[Greenbuilding] PV Tracking

[jfstraube]

PVwatts.org is a wonderful website calculator for PV output that I use all the time.  I and colleagues have compared its predictions with  measured output in lots of situations and found it to be quite good (seems to miss some of the temperature impacts but one can normally get to within the accuracy of the inverter).
In Ottawa, it predicts a full 2-axis tracker will produce 36% more electricity than ideally sloped fixed system. I beleive it.

Oh, and I have seen literally over a hundred 6 to 10 kW two-axis tracker in southern ontario, including a dozen with a 10 km radius of my home.

They have the observed benefit of tilting very steeply every winter morning and evening, thereby tipping snow off very effectively.  My neighbours 5 kW fixed array on the 7/12 pitch roof of his house seems to spend an awful lot of time in winter with snow cover.

John


On 2011-08-04, at 7:05 AM, Haudy Kazemi wrote:

> I think this may be playing a role.  When most people use the power output calculators/estimators, they look at the annual production figures not the daily figures.  A tracker in a high latitude may make larger difference in the summer than in the winter because the arc of the sun is longer, starting in the northeast and ending in the northwest.  A fixed array in those conditions will self-shade in the early and late parts of the day.  This may the root of the daily difference between the reported performance difference between the tracked and non-tracked array.
> 
> Roughly speaking, with guesstimate example numbers (actual values could probably be obtained by digging into an appropriate calculator):
> During summer, tracked array may outproduce the non-tracked array by the ~40% reported in this discussion thread.
> During spring/fall, tracked array may outproduce non-tracked array by 20%.
> During winter, with a short arc, tracked array may outproduce non-tracked array by 5%. 
> On an annual basis the tracked array may only exceed the non-tracked array by ~20%, even it does better than that in the summer.
> 
> Perhaps someone can check this in a calculator?
> 
> 
> 
> On 8/3/2011 8:00 PM, Nick Pyner wrote:
>> 
>> I just think nobody is taking the geography in to account.
>>  
>> There are plenty of PV installations around here, but I have never seen or heard of a tracking one. This is probably because there is no point in them. The situation could  be quite different in the more frigid parts of the world for two reasons.
>>  
>> 1. Even in what is laughably called the banana belt of Canada, the insolation is not that great, and the skies are not so clear, so you would need to chase every watt you can find.
>>  
>> 2. In the summer, the days are longer. Hence the practical window of opportunity may be as much as an hour wider, but the hourly march of the sun is the same.
>>  
>> A tracking system helps in both cases, and this heathen would imagine the more polar you get the more sense a tracker will make. 
>> 
>> Nick Pyner
>> 
>> Dee Why   NSW
>> 
>> -----Original Message-----
>> From: greenbuilding-bounces at lists.bioenergylists.org [mailto:greenbuilding-bounces at lists.bioenergylists.org]On Behalf Of RT
>> Sent: Wednesday, 3 August 2011 2:59 PM
>>  
>> I told him that I had been telling people (this List) that his single-axis tracking array had produced 40 and sometimes 44% more than the Enphase fixed array and that you (the Listmembers) were telling me that I was full of $#!+.
>> 
>> We both just shrugged our shoulders (as if to say "Nyeh! What can you do about  unbelieving heathens ?")
>> 
>> 
> 
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John Straube
www.BuildingScience.com



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