By logging data, the performance (yield) of a solar installation can be compared to other plants.

If you compare with other plants, which have about the same slope, orientation and geographical location, you know whether your installation all right.

I also think it is interesting to just compare with other provinces or countries.

By logging, you save the dates of previous years, and you always know for example what your yield was the same days of last year, and what the best day ever was.

Actually it suffices to use an equivalent facility to compare, but I compare in 4 different ways, simply because I like that.

Below are some ways to log.

1

At the end of each month, I compare the daily results of the past month with 3 other people who have a PV system in the same town or within a radius of 10 km.
For a good overview, we compare the revenue per kilowatt peak, and make a graph of it.

As one of the four plants, differs from the other 3, probably there is something wrong.

Click the image for an example.

2

SMA (the manufacturer of inverters) also maintains a web space available where, after registering, it is possible to make a website in an easy way.

The required data is sent via email with excel annex, by the program Sunny Data Control.
This service is free, but sometimes it takes a while before the data is processed, and the website is up to date.

3

With the program Sunny Report (that was made by Peter Schaich and translated from German into Dutch by Chrismir) you can automatically create a website on your PC and send it via FTP to your own web space
This way you can decide how many times a day you want to update your website.

To use this program, you must also install the program Sunny Data Control, as the data from excel files created by this program must be processed into tables and graphs.  (I used this program until 2009 but in 2010 I switched to the program below)

Click the image to visit the site of Chrismir, where Sunny Report is used.

4

The program JSunnyReports was created by Martin Kleinman, Martijn van der Pauw & Bastiaan Schaap.

The program has about the same features as above but is much more user friendly because the code is free to edit and adaptable to your own needs and tastes.  Also the graphs look much more modern.

To use this program, you must also install the program Sunny Data Control, as the data from excel files created by this program must be processed into tables and graphs.

Click the image for the example of my own site.

5

On the website: http://www.sonnenertrag.eu/ you can find incredible much information.

You can also share your data.  This data sharing can be done in 2 ways: You give your data (daily results of monthly returns) manually on the website or the data is collected daily around 10:00 on your own website or webspace.  So you need a web space to upload your own data.

Here you can compare over 3000 installations in 11 countries. The charts I find interesting: you can see how efficient your plant is compared to the rest of Europe, Belgium, province or municipality.

I am registered as "ED RAKET" with ID: 2608.