Save variable data periodly

Hello ZenonUsers!
I am very new to Zenon, and i wasn't able to find an answer to this question:
How do i save the value of a variable whenever it gets updated, so i can access & visualize it?
To give you further understanding of my problem, here's the complete scenario:
I have to visualize the energy that gets produced by a photovoltaik-cell. Therefor we already installed a microcontroller, that sends data periodly (the produced energy since the last measurement-cycle [WATT]). The controller is connected to a WindowsCE-PC via RS232, and supports ModBus-ASCII-protocol. I already added the driver, and created a variable with "object-type: analog-input". and INT as data-type.
I guess this variable gets updated within the update-time i configured (10000ms), and receives the new value of the Microcontroller. I now want to save the received data, because i have three charts/diagrams i want to create:
1. The energy produced from the start of the day until now
2. The energy produced within the last month
3. The energy produced last year
So i would have to read that data from wherever and however they are saved and draw my chart line with that... but HOW, and WHERE can i save this data? A SQL databse, or maybe a simple text file??

I hope there's someone who could help me.. project deadline: 23th April :o
thanks in advance,
-Andrew

This is a migrated post! Originally posted on 17.04.2014 by user andareas. Please be aware that information can be outdated.