still charge the battery. Look at:

http://www.elecdesign.com/Articles/A...262/6262.html#
This article appeared in Electronic Design, Sept 14 1998.

It describes a circuit for a Maximum-power-point-tracking
solar battery charger. The principle is simple: the
duty-ratio of a switch-mode power supply is continuously
modulated at about 50Hz. The change in output on each cycle
is used to determine whether a higher or lower duty-ratio
would increase the output power. A phase-sensitive detector
and feedback loop determines whether to increase or decrease
the average duty-ratio. It settles at the point of maximum
power.

As the article points out, it works for other energy sources
such as water-wheels and other devices where the shape of
the "energy curve" is not precisely known.

When used as a battery charger the voltage of the battery is
fairly constant, so "maximum power" means "maximum
current". At the solar cell end, we are working at maximum
power, although the voltage may vary. The "maximum power
transfer" condition is when 50% of the power goes to the
load, and 50% is dissipated in the cell. I don't know if
this is precisely true in a solar cell, but it certainly
implies considerable power dissipation in the cell, which
may shorten its life. On the other hand, a cell of 1 square
metre will have 1000 watts of solar power falling on it, and
may generate 100 watts of electrical power, of which we may
get 50 watts into our battery. The 50 watts dissipated in
the cell is much less than the 1000 watts from the sun - so
maybe it doesn't matter.

J.S.Blackburn,
London UK.

Duane

--
Home of the $35 Solar Tracker Receiver
http://www.redrok.com/electron.htm#led3X[*]
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mike wrote:

Then I turned the panel ever so slightly away from the sun.
I was amazed at how dramatically things changed with just
a small angle. Looks like I'd gain WAY more watt-hours/day
by tracking the sun
than by anything else I could think of.

Yep. It doesn't take much of an angle from perpendicular for a
silicon cell to act as a pretty fair mirror.

--
John Popelish

mike wrote:

Then I turned the panel ever so slightly away from the sun.
I was amazed at how dramatically things changed with just
a small angle. Looks like I'd gain WAY more watt-hours/day
by tracking the sun
than by anything else I could think of.

Yep. It doesn't take much of an angle from perpendicular for a
silicon cell to act as a pretty fair mirror.

--
John Popelish

Joel Kolstad wrote:
Watson A.Name - "Watt Sun, the Dark Remover" wrote:

My attitude is that rather than try to do this (and in the process lose
reliability), it's better to go supersize on the cells, add more area
and overall capacity to get you thru the cloudy days, and have a higher
capacity overall.


The argument usually goes that getting, say, 10-20% more power from a better
charge controller (one of these so-called 'maximum power point controllers')
can be cheaper (in additional expenditures) than getting 10-20% larger
panels. It's sometimes difficult to show, though, particularly on small
systems -- but MPPT controllers have been getting cheaper for awhile, now,
and I expect that eventually all but the cheapest/smallest will have this
functionality.

Last nite (Tue, 9pm) I watched a prog on PBS that was about getting
people to use more renewable resources, hosted by Cameron Diaz (hot
blonde movie star), who drives a Prius. They talked about getting every
home to have a solar panel, and selling power back to the utility co.
She also said that if everyone in the U.S. drove a hybrid vehicle, we
could completely eliminate oil shipments from the middle east. Well,
I'd go out and buy a Prius, but one of the guys at work has had his new
Prius since xmas and it took him 4 months or so to get it after
submitting a $500 earnest check to several dealerships to get on their
waiting list. They say they're trying to make more of them, but I think
they really don't want the prices to fall, since they're expensive to
make. In any case I'd like more solar power, but the initial outlay is
_not_ cheap.


---Joel Kolstad

Joel Kolstad wrote:
Watson A.Name - "Watt Sun, the Dark Remover" wrote:

My attitude is that rather than try to do this (and in the process lose
reliability), it's better to go supersize on the cells, add more area
and overall capacity to get you thru the cloudy days, and have a higher
capacity overall.


