Thursday, November 26, 2009

Said and done - the trees are gone!

After a full week of unshadowed operation is has becoome clear that solar energy is not always as "green" as everybody thinks. Shadow of any kind - even a tiny patch reduces the efficiency so dramatically that every effort to get the panel surface shadow-free is justified.

The reason for that effect is the serialization of cells within a module and the serialization of modules to form a "string" with sufficient input voltage for the inverter. A single solar P-N-element (the "cell") features typically only 0,5 Volts. It takes 60 or so cells to form a "module" creating a typical open-circuit voltage of 30 volts. 12-15 serially connected modules then create a string with 360 to 450 volts input at the inverter. Shadowing only one module or even only one cell within "pulls down" the whole string unless the current is lead through the bypass diodes, which means that the bypassed module is "cut out" effectively for the moment.

In that sense "trees" can be the natural enemy of  the solar entrepreneur.
In my case 4 massive 12-15m pine trees had to be victimized.

Monday, November 9, 2009

The German 9/11

Is it coincidence? This history laden date when an iconic building burst to pieces and nothing was like it was before thereafter. - Im am NOT writing about the Twin Towers - instead the 9th of November in German date format 9.11. is the much celebrated 20. anniversary of the fall of the Berlin Wall.
Even Google joins the celebrations all about with this Doodle Graphic

Everybody is being asked these days "Where have you been on that day"? and "Do you remember what you did on the 9th of November 1989.
Here is my story:
I worked for AMD at the time in the north German sales office near Hannover - a rather remote outpost on the global perspective of the CPU business. Two weeks before the 11/9 date I made up a visit to see customers in Berlin - not with the faintest idea on what was about to happen.  This meant to fly with one of allowed airlines of the former allied forces, that is you had to fly PanAm or BA through a special air corridor over the East German Communist territory.
So when the breaking news spread on the late evening of the 9th of November, quickly all travel slots to Berlin the next day filled within seconds. I was lucky to hold a valid reservation by pure coincidence on that very next day for Berlin.
So I took my video camera and made a record documenting the day - the 10th of November knowing that history was happening. The mood in Berlin was amazing - the whole City in "festival mode" people celebrating and cheering all about. At the same time it was unreal in a sense, a fairy tale atmosphere, where people felt like "give us a knock - we must be dreaming, it´s just too unbelievable to be true".
In retrospect, I should have brought my still camera as well and I could have taken some really historic pictures in high quality- what I do have is only a shaky VHS video but nevertheless it is a document of the rare luck of being at the right spot the right time.
As I think about it, I might edit out a 3min version and put it on YouTube...

Monday, November 2, 2009

Only logged data is good data

Another upgrade to my new solar panels: A data logger for worldwide live access

A - relatively sunny day in November - 6kg saved carbon oxide!
Check it out at

For all who really like to know what this graphic really means:
The yellow area shows electric power (Watt produced) over time. At 10h the system has been switched on the first time otherwise it would start at 7h30 am with a nice slope. The "ideal" graph on a really sunny day looks like a gaussian bell curve. The green and red line are the contributions of the two identical module fields, so it is expected that the lines stay always together at about 50% of the total power. At about 12am they divert heavily - this is shadowing. One module field is exposed to a tree shadow which dramatically reduces the production of the whole string. Approx. two hours later the two line begin to merge again, this is when the shadow reaches the second field as well reducing the overall effectiveness.
Now all of this is not new - I knew it would happen and the consequences are quite clear -

The trees must go!