[Mathieu] just finished analyzing the numbers from a month of solar energy harvesting. You may remember that he was curious to see what kind of energy can be collected from small solar cells used indoors. He built several copies of a test platform which collected data between December 16th and January 16th.

First of all, it’s not shocking to find out that rooms with no sunlight produced negligible energy during that time. When you think about it, if they had been gathering a statistically significant amount wouldn’t that mean the lighting used in those rooms was incredibly inefficient? In other words, there’s no way you need to be making that much light.

But he did find that proper positioning in rooms that catch sunlight during the day can result in usable energy for small loads. He established that a 0.5 Watt panel harvested just a bit more than half of what a 1 Watt panel did. But perhaps the most useful discovery was that it’s quite a bit more efficient to have a charging circuit store energy in a battery rather than directly powering a fixed load.

It will take us a few more viewings to really decide what we can take away from the experiment for our own projects. But we appreciate [Mathieu's] quest for knowledge and his decision to put this information out there so that others can learn from it.

Just like destroying an ant colony with a magnifying glass, there’s nothing like cooking hot dogs and roasting marshmallows with a nice parabolic reflector. Of course covering an old satellite dish with mylar or aluminum tape doesn’t take much skill, however cool it is. [Uwe] came up with a much more technical means of building a Fresnel reflector that will cook your hot dogs in seconds, but only on sunny days.

[Uwe] channeled a little bit of [Apollonius] when he realized that a flat cardboard ring with a section removed could be joined together into a conic section. The resulting section looks just like one concentric ring in a Fresnel reflector. [Uwe] wrote a small program in Visual Basic to calculate the necessary diameter and angle of his conic sections.

A bit of cardboard was cut out and pieced together with some very reflective aluminum tape. The resulting Fresnel reflector concentrates 117 times the normal solar radiation onto a small point. It’s more than enough to burn holes in construction paper, but we’ll be using a microwave for our lunch today.

[Steven Dufresne] does a lot of tinkering with solar-powered applications, a hobby which can be very time consuming if done right. One process he carries out whenever building a solar installation is creating a sun chart to determine how much (or little) sun the target area will get.

The process requires [Steven] to take elevation and Azimuth measurements of many different points, which often consumes about half an hour of his time. While taking measurements recently, he started thinking about how he could improve the process, and came up with a stellar solution that reduces the process down to a one-minute task.

In short, his shade finder tool uses a pulley, a pair of rollerblade wheels, and a pencil to accomplish a full shade survey in under a minute. The science behind the tool is best explained by [Steven], so be sure to check out his site for plenty of details and diagrams.

We have to say that we’re extremely impressed by his shade finder – hopefully his work can help others maximize the efficiency of their solar solutions.

Stick around after the jump to see a short video of the shade finder in action.

As winter is officially upon us, we’re pretty sure that the last thing most of you are thinking about is mowing your lawn. We would argue that it’s actually the ideal time to do so – that is, if you are interested in automating the process a bit.

[Robert Smith] has spent a lot of time thinking about his lawn, wanting a way to sit back and relax while doing his weekly trimming. He set off for the workshop to build an R/C electric lawnmower, and thoroughly documented the process in order to help you do the same.

On his web site, you will find a series of videos detailing every bit of the solar charged R/C lawnmower’s construction, taking you through the planning phases all the way to completion. [Robert] has provided just about anything you could possibly need including parts lists, schematics, code, and more.

If the short introductory video below has you interested, be sure to swing by his site for everything you need to build one of your own.

[Mathieu] was interested in using more solar cells for his everday electronics. He looked around but couldn’t find much information about using pholovoltaic for small indoor devices. We remember hearing some of the same things from [Dave Jones] in one of his EEVblog installments from a few years ago which looked at solar calculators; the only indoor solar gadget we can think of.

The quest for knowledge was on and [Mathieu] decided to build this indoor solar cell test platform. It’s a stable piece of hardware that allows him to run reliable tests in many different conditions. It’s designed to compare two identical cells. One is charging the Lithium cell, the other is driving a load directly. A second battery powers the platform separately from the solar circuits so that it can be used as a data logger. He collects, dumps, and graphs info from his test runs, then discusses his findings. We won’t spoil it, but the results are not great. Mostly you need sunlight to get real results as it’s just so much more powerful than artificial lighting.

