Due to systems renovation, the graph is complete nor accurate.

Energy yield of the 4 m², West oriented, 30° inclined, collector is monitored by the increase of watertemperature in the solar boiler (120 l).
The insolation is measured by shunting a small (1W) solar cell with a 0.1 ohm resistor. The voltage across the cell then is a linear measure for the total energy received.
All temperature sensors are DS18S20 chips, that have a 0.5°C resolution.

The bottom temperature can be higher than the middle of the boler. This may seem strange, but is easily explained by the bottom sensor being placed further away from the boiler vessel, with a thermal leak. Therefore the bottom temperature approaches the hall temperature more than the 'half of boiler' temperature does. On higher temperatures this is the cause of the bottom sensor losing temperature sooner than the half of boiler sensor.

Both temperatures and insolation are measured by a Soft-I/O device, which is read out by a php script, that is fired every 5 minutes using launchd.
The graphs are constructed using JPGraph and the web site is powered by MAMP.

All is served by a Mac OS 10.5 PowerBook G4/1GHz.