Motor Control

On 12/24/2015 4:33 PM, rickman wrote:
> On 12/24/2015 12:29 PM, Jessica Shaw wrote:
>>
>>
>> Any suggestions on avoiding the shadow casting of one panel on another!
>>
>> Any suggestion on the algorithm that I can use to solve this problem.
>> I found the following link
>>
>> http://www.lauritzen.biz/static/solutions/backtracking.pdf
>>
>
> I don't see how the back tracking shown in your link has much advantage.
>   The panels intercept the same amount of sun when backtracking... no,
> they intercept less sun.  If you keep the panels aimed as closely to the
> sun as possible, they will receive more sun along the edges which don't
> overlap.
>
> The solution to shadow casting is to space the panels further apart.
> That's pretty simple, no?

Look at the pictures in your link.  The back tracking example has a 
shorter shadow than the example without backtracking.  So backtracking 
intercepts less light and will produce less power.  The only reason I 
can think backtracking would be needed is if leaving parts of the panel 
unlit causes a problem with those solar cells restricting the current 
flow in the rest of the panel.

-- 

Rick

rickman  wrote:
> ... The only reason I 
>can think backtracking would be needed is if leaving parts of the panel 
>unlit causes a problem with those solar cells restricting the current 
>flow in the rest of the panel.

I believe the reason is just obtaining maximum power generation.

Increasing the panels shadowed area will decrease the power, while it
is possible that the areas still exposed will produce more power if
they are better aligned to the incoming light. (i.e., closer to
perpendicular.)

The optimal point will depend on each particular system, of course.

R.W.

I am sorry. I meant the following link 

http://www.lauritzen.biz/static/solutions/backtracking.pdf


I am looking for a generic formula that can program into my code. I am interested in back tracking because if the front panel cast shadow on to the rear panel than the rear panel will produce less power. 

On 12/24/2015 6:00 PM, Roberto Waltman wrote:
> rickman  wrote:
>> ... The only reason I
>> can think backtracking would be needed is if leaving parts of the panel
>> unlit causes a problem with those solar cells restricting the current
>> flow in the rest of the panel.
>
> I believe the reason is just obtaining maximum power generation.
>
> Increasing the panels shadowed area will decrease the power, while it
> is possible that the areas still exposed will produce more power if
> they are better aligned to the incoming light. (i.e., closer to
> perpendicular.)
>
> The optimal point will depend on each particular system, of course.

I think you are confused.  Unless having shade on part of a panel 
affects the performance of the rest (as in blocking current) of the 
panel the energy produced will be driven by the total area of the 
cross-section of the light intercepted by the panels.  It does not 
matter much what angle they are aligned to.  Look at the illustrations 
in her paper.  The larger shadow means more light is being intercepted 
when one panel obscures the light to the other.

-- 

Rick

I am sorry. I just did not get it. All I know that shadow can reduce the performance of the Solar Panel. 

On 12/24/15 4:34 PM, rickman wrote:
> On 12/24/2015 3:40 PM, Richard Damon wrote:
>> On 12/24/15 1:47 PM, Jessica Shaw wrote:
>>> Thanks for the reply! Can you give me the formula or Do you know a
>>> website or a simple paper where I can find the formula for back
>>> tracking. I looked as much as I could but was unable to find one. I
>>> found some papers but the math was too complicated.
>>>
>>
>> I haven't had to work out the formula, so don't have it handy. The most
>> complicated part is working out the Sun angle (projected onto your
>> panels), but you needed that before.
>>
>> For back tracking, it is simple Geometry using the spacing between rows
>> of panels, the size of the panels, and the angle of the sun to figure
>> out what angle to place the panels so they are just on the verge of
>> shadowing each other. (There are two possible solutions when you want to
>> use backtracking, but you want the 'flatter' one)
>
> Why would you want to use backtracking?  I think it results in less
> sunlight being collected by the panels.
>

 From what I read on backtracking, you are collecting just as much light 
on the panels as pointing directly at the sun and having part of one 
panel shadowed by part of the one in front of it. Same amount of light 
means same number of photo-electrons generated. The difference is that 
with backtracking, the light is uniform across the whole array, while 
direct pointing has maximal intensity over just part of the array.

Where it has the advantage is that you bias a panel to adjust its 
efficiency based on the light hitting the panel, and you need to bias a 
whole panel the same, so you can get better efficiency if the panel is 
uniformly lit.

