A Smarter Solar Water Heater

Installing solar power at a home is a great way to reduce electricity bills, especially as the cost of solar panels and their associated electronics continue to plummet. Not every utility allows selling solar back to the grid, though, so if you’re like [Rogan] who lives in South Africa you’ll need to come up with some clever tricks to use the solar energy each day while it’s available to keep from wasting any. He’s devised this system for his water heater that takes care of some of this excess incoming energy.

A normal water heater, at least one based on electric resistive heaters, attempts to maintain a small range of temperatures within the insulated tank. If the temperature drops due to use or loss to the environment, the heaters turn on to bring the temperature back up. This automation system does essentially the same thing, but allows a much wider range of temperatures depending on the time of day. Essentially, it allows the water heater to get much hotter during times when solar energy is available, and lets it drop to lower values before running the heater on utility electricity during times when it isn’t. Using a combination ESP32 and ATtiny to both control the heater and report its temperature, all that’s left is to program Home Assistant to get the new system to interact with the solar system’s battery charge state and available incoming solar energy.

While it’s an elegantly simple system that also affords ample hot water for morning showers, large efficiency gains like this can be low-hanging fruit to even more home energy savings than solar alone provides on paper. Effectively the water heater becomes another type of battery in [Rogan]’s home, capable of storing energy at least for the day in the form of hot water. There are a few other ways of storing excess renewable energy as well, although they might require more resources than are typically available at home.

A large, short set of tree stumps supports many smaller, straight trees atop them. They are on a picturesque mountain with a orange deciduous tree behind them.

Daisugi – Growing Straight Lumber Without Killing The Tree

In 14th Century Japan, there was a shortage of straight lumber for building and flat land on which to grow it. Arborists there developed a technique that looks like growing trees on top of trees, called daisugi.

Similar to the European practice of pollarding for firewood and basket materials, daisugi has been likened to bonsai on steroids. Starting with a Japanese cedar tree, one chops the top off the tree once it has grown to sufficient size to survive this initial shock. The following spring, you start carefully guiding the new growth through pruning to create tall, straight trunks on top of the “platform cedar.” Pruning takes place approximately every two years and harvesting every twenty. A daisugi tree can produce new shoots for several hundred years if properly maintained.

Although often used as a decorative technique today, it seems like an interesting way to grow your own perfect lumber if you have the room for it. We suspect the technique could be used on other species that lend themselves to pollarding like oak or maple, but harvest times and reliable straight trunks might vary. With sustainable production of wood for cross-laminated timber (CLT) and other advanced timbers being of growing importance, we wonder if these techniques could make a comeback?

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Open-Source Solar Modules

As the price of solar panels continues to fall, more and more places find it economical to build solar farms that might not have been able to at higher prices. High latitude locations, places with more clouds than sun, and other challenging build sites all are seeing increased green energy development. The modules being used have one main downside, though, which is that they’re essentially a black box encased in resin and plastic, so if one of the small cells fails a large percentage of the panel may be rendered useless with no way to repair it. A solar development kit like this one from a group called Biosphere Solar is looking to create repairable, DIY modules that are completely open source, to help solve this issue.

The modular solar panel is made from a 3D printed holster which can hold a number of individual solar cells. With the cells placed in the layout and soldered together, they are then sandwiched between a few layers of a clear material like acrylic or glass with a seal around the exterior to prevent water intrusion. Since the project is open-source any number of materials can be used for the solar cell casing, and with the STL file available it’s not strictly necessary to 3D print the case as other manufacturing methods could be used. The only thing left is to hook up a DC/DC converter if you need one, and perhaps also a number of bypass and/or blocking diodes depending on your panel’s electrical layout.

The project is still in active development, and some more information can be found at the project’s website. While the “recyclability” of large-scale solar farms is indeed a problem, it’s arguably one which has been overblown by various interests who are trying to cast doubt on green energy. A small build like this won’t solve either problem anytime soon, so the real utility here would be for home users with small off-grid needs who want an open-source, repairable panel. It’s a great method to make sure solar technology is accessible and repairable for anyone that wants it, and in a way this approach to building hardware reminds us a lot of the Framework laptops.

