If you were not aware, LEDs can also work in reverse: they deliver tiny amounts of current, in the microamp range, when illuminated. If you look on YouTube you can find several videos of solar panels built with arrays of LEDs, but powering an electric motor with a single 3 mm LED is something that we’ve never seen before. [Slider2732] built a small electric motor that happily runs from a green LED in sunlight.
The motor uses four coils of 1,000 ohms each. Using coils with many turns of very fine wire helps to draw less current while keeping an appropriate magnetic field for the motor to run. To keep friction at a minimum, the rotor uses a needle that hangs from a magnet. Four neodymium magnets around the rotor are periodically pushed by the coils, generating rotation. A simple two-transistor circuit takes care of the synchronization and yes, the motor does run on the four microamps provided by the LED, and runs pretty well.
Building motors is definitely an enjoyable activity, these small pulse motors can be built in just a couple of hours. You can use coils with just a few tens of turns which are much more easy to make but of course you will need something more than four microamps! The nice part of making an ultralow current motor like this is that it can run for a very long time on a tiny battery or even a capacitor, we invite you to try building one.
Solar cells have gotten cheaper and cheaper, and are becoming an economically viable source of renewable energy in many parts of the world. Capturing the optimal amount of energy from a solar panel is a tricky business, however. First there are a raft of physical prerequisites to operating efficiently: the panel needs to be kept clean so the sun can reach the cells, the panel needs to point at the sun, and it’s best if they’re kept from getting too hot.
Along with these physical demands, solar panels are electrically finicky as well. In particular, the amount of power they produce is strongly dependent on the electrical load that they’re presented, and this optimal load varies depending on how much illumination the panel receives. Maximum power-point trackers (MPPT) ideally keep the panel electrically in the zone even as little fluffy clouds roam the skies or the sun sinks in the west. Using MPPT can pull 20-30% more power out of a given cell, and the techniques are eminently hacker-friendly. If you’ve never played around with solar panels before, you should. Read on to see how!
The war of the currents was fairly decisively won by AC. After all, whether you’ve got 110 V or 230 V coming out of your wall sockets, 50 Hz or 60 Hz, the whole world agrees that the frequency of oscillation should be strictly greater than zero. Technically, AC won out because of three intertwined facts. It was more economical to have a few big power plants rather than hundreds of thousands of tiny ones. This meant that power had to be transmitted over relatively long distances, which calls for higher voltages. And at the time, the AC transformer was the only way viable to step up and down voltages.
But that was then. We’re right now on the cusp of a power-generation revolution, at least if you believe the solar energy aficionados. And this means two things: local power that’s originally generated as DC. And that completely undoes two of the three factors in AC’s favor. (And efficient DC-DC converters kill the transformer.) No, we don’t think that there’s going to be a switch overnight, but we wouldn’t be surprised if it became more and more common to have two home electrical systems — one remote high-voltage AC provided by the utilities, and one locally generated low-voltage DC.
Why? Because most devices these days use low-voltage DC, with the notable exception of some big appliances. Batteries store DC. If more and more homes have some local DC generation capability, it stops making sense to convert the local DC to AC just to plug in a wall wart and convert it back to DC again. Hackaday’s [Jenny List] sidestepped a lot of this setup and went straight for the punchline in her article “Where’s my low-voltage DC wall socket?” and proposed a few solutions for the physical interconnects. But we’d like to back it up for a minute. When the low-voltage DC revolution comes, what voltage is it going to be?
[Jared Sanson] has a solar power setup on his beach house, consisting of 6 panels and a 24V battery bank, supplied by Outback Inc. Their chargers and inverters pair over a seemingly proprietary connection with a controller known as the MATE. The MATE has a standard serial output which gives some details about the operation, but [Jared] wasn’t getting the detailed information they could get from the controller’s screen. This meant it was time to reverse engineer the proprietary connection instead, which [Jared] calls MateNET.
The controller interfaces with the chargers over a Cat5 cable. [Jared] initially suspected RS-485, but it turned out to be regular serial at 0-24V logic levels, at 9600 baud, 9n1. To figure out the pinout, [Jared] went through the MATE circuitry with a fine-toothed comb, discovering an ATMEGA32. Since both the MATE’s user output & its connection to the other equipment are both serial, a logic mux is used to split the ATMEGA32’s single UART between the two serial connections. With the physical layer sorted, it was time to figure out how the protocol worked.
Making solar cells out of silicon is difficult. There’s plenty of manufacturing steps, many of them at very high temperatures, and you need a high vacuum and a clean room. However, perovskite solar cells–cells made with hybrid organic-inorganic materials in a perovskite crystal structure–are relatively easy to make using wet chemistry involving solvents or vapor deposition.
In theory, silicon solar cells could be 30% efficient, but in reality, 25% seems to be a practical limit with commercial cells typically topping out at 20%. Perovskite cells are nearly that high now, and could be higher by stacking thin layers, each sensitive to different wavelengths of light.
A recent development at the Lawrence Berkeley National Laboratory may lead to even more efficient perovskite cells. Researchers found that certain crystal structures had a much higher efficiency than other structures. The problem now is figuring out how to produce the crystals to increase the prevalence of that structure.
What’s the size of a standard euro-palette, goes together in 15 minutes, and can charge 120 mobile phones at one time? At least one correct answer is Sunzilla, the open source solar power generator. The device does use some proprietary components, but the entire design is open source. It contains solar panels, of course, as well as storage capacity and an inverter.
You can see a video about the project below. The design is modular so you can pick and choose what you want. It also is portable, stackable, and easy to transport. The team claims they generate 900W of solar power and can store 4 kWh. Because of the storage device, the peak power out is 1600W and the output is 230V 50Hz AC.
[Oitzu] in Germany wrote in to let us know about a series of short but very informative blog posts in which he describes building a series of solar-powered, networked birdhouses with the purpose of spying on the life that goes on within them. He made just one at first, then expanded to a small network of them. They work wonderfully, and [Oitzu]’s documentation will be a big help to anyone looking to implement any of the same elements – which include a Raspberry Pi in one unit as a main gateway, multiple remote units in other birdhouses taking pictures and sending those to the Pi over an nRF24L01+ based radio network, and having the Pi manage uploading those images using access to the mobile network. All with solar power.