On 12/24/2015 11:51 PM, Richard Damon wrote:
> On 12/24/15 4:34 PM, rickman wrote:
>> On 12/24/2015 3:40 PM, Richard Damon wrote:
>>> On 12/24/15 1:47 PM, Jessica Shaw wrote:
>>>> Thanks for the reply! Can you give me the formula or Do you know a
>>>> website or a simple paper where I can find the formula for back
>>>> tracking. I looked as much as I could but was unable to find one. I
>>>> found some papers but the math was too complicated.
>>>>
>>>
>>> I haven't had to work out the formula, so don't have it handy. The most
>>> complicated part is working out the Sun angle (projected onto your
>>> panels), but you needed that before.
>>>
>>> For back tracking, it is simple Geometry using the spacing between rows
>>> of panels, the size of the panels, and the angle of the sun to figure
>>> out what angle to place the panels so they are just on the verge of
>>> shadowing each other. (There are two possible solutions when you want to
>>> use backtracking, but you want the 'flatter' one)
>>
>> Why would you want to use backtracking?  I think it results in less
>> sunlight being collected by the panels.
>>
>
>  From what I read on backtracking, you are collecting just as much light
> on the panels as pointing directly at the sun and having part of one
> panel shadowed by part of the one in front of it. Same amount of light
> means same number of photo-electrons generated. The difference is that
> with backtracking, the light is uniform across the whole array, while
> direct pointing has maximal intensity over just part of the array.
>
> Where it has the advantage is that you bias a panel to adjust its
> efficiency based on the light hitting the panel, and you need to bias a
> whole panel the same, so you can get better efficiency if the panel is
> uniformly lit.

That's the part I don't know about is how the panel reacts to part of it 
being unlit.  But you are not correct in thinking the same number of 
photons are picked up in each case.  When the panels are aligned to the 
sun, the total area of the sunlight being picked up is higher.  The 
panels are loosing some in the shadows, but there are two ends that are 
not involved in a shadow, the end in front at the bottom which is not 
shaded and the end at the back that does not shade anything else.  So 
the total area of sunlight received is higher than the area received 
when all of the panels are turned to prevent any shadows.

It is easy enough to draw the diagrams to show this.  Or just look at 
the illustrations provided by the OP.  I suspect the images are drawn by 
some program which shows the true shadows of the panels.  The two cases 
show longer shadows on the ground for the panels aligned perpendicular 
to the line from the sun and which cast shadows on each other.  The 
longer shadow on the ground clearly shows they intercept more light.

-- 

Rick

rickman wrote 

 The panels are loosing some in the shadows, but there are two ends that are 
not involved in a shadow, the end in front at the bottom which is not 
shaded and the end at the back that does not shade anything else.  So 
the total area of sunlight received is higher than the area received 
when all of the panels are turned to prevent any shadows. 

------------------------------------------------------------------------------
I did not understand this part. As in the diagram shows that front panel is casting shadow on the rear panel. So, the rear panel will produce less power because it is covered by the shadow. The photo cells will not produce electricity. 

On 12/25/15 12:29 AM, rickman wrote:
> On 12/24/2015 11:51 PM, Richard Damon wrote:

>>  From what I read on backtracking, you are collecting just as much light
>> on the panels as pointing directly at the sun and having part of one
>> panel shadowed by part of the one in front of it. Same amount of light
>> means same number of photo-electrons generated. The difference is that
>> with backtracking, the light is uniform across the whole array, while
>> direct pointing has maximal intensity over just part of the array.
>>
>> Where it has the advantage is that you bias a panel to adjust its
>> efficiency based on the light hitting the panel, and you need to bias a
>> whole panel the same, so you can get better efficiency if the panel is
>> uniformly lit.
>
> That's the part I don't know about is how the panel reacts to part of it
> being unlit.  But you are not correct in thinking the same number of
> photons are picked up in each case.  When the panels are aligned to the
> sun, the total area of the sunlight being picked up is higher.  The
> panels are loosing some in the shadows, but there are two ends that are
> not involved in a shadow, the end in front at the bottom which is not
> shaded and the end at the back that does not shade anything else.  So
> the total area of sunlight received is higher than the area received
> when all of the panels are turned to prevent any shadows.
>
> It is easy enough to draw the diagrams to show this.  Or just look at
> the illustrations provided by the OP.  I suspect the images are drawn by
> some program which shows the true shadows of the panels.  The two cases
> show longer shadows on the ground for the panels aligned perpendicular
> to the line from the sun and which cast shadows on each other.  The
> longer shadow on the ground clearly shows they intercept more light.
>

Backtracking would be used on very large arrays. On a very large array, 
the additional light collected by the first array when directly pointing 
at the sun is a very small part, and at some size gets surpassed by the 
improved efficiency over the rest of the array. The picture shows just 2 
panels, which shows the effect, but you would not use backtracking on 
that small of an array. My guess is the method is more intended for 
large commercial installations of hundreds of panels, so even a 1 
percent improvement in efficiency will out weigh the extra light on the 
first panel.

On 12/25/2015 10:17 AM, Jessica Shaw wrote:
> rickman wrote
>
>   The panels are loosing some in the shadows, but there are two ends that are
> not involved in a shadow, the end in front at the bottom which is not
> shaded and the end at the back that does not shade anything else.  So
> the total area of sunlight received is higher than the area received
> when all of the panels are turned to prevent any shadows.
>
> ------------------------------------------------------------------------------
> I did not understand this part. As in the diagram shows that front panel is casting shadow on the rear panel. So, the rear panel will produce less power because it is covered by the shadow. The photo cells will not produce electricity.

The panels that are tilted are picking up less light than the panels 
that are perpendicular to the light and so produce less electricity.

-- 

Rick