Precise Sundial Tells Time To The Minute

July 21, 2021 by Bryan Cockfield 16 Comments

We’re always a fan of an interesting or unique clock build around here, which often use intricate pieces of technology to keep time such as weights and gears, crystal oscillators, or even a global network of satellites in the case of GPS. While these are all interesting methods of timekeeping, the original method of tracking the sun is often forgotten. With this clock, the sun is the main method of keeping track of time, but unlike traditional sundials it has a number of advancements that let it keep surprisingly accurate time. (Google Translate from German)

While most sundials can only show hours, this one from [leon andré], a retired physicist, has a method for displaying minutes as well. It uses pinholes instead of shadows to keep track of the position of the sun, with the pinhole casting a bright spot of sunlight onto a diagram below. The diagram keeps track of the minutes, and consists of curved lines which help account for the sun’s changing path throughout a typical year. The dial keeps track of local solar time, as any sundial would, but by rotating it along its vertical axis it can be calibrated for the timezone that it’s in regardless of its position.

As far as clock builds go, one that is completely passive like this semi-digital sundial is fairly unique, especially for its accuracy. And, when set to local solar time, it will be the most reliable method of keeping time long-term than possibly any other clock we’ve seen before, as long as it’s not too cloudy outside. On the other hand, it is possible to augment a sundial with some modern technology as well.

Thanks to [Adrian] for the tip!

Live Energy Monitor Helps Plan Power-Hungry Appliance Use

July 20, 2021 by Donald Papp 8 Comments

There are a lot of good reasons to have a better understanding of one’s household power use, and that is especially true for those that do their own solar power collection. For example, [Frederick] determined that it would be more efficient to use large appliances (like a dishwasher or washing machine) when there was excess solar power available, but the challenge was in accessing the right data in a convenient way. His Raspberry Pi-based live energy monitor was the solution, because it uses an LED matrix to display live energy data that can be consulted at a glance.

Interestingly, this project isn’t about hacking the power meter. What this project is really about is conveniently accessing that data when and where it is best needed. [Frederick] has a digital power and gas meter with the ability to accept a small wireless dongle. That dongle allows a mobile phone app to monitor power usage, including whether power is being taken from or exported to the grid.

Since [Frederick] didn’t want to have to constantly consult his mobile phone, a Raspberry Pi using a Pimoroni Unicorn HAT HD acts as a glanceable display. His Python script polls the power meter directly over WiFi, then creates a live display of power usage: one LED for every 250 W of power, with the top half of the display being power used, and the bottom half representing power exported to the grid. Now the decision of when to turn on which appliances for maximum efficiency is much easier, not by automating the appliances themselves, but simply by displaying data where it needs to be seen. (This kind of thing, incidentally, is exactly the idea behind the Rethink Displays challenge of the 2021 Hackaday Prize.)

As for those of us without a digital power meter that makes it easy for residents to access power data? It turns out there is no reason a power meter’s wireless service interface can’t be sniffed with RTL-SDR.

Automate The Farm With Acorn

July 1, 2021 by Bryan Cockfield 40 Comments

Farming has been undergoing quite a revolution in the past few years. Since World War 2, most industrial farming has relied on synthetic fertilizer, large machinery, and huge farms with single crops. Now there is a growing number of successful farmers bucking that trend with small farms growing many crops and using natural methods of fertilizing that don’t require as much industry. Of course even with these types of farms, some machinery is still nice to have, so this farmer has been developing an open-source automated farming robot.

The robot is known as Acorn and is the project of [taylor] who farms in California. The platform is powered by an 800 watt solar array feeding a set of supercapacitors for energy storage. It uses mountain bike wheels and tires fitted with electric hub motors which give it four wheel drive and four wheel steering to make it capable even in muddy fields. The farming tools, as well as any computer vision and automation hardware, can be housed under the solar panels. This prototype uses an Nvidia Jetson module to handle the heavy lifting of machine learning and automation, with a Raspberry Pi to handle the basic operation of the robot, and can navigate itself around a farm using highly precise GPS units.

While the robot’s development is currently ongoing, [taylor] hopes to develop a community that will build their own versions and help develop the platform. Farming improvements like this are certainly needed as more and more farmers shift from unsustainable monocultures to more ecologically friendly methods involving multiple simultaneous crops, carbon sequestration, and off-season cover crops. It’s certainly a long row to hoe but plenty of people are already plowing ahead.

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The Regulatory Side Of Rolling Your Own Moderate Solar Farm

June 17, 2021 by Donald Papp 25 Comments

[Russell Graves] lives in Idaho and recently connected his solar installation to the grid, which meant adhering to regulatory requirements for both the National Electric Code (NEC) as well as complying with the local power company’s own regulations. His blog post is an interesting look at the whole regulatory process and experience, and is of interest to anyone curious about running their own solar farm, whether they have plans to connect it to the grid or not.

A circuit breaker that met NEC code, but not the power company’s requirements.

The power company has a very different set of priorities from the NEC, and part of [Russell]’s experience was in having to meet requirements that weren’t documented in the expected places, so study of the materials didn’t cut it. In particular, the power company needed the system to have disconnects with conductors that visually move out of position when disconnected. [Russell] was using NEC-compliant circuit breakers that met NEC code, but they didn’t meet the power company requirement for conductors that can be visually confirmed as being physically disconnected. Facing a deadline, [Russell] managed to finesse a compliant system that was approved, and everything got signed off just as winter hit.

