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Why is my current so low?

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Posted by Peter Mounsey on June 3, 2004, 10:12 pm
 
I've just fitted 4 Evergreen EC55 panels to my 24v system. Panels wired two
series strings in parallel. So, with 220 watts into 24 volts I should be
seeing 9.17 Amps - right?
What I am seeing is a maximum of 5 Amps in very intense Spanish sun, panels
correctly aligned and all panels producing the same power.

Am I missing something here or are rated outputs fantasy?
TIA, Peter.



Posted by Solar Guppy on June 3, 2004, 10:34 pm
 
http://www.evergreensolar.com/egsolar1/pdf/EC-50_v2.7e.pdf

Shows the EC-55 as 3.33 amps when at VMP (maximum power point)

Since you have two in series , that doubles the voltage but the current
remains the same

Since you have two strings in parallel , that would double the current to
6.66 amps

The EC-55 vmp is 16.5 volts , so two in series is 33 volts , and in your
configuration (best case) would be 33 volts at 6.66 amps which is 218 watts

So NO , your not going to see 9.17 amps , look at the data sheet

5 amps seems reasonable ... you'll need a mppt charge controller though to
see the 6.66 amps and  this and it will only be a solar noon on a perfect
day

It's has nothing to do with evergreen panels , all Silicon panels are this
way





Posted by Duane C. Johnson on June 4, 2004, 12:54 am
 Hi All;

Solar Guppy wrote:


It's probably quite warm in Spain now.
This will have the effect of reducing the panel efficiency.
So the resultant current will be even less than expected.


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Posted by Solar Guppy on June 4, 2004, 2:52 am
 Duane,

Si panels have a positive coefficient in regards to temperature ... So hot
panels put out more current , its the voltage that drops

From the same spec
http://www.evergreensolar.com/egsolar1/pdf/EC-50_v2.7e.pdf

Voc decreases 0.41% per C while current increases 0.088% per C , this is in
a rising temperature reference context





Posted by Duane C. Johnson on June 4, 2004, 4:22 am
 Hi Solar;

Solar Guppy wrote:


Thanks.  I had thought they both decreased but I
guess I was wrong.

Although the current increase is so small maybe
the rule of thumb would be closer to generally
calling it even.


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