Like many people, [yardleydobon] had a hard time locating his ceiling fan’s pull chain at night when his room is completely dark. Rather than continue to flail around blindly grasping for the chain, he decided to find a way to illuminate it instead.

He started off by disassembling a solar garden light, retaining the solar cell, photoresistor, and batteries. After paring down the electronics to the bare essentials, he mounted them inside a plastic battery storage case which he attached to the outside of the fan’s lamp. [yardleydobon] then ran a pair of wires from the electronics box down to end of the chain, where he added an LED and a translucent pull to diffuse the light.

He admits that it’s not the nicest looking modification around, but it does the job in a pinch. He has some ideas that he may put into play if he has the time to revise the design, and we bet that many of you do as well. If so, be sure to share them in the comments.

With grand plans of tenting out for several days at a music festival [Josh] needed a way recharge his portable devices. In the past he’s lugged around a 12V battery with him, but this year he wanted to make things easier. He ended retrofitting a camping light to do the job with the help of the summer sun.

The first step of the project was to source some rechargeable batteries. He toyed with the idea of Li-Ion cells but ended up going with NiMH because the charging is more forgiving and he got them at a great price. Because of the lower operating voltage (1.2V versus Alkaline’s 1.5V) he needed to squeeze two more into the lamp housing. Here you can see that he just managed to get them to fit in the wire-run area down the middle of the case.

Next comes the recharging circuit. He based his design around an ATmega44, using a voltage divider and the ADC to detect when the batteries are topped off. During the day this is connected to an external solar panel and it’s ready to charge his phone when he gets back at night.

As soon as the team at Revolt Labs heard Occupy Wall Street was coming to Boston, they decided to pick up their soldering irons in support of the throngs of protestors. They came up with a Solar charging USB box to keep those cell phones and digital cameras charged.

The case came direct from an Army surplus store. Originally, the box was used by the Dutch military to test the air for poison gas and signal when it was safe to remove a gas mask – hopefully not a portent of things to come.

On top of the box is five solar panels that output two watts each. A bit of breadboard holds a 7805 voltage regulator, a few caps and a diode. This regulated output goes to a USB hub and provides power for recharging.

For a cheap and easy project for our brothers without arms, we couldn’t think of a better project for the Occupy Boston tent city. Of course heating units will be needed at the Occupy protests this winter, but at least now the protesters have the means to power their communications equipment.

update: Once again, this has devolved into political argument and name calling. We, as hackaday, really couldn’t care less which party you are for or what your political beliefs are. We want to talk about the project, in this case a portable solar charger. We go to other sites to argue politics. Maybe you should try here.

The crew over at The Tech Junkies recently took another look at solar power and thought that the pricing had come down enough for them to consider powering their entire shop via the sun. Cheaper or not, they still didn’t want to pay retail for solar panels, so they decided to build their own instead.

They scoured eBay for a bit and scored a nice batch of “production error” solar cells for about $0.25/watt, which is a great deal. After unpacking and sorting the cells, they began fitting them into a set of old window panels they had sitting around their shop. The cells were wired together using tabbing wire, and after a quick test to ensure everything was working correctly, the panel was permanently set using epoxy.

In its current state, they estimate that their panel can generate 35 watts of power, though they have a few design changes in mind to raise that number a bit. The total cost was roughly $375 for enough materials to build 9 panels, which is pretty reasonable.

Be sure to check out their blog for a quick overview of what it takes to build a solar panel if you’re thinking of putting together one of your own.

[Michael] took a battery charger meant to be connected to mains power and converted it to work with a solar panel. This was a traditional 4 cell charger which charges the batteries in pairs. He kept that functionality, but added USB charging with a special over-current feature. That’s because his Android phone has a fast and slow USB charging mode. The slow mode makes sure that it draws 500 mA or less to stay within USB specifications. But the fast mode draws more current when the phone detects that the USB connection is attached to a wall charger. [Michael] added a switch that patches a pull-up resistor to the data line, signaling to the phone that it’s okay to switch to fast charging mode.

As for the power supply itself, you can see that [Michael] snapped off the part of the circuit board that housed the original regulator. He’s added his own 5V switching regulator which offers a wide input voltage range. This is connected to two banana plug sockets which can be connected to the solar panel.

[Mark] wrote in to share a little creation that he is calling the first solar-powered 3D printer in existence. While we can’t say that we totally agree with him on that title, we will give him the benefit of the doubt that this is the first solar-powered RepRap we have seen thus far.