How well does his solar farm work out? Sometimes the panels produce a lot of power, sometimes nearly nothing, but it has been up and running for all of winter and into spring. Over the winter, [Russell] pulled a total of 3.1 MWh from the grid, mainly because his home is heated with electric power. But once spring hit, he started pushing considerably more into the grid than he was pulling; on some days his setup produces around 95 kWh, of which about 70 kWh gets exported.

[Russell] didn’t go straight to setting up his own modest solar farm; we saw how he began by making his own ideal of a perfect off-grid office shed that ran on solar power, but it has certainly evolved since then and we’re delighted to see that he’s been documenting every bit of the journey.

Better Solvents Could Lead To Cleaner, Greener Perovskite Solar Cells

May 30, 2021 by Dan Maloney 18 Comments

Regardless of appearances, almost all scientific progress comes at a price. That which is hailed as a breakthrough technology that will save the planet or improve the lots of those living upon it almost always comes at a cost, which sometimes greatly outweighs the purported benefits of the advancement.

Luckily, though, solving these kinds of problems is what scientists and engineers live for, and in the case of the potentially breakthrough technology behind perovskite solar cells (PSCs), that diligence has resulted in a cleaner and safer way to manufacture them. We’ve covered the technology of perovskites in the past, but briefly, as related to photovoltaic cells, they’re synthetic crystals of organometallic cations bonded to a halide anion, so something like methylammonium lead tribromide. These materials have a large direct bandgap, which means a thin layer of the stuff can absorb as much solar energy as a much thicker layer of monocrystalline silicon — hence the intense interest in perovskites for cheap, easily manufactured solar cells.

The problem with scaling up PSC manufacturing has been the need for volatile and dangerous solvents to dissolve the perovskites. One such solvent, dimethylformamide (DMF), commonly used in pharmaceutical manufacturing and often a component of paint strippers, is easily absorbed through the skin and toxic to the liver in relatively low concentrations. Another common solvent, γ-butyrolactone (GBL), is a precursor to γ-hydroxybutyric acid (GHB), a common recreational club-drug known as “liquid ecstasy”.

In a recent paper, [Carys Wrosley] and colleagues at Swansea University showed that γ-valerolactone (GVL), a far less toxic and volatile solvent, could be effectively substituted for DMF and GBL in perovskite manufacturing processes. One of the most promising features of perovskites for solar cells is that the solution can be easily applied to transparent conductive substrates; the use of GVL as a solvent resulted in solar cells that were comparably efficient to cells made with the more dangerous solvents.

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Solar Plane Is Like One Big Flying Solar Panel

May 29, 2021 by Lewin Day 15 Comments

Solar-powered plane concepts typically focus on high-efficiency glider-type designs, so as to make the best possible use of the limited power available from the sun. [rctestflight] wanted to try a different school of thought, instead building a relatively inefficient plane that nonetheless packed a huge amount of solar panels on board.

The plane consisted of a pizza-box style design, with a simple foam rectangular wing that was absolutely covered in solar panels. The plane was controlled with an off-the-shelf autopilot, and fitted with cheap, no-brand MPPT modules to handle charging the batteries. The plane faced difficulties in flight, most often with stability, which led to the autopilot getting the plane lost on one occasion. However, one flight was achieved with a full one hour and thirty minute duration, indicating the solar panels were helping to extend flight times beyond what was capable with batteries alone.

Further research on the ground showed that the cheap MPPT modules were wasting power, and there was more to be had. A better MPPT module was subbed in and showed that the panels could generate up to 5 amps under good conditions, while the plane only needed roughly 4.2 amps to fly. This would allow for indefinite flight in sunny conditions, though probably would not allow enough energy to be banked to fly 24 hours round the clock due to the lack of power at night.

We’ve followed [rctestflight]’s solar plane experiments for a while now, and can’t wait to see the next iteration. Video after the break.

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Magic Pyramids Blink Eternal With The Power Of The Sun

May 16, 2021 by Kerry Scharfglass 21 Comments

Without knowing it, we’ve spent years watching [Jasper Sikken] piece together an empire of energy harvesting equipment, and now he’s putting the pieces together into wonderful creations. His recently finished solar harvesting pyramids are mesmerizing objects of geometric perfection we’d love to see glinting in the sun.

These solar harvesting pyramids are well described by their name. Each one contains a PCBA around 30mm on a side with a solar energy harvester built around the dedicated AEM10941 IC, a single solar cell, and a very bright green LED. [Jasper] calculates that the solar cell will charge the super capacitor at 20uA at with just 200 lux of light (a level typical for casual indoor spaces) letting it run indefinitely when placed indoors. Amazingly with the LED blinking for 15ms every 2 seconds it will run for 21 days in complete darkness. And that’s it! This is a software-free piece of hardware which requires no input besides dim light and blinks an LED indefinitely.

What about that super capacitor? It’s called a Lithium Ion Capacitor (LIC) and is a hybrid between a typical rechargeable lithium battery and an electrolytic capacitor, offering extremely high capacity in a convenient two leg through hole form factor. This one is a whopping 30 Farad at 3.8 V, and we first saw it when [Jasper] won the Hackaday Earth Day contest last month. Check out that link if you want to know more about their uses and how to integrate them.

For more detail about all of the components of the solar pyramid we need only turn to the Hackaday archives. In December 2019 [Tom Nardi] wrote about building a cheap degassing system for making some very familiar looking resin pyramids. And before that [Donald Papp] brought us another familiar piece of the pyramid when he wrote up a different 1″ x 1″ solar harvesting system that [Jasper] designed.

Check out the video after the break to see what one of these gems looks like from all sides. And for many more experiments leading up the final pyramid check out the logs on the Hackaday.io page.

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