The argument usually goes that getting, say, 10-20% more power from a better
charge controller (one of these so-called 'maximum power point controllers')
can be cheaper (in additional expenditures) than getting 10-20% larger
panels. It's sometimes difficult to show, though, particularly on small
systems -- but MPPT controllers have been getting cheaper for awhile, now,
and I expect that eventually all but the cheapest/smallest will have this
functionality.

Last nite (Tue, 9pm) I watched a prog on PBS that was about getting
people to use more renewable resources, hosted by Cameron Diaz (hot
blonde movie star), who drives a Prius. They talked about getting every
home to have a solar panel, and selling power back to the utility co.
She also said that if everyone in the U.S. drove a hybrid vehicle, we
could completely eliminate oil shipments from the middle east. Well,
I'd go out and buy a Prius, but one of the guys at work has had his new
Prius since xmas and it took him 4 months or so to get it after
submitting a $500 earnest check to several dealerships to get on their
waiting list. They say they're trying to make more of them, but I think
they really don't want the prices to fall, since they're expensive to
make. In any case I'd like more solar power, but the initial outlay is
_not_ cheap.


---Joel Kolstad

Watson A.Name \"Watt Sun - the Dark Remover\" wrote:
Last nite (Tue, 9pm) I watched a prog on PBS that was about getting
people to use more renewable resources, hosted by Cameron Diaz (hot
blonde movie star), who drives a Prius. They talked about getting every
home to have a solar panel, and selling power back to the utility co.
She also said that if everyone in the U.S. drove a hybrid vehicle, we
could completely eliminate oil shipments from the middle east. Well,
I'd go out and buy a Prius, but one of the guys at work has had his new
Prius since xmas and it took him 4 months or so to get it after
submitting a $500 earnest check to several dealerships to get on their
waiting list. They say they're trying to make more of them, but I think
they really don't want the prices to fall, since they're expensive to
make. In any case I'd like more solar power, but the initial outlay is
_not_ cheap.

While I'm all for using more renewable resources, and especially
ones that are environmentally friendly, it doesn't make sense to
cause yourself financial pain doing so. It makes sense to buy the
must fuel efficient vehicle that fits your needs but not to overspend
simply because it's a little better on the gas mileage.

That said, there are many things you can do that are quite affordable.
First, you could conserve energy. Replace old appliances with more
efficient ones, insulate your home better, weather-strip, storm windows,
compact fluorescent lights, activate the power saving on your computer,
use xeriscaping and all that lot. If you are a typical homeowners then
conservation alone could be as effective as putting up a $30,000 solar
panel setup.

Then you could buy more affordable renewable energy equipment such as
solar water heaters, air heaters, ovens, stoves and the like. You could
also change your diet to include less animal products. Raising animals
to produce food takes many times more resources (which often means
energy) as plants alone require.

There are also many alternatives to a Prius. One option would be to
get a diesel powered car and use biodiesel or get it converted to
run on straight vegetable oil. Another option is to buy an electric
car. Currently the only ones available are "city cars" which turn
out to be glorified golf carts but they are suitable for very local
driving and can sometimes work as a second car. Some folks have even
had great success with bicycles of various flavors. If you simply
must have a hybrid vehicle then a much wider selection of them should
be available within the next 10 to 15 years.

Anthony

Watson A.Name \"Watt Sun - the Dark Remover\" wrote:
Last nite (Tue, 9pm) I watched a prog on PBS that was about getting
people to use more renewable resources, hosted by Cameron Diaz (hot
blonde movie star), who drives a Prius. They talked about getting every
home to have a solar panel, and selling power back to the utility co.
She also said that if everyone in the U.S. drove a hybrid vehicle, we
could completely eliminate oil shipments from the middle east. Well,
I'd go out and buy a Prius, but one of the guys at work has had his new
Prius since xmas and it took him 4 months or so to get it after
submitting a $500 earnest check to several dealerships to get on their
waiting list. They say they're trying to make more of them, but I think
they really don't want the prices to fall, since they're expensive to
make. In any case I'd like more solar power, but the initial outlay is
_not_ cheap.