You might remember [Mark] from his previous exploits, but rest assured that there’s little possibility of anyone losing an eye with this one. He has taken his RepRap outdoors, and with the help of a solar panel plus a few batteries from Harbor Freight, he has the world’s first solar-powered RepRap*.

The trick behind keeping the RepRap running for such a long time with the sun as its only power source lies in the RAMPS board [Mark] uses. He has the 1.3 revision of the shield, which enables him to print objects loaded from an SD card rather than requiring a computer to be connected at all times.

So, if you happen to need the ability to print 3D objects where an extension cord cannot possibly reach, check out [Mark’s] setup and get to building!

* Maybe. Perhaps.

[Sebastian] wrote in to share his web site, where he has a bunch of different electronics projects. After looking through them, we found a pair that we thought you might find interesting.

The first project is a homebrew weather monitoring station that [Sebastian] put together. He designed a weather shield, incorporating humidity, pressure and light sensors, along with digital I/O ports for monitoring an anemometer. The entire setup is powered using solar panels, and data is relayed to his computer via an Xbee.

The second item that caught our eye was a digital camera pan and tilt rig. The system was built using a Lynxmotion pan and tilt kit, which is controlled by an Arduino. The code he provides allows him to capture very large composite images without having to spend too much time “sewing” them together. While this second project mostly consists of schematics for a base plate and pan/tilt code, it struck us as something that could be very useful for any budding photographers looking to take panoramic shots.

All of the schematics and code for his projects are available on his site, so be sure to look around – you might find something interesting!

The sun is a great source of energy, however, efficiently collecting this energy can be hard to do.  One thing that can improve the results of solar use is to actually track the sun’s movement. [fanman1981] hooked up his own homebrew solar tracker using some pretty clever techniques.

For this hack he used two Harbor freight 45 Watt solar kits, some struts on the bottom, and a Dish Network satellite dish bracket hooked up to an “old school” antenna motor.  Although one might think this device tracks the sun using some sort of sensor, it’s actually just a matter of hooking up the device to rotate at timed interval with a remote control.  This interval is figured out with the benefit of some charts on livingonsolar.com.

To see it in use, check out the video after the break.  He gives a good explanation about how everything was put together, but if you just want to see it move, fast forward to around 5:26, really quite impressive.

[via hackedgadgets]

Instructables user [flapke] has a Kobo eReader and wanted to add some solar cells to it in order to charge the battery for free. The modification is similar to others we have seen recently, though his work was done so well that it almost looks stock.

He started out by sourcing a pair of solar panels from DealExtreme that purported to supply 5.5v @ 80mA. Like most of us are inclined to do, he tested them before use and found that they actually put out around 50mA instead. While the performance was a bit off, they still fit his needs pretty well, as the charge current needed to be at or less than 100mA to avoid damaging the battery.

He opened the Kobo’s case, and carefully removed a section of the back panel to make room for the solar panels. Once they were soldered together in parallel, he wired them to the eReader’s battery through a Schottky diode to prevent the battery from draining.

While we think his solar modification is a great way to ensure that he never runs out of juice while reading by the pool, we would certainly add a bit of extra charge circuitry to ours to prevent damage to the battery. What do you think?

It’s always interesting to see what happens when hacking meets clothing – check out this pair of bikinis, for instance.

This first item, called the N12 bikini (mildly NSFW), comes from Continuum Fashion and is composed entirely from Nylon 12, hence the name. Shapeways uses 3D Selective Laser Sintering (SLS) to create the tiny circles that make up this piece of swimwear. The suit is held together by tiny stretchy strings made of the same nylon, and the bikini can be printed to order. It seems like an interesting idea, but we wonder how it would hold up against some big waves or a game of beach volleyball.

The second item is a bit more functional. Designer [Andrew Schneider] has put together a bikini that can solve all of your energy needs while sitting by the pool. His solar bikini is covered with hand-sewn flexible solar cells that work together to produce up to 5v, available via a USB connection. He claims that you are free to go swimming in the suit, so long as you dry out the USB port before using it again. For all the guys out there crying foul, don’t worry – he’s got a suit for you too. He’ll be putting together a men’s suit in the near future that powers a 1.5 amp Peltier cooler to keep your beer cold – we just don’t want to know where the hot side of the Peltier goes…