Seasonal changes in the solar path.

   Previously, I posted the impracticality of sensing resistors in a solar arry. I've decided that such sensors are needed. I do not have any of the design details of the MPPT controller I'm using, but I suspect the device is not up to parr with the rest of the system. A sensing resistor in series with the mainline will let me verify the power transfers taking place in the system. A small ADC board will convert analog data into computer compatible, digital data. I have all the parts and software on hand.

   If knowing the details of the panel system were crucial, I could insert a series of relays into the circuitry and a digital switching system to isolate each component in turn. Doing the same for the battery system would make SoC data available. I could then implement any of a series of algorithms.

   I stated in the last post, I would publish a series of graphs illustrating the seasonal changes in the amount of sunlight available. I do that here. First, I'll preface that series with a discussion of the variables involved.

   Throughout the year, the Sun's path through the sky changes. On June 21st, the Sun is closest to the Earth and highest in the sky at noon. On December 21, the Sun is farthest from the Earth and lowest in the sky at noon. Visualize an arc in the sky. The arc sinks lower as the days pass, until the lowest point occurs in December, then begins to rise till June, when the highest point is reached. This arc represents the path of the Sun throughout the day.

   One of the results is the lengthening of shadows in Winter. Since the Sun is lower in the sky at noon, the shadows will be longer. In Summer, the Sun is highest in the sky and the shadows will be shortest. What this means to me, is that solar energy is least when needed most, and most abundant, when needed least. For this reason, a system needs to be designed for Winter, the low energy months.

Note, in particular, the difference between the first, June 3, and the last, October 31. The difference is the effect of a changing solar path and shadows. Also note that most of the images were constructed from data collected on a clear day.

Here are the graphs: