Solar Charging Station

As part of the sustainable initiative at the NYU MakerSpace, a solar charging station was developed by the sustainability team to allow access to free solar energy to the NYU community. The project furthered to power a Bantam Tools Othermill 24/7.

Parts

Here is the list of parts of the solar panel charging station system. I only mentioned specifications that would be most often referenced, the full specifications can be found in their respective data sheets.


Solar Inverter

  • Power (2 AC Outlets): 1200W Rated

  • USB output: 1xDC 5V/2.4A (max)

  • Nominal input voltage: 9.8-16VDC

  • Nominal output voltage: 110-125VAC

  • 20A solar charge controller (PWM): 300Watt


Battery

  • Voltage: 12VDC

  • Amp Hours: 100Ah

  • Battery Power Type: Sealed Lead Acid (SLA AGM)

Parts

Solar Panel

  • Open Circuit Voltage (Voc): 24.3 V

  • Short Circuit Current (Isc): 5.21 A

  • Optimum Operating Voltage (Vmp ): 20.4 V

  • Optimum Operating Current (Imp ): 4.91 A

  • Maximum Power at STC: 100 W


Power Meter

  • Voltage: 300VDC (max)

  • Current 0-300A (max)


Cables & Miscellaneous

Schematic

Below is the schematic (link) for the solar panel charging station. The solar panel is represented as a fixed voltage source in the schematic, but is not the case in practice. The power meter and solar inverter were made as custom parts therefore simulation testing is not possible and is just for visualization purposes.

Assembly

I connected two ring crimp terminals (the largest ones in the kit) to the ends of the wires in the solar panel. These ring crimps were then connected to the charge controller +/- solar panel input via screw terminals. This supplies the energy generated from the panel to the inverter.

I then took the battery meter and connected the +/- voltage source connectors to the +/- terminals of the battery. This is to power the battery meter itself. I then connected the two ends of the shunt on the battery meter to the negative end of the battery to the negative end of the battery connector in the solar inverter.

The positive end of the battery is then directly connected to the positive end of the battery connector in the solar inverter.

That's all for the connections and your solar charging system should be ready to go for testing!

Testing

I want to check battery health since the battery is second hand by seeing how quickly it discharges and simultaneously see how quickly can the solar panel charge the station.

For testing, I decided to use the Othermill PCB Milling Machine to mill out a LED Name Badge. Here's the finished product of the board and a clip of the badge being milled. The badge is powered by a coin cell battery to light up 2 LED's. The traces were designed for aesthetic purposes along with the texts and images.

Here is a table of the voltage, amps, wattage, and watt-hours tracked by the power meter across the battery terminals.

Power Meter Readings

In row 2 under the Amps column, the reason why the current is negative is because that is when everything is off allowing for the solar inverter to charge the battery with the solar panel. When charging a battery the current reverses causing for a negative current reading. After components are turned on and there is a demand for power the battery begins to discharge to supply the power causing the current to reverse once again. Below is an image from How do Battery charging? Necessity of Battery charging By Er. Roshan Tajne to demonstrate the current behavior

Above is a PDF outlining a quick guide to the solar panel and how upgrades can be made. This was made for future staff at NYU MakerSpace who will carry on the project after me.