Real capacity

A

AK

Jan 1, 1970
0
Hi all;

I have a 5.9 KW solar system installed. I use 2 Sunny boy 2500
inverters and my panels are BP.

According to my contractor, I should be generating at least 7000 KWH
for the year. I'm standing at apx 5000 now, 10 months after the
install.

Any ideas what could be the problem? My house has a very good south
facing angled roof with no trees and obstructions. I thought I would
be generating more than 7000kwh...

Also, is there a difference between differrent panels, say between BP
and sharp? Is one more efficient than the other?

thx.

E

Ecnerwal

Jan 1, 1970
0
AK said:
Any ideas what could be the problem? My house has a very good south
facing angled roof with no trees and obstructions. I thought I would

Have you had rain recently? If not, you might have a severe case of dust
(so wash your panels and see if your daily production improves), or you
might have a problem your installer should correct (such as some panels
that are not properly connected).

A

Anthony Matonak

Jan 1, 1970
0
AK said:
I have a 5.9 KW solar system installed. I use 2 Sunny boy 2500
inverters and my panels are BP.

According to my contractor, I should be generating at least 7000 KWH
for the year. I'm standing at apx 5000 now, 10 months after the
install.

Well, figuring losses for temperature (20%) and inverter (10%) you're
looking at something like (5.9 kW * .80 * .90 = ) 4.25 kW actually
reaching the grid. I don't know your location but let's say you get
around 4.5 'sun hours' a day, on average. This works out to some
(4.5 * 365 * 4.25 = ) 6980 kWh/year.

How much sunlight you get any particular year will vary, of course,
and you can expect more during the summer than during the winter.
Any ideas what could be the problem? My house has a very good south
facing angled roof with no trees and obstructions. I thought I would
be generating more than 7000kwh...

You might not have a problem. Your system installer may have simply
used a generic estimate rather than actual weather data from your
location. This year may have weather slightly different from the last
couple of decades or you may have an accumulation of dust and dirt

You might try the PVwatts program and see if it's estimate is close
http://rredc.nrel.gov/solar/calculators/PVWATTS/
Also, is there a difference between differrent panels, say between BP
and sharp? Is one more efficient than the other?

No. They all use the same technology (crystalline PV cells) so they
all perform almost identically. They may fudge their test standards
though. It's always better to go with the PTC rating for a panel than
the STC rating.

Anthony

B

Bill Kaszeta / Photovoltaic Resources

Jan 1, 1970
0
Hi all;

I have a 5.9 KW solar system installed. I use 2 Sunny boy 2500
inverters and my panels are BP.

According to my contractor, I should be generating at least 7000 KWH
for the year. I'm standing at apx 5000 now, 10 months after the
install.

Any ideas what could be the problem? My house has a very good south
facing angled roof with no trees and obstructions. I thought I would
be generating more than 7000kwh...

Also, is there a difference between differrent panels, say between BP
and sharp? Is one more efficient than the other?

thx.
Some questions:

1. Where are you located?
2. Tilt of the array?

With this I may be able to estimate average annual output
(if I have sunshine and temperature data for your location).

A comparison of the last years rain and/or snow to historic
averages may indicate a better/worse than average year.

Bill Kaszeta
Photovoltaic Resources Int'l
Tempe Arizona USA
[email protected]

M

Martin Riddle

Jan 1, 1970
0
Judging from the headers he is on the east coast and near NY.
So 4.25 sun hours a day may be a bit much. 3.5 would be much more realistic.

4.25 * 365 * 3.5 = 5429.375

I'd say he is operating on par if thats the case.

Also these are AVERAGE insolation numbers, this may be a below average year for his area.

Cheers

A

Anthony Matonak

Jan 1, 1970
0
BobG said:
How much would KWH increase with a tracker? Another 10%?

I'm told it can be as much as 30% to 40% depending on several
factors. Works best in the summer, less well in the Winter.

Anthony

M

MrE

Jan 1, 1970
0
Do you use an MPPT charge controller? Otherwise you are throwing away the
evening and morning power. Voltage drops and charge current doesn't reach
the batteries. Also to get most power from panels, especially a huge array
like that, you'd use a mechanical tracker.

J

John P. Bengi

Jan 1, 1970
0
Who has the space to have these platforms moving around all over the yard or
roof?

Use the space for stationary panels and get more.

30% - 40% doesn't stand up in most practical/actual testing.

It can spread your peak charge out over a longer period though if you can't
take the shorter "surge"

J

John P. Bengi

Jan 1, 1970
0
Would you sacrifice 90% of your house space to get 30-40% more heating
efficiency?

You didn't read very closely. The 30-40% doesn't happen in real life and is
easily acheiveable with other methods with less maintenance.

Will the 30-40% pay for the fence you have to put around your yard to keep
the kids from getting wacked in the head with moving panels? Will it pay for
all the extra gas to mow the lawn around these idiotic panels mounts and the
concrete cow patties everywhere for the mounts?