While I'm all for using more renewable resources, and especially
ones that are environmentally friendly, it doesn't make sense to
cause yourself financial pain doing so. It makes sense to buy the
must fuel efficient vehicle that fits your needs but not to overspend
simply because it's a little better on the gas mileage.

That said, there are many things you can do that are quite affordable.
First, you could conserve energy. Replace old appliances with more
efficient ones, insulate your home better, weather-strip, storm windows,
compact fluorescent lights, activate the power saving on your computer,
use xeriscaping and all that lot. If you are a typical homeowners then
conservation alone could be as effective as putting up a $30,000 solar
panel setup.

Then you could buy more affordable renewable energy equipment such as
solar water heaters, air heaters, ovens, stoves and the like. You could
also change your diet to include less animal products. Raising animals
to produce food takes many times more resources (which often means
energy) as plants alone require.

There are also many alternatives to a Prius. One option would be to
get a diesel powered car and use biodiesel or get it converted to
run on straight vegetable oil. Another option is to buy an electric
car. Currently the only ones available are "city cars" which turn
out to be glorified golf carts but they are suitable for very local
driving and can sometimes work as a second car. Some folks have even
had great success with bicycles of various flavors. If you simply
must have a hybrid vehicle then a much wider selection of them should
be available within the next 10 to 15 years.

Anthony

Hi John;

John Popelish wrote:
mike wrote:

Then I turned the panel ever so slightly away from the sun.
I was amazed at how dramatically things changed with just
a small angle. Looks like I'd gain WAY more watt-hours/day
by tracking the sun than by anything else I could think of.

Bingo, that is my opinion also.

Yep. It doesn't take much of an angle from perpendicular
for a silicon cell to act as a pretty fair mirror.

Basically the power output will be:
COS(angle) * Watts
Watts is the output of the panel when aimed normal to the sun.
Angle is how far off of normal the panel is oriented.
0deg = 100%
8deg = 99%
11deg = 98%
18deg = 95%
30deg = 87%
45deg = 70%

However somewhere around 45deg or a bit more the cover glass
begins to act more like a mirror and the panel outputs much
less than allowed by the COS rule. Some panels can improve
on this with anti reflective coatings. These coatings may
not have a long lifetime though.

Now if you use a solar tracker the panel can be oriented
close to the ideal angle throughout the day. This significantly
improves the energy captured per day.

As an example:
At summer solstice where I live, 45deg latitude, the sun
subtends an angle of 270deg. That's an 18 hour day.

6 hours of the day the sun is actually behind a fixed panel.

Another 6 hours or so the sun is at an angle where the output
is low or negligible.

Only during 6 hours or so will the panel output significant
power. And the average power output is less than optimal.

A solar tracker in my location can theoretically harvest
3 times as much energy as a fixed panel.
OK, practically, due to weather and thick atmosphere the
output is 2.4 times according to the NREL data.

Other times of the year the improvement is not as much.
But even at winter solstice the improvement in output
is 1.4 times the fixed panel.

Solar trackers, at least the electronic bits, are really
low in cost, $35 for mine. The total cost including the
tracking mount is much cheaper than the cost of adding more
PV panels for the same outputs.

There are places where the tracking costs aren't cost effective.
The california sea coast and in maybe 50 miles or so is an
example. The local weather has lots of fogs which lower the
solar insolation except when the sun is high in the sky.

One must study the NREL data to see how cost effective
your location may be.

--
John Popelish

Duane

--
Home of the $35 Solar Tracker Receiver
http://www.redrok.com/electron.htm#led3X[*]
Powered by \ \ \ //|
Thermonuclear Solar Energy from the Sun / |
Energy (the SUN) \ \ \ / / |
Red Rock Energy \ \ / / |
Duane C. Johnson Designer \ \ / \ / |
1825 Florence St Heliostat,Control,& Mounts |
White Bear Lake, Minnesota === \ / \ |
USA 55110-3364 === \ |
(651)426-4766 use Courier New Font \ |
(my email: address) \ |
http://www.redrok.com (Web site) ===

Hi John;

John Popelish wrote:
mike wrote:

Then I turned the panel ever so slightly away from the sun.
I was amazed at how dramatically things changed with just
a small angle. Looks like I'd gain WAY more watt-hours/day
by tracking the sun than by anything else I could think of.

