Solar category

Bismuth Oxyiodide (BiOI)—A Non-toxic Alternative To Solar Cells

Bismuth is considered as a “green-element” and bismuth-based compounds are gaining attention as potentially non-toxic and defect-tolerant solar absorbers. The researchers of the University of Cambridge and the United States developed theoretical and experimental methods to show that bismuth, which sits next to lead (Pb) on the periodic table, can be used to make inexpensive solar cells.

Bismuth oxyiodide light absorbers
Bismuth oxyiodide light absorbers

The study suggests that solar cells including bismuth can have all the exceptional properties of lead-based solar cells but without any worries about toxicity. Another study by a different group discovered that bismuth-based solar cells have the ability to achieve a conversion efficiency of 22% which is comparable to the conversion efficiency of most advanced solar cell available in the market.

Many of the new materials recently investigated show limited photovoltaic performance. Bismuth Oxyiodide (BiOI) is one such compound and it is explored in detail through theory and experiment. Most of the solar cells commercially and domestically used are made from silicon (Si) which is efficient enough but has very low defect tolerance compared to bismuth oxyiodide. Low defect tolerance in silicon implies that the silicon needs to have very high levels of purity, making the production process energy-intensive.

Over the past several years researchers have been looking for an alternative to silicon for making solar cells cost effectively. The most promising group of these new materials are called hybrid lead halide perovskites. Unlike silicon, they don’t need such high purity levels. Hence, production is cheaper. But, the lead contained within perovskite solar cells represents a definite risk to all living beings and the environment. So, scientists are searching for non-toxic alternatives without compromising the performance.

Dr. Robert Hoye of Cambridge’s Cavendish Laboratory and Department of Materials Science & Metallurgy said,

We wanted to find out why defects don’t appear to affect the performance of lead-halide perovskite solar cells as much as they would in other materials.

The researchers are trying to figure out what’s special about the lead halide perovskites so that they can replicate their properties using non-toxic materials like bismuth.

Their research found that bismuth oxyiodide is as defect tolerant as lead halide perovskites are. Another interesting fact is, bismuth oxyiodide is stable in air for at least 197 days which is even better than some lead halide perovskite compounds. By sandwiching the bismuth oxyiodide between two oxide electrodes, the researchers successfully converted 80% of light to electrical charge.

Solar Power Module v2

Chip McClelland @ published his solar li-po battery charger based on MCP73871 to manage the solar and DC charging of the LiPo battery, TPS63020 Buck-Boost Converter and Maxim 74043 LiPo Fuel Gauge. He writes:

I build connected sensor which are often deployed in local parks where there is no access to utility power. Over the past couple years, I have been refining and testing my solar power modules and have arrived at this compact integrated design. I have a number of these deployed and they have been in continuous service for up to two years. I wanted to share this design in case it might be helpful for your projects. I would also greatly appreciate any input or suggestions on this design so v3 will be even better.

Solar Power Module v2 – [Link]

LiFePO4wered/Solar1 – Solar power supply for IoT devices

Patrick Van Oosterwijck @ writes:

Solar power is not trivial, especially if it needs to be reliable and have a long lifetime for outdoor deployment such as IoT sensor nodes. This project is an effort to create a complete, easy to use solar power system that provides the following features:
– LiFePO4 battery for high charge cycle count, high temperature performance and 3.2V output voltage (compatible with most chips used in IoT).
– Switch mode MPPT charge controller for high efficiency, 5-30V solar input range.
– Charge and output current up to 2A (depending on the battery capacity).
– Automatic heater control to bring the battery up to temperature before charging, ensuring maximum battery life.
– Low voltage cutoff disconnects the load from the battery when the battery voltage becomes too low, again ensuring maximum battery life.
– User can set MPPT voltage, charge current and connect an external thermistor if desired.

LiFePO4wered/Solar1 – Solar power supply for IoT devices – [Link]

Efficient Low-Cost Solar Energy Converter

Researchers at the École Polytechnique Fédérale de Lausanne and the Centre Suisse d’Electronique et de Microtechnique have invented a new device to store solar power while the sun’s not shining by converting it into Hydrogen. Although many current methods use the same approach to store energy, but this device rivals them in stability, efficiency and cost.

An effective and low-cost solution for storing solar energy © Infini Lab / 2016 EPFL


They combined commercially available components that have already proven effective in industry, such as Nickel, in order to develop a robust and effective system, that is  :made up of three interconnected, new-generation, crystalline silicon solar cells attached to an electrolysis system that does not rely on rare metals. The device is able to convert solar energy into hydrogen at a rate of 14.2%, and has already been run for more than 100 hours straight under test conditions.”

In order to develop this device, the researchers used layers of crystalline silicon and amorphous silicon to allow higher voltages. Thus, three cells in series generate a nearly ideal voltage for electrolysis.

