Zion: Solar Powered Desk

This will be the first one in my Smart Home series posts. Now that I have to work from my home desk, for don't know how many days, decided to revamp my desk with some electronic tweaks. My home desk may not be aesthetically the best one, but its awesome when it comes to its utility functions.

It occupies a small corner of my bedroom and is pluggable and moveable. Prima facie, it looks like a usual work desk, as I have tried best hiding most of its complexities to make it look clean, no clutter of wires.

I have been experimenting with this for few years now, trying and improving on many ideas, improvising based on observations and it's still ongoing. Its primary source of power is Solar power, with grid electricity as a backup option.

The Source

The desk obtains all its energy from these 140 watt solar panels mounted just outside of the window. Its a combination of three solar panels (50W+40W+50W) connected in parallel with total surface area of 6x2.5 feet. The window is facing West, and it's not top floor. So it gets direct sunlight only in second half of the day. The direct sunlight time is further limited by an early Sunset, thanks to the hills. Nonetheless the panels generate enough power for my desk, even in an ambient light. Average usual voltage at the panels is about 18V during the day.

Power Storage

The solar panels charge a 12V 65Ah battery, located right under the desk. I hate flooded lead-acid batteries due to the high maintenance and the hazardous fumes they generate. So I have chosen a dry battery, with no health hazard concerns and zero maintenance. Currently I am using an Exide sealed lead-acid battery. Usual lifespan of it is about 3 to 5 years.

Solar Charge Controller

Charging the battery directly from the solar panel can damage the battery and reduce its life. So a Charge Controller is must. I have tried and tested various solar charge controllers over years and finally settled down on this one ordered from Amazon. Its higher capacity one with microprocessor based control and can handle upto 260W for 12V and 520W for 24V solar panels. It has best heat dissipation, doesn't get heated at all. The built-in USB outlets are added advantage. In addition to the built-in LCD display, I have added an LED based voltage display, as you see at the bottom, so that the voltage is easily visible even during low light and at night.

It's extremely important to use right type and thickness of wires at right place to minimize losses and avoid risk of fire due to overheated wires. I am using 8 mm copper wires from battery to the controller and 4mm copper wires from solar to the controller and from controller to the load

The Load

So where all this energy collected being used? Its mainly used for lights, fans and charging all type of gadgets. All of them requiring DC only. The setup does not involve an inverter at all. I have always been avoiding introducing inverters due to their power inefficiencies. All the lights and fans are custom designed ones to run on 12V or 5V DC. Power is distributed to all consuming widgets from a small custom built hub where it's easy to add/remove connections as needed. The hub includes an additional fuse as a safety measure if some short circuit happens.

Charging all Electronic Gadgets:

Effectively it means that all my gadgets run purely on solar power. It includes all phones, tablets, smart watches, kindle, LED wall clock and even a tyre inflator that I use to pump air into my bicycle tyres.

Apart from the USB ports available in the solar charge controller, I have built couple of USB points right into the desk. This is a simple high ampere USB car adapter with added switch and an LED indicator.

Flexi Personal Fan:

This tiny custom built DC fan runs on 5V. Suffices a single person, can be turned to focus in any direction, safe even if you put your fingers through it while it's running. The blades are cut from a thin plastic sheet (Lid of a Shrikhand container to be specific :) ) and molded using a little heat treatment to give the right angles to the blade for optimum airflow. The blades are mounted on a DC motor from an old non-functional CD player. It is powered by a simple IC 7805 Voltage Regulator to convert 12V from battery to 5V necessary for the fan. The IC is mounted on same motor body itself so that the motor body acts as heatsink for the IC that can get super hot while stepping down the voltage.

A Static Fan:

There is another static fan that I once ordered from ebay. This one is a USB fan running on 5V.

Reading Lights

A 24 LED strip reverse mounted behind this fan acts as reading lights, the LEDs are not directly visible when you are at desk and generate nice ambient light for reading purpose.

Room Lighting:

Three different 12V LED panels with total of 156 LEDs generate enough light not only for desk but for whole room. All are mounted on big metal heatsinks and placed so as to produce ambient light with no direct sight. A separate 3 LED strip also acts as a night lamp.

Switch Panel:

Most lights/fans are controlled from this single switch panel at the back of the desk, not visible but easily reachable. It comprises of small DC switches mounted on a throwaway shaving-blades cartridge.

Charging Laptops:

When it comes to laptops, its not easy to charge them without inverter as most laptops need 19V as input and battery produces only 12V. I tried a small portable single output inverter for few days, but it gave up soon causing fluctuating output voltage. A portable car inverter is the next option I am going to try out now.

And finally the desk is equipped with power from the grid as a backup option, again, not so easily visible but reachable.