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Author Topic: Help with my maths  (Read 2164 times)
AndyB
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« on: August 13, 2008, 09:01:23 PM »

Hi guy's, i have attached graphs of the output of my 300W PV array and my poorly sited wind turbine from today. i would like to graph the data in real time but as a histogram for each hour of the day.  How do i do the math for each hour, I'm really stuck as to how to add it all up to get a sensible figure. would it be the value at each sample (IE every second) added together 3600 times to give the Amp/hour value?

sorry if I'm being an idiot

Andy


* wind2.JPG (71.94 KB, 1164x293 - viewed 355 times.)

* solar3.JPG (80.75 KB, 1183x311 - viewed 357 times.)
« Last Edit: August 13, 2008, 09:12:34 PM by AndyB » Logged

NON MEUS MENDUM
Ivan
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« Reply #1 on: August 13, 2008, 11:46:32 PM »

can't see the units you are measuring at the moment - are they watts?

Assuming you have real time watts measured once a second:

To get hourly kWh (ie ENERGY received each hour) add 3600 datapoints (1 second 'watts' readings) together.
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dhaslam
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« Reply #2 on: August 14, 2008, 12:33:18 AM »

A more informative way to present output figures is to use moving annual totals or when you  only have shorter periods to use moving totals  for a week or so.  The advantage of accumulating output over a period is that the graph remains fairly steady but movement up or down shows the trend. Accumulating totals for a day is a step in the right direction but it is still going to fluctuate a lot. 
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AndyB
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« Reply #3 on: August 14, 2008, 07:50:44 AM »

Thanks,

Firstly i made a massive school boy error by not putting units on my graph. it is in fact Amps.

I'm interested in the moving totals idea, is there any examples you could point me to?

Andy
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kristen
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« Reply #4 on: August 14, 2008, 09:05:14 AM »

I do smoothed graph of my daily meter readings.

So lets say I have

Row 1 : Headings

Row 2 onwards:

Column A Date
Column B Meter reading

Column C Weekly-running-average

Row 8 Column C =AVERAGE(B2:B8) - can't do this for earlier rows as I need 6 earlier values. Copy this formula down for subsequent rows

Column D 30-day running-average

Row 31 Column D =AVERAGE(B2:B31) - can't do this for earlier rows as I need 29 earlier values. Copy this formula down for subsequent rows

You could plot a graph, in Excel, with vertical bars for the daily values combines with a line graph of the average, which might look good - i.e. show peaks and troughs as well as smoothed average
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kristen
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« Reply #5 on: August 14, 2008, 09:19:35 AM »

Here is an example of the raw meter readings (approx weekly but shown on a daily scale), and a smoothed 4 week graph


* CapPro55.GIF (55.03 KB, 800x474 - viewed 317 times.)

* CapPro56.GIF (53.48 KB, 800x471 - viewed 320 times.)
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CeeBee
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« Reply #6 on: August 14, 2008, 10:03:04 AM »

How do i do the math for each hour, I'm really stuck as to how to add it all up to get a sensible figure. would it be the value at each sample (IE every second) added together 3600 times to give the Amp/hour value?

Perhaps the others have said enough already, anyway:

You've got readings of a current in amps every second. I think what you first want is the average current over the hour. So add up all the readings that hour, and divide by 3600. If some of the readings were missing for some reason, then add up those that you've got, and divide by the number of readings.

Having got average amps, then it's up to you what you then call the scale on your histogram. Just leave the number as it is, and calls it 'average current (amps)'. Or given that the period on your histogram is 1 hour, then plot the same number, but call it 'ampere hours (Ah)' - don't write "Amp/hour" - that looks like 'amps per hour' which is meaningless.

For a 'moving average', you do the same as above, but start your 'hour' at a different time, e.g. a minute later or whatever
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AndyB
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« Reply #7 on: August 14, 2008, 10:07:21 AM »

Perfect Ceebee, i will post my efforts some time. thanks for all your help guy's

Andy
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