“We wanted to develop a high performance system that can work under current conditions,” says Jan-Willem Schüttauf, a researcher at CSEM and co-author of the paper. “The heterojunction cells that we use belong to the family of crystalline silicon cells, which alone account for about 90% of the solar panel market. It is a well-known and robust technology whose lifespan exceeds 25 years. And it also happens to cover the south side of the CSEM building in Neuchâtel.”

This method, which outperforms previous efforts in terms of stability, performance, lifespan and cost efficiency, is published in the Journal of The Electrochemical Society. You can check the scientific paper here.


Arduino based sun tracking turret

Arduino Based Sun Tracker Turret

Sun tracker systems are widely used in solar panel setups to get maximum performance. You may want to use one in your personal solar panel setup. Now you can make your own with an Arduino, following the project that’s designed by RobotGeek Team and Wade Filewich.

Arduino based sun tracking turret
Arduino based sun tracking turret

Parts You’ll Need:

You should also upload the sketch in Arduino. So download it from GitHub –> desktopRoboTurretV3.

To upload the sketch in Arduino,

File → Sketchbook → desktopRoboTurretV3 → roboTurret3_solarTracker

Now click Upload.


Sun Tracker Turret Based On Arduino
Sun Tracker Turret Based On Arduino

Place the light sensors in correct position and wire them to Arduino accordingly. Any wrong positioning can generate strange behavior of the system.  Jumpers for the servos (pin 9, 10, and 11) are set to VIN, so that your servos function properly.

(NOTE: A 6V power supply will work just fine, and RoboTurret Kit includes one). Here is the chart of wiring:

Wiring list of servo and Arduino : Sun tracker
Wiring chart of servo,light sensor, potentiometer and Arduino : Sun tracker

There are two potentiometers. One is for controlling the speed of servos, and another is for controlling the sensitivity of sensors.

Set Up The Turret:

You should follow Desktop RoboTurret Assembly Guide to build the turret. After building, attach your sensors to the top plates as close to center as possible. Look at the picture:

Sensor Positions On Turret
Sensor Positions On Turret

The “+” shaped fins cast shadow on sensors. So, position of sensors should be correct else fins can’t cast shadow  on them accurately. Have a close view on sensor’s position:

Sensor position on turret : close lookup
Sensor position on turret : close view

While wiring through the plate, keep wires loose enough so that turret can move freely to aim at the Sun. At the back of the turret base, there is plenty of room to mount the two potentiometers.

The fins are 8 inches tall, which should be plenty to cast shadow on the sensors. I’ve used scrap cardboard for the fins, but you can use whatever material suits you best, so long as it is opaque and can throw a shadow.

Test It:

So, you finished the building process. Now let’s test it. Upload the code to Arduino and power up the system. Now hold a table lamp and move it. The turret should follow the movement. Adjust speed and sensitivity using the two potentiometers. Watch the video that demonstrates the system:

A very simple DIY solar-powered USB charger


Raj @ tipped us with his latest project. It’s a simple, but useful USB Solar powered charger able to charge a power bank or your smartphone.

Yesterday, I built a very simple DIY solar-powered USB charger for my TP-link 10400mAh USB Power Bank. All I needed was a 6V/3.5W solar panel and the TD1410-based 5V buck converter module. I bought both of them on Aliexpress for less than $8.

A very simple DIY solar-powered USB charger – [Link]

21.1% efficiency with Perovskite solar cells


Scientists have successfully developed a Perovskite solar call containing Cesium which has attained an efficiency of 21.1%, as well as a world record for reproducibility. by Denis Meyer @

In adding Cesium, the scientists at EPFL, let by Michael Saliba, have developed the first Perovskite compound with triple cations (Cs/MA/FA). These new films are more stable in hot conditions and less affected by fluctuations in environmental variables. They have confirmed efficiencies of 21.1%, and exit efficiency of 18% in operational conditions, even beyond 250 h.

21.1% efficiency with Perovskite solar cells – [Link]

SolarBoost – Make Your Own USB Solar Mobile Charger


SolarBoost is an open source smart interface that allows you to build your own powerful and portable solar charger for your phone and other mobile devices. It has two USB ports and can provide 5V @ 2A at each of them and is controlled by a 8-bit 32MHz Microchip PIC microcontroller. It is also equipped with various protection features like soft-start, over-temperature, over-charge, over-discharge, short-circuit and current limiter.

SolarBoost is the first open-hardware and open-source smart interface designed to give you the freedom and flexibility to make your own battery- and solar-powered power bank for charging cellphones, tablets, MP3 players, speakers, GPS navigators, and much more. Use it to also power your DIY electronics projects!

SolarBoost – Make Your Own USB Solar Mobile Charger – [Link]

Organic solar cells set new efficiency record


The German company Heliatek has developed new OPV multi-junction solar cells with an efficiency of 13.2%. This is a world record for organic solar cells.

Thanks to the excellent low light and high temperature behavior of the organic semiconductor, the electricity generation of the newly developed cells corresponds to the output of conventional solar cells with 16 to 17% efficiency when both are under real world conditions.

Organic solar cells set new efficiency record – [Link]