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Batteries A side view of my plug and play solar system

Published on March 4th, 2017 | by Nicholas Brown


Packaged Solar System Concept Demonstrates An Integrated Approach

March 4th, 2017 by  

A few years ago, I constructed a “plug and play” solar system concept, which contains a 12 volt solar power input, charge controller, lead-acid battery, 120 volt inverter, and 120 volt receptacles for experimental purposes. I wanted to see if this packaged concept could be practical, so I’ve been using it to power things such as my stereo, laptop, and tablet using a 20 watt solar panel. So far, I’ve had no issues with it, as the charge controller handled everything for me.

A side view of my plug and play solar system

Last month, I finally decided to take it to the next level and integrate an automatic transfer switch that monitors the battery, and seamlessly switches appliances to the grid in the event of an overload or a low state of charge (SOC), which may be necessary during prolonged cloudy periods. All I needed to make that work (for a small-scale project like this, which doesn’t connect to a household’s electrical wiring) was to plug a 120 volt power cord from it to a grid-connected power outlet as shown in the video below.

The primary objective of this project is to make solar system installation easier and hopefully cheaper by reducing the amount of on-site assembly required (for example: connecting the batteries, inverter, transfer switch, and charge controller).

While this is an off-grid concept, the inverter can be replaced if you want to connect it to the grid.


  • Battery capacity: 144 Wh (12 volts, 12 Ah)
  • Voltage: 12 volts
  • Output voltage: 120 volts

Capacity-wise, a unit of this size is best suited for wireless routers, modems, cordless phones, laptops, smartphones, tablets, and set-top boxes.

Transfer Switch Parts

  • 250 volt, 10 amp, 8-pin plug-in relay (Double Pole Double Throw, or DPDT)
  • TIP122 darlington transistor
  • 12 kOhm resistor
  • EFM8UB1 MCU kit
  • 1/2 watt resistive voltage divider

Current Status: It’s undergoing an upgrade, and will have a USB power supply for connection to USB wall outlets. shortly. The power supply has been constructed — I just need to install it and run the power cable.


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About the Author

writes on CleanTechnica, Gas2, Kleef&Co, and Green Building Elements. He has a keen interest in physics-intensive topics such as electricity generation, refrigeration and air conditioning technology, energy storage, and geography. His website is: Kompulsa.com.

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