Photovoltaic category

Researchers Developed Highly Durable Washable And Stretchable Solar Cells

Scientists of Japanese research institute RIKEN and the University of Tokyo have successfully developed a product that allows solar cells to continue to provide solar power after being washed, stretched and compressed. Takao Someya of Riken Center for Emergent Matter Science, a designated national R&D Institute in Japan, led the research team.

Washable and stretchable solar cell
Washable and stretchable solar cell

The research results were published in the journal Nature Energy and illustrated a photovoltaic material that could be used to make washable outer garments and wearable devices. The researchers say that the innovated solar cells will be a power source to low-power devices and can also be worn concurrently. This innovation might solve one of the biggest challenges of the Internet of Things (IoT), the requirement of a reliable power source to keep all devices connected.

The newly invented solar cells could power wearable devices that include health monitors and sensors for analyzing the heartbeat and body temperature. This could make prevention and early detection of potential medical problems possible. Though the concept of wearable solar cells is not unique, the previous wearable solar cell solutions suffered from the lack of one vital property i.e. long-term stability in air and water, including resistance to deformation.

The recent stretchable solar cell innovation has successfully achieved all of the most important features and is creating the way for the top-notch quality of modern wearable technology. The material on which their new device is based on is called PNTZ4T – a highly efficient polymer solar cell capable of small photon energy loss. The scientists deposited the device onto a parylene film which was then placed onto an acrylic-based elastomer. The construction method has proved to be particularly very durable.

The device produced 7.86 milliwatts per square meter based on a sunlight simulation of 100 milliwatts per square meter before considering resistance and durability. It showed the least decrease in efficiency when soaked in the water and when stretched. The efficiency decreased by only 5.4 percent and 20 percent respectively. Kenjiro Fukuda of RIKEN Center for Emergent Matter Science said,

We were very gratified to find that our device has great environmental stability while simultaneously having a good efficiency and mechanical robustness. We very much hope that these washable, lightweight and stretchable organic photovoltaic will open a new avenue for use as a long-term power source system for wearable sensors and other devices.

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.

Next Generation Solar Cell To Absorb Nearly All Solar Spectrum

Next Generation Solar Cell That Can Capture Nearly All Energy of Solar Spectrum

Researchers developed a multijunction solar cell on a GaSb substrate that can efficiently convert the long-wavelength photons typically lost in a multijunction solar cell into electricity. This prototype cell has an efficiency of 44.5% which is higher than conventional solar cells.

Next Generation Solar Cell To Absorb Nearly All Solar Spectrum
Next Generation Solar Cell To Absorb Nearly All Solar Spectrum

A GaAs-based cell is stacked mechanically with the GaSb-based materials to create a four-terminal, five junction cell with a spectral response range covering the region containing greater than 99% of the available direct-beam power from the Sun reaching the surface of the Earth. By comparison, the most typical solar cell can convert only one fourth of the available energy into electricity.

The working principle of this new solar cell is slightly different than the commonly available one. The cell is assembled in a mini-module that has a lens with a geometric concentration ratio of 744 suns. The lenses to concentrate sunlight onto tiny, microscale solar cells. As the solar cells have a very tiny form factor of  1 mm², solar cells using more complicated materials can be developed cost effectively.

The stacked cell acts like a filter with a particular material in each layer to absorb a specific range of wavelength of sunlight. The stacking procedure uses the transfer-printing technique which enables three dimensional modeling of these super-tiny devices with a high degree of precision.

Around 99 percent of the power contained in direct sunlight reaching the surface of Earth falls between wavelengths of 250 nm and 2500 nm. The entire range is not accessible by conventional solar panels as they are made from abundant, cheaper materials, such as silicon. Matthew Lumb, the lead author of the study and a research scientist at the GW School of Engineering and Applied Science, said,

Our new device is able to unlock the energy stored in the long-wavelength photons, which are lost in conventional solar cells, and therefore provides a pathway to realizing the ultimate multi-junction solar cell.

The cost of this specific solar cell is pretty high due to the high-end materials used and complex technologies implemented. However, the researchers achieved the upper limit of possibility in terms of efficiency. The new solar cell shows much promise in spite of being highly expensive. perhaps in future, the production cost can be reduced and the similar solar cell will be available commercially in the market.

Using a supercapacitor for power management and energy storage with a small solar cell

& @ writes:

In Part 1 of this series, we have reviewed solar cell performance, how to select and size the supercapacitor, requirements of supercapacitor charging circuits and charging IC characteristics. We will now use two case studies to illustrate these properties in detail.

Using a supercapacitor for power management and energy storage with a small solar cell – [Link]

MPPT solar charger

Lukas Fässler from Soldernerd has been working on revised version of his MPPT Solar charger project:

Over the last few weeks I have been quite busy with my MPPT Solar Charger project. I’ve built up a first board and started writing firmware for it. Since the last version was not too different in terms of hardware I was able to re-use most of that code. But I hadn’t even touched on the whole USB stuff back then so there was still a lot of work to do. While the project is still far from being complete I am happy to say that I’ve made quite some progress. Most importantly, the new design seems to work well and so far I haven’t found any mistakes in the board layout. But let’s go through this step by step.

MPPT solar charger – [Link]

BQ25504 Solar Cell LiPo Charger

by Pesky Products @

This is a small (0.5 x 0.5 inch) breakout board for Texas Instrument’s BQ25504 Ultra Low Power Boost Converter with Battery Management for Energy Harvesting Applications.

BQ25504 Solar Cell LiPo Charger – [Link]


Circuit implements photovoltaic-module simulator


José M Blanes and Ausiàs Garrigós writes:

Electronics engineers often use photovoltaic-module simulators to test dc/dc-power converters, inverters, or MPPT (maximum-power-point-tracking)-control techniques. The use of these simulators lets you work in the laboratory with predefined photovoltaic conditions, thus avoiding the drawbacks of real photovoltaic modules. Various commercial simulators are available, but they are often expensive.

Circuit implements photovoltaic-module simulator – [Link]

How to connect a Solar Inverter in 10 minutes

Let’s connect a solar power inverter for AC voltage output in just 10 minutes.

How to connect a Solar Inverter in 10 minutes – [Link]

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:

MPPT solar charger


Lukas Fässler show us his progress on the MPPT solar charger:

One of my main goals with this design is to achieve very low standby current, somewhere in the tens of microamps. The basis for this is a low-power buck on the basis of a Texas TPS62120 where the microcontroller can switch the output voltage between 2.2 and 3.3 volts nominally. This works as intended. With no load and the output voltage low, the supply consumes 12.9 microamps at 12V input voltage. With the high output voltage the idle current goes up to 14.3uA. Quite a bit of that current is due to the voltage divider that sets the output voltage. The regulator itself consumes about 9uA in both cases.

MPPT solar charger – [Link]