Easy Parabolic Mirror from a Trash Can Lid

Hackaday Solar Hacks -

Parabolic reflectors for solar applications are nice stuff, and making your own is a great project in itself. One of the easiest ways we have seen is that of [GREENPOWERSCIENCE], who uses nothing more than a trash can lid, mylar film, and tape. You need a way to make a partial vacuum though.

The idea is so simple that it´s almost like cheating. Cut a circle of mylar slightly larger than the lid, and tape it all around, taking care of stretching the mylar in the process. After you´re done with this, you end up with a nice flat mirror. Here´s where the vacuum is needed to force the film into parabolic shape. Extract the air from a little hole in the lid that was previously drilled, and tape it to prevent the loss of the vacuum. The atmospheric pressure on the mylar film will take care of the job, and magically you get a nearly-parabolic reflector ready for work.

In this other video, you can see the reflector in action burning stuff. One obvious problem with this technique is the loss of the vacuum after some time, about an hour according to the author. Here´s another way to make a more durable mirror also with mylar as the reflecting element, however the quality of the resulting mirror is not as good.


Filed under: solar hacks

How To Hack A Spacecraft To Die Gracefully

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Last week, the Rosetta spacecraft crashed into comet 67P/Churyumov-Gerasimenko after orbiting it since 2014. It was supposed to do that: the mission was at an end, and the mission designers wanted to end it by getting a close look at the surface of the comet. But this raises an interesting problem: how do you get a device that is designed to never stop to actually stop?

A spacecraft like Rosetta is built from the ground up to keep going, to reboot and go into a backup mode, phone home and wait for instructions if it encounters a problem. This is called a safe mode, and it has saved the spacecraft several times before. If it was left unfixed, when the spacecraft hit the comet, it would trigger a special safe mode called FDIR (Failure Detection, Isolation and Recovery) that would keep sending a diagnostic signal back to earth until the mission controllers responded.

But this mission was at an end, and if the probe was left constantly rebooting and transmitting a cry for help, it could interfere with other spacecraft using the same frequency. Even a weak signal could interfere with another spacecraft, so the designers wanted to shut it down completely.  So, they used an interesting approach: they patched the software on the spacecraft to stop it phoning home. The day before it was crashed into the comet, they sent it a patch that removed the safe mode and replaced it with a passive mode that hadn’t been used since before launch, where the spacecraft would simply sit and wait for instructions if it hit a problem. A few hours before the crash, this patch was activated, and the probe was now without a backup plan. So, when it hit the comet, it entered this passive mode, and it will stay in this mode for as long as the batteries last, forever waiting for a command to restart that will never come…

Thanks to [Daniel] for the tip!

Filed under: solar hacks

Homebrew Powerwall Sitting at 20kWh

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Every now and then a hacker gets started on a project and forgets to stop. That’s the impression we get from [HBPowerwall]’s channel anyway. He’s working on adding a huge number of 18650 Lithium cells to his home’s power grid and posting about his adventures along the way. This week he gave us a look at the balancing process he uses to get all of these cells to work well together. Last month he gave a great overview of the installed system.

His channel starts off innocently enough. It’s all riding small motor bikes around and having a regular good time.  Then he experiments a bit with the light stuff, like a few solar panels on the roof.  However, it seems like one day he was watching a news brief about the Powerwall (Tesla’s whole-home battery storage system) and was like, “hey, I can do that.”

After some initial work with the new substance it wasn’t long before he was begging, borrowing, and haggling for every used 18650 lithium battery cell the local universe in Brisbane, Australia could sell him. There are a ton of videos documenting his madness, but he’s all the way up to a partly off-grid house with a 20kWh battery bank, for which he has expansion plans.

There’s a lot of marketing flim flam and general technical pitfalls in the process of generating your own non-grid electricity. But for hackers in sunny areas who want to dump those rays into local storage this is an interesting blueprint to start with.

Filed under: home hacks, solar hacks

Characterizing a Death Ray… er, Solar Oven

Hackaday Solar Hacks -

Many of you will probably at some point have looked at a satellite dish antenna and idly wondered whether it would collect useful amounts of heat if you silvered it and pointed it at the sun. Perhaps you imagine a handy source of  solar-cooked hotdogs, or maybe you’re a bit of a pyromaniac.

[Charlie Soeder] didn’t just think about it, he did it. Finding a discarded offset-focus DirecTV dish, he glued a grid of 230 inch-square mirror tiles to it and set to investigating  the concentrated solar energy at its focus. 

Cotton waste, newspaper, and scraps of fabric char and burn with ease. A cigarette is lit almost from end to end, and it burns a hole right through a piece of bamboo. Most of the energy is in the form of light, so transparent or reflective items need a little help to absorb it from something dark. He demonstrated this by caramelizing some sugar through adding a few bits of charcoal to it, once the charcoal becomes hot enough to caramelize the sugar around it the spreading dark colour causes the rest of the sugar to caramelize without further help.

Solar furnace calculationsSolar furnace calculations

To gain some idea of the power of his solar furnace, he recorded a time series of temperature readings as it heated up some water darkened with a bit of charcoal to absorb heat. The resulting graph had a flat spot as a cloud had passed over the sun, but from it he was able to calculate instantaneous power figures from just below 30W to just below 50W depending on the sun.

He records his progress in the video you’ll find below the break. Will we be the only ones casting around for a surplus dish after watching it?

We don’t seem to have had many satellite dish solar furnaces here on these pages, but we have had a more conventional solar oven or two. This dish-based solution would probably benefit from a sun tracker.

Filed under: green hacks, solar hacks

Working in Peace With an Off-Grid Office Shed

Hackaday Solar Hacks -

Finding a good work space at home isn’t a trivial task, especially when you’ve got a wife and kid. A lot of us use a spare bedroom, basement, or garage as a space to work on our hobbies (or jobs). But, the lack of true separation from the home can make getting real work done difficult. For many of us, we need to have the mental distance between our living space and our working space in order to actually get stuff done.

This is the problem [Syonyk] had — he needed a quiet place to work that was separated from the rest of his house. To accomplish this, he used a Tuff Shed and set it up to run off-grid. The reason for going off-grid wasn’t purely environmental, it was actually more practical than trying to run power lines from the house. Because of the geology where he lives, burying power lines wasn’t financially feasible.

So, he poured a foundation, brought in a pre-assembled shed (a demo unit at a big discount), and got to work outfitting it for use as on office. The first step (and arguably a very important one), was to heavily insulate it. And, we do mean “heavily” — he used 3.5″ of rock wool (5.5″ on the ceiling) in addition to 2″ of foam board.

The insulation was essential, as the entire office is powered by solar panels (with a battery bank); keeping cooling and heating energy use down was paramount. Even with 2kW of panels, heating and cooling are still a huge portion of the energy usage, and he needed power to spare for his computer and other electronics. With the shed so well insulated, [Syonyk] has been able to keep the temperature inside at about 70ºF while the outside temperature is above 100ºF.

The rest of the build was straightforward, with sensible plywood walls and a desk taking up most of the space to hold his multiple computers. Of course, for the Hackaday crowd, a space like this would be best used for efficient hacking.

Filed under: green hacks, solar hacks
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