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 Post subject: Calculating actual Performance RatioPostPosted: Sat Nov 17, 2018 7:53 am

Joined: Sat Nov 17, 2018 7:37 am
Posts: 5
Hello
i wan to calculate how our install Solar Plant (150kw) is performing.

We have weather station installed at our solar site and it reports POA value in realtime.

I do have other things ready such as
Total solar panel Area (m2) (which is 954 m2 as Module area and 851 m2 as Cell area)
solar panel yield or efficiency(%) (which is 17.5% in our case)

I do not know how to use POA value from weather station in the calculation of PR.
Do i sum POA value of entire day? Do i take avg by sum and dividing it by 24 hr?

As per PVSyst report in the month of October, GlobInc for my site is 191.3 kWh/m2
I was reading number from my weather station, which gives around 600 POA at noon time.

Pls let me know how to calculate this.

Thanks
Nirav

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 Post subject: Re: Calculating actual Performance RatioPostPosted: Thu Nov 22, 2018 10:55 pm

Joined: Mon Apr 16, 2012 7:29 pm
Posts: 1680
The calculation of the Performance Ratio is explained in our FAQ How is calculated the PR (Performance Ratio) ?

In this equation, the E_Grid and GlobInc values are always taken as sums for the whole considered period.
Mathematically, it doesn't make sense to average Performance Ratio values over different periods.

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 Post subject: Re: Calculating actual Performance RatioPostPosted: Fri Nov 23, 2018 9:35 am

Joined: Sat Nov 17, 2018 7:37 am
Posts: 5

Here are some numbers:

Total (sum) kW/m2 for 24 hours = 871 (my pyranometer reports irradiance every 15 sec. I summed values all value of last 24 hrs)
E_Grid = 640 kWh
Pnom = is it total installed capacity? in my case solar plant it 171kWp.

But i seems i am doing something wrong here with numbers.

PR = E_Grid / (GlobInc * Pnom)
PR = 640 / (871 * 171)

I have attached screenshot of actual installation report (pvsyst)

 Attachments: 2018-11-23_13-01-11.jpg [ 87.93 KiB | Viewed 12244 times ]
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 Post subject: Re: Calculating actual Performance RatioPostPosted: Fri Nov 23, 2018 6:47 pm

Joined: Mon Apr 16, 2012 7:29 pm
Posts: 1680
The GlobInc value is not correct. It should be expressed in kWh/m2/day. Not kW/m2.

If you have measurements every 15 seconds, you have to calculate the average irradiance for each hour (or the order of 1000 W/m2 if at full sun).
Then you add all the hourly irradiances [W/m2 = Wh/h/m2] of your day and divide by 1000 for getting [kWh/m2/day].
The result should be of the order off 7-9 kWh/m2/day for a clear day and south-facing plane.

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 Post subject: Re: Calculating actual Performance RatioPostPosted: Fri Nov 23, 2018 7:34 pm

Joined: Sat Nov 17, 2018 7:37 am
Posts: 5
Oh ok...again Thanks for your help.

I have attached excel file containing my POA data for a day.
Then i made it hourly average and then did sum of all those hourly average.

Please see attached excel file if it is correct. kWh/m2/day coming to 4.32
Please correct me if i am wrong anywhere.

Thanks