Sun Tracking for More Solar Power – Part 1 – The Hardware

August 14, 2017 3D Printing, Grove, Grove I2C Mux Breakout Board, Grove OLED, I2C Mux Breakout Board, Matplotlib Graphs, Products, Python Raspberry Pi Software, Raspberry Pi, Software, Solar Power, SunAirPlus, SwitchDoc Products, Tutorials

IMG_4392 2Sun Tracking for More Solar Power – Part 1 – The Hardware

SwitchDoc Labs has built a lot of solar power systems over the past few years.   SunControl, Project Curacao2, Project Curacao,  SunAirPlus,  WeatherPi and the recent Solar Powered ESP8266.  We have fooled around with sun tracking systems, but we have never built one all the way out and then gathered the data to figure out if it was worth it.

In this series of postings, we are going to show you how to build a simple solar tracking system using a Raspberry Pi and a stepper motor.   The purpose of this project is to verify experimentally the gain in power from a solar panel from using tracking versus a fixed solar panel.

All the graphs in this series of posting are done using MatPlotLib on the Raspberry Pi.

There are four parts in this series of postings.

 

 

SunTracking – The Theory

We never seem to have quite enough power out of a single solar cell to run a Raspberry Pi all the time.  And the new Raspberry Pi’s take even more power.  One improvement you can make is to add the hardware to track the sun on your solar panels.  Tracking the sun can increase your solar power generation by 20%-30%.

Sunlight has two components, the “direct beam” that carries about 90% of the solar energy, and the “diffuse sunlight” that carries the remainder – the diffuse portion is the blue sky on a clear day and increases proportionately on cloudy days. As the majority of the energy is in the direct beam, maximizing collection requires the sun to be visible to the panels as long as possible.

At any fixed location the visible sun tracking across 180 degrees during an average 1/2 day period (more in spring and summer; less, in fall and winter). Local horizon effects reduce this somewhat, making the effective motion somewhere about 150 degrees. A solar panel in a fixed orientation between the dawn and sunset extremes will see a motion of 75 degrees to either side, will lose roughly 75% of the energy in the morning and evening. Rotating the panels to the east and west can help recapture those losses. This is why tracking the sun can improve your total output by about 20%-30%.

Now let’s see if those power improvement numbers are correct.   Verification by experiment!

The SunTracker System

Let’s take a look at the block diagram for SunTracker.

Figure1

There are two independent solar power systems, each run by a separate SunAirPlus solar power controller/data collector.   Each SunAirPlus has a 3 channel INA3221 current and voltage measuring I2C unit and is each connected to an identical Voltaic Systems 3.5W 6V solar panel.   We also have connected the 5V output of SunAirPlus to a 10W 10 Ohm load resistor (it is connected just to discharge the LiPo battery – more on that later).

The sun tracking solar panel is mounted on top of a 3D printed stand (ignore the cannon looking tubes on the front, they are left over from a previous experiment and then mounted on the shaft of a 5V Stepper motor.    The Stepper motor is driven by a Grove motor controller.

Because the two SunAirPlus controllers share the same I2C addresses, we use a Grove I2C 4 Channel Mux to switch between them.   We also are using one of the channels to drive the 5V Grove Motor Controller and the 5V stepper motor.   Each of the channels can be 3.3V or 5V, so this was a convenient way of doing that and still interfacing with the 3.3V Raspberry Pi.

One thing to remember about the way a solar power charger works is that the amount of power that will be used is dependent on the LiPo battery needing the power for charging.   LiPo batteries don’t like being under charged or over charged.   SunAirPlus has a LiPo charging chip that regulates the amount of power delivered to the battery.

The key to setting up this test is to discharge the battery with a 10 Ohm 10W resistor through the SunAirPlus 5V power supply (this protects the LiPo battery from being discharged too much).   You do this to both units so the battery is ready to take a full days worth of solar energy.   If you don’t do this (which we forgot to do on March 30th) you get the solar cell voltage graph below in Figure 2.  Note the solar panel voltage  climbs as the battery nears full charge.  Note further that the two batteries are in different charge state, with the Sun Tracked battery having a bigger charge than the non tracked battery.

Figure2
Figure 2 – LiPo Batteries Were Not Discharged on March 30
Figure3
Figure 3 – Appropriately Discharged LiPo Batteries

Figure 3 shows the solar voltage on March 31st when the battery has been discharged properly.

IMG_2607 2We also connected a Grove 128×64 OLED display to see what is going on real time with the SunTracker project.

 

What are Grove Connectors?

See our Grove Tutorial here.

Parts ListIMG_7861 3

 

Coming in Part 2

Next we  will go through the software used in SunTracker.