Re: [pvusers] Rated output vs reality

["Scott Willing" <willing@mb.sympatico.ca>]

On 19 Jul 2002 at 14:41, michael bearden wrote:

> I have a relatively new grid tied system with 28 Siemens SP75 panels,
> and a Sun-tie 2500 inverter.  I expected the panels to produce much
> nearer their label rating than what I am seeing even at peak hours now
> when I see 1400 watts from the inverter.  I was expecting something
> like 16kwh a day from this system when I installed it. Is this an
> acceptable power level for this installation? Thanks- Michael B.

I don't have the experience to answer that definitively, but I do have 
some questions.

1. What is the 1400W number? Total power produced at the output of 
the inverter, delivered to the grid, (?)

2. What is the resolution of the power display?

3. What is the temperature of the panels? 

4. What's the angle of incidence when you're making this assessment? 

5. Are the panels in a fixed mounting arrangement or on a tracker (I'm 
assuming the former)?

6. What's the nature of the site in terms of airborne pollution, haze, 
yadda yadda?

These are all factors that will affect the maximum power delivered. 
There are more, but since your Sun tie uses MPPT (maximum power 
point tracking) they should be less of a concern. 
 
Mr. Welch mentioned the Sunny Boy, which uses higher input voltage 
by rewiring your panels in longer series strings. I can see that helping, 
but if it were me I'd sure as heck want to (a) evaluate the power output 
of the array, adjusted for the above factors, by some other means than 
the Trace display, and (b) see the Sunny Boy do a significantly better 
job under the same conditions with the same array.

Not that (b) would be easy. Though it's hypothetically possible, 
arranging a reasonably valid A/B test would be a pain.

Scott Willing
Off-grid on an awesome 0.3kW (peak) PV power, yowsa.


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