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I have access to live solar irradiance data (in W/m²) at each minute of the day in my location, they come in 3 types: minimum, maximum and average. How do I make use of these datas to convert to kWh/m²/day?

I thought of summing each minute of irradiance data all up but it sounds ridiculous.

Thanks in advance!

  • most inverters do this for you, and many can export to sites like pvoutput.org so you can see your system and compare it to other systems (or you can go there now and see how systems near you perform) – Ⴖuі Jan 6 '16 at 7:21
  • "I have access to live solar irradiance data (in W/m²) at each minute of the day in my location" can you post where that data comes from and maybe even share link to api is there is one? – Marian Paździoch Apr 26 '16 at 18:07
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If your data is minute-by-minute then that's exactly what you need to do.

Adding all the minute-by-minute W/m² figures for a day (you should have 1440 of them, so use a spreadsheet or script) will give you the number of Wmin/m² incident radiation. So then divide by 60,000 to get kWh/m² for that day.

You might as well use the "average" value unless you know what the difference between the three, and how it applies to you. Then don't forget that to convert to kWh/m² generated you would need to take into account not just the panel efficiency but the angle of indcidence. At this point you'll be glad you created a spreadsheet/script because this calculation is best done based on the date/time of day/latitude.

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In addition to Chris' answer I'm going to give you a (IMO) clearer and more generic way of doing this:

If you need to convert units, always reduce your units to more fundamental units of the International System of Units that your two terms have in common.
See International System of Units

A Watt is a Joule per second, so 1 W/m² = 1 J/(m²s)
(I'm using brackets for clarity, but they are not required)

Likewise 1 kWh/m²/day reduces step-by-step

kWh/(m²day)
1000 Wh/(m²day)
1000W3600s/(m²day)
3600000J/(m²day)
3600000J/(m²86400s)
41.666 J/(m²s)

... and if you insist on using Watts this is 41.666 W/m²

Strictly speaking I could have left out the step converting 1 W to 1 J/s, but we are so used to express energy in Joules* that I reduce to that.

And as Chris says, whether to use use min/max/avg depends on what you want to calculate, not on your units.

* If you are not, you should. Distinguishing the absolute amount of energy from the amount per second makes things much clearer.

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