How much will that so-called 30-40% cost you?

A

Anthony Matonak

Jan 1, 1970
0
John said:
Who has the space to have these platforms moving around all over the yard or
roof?

Not everyone lives cheek to cheek with their neighbors in high density
housing. Even so, pole mounts are common and the panels can be mounted
above people's heads. True, they don't integrate in with a building
structure as aesthetically as, say, PV roofing tiles but you can't have
everything.
Use the space for stationary panels and get more.

If you don't have the space for moving panels then where do you find
the space for stationary ones? There is one advantage to fixed arrays.
They don't have moving parts that might breakdown in the 25 to 100 years
the panels are expected to work and fixed mounts are slightly cheaper.
30% - 40% doesn't stand up in most practical/actual testing.

I wonder where you got that idea. It all depends on a lot of different
factors, not the least where you are located and your local weather.
Generally speaking, for most of the United States, the 30%-40% figure
seems to be in the ballpark.

Anthony

J

John P. Bengi

Jan 1, 1970
0
First off PV panels are cheap when you compare them to a tracker for a
couple of $K To track the sun here you need to "wobble" these panels over 230 degrees for sun up to sun down. I got these figures from the Univ of Oregon computer website programme fo Michigan state. I kind of figured they had some information and research that gives them a little more accuracy than a snake oil saleman selling monster mechanisms that would get blown off my roof everytime I have a windstorm Heyyyyyyyy !!!! Anybody seen a wind turbine with PV blades?. Duane C. Johnson said: Hi John; Who has the space to have these platforms moving around all over the yard or roof? Tracked PV systems don't really take up much more roof area than fixed panels for the same energy throughput per day. Remember, you have less of those expensive PV panels. Use the space for stationary panels and get more. If the same space is properly covered with a tracked array the energy output would be about the same. However there would be a substantial savings in initial costs. 30% - 40% doesn't stand up in most practical/actual testing. Do you have any references to this? This is often what one would get in the November to February portion of the year. However, in the May to August the increase is more like 100%. Of course there a bunch of factors and one needs to study the NREL data set to see what your location can do. OK, tracking on a roof is not as good as a system that can turn more than 180 degrees which the roof mount can't do. It can spread your peak charge out over a longer period though if you can't take the shorter "surge" I rarely here anyone state this important factor. To go further, the spreading of power generation increases the likelihood that the power would be consumed directly by the user. This avoids the efficiency loss of passing the energy through ones batteries. I realize this thread has been about PV. But thermal collectors also have an increase. Especially those low efficiency flat plate collectors. These flat plate collectors only reach their best efficiency when the sun is normal to them. They have two loss mechanisms. 1. The cosine loss. (This is the same loss that PV has.) 2. Concentration loss. Concentration factor is 1X when the sun is strait on. Stasis temperature and operating temperature define the efficiency. When the sun is off axis the effective concentration factor is less than 1X. Causing stasis temperature to be lower while operating temperature is the same the efficiency must be less. Cooler yet. The concentration factor could be higher than 1x. Maybe 2X or 3X. This substantially increases system efficiency over the flat plate version. Especially in colder weather conditions. I would state this differently. I would say the increase can be as LOW as 30% to 40%. Duane -- Home of the$35 Solar Tracker Receiver
http://www.redrok.com/electron.htm#led3X [*]
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 \ |
[email protected] (my email: address) \ |
http://www.redrok.com (Web site) ===

J

John P. Bengi

Jan 1, 1970
0
OK to reciprocate, where do people get this 30-40% figure from?

Anybody say this, based on testing, and not have a hidden (or not so hidden)
agenda?

E

Endangered Bucket Farmer

Jan 1, 1970
0
Not everyone lives cheek to cheek with their neighbors in high density
housing. Even so, pole mounts are common and the panels can be mounted
above people's heads. True, they don't integrate in with a building
structure as aesthetically as, say, PV roofing tiles but you can't have
everything.

If you don't have the space for moving panels then where do you find
the space for stationary ones? There is one advantage to fixed arrays.
They don't have moving parts that might breakdown in the 25 to 100 years
the panels are expected to work and fixed mounts are slightly cheaper.

I would also be rather nervous about the higher risk of
weather damage to panels on trackers. A fixed, flush-
mounted panel on the roof will have a low profile
during a storm. But a tracker-mounted panel seems much
more vulnerable in high winds.

Although, of course, some fixed position panels are
also vulnerable. Like those mounted on poles, or on a
roof at a very different angle than the roof-slope
itself. But being fixed would give the possibility of
extra reinforcement, compared to something that has to
move.

I'm not taking sides either way, but I would consider
the local weather pattern risks in choosing between
fixed or tracking.

