Five Solar Air Heating Methods Tested

July 4, 2026 by Bryan Cockfield 55 Comments

For as good as solar panels are at converting sunlight directly into usable electricity, especially for how cheap they’re becoming, they can still only gather around 20-30% of the energy that hits them. That’s fine if you have a large roof or a huge tract of land, but if you have limited space and need to do something like heat a home, there are better options available to capture more of that energy. [Greenhill Forge] has built five solar air heating panels to test this concept, and do it much more inexpensively than commercial options.

These solar heaters use sunlight to heat a fluid, in this case air, and move that heated fluid to another space. Each panel is about two square meters, insulated on all sides except the top, and configured in a way that air can flow past something that the sun has heated. The first panel, a control, does not use a glazing to help trap this heat, but the rest all have a polycarbonate window to increase the greenhouse effect of the panels. The four remaining all experiment with the way air flows around a black corrugated steel sheet to gather more of the heat, with the fifth panel using a set of black screen instead.

With the panels all set out in the sun, [Greenhill Forge] is using a set of thermocouples from a previous project to measure the efficiency of each panel. Surprisingly, he found that the panel using the layers of screen was the best at gathering energy, although he notes several times that these types of panels are extremely sensitive to changes in physical configuration, so this is not the most definitive test possible. However, at only around $100 per panel it’s quite a deal if the goal is a usable space heater that doesn’t use any fuel or grid electricity.

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From Sugar To Ethanol Fuel With A Little Microbial Help

June 30, 2026 by Maya Posch 65 Comments

In these trying times it seems appropriate to work through some ‘what if ‘ scenarios, such as the local gas station suddenly not having any more gasoline to sell you, or said gas station ceasing to exist altogether. In that case it can be incredibly useful to be able to create your own gasoline alternative in the form of ethanol. As demonstrated by [Hyperspace Pirate] in a recent video this process is fairly straightforward once you have procured an appropriate feedstock, such as here sugar (sucrose).

Although baker’s yeast (Saccaromyces cerevisiae) is more commonly associated with the production of ethanol-laced drinks, there’s nothing that says that you cannot distill out the approximately 10-15% ethanol that results from a yeast feeding frenzy and resulting waste products.

How to do this distillation step is explained in the video, with the mixture heated and put through a self-made reflux column to deal with the fact that the water/ethanol mixture is an azeotropic mixture, meaning that a lot of water is expected to make its way out of the condenser along with ethanol without this measure to condense as much of the water vapor before it can make its way to the top of the column.

Ultimately the conversion rate of plain white sugar to ethanol is about 54%, with the rest turning into CO₂. With an appropriately converted combustion engine for running on 100% ethanol, it runs pretty well, though the final cost per liter of ethanol will heavily depend on your feedstock.

With the full costs of the electric heater of the distillation column taken into account – at 2.57 kWh/L – as well as the cost of the off-the-shelf sugar, [Hyperspace Pirate] with his Florida kWh cost of $0.12 paid around $2.62/L, or $9.91 per gallon. Even with how much prices at the gas pump have shot up recently, you’d pretty much need to find a free source of feedstock and otherwise optimize the process for it to make much sense, even in this economy.

That said, it’s crazy that the world of Mad Max doesn’t run on ethanol. If tomorrow a certain bubble were to implode and the global economy fell apart as a result, producing bioethanol would seem to be a highly marketable skill.

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A white man in a dark t-shirt and glasses stands next to a pegboard. On the pegboard is a cylindrical wooden bird house with a small piece of metal roof attached to the top. A set of heat lamps are suspended above and give the image a reddish-orange glow. 87˚F is in white text in the lower left corner.

Do Metal Roofs Turn A Bird House Into An Oven?

June 27, 2026 by Navarre Bartz 34 Comments

Birdhouses can be a great way to help out nesting birds in your area, but they can be a bit intensive to make. As part of a 500 birdhouse marathon, [Of Human and Nature] decided to test whether a metal roof would be safe or turn the birdhouse into an oven.

Most DIY birdhouses are made of wood to encourage cavity nesting species that would naturally find a hole in a tree to use the house. Unfortunately, an unprotected chunk of wood will deteriorate much faster than a whole tree full of holes might. A metal roof reduces the exposure to the elements, but does it make the box too hot?

[Of Human and Nature] heeded concerns from commenters and actually tested his hypothesis with a simple set of thermocouples, a heat lamp, and an assembled birdhouse. While the metal roof was held at 70˚C for four hours, the inside of the house stayed in the mid 20˚C range thanks to the separation between the roof and the actual box which allows air to flow between the two.

Maybe a metal roof could help you house your homing pigeons as well? If you want to spread the mesh with your birdhouse instead, how about a solar panel roof with a LoRa node?

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Come With Me If You Want To Weed: Autonomous Weedinator Robot Back For 2026

June 19, 2026 by Tyler August 18 Comments

The WEEDINATOR agricultural robot is one of the longer-running projects we’ve featured here on Hackaday. We first featured it way back in 2017 for that year’s Hackaday prize, and after a nearly a decade of work on-and-off it has hit a very important milestone: it is now an effective horticultural instrument, as you can see in the latest demo video below.

