Adding More Solar Panels to SkyCam and WeatherSense Sensors

Sometimes your solar powered sensors are in less than an ideal position or location to keep your batteries fully charged by the solar power system. A cloudy climate (and remember that solar panels will still generate power on cloudy days, but not nearly as much) or a less than ideal position that you are mounting your sensor. If you find yourself in such a situation, it is easy to add additional solar panels to your system. This is a tutorial for adding additional solar panels to SkyCam and other WeatherSense Solar sensors.

What is WeatherSense?

WeatherSense is an open source protocol and software that allows weather and environmental instruments communicate with the Raspberry Pi, ESP32 and Arduino based computers. You have ALL the software source code available to learn how these devices work and to make your own modification. A great way to learn and develop your own abilities.

The WeatherSense Sensors

SwitchDoc Labs has developed a set of WeatherSense compatible sensors and has several others in development. The current list of supported sensors are:

For more detailed information on WeatherSense, check out this article.

The Solar Powered SkyCam takes the most power of any of these sensors because it is WiFi and ESP32 based rather that 433MHz and a low power arduino 328p board (the Mini Pro Plus).

Power Consumption of WeatherSense Sensors

The average power consumption of all of the 433MHz WeatherSensor Sensors are given below.

Sensor	Average Current	Power	Notes
Solar Wireless Lightning Detection	23mA	115mW	With LEDs On
Solar Wireless Air Quality	26mA	130mW	With LEDs on and optional power reduction modification
Solar Wireless Earthquake Detection - AfterShock	23mA	115mW	WIth LEDs On

There are jumpers on each one of these so you can disable the LEDs on the Mini Pro Plus controller boards to save an additional 10mA. We haven’t done that because it is very helpful to see the LEDs during testing. Plus they are cool to look at night. With the included 330mA solar panel (nominally running at 5V when charging) producing 1650mW (milli Watt) of power, you can see that just a couple hours of good sun light will keep these batteries Chuck charged up. Below is a chart of the solar power performance of the Solar Air Quality Sensor. The Solar power data is recorded on the units and then sent to your Raspberry Pi. We LOVE data and this device generates a bunch of data that you can use to fine tune your system.

Power and Efficiency

Remember that to compare currents and voltages and calculate efficiencies, you need to calculate power (Watts). Power = Voltage * Current. For example, in the chart below, we can calculate the load power (the load is the MiniPro Plus and sensors) is 130mW (5V * 26mA – the 26mA takes into account turning the AQI sensor on for a minute every 15 minute – that doesn’t show up in the graphs). Now looking at the battery power, we calculate the power from the battery as 164mW (~4V*41.2mA). The efficiency of this system is equal to 1 – (load power)/(battery power) or 1-(130mW/164mW). This equation gives us an efficiency of about 79%. This is pretty normal for these kinds of power supplies at these current levels. Where does the rest of the power go? Into heat. The power supply uses that ~20% to boost the voltage from ~4V to 5V for the sensor and computer. Using this equation and the data below, we can also calculate the solar power to battery efficiency. Taking one point when the battery is being charge at a high rate we get a panel to battery efficiency of ~80% (1-(4V * 194mA)/(4.8V*202mA)).

Note that the Solar Panel is keeping the battery fully charged. When the solar panel voltage jumps up above 5V that means the battery is fully charged. Great to have all this data!

Curious about the performance of various small solar panels? Here is a benchmark test article.

Solar Powered SkyCam

The Solar Wireless SkyCam is a solar powered remote controlled low power ESP32 based camera that you build and can modify yourself. The ESP32 periodically wakes up from a low power mode (not deep sleep – we will publish another article about the problems with deep and light sleep on the ESP32. It’s a reliability problem with startup) takes a picture, solar data readings and packages the picture and data into MQTT packets for the data an the picture. We break the picture into chunks with error detection and error correction to ensure reliable transmissions to your Raspberry Pi.

You can have multiple SkyCams on one system to get a complete view of your local weather environment.