Bingo, that is my opinion also.

Yep. It doesn't take much of an angle from perpendicular
for a silicon cell to act as a pretty fair mirror.

Basically the power output will be:
COS(angle) * Watts
Watts is the output of the panel when aimed normal to the sun.
Angle is how far off of normal the panel is oriented.
0deg = 100%
8deg = 99%
11deg = 98%
18deg = 95%
30deg = 87%
45deg = 70%

However somewhere around 45deg or a bit more the cover glass
begins to act more like a mirror and the panel outputs much
less than allowed by the COS rule. Some panels can improve
on this with anti reflective coatings. These coatings may
not have a long lifetime though.

Now if you use a solar tracker the panel can be oriented
close to the ideal angle throughout the day. This significantly
improves the energy captured per day.

As an example:
At summer solstice where I live, 45deg latitude, the sun
subtends an angle of 270deg. That's an 18 hour day.

6 hours of the day the sun is actually behind a fixed panel.

Another 6 hours or so the sun is at an angle where the output
is low or negligible.

Only during 6 hours or so will the panel output significant
power. And the average power output is less than optimal.

A solar tracker in my location can theoretically harvest
3 times as much energy as a fixed panel.
OK, practically, due to weather and thick atmosphere the
output is 2.4 times according to the NREL data.

Other times of the year the improvement is not as much.
But even at winter solstice the improvement in output
is 1.4 times the fixed panel.

Solar trackers, at least the electronic bits, are really
low in cost, $35 for mine. The total cost including the
tracking mount is much cheaper than the cost of adding more
PV panels for the same outputs.

There are places where the tracking costs aren't cost effective.
The california sea coast and in maybe 50 miles or so is an
example. The local weather has lots of fogs which lower the
solar insolation except when the sun is high in the sky.

One must study the NREL data to see how cost effective
your location may be.

--
John Popelish

Duane

--
Home of the $35 Solar Tracker Receiver
http://www.redrok.com/electron.htm#led3X[*]
Powered by \ \ \ //|
Thermonuclear Solar Energy from the Sun / |
Energy (the SUN) \ \ \ / / |
Red Rock Energy \ \ / / |
Duane C. Johnson Designer \ \ / \ / |
1825 Florence St Heliostat,Control,& Mounts |
White Bear Lake, Minnesota === \ / \ |
USA 55110-3364 === \ |
(651)426-4766 use Courier New Font \ |
(my email: address) \ |
http://www.redrok.com (Web site) ===

Watson A.Name "Watt Sun - the Dark Remover" wrote:
Last nite (Tue, 9pm) I watched a prog on PBS that was about getting
people to use more renewable resources, hosted by Cameron Diaz (hot
blonde movie star), who drives a Prius.

Nice idea, although in her particular case I'd be willing to bet that she
could be driving a Hummer and it'd be a small drop in the amount of energy
she uses for transportation! (Due to all those jet rides...)

They talked about getting every
home to have a solar panel, and selling power back to the utility co.

I'm all for net metering (power company has to pay you the same for a
kilowatt-hour as what you would have had to pay to buy it from them), and
happily it is becoming more common in the U.S. Panels and controllers are
continuing to get cheaper as well. Additional government support could
really help improve how many people would seriously consider sticking
photovolataic panels on their roofs -- I imagine right now it's well under
1% of the population.

She also said that if everyone in the U.S. drove a hybrid vehicle, we
could completely eliminate oil shipments from the middle east.

We could do that as-is... there's plenty of oil in Alaska, after all, we've
just made the choice that protecting the environment up there is more
important right now than not importing oil from the middle east. (This is a
very involved topic -- if anything, the choice of where we get our oil from
is far more political than technical in nature anyway.)

---Joel Kolstad