Hacking A Xiaomi Air Purifier’s Filter DRM To Extend Its Lifespan

When [Unethical Info] was looking at air purifiers a while back, their eye fell on a Xiaomi 4 Pro, with a purchase quickly made. Fast-forward a while and suddenly the LCD on top of the device was showing a threatening ‘0% filter life remaining’ error message. This was traced back to an NFC (NTAG213) tag stuck to the filter inside the air purifier that had been keeping track of usage and was now apparently the reason why a still rather clean filter was forcibly being rejected. Rather than give into this demand, instead the NFC tag and its contents were explored for a way to convince it otherwise, inkjet cartridge DRM-style.

While in the process of reverse-engineering the system and doing some online research, a lucky break was caught in the form of earlier research by [Flamingo Tech] on the Xiaomi Air Purifier 3, who had obtained the password-generating algorithm used with the (password-locked) NFC tag, along with the target area of the filter’s NFC tag to change. Using the UID of the NFC tag, the password to unlock the NFC tag for writing was generated, which requires nothing more than installing e.g. ‘NFC Tools’ on an NFC-capable Android/iOS smartphone to obtain the tag’s UID and reset the usage count on the filter.

A password generating tool is provided with the [Unethical Info] article, and this approach works across a range of Xiaomi air purifiers, making it an easy fix for anyone who owns such a device but isn’t quite ready yet to shell out the big bucks for a fresh DRM-ed filter. This approach also saves one from buying more NFC tags, which was the case with the previous solution.

Kites Fill Electricity Generation Gaps

Looking at a wind turbine from first principles, it’s essentially a set of wings that generate lift in much the same way an airplane wing does. Putting the wings on a rotor and calling them “blades” is not a huge step away from that. But there’s no reason the wing has to rotate, or for that matter be attached to a fixed platform, in order to generate electricity. Anything that generates lift can be used, and this company is demonstrating that with their kite-powered wind generators.

Like other wind energy producers that have used kites to generate electricity, this one is similar in that the kite is flown in a figure-8 pattern downwind where it can harness energy the most efficiently, pulling out a tether which is tied to a generator. When fully extended, it is flown to a position where the wind doesn’t strike the kite as strongly and the tether is reeled in. Unlike other kite generators we’ve seen, though, this one is offered as a turnkey system complete with battery backup and housed in a self-contained shipping unit, allowing it to be deployed quickly to be used in situations where something like a diesel generator would be impossible to get or where the fuel can’t be obtained.

The company, called Kitepower, does note that these aren’t replacements for traditional wind turbines and would be used more for supporting microgrids. There are still some advantages to using kites over fixed turbine blades though: kites can reach higher altitude where the wind is stronger, and they require less materials for a given amount of energy production, often making them even more environmentally friendly and possibly more economical as well. Surprisingly enough, kites can also be used to generate energy even in places where there’s no wind at all.

A Practical Open Source Air Purifier

In the years since the start of the coronavirus pandemic, it’s fair to say we’ve all become a lot more aware of the air quality surrounding us. Many of us have added a CO2 monitor to our collection of tools, and quite a few will have an air filtration system too. There are plenty of devices on the market that fulfill this niche at varying qualities and prices, but shouldn’t a decent filter be something to make for yourself? [Naomi Wu] thinks so, and she’s put up the design for her Nukit open air purifier online under the GPLv3.

The principle of the unit is simple enough: it’s a box with an HVAC filter on the front and a set of computer fans on its side to draw air through. But it’s more than just a box, as there are three separate versions for wall-mount, hanging mount or a freestanding tower, and each one comes as a DXF file with all parts ready for laser cutting. It’s about as straightforward a way to get your hands on a well-designed and high quality air purifier as could be imagined.

[Naomi] has been quiet for a while in her familiar role as YouTube maker and guide to the nooks and crannies of her native Shenzhen, so it’s very positive to see her still active and producing projects after being warned off social media by the authorities. If you’d like to see another recent project of hers, look no further than her update to [Bunnie Huang]’s Shenzhen guide.

Solar Chimneys: Viable Energy Solution Or A Lot Of Hot Air?

We think of the power we generate as coming from all these different kinds of sources. Oil, gas, coal, nuclear, wind… so varied! And yet they all fundamentally come down to moving a gas through a turbine to actually spin up a generator and make some juice. Even some solar plants worked this way, using the sun’s energy to heat water into steam to spin some blades and keep the lights on.

A solar updraft tower works along these basic principles, too, but in a rather unique configuration. It’s not since the dawn of the Industrial Age that humanity went around building lots of big chimneys, and if this technology makes good sense, we could be due again. Let’s find out how it works and if it’s worth all the bluster, or if it’s just a bunch of hot air.

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