There have been some big changes over the years. For one, the scope of the project narrowed considerably with the adoption of a commercial tractor as the base, specifically an Iseki 321 . They picked the Iseki after examining several competitors, and it won out because its hydrostatic drive was best able to handle the very low speeds desired. It looks like they’re now focused on cultivation — that is, tearing out weeds mechanically — rather than the flame weeder they started with. The cultivators are of the claw type, and has three claws powered via the tractor’s hydraulics for control in all three axis: X, Y and Z. Of course the project now leverages modern computer vision toolsets, using a combination of OpenCV and YOLO26n running on a Jetson Nano board. The robotics half of the equation is handled on an STM32 Nucleo.

Aside from being one of our longer-running submissions, we have to call out the team for being one of the very few — perhaps the only — to go to the effort of creating a theme song for their project. If you’ve only got a minute to see the robot run, you might as well look at the second video embedded below and give a listen.

While WEEDINATOR has got the most persistence, they’re not the only ones in the garden robot game. We’ve seen projects using everything from concentrated sunlight to precision-applied herbicides to clear unwanted plants over the years.

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Building An Organic Flow Battery Based On Green Tea

June 17, 2026 by Maya Posch 9 Comments

As simple of a concept flow batteries are, the used chemicals can still be somewhat problematic in the context of a school experiment. To this end [Markus Bindhammer] decided to implement a flow battery version that uses compounds from green tea for its electrolyte, based on a German research paper from 2016.

These organic flow batteries can use gallic acid, pyrogallol as well as the polyphenols in green tea, making them rather safe even in the hands of more careless students. The demonstrated flow battery uses a carbon electrode with activated carbon around it to increase surface area, a platinum wire electrode, and a graphite foil as third electrode.

In the paper a silver electrode is also used, along with the additional electrodes, and a terracotta flower pot as the barrier between the carbon and graphite electrodes, with [Markus] further explaining that there are fortunately cheaper options than what he is using, especially with the flower pot instead of a special ceramic vessel.

The electrolyte solution has epigallocatechin gallate (EGCG) dissolved in it, which here comes in the form of finely ground green tea powder (commonly known as matcha), which so happens to be pretty rich in this substance. In the below graphic by [Markus] you can see the complete set of solutions and other relevant details.

Of course, the performance of this type of flow cell isn’t amazing, with a cell voltage of less than a volt and a few mA of current, but it’s enough to spin a small fan, and to light up a few LEDs. This would be more than enough to demonstrate the reaction and flow cells in general, as long as you don’t mind donating some tasty matcha to science.

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Bike-Powered Shredder Makes Short Work Of 3D Printer Waste

June 16, 2026 by Donald Papp 17 Comments

[Brogan M Pratt] and his students do a lot of 3D printing, and as such found themselves producing a lot of plastic waste. Seeing an opportunity, they built a bike-powered plastic shredder that turns a little human exercise into the power needed to transform waste plastic into small bits. Shredding plastic is a necessary first step for any sort of processing, so getting this part working reliably is as important as it is educational.

Shredding is a necessary first step to processing plastic waste.

Being in the Netherlands, using a bike makes perfect sense. But it turns out there’s a lot more to making a human-powered plastic shredder than simply bolting a sprocket to a shredder, looping the bike chain over it, then climbing on and working up a sweat.

In between the bike and the shredder is a large gear reduction, a fifteen kilogram flywheel, and a heavy-duty frame to anchor everything in the face of so much mass and torque. Add some covers and safety guards and the result is a stationary bike with a hopper for waste, a bin for output, and enough rotational torque and inertia to chew through stubborn bits without stalling.

Now that the shredder works, what’s the plan for all the little plastic shreds? The goal is to turn it back into usable filament which is obviously very useful, but we’ve also seen that compression molding plastic waste can work pretty well, too.

Being an educator, [Brogan] makes it clear that a bike-powered shredder, while pretty cool, is not the only missing link in sustainability. There is currently no easy way to recycle plastic at scale. But the shredder is a critical part of demonstrating the whole process in a hands-on way, and learning why recycling plastic at scale is a genuinely difficult job.

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Desalinating Seawater With Solar And No Brine

June 7, 2026 by Maya Posch 40 Comments

Although desalination is very commonly used these days to convert seawater into fresh water, one of the major disadvantages of current approaches is that commercial desalination plants produce a lot of brine, which has to be dumped somewhere ideally without causing major environmental issues. A new solar-thermal method as demonstrated by [Luheng Tang] et al. was published in Light: Science and Applications, with accompanying PR article.

This method is claimed to require no pre-treatment or leave brine, using special panels that wick water across their surface and then use solar radiation to distill this water. This differs from previous similar methods through a special surface treatment that prevents build-up of salts which would require cleaning or replacement.

The salts and other contaminants that would normally end up in the brine slough off these cells and can then be further processed to recover everything from plain table salt to lithium as well as gold, uranium and other substances of interest that are prevalent in seawater.

So far these self-cleaning cells have been tested with water from a number of oceans with a claimed 74% solar-to-vapor conversion efficiency and nearly 100% salt extraction. As always the challenge will be in scaling this up to industrial levels, but so far it looks promising.