Power Consumption on the Solar SkyCam

To measure the power consumption of the Solar Sky Cam, we hooked up a Raspberry PI to the SunAirPlus I2C interface connected to the SunAirPlus INA3221 on the solar controller (measures voltage and currents for the solar panel, battery and load). Then we used the Raspberry Pi DataLogger software to record the current through 4 cycles of picture taking to get a good average current reading to calculate power. Most of the power used by the Solar SkyCam comes when the ESP32 is fully awake and taking a picture. By default, the ESP32 wakes up every one minute to record solar data, take a picture and transmit that data to the Raspberry Pi. This is programmable from the Raspberry Pi (the Pi sends a control MQTT packet to the SkyCam ESP32) so to show the power difference, we ran three different scenarios for picture taking: Every 1 minute, 2 minutes or 3 minutes. Here are resulting current graphs:

SkyCam Power — SkyCam 2 Minute Picture Interval

Here is the power summary for the above charts and time intervals.

SkyCam Picture Interval	Current	Power	Notes
1 Minute	75.25mA	376mW	As of V19 of SkyCam ESP32 Software
2 Minutes	60.15mA	301mW	As of V19 of SkyCam ESP32 Software
3 Minutes	56.64mA	283mW	As of V19 of SkyCam ESP32 Software

Why do we specify the software version? We are still looking to further reduce the average current from SkyCam and hopefully will improve it on and ongoing basis. There are still some tricks that we might be able to get another 15mA or so by switching off some specific peripherals on the ESP32 and popping LEDs off the board.

The power used by SkyCam (at 1 minute intervals) is roughly 3 times the power used by the other WeatherSense Solar sensors. Why is this? Two main reasons:

1) SkyCam generates a bunch more data and does some really complex data crunching

2) SkyCam uses WiFi to send all this data back to the Raspberry Pi

Both of these things take a lot more power than the Mini Pro Plus and the 433MHz transmitter used in the other sensors.

With our test unit, we specifically placed it where it only got sun for part of the day and we found that it ran the battery down after about 3 days. No surprise there. Remember we are using over 300mW versus only about 100mW. Looking the curves, we conclude that adding one additional panel (doubling the solar power) should put us over the top in our test location.

NOTE: You may have a more sunny spot in mind for your SkyCam and in that case you should be fine. Our units have no trouble down in Palm Springs for example, but our company location in Spokane Washington is more cloudy in general (not as bad as Seattle however).

Adding an Additional 330mA Solar Panel to SkyCam and WeatherSense Instruments

We will be focusing on the Solar SkyCam in this assembly guide. Keep in mind that the process is the same for any of the other Solar WeatherSense sensors.

To add an additional solar panel (up to 4 if you wish) requires a solar panel junction board to keep the boards separate (in case of failure, partial covering, different performance, etc.). With this board we just plug it in and then add the solar panels.

The Solar Panel Connector Board has four diodes that protect the up to four solar panels and keeps the current flow heading for the battery even if one of the solar panels dies or is in the shade while the others are still working. This board comes with a 20cm female to female JST-2 cable for plugging into the solar input port of the Solar SkyCam solar power controller board.

The attached diodes are a Schottky 40 Volt 3A diode. Note, this board is limited to connecting 6V Solar Cells, even if the diode is rated at 40V. We choose the diode for it’s low forward diode drop (Vf = 0.45V) and the current rating.

Parts List

Following is the parts list for adding an additional panel. Up to three additional panels may be added this way. The Solar Bracket provided with the WeatherSense sensors (including the Solar SkyCam) only will mount 2 panels. You will have to improvise a four panel mounting bracket like this one on Thingiverse.

Plug the 20cm female to female JST-2 cable into the solar input on the SunAirPlus2 (or SunAirPlus 3) board in your Solar SkyCam kit. Plug the other end in the “To Solar Charger Board” input on the picture above. Next plug in your two 330mA solar panels. You are now done. Below we show you how the wiring works for the completed units.

Results

The below chart shows the information being transmitted from the SkyCam Solar Controller to the Raspberry Pi. While the current graph (we will update in a few days) only shows about 2 days of data, things are looking really good for keeping the batteries charged in our test location (which could be improved greatly by placing Solar SkyCam more in the sun with the panels facing south rather than south east as in our test setup).

We will be updating this chart over the next week.

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Tutorial: Adding More Solar Panels to SkyCam and WeatherSense Sensors