Stack valuates together to a daily bar

Hi

I am monitoring a solar panel. Every minute the watts are written into a the database. Now for better presentation I am trying to gather the data’s from every day and present the result for each day in only one bar, so I can see for example 7 bars in one week and can se what was the best day.

I am working with php and my string is looking like this:

/usr/bin/rrdtool graph /var/www/temperature/solarleistung_week.png -s -1week DEF:w1=/var/log/digitemp_rrd/solar_kw.rrd:watt:AVERAGE LINE1:w1#48d1cc:"Solarleistung in Watt" -h300 -w500 -y1:2 --color GRID#dddddd --color MGRID#aaaaaa.

How can I say to rrd to gather the data’s every day to one bar?

Regards

Marc