Greetings from ππ!
This is the web server ππ (pronounced "pie pie")—a Raspberry Pi experimental server. Currently ππ is preforming Operation Lux.
This Raspberry Pi single board computer was a present from our good friend Pluvius. He has a habit of giving everyone a nickname where a syllable is repeated twice. So in honer of this tradition we have named this computer ππ.
In July of 2014 ππ had a digital luminosity sensor added. Using this sensor, ππ will log the amount of daylight on an area of roof. This data will be used to select a solar panel that will be large enough to run ππ completely off the grid.
For details about how the project is assembled and operating, have a look at the section of my website for the project.
To the left is a meter showing the current amount of sunlight. During the day the meter can bounce around wildly. This is why long averages are needed to get an accurate measurement of total light energy.
The meter's major divisions are at 10,000 lx, starting at 0. The full scale is 130,000 lx, which is about when a solar panel is operating at it's rated power output (it is actually closer to 126,000 lx).
This graph shows the data logged thus far. Samples are gathered at regular intervals and the average over one minute is logged to a CSV file. The horizontal scale is time, and the Zoom in and Zoom out buttons will adjust this scale. By default the scale is set for 24 hours. The vertical scale is in lux (lx).
The can be moved by clicking on a location and dragging right or left. This allows the data to be explored in more detail if desired.
There are two useful number displayed at the top of the graph. The first is the average energy each day for all available data. This number is given in watt hours per meters squared days (Wh/m2·day). That is, watt hours of light energy that hit a one square meter area over a 24 hour period. This makes it easy to apply the value to a solar panel by using the panel's area and efficiency.
The second number is the amount of energy on the graph being displayed in watt hours per meters squared. This is most useful when viewing the power from an individual day.
Power Production Calculation
Here is a section to calculate how much power is produced from a solar panel with a given amount of light. The amount of light is usually given as a daily average (such as from the graph above). Then the details of the solar panel must be entered so power production can be calculated.
Some solar panels' specifications have already been setup and can be selected from a pull-down menu. This will fill in the panel's details for the calculation. Any solar panel can be used if the details about the panel are filled in. The size of the solar cells needs to be known (height and width in millimeters), the number of cells that make up the entire panel, and the STC wattage rating for the panel. This is used to calculate area and efficiency needed to calculate the power production by the panel for a given amount of light.