D

daestrom

Jan 1, 1970
0
Endangered Bucket Farmer said:
I would also be rather nervous about the higher risk of
weather damage to panels on trackers. A fixed, flush-
mounted panel on the roof will have a low profile
during a storm. But a tracker-mounted panel seems much
more vulnerable in high winds.

Although, of course, some fixed position panels are
also vulnerable. Like those mounted on poles, or on a
roof at a very different angle than the roof-slope
itself. But being fixed would give the possibility of
extra reinforcement, compared to something that has to
move.

I'm not taking sides either way, but I would consider
the local weather pattern risks in choosing between
fixed or tracking.

This is an interesting point. I think it depends on what type of hazard one
is thinking of. Certainly a fixed collector can have a stronger mounting to
withstand high winds. But a tracker could position the panels to minimize
damage from hail storms.

I guess it would depend on the type of weather in the area as to what kind
of 'protection' an installation would need.

daestrom

S

Sylvan Butler

Jan 1, 1970
0
=====================================
Well, would you like your business to make 30-40% more profit? How

I would too, if I could get it.

Cannot get it with a tracker.

First, you have to pay more to get a tracker. Even IF your tracker got
40% more power from the PV, since the tracker is NOT free, it is NOT a
40% return on the investment.

Every time I've checked, a tracker cost more than the PV it would
replace -- better investment just to buy more PV. In other words,

Finally, by definition, a tracker has moving parts, so is less reliable.

Personal example: I considerd about 800W on a tracker. The 8 panels
was all the tracker would hold. Tracker cost so much that instead, I
purchased 1200W of PV and built a shed (put the panels on the roof) for
less than buying 800W plus the tracker.

sdb

J

John [email protected] Bengi

Jan 1, 1970
0
Do you know what my roof would look like with a dual axis tracker that
actually fully tracks? The sun travel a full 230 degrees some days here. I
would have to raise the panels up another 6 feet to clear the roof peaks and
the neighbours would be calling Muldar and Scuzzy for UFOs.

I would also be out another $20k for mechanical nightmares that take maintenance and would be damaged by wind gusts. It was bad enough repairing the panel in the last wind storm. Luckily it only came out of it's frame and was OK but the banging on the roof lost me sleep for 48 hours until the snow melted off the slopes. Luckily it only lasted about 36 hours. Tough panel. Duane C. Johnson said: I can state a case for 30%..... energy vs time for one day with no tracker looks like a sine. Lets say the peak is 1 and the RMS is .707. The shape with a tracker is closer to a square pulse (sides more vertical), and the RMS in this case is closer to 1, so the improvement is 29.3%. You were right John.... that 30% was optimistic. I have been agreeing up to here, but the improvement in your example is 41.2%. 12hr / (12hr * .707 ) = 1.412 It's also only appropriate for a day when the sun rises due East and sets due west. Let's use your sine method for a different time of the year and at my location which has a latitude of 45 degrees. On the summer solstice the sun is above the horizon for 18 hours. Of course conventional non tracked panels can see light only when it is in front of the panel. So: 18hr/(12hr * .707) = 2.122 or an improvement of 112.2%. Of course this is a simple non real world example. Real improvements will be more or less than this dependent on local weather conditions. Also, don't forget Snell reflection loss. When the incoming light angle is too shallow the light is totally reflected. For glass this is around 45 degrees. Solar tracking doesn't present this loss at all. Duane -- Home of the$35 Solar Tracker Receiver
http://www.redrok.com/electron.htm#led3X [*]
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 \ |
[email protected] (my email: address) \ |
http://www.redrok.com (Web site) ===

D

daestrom

Jan 1, 1970
0
Duane C. Johnson said:
I have been agreeing up to here, but the improvement
12hr / (12hr * .707 ) = 1.412

It's also only appropriate for a day when the sun
rises due East and sets due west.

Let's use your sine method for a different time of
the year and at my location which has a latitude
of 45 degrees.

On the summer solstice the sun is above the horizon
for 18 hours. Of course conventional non tracked
panels can see light only when it is in front
of the panel. So:
18hr/(12hr * .707) = 2.122
or an improvement of 112.2%.

Of course this is a simple non real world example.
Real improvements will be more or less than this
dependent on local weather conditions.

Also, don't forget Snell reflection loss. When
the incoming light angle is too shallow the
light is totally reflected. For glass this is around
45 degrees. Solar tracking doesn't present this loss
at all.

You both seem to be using RMS values for the area under the sine wave of
insolation in the fixed collector case. Why?? Root-Mean-Square values
would be appropriate *if* the power of the panel was related to insolation
squared, but it is not. (of course, RMS is also valid when the power of a
resistive load is related to current squared, its much more common use)

The area under a sine wave is not 0.707 * peak value, it is more on the
order of 0.637 * peak value. This would dictate a much higher improvement
(Duane's calculation for summer might yield 18hr/(12hr*.637) = 2.35 or a 35%
improvement.

And as Duane points out, this is *before* reflection loss adjustments.

daestrom

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